city of dripping springs...april 2015 i pw://carollo/documents/client/tx/dripping...

8911 CAPITAL OF TEXAS HIGHWAY NORTH, SUITE 2200 • AUSTIN, TEXAS 78759 • P. 512.453.5383 • F. 512.453.0101pw://Carollo/Documents/Client/TX/Dripping Springs/9756A00/Deliverables/Feasibility Study/

CITY OF DRIPPING SPRINGS

DIRECT POTABLE REUSE FEASIBILITY STUDY

FINAL

April 2015

Texas Registered Engineering Firm F-882

4/10/2015

April 2015 i pw://Carollo/Documents/Client/TX/Dripping Springs/9756A00/Deliverables/Feasibility Study/

City of Dripping Springs Direct Potable Reuse Feasibility Study

TABLE OF CONTENTS Page No.

CHAPTER 1 ....................................................................................................................... 1-1

INTRODUCTION ................................................................................................................ 1-1

1.1 OVERVIEW ............................................................................................................ 1-1 1.2 WATER SUPPLY ................................................................................................... 1-1 1.3 WASTEWATER COLLECTION, TREATMENT AND DISPOSAL .......................... 1-3

1.3.1 South Regional Wastewater Treatment Plant ............................................. 1-3 1.3.2 Future Expansion of Wastewater Service ................................................... 1-4

1.4 DIRECT POTABLE REUSE ................................................................................... 1-4 1.5 STUDY OBJECTIVES ............................................................................................ 1-4

CHAPTER 2 ....................................................................................................................... 2-1

REGULATION OF POTABLE REUSE .............................................................................. 2-1

2.1 OVERVIEW ............................................................................................................ 2-1 2.1.1 Introduction to Potable reuse ...................................................................... 2-1 2.1.2 Water Rights and Project Permitting Approach .......................................... 2-2

2.2 POTABLE REUSE REQUIREMENTS AND GUIDELINES .................................... 2-3 2.2.1 Chemical Removal Goals and Requirements ............................................. 2-3 2.2.2 Pathogen Removal Goals and Requirements ............................................ 2-4 2.2.3 Potable Reuse in Other Parts of the U.S. ................................................... 2-5

CHAPTER 3 ....................................................................................................................... 3-1

WATER QUALITY GOALS ............................................................................................... 3-1

3.1 END USES DEFINE WATER QUALITY GOALS ................................................... 3-1 3.2 WATER QUALITY REQUIREMENTS FOR POTABLE REUSE ............................. 3-2

3.2.1 Salinity ........................................................................................................ 3-2 3.2.2 Nutrient Concentrations .............................................................................. 3-2 3.2.3 Other Chemicals of Concern ...................................................................... 3-2 3.2.4 Pathogens .................................................................................................. 3-3 3.2.5 TCEQ Effluent Characterization Requirements for DPR ............................ 3-4

3.3 WATER QUALITY REQUIREMENTS FOR DISCHARGE TO ONION CREEK ..... 3-5 3.3.1 Salinity 3-5 3.3.2 Nutrient concentrations ............................................................................... 3-5 3.3.3 Other Water Quality Parameters of Concern .............................................. 3-5 3.3.4 Pathogens .................................................................................................. 3-6

3.4 WATER QUALITY REQUIREMENTS FOR LAND APPLICATION VIA CANOPY SPRAY ................................................................................................... 3-6

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CHAPTER 4 ....................................................................................................................... 4-1

WASTEWATER TREATMENT .......................................................................................... 4-1

4.1 EXISTING WASTEWATER TREATMENT PLANT ................................................ 4-1 4.1.1 Flows 4-1 4.1.2 Current Effluent Water Quality .................................................................... 4-1

4.2 RETROFIT FOR BIOLOGICAL NUTRIENT REMOVAL ........................................ 4-2 4.3 PREVIOUS EVALUATION OF MEMBRANE BIOREACTOR ................................. 4-6

CHAPTER 5 ....................................................................................................................... 5-1

POTABLE REUSE ALTERNATIVES ................................................................................ 5-1

5.1 DPR TREATMENT EVALUATION ......................................................................... 5-1 5.1.1 Introduction to Treatment Train Concepts .................................................. 5-1 5.1.2 Pathogen Log Removal Goal Overview ...................................................... 5-3 5.1.3 Chemical Removal Mechanisms ................................................................ 5-4 5.1.4 Salinity Evaluation ...................................................................................... 5-5 5.1.5 Preliminary Sizing of the Proposed Treatment Concept ............................. 5-9

5.1.5.1 Ozonation ..................................................................................... 5-9 5.1.5.2 Biofiltration .................................................................................. 5-11 5.1.5.3 Ultrafiltration ............................................................................... 5-12 5.1.5.4 Inter-Process Storage Tank ........................................................ 5-13 5.1.5.5 Optional Granular Activated Carbon Adsorption ........................ 5-14 5.1.5.6 Ultraviolet Disinfection ................................................................ 5-14 5.1.5.7 Chemical Disinfection ................................................................. 5-15

5.1.6 Advanced Process Monitoring and the Engineered Storage Buffer ......... 5-16 5.2 DPR PROJECT ALTERNATIVES AND ELEMENTS ........................................... 5-19

5.2.1 Project Location Alternatives .................................................................... 5-19 5.2.1.1 South Regional Wastewater Treatment Site Location ................ 5-20 5.2.1.2 Upstream Site Location .............................................................. 5-20

5.2.2 Source Water Considerations ................................................................... 5-20 5.2.3 Collection System Tie-In ........................................................................... 5-21 5.2.4 Wastewater Treatment Plant Requirements ............................................. 5-21 5.2.5 Considerations for Advanced Treatment Source Water ........................... 5-21 5.2.6 Storage Considerations ............................................................................ 5-22

5.2.6.1 Effluent Storage .......................................................................... 5-22 5.2.6.2 Inter-Process Storage ................................................................. 5-22 5.2.6.3 Finished Water Storage .............................................................. 5-23

5.2.7 Drinking Water Distribution Tie-In ............................................................. 5-23 5.2.8 Effluent Disposal Infrastructure ................................................................. 5-23

5.2.8.1 Infrastructure for Effluent Discharge at South Regional Plant Site ............................................................................................. 5-23

5.2.8.2 Infrastructure for Effluent Discharge at Upstream Project Location ...................................................................................... 5-24

5.2.8.3 Land Application Infrastructure ................................................... 5-24 5.2.9 Ancillary Project Elements ........................................................................ 5-24

5.3 DISCUSSION OF INDIRECT POTABLE REUSE ................................................ 5-24 5.3.1 Augmentation of Onion Creek .................................................................. 5-24 5.3.2 Groundwater Augmentation ...................................................................... 5-25

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CHAPTER 6 ....................................................................................................................... 6-1

EFFLUENT DISPOSAL ALTERNATIVES......................................................................... 6-1

6.1 EFFLUENT DISPOSAL OVERVIEW ...................................................................... 6-1 6.1.1 TPDES Permitting ....................................................................................... 6-1 6.1.2 TLAP Permitting.......................................................................................... 6-1

6.2 EVALUATION OF LAND APPLICATION ............................................................... 6-2 6.2.1 Regulation .................................................................................................. 6-2

6.3 SUBJECT TRACT PROPOSED FOR LAND APPLICATION ................................. 6-2 6.4 LAND APPLICATION CALCULATIONS................................................................. 6-4

6.4.1 TABLE C-1 - A First Look (30 TAC 285 Method) ........................................ 6-4 6.4.2 TABLE C-2 - Detailed Water Balance ......................................................... 6-4

6.4.2.1 Water Balance Parameter Assumptions ....................................... 6-6 6.4.3 TABLE C-3 - Calculating the Volume of Effluent Storage Required ........... 6-7 6.4.4 TABLE C-4 – Nitrogen Uptake Calculations ............................................... 6-8 6.4.5 TABLE C-5 – Storage Pond Volume Calculation ........................................ 6-8 6.4.6 Costs 6-8 6.4.7 Discussion of Findings and Land Application Alternatives ......................... 6-9 6.4.8 Other Notes ................................................................................................ 6-9

6.5 DISCHARGE ........................................................................................................ 6-10 6.5.1 Water Quality Requirements for Discharge .............................................. 6-10 6.5.2 Discharge Infrastructure ........................................................................... 6-11

CHAPTER 7 ....................................................................................................................... 7-1

PLANNING LEVEL COST ANALYSIS .............................................................................. 7-1

7.1 APPROACH TO COST ANALYSIS ........................................................................ 7-1 7.2 DPR AT SOUTH REGIONAL PLANT SITE WITH DISCHARGE ........................... 7-2 7.3 DPR WITH LAND APPLICATION .......................................................................... 7-4 7.4 DPR AT UPSTREAM SITE .................................................................................... 7-7 7.5 COST COMPARISON ............................................................................................ 7-8

CHAPTER 8 ....................................................................................................................... 8-1

CONCLUSIONS AND NEXT STEPS................................................................................. 8-1

8.1 CONCLUSIONS ..................................................................................................... 8-1 8.2 NEXT STEPS ......................................................................................................... 8-2

CHAPTER 9 ....................................................................................................................... 9-1

REFERENCES ................................................................................................................... 9-1

9.1 REFERENCES ....................................................................................................... 9-1

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LIST OF APPENDICES APPENDIX A TCEQ EFFLUENT CHARACTERIZATION RECOMMENDATIONS APPENDIX B WASTEWATER TREATMENT MODEL OUTPUTS APPENDIX C EFFLUENT LAND APPLICATION CALCULATIONS

LIST OF TABLES Table 1.1 Dripping Springs Water Supply Company Service Summary ..................... 1-3 Table 2.1 Pathogen Concentration End Goals for Drinking Water ............................. 2-4 Table 4.1 Current and Projected Future Effluent Flows ............................................. 4-1 Table 4.2 Summary of Current Effluent Water Quality ............................................... 4-2 Table 4.3 Wastewater Model Influent Design Criteria ................................................ 4-2 Table 4.4 Wastewater Model Results for Filtered Effluent ......................................... 4-6 Table 5.1 Log Removal Overview of Reverse Osmosis-Based Treatment Train ....... 5-3 Table 5.2 Log Removal Overview of Ozone/Biofiltration Based Treatment Train ....... 5-4 Table 5.3 Basic Process Design Criteria for Ozone Process ................................... 5-11 Table 5.4 Basic Process Design Criteria for Biofiltration Process ............................ 5-12 Table 5.5 Basic Process Design Criteria for Ultrafiltration Process .......................... 5-13 Table 5.6 Basic Sizing Criteria for Inter-Process Storage Tank ............................... 5-14 Table 5.7 Basic Process Design Criteria for Ultraviolet Disinfection Process........... 5-15 Table 5.8 Basic Process Design Criteria for Final Chemical Disinfection ................. 5-16 Table 5.9 Process Monitoring Parameters for Advanced Treatment ........................ 5-18 Table 6.1 Alternative Scenarios for Land Application .............................................. 6-10 Table 7.1 Alternative 1A Capital Costs ...................................................................... 7-2 Table 7.2 Alternative 1A Operation and Maintenance Costs ..................................... 7-3 Table 7.3 Alternative 1B Capital Costs ...................................................................... 7-3 Table 7.4 Alternative 1B Operation and Maintenance Costs ..................................... 7-4 Table 7.5 Alternative 2A Capital Costs ...................................................................... 7-5 Table 7.6 Alternative 2B Capital Costs ...................................................................... 7-6 Table 7.7 Alternatives 2A and 2B Operation and Maintenance Costs ....................... 7-6 Table 7.8 Alternative 3 Capital Costs ........................................................................ 7-7 Table 7.9 Alternative 3 Operation and Maintenance Costs ........................................ 7-8 Table 7.10 Comparison of Costs for the Proposed Project Alternatives ...................... 7-9

LIST OF FIGURES Figure 1.1 Overview Map ........................................................................................... 1-2 Figure 4.1 Proposed BNR Treatment Schematic ........................................................ 4-4 Figure 4.2 Proposed Aeration Basin Configuration (Plan View) .................................. 4-5 Figure 5.1 Conceptual Process Flow Diagrams for Advanced Treatment Train

Alternatives ............................................................................................... 5-2 Figure 5.2 Salinity Mass Balance Schematic .............................................................. 5-6 Figure 5.3 Advanced Water Treatment System Process Flow Diagram.................... 5-10 Figure 5.4 Proposed Site Layout with Advanced Treatment at the South Regional

Wastewater Treatment Plant ................................................................... 5-17 Figure 6.1 Proposed Spray Irrigation Site Layout ....................................................... 6-3 Figure 6.2 Disposal Application Rates for Texas (30 TAC §285.90 Figure (1)) ........... 6-5

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LIST OF ABBREVIATIONS

ACO Assimilable organic carbon AOP Advanced oxidation process ASR Aquifer storage and recovery BAF Biologically active filter BOD Biochemical Oxygen Demand Carollo Carollo Engineers, Inc. CBOD5 Carbonaceous biological oxygen demand CE Effluent Electrical Conductivity CFU/100mL Colony-forming units per 100 milliliters City City of Dripping Springs CL Electrical Conductivity Limit Cl2 Chlorine CN Curve Number Ct Product of disinfectant concentration and contact time DBPs Disinfection byproducts DPR Direct Potable Reuse DSWSC Dripping Springs Water Supply Corporation EC Electrical Conductivity EQ equalization ESB engineered storage buffer ETs Evapotransipration values FRT Failure Response Time GAC Granular Activated Carbon Adsorption gpd Gallons per day HAAs Haloacetic acids HDPE High-density polyethylene IMLR internal mixed liquor recirculation system IPR Indirect Potable Reuse K Irrigation efficiency LAS Liquid ammonium sulfate lbs pounds LPHO Low pressure high output LRVs Log Removal Values MBR Membrane Bioreactor MCLs Maximum Contaminant Level mg/L Milligrams per liter Mgal Million gallons mgd Milllion gallons per day mJ Milli Joules MPN/L Most proable number per liter NaOCl Sodium hypochlorite

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ng/L Nanograms per Liter NWRI National Water Research Institute O3 ozone O3-BAF ozone-biofiltration PGMS Professional General Management Services ppm parts per million PUA West Travis County Public Utility Agency PVC Polyvinyl chloride RO Reverse Osmosis RWPF Raw Water Production Facility sf square foot TAC Texas Administrative Code TCEQ Texas Commission on Environmental Quality TDS Total dissolved solids THMs Trihalomethanes TN Total nitrogen TLAP Texas Land Application Permit TOC total organic carbon TOrCs Trace organic constituents TP total phosphorus TPDES Texas Pollutant Discharge Elimination System TSS Total Suspended Solids TWC Texas Water Code TWDB Texas Water Development Board UF ultrafiltration ug/L micrograms per liter USDA United States Department of Agriculture USEPA United States Environmental Protection Agency UV ultraviolet UVDGM Ultraviolet Light Disinfection Guidance Manual UVT Ultraviolet Light Transmittance WRRF WateReuse Research Foundation WWTP Wastewater Treatment Plant

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Chapter 1

INTRODUCTION

1.1 OVERVIEW The City of Dripping Springs is located in Hays County, Texas, twenty-five miles southwest of the State capital, Austin. The Austin metropolitan area is one of the fastest growing metropolitan areas in the nation (Forbes, 2015 and U.S. Census Bureau, 2014a). In addition, the U.S. Census Bureau ranked Hays County as the 14th fastest growing county in the U.S with a population increase of twelve percent between 2010 and 2013 (U.S. Census Bureau, 2014b).

Like much of Texas over the past several years, the City has experienced drought conditions ranging from moderate to severe (U.S. National Drought Mitigation Center, 2015). Drought conditions, along with an increase in population, have lead to strain on the City’s water supplies.

The City itself is also experiencing significant growth associated with its proximity to Austin, with several large tracts proposed for private development at various stages of permitting and build-out. Some of these have obtained their own wastewater permits for onsite treatment and disposal (CMA, 2013), but have indicated to the City that their preference would be to tie into the City’s existing wastewater collection and treatment system.

An overview map of the City is shown in Figure 1.1.

1.2 WATER SUPPLY The Dripping Springs Water Supply Corporation (DSWSC) provides drinking water and manages the drinking water distribution system for 1,402 active connections in the Dripping Springs area. The DSWSC operates four groundwater wells that have a joint capacity of 1.5 million gallons per day (MGD), and also has a contract with the West Travis County Public Utility Agency (PUA) to deliver up to 1 MGD of treated water purchased from the Lower Colorado River Authority (DSWSC, 2015).

Table 1.1 shows the sources and quantities of water purchased and provided by DSWSC for 2011-2014.

127,000 gpd Onsite Drip Irrigation

Future 35,000 gpd Drip Irrigation(City Athletic Fields)

DSWSC Well Field/Ground Storage Tank

Future 186,000 gpd Surface Irrigation(Caliterra Development)

South Regional WWTP

VICINTY MA Legend

Sanitary Sewer

Water Distribution System

Current and Future Irrigation Sites

City of Dripping Springs

100-Year FEMA Floodplain

VICINITY MAPFIGURE 1.1

CITY OF DRIPPING SPRINGSDIRECT POTABLE REUSE FEASIBILITY STUDY

O0 0.60.15 0.3

Miles

Dripping SpringsStudy Area


Table 1.1 Dripping Springs Water Supply Company Service Summary Direct Potable Reuse Feasibility Study City of Dripping Springs

2011 2012 2013 2014(2)

Active Connections 1,353 1,331 1,371 1,402

Water Purchased (Mgal)(3) 198 150.5 132 115

Water Pumped (Mgal)(4) 84 66.5 91.5 63

Total (Mgal) 282 217 223.5 178

(1) Data taken from Draft Feasibility Study (Analysis of Consolidating Water Utility Systems), dated Feb 2, 2015 (NewGen, 2015).

Notes:

(2) 2014 Data only for January through September. (3) Purchased water is from PUA, which enters the service area along Highway 270 from the east.

See Figure 1.1. (4) Pumped water is from local wells located on the south end of the service area. See Figure 1.1.

1.3 WASTEWATER COLLECTION, TREATMENT AND DISPOSAL Several studies have been conducted on behalf of the City with respect to strategies for wastewater collection, treatment, and disposal. While many of the outlying areas surrounding the City are currently still served by on-site septic systems, an existing core of the City is connected via sewer to the South Regional Wastewater Treatment Plant (South Regional Plant).

1.3.1 South Regional Wastewater Treatment Plant

The South Regional Plant treats the wastewater from municipal and commercial connections in the Dripping Springs area and is managed by Professional General Management Services (PGMS). The plant operates as a conventional activated sludge process that includes a mechanical bar screen, aeration, clarification, chlorination, and aerobic digestion. The plant is rated for 127,500 gallons per day (gpd) and currently treats an average flow of approximately 70,000 gpd.

The City currently holds a Texas Land Application Permit (TLAP; permit no. WQ0014488001), issued by the Texas Commission on Environmental Quality (TCEQ) that allows for disposal of the effluent from the South Regional Plant via drip irrigation on-site. A pending amendment to the City’s TLAP permit includes plans to implement cloth filters at the South Regional Plant in order to be able to meet draft permit requirements for spray irrigation at the Caliterra development once the flow at the South Regional Plant exceeds the existing TPDES permit capacity (CMA, 2014).


1.3.2 Future Expansion of Wastewater Service

The current approach to wastewater treatment and disposal for new residential developments in the City’s service area involves implementing small, decentralized treatment systems at several property developments, with effluent disposal consisting of surface or subsurface irrigation systems. However, given the given the capital expense, land required, and reverse economies of scale associated with each development operating its own wastewater treatment and disposal system, this approach is inefficient compared to centralized treatment solutions. In addition, the developers would prefer to tie into the City’s centralized system instead of devoting valuable tracts of land from each development to the disposal of effluent. In fact, a recent evaluation recommended centralized treatment and pursuing a permit for effluent discharge to Onion Creek in conjunction with a beneficial reuse authorization, despite anticipated public resistance to such a proposal (CMA, 2013).

1.4 DIRECT POTABLE REUSE Based on the City’s growth in the face of dwindling existing water supplies in the region and the expense of land application for effluent disposal, the City has tasked Carollo Engineers, Inc. (Carollo) with performing a study that considers the feasibility of direct potable reuse (DPR). A DPR project could simultaneously provide additional potable water resources to the City’s service area and also divert effluent from being discharged to Onion Creek.

A DPR project would be implemented with the intent to reuse as much as possible of the effluent produced by the City through treatment in an advanced water purification process and subsequent potable uses. However, for both permitting and technical reasons, an alternative disposal mechanism for effluent would still be needed as a backup to DPR. As part of the study, Carollo was therefore also tasked with a comparison of land application and discharge as the backup effluent disposal options to a DPR project.

1.5 STUDY OBJECTIVES The objective of this study is to determine the feasibility, treatment requirements, and planning-level cost for developing a direct potable reuse project to supplement drinking water supplies in the Greater Dripping Springs area and to minimize or eliminate the need for discharge of treated wastewater. Specifically, the goals of this study are to:

1. Develop water quality goals for the treated water for direct potable reuse (DPR);

2. Determine permitting requirements for a DPR project in the City;

3. Develop one or more feasible DPR alternatives;

4. Determine planning-level cost information for a preferred subset of the DPR alternatives; and

5. Develop a list of next steps for moving forward with a DPR project.


Chapter 2

REGULATION OF POTABLE REUSE

2.1 OVERVIEW In the broadest sense, “reuse” refers to the intentional use of treated effluent from wastewater treatment facilities for some beneficial purpose. Two main types of reuse exist: non-potable, and potable.

The State of Texas regulates water reuse through several methods, including the requirements for direct reuse (non-potable) described in Division 30 of the Texas Administrative Code, Chapter 210 (30 TAC 210) and 30 TAC 321 Subchapter P (satellite facilities), and indirect reuse through the Texas Water Code (TWC) Paragraph (§)11.042 governing bed and banks permits and TWC §11.046 governing return flows. The regulations for direct reuse include water quality requirements for Type I and Type II reclaimed water, which are both limited to non-potable uses, whereas the regulations governing indirect reuse do not include water quality requirements.

Faced with an urgent need for additional water supplies in parts of the state, the Texas Commission on Environmental Quality (TCEQ) has been approving direct potable reuse (DPR) projects, (the Raw Water Production Facility (RWPF) at Big Spring and the Emergency DPR Project in Wichita Falls), on a case-by-case basis in accordance under the innovative/alternative treatment clause in 30 TAC 290 that allows “any treatment process that does not have specific design requirements” listed in that chapter to be permitted.

