Attachment_A_-_DDW_August_2024_memo_and_Table_5_Summary_Sheet.PDF

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Public Works Department Water Resources Division

August 1, 2024

Saeedreza Hafeznezami Central District Engineer California State Water Resources Control Board Division of Drinking Water 500 North Central Ave., Suite 500 Glendale, CA 91203

RE: REVISED PROPOSED REVISIONS TO THE CHARNOCK WELL FIELD EARLY WARNING GROUNDWATER QUALITY

MONITORING PROGRAM

Dear Mr. Hafeznezami, The City of Santa Monica (The City) appreciates the opportunity to present the proposed revisions to the State Water Resources Control Board, Division of Drinking Water (DDW), to optimize the Charnock Well Field Early Warning Groundwater Quality Monitoring Program (Program). As discussed with the DDW at the September 14, 2022 meeting and as detailed in the response to DDW’s comments (letter dated June 7, 2024), the City is submitting this request to optimize the Program.

The purpose of the Program is to collect groundwater data from sentry wells within the 1-,2-, 5-, and 10-year capture zones of the Charnock Well Field to provide early warning of groundwater contamination migration towards the well field and to monitor water quality conditions in the vicinity of the well field. Monitoring is conducted in accordance with the DDW-approved Work Plan for Early Warning Groundwater Quality Monitoring, Charnock Well Field Restoration Project (WorleyParsons, 2013), which is provided as Attachment A for reference. Figure 1, provided as Attachment B, shows the current Program monitoring well network, Responsible Party (RP) sites, and the location of the Charnock Well Field. Please note that each RP is responsible for conducting groundwater monitoring in accordance with a Los Angeles Regional Water Control Board (LARWQCB)-approved work plan.

The proposed revisions, as described herein, include:

Update of the Program’s groundwater monitoring well network by replacing four dry Shallow Aquifer monitoring wells with four Upper Silverado Aquifer wells to enhance the monitoring network; and, Modify the list of laboratory analyses currently monitored as part of the Program to focus on key parameters based on a review of the extensive long-term monitoring data collected to date (2017-2022, five years) to provide a more targeted early warning monitoring plan.

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Proposed Revision to the Groundwater Monitoring Well Network

The City proposes to replace four dry Shallow Aquifer (SA) groundwater monitoring wells with four Upper Silverado Aquifer (USA) wells to enhance the coverage of the Program’s monitoring network. As pumping at the Charnock Well Field is not planned to be reduced for the foreseeable future, it is unlikely water levels in dry wells will recover. For this reason, it is recommended that the Program be modified such that four dry SA wells are replaced with existing USA regional monitoring wells, as summarized in Table 1.

Table 1 Current Program Wells and Proposed Replacement Wells

Regional Well or Piezometer

Current Early Warning

Monitoring Frequency

Well Status Recommendation for Existing Well

Proposed Replacement Well

Plume Tracking Monitoring Wells

Shallow Aquifer (SA) Wells RMW-10 Annual Dry Discontinue RMW-23 (USA Well)

RMW-20 Every 2 Years Almost Dry Discontinue RMW-6 (USA Well)

RMW-55 Every 2 Years Dry Discontinue RMW-13 (USA Well)

Upper Silverado Aquifer (USA) Wells RMW-9 Annual Good No Change N/A

RMW-19 Every 2 Years Good No Change N/A

RMW-54 Every 2 Years Good No Change N/A

Ambient Monitoring Wells

Shallow Aquifer (SA) Wells

RPZ-4(1) Every 3 Years Dry No Change N/A

RPZ-7(1) Every 3 Years Almost Dry No Change N/A

RPZ-9 Every 3 Years Perched Discontinue RMW-17 (USA Well)

Upper Silverado Aquifer (USA) Wells

RPZ-5 Every 3 Years Good No Change N/A

RPZ-6 Every 3 Years Good No Change N/A

RPZ-8 Every 3 Years Good No Change N/A

Note:

(1) Although SA Ambient monitoring wells RPZ-4 and RPZ-7 are dry or almost dry, they are retained with the ‘No change’ recommendation in order to monitor water elevations and water quality if saturated conditions re-establish in the regional shallow aquifer at distance from the well field.

As indicated in Table 1, the three ‘plume tracking’ (RMW-10, -20, and -55) and one ‘ambient’ (RPZ-9) SA early warning monitoring wells that are proposed to be replaced are currently dry. These dry SA monitoring wells are paired (i.e., nested well configuration) with four USA early warning monitoring wells (RMW-9, -19, -54 and RPZ-8) that are currently part of the Program and have the same monitoring frequency as their dry SA monitoring well counterparts. Note that there are no known mappable contaminant plumes remaining in the

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Charnock subbasin, so the distinction between plume tracking and ambient morning wells is no longer relevant. Therefore, the replacement wells are proposed as additional monitoring wells in various locations to maintain comprehensive coverage of the capture zones.

The proposed replacement monitoring wells (RMW-23, RMW-6, RMW-13, and RMW-17) are existing USA wells that are currently not part of the Program; however, they were previously a part of the Regional Groundwater Monitoring Program for the Regional Water Quality Control Board (RWQCB), which has now completed, where they were monitored for volatile organic compounds (VOCs) and fuel oxygenates on a semi-annual basis for over 20 years. The proposed replacement wells have been selected based on their locations relative to the well field, the USA capture zones, and PRP sites. The proposed monitoring frequency of the replacement wells are based on their position within the well field capture zones per the existing Program’s methodology (i.e., 1-year capture zone sampled every year, 2-year capture zone every 2 years, and 5- and 10-year capture zones every 3 years):

Monitoring wells RMW-13 and -17 are located within the 1-year capture zone, and they will be monitored annually.

Monitoring well RMW-23 is located within the 2-year capture zone and will be sampled every 2 years.

Monitoring well RMW-6 is located within the 10-year capture zone and will be sampled every three years.

In combination, the four replacement wells provide coverage of the 1-year, 2-year, and 10-year capture zones, prioritize wells that are closer to the Charnock Well Field, and augment the overall scope of the Program.

The rationale for inclusion of the proposed replacement wells is summarized in Table 2. The locations of existing Program wells and replacement wells are shown in Figure 2, provided as Attachment C.

