hf183 follow up sampling ms4 smg 095 final report

HF183 FOLLOW‐UP SAMPLING MS4‐SMG‐095 FINAL REPORT

Prepared For: County of San Diego DPW/Watershed Protection 5500 Overland Ave., Suite 410 San Diego, California 92123 Contract Number: 551462 TO74 Prepared By: Weston Solutions, Inc. 5817 Dryden Place, Suite 101 Carlsbad, California 92008 WESTON Project Number: 13245.419.074 May 2020

HF183 Follow-up Sampling MS4-SMG-095 i May 2020

Table of Contents

1 OVERVIEW ........................................................................................................................................ 1

1.1 Background .............................................................................................................................. 1

1.2 Sampling and Testing Objectives ......................................................................................... 1

2 METHODS .......................................................................................................................................... 2

2.1 Sampling Locations ................................................................................................................ 2

2.2 Sampling Frequency ............................................................................................................... 2

2.3 Sampling Methods .................................................................................................................. 2

2.4 Monitored Constituents ......................................................................................................... 5

3 RESULTS .............................................................................................................................................. 7

3.1 Inlet Investigations ................................................................................................................. 7

3.2 Monitored Flow ...................................................................................................................... 7

3.3 Human-Associated HF183 Molecular Marker ................................................................... 9

3.4 Physical Parameters .............................................................................................................. 10

3.5 Water Chemistry ................................................................................................................... 11

3.6 Groundwater Data ................................................................................................................ 13

3.7 Field Camera .......................................................................................................................... 14

4 DISCUSSION .................................................................................................................................... 15

4.1 Classification of Water Sample Geochemical Profiles – Piper Diagram ...................... 15

4.2 Comparison of Geochemical Profiles – Stiff Diagram ................................................... 17

4.3 Other Constituents ............................................................................................................... 18

5 CONCLUSIONS ............................................................................................................................... 19

6 REFERENCES .................................................................................................................................. 20 ATTACHMENTS

A – Field Data Sheets and Photos B – Laboratory Results C – Chain of Custody Forms D – QA/QC assessment E – CEDEN formatted EDDs F – County of San Diego Source Abatement Actions

HF183 Follow-up Sampling MS4-SMG-095 ii May 2020

List of Tables

Table 1. Monitored Parameters ....................................................................................................................... 6 Table 2. Average Flow Rate by Day and Time .............................................................................................. 9 Table 3. HF183 Sample Results for Dry Weather Sampling at MS4-SMG-095 ..................................... 10 Table 4. Water Chemistry Results and QC for Follow-Up Sampling at MS4-SMG-095 ...................... 11 Table 5. Water Chemistry Results for Follow-Up Sampling Period at Rainbow County Park ............ 12 Table 6. Chemistry Data for Regional Groundwater Reference Sites ..................................................... 13

List of Figures

Figure 1. Weir Discharge Equation ................................................................................................................. 3 Figure 2. Outfall Investigation Study Area ..................................................................................................... 4 Figure 3. HF183 Follow-up Study Locations ................................................................................................ 5 Figure 4. Hydrograph of Flow at MS4-SMG-095 throughout Follow-up Monitoring Period .............. 8 Figure 5. Field Camera Image of Flooded Outfall During Elevated Flow Measured on

October 14, 2019 .................................................................................................................................. 8 Figure 6. Piper Diagram of Geochemical Profile at MS4-SMG-095 and Rainbow County

Park ....................................................................................................................................................... 16

HF183 Follow-up Sampling MS4-SMG-095 iii May 2020

Acronyms and Abbreviations Caltrans California Department of Transportation COC chain-of-custody County County of San Diego Department of Public Works Watershed

Protection Program ddPCR droplet digital polymerase chain reaction DIC dissolved inorganic carbon DNA deoxyribonucleic acid EDG County of San Diego Department of Public Works Existing

Development Group ELAP EMA

Environmental Laboratory Accreditation Program EnviroMatrix Analytical, Inc.

EPA Environmental Protection Agency GAMA California Groundwater Ambient Monitoring and Assessment Program HF183 human-associated fecal marker I-15 Interstate-15 LOD limit of detection MS4 municipal separate storm sewer system ND not detected NHD National Hydrology Dataset NPDES National Pollutant Discharge Elimination System PCR QA QC

polymerase chain reaction quality assurance quality control

RMWD Rainbow Municipal Water District SM standard method SOP standard operating procedure USGS United States Geological Survey WESTON Weston Solutions, Inc.

