assessing seawater intake systems for desalination plants.pdf

8/9/2019 Assessing Seawater Intake Systems for Desalination Plants.pdf

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Assessing Seawater Intake

Systems for Desalination Plants

Subject Area: Water Resources and Environmental Sustainability


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About the Water Research FoundationThe Water Research Foundation (formerly Awwa Research Foundation or AwwaRF) is a member-supported,international, 501(c)3 nonprofit organization that sponsors research to enable water utilities, public healthagencies, and other professionals to provide safe and affordable drinking water to consumers.

The Foundation’s mission is to advance the science of water to improve the quality of life. To achieve thismission, the Foundation sponsors studies on all aspects of drinking water, including resources, treatment,distribution, and health effects. Funding for research is provided primarily by subscription payments fromclose to 1,000 water utilities, consulting firms, and manufacturers in North America and abroad. Additionalfunding comes from collaborative partnerships with other national and international organizations and theU.S. federal government, allowing for resources to be leveraged, expertise to be shared, and broad-basedknowledge to be developed and disseminated.

From its headquarters in Denver, Colorado, the Foundation’s staff directs and supports the efforts ofmore than 800 volunteers who serve on the board of trustees and various committees. These volunteersrepresent many facets of the water industry, and contribute their expertise to select and monitor researchstudies that benefit the entire drinking water community.

The results of research are disseminated through a number of channels, including reports, the Web site,Webcasts, conferences, and periodicals.

For its subscribers, the Foundation serves as a cooperative program in which water suppliers unite to pooltheir resources. By applying Foundation research findings, these water suppliers can save substantial costsand stay on the leading edge of drinking water science and technology. Since its inception, the Foundationhas supplied the water community with more than $460 million in applied research value.

More information about the Foundation and how to become a subscriber is available on the Web atwww.WaterResearchFoundation.org .

©2011 Water Research Foundation. ALL RIGHTS RESERVED.


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CONTENTS

LIST OF TABLES �� ix

LIST OF FIGURES �� xi

FOREWORD �� xv

ACKNOWLEDGMENTS �� xvii

EXECUTIVE SUMMARY �� xix

CHAPTER 1: INTRODUCTION �� 1

Intake Selection Requires Consideration of Multiple Issues �� 1

Technology Options �� 1Permitting Requirements �� 2

Environmental Impacts �� 3

Stakeholder Values �� 3

Utility Constraints and Interests�� 3

Project Objectives �� 4

Project Approach �� 5

CHAPTER 2: STATE-OF-THE-SCIENCE IN OCEAN INTAKE DESIGN AND

PERMITTING FOR SEAWATER DESALINATION �� 7

Overview �� 7

Controlling Parameters in the Intake Selection Process �� 8

Capacity �� 10

Geology �� 10

Cost �� 10

Water Quality �� 11

Environmental Impacts �� 11

Permitting �� 11

Sustainability�� 12

Intake Technologies �� 12

Open Intakes �� 12

Subsurface Intakes �� 17Co-Location of Seawater Intakes �� 30

Potential Alternative Approaches to Well Drilling�� 31

Environmental Impacts From Intake Construction and Operation �� 33

Overview of Ocean Biota of Concern �� 34

Impact of Intake Operation—Impingement and Entrainment �� 34

Impact and Mitigation Measures for Open Intakes�� 37



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Impact and Mitigation Measures for Seawater Intake Wells �� 54

Impact and Mitigation Measures for Subsurface Intakes �� 54

Permitting and Regulations �� 55

Overview of the Permitting Process �� 55

Federal Permitting Requirements �� 55

Select State Permitting Requirements �� 57Public and Stakeholder Involvement �� 63

Stakeholders Are Intrinsic to the Decision-Making Process �� 63

Relative Values of Trade-Offs �� 65

Tips for Successful Stakeholder Involvement �� 65

Guidance on Using Stakeholder Communications Tools �� 66

CHAPTER 3: UTILITY SEAWATER INTAKE EXPERIENCE SURVEY �� 69

Introduction �� 69

Methodology �� 69

Report Format �� 69

General Utility Characteristics �� 74Population Served, Desalination Capacity, and Intake Capacity �� 74

Planned and Installed Desalination Capacity �� 75

Desalination Market Drivers �� 75

Inuence of Global Warming Regulations on Treatment Planning �� 76

Seawater Intake Design Characteristics �� 78

Intake Type and Technologies �� 78

Intake Design Features �� 78

Screening Technologies �� 80

Capital and Operating Costs �� 80

Intake Operations �� 82

Environmental Impacts and Mitigation �� 84

Assessment of the Entrainment and Impingement Effects of Intake Systems �� 84

Loss of Habitat and Environmental Evaluation of Screen Designs �� 84

Permitting Experience �� 85

Permitting Requirements �� 85

Permitting Timelines �� 86

The Stakeholder Process �� 87

CHAPTER 4: CONTROLLING PARAMETERS IN SEAWATER INTAKE

DEVELOPMENT �� 89

Dening a Seawater Intake Scenario �� 89Information Needed for Evaluating the Intake Design Options �� 89