Table 2 Rationale for Selection of Each Proposed Replacement Well

Proposed Replacement Well (Capture Zone)

Proposed Sampling Frequency Rationale for Selecting Replacement Well

RMW-17

(1-Year)

Annual

Located in the 1-year USA capture zone. The well is situated southeast of the well field and is the closest monitoring well to the well field. Located between PRP sites and the well field (Figures 2 [Attachment B] and 3 [Attachment C]).

RMW-13

(1-Year)

Annual Located in the 1-year USA capture zone. The well is situated southeast of the well field, located between PRP sites and the well field (Figures 2 [Attachment B] and 3 [Attachment C]).

RMW-23

(2-Year)

Every 2 Years Located within the 2-year USA capture zone. The well is situated southeast of the well field, located between PRP sites and the well field (Figures 2 [Attachment B] and 3 [Attachment C]).

RMW-6

(10-Year)

Every 3 Years Located within the 10-year USA capture zone. The well is situated proximate to two PRP sites and upgradient of the well field (Figures 2 [Attachment B] and 3 [Attachment C]).

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The proposed Program monitoring schedule and monitoring well network are presented in Table 3 and Figure 3 provided in Attachment D, respectively, for Years 1 through 3. It is anticipated that the annual monitoring program will continue as outlined in Table 3 into the foreseeable future, unless well status changes, adverse water quality results indicate a need to modify the Program (e.g., increased frequency), or at such time as the City requests modifications to the Program and said modifications are approved by the DDW. Refer to Table 4 for proposed modified analytical schedule.

Table 3 Proposed Program Sampling Schedule

Year Year 1 Year 2 Year 3

Wells Sampled Yearly Wells, 2 & 3-year Wells Yearly Wells Yearly Wells

Regional Well/Piezometer ID

Sampling Frequency

Modified Analytical Schedule (Table 4)

Modified Analytical Schedule (Table 4)

Modified Analytical Schedule (Table 4)

Plume Tracking Monitoring Wells

Upper Silverado Aquifer (USA) Wells

RMW-9 Annual

RMW-13 Annual

RMW-17 Annual

RMW-6 Every 3 Years

RMW-23 Every 2 Years

RMW-19 Every 2 Years

RMW-54 Every 2 Years

Ambient Monitoring Wells Shallow Aquifer (SA) Wells

RPZ-4 Every 3 Years

RPZ-7 Every 3 Years

Upper Silverado Aquifer (USA) Wells RPZ-5 Every 3 Years

RPZ-6 Every 3 Years

RPZ-8 Every 3 Years

Proposed Revision of the List of Analytes

Based on a review of the extensive long-term monitoring data collected to date, the City is requesting a modification to the list of laboratory analyses currently conducted as part of the Program to focus on key parameters within the monitoring network. The intent of this request is to optimize the analysis suite to provide a more targeted early warning monitoring plan.

Dataset Evaluation and Analysis

A number of monitoring wells are sampled as part of both the Program and the (now terminated) RWQCB Charnock Well Field Regional Groundwater Quality Monitoring Program. For the purposes of the evaluation herein, all available water quality data collected from the Program for monitoring events between 2017 and

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2022 has been evaluated, as well as data collected under the Regional Groundwater Quality Monitoring Program from wells that overlap with the Program (this includes the replacement wells identified in Table 1).

Statistical analyses were carried out on all parameters, and a summary of this is provided in Attachment E.

For each parameter, Attachment E provides:

The number of sample results, the number and frequency (as a percentage) of detections and non-detections.

The date of the most recent detection (if applicable).

The number and frequency (as a percentage) of Maximum Contaminant Level (MCL) or DDW Notification Levels (NL) exceedances (if applicable).

The number and frequency (as a percentage) of Secondary MCL exceedances (if applicable).

A summary of the statistical analysis is provided below:

Three-hundred and five of the parameters evaluated were not detected at any time between 2017 and 2022.

Two-hundred and forty-two of the parameters evaluated had at least one detection between 2017 and 2022. Of these:

o Eighty-six of the parameters evaluated were classified as ‘unknown’ or Tentatively Identified Compounds (TICs).

o Twenty-five parameters had a detection frequency of less than 5% (not including ‘unknown’ compounds or TICs).

o One-hundred and thirty-one parameters had a detection frequency of greater than 5% (not including “unknown” compounds or TICs).

Rationale for Proposed Modification

Considering the monitoring data collected to date, sufficient information has been collected for an appropriate period of time (five years) and frequency to determine the prevalence and long-term spatial and temporal trends of many water quality parameters currently included in the Program. Based on the data collected and the statistical analysis in Attachment E, the City proposes to modify the analytical schedule as summarized below (note, the modified analyte list and rationale for proposed removal of any parameters is provided in Attachment F-1 and F-2):

Parameters currently included in the Program that fall into the categories described in the following sub-bullets will be maintained (Attachment F-1)_for analysis:

o Parameters that have been detected above MCLs or DDW NLs.

o Parameters that have been detected above Secondary MCLs.

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o Parameters that had a low frequency of detection (less than 5%) for the period 2017 through 2022 but are anticipated to provide continued value to meet the objectives of the Program.

o TICs for volatile organic compounds (VOCs).

o TICs for semi-volatile organic compounds (SVOCs).

Parameters currently included in the Program that fall into the categories described in the following sub-bullets are proposed for removal (Attachment F-2) from the analyte list for the Program:

o Parameters that have had no detections (0% detection frequency) for the period 2017 through 2022.

o Parameters that had a low frequency of detection (less than 5%) for the period 2017 through 2022 and are not anticipated to provide continued value to meet the objectives the Program.

1,2,3-Trichloropropane (TCP) concentrations were below the method reporting limit (MRL) of 0.000005 mg/L in all 111 results associated with the data between 2017 and 2022. While this data meets the criteria:

“Parameters that have had no detections (0% detection frequency) for the period 2017 through 2022.”, 1,2,3- TCP will be retained per the DDW’s request (provided via email on June 19, 2024).

On January 31, 2024, the City met with the DDW to discuss the proposed revisions to the early warning program, and the DDW requested additional information regarding Per- and Polyfluoroalkyl substances (PFAS) being monitored in the Charnock Well Field. PFAS are a large group of synthetic fluorinated chemicals that are very persistent in the environment and are therefore considered emerging chemicals of concern. In August 2019, the City conducted a single proactive monitoring analysis event for 12 PFAS compounds (listed in Table

4) from the five active production wells in the Charnock Well Field; all results returned below the reportable limit, and this data is available on SDWIS (City of Santa Monica – Water System Details).