Units of Measure

°C degrees Celsius cfs cubic feet per second gpm gallons per minute Meq/L Milliequivalents per Liter mg/L milligrams per Liter mL milliliter mS/cm millisiemens/centimeter

HF183 Follow-up Sampling MS4-SMG-095 1 May 2020

1 OVERVIEW

The County of San Diego Department of Public Works Watershed Protection Program (County) has requested the assistance of Weston Solutions, Inc. (WESTON®) to conduct dry weather flow monitoring and sampling for human associated fecal marker HF183 at one municipal separate storm sewer (MS4) outfall, MS4-SMG-095. 1.1 Background MS4-SMG-095 is sampled monthly as part of the Rainbow Creek HF183 Monitoring Program (WESTON, 2019a) which began in June 2019. Samples collected in July 2019 indicated the presence of HF183 (6,368 copies/100 milliliters [ml]). As a result of this detection, the County initiated a follow-up study to conduct weekly sampling at the outfall in August and September 2019. Of the eight samples collected, only one sample (August 28, 2019) contained quantifiable levels of HF183 (183,168 copies/100mL). Results for this study are reported in the 2018-2019 Rainbow Creek HF183 Monitoring Report (WESTON, 2020). In October 2019, the County initiated the MS4-SMG-095 follow up study to investigate potential sources of HF183. The study also included continuous dry weather flow monitoring, weekly sampling for four weeks at the outfall, analysis of samples for HF183 and minerals, as well as mineral analysis sampling of the municipal water supply at the nearby Rainbow County Park. Data from groundwater monitoring in the watershed were evaluated as part of this study to determine if the chemistry composition of the dry weather flows at the outfall were similar to the groundwater or to the municipal water supply. 1.2 Sampling and Testing Objectives The MS4-SMG-095 HF183 Follow-up Monitoring Study will be used to address the following questions:

1. Under what flow conditions is human-associated fecal marker HF183 observed at the MS4-SMG-095 outfall?

2. What are the patterns in the timing of flow at the outfall?

3. How does the chemical composition of dry weather flow at the outfall compare to possible sources including local treated water or groundwater?

4. How much does each water source influence the chemical composition of dry weather flows?


2 METHODS

2.1 Sampling Locations Outfall MS4-SMG-095 is located in the community of Rainbow along Old Highway 395, just east of Interstate-15 and 1,800' north of 2nd Street (Figure 2; 33.422 N, -117.1528 W). MS4-SMG-095 is situated within the Rainbow Creek sub-watershed, which is part of the larger Santa Margarita River Watershed in Northern San Diego County. Additional data sources were used to compare the water from the outfall to the local treated supply and to the regional groundwater profile. Samples from the municipal water supply were collected from the restroom faucet at Rainbow County Park (Figure 3; 33.413 N, -117.150 W). Groundwater was not sampled as part of this study, but data were obtained from the California Groundwater Ambient Monitoring and Assessment Program (GAMA) database. Samples collected earlier than 1970 or those that were missing multiple parameters to create a geochemical profile were excluded. Two previous monitoring studies at sites in the neighboring San Luis Rey River Watershed provided data as shown in (Figure 3). SD-843 is located south of Rainbow (33.381, -117.117) and was sampled in 2008 (Wright et al., 2005); PR-12 is located southeast of Rainbow at Red Mountain Reservoir data (33.393, -117.190) and was sampled in 2011 and 2016 (Davis and Shelton 2014).

2.2 Sampling Frequency Dry weather low flows were monitored continuously from October 11 through November 1, 2019. Samples were collected weekly at MS4-SMG-095 from October 2 to October 30, 2019 during dry weather (<0.1 inch precipitation in the preceding 72 hours). During the weekly sampling events, visual observations were recorded, water samples were collected during flowing or ponded conditions at the outfall and flow was estimated using the bottle-fill method. Samples were collected from Rainbow County Park on the same day as outfall sampling, beginning on October 9, 2019.

2.3 Sampling Methods On September 27, 2019, a team of two WESTON field scientists conducted a site visit to measure the dimensions inside the outfall pipe for weir fabrication, to select a location for camera mounting and to investigate potential sources of flow. WESTON fabricated a weir to assist in monitoring of dry weather flows at the outfall and installed it on October 11, 2019 along with one County-owned METER CTD-10 sensor and an EM60G data logger. The CTD-10 sensor was installed in the pond upstream of the weir, far enough away from the weir to avoid the nappe effect created as water is drawn down through the weir opening, allowing the sensor to measure flat, ponded water. The EM60G logged the data measured by the CTD-10 sensor at 5-minute intervals and uploaded it directly to a cloud network. The logger was housed in a locked metal box to deter vandalism. The relationship between water level above the v-notch of the weir and discharge has been well-studied and shown to be governed by the equation in Figure 11.

1 “San Diego County Hydrology Manual.” San Diego County Hydrology Manual, County of San Diego, Dept. of Public Works, Flood Control Section, 2003.


𝑄 𝑑𝑖𝑠𝑐ℎ𝑎𝑟𝑔𝑒, 𝑐𝑓𝑠 2.49 ∗ 𝑊𝑎𝑡𝑒𝑟 𝐿𝑒𝑣𝑒𝑙, 𝑓𝑒𝑒𝑡 .

