Appendix A

3525 Hyland Ave #200 ▪ Costa Mesa, CA 92626 ▪ Main: 714.662.2759

Additional Site Investigation Work Plan

California Military Department – Stockton Field Maintenance Shop #24

8020 South Airport Way, Stockton, California

GeoTracker ID T0607700742

23 August 2024

Prepared for:

California Military Department 10601 Bear Hollow Drive

Rancho Cordova, CA 95670

Prepared By:

Maqbool Qadir, P.E.

Senior Engineer

Chris Drabandt, P.G.

Senior Geologist/Senior Project Manager

8/23/2024

8/23/2024

Date Date

Additional Site Investigation Work Plan April 2024 Stockton Field Maintenance Shop #24

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TABLE OF CONTENTS

ACRONYMS AND ABBREVIATIONS ................................................................... I

1 INTRODUCTION

1.1 Purpose

1.2 Summary of Scope

2 ENVIRONMENTAL HISTORY

2.1 Wash Rack Investigation and Interviews

2.2 Soil and Groundwater Investigations

2.3 Soil and Groundwater Remediation

2.4 Quarterly, Semiannual, and Annual Groundwater Monitoring

3 PRE-FIELD ACTIVITIES

3.1 Permitting, Coordination, and Underground Utility Clearance

3.2 Health and Safety Plan

4 FIELD ACTIVITIES

4.1 Well/Boring Locations

4.2 Soil Boring Advancement

4.3 Soil Gas Well Construction and Decommissioning

4.3.1 Nested Soil Gas Well Construction

4.3.1 Soil Gas Well Decommissioning

4.4 Groundwater monitoring well construction

4.4.1 Well Development

4.4.2 Decontamination

4.5 Sampling Procedures

4.5.1 Sampling Methodology

4.5.2 Soil Sampling and Analysis

4.5.3 Groundwater Sampling and Analysis

4.5.4 Soil Gas Sampling and Analysis

4.6 QA/QC Sampling Procedures

4.7 Investigation-Derived Waste Management

4.8 Boring Locations Survey

4.9 Photographs and Documentation of all Field Activities

4.10 GeoTracker Upload

5 REPORTING

6 REFERENCES

Exhibits Exhibit 1: Soil Gas Probe Construction Diagram

Additional Site Investigation Work Plan August 2024 ii

Figures Figure 1: Site Location Map Figure 2: Proposed Soil Gas Probes and Monitoring Well Map Figure 3: 2023 Annual Groundwater Elevation Map Figure 4: 2023 Benzene in Groundwater Results Map Figure 5: 2023 TPHg in Groundwater Results Map Figure 6: 2023 TPHd in Groundwater Results Map Figure 7: Monitoring Well Diagram