Table 4 PFAS Compounds Analyzed in Charnock Wells (CH-13, 16, 18, 19, and 20) in August 2019 Perfluorobutanesulfonic Acid (PFBS) Perfluoroctane Sulfonic Acid (PFOS) Perfluorohexanoic Acid (PFHXA) Perfluoroheptanoic Acid (PFHPA) Perfluoroctanoic Acid (PFOA) Perfluorotetradecanoic Acid (PFTA) Perfluorohexane Sulfonic Acid (PFHXS) Perfluorodecanoic Acid (PFDA) Perfluorotridecanoic Acid (PFTRDA) Perfluorononanoic Acid (PFNA) Perfluorododecanoic Acid (PFDOA) Perfluoroundecanoic Acid (PFUNA)

No further analyses for PFAS have been conducted to date in the Charnock Well Field. Therefore, PFAS analysis will be included in the revised Program: the analysis will include all compounds under EPA Methods 533, and the four PFAS analytes not analyzed under EPA Method 533 will be analyzed using EPA Method 537.1. The City proposes to provide results for PFAS constituent monitoring to the DDW following the first sampling event to assess whether ongoing sampling is warranted. If there are no PFAS detections or low-level detections below the notification levels in the first year, PFAS sampling will continue at the regularly scheduled monitoring frequency to confirm the initial sampling results, as outlined in Table 3. If PFAS detections are above notification levels, additional sampling for those compounds detected above notification levels may be considered.

https://sdwis.waterboards.ca.gov/PDWW/JSP/WaterSystemDetail.jsp?tinwsys_is_number=2587&tinwsys_st_code=CA

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Table 5 provides a summary of the modified analyte list for the optimized Program, which the City proposes to implement in the next scheduled sampling event after DDW approval. This modified analytical suite is anticipated to provide sufficient data to meet the objectives for ongoing monitoring of groundwater quality as part of the Program and will continue to be included in the Early Warning Monitoring Reports provided to

DDW.

If groundwater conditions indicate any further modification may be required in the future, it will first be discussed with DDW, and the recommended modification will be submitted to DDW for approval prior to implementation.

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Table 5 Proposed Modified Analytical Program

Category Parameter Method

Inorganic Elements and Chemicals

Aluminum EPA 200.7 & 200.8

Antimony EPA 200.7 & 200.8

Arsenic EPA 200.7 & 200.8

Barium EPA 200.7 & 200.8

Boron EPA 200.7

Cadmium EPA 200.7 & 200.8

Calcium EPA 200.7

Chromium EPA 200.7 & 200.8

Cobalt EPA 200.7 & 200.8

Copper EPA 200.7 & 200.8

Cyanide EPA 200.7 & 200.8

Fluoride EPA 200.7 & 200.8

Iron EPA 200.7

Lead EPA 200.7 & 200.8

Lithium EPA 200.7

Magnesium EPA 200.7

Manganese EPA 200.7 & 200.8

Molybdenum EPA 200.7 & 200.8

Nickel EPA 200.7 & 200.8

Nitrate (as NO3) EPA 200.7 & 200.8

Nitrate + Nitrite (sum as nitrogen) EPA 200.7 & 200.8

Phosphorus EPA 200.7

Potassium EPA 200.7

Selenium EPA 200.7 & 200.8

Silica EPA 200.7

Sodium EPA 200.7

Strontium EPA 200.7

Tin EPA 200.7

Titanium EPA 200.7

Vanadium EPA 200.7 & 200.8

Zinc EPA 200.7 & 200.8

Radionuclides

Beta/photon emitters EPA 900.0 Gross Alpha particle activity (excluding radon and uranium) EPA 900.0

Strontium-90 EPA 905.0

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Category Parameter Method

Uranium EPA 200.8

Volatile Organic Compounds (VOCs)

1,2-Dichloroethane EPA 524.2

1,4-Dioxane EPA 522

1,2,3-Trichloropropane (1,2,3- TCP) EPA 524.2

Benzene EPA 524.2 cis-1,2-Dichloroethylene EPA 524.2

Dichloromethane (methylene chloride) EPA 524.2

Methyl-tert -butyl ether (MTBE) EPA 524.2

Tetrachloroethene EPA 524.2

Toluene EPA 524.2 trans-1,2-Dichloroethylene EPA 524.2

Trichloroethylene EPA 524.2

Vinyl Chloride EPA 524.2

Xylenes EPA 524.2

General Minerals and Physical Parameters

Aggressive Index (corrosivity) SW 9045C

Alkalinity, Total SM 2320B

Bicarbonate EPA 310.1

Carbonate (as CO3) EPA 310.1

Chloride EPA 300.0A

Hardness (Total as CaCO3) SM 2340B

Color SM 2120B

Odor threshold (at 60 deg C) SM 2120B pH EPA 150.1

Surfactants/Foaming Agents (MBAS) SM 5540C

Turbidity EPA 180.1

Chloride, mg/L -

Specific Conductance, µS/cm -

Sulfate, mg/L -

Total Dissolved Solids, mg/L -

Petroleum Hydrocarbons & Fuel Oxygenates tert-Butyl Alcohol (TBA) EPA 524.2 Total Petroleum Hydrocarbons as diesel (TPHd) EPA 8015B

Total Petroleum Hydrocarbons as gasoline (TPHg) EPA 8015B

Unregulated Volatile Organic Compounds (VOCs)

1,2,4-Trimethylbenzene EPA 524.2

2-Nitropropane EPA 524.2

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Category Parameter Method

Chloroacetonitrile EPA 524.2

Naphthalene EPA 524.2

Propionitrile EPA 524.2

TICs (see Attachment F-1 for full list) EPA 524.2

Unregulated Semi-Volatile Organic Compounds (SVOCs)

Naphthalene EPA 8270E

N-Nitrosodi-n-propylamine EPA 8270E

TICs (see Attachment F-1 for full list) EPA 8270E

Manufactured Chemicals Per- and Polyfluoroalkyl Substances (PFAS) EPA 533 & 537.1

Closure

The City requests approval for modification of the Program as outlined herein in a timely manner to allow for the inclusion of the replacement monitoring wells into the Program as soon as possible. Once DDW has provided approval, the City will begin sampling the replacement wells using the modified analytical schedule in the next scheduled sampling event.