Controlling Parameters in the Decision-Making Process �� 91

Incorporating the Decision-Controlling Elements Into a Decision Framework �� 92

Part 1� Dene the Options �� 92

Part 2� Evaluate the Options�� 93

Part 3� Compare the Options �� 94



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Contents | vii

CHAPTER 5: USING THE DESALINATION INTAKE DECISION TOOL �� 95

Step 1: Dene Intake Design Scenario �� 95

Step 2: Assess Technical and Logistical Feasibility of Options �� 95

Step 3: Identify Permitting Needs and Assess Permitting Feasibility�� 97

Step 4: Estimate Planning-Level Costs for Each Technology �� 100

General Guidelines for Estimating Intake Development Costs �� 101Step 5: Evaluate Pertinent Stakeholder Issues �� 101

Step 6: Grade and Rank the Viable Options �� 105

Grade the Options �� 105

Rank the Options�� 107

Final Step: Generate Project Reports �� 108

CHAPTER 6: CASE STUDIES�� 111

Case Study 1: Carlsbad Desalination Plant �� 111

Case Study 2: City of Santa Cruz/Soquel Creek Water District �� 129

APPENDIX A: SEAWATER INTAKE SYSTEMS FOR DESALINATION PLANTSUTILITY QUESTIONNAIRE SUPPLEMENTAL DATA �� 151

APPENDIX B: COST ESTIMATES FOR THE CARLSBAD CASE STUDY �� 159

REFERENCES �� 165

ABBREVIATIONS �� 171

DESALINATION INTAKE DECISION TOOL

(AVAILABLE ON CD-ROM PACKAGED WITH PRINTED REPORT AND WATERRF

WEBSITE)



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2�1 Partial list of existing seawater desalination plants and their respective intake types �� 9

2�2 Studies required for seawater open intakes �� 16

2�3 Studies required for seawater intake wells �� 25

2�4 Applicability of the various active and passive intake technologies to different

seawater intake locations �� 39

2�5 Major regulations and permits pertaining to seawater intake construction and

operation in California �� 59

2�6 Major regulations and permits pertaining to seawater intake construction andoperation in Florida �� 62

2�7 Major regulations and permits pertaining to seawater intake construction and

operation in Texas �� 64

3�1 Populations served by seawater desalination plant survey respondents �� 75

3�2 Summary of desalination capacities, intake capacities, and average intake ows for

reporting plants �� 75

3�3 Environmental impacts and mitigation study results �� 85

4�1 Elements of a dened intake planning scenario �� 90

4�2 Structural design options for seawater intakes�� 90

4�3 Controlling parameters in seawater intake planning and design �� 92

5�1 Denitions of overview scenario description parameters �� 97

5�2 Denitions of implementation feasibility scenario description parameters �� 99

5�3 Denitions of permitting assessment parameters �� 101

5�4 Denitions of cost estimation parameters and calculations �� 103

5�5 Denitions of stakeholder assessment parameters �� 105

5�6 Denitions of weighting parameters �� 106

TABLES



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1�1 Selecting an ocean intake design is complex �� 4

2�1 Typical on-shore (lagoon and channels) and off-shore (pipe) open wet-well intake,

line, and screen congurations �� 13

2�2 Vertical seawater intake well �� 19

2�3 Horizontal (Ranney) seawater intake well �� 19

2�4 Slant seawater intake well �� 21

2�5 HDD seawater intake well �� 22

2�6 Schematic of a seabed ltration intake system �� 27

2�7 Conceptual drawing of the seabed ltration intake system for the Fukuoka District,

Japan, SWRO Facility �� 28

2�8 Comparison of through-ow and dual-ow traveling water screen arrangements �� 43

2�9 Schematic of a through-ow vertical traveling screen �� 45

2�10 Schematic of a ne-mesh vertical traveling screen system �� 46

2�11 Chalk Point Generating Station, Maryland, barrier net conguration �� 50

2�12 Illustration of an off-shore narrow-slot wedgewire screen intake system �� 52

2�13 Example of a stakeholder process designed to lead to a recommendation in the form

of a group “opinion statement” �� 67

3�1a Instructions page of the Utility Seawater Intake Experience Survey �� 70

3�1b Page 1 of the Utility Seawater Intake Experience Survey �� 71

3�1c Page 2 of the Utility Seawater Intake Experience Survey �� 72

3�1d Page 3 of the Utility Seawater Intake Experience Survey �� 73

3�1e Additional information page of the Utility Seawater Intake Experience Survey �� 74

3�2 Planned and installed desalination capacity of the responding utilities �� 76

FIGURES



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xv

FOREWORD

The Water Research Foundation (Foundation) is a nonprot corporation that is dedicated

to the implementation of a research effort to help utilities respond to regulatory requirements

and traditional high-priority concerns of the industry� The research agenda is developed througha process of consultation with subscribers and drinking water professionals� Under the umbrella

of a Strategic Research Plan, the Research Advisory Council prioritizes the suggested projects

based upon current and future needs, applicability, and past work; the recommendations are for-

warded to the Board of Trustees for nal selection� The Foundation also sponsors research projects

through the unsolicited proposal process; the Collaborative Research, Research Applications, and

Tailored Collaboration programs; and various joint research efforts with organizations such as the

U�S� Environmental Protection Agency, the U�S� Bureau of Reclamation, and the Association of

California Water Agencies�

This publication is a result of one of these sponsored studies, and it is hoped that its nd-

ings will be applied in communities throughout the world� The following report serves not only as

a means of communicating the results of the water industry’s centralized research program but alsoas a tool to enlist the further support of the nonmember utilities and individuals�

Projects are managed closely from their inception to the nal report by the Foundation’s

staff and large cadre of volunteers who willingly contribute their time and expertise� The Foundation

serves a planning and management function and awards contracts to other institutions such as water

utilities, universities, and engineering rms� The funding for this research effort comes primarily

from the Subscription Program, through which water utilities subscribe to the research program

and make an annual payment proportionate to the volume of water they deliver and consultants and

manufacturers subscribe based on their annual billings� The program offers a cost-effective and

fair method for funding research in the public interest�

A broad spectrum of water supply issues is addressed by the Foundation’s research agenda:

resources, treatment and operations, distribution and storage, water quality and analysis, toxicol-ogy, economics, and management� The ultimate purpose of the coordinated effort is to assist water

suppliers to provide the highest possible quality of water economically and reliably� The true ben-

ets are realized when the results are implemented at the utility level� The Foundation’s trustees

are pleased to offer this publication as a contribution toward that end�

Roy L� Wolfe, Ph�D� Robert C� Renner, P�E�

Chair, Board of Trustees Executive Director

Water Research Foundation Water Research Foundation



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xix

EXECUTIVE SUMMARY

As coastal populations grow, traditional drinking water sources are struggling to keep up

with new demands� Tapping the ocean for potable water via seawater desalination is gaining popu-

larity as a potential water supply source� However, it can only be used where the associated regu-latory, ecological, and public relations challenges can be overcome� Of the three components of

seawater desalination (intake, treatment, and concentrate discharge), intake location and design

is often the most challenging aspect of the system in terms of technical strategy, regulatory chal-

lenges, and public perception�

OBJECTIVES

The goal of this project is to take a detailed, integrated view of the seawater intake planning

and implementation process through: (1) the presentation of an overview of the seawater intake

planning and implementation process, and (2) the provision of a methodology that walks the user

through the decision-making process�

BACKGROUND

The applicability of different intake types depends upon siting options, geology, local ecol-

ogy, cost, regulations, and stakeholder considerations� In many cases, implementing ocean desali-

nation requires a broad, integrated view of the hurdles and impacts associated with each intake

type as all the elements of the decision process are interrelated� An integrated approach is needed

to best navigate intake project planning�

While it is important to have a clear understanding of what intake alternatives are techni-

cally feasible, it does not always mean that these options can be implemented� Ocean desalination

projects often fail to become reality because ocean intake alternatives:

1� May adversely affect the environment (e�g�, entrainment, impingement, sustainability,

safety of other water sources); and/or

2� May not adequately address stakeholder values (e�g�, water rates, water quality speci-

cations, ecological issues)�

The intake design determines the quantity and quality of the feed water available for

treatment and must balance the needs and values of the local community and the ecosystem�

Consequently, selecting the appropriate technology for developing a seawater supply typically

considers a variety of information from many technical and non-technical sources� These include:

• Site conditions,

• Technology options,

• Permitting requirements,

• Environmental impacts,

• Stakeholder values, and

• Utility constraints and interests�



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Executive Summary | xxiii

PARTICIPANTS

The participating utilities for this project included:

• Cambria Community Services District, Cambria, California

• City of Corpus Christi, Texas

• City of Santa Cruz, California

• Long Beach Water Department, Long Beach, California

• Marin Municipal Water District, Corte Madera, California

• Marina Coast Water District, Marina, California

• Poseidon Resources, Stamford, Connecticut

• Tampa Bay Water, Clearwater, Florida

• Texas Water Development Board, Austin, Texas



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1

CHAPTER 1

INTRODUCTION

As coastal populations grow, traditional drinking water sources are struggling to keep up

with new demands� Water agencies are turning to alternative sources to keep the taps running andtheir communities satised� Tapping the ocean for drinkable water—that is to say—seawaterdesalination, is gaining popularity as a potential water supply source, but can only be used wherethe associated regulatory, ecological, and public relations challenges can be overcome�

Of the three components of seawater desalination (intake, treatment, and concentrate dis-charge), intake location and design is often the most challenging aspect of the system in terms oftechnical strategy, regulatory challenges, and public perception� These challenges are due, in part,to the relatively limited experience many managers and other decision-makers have with desalina-tion technology, the uncommon nature of using ocean intakes for traditional water agencies, and

the lack of a methodology to share knowledge from water utilities experienced in the desalinationimplementation process�

INTAKE SELECTION REQUIRES CONSIDERATION OF MULTIPLE ISSUES

The intake design determines the quantity and quality of the feed water and must balance

the needs and values of the local community and ecosystem� Consequently, selecting the appropri-ate technologies for developing a seawater supply typically considers a variety of informationfrom several sources to determine feasibility� These include:

• Site conditions,• Technology options,

• Permitting requirements,

• Environmental impacts,• Stakeholder values, and• Utility constraints and interests�

Technology Options

Intake alternatives include both surface and subsurface options� Each can be describedrather simply:

• Surface intakes. Surface intakes are located above the seaoor and are the most com-mon type of intake for large (>10 mgd) plants� They are typically concrete pipes that

include trash racks and screens to respectively remove debris and particulate matter(both organic and inorganic)� Surface intakes also require additional pre-treatmentdue to the presence of marine life and small particles that must be removed before thedesalination process�

• Subsurface intakes. Subsurface intakes are buried pipes and/or wells buried beneaththe beach/ocean oor� Compared to surface intakes, subsurface intakes are typically

limited in capacity due to local geology; however, the extensive pretreatment required



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for surface intakes is either eliminated or greatly reduced� Because of their limitedcapacity, subsurface intakes are less common than open intakes for large plants�

Rather than designing and constructing a new surface or subsurface intake, it is sometimes

possible to use existing infrastructure� The opportunities are very limited, but other “reuse” options

include:

• Shared existing intake. Co-locate a new, or share an existing intake (typically a power plant intake)�

• Converted existing intake. Convert an existing (e�g�, abandoned) intake or outfall

line into an intake for the desalination system� One example of this alternative was theconversion of an existing wastewater outfall in Santa Barbara into an intake for thecity’s (now decommissioned) ocean desalination plant�

Permitting Requirements

The permitting environment for ocean intakes is highly complex� It involves considerationof the environmental and social impacts associated with both the operation of the structure itselfand the construction process� It incorporates numerous State and Federal regulations (e�g�,Section 316(b) of the Clean Water Act (CWA), the California Coastal Act, Section 10 Approval forConstruction within Dredge and Fill Permits) and almost as many regulatory agencies�

For example, the construction of a new open water intake is typically a lengthy process

involving a wide array of resource and regulatory agencies� Applicable regulations usually require permits from:

• The Army Corps of Engineers,• The United States Environmental Protection Agency (EPA),

• The National Marine Fisheries Service,• U�S� Fish and Wildlife, and• State resource and environmental agencies through some combination of:

– Environmental Impact Report (EIR), – Environmental Impact Statement (EIS), – Environmental Assessment (EA),

– Biological Assessment, or – Categorical Exclusion (CatEx), – Endangered Species Act (ESA) Take Permit(s), – Essential Fish Habitat, marine mammal and other wildlife protection acts, and – National Pollutant Discharge Elimination System (NPDES) permit�

The State of California Task Force on Desalination has recommended that any new openwater intake for desalination would need to conduct 316(b) permitting and impact assessmentstudies of the proposed intake’s location, design, capacity and operations, as well as the EPA’s316(b) Phase II rule performance standards�



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Chapter 1: Introduction | 3

Environmental Impacts

The construction process and operation of the intake structure can adversely impact theenvironment� Construction-related concerns include erosion, disturbance of the local ecology, hab-itat destruction, impact of construction materials (e�g�, drilling lubricants), and the potential fordisturbance of pollutants from the soil/ocean bed� Construction impacts are primarily mitigated

using “Best Management Practices�”Operation of the intake structure has two major impacts on the biological organisms in the

source water body: impingement and entrainment� Ocean intakes employ screening devices to block large objects from entering the cooling water system (impingement)� Fish and other aquaticorganisms large enough to be blocked by the screens may become impinged if the intake velocityexceeds their ability to move away�

Other mitigation measures include selecting a sub-surface well technology with lowentrainment potential, reducing the intake velocity, using ne meshed screens to exclude smallerorganisms, and siting the intake location in a less sensitive area�

Stakeholder Values

Stakeholder involvement is now an important component of many water and wastewater public agency decisions� This is clearly evident in the process of siting an ocean intake, wherecoastal watchdog groups may look suspiciously at any project that could negatively impact themarine environment� For any project of this type to have a chance for success, managers mustinvolve stakeholders� Some of these methods include:

• Integrating technical and policy or value discussions in open forums,• Respecting formal regulatory processes (e�g�, EIRs) while using a stakeholder process

to overcome their limitations,

• Providing meaningful stakeholder roles and responding to their values while main-taining technical rigor and defensibility, and• Directing stakeholders to focus on water quality, environmental, and nancial out-

comes rather than the means used to achieve them�

Analytical Tools (e�g�, ranking and grading alternatives) help organize complex choices,while public participation methods (e�g�, workshops) are essential to interact with stakeholderseffectively about these choices� Using both sets of “tools” can facilitate successful integration ofstakeholders into the decision-making process�

Utility Constraints and Interests

Simply put, not every agency that wants to implement desalination will be able to do so� Nor will every agency want to put in the time, resources, and effort required to implement desali-nation� Limitations on funding, adverse (hydro) geologic conditions, inability to efciently over-

come stakeholder challenges, or simply the lack of a proper site can derail the most enthusiasticdesalination effort�



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Chapter 1: Introduction | 5

PROJECT APPROACH

This research project integrated consideration of all the above-mentioned inuences on thedecision-making process and developed four key deliverables:

1� A centralized state-of-the-science report on the technical, logistical, and social aspects

of intake selection (Chapter 2)�2� A summary of utility experience with the ocean intake planning, design, and imple-

mentation process (Chapter 3)�3� An easy-to-navigate decision tool that walks the user through the thought process of

understanding the benets and limits of available options and selecting the best choicefrom among them (a Microsoft Access-based version of this Tool is included on the

attached CD-ROM and described in Chapters 4 and 5)�4� Case studies that illustrate use of the Tool and execution of the decision-making pro-

cess (embedded in the software Tool on the attached CD-ROM and summarized inChapter 6)�

Through this project, public agencies will have a methodology to help them analyze their

own situation, compare it with similar efforts, and weigh the benets of desalination versus theeffort of implementation with respect to ocean intakes�



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7

CHAPTER 2

STATE-OF-THE-SCIENCE IN OCEAN INTAKE DESIGN AND

PERMITTING FOR SEAWATER DESALINATION

In seawater desalination, salt water is rst pumped into the desalination plant from anocean intake structure� From there it passes through the desalination system (generally reverseosmosis membranes) or a distillation process� The permeate (product) is re-mineralized (for drink-ing water this is typically to a minimum hardness of ~40 mg/L as CaCO3 and a minimum alkalinityof ~40 mg/L as CaCO3) either through lime addition or blending with another source� Finally, it ischlorinated/chloraminated and sent into the distribution system� The concentrate (reject) is usually

disposed of through an outfall back into the ocean� Of these three system components (intake,treatment, and concentrate discharge), the intake is often the most challenging aspect of the systemin terms of technical strategy, regulatory approvals, and public acceptance�

This document captures the state-of-the-science in ocean intake permitting and design asof April 2010� The intake technologies, associated environmental and permitting requirements,

and stakeholder issues considered in the Desalination Intake Decision Tool (the Microsoft Accessversion of this tool, DesalIntakeTool�mdb, is included on the attached CD-ROM) are reviewed�Supplemental information on potential new and emerging technologies, regulatory activities, andsome state-specic regulatory information is also provided�

OVERVIEW

Ocean intake alternatives include both surface and subsurface options; described simply:

• Open intakes are located above the seaoor and are the most common type of intakefor large (>10 mgd, or >38,000 m3/d, production) plants� They are typically concrete,

high-density polyethylene (HDPE), or ber-reinforced polymer (FRP) pipes withconcrete collars that include trash racks and screens to remove debris and particulatematter (both organic and inorganic), respectively� Surface intakes require addition ofa pre-treatment system prior to the desalination process to remove marine life andsmall particles in the feed water�

• Subsurface intakes are buried pipes and/or wells dug beneath the shoreline or oceanoor� Seawater is drawn through the subsurface into the intake pipe� The subsurface

geology typically limits capacity and performance (as compared to open intakes);however, the extensive pretreatment required for surface intakes is either eliminatedor greatly reduced because the subsurface acts as a natural lter� Because of their lim-ited capacity and the need (in some cases) to construct a lter bed around the screens,

subsurface intakes are less common than open intakes for large plants� The most popular type of subsurface intake is a series of wells drilled on or

beneath the shore� The orientation can be vertical, angled, or horizontal� Seawater isdrawn through the natural sand deposits into the wells� (Although they are technically“subsurface wells,” the geology and locations into which they are installed variessignicantly from all other subsurface options and thus these are often classied sepa-rately�) Vertical wells are usually located some distance (setback) from the sourcewater and thus tend to produce a blended groundwater-seawater mix� Certain well



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designs can be used to optimize the percentage of seawater by locating screened sec-tions further off-shore, under the ocean, using angled or horizontal well technologies�As with other types of subsurface intakes, wells typically greatly reduce or eliminatethe need for pretreatment prior to the desalination process; their practicality is dictated

by the local geology and groundwater quality� Any impacts to local fresh groundwater

and well day lighting from surface (e�g�, sand) erosion must be mitigated�• Co-location with an existing intake makes use of an existing intake system for a new(desalination) application� Seawater is withdrawn from an existing intake or outfallfor another facility system (almost always a power plant)� Typically, operational coor-dination and ground rules are negotiated with the intake co-owner up front so both the

intake operator and the site owner can operate efciently� Co-location solves the sourceof water issue, however there are a number of issues related to changing the “existinguse” classications for the water stream in the facility that would require design anduse changes (and possibly re-permitting) of the existing intake� This includes address-ing questions about prolonging the life of the power plants and impacts from futurechanges in ownership�

To date, wells are the most common types of intake in use (Table 2�1)� This may change asthe number of seawater desalination plants grows; current new locations under consideration aremuch more diverse than in the past�

Seawater intake wells have proven to be quite economical for desalination plants with a

capacity smaller than 10 mgd (production), while open ocean intakes have found wider applicationfor large seawater desalination plants� In general, regulatory agencies have indicated a preferenceto subsurface intake technologies (where feasible) as opposed to direct, open-water intakes due tothe reduced environmental impacts associated with these systems� Sometimes this preference cancurtail the development of a seawater source or treatment site� Generally, it will greatly increase

the unit cost for producing water� Clearly, the consideration of multiple engineering, cost, andstakeholder issues are an integrated part of the planning and design process�If a source of raw water from an existing system (e�g�, through co-location) is not readily

available, then the designer will consider whether it is best to take water from a direct seawaterintake or through a process of induced inltration using seawater intake wells or other type ofsubmerged intake system� Each method has advantages and disadvantages related to the site-

specic requirements� The overall feasibility and cost-to-benet analysis of these issues are usedto determine which approach is the most effective for each application�

In some cases, this will be an obvious choice relating to the site characteristics, the volumeof water required, and the geology at the project location� However, at many sites there will bemultiple feasible alternatives that will need to be evaluated in order to select the approach that

makes the most sense from both a cost and an operational standpoint�

CONTROLLING PARAMETERS IN THE INTAKE SELECTION PROCESS

A number of factors, including the required capacity, geology, cost, water quality, environ-mental or permitting issues, and sustainability will be important considerations when evaluatingwater supply/source options and selecting the most effective alternative for a particular applica-

tion� Conditions will differ from site-to-site� Each parameter will affect the operation and



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maintenance for any water supply system to be employed; so each factor needs to be evaluated todirect selection of the most effective alternative� One of a few key factors alone may simply elimi-nate, or conversely, nominate a particular technology as the most feasible�

Capacity

The desired capacity of the desalination plant may direct which options will be the mostfeasible� Small systems (20 mgd, or 76,000 m3/d) may nd that an open intakewill be the simplest, most practical, most cost-effective solution� For other, mid-range capacity

sites (5 to 20 mgd), planners often consider multiple alternatives�

Geology

Geology is perhaps the most critical issue to consider� Geologic and hydrogeologic condi-tions readily dictate whether a submerged intake is at all feasible� If the coastal deposits consist of

low permeability silts and clays, or low permeability consolidated (rock) formations, it may bedifcult or impossible to construct a submerged intake or inltration gallery� For submerged intakesto be practical, it is recommended that the transmissivity be >0�088 mgd/ft (1,100 m3/d/m)(Schwartz 2000, cited in Voutchkov and Bergman 2007) for a depth of ≥45 ft (≥14 m) (Voutchkovand Bergman 2007)�

If the coastal geology indicates that one or more porous geologic systems are present, these

water-bearing zones will need to be evaluated through a detailed hydrogeologic investigation tofurther quantify and qualify their potential for developing the necessary capacity� Other issues,such as seasonal erosion patterns (to ensure sufcient coastal aquifer deposits exist year-round),groundwater contamination, local groundwater use, impacts on seawater intrusion, potentialimpacts and interferences on nearby users, and recharge/inltration characteristics would also

need to be evaluated during this stage� In many cases, favorable soils/coastal aquifers exist at a prospective site; however, the hydraulic properties (e�g�, hydraulic conductivity and transmissiv-ity) may limit the capacity of each well, necessitating a large number of caissons that may not allt within the project site boundaries or within a reasonable acreage that would have to be purchased�

Cost

As the public, local government, and water utility managers evaluate the feasibility of sea-water desalination, its cost is often compared with other alternatives (which often includes notadding or losing system capacity)� This comparison is a signicant issue when determining whether

or not the project is viable� Since there are few full-scale desalination installations in the U�S�, littleis known about the costs for constructing these intake systems within the U�S�, especially wheresensitive environmental areas along the coast are concerned, since additional costs will be incurredduring investigative, design and construction phases� However, as a general rule, open intakeshave signicantly higher capital costs than well systems� For example, Wright and Missimer esti-mated a capital cost ratio (open intakes versus well systems) of approximately 1�8 to 2�0 for small(≤2�0 mgd, or ≤7,600 m3/d) installations (Wright and Missimer 1997)� Operation and maintenance

(O&M) costs can vary signicantly depending upon site-specic conditions (e�g�, well depth)�



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Chapter 2: State-of-the-Science in Ocean Intake Design and Permitting for Seawater Desalination | 11

Water Quality

The design of the treatment train for a desalination facility will depend on the quality of the proposed source water; therefore, this will inuence what type of intake is preferred� Water froman open intake requires signicant pretreatment to remove particles, dissolved natural organic mat-ter (NOM), aquatic organisms, oating or suspended debris, oil and grease-in short, anything that

could foul or affect the membranes within the main treatment system� Pretreatment costs should beincluded in this alternative when comparing its costs to submerged and seawater intake well alter-natives� Typically, well systems and properly designed submerged intakes provide satisfactory pretreatment using the natural geologic deposits to pre-lter the raw water before it enters the treat-ment plant� Results from testing at facilities using well and gallery systems typically show that rawwater turbidity and silt density index (SDI) values are maintained below membrane manufacturers’

recommendations (e�g�, Rovell 2001)� There are also instances where the salinity of the raw feedwater can vary according to the point of withdrawal� This also affects the treatment train design�When wells are considered, elevated concentrations of certain inorganic minerals like iron andmanganese can also necessitate pretreatment prior to the desalination process�

Environmental Impacts

The nature of the location of seawater intakes–in the coastal zone–places them in environ-mentally sensitive areas, where public perception can play a key role in acceptance of the project;regulatory approval can be difcult and costly� Environmental concerns include aesthetics, protec-tion of sh and game, disturbance to local ecosystems (e�g�, wetlands or other local ora andfauna), impacts upon existing land use, impacts to local water users, inuences on local freshwater

aquifers, and contamination from the construction process� Environmental restrictions may pre-clude one alternative or another from further consideration due to potential construction impacts,ecologic degradation from long-term operation of the system, or permitting difculty� Conversely,

on-shore sources of contamination that could be drawn hydraulically into the intake and impact thetreatment process and/or concentrate disposal (e�g�, anthropogenic hydrocarbons) should also beconsidered�

Permitting

The age-old question “can this be permitted?” reects the critical nature of successfullynavigating the regulatory process� In many instances, it is a matter of conducting the proper stud-ies, completing the requisite forms, and otherwise satisfying the requirements of the myriad agen-

cies that hold permitting controls over an activity or facility to be approved� Identifying theappropriate agencies and the specic interests of the various agencies is pivotal to ensuring that all

foreseeable regulatory contingencies and situations are considered and potential roadblocks areidentied early on in the planning and design process� In addition, where the source water may bea blend of seawater and freshwater from local sources, water rights issues may also be involved�(Tide-inuenced rivers can provide the opportunity to develop seawater supplies in some areas by

taking advantage of tidal cycles to obtain better quality water, less particles and/or organic mate-rial, and higher columns, timing intake operation to match the tidal cycle�) Groundwater rights canalso be an issue in some states�



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Sustainability

In addition to determining if a certain system can be physically designed, permitted, andconstructed at a given location, there needs to be sufcient condence that the desired owrate can be obtained over the lifespan of the installation� This includes consideration of both demand andexpected conditions (e�g�, recharge, tidal inuences, fouling, etc�)� This issue also factors into

design changes as pilot or demonstration systems are expanded or replaced by full-scale systems�

INTAKE TECHNOLOGIES

Open Intakes

An open (or direct) surface intake can range in design complexity from simply attaching an

intake pipe and screen assembly to an existing structure, to modifying an existing intake or outfallline that may have been inactive, to constructing a dedicated, stand-alone structure� A typical openintake design includes intake screens, conveyance piping, and a wet well or other mechanism for

housing the system pumps� Common intake design alternatives include the following:

• Dock-, pier- or bulkhead- (i�e�, existing structure) mounted screens,• Wet well intake sumps with subsurface intake lines that extend to off-shore screens,• Wet well intake sumps with exposed intake lines anchored on the seabed extending to

off-shore screens,• Wet wells constructed into rock bluffs/cliffs with an intake line drilled through the

rock into the seawater with or without an attached screen,

• Shoreline structures with open bay and bar rack screens,• Directionally drilled lines under and through the seabed with screens, and/or • Forebay/pump stations in sheltered settings (e�g�, sloughs or coves)�

The pump station is usually a wet well or sump structure in which pumps are mounted� Itis located on-shore at a site that allows easy access and connection to the desalination plant� These

structures can be quite large, as they usually include pumps, controls, chemical feed equipment (ifnecessary), large primary screening devices like bar rack screens, secondary traveling screenassemblies, multiple chambers, and a backwashing (sparging) system�

In some older facilities, the intake point-of-withdrawal is located at the shoreline� However,more recent regulations typically prefer that the point-of-withdrawal is further off-shore, awayfrom near-shore habitats and areas where oating debris may accumulate� Figure 2�1 illustrates the

common on-shore and off-shore design congurations�The intake line and screen are extended to a preferred (in terms of capacity and water qual-

ity) off-shore location� The conveyance piping can be installed in several ways: (1) from an opentrench/open cut in which the pipe is laid out to the screens; (2) a trenchless approach where the piping is installed below-grade by augering, microtunneling, or directionally drilling the borehole

from the pump station to the screens; (3) a simple above-grade layout where the pipe is laid on andanchored to the seabed; or (4) some combination of these options� If the pump station (sump) islocated close to the screens the conveyance pipe may be very short, or not required�

Intake screens can include multiple components (e�g�, primary bar racks followed by ner-opening traveling screen assemblies) or they can be simple, xed, passive screens installed away



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from areas likely to have a lot of debris or aquatic life present within the water column� The intake

screen openings are typically sized for regulatory compliance with regard to sh and aquatic life

protection and tted with backwash capabilities to help keep screen surfaces free from debris to

maintain suitable open area to meet design entrance velocities� The design should provide the abil-

ity to inspect and maintain/clean the screens periodically, especially in areas where a high-growth

environment is expected� In some cases, it may be necessary to incorporate standby, or backup,

screens so that system performance can be maintained if one screen needs to be removed from

service for maintenance�

Depending upon the screen design, a sh trap or diversion/avoidance feature may also be

required� While some intakes draw water in through an open pipe, operating problems have been

reported with the entry of plants, marine organisms, and debris where no screens are used�

No matter which conceptual design is followed, the intake screening assembly will need to

conform with various agencies’ design guidelines regarding the protection of sh� These are prin-cipally concerned with the velocity of the water as it enters the screen itself and the size of the

screen openings� These agencies include, but may not be limited to, the National Marine Fisheries

Service (NMFS), a division of the National Oceanic and Atmospheric Administration (NOAA),

and the appropriate state Department of Fish and Game (DFG) and Fish & Wildlife (DFW) agen-

cies� Permitting agencies will also likely consider intake design with regard to screen placement

such that it avoids areas of near-shore habitat for local aquatic life, and will require entrainment

and impingement studies�

Figure 2.1 Typical on-shore (lagoon and channels) and off-shore (pipe) open wet-well intake,

line, and screen congurations



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In summary, cost will always increase with capacity, but estimating expenses needs, inlarge part, to be done on a case-by-case basis� Much less-costly solutions can be followed if thereare existing structures in the area to which the intake screen and conveyance piping can be attached,such as bridge piers, bulkheads, or if existing infrastructure (e�g�, existing or abandoned intake or

outfall lines) can be modied for use� Since a pretreatment system will need to be used with an

open intake, the cost for the pretreatment must be considered with the open intake cost when compared with submerged alternative� Pretreatment systems can cost from several hundred thousanddollars to several millions of dollars� The cost of required entrainment and impingement studiesshould also be included�

Recent Innovations

Intake screening systems are fairly well dened and are regularly improved to comply withcurrent and anticipated environmental regulations with regard to sh protection� The principalinnovations relating to intake design applies to the methods used for installation of the conveyance piping from the pumping station to the screen location� While conventional open-trenching or

anchored/exposed piping approaches are still employed, the technologies for more environmen-tally friendly trenchless methods are being advanced to minimize impacts on the local environ-ment during pipe installation, including the increased use of microtunneling and modications tohorizontal directionally drilled (HDD) techniques�

Required Studies

As intake-screening devices are not designed to remove all organisms within the watersource, a number of studies relating to entrainment and impingement of biota are typically requiredto support the permitting process� Some of the common studies that may be required to satisfyregulatory and permitting bodies are presented in Table 2�2� The type of studies required will

depend on intake location and the ability of the selected screening technology to minimize entrain-ment and impingement�

Summary

The advantages and disadvantages of open intakes can be summarized as follows:

Pros

• In most cases, provided adequate biological fouling mitigation and control measuresare employed (i�e�, prevention of biological growth on intake screens and pipelines),

an open intake should be able to meet any required capacity since the ability to deliverthe needed supply is dictated by the diameter of the conveyance piping and the sizeand number of intake screens�

• Intake sizing is very exible; it should be possible to design an open intake to producecapacities ranging from several hundred gallons per minute to several hundred milliongallons per day in virtually any geology, from a bluff or cliff setting to a shallow beachsetting to an intake in a sheltered position such as within a harbor or slough�



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Table 2.2

Studies required for seawater open intakes

Intake location Study type Duration Cost

Shoreline intake • Entrainment and source water

ichthyoplankton/selected

meroplankton�• Hydrodynamic study of local,

ambient currents�

• Terrestrial surveys of biological

resources required at greeneld

site�

• Year-long monthly (sometimes

bi-monthly) plankton surveys

and seasonal to continuoushydrodynamic studies�

• Year-long quarterly surveys of

terrestrial plants and animals,

and intertidal/subtidal shoreline

communities that might be

disturbed by construction�

$0�5 to 1�5

million

Off-shore open

water intake

• Entrainment and source water


meroplankton�

• Hydrodynamic study of local,

ambient currents�

• Bathymetric survey�• Benthic surveys of bottom

communities in areas pipeline and

intake construction disturbances�



and seasonal to continuous

hydrodynamic studies�

• One time bathymetric survey�

• Year-long quarterly benthicsurveys of benthic and demersal



$0�75

to 1�75

million

Shoreline

screened intake



meroplankton�


ambient currents�

• Terrestrial surveys of biological

resources required at a greeneld

site�

• Screen performance testing,

usually in concert with

entrainment survey�



and seasonal to continuous



terrestrial plants and animals,

and intertidal/subtidal shoreline



• Quarterly (or monthly) screen-

performance tests�

$0�75

to 1�75

million

Off-shore

screened open

water intake


ichthyoplankton/ selected

meroplankton�


ambient currents�

• Underwater surveys of benthic

and demersal biological resources

required at a greeneld site�

• Screen performance testing,usually in concert with

entrainment survey�



and seasonal-to-continuous



benthic and demersal communities

along pipeline route and intake

construction area and intertidal/

subtidal shoreline communities thatmight be disturbed by construction�

• Quarterly (or monthly) screen-

performance tests�



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water supply is to come from induced inltration or some preferential direction, such as in acoastal well application� The primary benets to using a horizontal well (as opposed to a verticalwell) are:

1� It can be drilled from a central location with a long lateral reach (particularly advanta-geous for sites with limited above-ground access), and

2� The borehole is exposed to a greater surface area within the geologic formation, socapacity is typically enhanced (Delhomme et al� 2005)�

The caisson is sunk using the open-end caisson method—each circular section of the caissonis formed and poured on-site, at grade, and then sunk by excavating soil from inside the caisson� As

the soil is removed, the caisson sinks into the ground under its own weight� As each section sinks to

Figure 2.2 Vertical seawater intake well

Figure 2.3 Horizontal (Ranney) seawater intake well



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ground level, the subsequent section is tied-in, poured, and sunk� This process continues until thelowest section (which contains the ports for jacking the well screens) reaches the design elevationselected for screen placement� At this time, a concrete sealing plug is placed in the bottom of thecaisson so it can be dewatered and entered� The lateral well screens are then extended out through

the port assemblies cast into the walls of the lower caisson sections� Since the well screens are pro-

jected out near the base of the formation, maximum drawdown can be used and all the screens can be installed within the most hydraulically efcient aquifer zone, optimizing well screenefciencies�

Since the screens in these wells are placed horizontally, a higher rate of water withdrawalis possible than with vertical wells� As a result, fewer horizontal wells (than vertical wells) are

required to pump the same volume of water� Horizontal collector wells are typically designed towithdraw from 0�5 mgd to 5�0 mgd (1,900 to 19,000 m3/d) of raw water each� The caisson is con-structed of reinforced concrete with an inside diameter of 10 to 30 ft (3 to 9 m) and a wall thicknessof 1�5 to 3 ft (46 to 91 cm)� The caisson depth varies according to site-specic geologic conditions,ranging from approximately 30 to over 150 ft (9 to >46 m)� The number, length, and location ofthe horizontal lateral screens are determined based on a detailed hydrogeological investigation�

Typically, the diameter of the laterals ranges from 8 to 12 in (20 to 30 cm) and their length extendsup to 300 ft (91 m)� The size of the slot opening on the lateral screens is selected to accommodatethe grain-size of the underground soil formation� If necessary, an articial gravel-pack lter isinstalled around the screen to prevent sand inltration in ner-grained aquifer deposits�

As with vertical wells, horizontal wells can be located near the shoreline and unlike verticalwells, the well screens can be projected out away from near-shore inuences� This allows the per-

centage of seawater being withdrawn to be maximized (i�e�, minimizes the use of on-shore ground-water sources)�

Since the well screens are installed horizontally, they can be placed within the most advan-tageous zone within the aquifer with respect to hydraulic efciency and for selective water qualitywithdrawal where stratied conditions exist� Blank sections of casing can be increased near the

caisson to further concentrate the screened portion of the well (withdrawal point) off-shore to opti-mize the intake of seawater� Horizontal wells have been installed at

assessing seawater intake systems for desalination plants.pdf

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