2.1.1 Introduction to Potable reuse

Within potable reuse, one can define three main subcategories:

De facto reuse, which is the unintentional or unacknowledged reuse of treated effluent by users downstream of the point of discharge, is a practice that regularly occurs throughout Texas as upstream wastewater discharges are subsequently reused by downstream water users. Nearly all major river basins, including the Lower Colorado, contain examples of de facto reuse. As water demands increasingly strain available resources, both intentional indirect potable reuse (see below) and de facto reuse will continue to increase in frequency, and the distances between treated effluent discharges and raw water intakes will continue to shrink.


Indirect potable reuse (IPR), is similar to de facto reuse, in that treated effluent is discharged to an environmental system (called “environmental buffer”) that may consist of a river, lake (or reservoir), or aquifer before being withdrawn for potable use. States vary in their regulation of IPR. Texas regulates IPR water quality based on existing wastewater discharge and surface (or groundwater) treatment rules in much the same way de facto reuse is regulated. Thus, the distinction between IPR and de facto reuse is limited to the intent to reuse the water for potable purposes, as evidenced by the procurement of water rights associated with the treated effluent discharged. As a side note, the State of California regulates IPR separately from existing wastewater and drinking water regulations, as described in more detail below.

Direct potable reuse (DPR), is the direct reuse of treated effluent that has been subjected to significant advanced water treatment for potable purposes. Specifically, DPR is distinguished from IPR by the lack of an environmental buffer into which treated effluent is discharged before being withdrawn for potable purposes. Practically speaking, this reduces the total “cycle time” for potable reuse from a timeframe of weeks to years in the case of de facto reuse and IPR to as little as a few days or less for DPR projects. This close coupling of treated effluent to drinking water has significant implications on treatment and monitoring requirements.

2.1.2 Water Rights and Project Permitting Approach

While a water rights and detailed permitting analysis is outside the scope of this study, the following is a brief summary of the situation anticipated to apply to this project:

For a DPR project such as the one discussed in this study, the water rights situation is generally pretty straightforward. Unless there are specific provisions in water supply contracts that stipulate otherwise, the treated effluent from a WWTP is not subject to reappropriation unless it is discharged to a Water of the State. In a DPR scenario, this discharge does not occur, leaving full consumptive ownership of the water in the hands of the entity producing the treated effluent. While Carollo anticipates that the City should have full consumptive rights to the treated effluent from South Regional Plant, including the option to sell to a third party, the City should confirm this before proceeding with the project.

In that sense, the water rights situation of a DPR project is much like that of a direct (non-potable) reuse scenario, which involves application and TCEQ approval of a 210 authorization for reuse. Because it falls outside the purview of existing specific regulation, the DPR project itself is then subject to an exception letter approval process administered by the Water Supply Division at TCEQ. The focus of the analysis in this study, as it pertains to permitting, is to meet water quality and treatment requirements anticipated to be set by the Water Supply Division.


As the project progresses, close coordination with TCEQ will be necessary to determine whether the conditions assumed above apply to the City and this project and to determine all permitting and approval requirements.

2.2 POTABLE REUSE REQUIREMENTS AND GUIDELINES Pathogens and chemicals constitute the two main classes of constituents of concern in potable reuse.

2.2.1 Chemical Removal Goals and Requirements

A large number of chemicals known to be detrimental to human health above certain concentrations are regulated through maximum contaminant levels (MCLs). Drinking water must be treated to meet these standards regardless of the source. Therefore, any treated effluent that is proposed for supply augmentation should be tested for the full suite of these compounds. A copy of TCEQ’s recommendations for effluent characterization is provided in Appendix A.

Besides the chemical (and radiological) constituents explicitly regulated through MCLs, a wealth of research has been conducted on the concentrations of unregulated trace organic constituents (TOrCs) in wastewater, their attenuation through conventional WWTPs, and their further breakdown during advanced treatment (Baronti et al, 2000; Lovins et al., 2002; Schäfer et al., 2005; Sedlak et al., 2006; Steinle-Darling et al., 2010; Linden et al., 2012; Salveson et al., 2010; Salveson et al., 2012; Snyder et al., 2012; and many others). These constituents include pharmaceuticals, personal care products, consumer chemicals, flame retardants, and others, some of which have endocrine disrupting, carcinogenic, and/or other potentially harmful properties at sufficiently high concentrations. Due to this fact (and some help from media interest), this group of constituents has often been the cause of more public concern than the pathogens discussed below. However, the vast majority of TOrCs are present in treated effluent, if at all, at concentrations that are not of concern for human health (Trussell et al., 2013).

Disinfection byproducts (DBPs) are another suite of parameters that warrant consideration for potable reuse projects. Conventional DBPs, such as trihalomethanes (THMs), Haloacetic Acids (HAAs), bromate, and chlorate, are regulated by the Stage 1 and Stage 2 Disinfectant and Disinfection Byproduct Rules (USEPA, 1998 and 2006a). N-Nitrosodimethylamine (NDMA) and other nitrosamines have been considered for regulation by the USEPA for over a decade (they are on the Unregulated Contaminant Monitoring Rule 2 list and the Candidate Contaminant List 3), and NDMA has a California Notification Level of 10 nanograms per liter (ng/L), which is considered the minimum treatment benchmark by the California utilities currently implementing potable reuse.


2.2.2 Pathogen Removal Goals and Requirements

With respect to current drinking water regulations, the pathogens of primary concern for potable reuse include enteric viruses, such as Adenovirus, Norovirus, and Enterovirus, and the protozoa Giardia and Cryptosporidium. In some cases, though not in Texas, enteric bacteria (such as Salmonella) are also considered. Because treated effluent is generally not considered an acceptable “source water” under existing drinking water regulations (it is neither a groundwater, nor a surface water, nor a groundwater under the influence of surface water), the treatment requirements in current drinking water regulations are generally considered inadequate for the protection from the health risk presented by pathogens. Therefore, additional requirements for pathogen control that are specific to potable reuse have been developed. These are discussed in more detail in Chapter 3.

Water treatment regulations for pathogens are predicated on reducing the risk of infection to minimal levels. Table 2.1 identifies the concentration end goals for targeted pathogens that correspond to a modeled, annual risk of infection of 1 in 10,000 or less (Trussell et al., 2013). TCEQ’s case-by-case approach to developing treatment requirements for potable reuse projects is based on determining the difference between the values in Table 2.1 and the measurement of project-specific effluent pathogen concentrations.

Table 2.1 Pathogen Concentration End Goals for Drinking Water Direct Potable Reuse Feasibility Study City of Dripping Springs

Pathogen Giardia (cysts/L)

Cryptosporidium (oocysts/L)

Enteric virus (MPN/L)

Potable goal 6.80E-06 3.00E-05 2.22E-07

(1) End goals are based on achieving a risk level of 1 in 10,000 annual risk of infection as listed by Trussell et al. (2013); values confirmed by personal communication with TCEQ staff.

Notes:

Beyond the theoretical calculation of log removal credits, TCEQ also requires significant pilot testing to be completed before a project can achieve final approval. This can be achieved from operation of a dedicated, smaller-scale pilot unit that appropriately mimics the proposed final treatment solution, or though “full scale verification.”

This second approval method allows treatment facilities to be approved for construction without completing a pilot study prior to design of the full-scale system. With a full-scale verification approach, which was the basis for the City of Wichita Falls Emergency DPR project, for example, the full-scale facilities are operated in “pilot mode” to collect the data necessary for final approval while finished water is sent to disposal pending final approval by TCEQ to deliver water. Given the relatively small scale of the proposed DPR plant for the City of Dripping Springs, the second piloting option may be more cost effective.


2.2.3 Potable Reuse in Other Parts of the U.S.

The most recent industry recommendations for potable reuse treatment – beyond meeting existing water quality goals for drinking water – include pathogen control that achieves at minimum 12-log virus, 10-log protozoa (Giardia and Cryptosporidium), and 9-log removal or inactivation of total coliform (as a surrogate for Salmonella). This was established by a panel of national experts convened by the National Water Research Institute in the context of WateReuse Research Foundation Project (WRRF) No.11-02, Equivalency of Advanced Treatment Trains for Potable Reuse (Trussell et al., 2013). The State of California has recently adopted regulations for indirect potable reuse (via groundwater injection only), which requires 12-log virus, 10-log Giardia, and 10-log Cryptosporidium removal (CDPH, 2014).

Unlike the requirements put forth by TCEQ, the log removal recommendations and requirements, put forth by the NWRI Panel and the State of California respectively, allow for treatment that occurs throughout the entire treatment train, from the upstream end of wastewater treatment facilities to the finished potable water produced from a downstream water treatment plant. Specifically, this approach gives credit for primary, secondary, and tertiary wastewater treatment, whereas TCEQ does not.

Therefore, while the total log removal requirements put forth by TCEQ in its currently approved DPR projects have lower numerical values, TCEQ’s approval process does not allow any treatment credits to be claimed at the wastewater treatment plant. In general, the stringency of the criteria developed for WRRF 11-02 and those applied by TCEQ appear to be similar. In fact, they are based on the same fundamental pathogen goal concentrations in drinking water cited in Table 2.1.

The water rights issues associated with reuse (potable and non-) across the U.S. vary significantly from state to state and are not covered here.


Chapter 3

WATER QUALITY GOALS

3.1 END USES DEFINE WATER QUALITY GOALS In any DPR project, the main water quality goals are defined by meeting requirements for potable use. However, in this project, two additional sets of constraints may be placed on water quality. These requirements are associated with the two disposal alternatives for the treated effluent that will serve as the source water for DPR.

It is important to note that while the purpose of implementing a DPR project would be to divert all treated effluent for potable reuse such that no water is wasted via disposal, a permitted disposal option must be included in any DPR project. This permitted disposal option is required from a regulatory perspective, as with any reuse authorization (30 TAC 210). It is also imperative that such a backup disposal option exist for the protection of public health in the event of a process failure during advanced treatment.

Hence, the three categories of potential effluent end-use are evaluated include:

1. Potable use,

2. Discharge to Onion Creek, and

3. Land application via canopy spray.

Each of these use categories is associated with a set of water quality requirements, discussed in more detail in the sections below. In general, however, they can be broken down into four main categories:

1. Salinity

2. Nutrient concentrations

3. Other Water Quality Parameters of Concern

4. Pathogens

Therefore, the following sections will discuss the water quality requirements associated with each use category for each of the water quality parameter categories listed above.


3.2 WATER QUALITY REQUIREMENTS FOR POTABLE REUSE

3.2.1 Salinity

Texas has enforceable secondary standards for salinity, which comprise the following:

• Total dissolved solids (TDS), with a limit of 1,000 milligrams per liter (mg/L),

• Sulfate, with a limit of 300 mg/L, and

• Chloride, with a limit of 300 mg/L.

These limits must be maintained by any drinking water supply and serve as the goals for this project as well.

3.2.2 Nutrient Concentrations

“Nutrients” as a category do not directly apply to drinking water quality limits. However, two inorganic nitrogen compounds, nitrate and nitrite, considered nutrients in the aquatic environment, are also limited in drinking water. The drinking water MCL for nitrate is 10 mg/L as nitrogen (N). The drinking water MCL for nitrite is 1 mg/L as N. The total nitrate plus nitrite MCL is also 10 mg/L as N.

The nitrate and combined nitrate/nitrite limit is higher than the total nitrogen limit anticipated for effluent discharge (6 mg/L as N, for ammonia, nitrite, and nitrate combined; see Section 3.3.2) and will therefore be met if the anticipated standards for discharge are being met.

However, the acute nature of nitrate and nitrite toxicity to humans, which is manifested as methemoglobinemia (known as “blue baby syndrome” in infants) means that it is more critical to meet this goal consistently.

Therefore, the Carollo proposes an effluent total nitrogen goal of less than 5 mg/L regardless of the effluent permitting requirements.

This limit is also anticipated to maintain nitrite concentrations well below the MCL of 1 mg/L. Additional removal of nitrogen species is anticipated in advanced treatment, though some addition (ammonia, for formation of chloramines) will also occur.

3.2.3 Other Chemicals of Concern

As discussed in Chapter 2, water quality goals for chemical constituents should include any constituents that are currently regulated in drinking water. These include organic chemicals, inorganic chemicals, radionuclides, and other parameters.


Existing drinking water regulations were not intended for use in intentional potable reuse scenarios, especially DPR, and therefore do not take into account the added risk of coupling a wastewater source directly with a drinking water supply. Beyond the additional treatment requirements put in place by TCEQ with respect to pathogen control for DPR (see Section 3.2.4), screening for and tracking the removal of unregulated constituents therefore represents an appropriate standard of care for a DPR project. In addition, while not directly regulated by TCEQ, the inclusion of treatment processes that are able to adequately address the presence of unregulated chemical constituents are anticipated to be required as part the case-by-case approval process for a DPR project.

Additional water quality goals for the project should therefore include meeting the screening values for unregulated constituents as developed by Trussell et al. (2013). These screening values cover several classes of constituents, including unregulated disinfection byproducts, pharmaceuticals and personal care products. As noted by Trussell et al. (2013), the concentrations of most of these chemicals are anticipated to be well below their health screening levels even in secondary effluent. The design goals of the advanced treatment process train proposed include the purpose of reducing the concentrations of these unregulated constituents even further.

In summary, the treatment goals for chemicals of concern include meeting all primary and secondary drinking water standards. In addition, unregulated chemicals listed by Trussell et al. (2013) will be tracked for their removal during the pilot testing phase.

3.2.4 Pathogens

Pathogen removal requirements for DPR projects in Texas are determined for each applicant on a case by case basis as a function of pathogen concentrations found in the effluent and final drinking water goal concentrations of 2.2 x 10-7

most-probable number (MPN)/L enteric virus, 6.8 x 10-6, cysts/L Giardia and 3.0 x 10-5 oocysts/L Cryptosporidium, respectively (see Table 2.1). Because these concentrations cannot be verified directly by measurement, treatment requirements are based on establishing “log removal values” (LRVs) that are credited to treatment processes, where 1-log corresponds to 90% removal, and 4-log corresponds to 99.99% removal, etc.

Based on their respective effluent sampling results, the DPR project in Big Spring is required to achieve 8-log virus, 6-log Giardia, and 5.5-log Cryptosporidium inactivation and the DPR project in Wichita Falls must meet 9-log virus, 7-log Giardia, and 5.5-log Cryptosporidium inactivation. In addition, since its original “emergency” permit approval for temporary operation over a 6-month period, the Wichita Falls project has added an additional disinfection step to increase its overall LRVs for protozoa (Giardia and Cryptosporidium).


Given that the South Regional Plant will need to be upgraded to achieve nutrient removal (see Chapter 4), it is not constructive to sample the existing effluent to determine precise LRV requirements at this time. Therefore, for the purposes of this study, the project team assumed values that correspond to the upper 95th percentile of those measured at six wastewater treatment plants by Rose et al. (2004), as reported in more detail by Olivieri et al. (2007).

Based on these conservative assumptions, the design goals for the advanced water treatment plant developed in this study include minimum LRV targets of 9-log virus, 9-log Giardia, and 7.5-log Cryptosporidium.

These assumed values are the same or slightly higher than those required for the two existing DPR facilities in Texas.

3.2.5 TCEQ Effluent Characterization Requirements for DPR

To determine the treatment requirements for a DPR project, TCEQ requires that the source water proposed for the DPR project, generally secondary effluent, be characterized with respect to chemical and microbial constituents. A copy of the current recommendations provided by TCEQ for this effluent characterization process is provided in Appendix A.

In summary, TCEQ recommends screening for all chemicals that are regulated in drinking water, pathogens, specifically virus and protozoa (as discussed in Section 3.2.4), and bulk water quality parameters. The data collected must be able to adequately represent seasonal variability in water quality, which means that the listed parameters must be sampled more than once over the course of at least one year.

TCEQ specifically recommends sampling effluent over a period of one year, including 24 samples analyzed for “microorganisms, nitrate, nitrite, pH, and temperature” (though the specific microorganisms included in this 24-sample recommendation are not listed specifically) and at least four samples for the other chemicals listed (see Appendix A).

Based on previous project experience, the analytical costs associated with screening effluent, monitoring during pilot testing, and periodic confirmation testing during routine operation can be significant.


3.3 WATER QUALITY REQUIREMENTS FOR DISCHARGE TO ONION CREEK

3.3.1 Salinity

Per existing TCEQ guidance (TCEQ, 2010), salinity is not considered in TPDES permitting for flows under 1 mgd. That alone is sufficient to determine that salinity will not create a restriction for discharge to Onion Creek.

Therefore, no salinity restrictions on a discharge to Onion Creek are anticipated for this project.

3.3.2 Nutrient concentrations

Onion Creek is located in the Barton Springs Edwards Aquifer contributing zone. Amongst other factors, this makes it very sensitive to nutrient addition. Consequently, there are currently no TPDES permits for discharging wastewater effluent directly into Onion Creek. Based on an existing permit (for Hays County Water Control and Improvement District No.1 (Belterra Subdivision), WQ0014293001) for discharge into Bear Creek, a tributary of Onion Creek, the expected water quality requirements for discharge into Onion Creek would include strict restrictions on total nitrogen and total phosphorus.

For the purposes of this study, the water quality limits for discharge to Onion Creek are assumed as follows:

• Total nitrogen (TN) limit: 6 mg/L as N

• Total phosphorus (TP) limit: 0.5 mg/L as phosphorus (P)

Additional water quality modeling will be required to determine if these assumed values are appropriate. Such modeling is outside the scope of this study.

3.3.3 Other Water Quality Parameters of Concern

Traditional wastewater effluent loading parameters, such as biochemical oxygen demand (BOD) and total suspended solids (TSS) are also anticipated to be restricted to relatively low concentrations in Onion Creek. As discussed above for nutrients, the precise determination of proposed discharge limits it outside the scope of this study. However, based on the implementation of biological nutrient removal to reduce nutrient concentrations to the values listed above and the planned implementation of cloth filters as outlined in the pending Major Permit Amendment to the City’s existing TLAP Permit (No. WQ0014488001), organic and solids concentrations (BOD and TSS) should not be limiting factors.


For the purposes of this study, the water quality limits for discharge to Onion Creek are assumed as follows:

• BOD5 limit: 5 mg/L

• TSS limit: 5 mg/L

In addition, the following are anticipated to be required:

• 6.0 < pH < 9.0

• Chlorine disinfection with a minimum combined chlorine residual of 1 mg/L after minimum of 20 minutes of contact time

3.3.4 Pathogens

A typical pathogen limit for wastewater discharge, 126 CFU/100mL E. Coli, is assumed to be adequate in this case. The existing chlorine contact basin with the contact time and residual requirements listed above will be adequate for achieving this standard. The planned cloth filters will provide additional pathogen removal capacity, especially for larger microbes such as Giardia and Cryptosporidium. Thus pathogen removal and/or inactivation are not anticipated to be limiting requirements for discharge to Onion Creek.

3.4 WATER QUALITY REQUIREMENTS FOR LAND APPLICATION VIA CANOPY SPRAY

In general, the water quality requirements for land application are anticipated to be much less stringent than those for discharge to Onion Creek, as follows:

• BOD5 < 20 mg/L daily average

• TSS < 20 mg/L daily average

In addition, the following are anticipated to be required:

• 6.0 < pH < 9.0

• Chlorine disinfection with a minimum combined chlorine residual of 1 mg/L after minimum of 20 minutes of contact time

These limits are representative of standard permit conditions for spray irrigation in location where there is no public access, such as the tract of land proposed for application evaluated for the purposes of this study (see Chapter 6).

No restrictions on concentrations of nutrients, salinity, pathogens, or other chemicals are anticipated.


Chapter 4

WASTEWATER TREATMENT

4.1 EXISTING WASTEWATER TREATMENT PLANT The City sends wastewater to the Dripping Springs South Regional Wastewater Treatment Plant (South Regional Plant) located on the South side of Farm-to-Market Road 150 approximately one mile east of Ranch Road 12 in Dripping Springs, Texas. The City owns the South Regional Plant, but the plant is operated on a contract basis by PGMS.

The South Regional Plant is a conventional activated sludge process that includes a bar screen, aeration, clarification, chlorination, and aerobic digestions. Treated effluent is held in a storage tank prior to disposal via subsurface drip irrigation.

4.1.1 Flows

A summary of the South Regional Plant’s actual and projected wastewater flows are shown in Table 4.1. Effluent from the South Regional Plant is stored in an effluent storage tank with a capacity of 333,000 gallons before being land applied at on-site drip irrigation fields.

Table 4.1 Current and Projected Future Effluent Flows Direct Potable Reuse Feasibility Study City of Dripping Springs

Parameter Flow (gpd) (1)

Current Plant Flow 70,000

Existing Plant Design Flow 127,500

2020 Projected Flow 348,500

(1) Source: CMA (2014). Notes:

4.1.2 Current Effluent Water Quality

A summary of current effluent characteristics are shown in Table 4.2. These are compared to the anticipated or recommended water quality goals discussed in Chapter 3. Based on this comparison, the current operation of the South Regional Plant meets organic and solids concentration goals except during brief periods of excursion, but does not meet nitrogen species concentration goals. Phosphorus data were not available for analysis.

More consistent operational oversight at the existing facilities would likely be sufficient to consistently meet organics and solids concentration goals. However, the existing facilities are inadequate to achieve the low nutrient concentration goals determined in Chapter 3.


Table 4.2 Summary of Current Effluent Water Quality Direct Potable Reuse Feasibility Study City of Dripping Springs

Parameter (all in mg/L) Permit

(1) Goal

(2) Mean Median Min

(3) Max

(4) N(5)

Biological Oxygen Demand (BOD) 20 5 3.6 3.0 <1.0 25 272

Total Suspended Solids (TSS) 20 5 5.4 5.0 <1.0 27 318 Total Nitrogen NL(6) 5 18.8 16.3 1.25 141 98 Ammonia as Nitrogen NL(6) 2 7.29 1.65 <0.05 45.9 176 Nitrate/Nitrite as Nitrogen NL(6) 5 21.3 21.3 <0.05 141 269

Samples taken between 2008 and 2014. Notes:

(1) Current permit conditions (WQ0014488001) (2) Anticipated or recommended water quality goals as described in Chapter 3. (3) Min(4)

imum value. Where preceded by “<”, numbers indicate value was below detection. Max

(5) Number of samples collected. imum value.

(6) No Limit for these parameters exists under the current permit.

4.2 RETROFIT FOR BIOLOGICAL NUTRIENT REMOVAL As part of the Dripping Springs Direct Potable Reuse project, Carollo evaluated the feasibility of implementing a biological nutrient removal process to achieve a total nitrogen (TN) limit of 6 mg/L and a total phosphorus (TP) limit of 0.5 mg/L. Historical wastewater data for the period 2008-2014 was used to develop the design criteria for this evaluation. The influent wastewater design criteria are displayed in Table 4.3. The maximum month flow of 0.5 mgd represents the proposed permitted flow rate for the facility.