Figure 1. Weir Discharge Equation

After the sensor was installed, the vertical difference in elevation between the sensor and the bottom of the v-notch on the weir was measured. The difference measured is the water level above the sensor required to reach the v-notch. A water level greater than this measurement indicates water is flowing through the v-notch. The water level measured by the sensor, when reduced by the vertical difference measured, is equivalent to the water level above the v-notch, and subsequently a flow rate through the v-notch can be calculated using the equation in Figure 1.

A motion-activated camera with solar-powered battery and remote cellular connection was also installed on October 11, 2019. WESTON consulted with the County to determine the appropriate location for camera installation, which was installed inside the pipe facing the outlet. WESTON coordinated with the County to obtain an encroachment permit prior to equipment installation. Photographs of the site are provided in Attachment A.

All samples were collected by WESTON field scientists. Sampling methods are consistent with Standard Methods 9060 (“Collection and Preservation of Samples”) and the National Pollutant Discharge Elimination System (NPDES) Storm Water Sampling Guidance Document (USEPA, 1992). Water samples were collected from the outfall following the clean hands technique, as outlined in WESTON SOP FLD038.01. In order to avoid any potential contamination, scientists wore clean, non-powdered, disposables gloves each time a sample was collected and new, disposable clean syringes were used to collect water in low flow and ponded water situations. While one member of the field team collected the water sample, the other member of the field team took notes on the designated field data sheet and took photographs documenting conditions at each site.

Each field sample was labeled and identified with the project title, site, date and time of sample collection, and preservation method. Upon collection, samples were stored in coolers and on ice until delivery to EMA and to WESTON’s Molecular laboratory. All samples were delivered to the laboratories promptly in order to meet recommended holding times.


Figure 2. Outfall Investigation Study Area


Figure 3. HF183 Follow-up Study Locations

2.4 Monitored Constituents Samples collected from MS4-SMG-095 were analyzed for human-associated fecal marker HF183 by droplet digital Polymerase Chain Reaction (ddPCR) at the WESTON Molecular Laboratory. Results are included as Attachment B. Samples collected from the outfall and Rainbow County Park were also analyzed for fluoride, total residual chlorine, nitrate as N, total dissolved solids, total boron, total iron, total calcium, total magnesium, total sodium, total potassium, carbonate alkalinity, bicarbonate alkalinity, chloride and sulfate (Table 1) by EnviroMatrix Analytical, Inc. (EMA), an Environmental Laboratory Accreditation Program (ELAP)-certified laboratory (Certification No. 2564). All samples were delivered on ice inside coolers to WESTON’s Molecular Laboratory or EMA for analysis. Prior to transport, chain of custody (COC) forms were filled out and the original signed COC forms were inserted in a sealable plastic bag and placed inside the coolers. WESTON’s Molecular lab and EMA properly and safely preserved or disposed of the samples after the analyses were complete and analytical quality assurance (QA)/quality control (QC) procedures were reviewed and accepted. Field quality assurance/ quality control samples including field duplicates and field were collected to equal 5% of total samples and blanks.


Table 1. Monitored Parameters

Parameter Method Target Reporting Limits (mg/L unless specified)

HF183 ddPCR 29 copies/100 mL*

Fluoride SM4500 F C 0.1

Total Residual Chlorine SM4500 Cl G 0.05

Nitrate as N EPA 353.2 0.05

Total Dissolved Solids SM2540 C 20

Boron (Total) EPA 200.7 0.5

Iron (Total) EPA 200.8 0.01

Calcium (Total) EPA 200.7 0.5

Magnesium (Total) EPA 200.7 0.5

Sodium (Total) EPA 200.7 0.5

Potassium (Total) EPA 200.7 1.0

Carbonate Alkalinity SM2320B 5.0

Bicarbonate Alkalinity SM2320B 5.0

Chloride SM4500 Cl B 0.05

Sulfate SM4500 SO4 E 5.0 * Limit of detection HF183 – human-associated fecal marker ddPCR – droplet digital polymerase chain reaction mL - milliliter SM – Standard Method EPA -Environmental Protection Agency

Samples for HF183 were filtered within 6 hours in accordance with SOP LAB074.01 (Filtration Protocol for Samples for Molecular Analysis) and Deoxyribonucleic acid (DNA) extracted from the filters using the GeneRite DNA-EZ ST1 kit according to SOP LAB078.00 (GeneRite DNA-EZ Extraction (500/350)). The purified sample extracts were then tested for the HF183 marker via ddPCR on a BioRad QX200 ddPCR System. Assay details, reporting limits, and details of ddPCR/QC are described in the Rainbow Creek HF183 Quality Assurance Project Plan (WESTON 2019a).