The City appreciates the DDW’s continued support of the Project. If you have any questions, please contact me at (424) 299-6733 or via email at alex.waite@santamonica.gov.

Sincerely, Alex Waite, P.E.

Senior Civil Engineer City of Santa Monica 2500 Michigan Ave, Bldg. 1 Santa Monica, CA 90404

CC: Sean McCarthy, State Water Resources Control Board — Division of Drinking Water (via email)

Ashley Dummer, State Water Resources Control Board — Division of Drinking Water (via email)

Terry Kim, State Water Resources Control Board — Division of Drinking Water (via email)

Matthew Megill, State Water Resources Control Board — Division of Drinking Water (via email) mailto:sunny.wang@santamonica.gov.

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ATTACHMENTS

Attachment A: Work Plan for Early Warning Groundwater Quality Monitoring, Charnock Well Field Restoration Project (WorleyParsons, 2013)

Attachment B: Figure 1 - Current Charnock Well Field Early Warning Groundwater Quality Monitoring Well Network

Attachment C: Figure 2 – Locations of Proposed Upper Silverado Aquifer Wells

Attachment D: Figure 3 - Proposed Charnock Well Field Early Warning Groundwater Quality Monitoring Well Network

Attachment E: Statistics for All Available Water Quality Data (2017-2022) [electronic attachment]]

Attachment F: Modified Analyte List and Rationale [electronic attachment]

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Attachment A Work Plan for Early Warning Groundwater

Quality Monitoring, Charnock Well Field

Restoration Project (WorleyParsons, 2013)

CITY OF SANTA MONICA

Work Plan for Early Warning Groundwater Quality Monitoring Charnock Well Field Restoration Project

City of Santa Monica

H0444

September 2012

Revised March 1, 2013

Environment & Water Resources

3901 Via Oro Avenue, Suite 100 Long Beach, CA 90810-1800 USA Telephone: +1 310 547 6400 Facsimile: +1 310 547 6410 worleyparsons.com

© Copyright 2012 WorleyParsons

WORKPLAN FOR EARLY WARNING GROUNDWATER QUALITY MONITORING

CHARNOCK WELL FIELD RESTORATION PROJECT

March 1 2013 Revised Early Warning Groundwater Quality Monitoring Workplan for DPH FINAL Text.doc Page iii

Disclaimer

The information presented in this document was compiled and interpreted exclusively for the purposes stated in this document. WorleyParsons provided this report for City of Santa Monica solely for the purpose noted above.

WorleyParsons has exercised reasonable skill, care, and diligence to assess the information acquired during the preparation of this report, but makes no guarantees or warranties as to the accuracy or completeness of this information. The information contained in this report is based upon, and limited by, the circumstances and conditions acknowledged herein, and upon information available at the time of its preparation. The information provided by others is believed to be accurate but cannot be guaranteed.

WorleyParsons does not accept any responsibility for the use of this report for any purpose other than that stated and does not accept responsibility to any third party for the use in whole or in part of the contents of this report. Any alternative use, including that by a third party, or any reliance on, or decisions based on this document, is the responsibility of the alternative user or third party.

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CONTENTS

1. INTRODUCTION

1.1 Purpose of the Early Warning Groundwater Quality Monitoring

1.2 Site Location and Hydrogeologic Setting

2. EARLY WARNING GROUNDWATER QUALITY MONITORING

2.1 Monitoring Well Selection for Early Warning Monitoring

2.2 Early Warning Groundwater Monitoring Schedule

2.3 Monitoring Well Sampling

2.4 Quality Assurance/Quality Control

2.5 Analytical Schedule

3. CLOSURE

4. REFERENCES

Tables

TABLE 1 EARLY WARNING GROUNDWATER MONITORING WELLS: PROPOSED

MONITORING FREQUENCY

TABLE 2 ANALYTICAL SCHEDULE AND REPORTING LIMITS FOR EARLY WARNING

GROUNDWATER MONITORING WELLS

Figures

FIGURE 1 SITE LOCATION MAP

FIGURE 2 MONITORING WELLS FOR EARLY WARNING GROUNDWATER MONITORING,

SHALLOW AQUIFER

FIGURE 3 MONITORING WELLS FOR EARLY WARNING GROUNDWATER MONITORING,

UPPER SILVERADO AQUIFER

Appendix

APPENDIX 1 ENVIRON PROTOCOL: SAMPLING OF GROUNDWATER MONITORING WELLS

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LIST OF ACRONYMS AND ABBREVIATIONS

1,1-DCE 1,1-dichloroethene bgs below ground surface

City City of Santa Monica

DPH California Department of Public Health

EPA Environmental Protection Agency

MTBE methyl-t-butyl ether

PCE tetrachloroethene

RWQC Raw Water Quality Characterization

TBA tert-butyl alcohol

TCE trichloroethene

US United States

VOC volatile organic compound

CHARNOCK WELL FIELD RESTORATION PROJECT

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1. INTRODUCTION

This document presents the Workplan for Early Warning Groundwater Quality Monitoring for the City of

Santa Monica’s (City) Charnock Well Field. This workplan has been prepared to collect groundwater quality data from the Charnock well field to provide early warning of the groundwater contamination migrating to the well field, to validate model predictions of plume behavior, and to track overall raw water quality conditions within the 10-year capture zone of the Charnock well field. This workplan is submitted to the California Department of Public Health (DPH) as part of the drinking water permitting process for the Charnock Water Treatment Unit and associated facilities.

1.1 Purpose of the Early Warning Groundwater Quality

Monitoring

The purpose of this Early Warning Groundwater Quality Monitoring is to collect groundwater data using sentry wells in order to validate model predictions of methyl-t-butyl ether (MTBE) and tert-butyl alcohol

(TBA) plume behavior created using previous groundwater monitoring data from wells within the area, and to track overall raw water quality conditions within the 10-year capture zone at the Charnock well field.