Table 4.3 Wastewater Model Influent Design Criteria Dripping Springs WWTP Direct Potable Reuse City of Dripping Springs

Parameter Annual Average Maximum Month Wastewater flow, mgd 0.35 0.50

Five-day carbonaceous biological oxygen demand (CBOD5), mg/L

270 265

Total suspended solids (TSS), mg/L 300 295

Total Kjeldahl nitrogen (TKN), mg/L 60 59

Ammonia nitrogen (NH3-N), mg/L 46 44

Total phosphorus (Total P), mg/L 7.7 7.5

Alkalinity, mg/L 350 350

Seven-day average effluent temperature, °C 18-28 18-28


The selected configuration to achieve the target TP and TN limits was a four-stage Bardenpho process. The addition of an external carbon source to the second anoxic zone would be required to achieve the TN limit reliably. For this evaluation, methanol was selected as the external carbon source. Other chemicals that can be used to enhance denitrification are acetic acid, ethanol, sucrose, and Micro-C. The implementation of chemical polishing would be required to achieve the TP limit reliably. For this evaluation, alum was selected as the polishing chemical. Other chemicals that can be use for chemical polishing include ferric chloride, ferric sulfate, ferrous chloride, and sodium aluminate. A conceptual schematic of the Bardenpho process is shown in Figure 4.1. This process can be implemented in the existing facility by commissioning the remaining volume of the existing aeration basin, installing baffles to provide four zones (anoxic 1, oxic 1, anoxic 2, and oxic 2), and providing an internal mixed liquor recirculation (IMLR) system. A plan view of the proposed basin configuration is shown in Figure 4.2.

PROCESS FLOW FOR PROPOSED BIOLOGICAL NUTRIENTREMOVAL UPGRADES TO EXISTING WASTEWATER TREATMENT PLANT

FIGURE 4.1


pw:\\PHX-POP-PW.Carollo.local:Carollo\Documents\Client\TX\Dripping Springs\9756A00\Deliverables\Graphics\Figure 4.1.ai

Alum

Bar Screen(Existing)

Return Activated Sludge

Secondary Treatment(Existing Aeration Basins Reconfigured for BNR)

Recycle

Waste Activated Sludge

Clarifiers(Existing)

Oxic OxicAnoxic Anoxic

Chlorine Contact(Existing)

To 210 Reuseor EffluentDisposal

To AdvancedTreatmentfor DPR Filters

(Proposed)

Aerobic Digesters(Existing)

Sludge HauledOff-Site

Methanol

EffluentStorage

pw://Carollo/Documents/Client/TX/Dripping Springs/9756A00/Deliverables/Feasibility Study/Graphics/Fig_4.2.docx

PROPOSED AERATION BASIN CONFIGURATION (PLAN VIEW)

FIGURE 4.2




Steady-state simulations were conducted using BioWin version 4.1. Table 4.4 presents a summary of the modeling results for the effluent characteristics. A summary of the results is included in Appendix B.

Table 4.4 Wastewater Model Results for Filtered Effluent Dripping Springs WWTP Direct Potable Reuse City of Dripping Springs

Parameter Annual Average(1) Maximum Month

(28°C) Maximum Month

(18°C)

Wastewater flow, mgd 0.35 0.50 0.5 CBOD5, mg/L 1.2 1.3 1.5

TSS, mg/L 0.7 1.1 1.1

TN, mg/L 4.5 5.1 5.5

NH3-N, mg/L 0.1 0.3 1.5 TP, mg/L 0.18 0.17 0.28

Alkalinity, mg/L 46 69 70

(1) Annual average values calculated at 22 degrees Celcius (°C). Notes:

The model results indicated that by modifying the existing basins, the facility will have sufficient capacity to achieve the TN and TP goals at the proposed design flow (0.5 mgd) without additional aeration basin volume or additional polishing steps. In the future, the addition of deep bed filters could help polish effluent if additional capacity were needed.

The effluent alkalinity for all modeled scenarios was low, suggesting that the implementation of an alkalinity addition system might be required. The influent alkalinity value in the design criteria was based on a single measurement because the City does not monitor this parameter. Carollo recommends the routine monitoring of alkalinity to determine whether alkalinity addition will be required.

4.3 PREVIOUS EVALUATION OF MEMBRANE BIOREACTOR An alternative to the implementation of the process changes discussed above for achieving the TN and TP goals is to retrofit the South Regional Plant with membranes to implement a membrane bioreactor (MBR). A previous initial evaluation and preliminary cost estimate for converting the South Regional Plant into a membrane bioreactor (MBR) was conducted by others (CMA, 2012). No additional evaluation of this option was conducted; however, the existing cost estimate was used to develop a project alternative (Alternative 1B, see Chapter 7) based on this potential MBR retrofit and cost estimate.


Chapter 5

POTABLE REUSE ALTERNATIVES

5.1 DPR TREATMENT EVALUATION

5.1.1 Introduction to Treatment Train Concepts

No single treatment technology can or should be relied upon to provide sufficient treatment for any potable application. The multi-barrier approach is especially important in treatment for (direct) potable reuse due to the close coupling between wastewater and potable use. Thus, while in theory, it would be possible to achieve the log removal credits necessary for the project with just one technology (irradiation with ultraviolet light, for example), it is important to include a number of different treatment processes with different modes of action to create a robust and reliable overall treatment process or “treatment train.”

For this project, two main treatment train concepts were considered:

1. Trains that center around an RO membrane as a main mode of contaminant removal, and

2. Trains that center around the combination of ozonation and biofiltration as the main mode of contaminant removal.

While each of these central treatment concepts provide significant attenuation of both chemicals and pathogens, it is difficult in either case to rely upon pathogen log removal credits from the central process alone. Therefore, each of the candidate treatment trains were augmented by additional steps that provide some additional chemical treatment capacity but have the main purpose of achieving significant disinfection and the associated pathogen log removal credits. These treatment train concepts are shown in Figure 5.1.

CONCEPTUAL PROCESS FLOW DIAGRAMS FORADVANCED TREATMENT TRAIN ALTERNATIVES

FIGURE 5.1



RO Based Train

Non-RO Based Train

Ultrafiltration Reverse OsmosisUltraviolet Disinfection/

Advanced OxidationProcess

NH3

ChlorineDisinfection Engineered

StorageBuffer

NaOCl

UltrafiltrationBiologically Active

Filter

AdvancedOxidationProcess

From EffluentHolding Tank

To DistributionUltravioletDisinfection Chlorine

DisinfectionEngineered

StorageBuffer

O3

NH3

NaOCl

From EffluentHolding Tank

To Distribution


5.1.2 Pathogen Log Removal Goal Overview

Both treatment trains are anticipated to achieve the treatment goals for chemicals and pathogens described in Chapter 3. Table 5.1 and Table 5.2 show an approximate allocation of pathogen log removals to each of the two treatment trains and provide notes on the efficacy with respect to chemical removal. Note that the formal pathogen inactivation credits are achieved by the same technologies in each train (micro- or ultrafiltration, ultraviolet irradiation, and chemical disinfection).

Table 5.1 Log Removal Overview of Reverse Osmosis-Based Treatment Train Direct Potable Reuse Feasibility Study City of Dripping Springs

Treatment Step

Anticipated LRVs(1)

Notes on Treatment V(2) G(3) C (4)

Ultrafiltration(5) 0 4 4 Particulate-associated chemical removal, filtration of protozoa (G/C)

Reverse Osmosis +(6) + + Near-complete removal of most dissolved chemicals

Ultraviolet Irradiation with Advanced Oxidation 6 6 6 Oxidation of remaining chemicals

Chemical Disinfection 6 + 0 Disinfection byproduct formation limited by lack of precursors

Total 12 10 10

(1) Log Removal Values Notes:

(2) Enteric Virus (3) Giardia (4) Cryptosporidium (5) Microfiltration is the standard approach, but ultrafiltration could also be used. Ultrafiltration

provides more credit for Giardia and Cryptosporidium removal. (6) Plus sign (+) denotes additional pathogen removal potential for which LRVs are not credited.


Table 5.2 Log Removal Overview of Ozone/Biofiltration Based Treatment Train Direct Potable Reuse Feasibility Study City of Dripping Springs

Treatment Step

Anticipated LRVs(1)

Notes on Treatment V(2) G(3) C (4)

Ozonation ++(5) + 0 Ozone-mediated advanced oxidation of chemicals into assimilable organics

Biofiltration 0 + +

Particulate-associated chemical removal, filtration of protozoa (G/C), and biotransformation of assimilable organics

Ultrafiltration 0 4 4 Particulate-associated chemical removal, filtration of protozoa (G/C)

Ultraviolet Irradiation 6 6 6 Pathogen inactivation

Chemical Disinfection 6 + 0 Pathogen inactivation; formation of byproducts a concern.

Total 12 10 10

(1) Log Removal Values Notes:

(2) Enteric Virus (3) Giardia (4) Cryptosporidium (5) Plus sign (+) denotes additional pathogen removal potential for which LRVs are not credited. A

double plus sign denotes significant (3-log or more) inactivation shown in challenge studies.

5.1.3 Chemical Removal Mechanisms

The main distinction between the two train concepts lies in the method of chemical removal:

With reverse osmosis (RO), the chemicals are physically separated from the product water (permeate) by a membrane. This creates a waste stream that contains all the constituents removed from the water at higher concentrations, including salt, any pathogens, and organic and inorganic chemical contaminants. Disposal of this high-salinity waste stream must be addressed. In addition, this waste stream constitutes between 20 and 25 percent of the total flow that enters the treatment process, which is then lost for potable use.

With ozone-biofiltration (O3/BAF), the water is exposed to a strong oxidant (O3), which breaks down large organics into smaller, assimilable organic carbon (AOC). This AOC is then broken down further by the BAF, removing a significant fraction of the organic carbon in the water, and removing or transforming residual concentrations of many TOrCs, including pharmaceuticals, personal care products, and other trace organic compounds. The only waste stream from this process (filter backwash) can be recycled to the head of the South Regional Plant, which allows this process to recapture nearly 100% of the water.


The downside of the O3/BAF process compared to an RO process is that the former does not remove salt. Therefore, it is only applicable to projects where:

1. The salinity of the existing wastewater does not exceed potable water quality end goals, and

2. If the proposed projects passes the first test above, the “recycle” of this slightly higher salinity purified water into the potable distribution must also not result in a steady-state potable salinity that exceeds the end goal.

Therefore, to continue evaluating the second treatment train concept, a salinity evaluation must be conducted.

5.1.4 Salinity Evaluation

The affects of a DPR approach without salinity removal on steady-state potable water salinity can be estimated using a simple mass balance approach, which is graphically represented in Figure 5.2. The mass balance equations that can be derived from this figure include:

QIN + TDSIN = QS*TDSS + QDPR*TDSDPR (1)

QIN = QS + QDPR

TDSWW = TDSEFF (2)

and

TDSEFF = TDSDPR (3)

Where Q = flow in mgd and TDS = total dissolved solids in mg/L. The subscripts denote flows as follows: S = supply from external potable source (PUA), IN = potable water supplies to customers (average), WW = wastewater, EFF = treated effluent, and DPR = advanced-purified water from DPR.

We can define an additional equation that described the salinity added through municipal use:

TDSWW = TDSIN + TDSADD (4)

where TDSADD is the amount of salinity added through municipal use.

SALINITY MASS BALANCE SCHEMATICFIGURE 5.2



LegendQ = Flow (mgd)TDS = Total Dissolved Solids (mg/L)

S = Supply from Potable Source (PUA)IN = Potable Water Supplied to ResidentsWW = WastewaterEFF = Treated EffluentDPR = Advanced-Purified Water from DPR

Subscripts:

Flow LossesSalinity Addition

QS*TDSS QIN*TDSIN

QDPR*TDSDPR

QWW*TDSWW QEFF*TDSEFF

Flow Losses Flow Losses

SourceWater Blend Municipal

Use WWTPAdvanced

WaterTreatment


The object of this calculation is to define both TDSDPR. and TDSIN. If TDSDPR is below the water quality goal (1,000 mg/L, see Chapter 3), no additional blending with existing source water is necessary to maintain overall water salinity at acceptable levels and no desalination is needed.

If TDSDPR is above the water quality goal, then an evaluation of TDSIN is needed. If TDSIN is below the water quality goal, then careful consideration of blending with existing water supplies is needed to remain below the water quality goal in all parts of the distribution system if desalination is to be avoided. If TDSIN is above the water quality goal, then either desalination is needed or additional lower-TDS water is needed for blending.

Based on the rearrangement of equation (1) above,

TDSIN = QS*TDSS + QDPR*TDSDPR / QIN

= [QS*TDSS + QDPR*(TDSIN + TDSADD)]/ QIN

= (QS*TDSS + QDPR*TDSADD) / (QIN – QDPR)

= (QS*TDSS + QDPR*TDSADD) / (QS) (5)

If one assumes a given fraction of the water supply to be constituted by the water produced from DPR (XDPR), one can substitute QDPR = XDPR*QS into equation (6) and obtain the following:

TDSIN = (QS*TDSS +XDPRQS*TDSADD) / (QS)

TDSIN =TDSS +XDPR*TDSADD (6)

And thus TDSDPR can be calculated:

TDSDPR = TDSWW = TDSIN + TDSADD. (7)

The addition of salinity (TDSADD) from municipal use can range widely, from 150 mg/L to 380 mg/L (Asano et al., 2007; Table 3-11). An estimate of this value for the City was calculated to be approximately 250 mg/L, based on TDS data for PUA (262 mg/L) and DSWSC wells (758 mg/L) provided for years 2007 through 2012 (CMA Engineering, Inc. (CMA), 2013.; see Table 6), the relative fraction of the supply sourced from DSWSC wells pumped in 2013 (40%, see Table 1.1), with results in an average supply salinity of 465 mg/L as TDS. Subtracting this from the average effluent salinity for 2012-2013, 722 mg/L TDS (CMA, 2013; see Table 5), yields 257 mg/L TDS added during use of that water.


For these two scenarios, it was also assumed that the fraction of the total water supplied would not exceed 25%. For reference, based on a very simplistic comparison of current flows, the DSWSC provided approximately 600,000 million gallons (Mgal) in flow in 2013 (Table 1.1), whereas the South Regional Wastewater Treatment Plant was seeing approximately one-tenth that amount. Thus the 25% DPR fraction (XDPR) is a high-end estimate.

Scenario #1: All DSWSC Well Water Plus DPR

This scenario assumes that DSWSC continues to pump water from its wells, but that the remaining demand was made up with DPR water; thus the 2014 average supply salinity from the DSWSC wells is used for TDSS. This represents a conservative estimate of the highest steady-state salinity concentrations anticipated in the case of a DPR project without desalination.

DSWSC supply salinity (TDSS) per CMA (2013) = 758 mg/L

Assume TDSADD = 250 mg/L

Thus:

TDSIN =TDSS +XDPR*TDSADD = 758 mg/L +0.25*250 mg/L = 820 mg/L

and

TDSDPR = TDSIN + TDSADD = 820 mg/L + 250 mg/L = 1,070 mg/L

Therefore, no average system salinity concerns are identified in this scenario, though the salinity of the steady-state DPR water is calculated to be above slightly the maximum concentration goal beyond which one must consider blending ratios with existing treated water in order to ensure that no portions of the distribution receive water that exceeds the 1,000 mg/L TDS limit.

Scenario #2: DPR Offsets Well Pumping

This scenario assumes that the water provided to the City does not contain water from the DSWSC wells. Thus the 2014 average supply salinity for water from PUA is used for TDSS.

PUA supply salinity (TDSS) per CMA (2013) = 263 mg/L

Assume TDSADD = 250 mg/L

Thus:

TDSIN =TDSS +XDPR*TDSADD =263 mg/L +0.25*250 mg/L = 326 mg/L

and

TDSDPR = TDSIN + TDSADD = 326 mg/L + 250 mg/L = 576 mg/L


This calculation illustrates that not only should there be no concerns with respect to increases if water from DPR replaced the water pumped from the DSWSC wells, it would likely lead to an improvement in salinity for those residences currently receiving well water from the DSWSC wells.

Thus, salinity removal is not a critical feature of the advanced treatment process for this project. Based on the above, coupled with a lack of practical disposal options for RO concentrate from an advanced treatment facility and the desire to recapture as much of the flow as possible, the project team has selected the ozone-biofiltration treatment concept for further evaluation.

5.1.5 Preliminary Sizing of the Proposed Treatment Concept

Based on the analysis above, the O3-BAF based treatment concept shown conceptually in Figure 5.1 was evaluated in more detail to determine the feasibility and cost associated with such a treatment scheme.

A more detailed conceptual process flow diagram for this concept is shown in Figure 5.3. The purpose of each treatment process is summarized in the following:

5.1.5.1

Ozonation of secondary effluent produces an advanced oxidation process (AOP) in which hydroxyl radicals are formed that oxidize a large variety of organic and inorganic constituents that remain in the water after secondary treatment in the wastewater treatment plant. These constituents are by definition those that are more difficult to break down during biological treatment.

Ozonation

While the ozonation process does not generally result in reductions in bulk organic measures such as TOC, it transforms the organic constituents into more readily biodegradable substances, also known as assimilable organic carbon (AOC). This AOC is then further degraded and mineralized during the subsequent Biofiltration step, in which 30 to 40 percent removal of TOC is generally achieved (Gerringer et al., in prep).

One downside of the ozonation process is the potential formation of disinfection byproducts (DBPs), including nitrosamines (mainly N-nitrosodimethylamine or NDMA) and bromate. The formation of nitrosamines can be mitigated by subsequent removal during Biofiltration. However, the bromate, once formed, is difficult to remove, and has a drinking water MCL of 10 micrograms per liter (ug/L). The formation of bromate is dependent on the incoming concentration of bromide, which is a reflection of the bromide present in the City’s drinking water supply. While no data are available for bromide in the DSWSC water supply, the bromide concentrations in water obtained from the Highland Lakes, which form a significant portion of the DSWSC portfolio, indicate that bromide concentrations range between 150 and 200 micrograms per liter. This concentration range is high enough to warrant close tracking of bromate formation during pilot testing and adjustment of ozonation design parameters as warranted.

ADVANCED WATER TREATMENT SYSTEM PROCESS FLOW DIAGRAMFIGURE 5.3



Air Scour

UndisinfectedSecondary

Effluent

Overflow Overflow

Cl2 (NaOCl)

Pipe LoopContractor

Contact TimePipe Loop

BackwashEqualization

Tank

WasteHauledOff-Site

EqualizationTank

To WWTPHeadworks

ReturnPumps

UF Backwash

UFNo. 1

UFNo. 2

BAFNo. 2

BAF Backwash

To EffluentStorageTank

Overflowto WWTPHeadworks

EngineeredStorageBuffer

GAC Contactor(Optional)Effluent

StorageTank

OzoneDestruct

FromPlantWater

O3

Coagulant

PSA

BAFNo. 1

OzoneDestruct

NH3 (LAS)

O3PSA

UV UV UV UV

Ozone Generation

(Optional)

CIP System

CIP Returnand Disposal

C

C

to Distribution


The likely presence of significant bromide concentrations means that the ozonation step proposed for this treatment train will likely be limited by bromate formation. Hence, the proposed ozone dose is limited to less than a one-to-one ratio of ozone to incoming TOC (assumed to be 7 to 10 mg/L). An ozone dose in the range 0.8 to 1 times the TOC concentration should achieve the desired AOP reaction described above (Gerringer et al., in prep.), however, it will not provide a measurable ozone residual. The use of a sub-residual ozone dose means that no disinfection credits will be pursued for this treatment step. However, based on previous and ongoing research work, significant pathogen attenuation, especially of viruses (up to 5-log), occurs even at sub-residual ozone doses in wastewater effluent. Therefore, this process provides a significant safety factor for pathogen inactivation.

The preliminary design parameters for the ozone process shown in Table 5.8 reflect these trade-offs, with an assumed delivered dose of 7 mg/L. The generator size is then calculated as 30 lb/day (0.5 mgd * 7 mg/L * 8.34 lb/day/mgd/mg*L / 0.95; where 0.95 is the ozone transfer efficiency). More detailed dosing will be determined during pilot testing.

Table 5.3 Basic Process Design Criteria for Ozone Process Direct Potable Reuse Feasibility Study City of Dripping Springs

Parameter Units Value

Influent Flow mgd 0.5

Delivered Dose mg/L 7

Transfer efficiency % 95

Generator size lbs/day 30

Effective Recovery % 100

Effluent Flow mgd 0.5

5.1.5.2

As discussed above, the primary function of the biofilter is to transform and mineralize AOP formed during the preceding ozonation step. A reduction of TOC in the range of 30-40 percent is anticipated during this treatment step. The biofilter also serves to reduce any concentrations of nitrosamines formed during ozonation.

Biofiltration

The biofilter also has a number of additional benefits, similar to those associated with conventional media filtration. These include reductions in TSS and turbidity due to the removal of particles, which also removes any chemicals or pathogens attached to those particles. Additionally, the filters contribute directly to the removal of protozoa (Giardia and Cryptosporidium) through sieving action. The bulk particle removal is of benefit to the downstream ultrafiltration process, as it will reduce the fouling experienced by the membranes. The removal of pathogens, though, once again, not formally credited with any


log removal values, also serves as another safety factor in the pathogen removal achieved by the overall treatment train.

The preliminary sizing of the filters shown in Table 5.4 reflect a conservative approach to this relatively inexpensive process within the treatment train, with an empty bed contact time of 20 minutes and two filters at 140 square feet (sf) filter area each. This results in a conservative steady-state filtration rate of less than 2 gallons per minute per square foot (gpm/sf) and provides complete redundancy when compared to TCEQ’s drinking water filtration rate cap of 5 gallons per minute per square foot (gpm/sf). The backwash volume per filter is calculated based on a 15-minute backwash time at 16 gpm/sf.

Table 5.4 Basic Process Design Criteria for Biofiltration Process Direct Potable Reuse Feasibility Study City of Dripping Springs


Influent Flow mgd 0.5

Filter Type -- gravity

Filter Media -- GAC

Empty Bed Contact Time min 20

Number of filters No. 2

Target flow per filter mgd 0.25

Maximum loading rate gpm/sq ft 5

Target loading rate gpm/sq ft ≤ 2

Backwash type -- air scour

Backwash rate gpm/sq ft 16

Filter area (assumed) sq ft 280

Volume needed for backwash gal 33,600

Backwash frequency day-1 1

Average Backwash Loss mgd 0.067

Backwash water destination

Filtrate flow (average) mgd 0.5

5.1.5.3

The ultrafiltration (UF) step provides an additional, more stringent, layer of particle removal. It also constitutes the first treatment process for which formal LRVs are targeted, with a 4-log target for protozoa (Giardia and Cryptosporidium) based on direct integrity testing per the Membrane Filtration Guidance Manual (US EPA, 2005).