3 RESULTS

3.1 Inlet Investigations An initial investigation of the MS4 system upstream of MS4-SMG-095 was conducted on September 27, 2019. The investigation began on the west side of Interstate-15 (I-15) about 300 feet south of where the onramp at Rainbow Valley Blvd. converges with I-15. The drainage area drains from the base of the granite hillside to the west, down toward a series of brow ditches along the shoulder of the southbound side of I-15. These brow ditches lead to two parallel inlets that connect to the MS4 pipes underneath I-15 and Highway 395, and ultimately link up with MS4-SMG-095 and MS4-SMG-096. Deposited human fecal material and toilet paper was observed in the brow ditches, vegetation and both inlets. The County’s Existing Development Group (EDG) coordinated with the California Department of Transportation (Caltrans) to address this potential source. Caltrans cleaned the area along the brow ditches, trimmed vegetation to reduce coverage, and cleaned the stormwater conveyance system. Additional description of these abatement actions are provided in Attachment F. EDG also worked with the County Department of Public Works, Roads Division to trim vegetation near MS4-SMG-095 to reduce the potential for human activities. During the initial reconnaissance on September 27, 2019, ponded water inundated the pipe approximately 12 feet upstream of the outfall at MS4-SMG-095. Meanwhile, the inlets on I-15 were observed to be dry. The distance from the brow ditch to the outlet is approximately 360 feet though the MS4. The 24-inch pipe was observed to be affected by mineralization along a joint approximately 40 feet upstream of the outfall. Ponding limited access to the pipe and the origin of the seepage was not determined.

3.2 Monitored Flow Dry weather flows were monitored continuously at MS4-SMG-095 from October 11 through November 1, 2019. Figure 4 presents the flow rate measured for the entire monitoring period. Measured flow ranged from 0 to 88.7 gallons per minute (gpm) with an average of 0.107 gpm. The majority of measurements indicated water level was below the crest of the weir. The highest monitored flow was measured on October 14, 2019 at 9:45 when a large pulse of water was measured (Figure 4). Approximately 3,000 gallons of water flowed through the outfall in less than three hours. Figure 5 provides a photograph of the outfall during the time period of increased flow on October 14. WESTON staff revisited the inlets along Southbound I-5 on October 14th, after the pulse flow. Despite observations of higher water levels at the outfall, the inlets were dry and showed no signs of recent moisture. No rain was measured during the study period at the nearest County ALERT Station (Rainbow County Park), confirming that all flows observed were dry weather discharges.


Flow rate measured on October 4, 2019 peaked at 88.7 gpm

Figure 4. Hydrograph of Flow at MS4-SMG-095 throughout Follow-up Monitoring Period

Figure 5. Field Camera Image of Flooded Outfall During Elevated Flow Measured on

October 14, 2019


Table 2 presents the average flow rate by day of the week and time of day. The large volume event measured on Monday October 14th was removed from the average calculation to examine patterns in weekly flow. The highest average flows were measured on Wednesday mornings between 6 and 9 am. The Wednesday average for this period was elevated due to an increase in flow measured on the morning of Wednesday, October 16.

Table 2. Average Flow Rate by Day and Time

Time Average Flow Rate (gpm)

Sunday Monday Tuesday Wednesday Thursday Friday Saturday 0:00 0 0 0.000028 0.003446 0.001199 0 0 1:00 0 0 0.000276 0.002726 0.001085 0 0 2:00 0 0 0.000191 0.005422 0.001510 0 0 3:00 0 0 0 0.008576 0.002386 0 0 4:00 0 0 0 0.009455 0.003573 0 0 5:00 0 0 0 0.013577 0.002288 0 0 6:00 0 0 0 0.016589 0.001354 0 0 7:00 0 0 0 0.016585 0.003446 0 0 8:00 0 0 0 0.019151 0.000282 0 0 9:00 0 0 0.000004 0.000027 0 0 0

10:00 0 0 0.000024 0 0 0 0 11:00 0 0 0 0 0 0 0 12:00 0 0 0 0 0 0 0 13:00 0 0 0.000020 0 0 0 0 14:00 0 0 0.000036 0 0 0 0 15:00 0 0 0.000451 0 0 0 0.000008 16:00 0 0 0.000985 0 0 0 0.000040 17:00 0 0 0.002253 0 0 0 0.000268 18:00 0 0 0.001825 0 0 0 0.000561 19:00 0 0 0.001510 0 0 0 0.000081 20:00 0 0 0.001510 0 0 0 0 21:00 0 0 0.004857 0.000004 0 0 0 22:00 0 0 0.004857 0.000004 0 0 0 23:00 0 0.000020 0.004857 0.000675 0 0 0

* Does not include large pulse of approximately 3,000 gallons of water that occurred between approximately 09:25 and 12:15 on Monday, October 14, 2019. gpm – gallons per minute 3.3 Human‐Associated HF183 Molecular Marker Beginning in June 2019, MS4-SMG-095 was sampled monthly as part of the Rainbow Creek HF183 Monitoring Program. The sample collected in July 2019 indicated the presence of HF183 (6,368 copies/100mL). As a result of this detection, the County initiated a study to conduct weekly sampling at the outfall in August and September 2019. Of the eight samples collected, only one sample (August 28, 2019) contained quantifiable levels of HF183 (183,168 copies/100mL) (WESTON, 2020). The


County initiated the MS4-SMG-095 Follow-up Study in October 2019 to investigate potential sources of HF183. Table 3 presents HF183 results from all three studies.