Additional Site Investigation Work Plan April 2024

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ACRONYMS AND ABBREVIATIONS

AS Air sparging bgs below ground surface

BTEX Benzenes, toluene, ethylbenzene, and total xylenes

ºC Degrees Celsius

CAARNG California Army National Guard

CMD California Military Department

COC Constituent of concern

C-O-C Chain-of-custody

COPC Constituent of potential concern

CSMS Combined Support Maintenance Shop

CVRWQCB Central Valley Regional Water Quality Control Board

1,2-DCA 1,2-Dichloroethane

DO Dissolved oxygen

DOT Department of transportation

DPT Direct push technology

DTSC Department of Toxic Substance Control

ECM ECM Consultants

EPA Environmental Protection Agency

ESL Environmental Screening Level

FMS Field Maintenance Shop

HASP Health and Safety Plan

HSA Hollow stem auger

HVDPE High-vacuum dual phase extraction

ISCO In Situ Chemical Oxidation

LEL Lower explosive limit mL/min Milliliters per minute

MIP Membrane interface probe

MRP Monitoring and reporting program

NAD 83 North American Datum of 1983

NAVD 88 North American Vertical Datum of 1988

NAP Natural attenuation parameter

NTU Nephelometric Turbidity Unit

OSHA Occupational Health and Safety Administration

ORP Oxidation-reduction potential

OTIE Oneida Total Integrated Enterprises

OWS Oil-water separator

PID Photoionization detector

QA/QC Quality assurance/quality control

RACR Remedial Action Completion Report

SFBRWQCB San Francisco Bay Regional Water Quality Control Board

SGP Soil Gas Probe

SJCEHD San Joaquin County Environmental Health Department

SVE Soil vapor extraction

PCE tetrachloroethene

TCE trichloroethene

TOC Top of casing

TPHd Total petroleum hydrocarbons as diesel

TPHg Total petroleum hydrocarbons as gasoline

USA North Underground Service Alert of Northern California

USCS Unified Soil Classification System

USEPA United States Environmental Protection Agency

UST Underground storage tank

VEG Vapor Energy Generator

VOC Volatile organic compound

% percent

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1 INTRODUCTION

On behalf of the California Military Department (CMD), ECM Consultants (ECM) has prepared this Wash Rack Investigation Work Plan (Work Plan) to further delineate the lateral and vertical extents of contaminants of concern (COCs) at the CMD Stockton Field Maintenance Shop (FMS) #24 (Site), located at 8020 South Airport Way, Stockton, California. Petroleum hydrocarbons and volatile organic compounds (VOCs) remain in soil, groundwater, and soil gas at concentrations that may warrant further monitoring or Site investigation. The major COCs at the Site include total petroleum hydrocarbons as gasoline (TPHg), total petroleum hydrocarbons as diesel (TPHd), naphthalene, benzene, toluene, ethylbenzene, and total xylenes (BTEX), and 1,2-dichloroethane (DCA). Chlorinated VOCs, including trichloroethene (TCE) and tetrachloroethene (PCE), have been recently detected at the Site from a suspected wash rack located on the northeast corner of the Combined Support Maintenance Shop (CSMS). Figure 1 depicts the location of the FMS #24 Facility on South Airport Way. Figure 2 is a site map showing the locations of the FMS, CSMS, wash rack, and existing and proposed groundwater monitoring wells and soil gas probes.

1.1 PURPOSE

This Work Plan has been prepared pursuant to the Central Valley Regional Water Quality Control Board (CVRWQCB) Request for Sampling and Additional Investigation, California Army National Guard (CAARNG) Stockton, Facility, Field Maintenance Shop #24 (FMS), 8020 South Airport Way, Stockton, San Joaquin County, California, dated 25 May 2023. This Work Plan proposes investigating COC impacts from historical sources (FMS #24) and suspected operations (CSMS wash rack) in groundwater, soil, and soil gas. The investigation considers the potential for contamination in the surface and subsurface soil and groundwater. Upon completion of the Site investigation, a Site Investigation report will be submitted to the CVRWQCB and include all analytical data, field monitoring logs, and monitoring well information (e.g., latitudes, longitudes, elevations, depth to water, well construction information, site maps, and boring logs).

1.2 SUMMARY OF SCOPE

This Work Plan covers the following scope.

1. Permitting and third-party underground utility clearance

2. CSMS coordination and access

3. Utilizing a Site-specific Health and Safety Plan (HASP)

4. One (1) direct push technology soil boring will be advanced to the groundwater table and converted into a groundwater monitoring well (Figure 2). Recent groundwater monitoring data shows that the first groundwater is anticipated to be encountered between 25 to 40 feet bgs. Soil samples will be screened in the vadose zone at two to three-foot intervals.

Up to 3 soil samples may be collected from the boring. One (1) proposed monitoring well (FMS-MW10) will be installed at a depth of approximately 45 feet bgs by hollow-stem auger over-drilling. Groundwater samples will be collected following well development.

5. Two (2) soil borings will be advanced to approximately 15 feet bgs and converted into shallow and deep nested soil gas probes (FMS-SGP-5 and FMS-SGP-6) based on lithology (Figure 2). Screens will be set at approximately 10 and 15 feet bgs but final depth will be selected based on lithology. Soil gas samples will be collected following equilibration.

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6. Four (4) existing soil gas probes (FMS-SGP-1 to FMS-SGP-4) will be decommissioned and filled with cement.

7. Soil, groundwater, and soil gas samples will be analyzed for COCs, including total petroleum hydrocarbons and VOCs.

8. Transport and dispose of solid and liquid waste generated during well installation and soil boring activities.

9. A report will be prepared summarizing the results and all the Site Investigation activities.

2 ENVIRONMENTAL HISTORY

The primary source for petroleum hydrocarbons and related compounds at the Site is the former diesel and gasoline USTs. The former 10,000-gallon gasoline and 5,000-gallon diesel USTs were single-walled steel tanks installed in the early 1950s when the FMS began site fuel operations.

The USTs and associated piping were removed in 1996 (Versar 2004). Soil samples collected during UST and piping removal indicated that diesel fuel and gasoline releases impacted site soils. Subsequent site investigations, groundwater monitoring, and remediation activities conducted at the Site are summarized below.

2.1 WASH RACK INVESTIGATION AND INTERVIEWS

In preparation for site investigation ECM contacted CMD staff Mr. Christopher Chavez, Automotive Supervisor (Personal Communication, 6 November 2023) via email and interviewed Sergeant First Class, Mr. Lupian in person on 16 November 2023 to obtain information about the wash rack operations and history. Below is a summary of ECM’s findings.

Mr. Chavez said the wash rack is in use daily, but he could not provide a starting date or estimate as to how long it has been operating. Mr. Chavez stated that no cleaning agents are used in the wash rack, rather a heated pressure washer is used that helps break down the residual fluids and grease. He noted that no fluids are drained directly into the wash rack, but steam cleaned residual fluids, grime, and grease do go to an oil-water separator (OWS). Mr. Chavez stated that the concrete base of the wash rack is in good condition.

In his in-person interview, Mr. Lupian stated the wash rack has been operational at least since 2018 and he too could not provide a start date. The facility has used a heated pressure washer to clean parts since 2018, and the pressure washer drains into the OWS located beneath the wash rack area. The oil collection and cleanout chamber for the below ground OWS is in the driveway adjacent to the wash rack entrance. Per Mr. Lupian, product (waste oil and solvents) collected in the OWS is removed and disposed of by a facility contractor on an as-needed basis.