Ultrafiltration


Basic process design parameters are summarized in Table 5.5. The membrane flux target, at 25 gallons per square foot per day (gfd) is on the low end for UF applications but is estimated conservatively based on the reuse application. The current preliminary design parameters assume two parallel UF trains each sized for 0.25 mgd. This provides operational redundancy to keep downstream processes running while one skid is being backwashed (daily for 90 minutes each). However, it does not provide full process redundancy, resulting in an average capacity loss of approximately 7% and reducing average flows to a maximum of 0.47 mgd.

An additional 5 percent of flow is lost in the form of the water needed for backwash and cleaning, which is taken from the process equalization and backwash water storage tank. Cleaning cycles and process recovery are based on industry standard values and will be fine-tuned during piloting.

However, these flow limitations will only become significant once the actual flows to the plant exceed this flow rate. As part of detailed design, the project team may consider upsizing the UF process sufficiently to meet an average of 0.5 mgd throughput.

Table 5.5 Basic Process Design Criteria for Ultrafiltration Process Direct Potable Reuse Feasibility Study City of Dripping Springs

Influent flow mgd 0.5

Flux gfd 20-25

Number of units No. 2

Capacity of each unit mgd 0.25

Recovery clean duration min 240

Maintenance clean duration min 90

Backwash water destination WWTP headworks

Recovery % 95

Average UF Filtrate flow rate mgd 0.5

5.1.5.4

As shown in

Inter-Process Storage Tank

Figure 5.3, an inter-process storage tank is proposed between the ultrafilters and the UV reactors for two purposes: (1) flow equalization and (2) biofilter and UF backwash water storage. This second purpose is important to maintaining an active microbial community in the biofilter, as water in this inter-process storage tank does not contain a disinfectant residual. This purpose also controls the size of the tank.


Basic tank sizing criteria are summarized in Table 5.6. The volume of water needed to backwash each biofilter is estimated at 33,600 gallons (15 min * 140 sf * 16 gpm/sf). A conservative sizing of 100,000 gallons is proposed at this time to provide additional process equalization capacity.

The total flow and capacity losses combined manifest themselves in the average flow leaving the EQ tank, which is limited to 0.38 mgd (0.067 mgd filter backwash plus 0.025 mgd UF cleaning losses plus 0.03 mgd UF process inefficiency during cleaning). Once again, these limitations will only manifest themselves once the incoming flow from the wastewater treatment plant nears the 0.5 mgd design criterion.

For the detailed design, the project team may consider both phasing the treatment design to match incoming effluent supplies as well as upsizing treatment processes in order to preserve a total 0.5 mgd finished water production capacity.

Table 5.6 Basic Sizing Criteria for Inter-Process Storage Tank Direct Potable Reuse Feasibility Study City of Dripping Springs

Minimum size per BAF gal 33,600

Proposed size gal 100,000

Total flow/capacity losses during backwash/cleaning mgd 0.12

Average product flow from EQ mgd 0.38

5.1.5.5

An option al granular activated carbon (GAC) filtration step will be considered between the inter- process storage tank and the UV reactors in order to remove any remaining precursor compounds that might result in the formation of regulated disinfection byproducts in the downstream chemical disinfection step. The GAC will also help increase the UV transmittance of the water, leading to better disinfection. This process step is not currently included in the cost estimate because the project team anticipates that it will not be needed. This determination will be made during pilot testing.

Optional Granular Activated Carbon Adsorption

5.1.5.6

The only purpose of the ultraviolet irradiation (UV) process is pathogen inactivation. This process is currently targeted with achieving 6-log removal for all three relevant pathogen classes (virus, Giardia, and Cryptosporidium). The controlling organism for UV inactivation is virus, which requires the highest dose per log removal credit awarded.

Ultraviolet Disinfection


Basic process design parameters are summarized in Table 5.7. Detailed reactor selection was beyond the scope of this study, however at least two reactors in series will be needed to achieve 6-log reduction because validation of any reactors for drinking water use based on the Ultraviolet Light Disinfection Guidance Manual (UVDGM; US EPA, 2006) it limited to 4-log. Per the UVDGM (see Table 1.4), the minimum UV dose to achieve 4-log virus removal is 186 milli-Joules per centimeter squared (mJ/cm2). Under the assumption that two reactors in series will be needed, this dose is chosen as the target dose per reactor in order to achieve 6-log through two reactors plus a safety factor of 1-log per reactor. An additional, redundant reactor is proposed to protect against system downtime.

A UV transmittance (UVT) of 85 percent is anticipated based on typical UF filtrate water quality. While previous sections have discussed flow losses throughout the treatment train, each train element is currently sized for 0.5 mgd flow for simplicity. This will also reduce the upsizing requirements needed to reach a final finished water flow of 0.5 mgd.

Table 5.7 Basic Process Design Criteria for Ultraviolet Disinfection Process Direct Potable Reuse Feasibility Study City of Dripping Springs

Design flow mgd 0.5

Type -- LPHO

Virus Log Removal Target log ≥ 6

Number Reactors in Series No. n+1(1)

Dose per Reactor (target 4-log virus) mJ/cm2 186(1)

Incoming UV Transmittance % 85

Process Recovery % 100

Average final product water flow mgd 0.38

(1) The design requirement is that at least one redundant reactor be provided. The target dose per reactor is based on the assumption that n=2. A different design dose per reactor may be chosen if more than three reactors are placed in series.

Notes:

5.1.5.7

A final chemical disinfection step rounds out the pathogen log removal requirements. As mentioned above, each train element is currently sized for 0.5 mgd flow. In order to achieve significant disinfection, a period of free chlorination (achieved through dosing of sodium hypochloride, NaOCl) is required before the addition of ammonia (in the form of liquid ammonium sulfate, LAS) to form a chloramines-based residual for distribution. The dosing point for the NaOCl is set upstream of the UV reactors, both to take advantage of additional residence time within the reactors, as well as to provide the potential for an AOP reaction should the UV dose be sufficient to create one. The effect of this potential AOP will be tested during piloting.

Chemical Disinfection


Basic process design parameters are summarized in Table 5.8. The target Ct of 6.8 mg/L-min as Cl2 is based on achieving 4-log virus removal at 8°C per US EPA Ct tables. With a 4 mg/L target residual, a contact time of 2 minutes, and an in-pipe flow rate of 1.7 feet per minute or less, a total contact pipe length of 200 feet or more is required. To achieve this flow rate, a 10-inch pipe is proposed that exits the advanced treatment building on the south end and runs north the length of the building to the engineered storage buffer tank (see Figure 5.4). The resulting pipe has a length-to-width ratio of 250, comfortably within the requirements of the criterion of >100 needed for a T10 baffle factor of 1.

The chlorine dosing requirement of 6 mg/L assumes a 2 mg/L instantaneous chlorine demand, which will be fine-tuned during pilot testing. The ammonia dosing requirement is based on a 4.25:1 mass ratio of free chlorine residual (as Cl2) to ammonia residual (as N).

Table 5.8 Basic Process Design Criteria for Final Chemical Disinfection Direct Potable Reuse Feasibility Study City of Dripping Springs


Design flow mgd 0.5

Target Ct for free chlorine mg/L-min 6.8

Chlorine target residual mg/L as Cl2 4

Chlorine (NaOCl) target dose mg/L as Cl2 6

Free chlorine contact time goal min 2

Pipe length for free Cl2 contact ft 200

Liquid ammonium sulfate (LAS) dosing location Engineered Storage Buffer inlet

LAS target dose mg/L as N 1

5.1.6 Advanced Process Monitoring and the Engineered Storage Buffer

Advanced treatment for potable reuse requires not only advanced treatment processes, but advanced monitoring of those processes. Based on ongoing research to define the appropriate level of advanced monitoring for DPR projects, process monitoring should consist of a combination of online or rapid response surrogate measures and periodic confirmation sampling.


AdvancedTreatmentBuilding

Purified Water PS

Existing sewer

To existing drip disposal

ExistingEffluent Storage

Target pipe leng

th fo

r Ct credits = 200

ft

Effluent PS (exist. future)

Existing (future)Effluent Conveyance

LAS

to DSWSCGround Storage Tank

1 MGPurified Water Storage

Legend: Raw WastewaterExisting EffluentFuture Undisinfected Secondary EffluentFuture Reclaimed Water Purified WaterFilter BackwashOff‐Spec Water Flows

ExistingWWTP

(upgraded to BNR)

FutureReclaimed Storage Future

Filters

Cl2

Scale: 100 ft

PROPOSED SITE LAYOUT WITH ADVANCED TREATMENT AT THE SOUTH REGIONAL WASTEWATER TREATMENT PLANT

FIGURE 5.4




In particular, to mitigate the risks of the close coupling between wastewater and finished drinking water, the concept of “Failure Response Time” (FRT) was developed for WateReuse Research Foundation Project No. 12-06 (Steinle-Darling et al, in prep) as a means to define the amount of storage “holding time” is needed to confirm that finished water meets all the quality specifications before it can be released into the distribution system. The failure response time for any given process is determined by the monitoring method that conservatively and conclusively confirms process efficacy. Whereas other bulk water surrogates (turbidity, TOC) may be monitored more frequently for the purpose of process adjustment and optimization, the monitoring method used to determine process integrity must provide a conservative estimate of the log removal value provided by each process (direct integrity test for UF, for example). If this value is not met, the treatment train is shut down until and/or water is diverted until corrective measures are taken.

Table 5.9 provides a preliminary summary of the process monitoring parameters proposed for the advanced treatment train. This table includes both surrogate process monitoring techniques and those monitoring processes deemed appropriate for determining actual process integrity. Based on the information provided, monitoring of the ultrafiltration process controls the overall train FRT and thus the proposed project requires at least 24 hours of engineered storage buffer residence time before advanced-purified water can be introduced into the distribution system.

Table 5.9 Process Monitoring Parameters for Advanced Treatment Direct Potable Reuse Feasibility Study City of Dripping Springs

Process Monitoring Parameter Target Frequency FRT(1)

Secondary TOC < 10 mg/L online

Effluent UV254 TBD(2) online

Nitrate, max < 10 mg/L as N online

Total inorganic nitrogen (24-hour average) < 5 mg/L as N online

Flow <0.5 mgd online

Ozone O3:TOC Ratio(3) 0.5 to <1.0 online

Biofiltration Turbidity <0.3 NTU(4) online

TOC <5 mg/L online

Ultrafiltration Direct integrity test >4-log pass daily 24-36 hours

Benchtop particle counts TBD(2) 2 per day <24 hours*

Turbidity TBD(2) online


Table 5.9 Process Monitoring Parameters for Advanced Treatment Direct Potable Reuse Feasibility Study City of Dripping Springs

Process Monitoring Parameter Target Frequency FRT(1) Ultraviolet UV intensity sensors TBD online 15 min*

Disinfection UVT >80% online 15 min

Chemical Cl2 residual at 2-3 mg/L as Cl2 online 15 min*

Disinfection Storage tank inlet

(1) Failure Response Time. Only monitoring methods that are used to achieve LRVs are associated with an FRT. The controlling FRT for each process is shown with an asterisk (*).

Notes:

(2) To Be Determined. (3) The ozone to TOC ratio (O3;TOC) range will be determined during pilot testing to maximize

pathogen and TOrC destruction while limiting bromate formation to acceptable levels. (4) The filter effluent turbidity criterion proposed here is based on meeting the 95 percentile

combined filter effluent turbidity limit under the Long Term 2 Enhanced Surface Water Treatment Rule (EPA, 2010).

Based on the DPR projects currently approved and operating in Texas, it is anticipated that TCEQ will require a process monitoring scheme that is similar to the one proposed in Table 5.9, though to date the TCEQ has not formally required a coupling of that monitoring scheme to an engineered storage buffer. However, the project team considers the implementation of an engineered storage buffer an appropriate and necessary safeguard for the protection of public health.

Should in the future, monitoring methods be developed that reduce the overall process FRT for ultrafiltration, a smaller storage tank could be considered.

5.2 DPR PROJECT ALTERNATIVES AND ELEMENTS Advanced treatment for potable reuse, while critically important, is only one aspect of an overall DPR project. This section discusses the surrounding project alternatives and elements, including project location, source water considerations, pipelines, pumping, and storage. All of these elements can affect project feasibility, cost, and, indirectly or directly, the water quality produced by the DPR project as a whole.

On-site elements outside the scope of the advanced treatment train are shown in Figure 5.4.

5.2.1 Project Location Alternatives

Two site locations for the implementation of an advanced treatment for DPR are considered in this study: the existing South Regional Plant site, and an “upstream site” for which the precise location has not yet been determined.


5.2.1.1

The South Regional Plant site has a number of advantages. These include the existing collection system and wastewater treatment infrastructure, having all the City’s treatment facilities located in one central location, and the proximity of the DSWSC well field ground storage tank, into which advanced-purified water could be introduced.

South Regional Wastewater Treatment Site Location

Based on the location of the subject tract of land made available for land application disposal of effluent (see Chapter 6), this is also the only location for which land application is considered.

5.2.1.2

A second, conceptual, upstream site is also considered in this study. The treatment plants (both wastewater and advanced treatment) would be located on a currently undeveloped site at one of the proposed new developments near the City. Several actual sites have been considered by the City but none have been confirmed for the purpose of this study.

Upstream Site Location

Due to the undefined location of the upsteam site location, the geography-associated project elements (mainly conveyance infrastructure) have been based on generic assumptions and are subject to change depending on the final location selection, if an upstream site is selected. The main components of the study, however, relate to on-site elements necessary for DPR (advanced treatment and storage), which do not vary between site locations at the level of planning implemented for this study.

In the following, more detailed assessments are made with respect to the South Regional Plant site location and applied, as appropriate, to the upstream site.

5.2.2 Source Water Considerations

A detailed source water assessment is outside the scope of this study. However, the following summarizes some of the items that should be addressed and/or confirmed for the project to proceed.

As with any drinking water supply, one must consider and assess the source water intended for potable consumption. For a DPR project, this goes beyond looking only at the secondary effluent characteristics. In analogy to conventional drinking water sources, sourced from “watersheds”, a “sewershed” assessment should be conducted to confirm the nature of discharges into the City’s collection system. The current study presumes, based on the limited existing commercial and absence of light and heavy industrial activity in the City’s vicinity, that industrial discharges to the City’s collection system do not occur.


5.2.3 Collection System Tie-In

If the project is located at the South Regional Plant site, which has been the basis for most of the treatment assumptions discussed above, no additional work will be needed to tie into the existing collection system, as it already conveys the full flow of the City’s wastewater to the South Regional Plant.

For an upstream site location, a sewer force main would be constructed that pulled wastewater from the existing lift station located in the City’s downtown area. An 8-inch PVC sewer force main extending between 1 and 2 miles from the existing lift station to the project site was assumed.

5.2.4 Wastewater Treatment Plant Requirements

Proposed wastewater treatment plant improvements at South Regional Plant are discussed in Chapter 4.

For the upstream location, a completely new wastewater treatment plant would need to be constructed. For costing purposes, a 0.5 mgd plant was sized based on industry standard costs for a small-scale biological nutrient removal plant that would meet the same criteria as the upgraded plant discussed in Chapter 4.

5.2.5 Considerations for Advanced Treatment Source Water

The existing South Regional Plant has a chlorine contact basin for wastewater disinfection per TCEQ requirements (minimum of 20 min of contact time and 1 mg/L combined chlorine residual). While this disinfection step is required for subsequent effluent disposal, it has the potential to create problems for the downstream advanced treatment process in two significant ways:

1. The combination of effluent organic matter and free chlorine may create disinfection byproducts that are not regulated for wastewater discharge but are regulated in drinking water applications. Once formed, it is difficult to remove such disinfection byproducts.

2. The disinfectant residual that is required for effluent disposal would be detrimental to the biological community within the biofilter that is responsible for significant organics removal during advanced treatment. Recent pilot testing work performed at the Santa Clara Valley Water District (in California) by Carollo as shown that TOC removal by post-ozone biofilters in chlorinated effluent was reduced to 20%, whereas a robust post-ozone biofilter is expected to remove 30-40% of TOC. The chlorine residual could be chemically quenched, but any carry-over of the quenching agent would negatively affect the effectiveness of the ozone process, such that avoiding the chlorination step altogether is preferable.


Based on these two factors, the project team recommends that effluent for advanced treatment be sourced from the clarifier of the South Regional Plant before the chlorine contact basin.

At an upstream site, the issue could be avoided altogether by implementing a different mode of effluent disinfection, such as UV.

5.2.6 Storage Considerations

5.2.6.1

The separation of the effluent slated for advanced treatment and any effluent directed to non-potable uses prior to the existing chlorination step at the South Regional Plant means that two effluent storage tanks are necessary, one containing disinfected effluent slated for disposal and/or non-potable uses, and one containing undisinfected effluent for advanced treatment.

Effluent Storage

This would be needed as a backup option, even if all the effluent were slated for advanced treatment and subsequent potable reuse. In the event of a precautionary process or maintenance shut-down, undisinfected effluent from might need to be redirected back through the chlorine contact basin and into the existing effluent storage tank prior to disposal. However, given that significant disinfection activity occurs in most of the downstream advanced treatment processes that would easily allow the water to meet numerical pathogen standards for discharge or Type I reuse, TCEQ may allow the water to be discharged without returning it to the chlorine contact basin.

For non-potable uses, the updates proposed in the permit amendment application are assumed to proceed with the installation of cloth filters for effluent filtration. A second effluent storage tank (333,000 gallons) and an effluent pump station, as proposed in Amendment No. 1, are also assumed to be available (see Figure 5.4) and not separately addressed in the cost estimate for this report.

Proposed disinfected and undisinfected effluent flow paths and return loops are shown conceptually in Figure 5.4.

A similar scheme would be implemented at an upstream site but is not explicitly considered as part of this study.

5.2.6.2

The inter-process storage tank, currently proposed at 100,000 gallon capacity, is discussed as part of advanced treatment in Section 5.1.

Inter-Process Storage


5.2.6.3

The finished water storage tank proposed for this project serves two important purposes:

Finished Water Storage

1. It serves as a reservoir for finished water that can be metered into an existing distribution system storage tank (the existing ground storage tank located at the DSWSC well field, for example).

2. More importantly, it serves as an engineered storage buffer, or ESB. As discussed in Section 0, the concept of an ESB was developed to help mitigate the increased risk to public health derived from the close coupling of wastewater and water in a DPR scenario. Per the analysis provided in that section, at minimum 24 hours’ worth of retention time is needed to meet storage requirements.

Assuming a ground storage tank with 3-4 baffles results in a T10 baffling factor of 0.5. That means the minimum total storage volume needed is 1 million gallons (MG, based on 0.5 mgd * 24 hours / 0.5 * 1 day/24 hours). The tank currently proposed for this study is sized for the minimum volume of 1 MG. Once actual flows approach the 0.5 mgd design flow, an updated assessment of storage requirements per Section 0 should be conducted to determine if additional storage is advisable.

5.2.7 Drinking Water Distribution Tie-In

For both the South Regional Plant site and an upstream project location, water must be conveyed between the finished water storage tank and the point at which the water is introduced into the existing drinking water distribution system serving the City.

For the South Regional Plant site, the necessary infrastructure includes a 0.5 mgd high service pump station and an 8-inch PVC water line with a cost allowance for a tunneled and cased crossing of Onion Creek to reach the existing DSWSC tank located north of the wellfield.

For an upstream location, the requirements are less well defined. For the purposes of this study, a 0.5 mgd high service pump station, approximately one mile of 8-inch PVC pipe and one tunneled and cased highway crossing were assumed. A pre-existing distribution system water storage tank into which the pipeline would tie was assumed.

5.2.8 Effluent Disposal Infrastructure

5.2.8.1

Discharge from the South Regional Plant Site can be either by gravity through an outfall directly into Onion Creek, or by pumping to a different site for discharge. For the purpose of this evaluation, the pumping scenario was assumed to be conservative.

Infrastructure for Effluent Discharge at South Regional Plant Site


5.2.8.2

For an upstream project location, a gravity outfall from the new WWTP to an adjacent drainage channel is assumed. This channel would eventually drain to Onion Creek. Therefore, the outfall structure is the only cost item associated with effluent discharge at an upstream project location site.

Infrastructure for Effluent Discharge at Upstream Project Location

5.2.8.3

The infrastructure needed at the land application site is discussed in detail in Chapter 6. In addition to the on-site requirements (storage pond and irrigation infrastructure), an effluent pump station and 8 inch transmission main to the spray irrigation site would be required.

Land Application Infrastructure

5.2.9 Ancillary Project Elements

A detailed analysis and cost estimate of on-site civil, electrical, mechanical, piping, and pumping, is beyond the scope of this study. Standard cost multipliers were used to account for these project elements. The advanced treatment building was sized generously based on basic equipment layouts (not provided).

All advanced treatment cost estimates are based on the South Regional Plant location, but at the level of detail provided are equally applicable to an upstream site.

5.3 DISCUSSION OF INDIRECT POTABLE REUSE Typically, an indirect (potable) reuse project involves augmentation of a source water with reclaimed water that can then be withdrawn at a later time for potable use. These can be divided into surface water augmentation and groundwater augmentation projects. Augmentation of Onion Creek and augmentation of local groundwater are discussed in the following.

5.3.1 Augmentation of Onion Creek

Surface water augmentation IPR projects are permitted based on water quality requirements for discharge into the receiving water body (in this case, Onion Creek) and an allocation of water rights to the augmented flows provided via the discharge conveyed through a “bed and banks” permit. Hence, the water quality of the effluent needed for IPR via Onion Creek is anticipated to be very similar to that anticipated for a discharge permitted as a backup option to a DPR project. A detailed permitting analysis of indirect reuse is not within the scope of this study.

From a technical perspective, surface water augmentation projects are typically most successful for larger water bodies (reservoirs or larger rivers) that have continuous flow from which water can be withdrawn. Therefore, indirect potable reuse via discharge and subsequent withdrawal from Onion Creek, a low- and intermittent-flow watercourse, would be a challenge and is not further considered as part of this study.


5.3.2 Groundwater Augmentation

An evaluation of potable reuse via groundwater augmentation is wholly outside the scope of this study and therefore only a short summary to illustrate the possibility is presented here.