1.2 Site Location and Hydrogeologic Setting

The Charnock well field is located at 11375 Westminster Avenue in the City of Los Angeles. The well field is located in the Charnock Sub-Basin, one of several fault-block Sub-Basins that make up the

Santa Monica groundwater basin (Figure 1). In the modeled area, the Charnock Sub-Basin trends northwest-southeast and is bordered by a Coastal Sub-Basin to the west and the Crestal Sub-Basin to the east. The Charnock Fault, a relatively impermeable structure throughout its length and depth, separates the Coastal Sub-Basin from the Charnock Sub-Basin. The Overland Fault, also relatively impermeable except near the surface, separates the Crestal Sub-Basin from the Charnock Sub-Basin.

The Charnock Sub-Basin is approximately one mile wide and ten miles long.

The Charnock Sub-Basin contains two aquifers: (1) the Shallow Aquifer, and (2) the Silverado Aquifer.

The Silverado Aquifer is sub-divided into two zones, (a) the Upper Silverado, and (b) the Lower

Silverado. The Charnock wells are screened in the Upper and Lower Silverado Aquifers. The Upper and Lower Silverado Aquifers were the source of groundwater supply until the well field was shut down in 1996 following the discovery of MTBE contamination in the groundwater.

The Silverado Aquifer is present at depths from approximately 100 to 500 feet below ground surface

(bgs) and ranges from approximately 90 to 300 feet thick, and consists primarily of coarse-grained sediments. The Silverado Aquifer is the uppermost water-producing zone within the northern part of

CHARNOCK WELL FIELD RESTORATION PROJECT

March 1 2013 Revised Early Warning Groundwater Quality Monitoring Workplan for DPH FINAL Text.doc Page 2 the Charnock Sub-Basin, and has been the uppermost water-producing zone within much of the Sub-

Basin during periods of relatively heavy groundwater extraction.

Above the Silverado aquifer are two shallower aquifers: (1) the Shallow Aquifer, and (2) an alluvial or surficial aquifer (Perched Aquifer). Much of the Shallow Aquifer was relatively dry during pumping from the Charnock well field, but after pumping ceased in 1996, the saturated thickness of the Shallow

Aquifer increased. Between the Shallow Aquifer and the Silverado Aquifer is the San Pedro Aquitard, a low permeability unit that allows for perched water to occur in places within the Shallow Aquifer

(Environ, 2000).

The Shallow Aquifer is encountered at depths of 30 to 150 feet bgs and ranges from approximately 15 to 80 feet thick. It consists of predominantly coarse-grained sediments. This unit comprises the uppermost water-bearing zone within the south-central part of the Sub-Basin.

CHARNOCK WELL FIELD RESTORATION PROJECT

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2. EARLY WARNING GROUNDWATER QUALITY MONITORING

The MTBE and TBA plumes in the Charnock Sub-Basin are extremely well characterized, including not only 50 regional monitoring wells but also dozens of monitoring wells at individual PRP sites. The regional monitoring wells have been monitored on a quarterly to semi-annual basis for over 13 years, and there are also many years of data from quarterly monitoring of individual PRP sites, which the City tracks on a quarterly basis. These data were used to construct and calibrate the groundwater flow and solute transport model used to estimate the plume migration to the well field, and influent concentration once pumping at Charnock resumes. The modelling is described in detail by WorleyParsons, 2010.

Because the plume is so well characterized and plume behavior is so well known, the purpose of the proposed early warning groundwater quality monitoring is mainly to validate model predictions of plume behavior, and to track overall raw water quality conditions within the 10-year capture zone of the

Charnock well field. Monitoring for early warning groundwater quality will consist of sampling groundwater from selected monitoring wells completed in the Shallow and Upper Silverado aquifers, detailed below.

2.1 Monitoring Well Selection for Early Warning Monitoring

A network of 50 monitoring wells and piezometers have been installed in the vicinity of the Charnock well field. Of these approximately equal numbers are completed in the Shallow Aquifer (21 wells) and the Upper Silverado Aquifer (23 wells), with three wells each completed in the Lower Silverado Aquifer and perched aquifer zones. As previously noted, the principal aquifer units that are contaminated with

MTBE and TBA from fuel releases are the Shallow Aquifer and the Upper Silverado Aquifer.

Of these, twelve wells have been selected for early warning groundwater quality monitoring of the

Shallow Aquifer and Upper Silverado Aquifer. In each aquifer, wells were selected to represent varying distances from the well field, i.e., in the 2-year, 5-year and 10-year capture zones, and also different directions from the well field. Well were selected for two monitoring purposes:

1. To track known MTBE plume migration toward the well field and

2. To monitor ambient groundwater quality within the Charnock Sub-Basin.

Of the twelve wells selected, six are completed in the Shallow Aquifer, and six in the Upper Silverado

Aquifer. The wells selected for groundwater quality sampling are shown in Figure 2 (Shallow Aquifer) and Figure 3 (Upper Silverado Aquifer), along with the respective capture zones for the Charnock wells, and simulated MTBE plumes for September 2006.

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The rationale for selection of each well is provided below:

SHALLOW AQUIFER WELLS

(A) Plume Tracking Wells

RMW-10: Southeast of the well field in the 1 to 2 year capture zone, near the northwest edge of the MTBE plume. This will become the leading edge of the MTBE plume once the Charnock well field begins pumping;

RMW-20: Southeast of the well field, toward the intersection of Sepulveda and Venice, in the 2 to 5 year capture zone, within the upgradient portion of the MTBE plume;

RMW-55: South-southeast of the well field in the 2 year capture zone, within the MTBE plume, near the downgradient leading edge;

(B) Ambient Groundwater Quality Monitoring Wells

RPZ-4: East of the well field in the 5 to 10 year capture zone;

RPZ-7: Northeast of the well field in the 5 to 10 year capture zone;

RPZ-9: East of the well field in the 5 year capture zone.

UPPER SILVERADO AQUIFER WELLS

(A) Plume Tracking Wells

RMW-9: Southeast of the well field in the 1 year capture zone, downgradient of the plume between the MTBE plume and the well field;

RMW-19: Southeast of the well field, toward the intersection of Sepulveda and Venice, in the 5 to 10 year capture zone, within the MTBE plume;

RMW-54: South-southeast of the well field in the 2 to 5 year capture zone, on the downgradient edge of the MTBE plume;

(B) Ambient Groundwater Quality Monitoring Wells

RPZ-8: East of the well field in the 5 to 10 year capture zone;

RPZ-5: East of the well field just beyond the 10 year capture zone;

RPZ-6: Northeast of the well field in the 5 to 10 year capture zone.