An automotive parts washing station is inside the combined support maintenance shop, next to the wash rack entrance. Mr. Lupian stated that this is a microbial parts-washing system that utilizes surfactant-based degreasing solutions named SmartWasher® and OzzyJuice®.

According to the Safety Data Sheets (SDSs), neither of these contain listed VOCs. The contractor that services the wash rack also collects and disposes of material collected in the parts washer collection system.

Neither Mr. Lupian nor Mr. Chavez were aware of any historical spills. If any spills were to occur the facility would be required to document spills in a Spill/Incident Report Form.

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2.2 SOIL AND GROUNDWATER INVESTIGATIONS

Grab groundwater sampling performed in association with follow-up investigations in 2004 (Versar) and 2007 (URS 2007) confirmed site groundwater impacts by petroleum hydrocarbons and related VOCs.

A site investigation performed by Oneida Total Integrated Enterprises (OTIE) in March 2010 included the advancement of five soil borings that were subsequently converted to groundwater monitoring wells (FMS-MW1 through FMS-MW5; Figure 2). Subsequent quarterly (April 2010 to February 2012) and semiannual groundwater monitoring (December 2011 and July 2012) events further confirmed the findings of previous groundwater investigations at the Site.

From 7 to 18 May 2012, OTIE conducted a soil vapor extraction (SVE), air sparging (AS), and high-vacuum dual-phase extraction (HVDPE) treatability study involving four soil borings converted to four SVE wells: FMS-SVE1, dual-nested AS wells FMS-AS1A/B, and HVDPE wells FMS-DPE1 and FMS-DPE2 (Figure 2). The treatability study included one day of SVE testing, two days of AS testing, and two days of HVDPE testing (OTIE 2012).

In February 2013, OTIE advanced 15 membrane interface probe (MIP) borings (MIP-1 through MIP-15) to depths ranging between 45 and 65 feet bgs within the primary source area, an approximately 2,500-square-foot area near the former USTs (OTIE 2013a, OTIE 2013b). The results of the OTIE MIP study provided detailed lithological data and further delineated the horizontal and vertical extents of contamination within the source zone soils and groundwater.

Following analysis of the MIP data, three groundwater monitoring wells were installed between March 6 and 8, 2013. Two wells (FMS-MW6 and FMS-MW7) were placed adjacent to MIP boring locations MIP-14 and MIP-06, and one well (FMS-MW8) was located to evaluate the impact of contaminants of potential concern (COPCs) cross-gradient to the primary source area. At the request of the CVRWQCB, an additional groundwater monitoring well (FMS-MW9) was installed downgradient (northeast) of the source area (Figure 2).

2.3 SOIL AND GROUNDWATER REMEDIATION

The results from the OTIE MIP study, well installations, sampling, and specific capacity testing are summarized in the Technical Letter Report submitted to the CVRWQCB on 14 May 2013 (OTIE 2013a). Using historic assessment data and the results of their investigation, OTIE developed a remedial action treatment program using In-Situ Chemical Oxidation (ISCO) technologies to target the soil and groundwater within the 2,500-square-foot source area. OTIE implemented the ISCO treatment in September 2013 and completed 30-day, 90-day, and 180-day post-injection monitoring per the approved Work Plan for Implementing Interim Remedial Action by In-Situ Chemical Oxidation Treatment (OTIE 2013b). A complete summary and results were provided by OTIE in the Interim Remedial Action Completion Report for In-situ Chemical Oxidation Treatment (OTIE 2014).

In February 2014, ECM completed a second MIP investigation (15 MIP borings and two soil borings) to delineate further the horizontal and vertical impacts to soil and groundwater in the source area. The 2014 MIP soil and groundwater investigation results were presented in the Final Summary Letter Report for Additional Groundwater and MIP Investigation (ECM 2014).

On behalf of the CMD, ECM performed two more rounds of ISCO injections (July/August 2014 and 2015) and post-injection monitoring at the Site. In July and August 2014, ECM performed 36 ISCO injection borings in the source area in the vicinity of FMS-MW5, FMS-MW6, and FMS-MW7.

Injection points were generally advanced to a depth of 45 feet bgs. ISCO reagents were injected over a 10-foot interval between 35 to 45 feet bgs, except for three locations with a 20-foot injection

▪ Page 4 ▪ interval between 25 to 45 feet bgs. ECM also completed 30-day, 90-day, and 180-day post-injection monitoring to comply with monitoring and reporting program (MRP) requirements and reported the results separately from the quarterly groundwater monitoring report. A complete summary of the 2014 ISCO injections and post-injection monitoring results were presented in the Remedial Action Completion Report (RACR) for In-situ Chemical Oxidation (ECM 2015a).

During the ISCO injections in July and August 2015, ECM completed 28 ISCO injection borings in the source area. Injection borings were generally advanced to a depth of 45 bgs (ECM 2015b).

ISCO reagents were injected over a 10-foot interval, between 35 to 45 feet bgs, except for four locations within the UST concrete pad, which were pre-drilled to penetrate the UST concrete anchor pad. Those four locations had a 20-foot injection interval from 35 to 55 feet bgs (ECM 2016a). ECM also performed post-injection monitoring to comply with the Site MRP requirements.