Based on limited examples of groundwater augmentation with reclaimed water in Texas to date, it is anticipated that advanced treatment to potable standards would be required for augmentation of groundwater in an “aquifer storage and recovery” (ASR) scheme, in which the aquifer mainly serves as a storage reservoir for excess water “banked” in times of plenty and withdrawn for potable use as the need arises.

It is possible that this could be accomplished by augmenting the aquifer from which the existing DSWSC wells currently draw, though a detailed hydrogeological study would need to be conducted to verify this. Even if technically feasible, injection of even advanced-treated water into the protected Edwards Aquifer (or even through it, in order to reach the deeper Trinity Aquifer) may be difficult.


Chapter 6

EFFLUENT DISPOSAL ALTERNATIVES

6.1 EFFLUENT DISPOSAL OVERVIEW The most common permit for large volume wastewater discharge is the Texas Pollutant Discharge Elimination System (TPDES) permit that allows for treated effluent to be discharged directly into a receiving water body. The alternative to TPDES permits for effluent disposal is the Texas Land Application Permit (TLAP). The TLAP permit allows for wastewater effluent to be land applied rather than released into waters of the state.

6.1.1 TPDES Permitting

The TPDES permit refers to a wastewater discharge permit regulated by the TCEQ in which wastewater effluent is discharged into a water of the state (TCEQ, 2014).

Should surface discharge be selected as a means of backup effluent disposal for the project, Onion Creek is the proposed receiving water body for effluent from the project. Onion Creek is a small tributary of the Colorado River near Dripping Springs, which begins 12 milers southeast of Johnson City and flows approximately 79 miles eastward to the Colorado River (Texas State Historical Association, 2013). Portions of Onion Creek, including those downstream of Dripping Springs, are located within the recharge and contributing zones of the Barton Springs Segment of the Edwards Aquifer. To date, the TCEQ has issued only one TPDES permit within the recharge and contributing zones of the Barton Springs Segment of the Edwards (Hays County Water Quality Control and Improvement District No. 1, permit no. WQ0014293001, which permits discharge to Bear Creek, a tributary of Onion Creek).

6.1.2 TLAP Permitting

Effluent disposal under a TLAP permit has been the primary means of effluent disposal in the recharge and contributing zones of the Barton Springs Segment of the Edwards Aquifer, including the area around Dripping Springs. This is because the land-applied effluent receives additional treatment from the plant roots and the soil column before infiltration. In addition, the vegetative cover removes water by means of evapotranspiration and converts nutrients and other constituents via plant uptake and biodegradation.


6.2 EVALUATION OF LAND APPLICATION As part of the current study, the project team was tasked with evaluating land application as a disposal alternative for up to 0.5 mgd of wastewater effluent. While current effluent flows produced by the City at its South Regional Plant are still significantly below this level, the City anticipates that 0.5 mgd effluent flow will be reached in the foreseeable future. The purpose of this evaluation is to determine the feasibility and cost implications of developing a land application program that will meet this 0.5 mgd design flow based on a specific parcel of land made available by a private party for this purpose.

6.2.1 Regulation

The TCEQ has established standards for the design of surface application systems as presented in Title 30 of the Texas Administrative Code (TAC) Chapter 309 (30 TAC §309). Chapter 309 specifies the required criteria for (1) sizing the spray field, (2) determining the application rate, and (3) calculating the volume of effluent storage required. Additional guidance is provided by TCEQ in the form of instructions for completing domestic wastewater permit applications (Form TCEQ-10053-Instruction). Any owner of a municipal/domestic facility that generates wastewater discharge authorization from the TCEQ to dispose of wastewater adjacent to waters in the state by direct discharge (TPDES) or by irrigation, evaporation, or subsurface disposal (TLAP) mush apply for a permit. Dripping Springs, in its current capacity to dispose of wastewater through drip-irrigation methods, has an existing TLAP permit that would be amended to include this land application phase, if desired.

6.3 SUBJECT TRACT PROPOSED FOR LAND APPLICATION The subject tract for the proposed land application is approximately 186 total acres. With access to the property off FM150, the tract is approximately 7,000 feet directly east of the existing South Regional Plant. The location of the subject tract relative to the South Regional Plant is shown in Figure 6.1.

With the exception of an approximated 50 ft. aerial easement (6.6 acres) traversing through the main body of the tract, the canopy is uniformly dense with cedar trees. The easement area has been cleared and can easily be seen in aerial imagery. Topography of the tract generally slopes downward south east but is rather non-uniform. The tract is located at approximate Latitude: 30° 9'37.54"N Longitude: 98° 3'22.65"W.

Source: Esri, DigitalGlobe, GeoEye, i-cubed, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AEX, Getmapping, Aerogrid, IGN, IGP, swisstopo, andthe GIS User CommunityINFRASTRUCTURE OVERVIEW FOR CANOPY SPRAY IRRIGATION

FIGURE 6.1CITY OF DRIPPING SPRINGS


Proposed Land Application Site

Onsite DripIrrigation Site

Existing WWTPSite

Option 2

Option 1

O

Onion Creek

Effluent Storage Pond

LegendProposed Treated EffluentTransmission Line (8-inch PVC)Major Irrigation LineIrrigated AreasEasement Access (No

Sanitary SewerWater Distribution SystemCity of Dripping Springs100-Year FEMA Floodplain

0 0.2 0.40.1Miles


6.4 LAND APPLICATION CALCULATIONS The ability of a tract of land to support land application of effluent is determined by its ability to absorb water, nitrogen, and salts. Mass balance calculations for each of these substances form the basis of TPDES permitting. The following sections describe the approach taken by the project team to calculate these mass balances and determine if, and how, the subject tract could support land application of 0.5 mgd effluent form the South Regional Wastewater Treatment Plant.

Detailed calculations and the tables referenced in this section are provided in Appendix C.

6.4.1 TABLE C-1 - A First Look (30 TAC 285 Method)

A first look screening methodology for land application is provided in 30 TAC §285 relating to On-Site Sewage Facilities. The basis for this approach is a map (30 TAC §285.90(1)) showing estimates for maximum application rates for surface application of treated effluent across the State of Texas. This map has been reproduced in Figure 6.2.

The parameters for this method are presented in Table C-1. This calculation relies on a total usable irrigation area calculated as detailed in Table C-2, and a maximum surface application rate of 0.0545 gallons per day per square foot (gpd/sf). This was determined by locating Hays County on Figure 6.2 and averaging the two zone line values (0.045 and 0.064). By using this simplistic approach as a first evaluation, the estimated daily disposal volume of the tract was determined to be 397,000 gallons per day.

6.4.2 TABLE C-2 - Detailed Water Balance

The Chapter 285 first-look methodology (above) provided the first evaluation of a possible disposal volume. Through detailed monthly water balance calculations (Table C-2 and Table C-3), a more comprehensive approach was also considered. The site-specific crop data, curve number, evaporation, and pond storage volume were used to verify that a higher surface application rate could be achieved. Although the first-look spreadsheet (Table C-1) indicated a maximum disposal volume of less than 0.4 mgd, the use of site-specific data and an increased storage volume supported a design flow of 0.5 MGD.

The full suite of parameters used for the calculations are shown in Appendix C.


DISPOSAL APPLICATION RATES FOR TEXAS (30 TAC §285.90 FIGURE (1))

FIGURE 6.2




6.4.2.1

The monthly water balance calculations (Table C-2), the required computations confirming that the subject tract of land could support a land application. The maximum application rate is governed by the size and parameters of the subject tract of land (such as the curve number, the conductivity values, and the canopy density). By using the monthly water balance spreadsheet, an average precipitation, average runoff, average infiltration rate, and average evapotranspiration rate was determined. By determining the total water needs (in inches) per square foot, the maximum amount of effluent allowable was calculated as the maximum application rate. The maximum application rate was calculated as 0.11 gpd/sf.

Water Balance Parameter Assumptions

Assumptions upon which selected parameters were based are explained in the following.

Curve Number

A curve number (CN) of 73 was determined based the hydrologic soil group designation for the greater Austin Area and a determination that the subject tract represented Pinyon-juniper woods with fair hydrologic condition. Per TCEQ guidance, the CN can be looked up based on these parameters in a USDA publication (USDA, 1986; see Table 2.2-d), which also classifies the Austin area with a hydrologic soil group designation of C (USDA, 1986; see 1986 Appendix A-1).

Conductivity Parameters

The effluent water conductivity (CE) was estimated based on conversion of a single available effluent TDS measurement of 600 parts per million (ppm), collected in February 2014. Using a conversion factor of 670 ppm TDS per milliMho per centimeter (mMho/cm) mMho/cm results in CE = 0.9 mMho/cm. A value of 1.0 mMho/cm was used to be conservative.

The assumed allowable conductivity (CL) was determined based on the salinity tolerance of Cedar (Ashe Juniper). Per 30 TAC §309.20, Table 3, relatively salt tolerant crops can tolerate an EC of between 6.0 mMho/cm and 8.0 mMho/cm. A maximum limit of 7.0 mMho/cm was assumed.

Usable Irrigation Area

Usable irrigation area of 160 acres was determined based on the total acreage of the subject tract of land (186 acres), an assumption of 95% canopy density, and subtraction of space devoted to the effluent holding pond surface area (10.74 acres, calculated as described in Table C-6) and to an existing cleared power line easement running across the property (6.6 acres, see Figure 6.1).


Irrigation Efficiency

An irrigation efficiency (K) of 75% was determined based on the use of permanent sprinklers for canopy spray irrigation, which have a range of efficiencies between 70% and 80% (Solomon, 1986). Thus the average efficiency was assumed.

Precipitation

Precipitation data was collected from the Texas Water Development Board (TWDB, 2015) and combined into a monthly historic table of monthly precipitation from 1940 to 2013 (~60 years). Monthly averages were calculated over this time period and are shown in Table C-2 (Column 2).

Evapotranspiration

Specific evapotranspiration values (ETs) for Cedar (Ashe Juniper) were not located for this project. Instead, average ET values for the Austin area were used (TAMUAE, 2013). Based on field data collected in the Edwards Plateau, removal of Ashe Juniper and reestablishment of native grasslands results in 1.5 inches to 2.4 inches of additional runoff/infiltration per year (Conner et al, 2009).

Taking 2 inches as a round number within that range, that represents 6% of the total average annual precipitation in the Austin area (34.2 inches). Therefore, a correction factor of 6% was applied to the ETs in Table C-2 (Column 5) to account for the additional ET attributed to Cedar compared to native grasslands.

Evaporation from Reservoir Surface

Evaporation data was collected from the TWDB (2015).

6.4.3 TABLE C-3 - Calculating the Volume of Effluent Storage Required

The volume of effluent storage required was determined based on the accumulated storage values (Column 20) in Table C-3. The storage volume calculation was calculated by taking the effluent applied to the land (Column 13) as calculated from the water balance in Table C-2, the maximum rainfall event (Column 14B) and the minimum evaporation event (Column 18B) to determine the required storage per month (Column 19). The accumulated storage (Column 20) sums the accumulated monthly storage and calculates the storage (in ac-ft) required for the property. The storage duration (days) is also calculated.

For a 0.5 mgd design flow, the storage requirement was calculated to be 87 days, resulting in a required storage volume of 134 ac-ft.


6.4.4 TABLE C-4 – Nitrogen Uptake Calculations

Nitrogen uptake calculations were also completed to verify that the subject tract of land could support the applied nitrogen loading proposed. Based on the assumed average daily flow of 0.5 mgd with an effluent total nitrogen concentration of 10 mg/L (assumed conservatively based the DPR water quality goal of 5 mg/L discussed in Chapter 3), the estimated total nitrogen applied was about 15,000 pounds per year (lbs/yr).

An estimated 150 lbs/yr per acre nitrogen uptake was assumed for Cedar woodlands as a conservative estimate based on the range of nitrogen uptake amounts given for mature forests of various types (Fedler et al., 2006; see Table 5.1), the minimum area required to assimilate 15,000 lbs/yr total nitrogen was calculated as slightly more than 100 acres.

Because the tract of land is larger than 100 acres, the nitrogen uptake will not be the limiting factor for the maximum application rate. Note that this calculation assumes treatment upgrades to the existing South Regional Plant necessary for a DPR project. Current effluent nitrogen concentrations are significantly higher and would likely become a limiting factor in the absence of these upgrades.

6.4.5 TABLE C-5 – Storage Pond Volume Calculation

The storage pond dimensions are calculated in Table C-5 and are based on achievable pond depth (assumed to be 15 ft), side slopes (assumed at 4:1), and free board (assumed at 1 ft). These parameters coupled with the required volume (134 ac-ft minimum) were used to determine the pond property dimensions A, B, and L. The approximated dimensions of A, B, and L were determined to be 750 ft, 750 ft, and 715 ft, respectively. The usable volume for the pond does not include the freeboard volume, as the freeboard volume is considered a safety factor. Per rule, a 10 ft berm around the pond is required for access and was included in the total area calculations. This should be increased to 20 ft (for truck access) if the pond will be located near a property line. The total footprint of the pond was calculated to be 12.3 acres.

6.4.6 Costs

A planning-level cost estimate for the on-site portions of a land-application disposal is presented in Table C-6. A detailed layout of the irrigation system was not completed for this high-level analysis. Instead, a series of irrigation infrastructure parameters were used to determine the approximate quantity of each item based on the total irrigated acreage.

The sprinkler heads required for the irrigated area was determined by taking the Total Irrigated Area and dividing it by the lateral and main sprinkler spacing. Subsequently, the total polyvinyl chloride (PVC) and high-density polyethylene (HDPE) flex pipe needed was assumed based on the amount of pipe required per zone. The excavation and geotextile layers were assumed based on the design parameters of Table C-5 for the pond.


Two alternative alignments are proposed for the pipeline to convey treated effluent from the South Regional Plant to the subject tract for spray irrigation, Option 1 and Option 2. Option 1 represents a longer alignment but requires less easement access, whereas Option 2 takes a shorter route but requires easement access to cross one or more properties. See Figure 6.1 to compare the potential alignments.

The total on-site cost of land application infrastructure is estimated at approximately $6 million. In addition, the cost of the conveyance infrastructure (pump station and pipeline cost estimated for the alignment corresponding to Option 1) was estimated just under $2 million, for a total of approximately $8 million (see also Table 6.1). The on-site and conveyance costs are listed separately in Chapter 7, where the total cost of each proposed project alternative is presented.

6.4.7 Discussion of Findings and Land Application Alternatives

The monthly water balance calculations (Table C-2) and the storage volume calculations (Table C-3) indicate that the subject tract of land could feasibly support a design flow of 0.5 mgd. Table C-4 (Nitrogen Uptake Calculations) also confirmed that the tract could support the nitrogen loading at a 10 mg/L total nitrogen effluent concentration.

The subject tract, however, is not an ideal candidate for a 0.5 mgd design flow as evidenced by the long storage requirement that results in a large (and costly) storage pond. Increasing the storage requirements also decreases the acreage of the tract available for irrigation (because the pond surface area increases), which iteratively increase the amount of storage required. By increasing the total tract area available for irrigation or by lowering the design flow, the volume of the storage pond could be decreased. Table 6.1 shows a summary of the baseline scenario described in the sections above and documented in Appendix C. In addition, Table 6.1 shows the results of several other exploratory scenarios in which either the application rate and/or the available irrigation area are varied.

6.4.8 Other Notes

The design of land application systems is based on long-term average climate data. Calculations based on this long-term data are done to determine the spray field size, application rate, and volume of required effluent storage. Although the calculations Carollo performed are considered conservative and utilized maximums and minimums over the course of ~60 year, past measurements are not a guarantee on future conditions.


Table 6.1 Alternative Scenarios for Land Application Direct Potable Reuse Feasibility Study City of Dripping Springs

Scenario(1)

Design Flow (mgd)

Total Usable Irrigation Area (ac)

Storage Required

(ac-ft) (days) Planning-Level Project Cost(2)

Baseline (186 acres total tract area at 0.5 mgd flow)

0.5 159 134 87 $8,067,000

100-acre storage by varying irrigation area

0.5 268 100 65 $7,150,000

60-day storage by varying irrigation area

0.5 300 92 60 $6,882,000

60-day storage by varying design flow

0.27 166 49 60 $3,895,000

30-day storage by varying design flow

0.18 169 16 30 $2,261,000

(1) Baseline scenario calculation tables are included in Appendix C. Other scenario calculations are not included.

Notes:

(2) Planning level project costs include on-site costs for the effluent holding pond and the land application infrastructure as calculated by the tables shown in Appendix C, plus the cost of the pump station and pipeline to convey treated effluent from the South Regional Plant Site, as estimated in Chapter 7 (and scaled linearly in reduced flow scenarios). The same multipliers are applied as for the project alternative cost estimates provided in Chapter 7 (30% unidentified project elements, 15% contractor overhead, profit, and risk, and 15% engineering, legal and administrative fees). Costs shown do not include the cost of land.

6.5 DISCHARGE The discussion of discharge alternatives is limited to a technical evaluation of achieving anticipated water quality requirements and the infrastructure necessary to deliver water to a suitable point of discharge. A detailed discussion of the effort required for TPDES permitting is not within the scope of this study.

6.5.1 Water Quality Requirements for Discharge

The water quality requirements for discharge are discussed in detail in Chapter 3. Section 3.3 discusses anticipated nutrient goal concentrations (6 mg/L total nitrogen and 0.5 mg/L total phosphorus) as well as the fact that solids and organics loading should not be limiting factors once biological treatment is implemented for nutrient removal and cloth filters are in place to control solids in the effluent.


6.5.2 Discharge Infrastructure

The infrastructure required for discharge is discussed as part of the project alternatives descriptions in Chapter 5. Section 5.2.8 describes the infrastructure needs anticipated for each of the two potential outfall locations, both of which eventually discharge into Onion Creek. In each case, the discharge infrastructure needs are assumed to be limited to the construction of gravity outfall structures.


Chapter 7

PLANNING LEVEL COST ANALYSIS

7.1 APPROACH TO COST ANALYSIS In this chapter, all of the project elements discussed in previous chapters are assembled into three main conceptual project alternatives, two of which are divided into sub-alternatives. Planning-level cost estimates are calculated for each project element and then the cost for each project alternative is determined as a sum of the cost associated with each applicable project element. For each Project Alternative, an overview of the elements included in the alternative is followed by tables that provide capital and operation and maintenance (O&M) costs.

The cost estimates provided in this chapter are considered Class 4 Budget Estimates as defined by the AACE International's Revised Classification (1999) with an expected accuracy range of +30 percent or -15 percent. These cost estimates are based upon the Engineer's perception of current conditions in the project area and are subject to change as variances in the cost of labor, materials, equipment, services provided by others or economic conditions occur. Since the Engineer has no control over these factors, she cannot warrant or guarantee that actual bids will not vary from the costs presented herein. These estimates do, however, reflect the Engineer's professional opinion of accurate costs at this time.

Due to this level of planning, these costs are escalated with a standard 30% added multiplier for unidentified project elements. Due to its unique application, the advanced treatment process was evaluated in more detail than the remainder of the project elements, therefore a lower 15% added multiplier for unidentified elements has been included for that portion of the project cost. Standard planning-level multipliers for contractor overhead and profit (15%) and engineering and legal services (15%) are also included.


7.2 DPR AT SOUTH REGIONAL PLANT SITE WITH DISCHARGE Alternative 1 consists of DPR at the South Regional Plant Site with backup discharge to a drainage feature that discharges into Onion Creek. The project elements associated with this alternative include

1. Upgrades to the existing South Regional Plant: a. For Alternative 1a, these upgrades are based on the analysis provided in

Chapter 4 (and further documented in Appendix B) for biological nutrient removal retrofits;

b. For Alternative 1b, a previously proposed MBR retrofit (CMA, 2012) to achieve the same water quality goals;

2. Advanced treatment and engineered storage buffer;

3. Infrastructure to connect finished water to the DSWSC wellfield storage tank; and

4. An outfall structure constructed at the proposed Caliterra effluent holding pond. This discharge alternative assumes an existing effluent pump station and pipeline associated with the 210 reuse at Caliterra proposed as part of Amendment No. 1 to the existing TLAP permit.

Table 7.1 Alternative 1A Capital Costs Direct Potable Reuse Feasibility Study City of Dripping Springs

Description Total

Upgrades to Existing WWTP for Biological Nutrient Removal $426,000

Advanced Treatment Facilities and Engineered Storage Buffer $4,821,000

Connection to Existing Water Infrastructure $462,000

Discharge Structure $75,000

TOTAL DIRECT COST $5,784,000 Unidentified Project Elements –

30% $289,000 All but Advanced Treatment System

Advanced Treatment System 15% $723,000

Subtotal $6,796,000 General Contractor Overhead, Profit & Risk 15% $1,019,000

TOTAL ESTIMATED CONSTRUCTION COST $7,815,000 Engineering, Legal, and Administrative Fees 15% $1,172,000

TOTAL ESTIMATED PROJECT COST $8,987,000


Table 7.2 Alternative 1A Operation and Maintenance Costs Direct Potable Reuse Feasibility Study City of Dripping Springs

Description Total

WWTP with Biological Nutrient Removal $62,000

Advanced Treatment Facilities $104,000

Advanced Treatment Facilities Operations Staff

$368,000


Outfall Structure

$0

Annual O&M Cost

$539,000

Table 7.3 Alternative 1B Capital Costs Direct Potable Reuse Feasibility Study City of Dripping Springs

Description Total

Existing WWTP Upgraded to Membrane Bioreactor $4,084,000

Advanced Treatment Facilities (without UF) and Engineered Storage Buffer $4,821,000


Outfall Structure $75,000

TOTAL DIRECT COST $9,442,000

Unidentified Project Elements

All but Advanced Treatment System 30% $1,387,000


Subtotal $11,552,000

General Contractor Overhead, Profit & Risk 15% $1,733,000

TOTAL ESTIMATED CONSTRUCTION COST $13,285,000

Engineering, Legal, and Administrative Fees 15% $1,993,000



Table 7.4 Alternative 1B Operation and Maintenance Costs Direct Potable Reuse Feasibility Study City of Dripping Springs

Description Total

WWTP with Membrane Bioreactor $104,000

Advanced Treatment Facilities (without UF) $65,000


$368,000


Outfall Structure $0

Annual O&M Cost

$542,000

7.3 DPR WITH LAND APPLICATION Alternative 2 consists of DPR at the South Regional Plant Site with backup land application of the effluent to the subject tract discussed in Chapter 6. The project elements associated with this alternative are similar to those for Alternative 1, except for effluent disposal:

1. Upgrades to the existing South Regional Plant based on the analysis provided in Chapter 4 (and further documented in Appendix B) for biological nutrient removal;


3. Infrastructure to connect finished water to the DSWSC wellfield storage tank;

4. Effluent pump station and pipeline to convey effluent to land application site along two potential alignments (Option 1 and Option 2, forming Alternatives 2a and 2b, respectively); and

5. Land application infrastructure, including effluent holding pond and sprinkler system.


Table 7.5 Alternative 2A Capital Costs Direct Potable Reuse Feasibility Study City of Dripping Springs

Description Total




Connection to Land Application Infrastructure (Option 1, see Figure 6.1)

$1,065,000

Land Application Infrastructure $3,627,000





Subtotal $12,798,000

General Contractor Overhead, Profit & Risk 15% $1,920,000

TOTAL ESTIMATED CONSTRUCTION COST $14,718,000

Engineering, Legal, and Administrative Fees 15% $2,208,000



Table 7.6 Alternative 2B Capital Costs Direct Potable Reuse Feasibility Study City of Dripping Springs

Description Total



Pumping Finished Water to DSWSC Wells $462,000

Connection to Land Application Infrastructure (Option 2, see Figure 6.1)

$912,000

Land Application Infrastructure $3,627,000








Table 7.7 Alternatives 2A and 2B Operation and Maintenance Costs Direct Potable Reuse Feasibility Study City of Dripping Springs

Description Total

WWTP with Biological Nutrient Removal $62,000



$368,000


Pumping Effluent to Land Application Site

$6,000

Land Application Infrastructure $120,000

Annual O&M Cost $665,000


7.4 DPR AT UPSTREAM SITE Alternative 3 consists of DPR at the upstream site with backup discharge to a drainage feature that discharges into Onion Creek. The project elements associated with this alternative include

1. Collection system tie-in from existing downtown booster pump station;

2. A new wastewater treatment plant with biological nutrient removal to meet the same effluent water quality goals as discussed in Chapter 3;


4. Infrastructure to connect finished water to a presumed existing distribution system water storage tank; and

5. A gravity outfall structure that discharges effluent into an adjacent drainage channel that eventually discharges into Onion Creek.