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2.2 Early Warning Groundwater Monitoring Schedule

The proposed groundwater monitoring schedule depends on the type of early warning monitoring well and it’s position within the capture zone of the well field, with wells within a shorter capture time to the wellfield scheduled for more frequent monitoring, and wells with a greater capture time to the well field monitored less frequently, as described below. The locations of the early warning monitoring wells with respect to the Charnock Well Field capture zones are shown in Figures 2 and 3, for the Shallow Aquifer and Upper Silverado aquifers, respectively.

1. Plume Tracking Wells: The new direction of MTBE and TBA plume migration is toward the wellfield now that pumping has resumed. The proposed 97-005 groundwater quality monitoring frequency for each plume tracking well along with their position relative to the

Charnock Well Field capture zones are given in the following Table 1. For wells identified for plume tracking, Shallow Aquifer well RMW-10 and Upper Silverado Aquifer well RMW-9,are within the 1.5 year and 0.9 year capture zone of the well field, and downgradient of the MTBE plume, and are therefore scheduled for annual 97-005 groundwater quality monitoring. The capture zones for wells Shallow Aquifer monitoring wells RMW-55 and RMW-20 are 2 and 3 years, respectively; Upper Silverado Aquifer monitoring wells RMW-54 and RMW-19 are within the 2.5 and 6 year capture zones, respectively. Therefore, the proposed monitoring frequency for 97-005 groundwater quality monitoring is every two years. Should unexpected results or detections of concern be identified, the monitoring frequency will be revisited in consultation with DPH.

2. Ambient Groundwater Quality Monitoring Wells: The wells for ambient groundwater quality monitoring are located in portions of the basin without current MTBE or TBA plumes, and therefore there is no current petroleum hydrocarbon contamination to be monitored near the ambient groundwater quality monitoring wells. These wells are precautionary, to help identify new or presently unknown contamination in portions of the Sub-Basin that are not contaminated. Also, these wells, as given in Table 1. below, are in the Charnock subbasin at some distance from the Charnock well field within capture zones ranging from 5 years to 11 years from the Charnock Well Field, Therefore these wells are located in areas where travel time to the well field is at least 5 years. Consequently, groundwater quality monitoring every three years should be adequate to identify any new contamination and provide time for appropriate action. Should unexpected results or detections of concern be identified, the monitoring frequency will be revisited in consultation with DPH.

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TABLE 1. EARLY WARNING GROUNDWATER MONITORING

WELLS: PROPOSED MONITORING FREQUENCY

Charnock Well Field Capture

Zone (years)

Proposed Monitoring

Frequency, Title 22 Analytical

(years) Plume Tracking Monitoring Wells

Shallow Aquifer RMW-10 1.5 yearly RMW-55 2 2 years

RMW-20 3 2 years

Upper Silverado Aquifer RMW-9 0.9 yearly

RMW-54 2.5 2 years

RMW-19 6 2 years

Ambient Monitoring Wells

Shallow Aquifer

RPZ-4 7

3 years RPZ-6 6

RPZ-9 5

Upper Silverado Aquifer

RPZ-5 11

3 years RPZ-6 9

RPZ-8 7

Note that the City’s current regional well monitoring program, under the guidance of RWQCB, will continue on it’s schedule of semi-annual, annual or tri-annual to provide a more complete mapping of

MTBE and TBE plume extent on a semi-annual basis. Monitoring data from the early warning groundwater quality monitoring will be augmented with additional data from the regional monitoring well program and data from individual PRP site monitoring to verify that plume migration behavior and concentrations are within the range expected.

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2.3 Monitoring Well Sampling

Sampling of the selected monitoring wells for early warning groundwater quality monitoring will be conducted in conjunction with ongoing semi-annual groundwater monitoring that is being conducted by the City. Each of the monitoring wells selected for the groundwater quality monitoring will be purged and sampled using the same protocols as the ongoing RWQCB-approved groundwater monitoring program. Prior to sampling, each well will be purged using a decontaminated submersible pump. Field parameters will be monitored during purging using a flow-through cell, and recorded. After purging, samples will be collected using a disposable plastic bailer. Samples will be transferred into pre-cleaned sampling containers with appropriate preservatives provided by the analytical laboratory.

Details of the purging and sampling protocols, including decontamination, by Environ (for the City’s regional well monitoring program) are included in Appendix 1.

2.4 Quality Assurance/Quality Control

Field Quality Control Samples

In order to evaluate the precision and accuracy of analytical data, quality control samples will be prepared as described below. These samples will be collected, or prepared and analyzed by the laboratory, as specified below. Additional details are provided in Appendix 1.

Trip Blanks

A trip blank consists of contaminant-free liquid generated by the container preparer at the laboratory, transported to the field along with the empty sample containers, kept with the sample containers continually, and returned to the laboratory without being opened. Each trip blank will be analyzed for volatile organic compounds (VOCs) by EPA Method 524.2. Frequency of analysis will be one per shipping container with samples for volatile organic parameters.

Duplicates

Duplicate sample is collected at the near-identical time and location of the primary sample. The procedures for obtaining the duplicate are identical to the original; the same container type and sampling technique are used. Each duplicate sample will be analyzed for (VOCs) by EPA Method

524.2, as specified for the primary sample. The frequency of duplicate sample collection will be 20%, that is, one per quarterly sampling event (six wells) and two per annual sampling event (12 wells).

Equipment Rinsate Blanks

Equipment rinsate blanks are used to confirm that the sample bottles and the sampling procedures are not introducing contamination into the samples. Equipment blanks are collected only at wells that are sampled using non-dedicated sampling equipment. After decontamination of the sample pump or bailer and prior to its use, de-ionized water is poured into and through the pump or bailer, and then

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Method 524.2, specified for groundwater samples collected at that well. For this program, the frequency of equipment rinsate blanks will be one per well cluster or sampling site.

Data Validation

Data validation will be conducted following USEPA protocol. All primary sample data collected (i.e., for this program the data from one well) will be validated following USEPA Level II guidelines.