Per an approved CVRWQCB work plan (ECM 2016b), Adanta-ECM JV implemented additional remedial actions consisting of Vapor Energy Generator (VEG) technology and ISCO for soil and groundwater remediation between October and December 2016. The VEG steam injection wells were installed in the last week of October 2016, and the VEG System was operated intermittently at FMS #24 between 7 November and 8 December 2016.

Adanta-ECM completed 23 ISCO injection borings in three targeted treatment areas during a single event. Adanta-ECM oversaw the ISCO injection event on 13 December 2016 and completed the work by 15 December 2016. Injection borings were generally advanced to a depth of 45 feet bgs. ISCO reagents were generally injected over a 10-foot target treatment interval, between 35 to 45 feet bgs. During this injection event, 2,204 pounds (lbs.) of PersulfOx® and 1,278 lbs. of ORC-Advanced® were mixed with water and injected. Results and associated post- ISCO monitoring were reported separately from this semiannual groundwater monitoring event in the 2018 RACR (ECM 2018).

2.4 QUARTERLY, SEMIANNUAL, AND ANNUAL GROUNDWATER MONITORING

Quarterly groundwater monitoring was conducted at the Site between March 2013 and June 2016, with Star completing the quarterly monitoring events through the second quarter of 2015. CMD contracted ECM to conduct groundwater monitoring starting with the 2015 third quarter event.

The third quarter 2016 groundwater monitoring report requested semiannual monitoring and reporting and was subsequently approved by the CVRWQCB. ECM has completed the last five semiannual groundwater and soil gas sampling monitoring and reporting events since November 2019 (ECM 2020a, ECM 2020b, ECM 2021a, ECM 2021b).

The CVRWQCB letter dated 27 May 2022 detailed that groundwater sampling frequency will be conducted annually beginning in 2022 and the discontinuation of natural attenuation parameters (NAPs) in 2022. Accordingly, groundwater monitoring wells at the Site (FMS-MW1 through FMS- MW9) are currently sampled annually.

Per the 2022 CVRWQCB letter, a revision to the 2021 Annual Report with chlorinated solvents for both soil vapor and groundwater was requested. Additionally, the CVRWQCB requested a work plan to 1) investigate the CSMS wash rack and submit a draft investigation work plan to assess whether potential discharges from the wash rack pose a risk to human health and water quality, 2) conduct annual monitoring, and 3) submit a work plan for the installation of a downgradient monitoring well(s), decommissioning of soil gas probes, and replacement of select soil gas probes with nested probes. This request was reiterated in the CVRWQCB’s letter of May 2023, cited in Section 1.1 above. These items are addressed in this Work Plan.

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3 PRE-FIELD ACTIVITIES

3.1 PERMITTING, COORDINATION, AND UNDERGROUND UTILITY CLEARANCE

Prior to conducting any drilling activities, the contractor will procure a California C-57 licensed driller to perform all intrusive work. All work will be coordinated with the appropriate regulatory agencies and airport authorities. A monitoring well permit, and soil boring permit will be obtained from the San Joaquin County Environmental Health Department (SJCEHD).

The contractor will contact Underground Service Alert of Northern California (USA North, aka 811 DigAlert) to identify public and private subsurface utilities in the investigation area a minimum of 72 hours in advance of intrusive field work. All utilities will be marked in the field. Under the direct supervision of the contractor, an independent utility locator will verify clearance of each proposed boring location from underground utilities and fuel systems. The utility clearance survey will include locating fuel system pipelines and associated components, water, electrical, gas, fuel, communication, and sewer utility lines. Upon completion of the independent utility clearance, the contractor will confirm the proposed well locations with representatives from the CMD.

Soil boring and monitoring wells will be located at a safe distance from any fuel pipeline or other underground utility features. Soil borings and monitoring wells will be placed at least six feet beyond the safe drilling distance from any fuel pipeline or fuel system component to prevent damage to the fuel system components.

3.2 HEALTH AND SAFETY PLAN

All work will be conducted per the Site-specific HASP1 and updated to include drilling and well development activities prepared in accordance with Occupational Health and Safety Administration (OSHA) guidelines. A copy of the HASP will be kept onsite for field personnel to reference. The HASP lists the project’s key personnel, route to the nearest emergency room/hospital, Safety Data Sheets for the chemicals of concern, and proposed action response levels.

4 FIELD ACTIVITIES

Central Valley Water Board staff requests to be present when determining the groundwater monitoring well location and to observe the soil gas probe and groundwater monitoring well installations. Contractor to provide the scheduled field dates when available prior to commencing field activities. Initial soil borings will be advanced using direct push technology (DPT) drilling.

Before drilling, a hand auger or post-hole digger will be used at each boring location to advance the borings to a depth of 5 feet bgs to avoid any potential contact with unidentified utilities. Once a depth of 5 feet bgs is reached, the drill rig will advance the DPT to the target depth to identify lithology. Borings will be converted into two nested soil gas wells and one groundwater monitoring well. Borings will be over-drilled with a small-diameter auger drill rod to install the wells. The continuous DPT soil core will be field screened and logged to determine lithology. Soil samples from the vadose zone will be collected for laboratory analysis. Below are additional details on nested soil gas probe installation, groundwater monitoring well installation, and sampling procedures.