Table 7.8 Alternative 3 Capital Costs Direct Potable Reuse Feasibility Study City of Dripping Springs

Description Total

Sewer Infrastructure

$655,000

New Wastewater Treatment Plant

$4,000,000



Outfall Structure $117,000









Table 7.9 Alternative 3 Operation and Maintenance Costs Direct Potable Reuse Feasibility Study City of Dripping Springs

Description Total

Sewer Infrastructure (not included)

$0

WWTP with Biological Nutrient Removal

$62,000


Advanced Treatment Facilities Operations Staffing

$368,000


Outfall Structure $0

Annual O&M Cost $541,000

7.5 COST COMPARISON A final cost comparison between the five alternatives evaluated for planning level cost is provided in Table 7.10. As shown, Alternative 1a is the most economical alternative for the implementation of DPR, based on the assumptions and limitations provided in this report.

Subject to the same limitations, Table 7.10 shows that the increase in capital cost associated with electing to dispose of effluent from the South Regional Plant Site via land application at the subject tract discussed in Chapter 6 rather than discharge it to a drainage channel that flows into Onion Creek is approximately $8 million, and the operation and maintenance cost premium of doing so is approximately $126,000 per year.

Implementing DPR at an upstream site would require more capital investment due to the cost of constructing a new wastewater treatment plant.

The total cost to produce water is shown in the last two columns of Table 7.10. It is important to note that these costs include the cost of wastewater treatment, which is typically not included in the cost of water for a DPR project. The cost of water shown for Alternatives 1A, 2A and 2B, which include only a small retrofit cost for the existing wastewater treatment plant but do include the O&M cost to maintain the full plant, are most representative of the cost to produce water from a given effluent.


Table 7.10 Comparison of Costs for the Proposed Project Alternatives Direct Potable Reuse Feasibility Study City of Dripping Springs

Alt

(1) Capital ($MM)

Debt Service ($MM/yr)(2)

O&M ($MM/yr)

Total Cost of Water ($/ac-ft) ($/kgal)

1A 8.9 0.7 0.54 2,250 6.90

1B 15.3 1.2 0.54 3,157 9.69

2A 16.9 1.4 0.67 3,612 11.08

2B 16.7 1.3 0.67 3,575 10.97

3 15.8 1.3 0.54 3,237 9.93

(1) Notes:

Alt

(2) The annual cost of debt service is calculated from the capital cost based on a 20-year project life at a 5% annual discount rate.

ernatives: 1A – DPR at South Regional Plant Site with BNR retrofits and effluent discharge 2B – DPR at South Regional Plant Site with MBR retrofits and effluent discharge 2A – DPR at South Regional Plant Site with BNR retrofits and effluent land application (Option 1) 2B – DPR at South Regional Plant Site with BNR retrofits and effluent land application (Option 2) 3 – DPR at Upstream Site with new BNR plant and effluent discharge

Another important observation is that the cost of operation and maintenance (O&M) represents a significant fraction of the overall cost of water, ranging from over 30% for Alternative 1A to about 25% for Alternative 3. The high O&M cost estimates are due in large part to the cost of paying for 24-hour, 7-days per week operational staff presence at the advanced treatment facility (see Tables 7.2, 7.4, 7.7, and 7.9).

Costs associated with operator staffing are not anticipated to change significantly with the size of the plant within the size range that is realistic for the City. At a higher design flow rate, the relative cost of operator staffing would diminish proportionally. The converse is also true: at lower flow rates, the cost of staffing the plant for 24/7 operation would become proportionally larger.


Chapter 8

CONCLUSIONS AND NEXT STEPS

8.1 CONCLUSIONS The purpose of this study was to determine the feasibility, treatment requirements, and planning level cost for developing a direct potable reuse (DPR) project to supplement drinking water supplies in Dripping Springs and to minimize or eliminate the need for discharge of treated wastewater. As a corollary to these goals, the project team was also tasked with evaluating effluent disposal alternatives, specifically discharge to Onion Creek and land application at a specific land application site, for feasibility and estimated cost.

This report discusses regulatory (Chapter 2) and water quality requirements (Chapter 3) for a DPR project and how these can be achieved through treatment upgrades at the existing South Regional Wastewater Treatment Plant (Chapter 4) and advanced treatment and storage of advanced purified water prior to distribution (Chapter 5). Effluent disposal alternatives are evaluated in detail (Chapter 6). Finally, project alternatives composed of all the elements discussed in Chapters 4 through 6 were assembled and evaluated for planning-level capital, operation and maintenance costs (Chapter 7).

Based on this evaluation, DPR is feasible for the City. Land application of 0.5 mgd treated effluent at the proposed tract of land is also feasible. However, the total project cost of the land application infrastructure exceeds the cost of constructing a simple outfall structure for discharge by nearly $8 million. This figure does not include the cost of land. Operation and maintenance costs for the land application option include maintenance of the pump station, pipeline, and irrigation facilities, for a total of approximately $126,000 per year, whereas an outfall, as a passive concrete structure, is associated with minimal maintenance once built.

The most cost-effective project option of those considered in Chapter 7 is Alternative 1A, which includes minor retrofits to the existing South Regional Plant, subsequent ozone-biofiltration based advanced treatment, and engineered storage at the South Regional Plant Site. Given the extent of treatment required for such a project and the need to have on-site operations staff dedicated to the South Regional Plant Site at all times (24/7), the estimated cost of water produced ($2,250 per acre-foot or $6.9 per 1,000 gallons) is relatively high.

It would be appropriate to compare this cost to the wholesale cost of water the DSWSC sells. However, due to the significant fees paid for new connections (NewGen, 2015), and the mix of well water and PUA water sources, it is difficult to determine a definitive wholesale cost of water. For one point of comparison, the estimated cost of water from Alternative 1A is still below the average retail price paid by DSWSC customers at $8.50 per 1,000 gallons (calculated based on dividing the volume of water sold in 2014 by the 2014 revenue; NewGen, 2015; see Table 2).


In the face of dwindling conventional water supplies and the associated increasing costs of water, the value of a water supply that is under local control and drought-proof, such as that sourced from a DPR project, is difficult to quantify but certainly significant. The City must now evaluate whether this value is sufficient to justify proceeding with the project.

8.2 NEXT STEPS If the City decides to pursue a DPR project, a number of steps will be needed before the project could proceed to detailed design and construction. These include the following actions that could be undertaken immediately:

1. Complete wastewater plant retrofits for biological nutrient removal. This would include the following items:

a. Sampling of selected water quality parameters;

b. Detailed design of retrofit; and

c. Implementation of the retrofit.

2. Pursue an effluent disposal alternative. This action is independent of other steps but necessary to successful completion of a DPR project.

3. Pursue a proactive public participation program. A discussion of the role of public perception in DPR projects was outside the scope of this report. However, a large body of literature and resources exist to support the development of public outreach programs for potable reuse projects.

Once the wastewater treatment plant retrofits are completed, the following subsequent steps can then be completed:

4. Characterize the upgraded wastewater treatment plant’s effluent water quality. This would include the following items:

a. Prepare an effluent characterization sample plan;

b. Obtain TCEQ approval for the effluent characterization plan; and

c. Collect samples and evaluate results.

5. Perform preliminary engineering for the proposed advanced treatment facility based on effluent water quality results and the initial sizing completed for this report.

6. Pilot testing of the proposed treatment process. This includes the following items:

a. Develop a pilot testing protocol;

b. Obtain TCEQ approval for the pilot testing protocol;

c. Perform pilot testing; and

d. Refine preliminary engineering of the treatment process based on pilot testing results.


Chapter 9

REFERENCES

9.1 REFERENCES Azadpour-Keeley, A., B. Faulkner, and J. Chen. 2003. Movement and Longevity of Viruses

in the Subsurface. USEPA Ground Water Issue Report No. 540S03500.

Baronti, C., R. Curini, G. D’Ascenzo, A. DiCoricia, A. Gentili, and R. Samper. 2000. Monitoring Natural and Synthetic Estrogens at Activated Sludge Sewage Treatment Plants and in a Receiving River Water. Environ. Sci. Technol., 34(24): 5059-5066.

California Department of Public Health (CDPH). 2014. Groundwater Replenishment Using Recycled Water. DPH-14-003E, dated June 18, 2014.

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Gerringer et al., in prep. Equivalency of Advanced treatment Trains for Direct Potable Reuse, Final Report to the WateReuse Research Foundation for Project No. 11-02, in preparation.

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April 2015 pw://Carollo/Documents/Client/TX/Dripping Springs/9756A00/Deliverables/Feasibility Study/

Direct Potable Reuse Feasibility Study

APPENDIX A – TCEQ EFFLUENT CHARACTERIZATION RECOMMENDATIONS

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Background Related to Monitoring Wastewater Effluent Intended for use as Drinking Water

As water resources are diminished by drought, Texas communities may seek approval to reuse (reclaim) wastewater to produce drinking water. Wastewater is subject to contamination from microbes and chemicals; many of these contaminants have been identified, but some are not yet regulated.

Sampling Wastewater Effluent proposed as a Drinking Water Source

The Texas rules require that any entity proposing to use a new source of water must identify the quality of that source water. Wastewater effluent is by definition fecally impacted, and is subject to the presence of chemicals of human origin. Therefore, it is critical that the quality of wastewater effluent be characterized before use as a drinking water source.

Texas adopts specific rules under 30 TAC 210 for reclaimed water quality. However, the 30 TAC 210 standards do not address all of the chemical and microbial constituents of concern in drinking water. Drinking water rules are based on removal of constituents at levels found in ambient water, which is of higher quality than wastewater effluent.

The list presented here is for planning purposes only and is subject to change. A public water system (PWS) may wish to sample additional constituents that are not listed here. Additionally, when a PWS requests that they be granted permission to use wastewater effluent as a drinking water source, the TCEQ may require additional, site-specific testing.

Locations

The wastewater effluent that is intended as a new source of drinking water should be characterized. It is recommended that any water streams intended for blending with the wastewater be characterized as well. Likewise, any raw water used for treatment as surface water should be sampled. Treated water should be analyzed in accordance with the site-specific requirements applied by the TCEQ.

Sampling at various stages in the process allows a PWS to demonstrate the source of any pathogens or chemical contaminants. A map showing the sampling locations, and a list describing the sample location(s) should be provided to the TCEQ when the sampling regime is proposed.

Frequency

Although a single ‘snapshot’ view of water quality may be considered sufficient by a PWS’s design engineer, that snapshot must be viewed as a non-statistically representative sample.

Seasonal variation

The TCEQ requires that wastewater intended for use as a drinking water source be characterized over a period of time that includes seasonal variation. Without seasonal data, changes in quality cannot be scientifically factored into treatment plant design. Indoor use of drinking water increases in the summer, suggesting that the contaminant

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levels in summer may be less than those in the winter. PWSs often use different initial sources of raw water on a seasonal basis, so that the baseline water quality characteristics can change seasonally. A system may use surface water as their initial source, but also use well water during the high-demand summer periods.

Schedule

At a minimum, wastewater effluent should be sampled 24 times at approximately equal intervals over a period of one year for microorganisms, nitrate, nitrite, pH, and temperature. Wastewater effluent should be sampled for other chemicals and water quality parameters a minimum of four times over the same one year period: two times representative of the typical extreme temperatures in the wastewater effluent, one time when effluent temperatures are generally falling approximately midway between the extreme temperatures, and one time when effluent temperatures are generally rising approximately midway between the extreme temperatures.

Samples should be collected from other locations, such as at proposed blending points or surface water intakes, at least 6 times at approximately equal intervals over the same one year period.

Lists of Analyses

The constituents of concern in wastewater effluent can be broadly grouped as microbes or chemicals and other constituents such as hardness and pH. Although the lists of recommended analytes are not exhaustive, they provide a starting place for planning. The EPA’s Unregulated Contaminant Monitoring Regulation 3 (UCMR3) will apply to all large water systems that serve more than 10,000 people and selected small water systems. Constituents identified for monitoring under UCMR3 are included in the monitoring for wastewater effluent.

List of Microorganisms Identified for Sampling in Wastewater Effluent

Proposed for use as a Drinking Water Source

MICROBIALS Method1 Regulated?

Viruses2

†Total Virus 1615 Yes

**Endovirus 1615 UCMR32,3

**Norovirus

*Rotavirus 1 No2

*Poliovirus 1 No2

*Echoviruses 1 No2

*Coxsackie viruses group A and B 1 No2

*Adenovirus 1 No2

*Hepatitis A 1 No2

Protozoans

†Cryptosporidium 1623 Yes

†Giardia

*Naegleria fowleri 5 No

*Cyclospora 5 No

*Microsporidia (fungus) 5 No

Bacteria

†Total coliform (indicator) 16044 Yes3

†Escherichia coli (E. coli) (indicator) 16044 Yes3

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MICROBIALS Method1 Regulated?

*Enterococci 1600,

1106

No

*Salmonella (and / or Shigella, Campylobacter, Pseudomonas5)

1200 No

*Aeromonas 1605 No

*Heterotrophic plate count (indicator) 9215 No

† Required to be sampled. * Recommended for sampling. ** Highly recommended for sampling. 1 Method listed is an EPA method unless otherwise noted. List of methods is not

exhaustive, but is included for reference only. 2 Viruses are regulated as a group through treatment technique requirements of the

EPA’s Surface Water Treatment Rules and Ground Water Rule 3 Regulations cover distribution levels and removal requirements. 4 Several approved methods exist. A PWS should propose one of these approved

methods for analysis. 5 Methods are in development. A PWS should propose the method they plan to use.

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List of Chemicals and Other Constituents Identified for Sampling in

Wastewater Effluent Proposed for use as a Drinking Water Source

CHEMICALS Method1 Regulated

Disinfection byproducts

†Trihalomethanes 524 Yes2

†Haloacetic acids (also report bromochloroacetic acid (BCAA))

552 Yes2

(BCAA is not

regulated)

**Nitroso-dimethylamine (NDMA) 521 UCMR33

**Nitroso-pyrrolidine (NPYR)

*Any other DBPs expected to occur on a site-specific basis, for example chlorite, if chlorine

dioxide is used.

Organic chemicals

†SOC (Regulated (and tentatively identified unregulated) synthetic organic chemicals): Alachlor, atrazine,

benzo(a)pyrene, di(ethylhexyl)-adipate, di(ethylhexyl)-phthalate, endrin, heptachlor, heptachlor epoxide,

hexachlorobenzere (HCB), Hexachlorocyclopentadiene, lindane, methoxychlor, pentachlorophenol (PCP), simazine.

525.2 Yes

†SOC (Regulated (and tentatively identified unregulated)

synthetic organic chemicals): 2, 4, 5-TP (Silvex), 2,4-D, Dalapon, Dinoseb, pentachlorophenol, picloram

515.4 Yes

†SOC Chlordane, toxaphene (and unregulated aroclor species)

531.1 Yes

†EDP/DBCP (ethylene dibromide & 1,2-dichloro-3-propane)

504.1 Yes

†carbofuran, oxamyl (Vydate) 531.1 Yes

†Glyphosate 547 Yes

†2,3,7,8-TCDD (Dioxin) 1613 Yes

*Diquat 549.2 Yes

*Endothall 548.1 Yes

†VOC (Regulated (and tentatively identified unregulated) volatile organic chemicals): 1,1,1,2-Tetrachloroethane, 1,1,2,2-Tetrachloroethane, 1,1-Dichloroethylene, 1,2-dichloroethane, 1,2-dichloropropane, 1,2,4-trichlorobenzene, benzene, carbon tetrachloride, cis-1,2-dichloroethylene, dichloromethane, ethylbenzene,

monochlorobenzene, o-dichlorobenzene, para-dichlorobenzene, styrene, tetrachloroethylene, toluene, trans-1,2-dichloroethylene, trichloroethylene, vinyl chloride, xylenes

524.2 Yes

**Pharmaceutical indicators: 17-α-ethynylestradiol (ethinyl estradiol), 16-α-hydroxyestradiol (estriol),

equilin, estrone, testosterone, 4-androstene-3,17-dione

537 UCMR3

**Chemicals of human origin: Perfluorooctanesulfonic

sulfonate (PFOS), perfluorooctanoic acid (PFOA) perfluorononanoic acid (PFNA) perfluorohexanesulfonic acid (PFHxS) perfluoroheptanoic acid (PFHpA) perfluorobutanesulfonic acid (PFBS)

537 UCMR3

**Sucralose 4 No

*1,4 dioxane 522 No

*Caffeine 1694 No

*N,N-Diethyl-meta-toluamide (DEET) 633 No

*Gemfibrozil 1694 No

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CHEMICALS Method1 Regulated

*Iopromide 1694 No

Inorganic chemicals

†Nitrate/nitrite, as nitrogen 300.0 Yes

†Other regulated minerals: fluoride, chloride, sulfate, total dissolved solids (TDS)

†Regulated primary metals: Antimony, arsenic, barium, beryllium, cadmium, chromium, mercury, selenium, thallium

200.5 Yes

†Regulated secondary metals: Aluminum, copper, iron,

manganese, silver, zinc

†Asbestos (if asbestos/cement pipe is used in drinking water distribution, wastewater collection, or associated piping)

100.2 Yes

*Cyanide 335.4 Yes

*Sodium 200.7 Yes2

*Perchlorate 314 UCMR2

Other water quality parameters

†pH

†Temperature

*Bicarbonate and carbonate alkalinity

*Total hardness

*Total suspended solids

*Total chlorine, free chlorine, monochloramine

*Ammonia

† Required to be sampled. * Recommended for sampling. ** Highly recommended for sampling. 1 Method listed is an EPA method unless otherwise noted. List of methods is not

exhaustive, but is included for reference only. 2 Regulated in distribution systems.

3 Regulatory monitoring requirements, not health-based standards. 4 Acceptable methods exist but have not yet been approved by the EPA.

It is generally understood that the cost of analysis may be a concern to a PWS. A system should consider this cost in planning. Based on industry experience, the cost of sampling prior to design is offset by the ability to design treatment based on actual levels of contaminants. If the raw wastewater is not fully characterized, regulators may require additional safety factors which may result in additional treatment needs with their associated additional costs.

It is recommended that the ‘starred’ analytes in the list above be included in analyses. The intent of the sampling is to establish what viral, bacterial, protozoan, and chemical contaminants are present in order to protect public health; an acceptable sampling regime will ensure that characterization is accomplished.

In general, analyses should be performed at NELAC-accredited laboratories using EPA-approved methods. Where those labs or methods are unavailable, a PWS should identify a capable lab and request permission for its use. Methods listed in these tables are recommendations; other approved EPA-methods exist, and may be proposed for use.

The analytes of greatest concern are those with documented, immediate negative health effects (“acute” health effects), such as pathogens and nitrate/nitrite. It may be acceptable for a system to perform sampling for constituents that have long-term health effects, like regulated organics, less frequently than sampling for pathogens or nitrate/nitrite.

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Depending on the treatment method selected by the PWS, it may be necessary for a PWS to perform additional sampling to characterize the impact on treatment. For example, selenium interferes with adsorption under some conditions; if adsorption is used for treatment, additional selenium sampling may be required.

Results

Results should be tabulated in a clear, easy-to-read manner for submittal; analytical detail such as the quality assurance documentation needs to be submitted. The summary tables should be organized with sample sites in order of extent of treatment; for sampling over a period of time, analyses should be presented in the order that the samples were collected. The summary tables should contain the units of measurement.

Notes Related to Sampling for Chemicals of Emerging Concern

Simultaneously, the drinking water industry and EPA are becoming concerned about contaminants of emerging concern (CEC). Many of the CEC are of human origin, especially pharmaceuticals and personal care products.

Public concern regarding these CECs is very high, and the EPA is researching their presence through the Contaminant Candidate List and Unregulated Contaminant Monitoring Regulation (UCMR) process. As of 2012, the EPA has not determined or set health-based maximum contaminant levels (MCLs) for these potentially harmful microbes and chemicals. Additional research into ambient levels of CEC chemicals is ongoing. Therefore, levels identified in wastewater intended for use as drinking water will be compared to levels present in ambient water in order to determine the relative risk of wastewater effluent as contrasted with ambient (river or lake) waters. If the EPA sets MCLs, further characterization may be necessary (see References).

Analytical methods do not yet exist for some of these CEC chemicals. The best current methods for CEC chemicals are captured in the EPA’s Unregulated Contaminant Monitoring Regulations (UCMRs), 1 through 3.

Although the UCMR contaminants are not required by EPA to be sampled in all direct and indirect reuse sources, the list provides a well-researched source of information for chemicals that EPA is most likely to regulate in the future, and that are most likely to have negative health effects.