Table 3. HF183 Sample Results for Dry Weather Sampling at MS4-SMG-095

Study Date HF183

(copies/100 mL)

Rainbow Creek HF183 Monthly Monitoring

7/18/2019 6,368

Weekly Follow-Up Monitoring

8/7/2019 ND

8/15/2019 ND

8/22/2019 ND

8/28/2019 183,168

9/4/2019 ND

9/11/2019 ND

9/19/2019 ND

9/25/2019 ND

MS4-SMG-095 Follow-Up Sampling

10/2/2019 ND

10/9/2019 ND

10/16/2019 ND

10/23/2019 ND

10/30/2019 ND ND - Not detected above limit of detection

3.4 Physical Parameters Water temperature fluctuated throughout the monitoring period, within a range of 10.6°C to 18.8°C (Figure 6). Temperature exhibited a diurnal flux which became muted from October 21 to October 26, 2019. Overall temperature rose by two degrees during the first week, plateaued from October 21 to October 26, 2019 and then dropped on October 26, 2019 by about five degrees, where it remained for the duration of the study. Specific Conductance changed more gradually than temperature, with two exceptions. Conductivity was overall lowest at the beginning of the study, at approximately 0.6 mS/cm. A sudden increase in conductivity occurred on October 14, 2019 with an increase of 0.2 mS/cm. Conductivity fluctuated at this level, then decreased on October 16, 2019.


Figure 6. Physical Profile of Water at MS4-SMG-095 during Follow-up Monitoring Period

3.5 Water Chemistry Results from laboratory analysis of samples collected at MS4-SMG-095 are presented in Table 4. There were no detections in any of the samples for total boron, carbonate or total residual chlorine. The most common cations (positively charged ions) found in water include calcium, magnesium, sodium and potassium; while the most common anions (negatively charted ions) are bicarbonate, chloride and sulfate (United States Geological Survey [USGS], 2002). The samples taken on October 16, 2019 contained the highest levels of the anions bicarbonate and sulfate as well as the highest levels of the cations calcium, sodium, and potassium. The highest levels of iron were measured on October 30 (3.26 mg/L), an order of magnitude greater than measured in the other samples.

Table 4. Water Chemistry Results and QC for Follow-Up Sampling at MS4-SMG-095

Analyte Sample Results (mg/L)

Quality Control Sample Results (mg/L)

10/09/19 10/16/19 10/23/19 10/30/19 Field

Duplicate Field Blank

Boron <0.25 <0.25 <0.25 <0.25 <0.25 <0.25 Calcium 46 59.1 51.8 54.5 51.6 0.35J Iron 0.402 0.217 0.246 3.26 0.204 0.016 Magnesium 20.2 20.5 20 21.4 20.4 <0.100 Potassium 1.11 6.63 1.94 4.07 1.86 <1.00 Sodium 61.9 65.2 62 65.1 62 0.21J Bicarbonate 92 186 152 166 152 <5 Carbonate <5 <5 <5 <5 <5 <5 Chloride 28 28 26 29 26 <0.05

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

20.0

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

11‐Oct

12‐Oct

13‐Oct

14‐Oct

15‐Oct

16‐Oct

17‐Oct

18‐Oct

19‐Oct

20‐Oct

21‐Oct

22‐Oct

23‐Oct

24‐Oct

25‐Oct

26‐Oct

27‐Oct

28‐Oct

29‐Oct

30‐Oct

31‐Oct

Temperature (°C)

Specific Conductan

ce (mS/cm

)Specific Conductance Temperature (°C)


Table 4. Water Chemistry Results and QC for Follow-Up Sampling at MS4-SMG-095


Quality Control Sample Results (mg/L)

10/09/19 10/16/19 10/23/19 10/30/19 Field

Duplicate Field Blank

Fluoride 0.142 0.388 0.188 0.217 0.184 <0.031 Sulfate 36.2 54.4 32.2 48 30.9 <1.0 Total Dissolved Solids 429 475 425 461 389 <1.0 Total Residual Chlorine <0.05H <0.05H <0.05H <0.05H <0.05H <0.05H Nitrate as N 32.6 16.8 20.1 22 20.3 0.01J

< - Analyte not detected in the sample above the method detection limit. J- Result detected above the method detection limit but below the reporting limit. H - Sample was received outside of EPA recommended 15-minute holding time for analysis. However, sample was

analyzed immediately upon receipt. mg/L – milligram per liter. Chemistry results from samples collected from the public water supply at Rainbow County Park are provided in Table 5. There were no detections of boron or carbonate in samples from the park or in the outfall. Sodium and potassium concentrations were similar between the outfall and the park. Concentrations of fluoride, chloride, residual chlorine, and sulfate in samples from the park were higher than those observed in the samples from MS4-MSG-095. Concentrations of all other monitored constituents were higher in the outfall samples.