1 ECM. 2022. Health and Safety Plan. May 26.

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4.1 WELL/BORING LOCATIONS

Figure 2 depicts the locations of existing soil gas probes and groundwater monitoring wells, the two proposed soil gas probes, and one proposed monitoring well. The proposed nested soil gas probes FMS-SGP-5 and FMS-SGP-6 will be located along the north property fence and north of the wash rack, respectively. The proposed groundwater monitoring well (FMS-MW10) will be placed adjacent to the wash rack area at the northeast corner of the CSMS building. These locations will delineate impacts to soil and groundwater as follows:

• The proposed nested soil gas well FMS-SGP-5 will delineate soil impacts along the fence north of the CSMS building.

• The proposed nested soil gas well FMS-SGP-6 will delineate soil impacts immediately north of the wash rack.

• Groundwater monitoring well FMS-MW10 will delineate soil and groundwater impacts north of the wash rack. This location is immediately downgradient (Figure 3) of the leading edge of the known groundwater plume delineated by wells FMS-MW3 and FMS-MW4 (Figures 4, 5, and 6).

4.2 SOIL BORING ADVANCEMENT

Under the direct supervision of a licensed California Professional Geologist, a California C-57 licensed driller will advance three DPT borings for soil investigation. The DPT drilling will collect soil samples with a dedicated 3.25-inch-diameter by 4-foot-long acetate lined macro-core sleeve.

Continuous soil core will be logged to determine lithology. Boring logs will include the Unified Soil Classification System (USCS) descriptions of soil types by visual and tactile methods; soil color, consistency (e.g., dense, loose, soft, stiff), particle angularity/ roundedness, and estimated gradation; time, date, depth below ground surface, and identification number of all soil samples;

depth to first-encountered water; and depth of equilibrated water table if encountered.

Soil borings will be field screened using a photoionization detector (PID) at no less than 5-foot intervals. The PID will be calibrated using on-site gas calibration techniques at the beginning of each field day. Up to three (3) samples per soil boring will be collected from above, at, and below elevated PID readings. If no elevated PID readings are measured, one sample will be taken at the midpoint of the soil boring and the bottom of the boring (above the water table, if encountered).

In the soil borings to be converted into nested soil gas wells, one soil sample will be collected from each proposed screen interval at approximately 10 and 15 feet bgs. Soil samples will be shipped to a California-certified laboratory and analyzed for COCs.

4.3 SOIL GAS WELL CONSTRUCTION AND DECOMMISSIONING

This section describes the procedures and regulations for the installation of the proposed nested soil gas wells (FMS-SGP-5 and FMS-SGP-6) and the decommissioning of current soil gas probes

(FMS-SGP-1, FMS-SGP-2, FMS-SGP-3, FMS-SGP-4)

4.3.1 Nested Soil Gas Well Construction

Two (2) nested soil gas wells will be installed at the Site. Each soil gas well will be advanced to a target depth of 15 feet bgs. The shallow soil gas screens will be set at approximately 5 feet bgs (based on coarse-grained lithology) and signified with an “A.” The deep soil gas screens will be set at approximately 15 feet bgs (based on coarse-grained lithology) and signified with an “B.” For example, soil gas well FMS-SGP-5B is the soil gas probe at approximately 15 feet bgs. If depths

▪ Page 7 ▪ are modified based on lithology, soil gas probe points will be set a minimum of 5 vertical feet apart.

The soil gas well construction details are shown in Exhibit 1 (DTSC 2015). The wells will have a total depth of 15 feet with a diameter of 3.25 inches. Approximately six inches of Monterey #3 sand (filter pack) will be placed at the bottom of the borehole to minimize airflow disruption to the sampling tip, and a temporary stainless steel or ceramic soil gas point will be set at 14.5 feet bgs.

The soil gas point will be attached to 0.25-inch full or lined Teflon® tubing and shut off at the surface using a Luer lock valve (or similar). An additional six inches of sand will be placed on top of the soil gas probe (deep sand filter pack between 14 to 15 feet bgs). One foot (13 to 14 feet bgs) of dry bentonite granules will be placed immediately above the filter pack. Eight feet of hydrated bentonite (5 to 13 feet bgs) will be placed above the dry bentonite as the transitional seal. The shallow zone will be constructed similarly with the shallow filter pack is between 4 and 5 feet bgs.

The bentonite should be hydrated in a container at the surface, slowly placed, and tamped down the borehole. The dry granular bentonite between the sand pack and the hydrated bentonite prevents hydrated bentonite from infiltrating the filter pack. A cement/bentonite mixture may be used above the dry bentonite to seal the borehole annulus, consistent with California Department of Water Resources Bulletin 74-90 (California Well Standards) (DWR 1991).

A down-hole rod or tremie pipe should be used to support the well tubing in the borehole. The support rod ensures that the probe tip is placed at the proper depth and that the tubing is not touching the well walls. The support rod should be constructed to avoid cross-contamination or ambient air intrusion. Once fill material enters the support rod, the rod will be lifted incrementally to ensure direct connection of well materials and surround lithology. The support rod is only for installation aid and will not remain in the soil boring.