Additionally, as interest in chemicals of emerging concern grows, researchers have identified chemicals that can indicate the presence of anthropogenic contamination, but that are not harmful to human health.

Pharmaceutical indicators

The UCMR3 list includes estrogenic hormones used in pharmaceuticals. It is recommended that reuse sources be evaluated for these chemicals using analytical method 537.

Personal care product indicator

The UCMR3 list includes 1,4 dioxane, which is used in personal care products such as soaps and makeup. It is recommended that reuse sources be evaluated for 1,4 dioxane using method EPA 522.

Chemicals of human origin

New research has identified sucralose as an excellent, conservative, easy-t0-measure indicator that water contains chemicals of human origin. Sucralose is not biologically

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degraded, so it passes through wastewater biological treatment plants unchanged. Sucralose should be quantified in reuse sources.

Additionally, EPA identified six perfluorinated compounds that may indicate contamination from human industrial activities. These compounds (perfluorooctanesulfonic sulfonate (PFOS), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorohexanesulfonic acid (PFHxS), perfluoroheptanoic acid (PFHpA), and perfluorobutanesulfonic acid (PFBS)) should be quantified using method EPA 537 (1.1).

Disinfection byproducts of emerging concern

Wastewater sources are frequently chlorinated during the wastewater treatment process. Regulated disinfection byproducts (trihalomethanes and haloacetic acids) are known to frequently occur at levels of concern in wastewater. Additionally, the EPA has identified the presence of other potentially carcinogenic disinfection byproducts called nitrosamines. It is recommended that the two most-frequently occurring nitrosamines (nitroso-dimethylamine (NDMA) and Nitroso-pyrrolidine (NPYR)) be quantified using method EPA 521.

References

1. “Guidelines for Water Reuse,” (EPA/625/R-04/108); U.S. Environmental

Protection Agency, Municipal Support Division, Office of Wastewater

Management, Office of Water; September 2004; available at:

http://www.epa.gov/nrmrl/wswrd/dw/smallsystems/pubs/625r04108.pdf

2. “Revisions to the Unregulated Contaminant Monitoring Regulation (UCMR 3) for

Public Water Systems,” (77 FR 26072); U.S. Environmental Protection Agency;

May 5, 2012

http://www.epa.gov/nrmrl/wswrd/dw/smallsystems/pubs/625r04108.pdf



APPENDIX B – WASTEWATER TREATMENT MODEL OUTPUTS

File C:\Users\tshimada\Desktop\Dripping Springs AA 18 deg.bwc 1

BioWin user and configuration data Project details Project name: Dripping Springs Project ref.: 9756A.00 Plant name: Dripping Springs WWTP User name: tshimada Created: 3/10/2015 Saved: 3/11/2015 Scenario: Annual Average Conditions Steady state solution Target SRT: 4.00 daysSRT #0: 3.98 days Temperature: 18.0°C Flowsheet

Configuration information for all Bioreactor units Physical data Element name Volume [Mil. Gal] Area [ft2] Depth [ft] # of diffusers Anox 1 0.0346 289.0842 16.000 Un-aerated Anox 2 0.0692 578.1684 16.000 Un-aerated Oxic 1 0.0985 822.9710 16.000 186 Oxic 2 0.0346 289.0842 16.000 66

Operating data Average (flow/time weighted as required) Element name Average DO Setpoint [mg/L] Anox 1 0 Anox 2 0 Oxic 1 2.0 Oxic 2 2.0 Aeration equipment parameters Element name k1 in C =

k1(PC)^0.25 + k2 k2 in C = k1(PC)^0.25 + k2

Y in Kla = C Usg ^ Y - Usg in [m3/(m2 d)]

Area of one diffuser % of tank area covered by diffusers [%]

Anox 1 2.5656 0.0432 0.8200 0.4413 10.0000 Anox 2 2.5656 0.0432 0.8200 0.4413 10.0000 Oxic 1 2.5656 0.0432 0.8200 0.4413 10.0000 Oxic 2 2.5656 0.0432 0.8200 0.4413 10.0000

Influent Anox 1 Anox 2Oxic 1 Oxic 2 Effluent

WAS

AlumMethanol


Configuration information for all Model clarifier units Physical data Element name Volume[Mil. Gal] Area[ft2] Depth[ft] Number of layers Top feed layer Feed Layers Model clarifier5 0.3388 3019.0000 15.000 10 6 1 Operating data Average (flow/time weighted as required) Element name Split method Average Split specification Model clarifier5 Flow paced 75.00 %

Element name Average Temperature Reactive Model clarifier5 Uses global setting No

Configuration information for all COD Influent units Operating data Average (flow/time weighted as required) Element name Influent Time 0 Flow 0.35 Total COD mgCOD/L 593.60 Total Kjeldahl Nitrogen mgN/L 59.80 Total P mgP/L 7.69 Nitrate N mgN/L 0 pH 7.30 Alkalinity mmol/L 6.98 ISS Influent mgISS/L 50.80 Calcium mg/L 80.00 Magnesium mg/L 15.00 Dissolved oxygen mg/L 0 Element name Influent Fbs - Readily biodegradable (including Acetate) [gCOD/g of total COD] 0.1379 Fac - Acetate [gCOD/g of readily biodegradable COD] 0.1500 Fxsp - Non-colloidal slowly biodegradable [gCOD/g of slowly degradable COD] 0.7791 Fus - Unbiodegradable soluble [gCOD/g of total COD] 0.0500 Fup - Unbiodegradable particulate [gCOD/g of total COD] 0.1874 Fna - Ammonia [gNH3-N/gTKN] 0.7500 Fnox - Particulate organic nitrogen [gN/g Organic N] 0.5923 Fnus - Soluble unbiodegradable TKN [gN/gTKN] 0.0200 FupN - N:COD ratio for unbiodegradable part. COD [gN/gCOD] 0.0188 Fpo4 - Phosphate [gPO4-P/gTP] 0.4038 FupP - P:COD ratio for unbiodegradable part. COD [gP/gCOD] 0.0110 FZbh - OHO COD fraction [gCOD/g of total COD] 0.0200 FZbm - Methylotroph COD fraction [gCOD/g of total COD] 1.000E-4 FZaob - AOB COD fraction [gCOD/g of total COD] 1.000E-4 FZnob - NOB COD fraction [gCOD/g of total COD] 1.000E-4 FZaao - AAO COD fraction [gCOD/g of total COD] 1.000E-4 FZbp - PAO COD fraction [gCOD/g of total COD] 1.000E-4 FZbpa - Propionic acetogens COD fraction [gCOD/g of total COD] 1.000E-4 FZbam - Acetoclastic methanogens COD fraction [gCOD/g of total COD] 1.000E-4 FZbhm - H2-utilizing methanogens COD fraction [gCOD/g of total COD] 1.000E-4 FZe - Endogenous products COD fraction [gCOD/g of total COD] 0


Configuration information for all Metal addition units Operating data Average (flow/time weighted as required) Element name Alum Metal mg/L 150000.00 Other Cations (strong bases) meq/L 5.00 Other Anions (strong acids) meq/L 16697.46 Total CO2 mmol/L 7.00 Flow 2.64172037284185E-5

Configuration information for all Dewatering unit units Operating data Average (flow/time weighted as required) Element name Split method Average Split specification Dewatering unit6 Flow paced 5.00 %

Element name Percent removal Dewatering unit6 60.00 Configuration information for all Splitter units Operating data Average (flow/time weighted as required) Element name Split method Average Split specification Splitter9 Flowrate [Side] 0.0142693612270991 Splitter11 Flow paced 200.00 %

Configuration information for all Stream (SV) Influent units Operating data Average (flow/time weighted as required) Element name Methanol Methanol mgCOD/L 1188000.00 Flow 5E-6


BioWin Album Album page - Anoxic 1 Anox 1 Parameters Conc. (mg/L) Mass rate (lb/d) Notes Volatile suspended solids 2073.13 22763.61 Total suspended solids 2809.57 30849.89 Particulate COD 3097.08 34006.89 Filtered COD 38.91 427.27 Total COD 3135.99 34434.16 Soluble PO4-P 1.43 15.73 Total P 76.78 843.08 Filtered TKN 16.23 178.18 Particulate TKN 150.13 1648.48 Total Kjeldahl Nitrogen 166.36 1826.66 Filtered Carbonaceous BOD 5.36 58.81 Total Carbonaceous BOD 897.76 9857.72 Nitrite + Nitrate 0.23 2.54 Total N 166.59 1829.20 Total inorganic N 14.23 156.23 Alkalinity -999.00 -4975.60 mmol/L and kmol/d pH 7.04 Volatile fatty acids 1.28 14.02 ISS precipitate 99.98 1097.83 ISS cellular 106.47 1169.08 ISS Total 736.44 8086.29 Ammonia N 14.00 153.69 Nitrate N 0.10 1.11 Parameters Value Units Element HRT 0.6 hours Velocity gradient 70.76 1/s VSS destruction 0 % Total solids mass 811.27 lb Total readily biodegradable COD 3.04 mg/L OUR - Total 0.00 mgO/L/hr OUR - Carbonaceous 0.00 mgO/L/hr OUR - Nitrification 0.00 mgO/L/hr Nit - Ammonia removal rate 0.00 mgN/L/hr Nit - Nitrous oxide production rate 0.02 mgN/L/hr Nit - Nitrite production rate 0.00 mgN/L/hr Nit - Nitrate production rate 0 mgN/L/hr Denit - Nitrate removal rate 4.94 mgN/L/hr Denit - Nitrite removal rate 5.15 mgN/L/hr Denit - N2 production rate 8.85 mgN/L/hr Deamm - Ammonia removal rate 0.00 mgN/L/hr Deamm - Nitrite removal rate 0.00 mgN/L/hr Deamm - Nitrate production rate 0.00 mgN/L/hr Deamm - N2 production rate 0.00 mgN/L/hr Off gas flow rate (dry) 0.23 ft3/min Off gas Oxygen 0 % Off gas Carbon dioxide 62.56 % Off gas Ammonia 0 % Off gas Hydrogen 11.73 % Off gas Methane 0.01 % Off gas Nitrous oxide 0.04 % Actual DO sat. conc. 9.43 mg/L OTR 0 lb/hr SOTR 0 lb/hr OTE 100.00 % SOTE 100.00 % Air flow rate 0 ft3/min (20C, 1 atm) Air flow rate / diffuser 0 ft3/min (20C, 1 atm) # of diffusers 66.00


Album page - Anoxic 2 Anox 2 Parameters Conc. (mg/L) Mass rate (lb/d) Notes Volatile suspended solids 2045.72 10512.04 Total suspended solids 2783.78 14304.61 Particulate COD 3049.86 15671.89 Filtered COD 32.73 168.18 Total COD 3082.59 15840.07 Soluble PO4-P 1.44 7.38 Total P 76.78 394.54 Filtered TKN 5.62 28.85 Particulate TKN 150.91 775.46 Total Kjeldahl Nitrogen 156.53 804.32 Filtered Carbonaceous BOD 1.07 5.51 Total Carbonaceous BOD 864.82 4443.91 Nitrite + Nitrate 0.29 1.47 Total N 156.81 805.79 Total inorganic N 4.27 21.96 Alkalinity -999.00 -2328.48 mmol/L and kmol/d pH 6.98 Volatile fatty acids 0.19 0.99 ISS precipitate 99.98 513.76 ISS cellular 108.10 555.49 ISS Total 738.06 3792.57 Ammonia N 3.99 20.48 Nitrate N 0.11 0.58 Parameters Value Units Element HRT 2.7 hours Velocity gradient 70.54 1/s VSS destruction 0.41 % Total solids mass 1607.64 lb Total readily biodegradable COD 1.41 mg/L OUR - Total 0.00 mgO/L/hr OUR - Carbonaceous 0.00 mgO/L/hr OUR - Nitrification 0.00 mgO/L/hr Nit - Ammonia removal rate 0.00 mgN/L/hr Nit - Nitrous oxide production rate 0.01 mgN/L/hr Nit - Nitrite production rate 0.00 mgN/L/hr Nit - Nitrate production rate 0 mgN/L/hr Denit - Nitrate removal rate 1.78 mgN/L/hr Denit - Nitrite removal rate 2.11 mgN/L/hr Denit - N2 production rate 3.47 mgN/L/hr Deamm - Ammonia removal rate 0.00 mgN/L/hr Deamm - Nitrite removal rate 0.00 mgN/L/hr Deamm - Nitrate production rate 0.00 mgN/L/hr Deamm - N2 production rate 0.00 mgN/L/hr Off gas flow rate (dry) 0.47 ft3/min Off gas Oxygen 0 % Off gas Carbon dioxide 58.60 % Off gas Ammonia 0 % Off gas Hydrogen 10.70 % Off gas Methane 0.03 % Off gas Nitrous oxide 0.07 % Actual DO sat. conc. 9.43 mg/L OTR 0 lb/hr SOTR 0 lb/hr OTE 100.00 % SOTE 100.00 % Air flow rate 0 ft3/min (20C, 1 atm) Air flow rate / diffuser 0 ft3/min (20C, 1 atm) # of diffusers 131.00


Album page - Oxic 1 Oxic 1 Parameters Conc. (mg/L) Mass rate (lb/d) Notes Volatile suspended solids 2054.25 22556.25 Total suspended solids 2792.51 30662.66 Particulate COD 3063.11 33633.84 Filtered COD 32.05 351.87 Total COD 3095.15 33985.71 Soluble PO4-P 1.36 14.94 Total P 76.78 843.08 Filtered TKN 5.53 60.76 Particulate TKN 150.99 1657.89 Total Kjeldahl Nitrogen 156.52 1718.65 Filtered Carbonaceous BOD 1.59 17.49 Total Carbonaceous BOD 874.34 9600.52 Nitrite + Nitrate 9.69 106.36 Total N 166.21 1825.01 Total inorganic N 12.76 140.16 Alkalinity -999.00 -4975.60 mmol/L and kmol/d pH 6.81 Volatile fatty acids 0.02 0.20 ISS precipitate 99.98 1097.81 ISS cellular 108.30 1189.22 ISS Total 738.27 8106.40 Ammonia N 3.08 33.80 Nitrate N 4.92 53.99 Parameters Value Units Element HRT 1.8 hours Velocity gradient 164.15 1/s VSS destruction 0.91 % Total solids mass 2295.51 lb Total readily biodegradable COD 1.90 mg/L OUR - Total 43.33 mgO/L/hr OUR - Carbonaceous 22.47 mgO/L/hr OUR - Nitrification 20.86 mgO/L/hr Nit - Ammonia removal rate 5.54 mgN/L/hr Nit - Nitrous oxide production rate 0.05 mgN/L/hr Nit - Nitrite production rate 5.44 mgN/L/hr Nit - Nitrate production rate 2.81 mgN/L/hr Denit - Nitrate removal rate 0.13 mgN/L/hr Denit - Nitrite removal rate 0.09 mgN/L/hr Denit - N2 production rate 0.16 mgN/L/hr Deamm - Ammonia removal rate 0.00 mgN/L/hr Deamm - Nitrite removal rate 0.00 mgN/L/hr Deamm - Nitrate production rate 0.00 mgN/L/hr Deamm - N2 production rate 0.00 mgN/L/hr Off gas flow rate (dry) 305.27 ft3/min Off gas Oxygen 18.51 % Off gas Carbon dioxide 2.40 % Off gas Ammonia 0 % Off gas Hydrogen 0.09 % Off gas Methane 0.00 % Off gas Nitrous oxide 0.00 % Actual DO sat. conc. 9.43 mg/L OTR 36.54 lb/hr SOTR 109.88 lb/hr OTE 11.42 % SOTE 35.12 % Air flow rate 306.61 ft3/min (20C, 1 atm) Air flow rate / diffuser 1.65 ft3/min (20C, 1 atm) # of diffusers 186.00


Album page - Clarifier Model clarifier5 Parameters Conc. (mg/L) Mass rate (lb/d) Notes Volatile suspended solids 1.29 3.80 Total suspended solids 1.76 5.19 Particulate COD 1.92 5.66 Filtered COD 31.37 92.48 Total COD 33.29 98.13 Soluble PO4-P 0.37 1.08 Total P 0.41 1.22 Filtered TKN 2.72 8.01 Particulate TKN 0.10 0.28 Total Kjeldahl Nitrogen 2.81 8.29 Filtered Carbonaceous BOD 1.06 3.12 Total Carbonaceous BOD 1.60 4.70 Nitrite + Nitrate 3.33 9.82 Total N 6.14 18.11 Total inorganic N 3.72 10.95 Alkalinity 3.53 4.73 mmol/L and kmol/d pH 6.84 Volatile fatty acids 0.00 0.01 ISS precipitate 0.07 0.20 ISS cellular 0.07 0.20 ISS Total 0.47 1.39 Ammonia N 0.38 1.13 Nitrate N 2.97 8.76 Parameters Value Units Element HRT 13.20 hours Percent TSS removal 99.96 % Percent COD removal 99.38 % Percent BOD removal 99.89 % Percent TKN removal 98.95 % Percent Tot. P removal 99.69 % Height of specified concentration 1.64 ft Total solids mass 2089.51 lb Surface overflow rate 117.01 gal/(ft2 d) Solids loading rate 4.72 lb/(ft2 d) Album page - Effluent Effluent Parameters Conc. (mg/L) Mass rate (lb/d) Notes Volatile suspended solids 0.54 1.52 Total suspended solids 0.74 2.08 Particulate COD 0.81 2.26 Filtered COD 31.37 87.89 Total COD 32.18 90.16 Soluble PO4-P 0.37 1.02 Total P 0.39 1.08 Filtered TKN 2.72 7.61 Particulate TKN 0.04 0.11 Total Kjeldahl Nitrogen 2.76 7.72 Filtered Carbonaceous BOD 1.06 2.96 Total Carbonaceous BOD 1.28 3.60 Nitrite + Nitrate 3.33 9.34 Total N 6.09 17.06 Total inorganic N 3.72 10.41 Alkalinity 3.53 4.49 mmol/L and kmol/d pH 6.84 Volatile fatty acids 0.00 0.01 ISS precipitate 0.03 0.08 ISS cellular 0.03 0.08 ISS Total 0.20 0.56 Ammonia N 0.38 1.08 Nitrate N 2.97 8.33


Album page - Waste WAS Parameters Conc. (mg/L) Mass rate (lb/d) Notes Volatile suspended solids 4761.88 567.06 Total suspended solids 6507.61 774.95 Particulate COD 7092.17 844.56 Filtered COD 31.37 3.74 Total COD 7123.54 848.30 Soluble PO4-P 0.37 0.04 Total P 179.54 21.38 Filtered TKN 2.72 0.32 Particulate TKN 353.08 42.05 Total Kjeldahl Nitrogen 355.80 42.37 Filtered Carbonaceous BOD 1.06 0.13 Total Carbonaceous BOD 1991.30 237.13 Nitrite + Nitrate 3.33 0.40 Total N 359.13 42.77 Total inorganic N 3.72 0.44 Alkalinity -999.00 -53.96 mmol/L and kmol/d pH 6.84 Volatile fatty acids 0.00 0.00 ISS precipitate 247.95 29.53 ISS cellular 255.08 30.38 ISS Total 1745.73 207.89 Ammonia N 0.38 0.05 Nitrate N 2.97 0.35

File C:\Users\tshimada\Documents\Projects\Texas\Dripping Springs\Models\Dripping Springs AA 22deg.bwc 1

BioWin user and configuration data Project details Project name: Dripping Springs Project ref.: 9756A.00 Plant name: Dripping Springs WWTP User name: tshimada Created: 3/10/2015 Saved: 3/30/2015 Scenario: Annual Average Steady state solution Target SRT: 4.00 daysSRT #0: 3.98 days Temperature: 22.0°C Flowsheet



k1(PC)^0.25 + k2 k2 in C = k1(PC)^0.25 + k2





WAS

AlumMethanol


BioWin Album Album page - Anoxic 1 Anox 1 Parameters Conc. (mg/L) Mass rate (lb/d) Notes Volatile suspended solids 2067.47 22701.59 Total suspended solids 2814.25 30901.42 Particulate COD 3087.73 33904.38 Filtered COD 37.66 413.47 Total COD 3125.39 34317.85 Soluble PO4-P 1.35 14.77 Total P 78.76 864.85 Filtered TKN 15.27 167.71 Particulate TKN 149.92 1646.19 Total Kjeldahl Nitrogen 165.19 1813.90 Filtered Carbonaceous BOD 4.81 52.83 Total Carbonaceous BOD 880.91 9672.74 Nitrite + Nitrate 0.60 6.56 Total N 165.79 1820.46 Total inorganic N 13.63 149.71 Alkalinity -999.00 -4975.62 mmol/L and kmol/d pH 7.02 Volatile fatty acids 0.58 6.39 ISS precipitate 110.02 1208.08 ISS cellular 106.54 1169.90 ISS Total 746.77 8199.83 Ammonia N 13.04 143.15 Nitrate N 0.46 5.04 Parameters Value Units Element HRT 0.6 hours Velocity gradient 75.35 1/s VSS destruction 0 % Total solids mass 812.62 lb Total readily biodegradable COD 2.49 mg/L OUR - Total 0.00 mgO/L/hr OUR - Carbonaceous 0.00 mgO/L/hr OUR - Nitrification 0.00 mgO/L/hr Nit - Ammonia removal rate 0.00 mgN/L/hr Nit - Nitrous oxide production rate 0.02 mgN/L/hr Nit - Nitrite production rate 0.00 mgN/L/hr Nit - Nitrate production rate 0.00 mgN/L/hr Denit - Nitrate removal rate 7.33 mgN/L/hr Denit - Nitrite removal rate 4.46 mgN/L/hr Denit - N2 production rate 8.76 mgN/L/hr Deamm - Ammonia removal rate 0.00 mgN/L/hr Deamm - Nitrite removal rate 0.00 mgN/L/hr Deamm - Nitrate production rate 0.00 mgN/L/hr Deamm - N2 production rate 0.01 mgN/L/hr Off gas flow rate (dry) 0.24 ft3/min Off gas Oxygen 0 % Off gas Carbon dioxide 63.61 % Off gas Ammonia 0 % Off gas Hydrogen 8.77 % Off gas Methane 0.00 % Off gas Nitrous oxide 0.03 % Actual DO sat. conc. 8.76 mg/L OTR 0 lb/hr SOTR 0 lb/hr OTE 100.00 % SOTE 100.00 % Air flow rate 0 ft3/min (20C, 1 atm) Air flow rate / diffuser 0 ft3/min (20C, 1 atm) # of diffusers 66.00

File C:\Users\tshimada\Documents\Projects\Texas\Dripping Springs\Models\Dripping Springs MM 18 deg.bwc 1