Table 5. Water Chemistry Results for Follow-Up Sampling Period at Rainbow County Park


10/09/19 10/16/19 10/23/19 10/30/19 Boron <0.25 <0.25 <0.25 <0.25 Calcium 35.3 30.6 32.4 30.7 Iron 0.022 0.011 0.013 0.027 Magnesium 14.9 14.2 15.1 14.4 Potassium 3.45 3.14 3.33 3.05 Sodium 64.2 57.2 61.3 59.3 Bicarbonate 76 72 72 72 Carbonate <5 <5 <5 <5 Chloride 58 70 61 61 Fluoride 0.734 0.633 0.645 0.728 Sulfate 75.6 87.8 61.9 65 Total Dissolved Solids 324 311 264 322 Total Residual Chlorine 1.84H 2.17H 2.18H 2.17H Nitrate as N 0.13 0.15 0.2 0.07

< - Analyte not detected in the sample. H - Sample was received outside of EPA recommended 15-minute holding time for analysis. However, sample was analyzed immediately upon receipt.


3.6 Groundwater Data Groundwater data was accessed from the Groundwater Ambient Monitoring and Assessment Program (GAMA) database in order to compare groundwater chemical composition to the composition of MS4-SMG-095 and the Rainbow municipal water source (Rainbow County Park). The two nearest available groundwater wells with recent data were in an adjacent watershed. SD-843 is located south of Rainbow (33.381, -117.117) and has detailed sample data from 2008 (Wright et al. 2005). PR-12 is located southeast of Rainbow at Red Mountain Reservoir data (33.393, -117.190) and has detailed sample data from 2011 and 2016 (Davis and Shelton, 2014). Closer sites from 1970 or earlier lacked many analytes and were excluded from the analysis. Results from PR-12 and SD-843 are provided in Table 6.

Table 6. Chemistry Data for Regional Groundwater Reference Sites


GAMA-PR-12 GAMA-PR-12 GAMA-SD-843 09/14/11 10/26/16 09/29/08

pH 7.2 7.4 7.2 Alkalinity (CaCO3) 118 125 NS Bicarbonate Alkalinity as CACO3 NS NS 229 Carbonate Alkalinity as CACO3 NS NS 188 Boron 0.103 0.133 0.0556 Calcium 58.7 64.1 126 Iron 0.0049 0.007 0.02 Magnesium 32.5 33.9 41.5 Potassium 1.88 1.97 1.89 Sodium 73.7 77.4 52.5 Chloride 93.4 93.8 141 Fluoride 0.19 0.19 0.106 Sulfate 191 191 129 Total Dissolved Solids NS NS 764 Nitrate as N* 1.16 0.64 20.18

NS – No data available * Recorded as nitrate in groundwater data; converted to nitrate as N for this study

The groundwater data downloaded from GAMA included nitrate in a different form than the samples collected from MS4-SMG-095 and Rainbow County Park. The GAMA data reported nitrate, while this study reported nitrate as N. To allow for comparison between historical groundwater data and the data collected for this study, nitrate data from GAMA was converted into nitrate as N (nitrate as N = nitrate / 4.42). In addition, the groundwater data provided carbonate and bicarbonate in different forms than were collected in this study, including ‘Bicarbonate Alkalinity as CACO3’ and ‘Carbonate Alkalinity as CACO3’ at SD-843 and Alkalinity (CaCO3) at PR-12. These values are not directly comparable to results from the samples collected at MS4-SMG-095 and Rainbow County Park. For purposes of this study, sample pH was used to approximate which form of dissolved inorganic carbon (DIC) was likely to dominate the sample (Wood, 2019; Weiner, 2013). All three groundwater samples fell within the


pH range of 6.35 to 10.33 (Table 6). Based on this pH it was assumed that the majority of DIC in the samples consisted of bicarbonate. 3.7 Field Camera The field camera captured a wide variety of activity at the outfall. The camera was useful for describing the pulse flow which occurred on October 14, 2019 (Figure 4). The timing, height and contents of the flow were all visible in field camera images throughout the pulse flow. Throughout the monitoring period, fauna were highly active at the outfall, including avifauna, rodents, and larger mammals (Figure 9). Activities downstream of the outfall, including clearing of vegetation by DPW Roads crews were also captured. However, images from the field camera did not identify a direct source of HF183.

Figure 9. Field Camera Image of Nocturnal Fauna at MS4-SMG-095 on October 23, 2019


4 DISCUSSION

4.1 Classification of Water Sample Geochemical Profiles – Piper Diagram To classify the geochemical composition of the outfall water samples and compare to the composition of the municipal water supply and of the groundwater samples, a Piper diagram was generated (Piper, 1944) (Figure 6). Samples which cluster near one another on a Piper diagram or fall within the same classification are considered to be more similar in their geochemical composition and more likely to share a source of water. To determine the dominant ions in each water sample, the ion concentrations were converted to milliequivalents (meq)/Liter and the percentage of total meq for each ion was calculated. For cations, the percent of calcium, percent of magnesium and the sum of sodium and potassium was calculated and plotted. To determine the dominant anions; the percent of sulfate, percent of chloride and the sum of carbonate and bicarbonate was calculated and plotted. The piper diagram is composed of three sub-diagrams, which compare the percentages for the cations (left triangle), anions (right triangles), and the composite of anions and cations (diamond). The composite is a matrix transformation of the proportion of the cations, sodium and potassium, out of the total cations and the proportion of the anions, sulfate and chloride, out of the total anions. Interpretation of the diagram is based on the intersection of lines drawn from each axis to represent the relative proportion of each component.