Wells will be completed at the surface in well boxes, and tubing will be closed off using a Luer lock valve, gas-tight valve, or a fitting for capping the tubing to minimize air intrusion from the surface. Well boxes will be completed 0.25-inch above the existing grade to prevent surface runoff infiltration.

4.3.2 Soil Gas Well Decommissioning

Soil gas wells will be decommissioned in accordance with the California Well Standards (Bulletin 74-90) and SJCEHD requirements (Well Standards, SJCEHD, 2005). The SJCEHD requires wells to be destroyed by over drilling to remove soil gas well materials. A minimum one-foot diameter opening will be excavated to at least 3 feet bgs and filled with cement to accommodate future use of the site. The existing soil gas probes (FMS-SGP-1, FMS-SGP-2, FMS-SGP-3, FMS-SGP-4) will be decommissioned by first removing the well casings followed by over drilling and tremie pipe cement grout from the bottom of the boring to the surface and completed to match the surrounding grade. Over-drilled material to be placed in drums to be managed with IDW

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Exhibit 1. Soil Gas Probe Construction Diagram

4.4 GROUNDWATER MONITORING WELL CONSTRUCTION

Soil boring FMS-MW10 be over-drilled by a minimum 8-inch diameter hollow-stem auger for well placement. The well construction details are shown in Figure 7. The groundwater monitoring well will be completed to a total depth of approximately 50 to 60 feet bgs using 2-inch diameter Schedule 40 PVC casing. The monitoring well will be screened from approximately 30 to 60 feet bgs, constructed with a 0.020-inch slotted screen, and #2/12 sand filter pack based upon static groundwater levels. The filter pack will be placed using tremie pipe from the bottom of the borehole to one foot above the top of the screened interval.

A minimum 2-foot-thick hydrated bentonite transitional seal will be placed using tremie pipe above the filter pack. The bentonite transitional seal will be composed of uncoated, bentonite pellets or bentonite chips. Potable water will be used to hydrate the bentonite seal. The transitional seal will hydrate for one hour before placing any annular seal grout material. Actual time to hydrate will

▪ Page 9 ▪ depend on Site-specific conditions and will be determined by the field geologist in consultation with the California-registered Professional Geologist. The annular seal will consist of a cement-bentonite-grout mixture (3-5% Bentonite) set from the bentonite transitional seal the surface. The final step will be to install a flush-mount well box raised 0.25 inches above the surrounding grade.

4.4.1 Well Development

After allowing groundwater to stabilize and cement to cure for 24 hours, the field geologist will measure static groundwater elevations (and free product if present) using an interface probe.

After measuring groundwater elevation, wells will be developed by surging and bailing. Once the well has been sufficiently cleared by bailing, a submersible pump will be used to clean the length of the well screen by running the pump at the highest flow without significant drawdown from the top to bottom in 1 to 2-foot increments. Water quality will be considered stable at the following parameter markers.

• Turbidity less than 10 nephelometric turbidity units (NTUs)

• pH varying less than 0.1 pH units between readings

• Temperature change 0.8-degree Celsius (°C) or less

• Conductivity change of less than 3 percent (%)

All constructed wells will be developed in compliance with the California Department of Water Resources Bulletin 74-90.

4.4.2 Decontamination

Sampling equipment must be cleaned and decontaminated prior to use. Conventional procedures for cleaning and decontaminating sampling equipment can be used but must adhere to the following decontamination guidance:

• The use of laboratory-supplied deionized water is preferred for cleaning and decontamination;

• Commercially available deionized water may be used for cleaning and decontamination;

• Municipal drinking water may be used for cleaning or decontamination;

• Do not use Decon 90®;

• Alconox®, Liquinox®, Citranox®, and SimpleGreen® can be used for equipment cleaning and decontamination; and

• Sampling equipment can be scrubbed using a polyethylene or PVC brush to remove particulates.

4.5 SAMPLING PROCEDURES

Conventional sampling procedures can be used to collect samples for analysis. Powderless nitrile gloves must be worn on hands before collecting samples, handling sample containers, or handling sampling equipment. The sampling Site should be evaluated prior to sampling to identify potential contamination risks and to select dedicated eating, staging, and sampling areas.

4.5.1 Sampling Methodology

The contractor will adhere to the guidelines and recommendations for sampling equipment, sampling containers, personal protective equipment and field clothing, sun and biological protection, personal care products, and food packaging.

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4.5.2 Soil Sampling and Analysis

Each soil sample for laboratory analysis will be placed in an appropriate laboratory-approved container for submittal to the laboratory for analysis. The sample name will consist of the nomenclature, “FMS-MWnn-xx,” where “nn” = well ID, and “xx” = is the depth collected in feet bgs.

A label on each sealed sample will identify the project name, sample number, sampling date and time, and requested laboratory analysis. Samples will be placed into a chilled cooler for transport to a State of California-licensed environmental laboratory for analyses. A completed chain-of-custody (C-O-C) form will accompany all samples.