2.5 Analytical Schedule

All groundwater samples collected for early warning monitoring will be analyzed for the list of chemicals under Title 22 of the California Code of Regulations. A complete listing of the analytes together with method detection limits and reporting limits are provided in Table 2. The listing includes tentatively identified compounds (TICs) including Non-Target Volatile Organic Compounds and Non-Target Semi-

Volatile Organic Compounds. The schedules in Table 2 include inorganics (Title 22 Chapter 15 Article

4), VOCs (Article 5.5); Non-volatile synthetic organic chemicals (Article 5.5); Radioactivity (Article 5);

Secondary Drinking Water Standards (Article 16), and Unregulated Chemicals (Article 17).

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3. CLOSURE

We trust that this workplan satisfies your current requirements and provides suitable documentation for your records. If you have any questions or require further details, please contact the undersigned at any time.

Report Prepared by

WorleyParsons

Mark Trudell, PG, CHG

Project Manager

Senior Review by

Taly Williams

Senior Environmental Engineer

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4. REFERENCES

Environ, 2000. “Charnock Initial Regional Response Activities (CIRRA) Task 9, Conceptual Flow and

Transport Model Report”, August 17, 2000.

WorleyParsons, 2010. Effective Monitoring and Treatment, Charnock Well Field Restoration Project, City of Santa Monica. June 2010.

CHARNOCK WELL FIELD RESTORATION PROJECT

196703_2.DOC

Tables

TABLE 2 - ANALYTICAL SCHEDULE AND REPORTING LIMITS FOR EARLY

WARNING GROUNDWATER MONITORING WELLS

(a) Inorganic Elements and Chemicals Charnock Well Field Santa Monica, California

Category Parameter Method DLR a MCL a

Aluminum EPA 200.7 & 200.8 0.05 0.2 b, 1.0 Antimony EPA 200.7 & 200.8 0.006 0.006 Arsenic EPA 200.7 & 200.8 0.002 0.05 Asbestos EPA 200.7 & 200.8 0.2 MFL>10µm 7.0 MFL Barium EPA 200.7 & 200.8 0.1 1.0 Beryllium EPA 200.7 & 200.8 0.001 0.004 Boron EPA 200.7 0.1 - Cadmium EPA 200.7 & 200.8 0.001 0.005 Calcium EPA 200.7 1.0 - Cerium EPA 200.7 0.5 - Chromium EPA 200.7 & 200.8 0.01 0.05 Cobalt EPA 200.7 & 200.8 0.01 - Copper EPA 200.7 & 200.8 0.05 1.0 b, 1.3 c

Cyanide EPA 200.7 & 200.8 0.1 0.15 Fluoride EPA 200.7 & 200.8 0.1 2.0 Iron EPA 200.7 0.1 0.3 b

Lead EPA 200.7 & 200.8 0.005 0.015 c

Lithium EPA 200.7 0.01 - Magnesium EPA 200.7 1.0 - Manganese EPA 200.7 & 200.8 0.005 0.05 b

Mercury EPA 200.7 & 200.8 0.001 0.002 Molydenum EPA 200.7 & 200.8 0.01 - Nickel EPA 200.7 & 200.8 0.01 0.1 Nitrate (as NO3) EPA 200.7 & 200.8 2.0 45 Nitrate + Nitrite (sum as nitrogen) EPA 200.7 & 200.8 - 10 Nitrite (as nitrogen) EPA 200.7 & 200.8 0.4 1.0 Perchlorate EPA 200.7 & 200.8 0.004 0.006 Phosphorus EPA 200.7 1.0 - Potassium EPA 200.7 1.0 - Selenium EPA 200.7 & 200.8 0.005 0.05 Silica EPA 200.7 0.5 - Silt Density Index ASTM D4189 - - Silver EPA 200.7 & 200.8 0.005 0.1 b

Sodium EPA 200.7 1.0 - Strontium EPA 200.7 1.0 - Thallium EPA 200.7 & 200.8 0.001 0.002 Thorium EPA 200.8 0.001 - Tin EPA 200.7 0.1 - Titanium EPA 200.7 0.1 - Vanadium EPA 200.7 & 200.8 0.003 - Zinc EPA 200.7 & 200.8 0.05 5.0 b

DLR - Detection Limit for purposes of Reporting

MCL - Maximum Contaminant Level

MFL - million fibers per liter, MCL and DLR for fiber exceeding 10 µm in length µm - micrometers mg/L - milligrams per liter a - units in mg/L, unless otherwise stated b - Secondary MCL c - Regulatory Action Level; if system exceeds, it must take certain actions such as additional monitoring, corrosion control studies and treatment, and for lead, a public education program; replaces MCL

Source: WorleyParsons Komex, 2008.

Inorganic Elements & Chemicals

Table 2 Early Warning GWM Analytical Schedule.xls Page 1 of 12

(b) Radionuclides Charnock Well Field Santa Monica, California

Category Parameter Method DLR a MCL a

Radium-228 EPA 904.0 1 pCi/L

Uranium EPA 200.8 1 pCi/L 20 pCi/L Beta/photon emitters EPA 900.0 4 pCi/L d 4 millirem/year e

Strontium-90 EPA 905.0 2 pCi/L 8 pCi/L f

Tritium EPA 906.0 1,000 pCi/L 20,000 pCi/L g

DLR - Detection Limit for purposes of Reporting

MCL - Maximum Contaminant Level pCi/L - picocuries per liter µS/cm - microsiemens per centimeter a - units in mg/L, unless otherwise stated d - Gross Beta particle activity e - annual dose equivalent to the total body or any internal organ f - equal to 4 milligrams per year dose to bone marrow g - equal to 4 milligrams per year dose to total body

Source: WorleyParsons Komex, 2008.