Figure 6. Piper Diagram of Geochemical Profile at MS4-SMG-095 and Rainbow County

Park

The anion percentages at both of the groundwater well sites were similar to the anion percentages at MS4-SMG-095. Both of the groundwater well sites and MS4-SMG-095 were dominated by bicarbonate anions. The samples from Rainbow County Park were not as similar to MS4-SMG-095 as the groundwater samples and had no dominant anion type. With respect to cations, the samples from MS4-SMG-095 were most similar to samples from the groundwater well site PR-12. The samples from Rainbow County Park were also similar to MS4-SMG-095 but had a slightly lower calcium percentage. SD-843 was not as similar to MS4-SMG-095 due to the higher percentage of calcium. A comparison of the combined anion and cation composition indicates that MS4-SMG-095 is more geochemically similar to the groundwater well sources than to the Rainbow County Park samples. MS4-SMG-095 and SD-843 are both classified as magnesium bicarbonate type, and PR-12 is a mixed type verging on magnesium bicarbonate type. While PR-12 does not share the same classification type as the outfall, it does appear to have a more similar geochemical profile than SD-843. Rainbow County Park was mixed type verging on sodium chloride type.


4.2 Comparison of Geochemical Profiles – Stiff Diagram A Stiff diagram (Stiff, 1951) was used to the compare the geochemical composition of the outfall samples with the composition of the groundwater and Rainbow County Park samples. A Stiff diagram offers a visual comparison of the relative proportions and quantity of the ions at a site. Cations are plotted on the left side of the diagram and anions on the right. A similar shape between two diagrams indicates a similar geochemical composition. Figure 8 presents a Stiff diagram for MS4-SMG-095, Rainbow County Park and both groundwater wells. To integrate multiple samples for a single site, the average molecular equivalent concentration was used for each analyte; there were four water chemistry samples taken at both MS4-SMG-095 and Rainbow County Park, two samples from PR-12 and one at SD-843. In general, the geochemical profile of samples from MS4-SMG-095 are least similar to the profile of groundwater samples from SD-843. MS4-SMG-095 samples are more similar to Rainbow County park (with the exception of higher calcium at Rainbow County Park) and PR-12 (with the exception of bicarbonate).

Figure 8. Stiff Diagrams of Average Anion and Cation Concentration by Site. (Clockwise from upper left: MS4-SMG-095, Rainbow County Park, GAMA-SD-843, GAMA-PR-12)


4.3 Other Constituents In addition to the Piper and Stiff diagrams, the concentrations of several constituents may be useful in determining the source of dry weather flows at MS4-SMG-095. For instance, fluoride is added to municipal water supplies to improve dental health, including to the supplies provided to the Rainbow Municipal Water District (RMWD). The RMWD receives 100% of potable water supply from the Lake Skinner Water Treatment Plan or the Twin Oaks Valley Water Treatment Plant2. According to the 2018 Annual Water Quality Information Consumer Confidence Report fluoride levels from the two water sources ranged from 0.5-1.1 mg/L (RMWD, 2018). Concentrations in samples collected at the Rainbow County Park ranged from 0.633 to 0.734 mg/L while concentrations in samples from the groundwater wells were much lower, ranging from 0.106 to 0.19 mg/L. MS4-SMG-095 fluoride concentrations ranged from 0.142 to 0.388 mg/L, slightly higher than the groundwater samples but lower than the samples from Rainbow County Park. The highest concentration of fluoride at MS4-SMG-095 was measured in the sample on October 16, 2019 two days after the surge of approximately 3,000 gallons that occurred on October 14, 2019. Chlorine is added as a disinfection agent in the treatment of municipal water supplies. In the RMWD water supply residual chlorine concentrations range from 1.63-2.48 mg/L (RMWD, 2018). Residual chlorine levels in the Rainbow County Park samples ranged from 1.84 to 2.17, within the range reported by the RMWD. While total residual chlorine is not a reliable indicator as it is highly volatile the presence of high levels in MS4 samples may indicate a municipal water source (Geosyntec, 2018). Residual chlorine was not detected at MS4-SMG-095 during this study.