BioWin user and configuration data Project details Project name: Dripping Springs Project ref.: 9756A.00 Plant name: Dripping Springs WWTP User name: tshimada Created: 3/10/2015 Saved: 3/30/2015 Scenario: Maximum Month Conditions Steady state solution Target SRT: 4.00 daysSRT #0: 3.99 days Temperature: 18.0°C Flowsheet



k1(PC)^0.25 + k2 k2 in C = k1(PC)^0.25 + k2





WAS

AlumMethanol





Configuration information for all Stream (SV) Influent units Operating data Average (flow/time weighted as required) Element name Methanol Methanol mgCOD/L 1188000.00 Flow 9.99891161120639E-6


BioWin Album Album page - Anoxic 1 Anox 1 Parameters Conc. (mg/L) Mass rate (lb/d) Notes Volatile suspended solids 2803.13 44117.14 Total suspended solids 3795.26 59731.73 Particulate COD 4182.73 65829.88 Filtered COD 36.73 578.04 Total COD 4219.45 66407.92 Soluble PO4-P 1.32 20.74 Total P 103.86 1634.53 Filtered TKN 15.31 240.89 Particulate TKN 205.02 3226.74 Total Kjeldahl Nitrogen 220.33 3467.63 Filtered Carbonaceous BOD 5.19 81.67 Total Carbonaceous BOD 1216.41 19144.51 Nitrite + Nitrate 0.20 3.22 Total N 220.53 3470.84 Total inorganic N 13.37 210.42 Alkalinity -999.00 -7131.73 mmol/L and kmol/d pH 7.04 Volatile fatty acids 1.33 21.00 ISS precipitate 136.04 2141.04 ISS cellular 146.38 2303.83 ISS Total 992.13 15614.59 Ammonia N 13.17 207.20 Nitrate N 0.09 1.36 Parameters Value Units Element HRT 0.4 hours Velocity gradient 70.94 1/s VSS destruction 0 % Total solids mass 1095.88 lb Total readily biodegradable COD 3.00 mg/L OUR - Total 0.00 mgO/L/hr OUR - Carbonaceous 0.00 mgO/L/hr OUR - Nitrification 0.00 mgO/L/hr Nit - Ammonia removal rate 0.00 mgN/L/hr Nit - Nitrous oxide production rate 0.02 mgN/L/hr Nit - Nitrite production rate 0.00 mgN/L/hr Nit - Nitrate production rate 0 mgN/L/hr Denit - Nitrate removal rate 6.23 mgN/L/hr Denit - Nitrite removal rate 6.92 mgN/L/hr Denit - N2 production rate 11.65 mgN/L/hr Deamm - Ammonia removal rate 0.00 mgN/L/hr Deamm - Nitrite removal rate 0.00 mgN/L/hr Deamm - Nitrate production rate 0.00 mgN/L/hr Deamm - N2 production rate 0.00 mgN/L/hr Off gas flow rate (dry) 0.23 ft3/min Off gas Oxygen 0 % Off gas Carbon dioxide 63.56 % Off gas Ammonia 0 % Off gas Hydrogen 11.70 % Off gas Methane 0.01 % Off gas Nitrous oxide 0.03 % Actual DO sat. conc. 9.43 mg/L OTR 0 lb/hr SOTR 0 lb/hr OTE 100.00 % SOTE 100.00 % Air flow rate 0 ft3/min (20C, 1 atm) Air flow rate / diffuser 0 ft3/min (20C, 1 atm) # of diffusers 66.00

File C:\Users\tshimada\Desktop\Dripping Springs MM 28 deg.bwc 1

BioWin user and configuration data Project details Project name: Dripping Springs Project ref.: 9756A.00 Plant name: Dripping Springs WWTP User name: tshimada Created: 3/10/2015 Saved: 3/11/2015 Scenario: Maximum Month Conditions Steady state solution Target SRT: 4.00 daysSRT #0: 3.98 days Temperature: 28.0°C Flowsheet



k1(PC)^0.25 + k2 k2 in C = k1(PC)^0.25 + k2





WAS

AlumMethanol


BioWin Album Album page - Anoxic 1 Anox 1 Parameters Conc. (mg/L) Mass rate (lb/d) Notes Volatile suspended solids 2603.57 40976.01 Total suspended solids 3614.16 56880.96 Particulate COD 3892.83 61266.77 Filtered COD 34.64 545.10 Total COD 3927.46 61811.88 Soluble PO4-P 1.27 20.06 Total P 105.21 1655.78 Filtered TKN 13.88 218.40 Particulate TKN 186.61 2936.97 Total Kjeldahl Nitrogen 200.49 3155.37 Filtered Carbonaceous BOD 4.39 69.11 Total Carbonaceous BOD 1028.10 16180.55 Nitrite + Nitrate 1.54 24.19 Total N 202.03 3179.56 Total inorganic N 13.28 208.94 Alkalinity -999.00 -7131.67 mmol/L and kmol/d pH 7.03 Volatile fatty acids 0.32 5.06 ISS precipitate 169.83 2672.90 ISS cellular 132.01 2077.58 ISS Total 1010.58 15904.95 Ammonia N 11.74 184.75 Nitrate N 1.44 22.72 Parameters Value Units Element HRT 0.4 hours Velocity gradient 82.75 1/s VSS destruction 0 % Total solids mass 1043.59 lb Total readily biodegradable COD 2.30 mg/L OUR - Total 0.00 mgO/L/hr OUR - Carbonaceous 0.00 mgO/L/hr OUR - Nitrification 0.00 mgO/L/hr Nit - Ammonia removal rate 0.00 mgN/L/hr Nit - Nitrous oxide production rate 0.01 mgN/L/hr Nit - Nitrite production rate 0.00 mgN/L/hr Nit - Nitrate production rate 0.00 mgN/L/hr Denit - Nitrate removal rate 11.47 mgN/L/hr Denit - Nitrite removal rate 5.62 mgN/L/hr Denit - N2 production rate 11.61 mgN/L/hr Deamm - Ammonia removal rate 0.00 mgN/L/hr Deamm - Nitrite removal rate 0.01 mgN/L/hr Deamm - Nitrate production rate 0.00 mgN/L/hr Deamm - N2 production rate 0.01 mgN/L/hr Off gas flow rate (dry) 0.26 ft3/min Off gas Oxygen 0 % Off gas Carbon dioxide 64.33 % Off gas Ammonia 0 % Off gas Hydrogen 5.69 % Off gas Methane 0.00 % Off gas Nitrous oxide 0.02 % Actual DO sat. conc. 7.84 mg/L OTR 0 lb/hr SOTR 0 lb/hr OTE 100.00 % SOTE 100.00 % Air flow rate 0 ft3/min (20C, 1 atm) Air flow rate / diffuser 0 ft3/min (20C, 1 atm) # of diffusers 66.00


Album page - Anoxic 2 Anox 2 Parameters Conc. (mg/L) Mass rate (lb/d) Notes Volatile suspended solids 2575.55 19041.15 Total suspended solids 3587.55 26522.92 Particulate COD 3845.03 28426.51 Filtered COD 29.35 216.96 Total COD 3874.38 28643.47 Soluble PO4-P 1.34 9.94 Total P 105.21 777.79 Filtered TKN 3.12 23.04 Particulate TKN 187.14 1383.51 Total Kjeldahl Nitrogen 190.25 1406.55 Filtered Carbonaceous BOD 0.58 4.28 Total Carbonaceous BOD 995.01 7356.18 Nitrite + Nitrate 1.50 11.12 Total N 191.76 1417.67 Total inorganic N 3.02 22.30 Alkalinity -999.00 -3350.08 mmol/L and kmol/d pH 6.94 Volatile fatty acids 0.04 0.33 ISS precipitate 169.83 1255.57 ISS cellular 133.43 986.49 ISS Total 1012.00 7481.77 Ammonia N 1.51 11.18 Nitrate N 1.46 10.79 Parameters Value Units Element HRT 1.9 hours Velocity gradient 82.38 1/s VSS destruction 0.36 % Total solids mass 2071.82 lb Total readily biodegradable COD 0.79 mg/L OUR - Total 0.00 mgO/L/hr OUR - Carbonaceous 0.00 mgO/L/hr OUR - Nitrification 0.00 mgO/L/hr Nit - Ammonia removal rate 0.00 mgN/L/hr Nit - Nitrous oxide production rate 0.00 mgN/L/hr Nit - Nitrite production rate 0.00 mgN/L/hr Nit - Nitrate production rate 0.00 mgN/L/hr Denit - Nitrate removal rate 5.19 mgN/L/hr Denit - Nitrite removal rate 2.64 mgN/L/hr Denit - N2 production rate 5.32 mgN/L/hr Deamm - Ammonia removal rate 0.00 mgN/L/hr Deamm - Nitrite removal rate 0.00 mgN/L/hr Deamm - Nitrate production rate 0.00 mgN/L/hr Deamm - N2 production rate 0.00 mgN/L/hr Off gas flow rate (dry) 0.58 ft3/min Off gas Oxygen 0 % Off gas Carbon dioxide 59.83 % Off gas Ammonia 0 % Off gas Hydrogen 5.83 % Off gas Methane 0.00 % Off gas Nitrous oxide 0.02 % Actual DO sat. conc. 7.84 mg/L OTR 0 lb/hr SOTR 0 lb/hr OTE 100.00 % SOTE 100.00 % Air flow rate 0 ft3/min (20C, 1 atm) Air flow rate / diffuser 0 ft3/min (20C, 1 atm) # of diffusers 131.00



APPENDIX C – EFFLUENT LAND APPLICATION CALCULATIONS

TABLE C-1: FIRST LOOK (CHAPTER 285 METHOD)

Total Usable Irrigation Area ATotal 159.37 acres

Maximum Surface Application Rate (per TAC Chapter 285 - Figure 1) --- 0.0545 gpd/sf

Estimated Daily Disposal Volume Q 378,336 gpd

Crop Data CROP Ashe Juniper 5.26 ac-in/ac/moCurve Number CN 73 0.11 gpd/sf

Effluent Water Conductivity Ce 1.00 748,303 gpdAssumed Allowable Conductivity CL 7.00

134 Ac-FtPond Surface Area APond 11.65 ac 87 Days

Powerline Easement AEasement 6.6 ac 43,655,944 GallonsEasement Canopy Density DCanopy 0% percent

Tract Canopy Density DCanopy 95% percent 11.6 acTotal Tract Acreage ATract 186 ac 15.0 Feet

Total Usable Irrigation Area ATotal 159 ac 135.1 ac-ftIrrigation Efficiency K 75% 44,012,160 Gallons

Design Flow Q 0.500 MGD 88 DaysEffluent Available Application AR 3.51 in/ac/mo

Low Net Evaporation --- 3.59 feetMaximum Annual Precipitation --- 47.12 Inches

1 2 3 4 5 6 7 8 9A 9B 10 11

Average Precipitation

Average Runoff

Average Infiltration of

Rainfall

Average Evapotranspir

ationReq. Leaching

Total Water Needs

Effluent Required in Root Zone

Evaporation From

Reservoir Surface

Net Evaporation from Surface

Effluent Applied to

Land

Consumption from

Reservoir

in in in in in in in ft in in in/acPRECIP RUN Ri (1) ET Leach TWN ERRZ EFRS EFRS EAL CFR

January 1.72 0.20 1.51 2.41 0.15 2.55 1.04 0.18 0.16 1.39 1.55February 2.04 0.34 1.70 2.88 0.20 3.08 1.38 0.21 0.18 1.83 2.02

March 2.12 0.37 1.74 4.60 0.48 5.08 3.33 0.32 0.28 4.44 4.72April 2.69 0.68 2.02 5.59 0.59 6.18 4.16 0.38 0.34 5.55 5.89May 3.90 1.46 2.44 6.77 0.72 7.49 5.05 0.41 0.36 6.73 7.09June 3.33 1.07 2.26 7.58 0.89 8.46 6.20 0.54 0.47 8.27 8.74July 1.97 0.31 1.66 7.65 1.00 8.65 6.99 0.62 0.55 9.32 9.87

August 2.12 0.37 1.74 7.69 0.99 8.68 6.93 0.60 0.53 9.24 9.77September 3.32 1.06 2.26 5.90 0.61 6.51 4.25 0.45 0.40 5.67 6.07

October 3.26 1.02 2.24 4.64 0.40 5.04 2.81 0.37 0.32 3.74 4.06November 2.15 0.39 1.76 2.90 0.19 3.09 1.33 0.26 0.23 1.78 2.01December 1.80 0.24 1.56 2.34 0.13 2.47 0.91 0.19 0.16 1.21 1.38

Total 30.43 7.51 22.92 60.96 6.34 67.30 44.38 4.54 3.98 59.18 63.16

12 13 14A 14B 15 16 17 18A 18B 19 20Effluent

Applied to Land

Mean Rainfall Distribution

Rainfall (Max) Runoff (Max)Infiltrated Rainfall

Total Available

Water

Distribution of Mean

Evaporation

Net Evaporation

(MIN)Storage

Accumulated Storage

in/ac/mo % in in in in % % in-ac/acEAL MDR RMAX RUMAX Ri (2) TAW DoM NetE S AS

January 3.51 5.6% 2.66 0.66 2.00 5.52 4.0% 0.13 2.66 7.88February 3.51 6.7% 3.16 0.96 2.20 5.72 4.6% 0.14 2.20 10.09

March 3.51 7.0% 3.28 1.04 2.25 5.76 7.0% 0.22 -0.48 9.61April 3.51 8.9% 4.17 1.65 2.52 6.03 8.4% 0.27 -1.63 7.98May 3.51 12.8% 6.04 3.13 2.92 6.43 9.0% 0.28 -2.87 5.11June 3.51 11.0% 5.16 2.41 2.75 6.27 11.9% 0.37 -4.47 0.63July 3.51 6.5% 3.05 0.89 2.16 5.68 13.7% 0.43 -5.57 0.00

August 3.51 7.0% 3.28 1.03 2.25 5.76 13.3% 0.42 -5.48 0.00September 3.51 10.9% 5.14 2.39 2.75 6.26 10.0% 0.32 -1.82 0.00

October 3.51 10.7% 5.05 2.32 2.73 6.24 8.1% 0.26 0.17 0.17November 3.51 7.1% 3.33 1.07 2.26 5.78 5.8% 0.18 2.22 2.40December 3.51 5.9% 2.79 0.73 2.06 5.57 4.1% 0.13 2.83 5.23

TOTAL 42.18 100% 47.12 18.26 28.86 71.03 100% 3.15 -12.23 49.10

Month

Month

TABLE C-3: STORAGE VOLUME CALCULATIONS

TABLE C-2: MONTHLY WATER BALANCE CALCULATIONS

Storage Days

Pond Volume Provided

Cedar / Grassland ET correction Factor

6.0 %

CHAPTER 285 METHOD

Actual Storage Days

Required Pond Volume

Maximum Application Rate

Pond Depth

Pond Volume Provided

Storage Required

Pond Surface Area

M:\Data\1045\004\CanopySprayCalcs_and_Costs.xlsx,WATER BALANCE

TABLE C-4: NITROGEN UPTAKE CALCULATIONS

Daily Average Flow to Irrigation Field Q 500,000 gal/day 0.50 MGDEffluent Total Nitrogen Cn 10 mg/L

Crop Cedar Annual crop nitrogen uptake Ny 150 lbs/yr/ac

Base soil intake rate IB 0.25 in/hrSprinkler spacing, lateral SI 50 ft

Sprinkler spacing, main Sm 50 ftMaximum surface water storage SS 0.2 in

NITROGEN LIMITING CALCULATIONSEstimated lbs of total nitrogen applied Tn 15,220.50 lbs/year

Minimum area needed of spray field (assuming nitrogen land limiting) Arean 4,420,033.20 ft2 101.47 ac

CANOPY SPRAY PARAMETERS

Carollo Engineers, Inc.

TABLE C-5: STORAGE POND VOLUME CALCULATION

A @ WSE 722.0 ft A @ Property 750.0 ft Hypot Length 1.00 ftB @ WSE 722.0 ft B @ Property 750.0 ft Opposite Length - ftL @ WSE 687.0 ft L @ Property 715.0 ft

Area @ Bottom 8.05 ac0.00 radians A @ top 730.0 ft Area @ WSE 11.39 ac0.00 degrees B @ top 730.0 ft Area @ TOB 11.65 ac

L @ top 695.0 ftTotal Pond Depth 15 ft A @ mid-point (Exc) 670.0 ft A @ mid-point (Detent) 666.0 ftSide Slope 4 : 1 B @ mid-point (Exc) 670.0 ft B @ mid-point (Detent) 666.0 ftBerms 10.0 ft L @ mid-point (Exc) 635.0 ft L @ mid-point (Detent) 631.0 ftFree Board 1.0 ft A @ bottom 610.0 ftWater Depth 14.0 ft B @ bottom 610.0 ftSide Slope Offset 60 ft L @ bottom 575.0 ft

Excavation Volume 6,381,750 Cu Ft 236,360 Mitigation Freeboard 11.44 Ac-FtTOTAL VOLUME 146.50 Ac-Ft

Usable Volume (w/o FB) 5,883,444 Cu Ft 217,910 Cu Yd135.07 Ac-Ft

Footprint 536,250 Sq Ft 12.31 Acres

Angle

Cu Yd=(A-mid_Exc+B-mid_Exc)/2*L-mid_Exc*Depth

=(A_Prop+B_Prop)/2*L_Prop

=(A-mid_Det+B-mid_Det)/2*L-mid_Det*Depth

TOB

Property

Bottom


TABLE C-6: OPINION OF PROBABLE COSTS

Pond Surface Area APond 11.6 acPowerline Easement AEasement 6.6 ac

Easement Canopy Density DCanopy 0% percentTract Canopy Density DCanopy 95% percent

Total Tract Acreage ATract 186 acTotal Irrigated Area Airr 174 ac

Sprinkler spacing, lateral SI 30 ftSprinkler spacing, main Sm 30 ft

Sprinkler Heads Required --- 8400Sprinkler Heads to a Zone --- 5.00 heads

Zones Required --- 1680Assumed 1/2" HDPE flex pipe per zone --- 50 ftAssumed 3/4" HDPE flex pipe per zone --- 100 ft

Pump and Manifold Cost Items Qty Unit Est. Price Total500 GMP pump with 8-inch discharge column assembly, motor, cable, and air vacuum release valve. 2 EA $1,200 $2,400

Irrigation manifold connecting storage pond pumps to distribution system, including micelaneous piping, valves, and fitting, and all other incidental pipe-related costs, including all installation, complete in place.

1 LS $55,000 $55,000

Industrial Mainifold Timer Switch, including installation, complete in place 1 LS $6,000 $6,000 Security fencing and gate around pump station, including installation, complete in place 80 LF $35 $2,800

Precast concrete building (assumed 20'X16') including foundation, uncluding installation, complete in place. 1 LS $10,000 $10,000

SUBTOTAL: $76,200

Sprinkler Head Cost Items Qty Unit Est. Price Total25-35' 6.0 GPM Rotor gear drive spray nozzle @ approximated 30' offsets, including installation, including all incidentals, complete in place. 8,400 EA $25.00 $210,000

SUBTOTAL: $210,000

System Pipe Cost Items Qty Unit Est. Price Total

1/2" PVC spray nozzel riser pipe (assumed @ 3' in length), including installation, including all incidentals, complete in place (as a function of nozzles). 25,000 LF $0.50 $12,500

1/2" X 100' HDPE flex pipe from zone trannsmission pipe to sprinkler spray nozzles (as a function of zone count), including all site preparation, excavation, and any backfill necessary, and all other incidentals, complete in place.

840 EA $25.00 $21,000

3/4" X 100' HDPE flex pipe from zone trannsmission pipe to sprinkler spray nozzles (as a function of zone count), including all site preparation, excavation, and any backfill necessary, and all other incidentals, complete in place.

1,700 EA $33.00 $56,100

1" X 10' schedule 40 PVC pipe for zone transmission to flex pipe, including all site preparation, excavation, and any backfill necessary, and all other incidentals, complete in place.

6,000 EA $6.50 $39,000

3" X 10' Schedule 40 PVC pipe for force main to zones, including installation, including all site preparation, excavation, and any backfill necessary, and all other incidentals, complete in place.

600 EA $10.50 $6,300

Plastic valve boxes (assumed 1'X2'), including instllation, complete in place. 336 EA $25.00 $8,400 SUBTOTAL: $143,300

Fittings Cost Items Qty Unit Est. Price Total

1/2" reducers, tees, couplings, extenders, valves, and other incidental pipe-related costs for establising the irrigation system (as a function of pipe lengths) 4,200 EA $0.75 $3,200

3/4" reducers, fittings, couplings, extenders, valves, and other incidental pipe-related costs for establising the irrigation system (as a function of pipe lengths) 8,500 EA $1.00 $8,500

1" reducers, fittings, couplings, extenders, valves, and other incidental pipe-related costs for establising the irrigation system (as a function of pipe lengths) 18,000 EA $1.25 $22,500

3" reducers, fittings, couplings, extenders, valves, and other incidental pipe-related costs for establising the irrigation system (as a function of pipe lengths) 1,800 EA $2.00 $3,600

SUBTOTAL: $37,800.00

Storage Pond Cost Items Qty Unit Est. Price TotalExcavation Required 236,360 CY $8.00 $1,890,880

Geotextile Protective Layer, including installation, mobilization, required penetrations, secondary and geocomposite liner (if required), complete in place. 507,350 SF $2.50 $1,268,375

SUBTOTAL: $3,159,255

$76,200 $210,000 $143,300 $37,800

$3,159,255

$3,627,000 30% $4,715,000

15% $5,422,000

15% $6,235,000

Table of Parameters Used in Cost Calculations

In examining items with regard to cost, because this estimate is for the purpose of planning, estimated costs include a contingency factor. Also, costs should be considered high-level and subject to change as detailed information (survey, geotechnical, environmental, real estate, etc.) is revealed. Methods of analysis used in the development of this cost estimate are consistent with a planning level of this detail. costs specified for the proposed infrastructure is intended only as 1) a guide for preliminary and follow-on detailed engineering and 2) a basis for preliminary estimate of cost for infrastructure development. While procedures consistent with this cost estimate are generally used, approximations and engineering judgment was sometimes used because of the planning level nature of this estimate and the unavailability of some data.

$6,235,000 GRAND TOTAL:

Construction Cost Totals

Engineering Fees and Legal

Contractor Overhead and Risk

Unidentified ElementsTOTAL

Storage Pond Cost ItemsFittings Cost Items

System Pipe Cost ItemsSprinkler Head Cost Items

Pump and Manifold Cost Items