Soil samples will be analyzed for COCs by the following methods:

• TPH-d by U.S. Environmental Protection Agency (EPA) Method 8015B;

• TPH-g by EPA Method 8260B; and

• VOCs (full list) by EPA Method 8260B, including BTEX, PCE, 1,2-DCA and TCE.

• One composite soil sample for Title 22 Metals, including mercury by EPA Method

6010/7471 (for waste profile)

• Extra volume of soil will be collected for toxicity characteristic leaching procedure

(TCLP) by EPA Method 1611 (for waste profile)

4.5.3 Groundwater Sampling and Analysis

Prior to sampling the wells, all wells will be gauged to establish groundwater flow direction and gradient across the Site. Newly constructed monitoring wells will be sampled after 48 hours of stabilization following well development. Groundwater wells will be purged and sampled following the USEPA guidance for low-stress (low-flow) purging and sampling (USEPA, 1996). During purging, field measurements for dissolved oxygen (DO), oxidation/reduction potential (ORP), pH, electrical conductivity, temperature, and turbidity will be recorded. The contractor should allow for water quality parameter stabilization before collecting samples.

A label on each sealed sample will identify the project name, sample number, sampling date and time, and requested laboratory analysis. Groundwater will be placed directly into laboratory-supplied bottles. Samples will be labeled and placed into a chilled cooler for transport to a State of California-licensed environmental laboratory for analysis under C-O-C protocol. Groundwater samples will be analyzed for COCs by the following methods:

• TPH-d by EPA Method 8015B;

• TPH-g by EPA Method 8260B; and

• VOCs (full list) by EPA Method 8260B including BTEX, PCE, 1,2-DCA and TCE.

• Title 22 Metals, including mercury by EPA Method 6020/7472 (for waste profile)

In accordance with the CVRWQCB monitoring requirements, the proposed new well FMS- MW10, after installation and development, will be monitored quarterly for the first year and then annually thereafter. A licensed Land Surveyor will survey the new wells and calibrate them with the existing wells onsite.

4.5.4 Soil Gas Sampling and Analysis

Rainfall decreases the air-filled porosity of the shallow soil, thereby limiting diffusional transport of volatile contaminants. Also, soil gas contaminants may partition into the clean infiltrating rainwater, both of which may potentially bias soil gas sampling results. Hence, soil gas sampling should not occur during a significant rain event and should only occur after five days without a

▪ Page 11 ▪ significant rain event. A significant rain event is defined as 1/2 inch or greater of rainfall during a 24-hour period. Barometric pressure fluctuations associated with the passage of frontal systems can introduce atmospheric air into the shallow vadose zone. Therefore, soil gas sampling should be delayed until frontal systems have passed the area.

Subsurface conditions are disturbed during drilling and probe placement. To allow for the subsurface to equilibrate back to representative conditions. Soil gas probes installed with the direct push method, the purge volume test, leak test and soil gas sampling will not be conducted for at least two hours following gas probe installation. Soil gas probe installation method and equilibration will be recorded in the field logbook or field form.

Soil gas probes will be leak tested, purged, and sampled in accordance with July 2015 Department of Toxic Substances (DTSC) Active Soil Gas Investigations Advisory1. During purging, subsurface soil gas conditions will be field screened using a five-gas meter (oxygen, carbon monoxide, hydrogen sulfide, lower explosive limits [LEL], and VOCs).

Shroud Design The shroud should be designed to contain the entire sampling train and the soil gas well annulus.

The size of the shroud depends on the sampling equipment used but should be designed to minimize the shroud volume and gaseous leak tracer compound used. The sampling train should be constructed of material that does not react with the sample analytes and will not off-gas or adsorb volatile compounds. The sampling equipment should be clean, and shut-in tested prior to use. Soil gas probes installed with good seals throughout the borehole annulus and the use of compression fittings provide assurance against ambient air leaks.

Shut-in Test Prior to purging or sampling, a shut-in test should be conducted to check for leaks in the above-ground sampling system. To conduct a shut-in test, assemble the above-ground valves, lines and fittings downstream from the top of the probe. Evacuate the system to a minimum measured vacuum of about 100 inches of water using a purge pump. The test is conducted while the sampling canister is attached with its valve in the closed position. Observe the vacuum gauge connected to the system with a “T”-fitting for at least one minute or longer. If there is any observable loss of vacuum, the fittings are adjusted until the vacuum in the sample train does not noticeably dissipate. After the shut-in test is validated, the sampling train should not be altered.

The vacuum gauge should be calibrated and sensitive enough to indicate a water pressure change of 0.5 inches. A shut-in test is not a replacement for a leak test.

Leak Test A leak test is used to evaluate whether ambient air is introduced into the soil gas sample during the collection process. Atmospheric leakage occurs in three ways:

• Advection through voids in the probe packing material and along the borehole sidewall;

• Advection directly through the soil column; and

• Through the fittings in the sampling train at the surface.

A leak test should be conducted at every soil gas well each time a soil gas sample is collected to evaluate the integrity of the sample. Introducing ambient air may result in an underestimation of actual site contaminant concentrations or, alternatively, may introduce external contaminants into samples from ambient air. The two types of leak check compounds available for use when soil gas sampling are liquid compounds and gaseous compounds. Helium is anticipated to be used as the leak test gas method which will in turn be analyzed by the laboratory in each sample.