2 Information obtained from www.rainbowmwd.com


5 CONCLUSIONS

The first question posed by this study is to understand the flow conditions where human associated fecal marker HF183 is observed at the outfall, MS4-SMG-095. During the monitoring period, there were no detections of HF183 in samples from the outfall. However, detections during two previous studies indicate that HF183 is intermittently detected at this outfall and is not persistently present. Site observations indicated a potential source of HF183 may be human defecation along the southbound side of the I-15 freeway. The County coordinated with Caltrans to address this potential source and reduce potential for recurrence. Caltrans cleaned the area and also trimmed vegetation to reduce cover and discourage human activities. A full description of these cooperative abatement activities is provided in Attachment F. The second study question seeks to understand the patterns in timing of dry weather flows at MS4-SMG-095. The highest average flow (excluding the large flow event on October 14, 2019) was observed on Wednesday and Thursday mornings, and Tuesday evenings. The large discharge of approximately 3,000 gallons of water on October 14, indicates that intermittent discharges may be occurring and may be the transport mechanism for the intermittent detections of HF183. Several approaches were used to answer the remaining two study questions, how does the chemical composition of dry weather flow at the outfall compare to possible sources including local treated water or groundwater and how much does each water source influence the chemical composition of dry weather flows? Geochemical analysis of dry weather samples and comparison with the municipal water supply as well as nearby groundwater indicate that groundwater is likely contributing to dry weather flows in the outfall but was unable to rule out the influence of the municipal water supply.


6 REFERENCES

Boehm A.B., Graham K.E., and Jennings W.C. 2018. Can We Swim Yet? Systemic Review, Meta- Analysis, and Risk Assessment of Aging Sewage in Surface Waters. Environmental Science & Technology, 52(17), pp.9634-9645.

City of San Diego. 2020. https://www.sandiego.gov/public-utilities/sustainability/recycled-

water/quality. Accessed February 13, 2020. Davis T.A. and Shelton J.L. 2014. Groundwater-quality data in the Santa Cruz, San Gabriel, and

Peninsular Ranges Hard Rock Aquifers study unit, 2011–2012—Results from the California GAMA Program. U.S. Geological Survey Data Series, 874.

Geosyntec Consultants (Geosyntec). 2018. Detecting Groundwater in Dry Weather MS4 Discharges. San

Diego County Watershed Protection Division. San Diego, CA.

Green H.C., Haugland R.A., Varma M., Millen H.T., Borchardt M.A., Field K.G., Walters W.A., Knight R., Sivaganesan M., Kelty C.A. and Shanks O.C. 2014. Improved HF183 Quantitative Real-Time PCR Assay for Characterization of Human Fecal Pollution in Ambient Surface Water Samples. Applied and Environmental Microbiology, 80(10), 3086-3094.

Griffith J.F., Layton B.A., Boehm A.B., Holden P.A., Jay J.A., Hagedorn C., McGee C.D., and Weisberg S.B. 2013. The California Microbial Source Identification Manual: A Tiered Approach to Identifying Fecal Pollution Sources to Beaches; Technical Report 804. Southern California Coastal Water Research Project (SCCWRP): Costa Mesa, CA.

Piper, A.M. 1944. A Graphic Procedure in the Geochemical Interpretation of Water-Analyses. Eos, Transactions American Geophysical Union, 25(6), 914–928.

Rainbow Municipal Water District. 2018. Annual Water Quality Information 2018 Consumer Confidence Report. July 2019. Accessed at https://www.rainbowmwd.com/files/a991d2a5b/RMWD_CCR2018.pdf.

Stiff, H.A., Jr.. 1951, The interpretation of chemical water analysis by means of patterns: Journal of

Petroleum Technology, v. 3. no. 10, section 1: p15,16 and section 2: p3. USEPA (United States Environmental Protection Agency). 1992. NPDES Storm Water Sampling

Guidance Document. Washington D.C. EPA 833-8-92-001. USGS (United States Geological Survey). 2002. Water Quality and Environmental Isotopic Analyses

of Ground-Water Samples Collected from the Wasatch and Fort Union Formation in Areas of Coalbed Methane Development – Implications to Recharge and Ground-Water Flow, Water, Powder River Bain, Wyoming. Water Resources Investigations Report 02-4045. 2002.

Weiner, E.R. 2013. Applications of Environmental Aquatic Chemistry (3rd ed.). Boca Raton, FL:

CRC Press.

WESTON (Weston Solutions, Inc.). 2019a. Rainbow Creek HF183 Monitoring Plan. Prepared for the County of San Diego Watershed Protection Program. November 2019.


WESTON (Weston Solutions, Inc.). 2019b. Quality Assurance Project Plan Rainbow Creek HF183 Monitoring. Prepared for the County of San Diego Watershed Protection Program. November 2019.

WESTON (Weston Solutions, Inc.). 2020. 2018-2019 Rainbow Creek HF183 Monitoring Report. Prepared for the County of San Diego Watershed Protection Program. January 2020.

Wood. 2019. 2018 Dry Weather MS4 Outfall Flow Source Investigation – Final Report. Prepared for the County of San Diego Watershed Protection Program. October 2019.

Wright M.T., Belitz K. and Burton C.A. 2005. California GAMA Program—Ground-water quality in the San Diego Drainages hydrogeologic province, California. U.S. Geological Survey Data Series, 129.

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