5 pCi/L (combined radium-226 & -

228) Gross Alpha particle activity (excluding radon and uranium)

EPA 900.0 3 pCi/L 15 pCi/L Radionuclides

Radium-226 EPA 903.1 1 pCi/L

Table 2 Early Warning GWM Analytical Schedule.xls Page 2 of 12

(c) Volatile Organic Chemicals (VOCs) Charnock Well Field Santa Monica, California

Category Parameter Method DLR a MCL a

Benzene EPA 524.2 0.0005 0.001 Carbon Tetrachloride EPA 524.2 0.0005 0.0005 1,2-Dichlorobenzene EPA 524.2 0.0005 0.6 1,4-Dichlorobenzene EPA 524.2 0.0005 0.005 1,1-Dichloroethane EPA 524.2 0.0005 0.005 1,2-Dichloroethane EPA 524.2 0.0005 0.0005 1,1-Dichloroethylene EPA 524.2 0.0005 0.006 cis-1,2-Dichloroethylene EPA 524.2 0.0005 0.006 trans-1,2-Dichloroethylene EPA 524.2 0.0005 0.01

1,2-Dichloropropane EPA 524.2 0.0005 0.005 1,3-Dichloropropene EPA 524.2 0.0005 0.0005 Ethylbenzene EPA 524.2 0.0005 0.3 Methyl-tert -butyl ether (MTBE) EPA 524.2 0.003 0.005 b, 0.013

Styrene EPA 524.2 0.0005 0.1 1,1,2,2-Tetrachloroethane EPA 524.2 0.0005 0.001 Tetrachloroethane EPA 524.2 0.0005 0.005 Toluene EPA 524.2 0.0005 0.15 1,2,4-Trichlorobenzene EPA 524.2 0.0005 0.005 1,1,1-Trichloroethane EPA 524.2 0.0005 0.2 1,1,2-Trichloroethane EPA 524.2 0.0005 0.005 Trichloroethylene EPA 524.2 0.0005 0.005 Trichlorofluoromethane EPA 524.2 0.005 0.15

Vinyl Chloride EPA 524.2 0.0005 0.0005 Xylenes EPA 524.2 0.0005 1.750 h

DLR - Detection Limit for purposes of Reporting

MCL - Maximum Contaminant Level mg/L - milligrams per liter a - units in mg/L, unless otherwise stated b - Secondary MCL h - MCL is for either single isomer or the sum of the isomers

Source: WorleyParsons Komex, 2008.

EPA 524.2

EPA 524.2

EPA 524.2 1.2

0.005

Monochlorobenzene (Chlorobenzene)

0.0005 0.07

VOCs Dichloromethane (methylene chloride)

0.0005

1,1,2-Trichloro-1,2,2- Trifluoroethane

0.01

Table 2 Early Warning GWM Analytical Schedule.xls Page 3 of 12

(d) Non-Volatile Synthetic Organic Chemicals (SOCs) Charnock Well Field Santa Monica, California

Category Parameter Method DLR a MCL a

Alachlor EPA 505 & 525.2 0.001 0.002 Atrazine EPA 525.2 0.0005 0.001 Bentazon EPA 515.4 0.002 0.018 Benzo(a)pyrene EPA 525.2 0.0001 0.0002 Carbofuran EPA 531.1 & 531.2 0.005 0.018 Chlorodane EPA 505 & 525.2 0.0001 0.0001

1,2-D EPA 515.4 0.01 0.07

Dalapon EPA 515.4 0.01 0.2 Dibromochloropropane EPA 504.1 0.00001 0.0002 Di(2-ethylhexyl)adipate EPA 525.2 0.005 0.4 Di(2-ethylhexyl)phthalate EPA 525.2 0.003 0.004 Dinoseb EPA 515.4 0.002 0.007 Diquat EPA 549.2 0.004 0.02 Endothall EPA 548.1 0.045 0.1 Endrin EPA 505 & 525.2 0.0001 0.002 Ethylene Dibromide EPA 504.1 0.00002 0.00005 Glyphosate EPA 547 0.025 0.7 Heptachlor EPA 505 & 525.2 0.00001 0.00001 Heptachlor Epoxide EPA 505 & 525.2 0.00001 0.00001 Hexachlorobenzene EPA 525.2 0.0005 0.001 Hexachlorocyclopentadiene EPA 525.2 0.001 0.05 Lindane EPA 505 & 525.2 0.0002 0.0002 Methoxychlor EPA 525.2 0.01 0.03 Molinate EPA 525.2 0.002 0.02 Oxamyl EPA 531.1 & 531.2 0.02 0.05 Pentachlorophenol EPA 515.4 & 525.2 0.0002 0.001 Picloram EPA 515.4 0.001 0.5 Polychlorinated Biphenyls (PCBs) EPA 505 0.0005 0.0005 Simazine EPA 525.2 0.001 0.004 Thiobencarb EPA 525.2 0.001 0.001 b, 0.07 Toxaphene EPA 505 0.001 0.003 2,3,7,8-TCDD (Dioxin) EPA 1613 5.E-09 3.E-08 2,4,5-TP (Silvex) EPA 515.4 0.001 0.05 Tentatively Ident. Cmpds (TICs) EPA 525.2 * -

DLR - Detection Limit for purposes of Reporting MCL - Maximum Contaminant Level mg/L - milligrams per liter a - units in mg/L, unless otherwise stated b - Secondary MCL

* - Tentatively Identified Compound; no reporting limit available, assume 0.05 mg/L Source: WorleyParsons Komex, 2008.

Non-Volatile

SOCs

Table 2 Early Warning GWM Analytical Schedule Revised.xlsPage 4 of 12

(e) General Properties Charnock Well Field Santa Monica, California

Category Parameter Method DLR a MCL a

Aggressive Index (corrosivity) SW 9045C 0.01 - Alkalinity, Total SM 2320B 2.0 - Bicarbonate EPA 310.1 1.0 - Carbonate (as CO3) EPA 310.1 1.0 - Chloride EPA 300.0A 1.0 - Hardness (Total as CaCO3) SM 2340B 10 -

Category Parameter Method MRL a MCL a

Color SM 2120B 3 ACU 15 Units b

Foaming Agents (MBAS) SM 5540C 0.05 0.5 b

Odor threshold (at 60oC) SM 2120B 1 ton 3 Units b pH EPA 150.1 0.01 - Turbidity EPA 180.1 0.05 NTU 5 Units b

Recommended Upper Short Term Total Dissolved Solids, mg/L 500 1,000 1,500 Specific Conductance, µS/cm 900 1,600 2,200 Chloride, mg/L 250 500 600 Sulfate, mg/L 250 500 600

DLR - Detection Limit for purposes of Reporting

MCL - Maximum Contaminant Level

MBAS - Methylene Blue Active Substances mg/L - milligrams per liter µS/cm - microsiemens per centimeter

ACU - Apparent Color Units

NTU - Nephelometric Turbidity Units a - units in mg/L, unless otherwise stated b - Secondary MCL

Source: WorleyParsons Komex, 2008.

MCL Ranges

General Minerals

Genera…