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The calculation of a leak is based on the ratio of tracer compound concentration in the shroud to that in the sample, assuming that the tracer compound is continuously infused during sampling.

The tracer compound in the shroud should be kept within ± 10% of its target value, and if not achieved then its lowest measured value should be used for calculation purposes.

The soil gas probe and sampling train assembly can be field screened for leaks by drawing purge gas through the well and then through the tracer compound detector while the shroud is in position and filled with the initial tracer compound concentration. Detecting a significant leak in the probe or sampling train at the time of sampling provides the opportunity for the field crew to correct the leak early in the sampling process, thereby ensuring the samples analyzed by the laboratory meet the project- specific DQOs.

Purge Volume Test The purpose of a purge volume test is to ensure that stagnant air is removed from the sampling system and to ensure that samples are representative of subsurface conditions. The purge volume test should be completed after the shut-in and leak test. The test well should be located near the contaminant source zone and in a lithologic unit where soil gas concentrations are anticipated to be elevated. The purge volume test is conducted by collecting and analyzing a sample for target compounds after removing one, three and 10 purge volumes. The purge volume test samples should be analyzed with the same analytical method as the constituents of concern.

One purge volume includes the following volumes:

• The internal volume of tubing;

• The void space of the sand pack around the probe tip; and

• The void space of the dry bentonite in the annular space.

Conduct the purge test at the same flow rate and applied vacuum as will be used to collect the soil gas samples. Select the appropriate purge volume based on the highest concentration of the compound(s) of concern detected during the purge volume test. If VOCs are not detected in any of the step purge tests, a default of three purge volumes will be used.

The purge test data will be included in the report to support the purge volume selection. The data set will include the purge volume test as well as the flow rate, vacuum exerted on the formation, and duration of each purge step.

Purge/Sample Flow Rate Flow rates between 100 to 200 milliliters per minute (mL/min) and vacuums less than 100 inches of water should be maintained during purging and sampling to minimize stripping (partitioning of gas from pore water to soil gas), to prevent ambient air from diluting the soil gas samples, and to reduce variability between contractors. Maintaining these flow rates and vacuums will increase the likelihood that representative samples will be collected. A vacuum gauge should be used between the soil gas sample tubing and the soil gas purging device to verify that 100 inches of water or less is maintained during sampling.

Soil Gas Analysis A California-certified laboratory will provide sample collection equipment and sample analysis.

Samples will be collected in 1-liter Summa® Canisters with dedicated flow regulators. The field crew will record the pressure upon start and completion of the sampling. Typically, canisters are returned to the stationary laboratory with a slight vacuum. Pressure measurements will be collected using a calibrated pressure gauge, using the same gauge at the laboratory and in the field. Field crews will only rely on canister-dedicated pressure gauges if the gauges are calibrated

▪ Page 13 ▪ and working properly. Samples will be analyzed by USEPA modified analytical method TO-15 for TPH-g and VOCs, and by TO-17 for TPH-d.

A chain of custody form will be completed in the field and include any relevant problems encountered during sample collection. The starting and ending pressures for passivated stainless-steel canisters should be recorded on the chain of custody form. To avoid loss or damage, the chain of custody forms should be placed into a sealable bag and attached to the inside of the shipping container.

4.5.4.1 Soil Gas Sampling in Low-Permeability Soil

If soil gas permeability is low within the soil gas process and does not allow sustainable purging at appreciable flow rates without applying excessive vacuum, the alternate low permeability sampling may be conducted. Low flow or no flow conditions correspond to conditions where the minimum flow rate of 100 mL/min cannot be sustained at the maximum applied vacuum of 100 inches of water. ECM followed the protocols as defined by the 2015 DTSC Advisory Active Soil Gas Investigation, Appendix D, and are summarized below. They include the alternative low-flow sample collection method.

Sampling Method

A modified purging and sampling procedure will be used for low-flow vapor probes. Soil gas sampling trains will be leak tested and assessed using the shut-in tests as stated above. Vacuum of the soil gas probe will be applied under a vacuum of 100 inches of water before the flow diminished to a negligible amount, considered to be a flow rate of <100 mL/min. The soil gas well probe valve will then be closed to allow the vacuum to dissipate and to allow the soil gas to slowly enter the sand pack and tubing from the surrounding soils (pulsing). When the vacuum is dissipated, the probe valve will be reopened, and another aliquot of soil gas is collected. This procedure will be repeated until the soil gas well is adequately purged and sampled. In this manner, probes will be appropriately purged, and enough sample volume collected for analysis.

High-quality data can be produced by implementing the following field practices while sampling:

• Good annular seals;

• Careful monitoring of flow rate and vacuum during purging and

• Use of tracer gas for leak testing.

The rate of vacuum dissipation will be monitored with a dedicated vacuum gauge. Additional pressure gauges, fittings, and a flow meter are needed to implement this procedure in the field.

Prior to purging and sampling, the sampling system will be shut-in tested to ensure that vacuum rebound is attributable to subsurface processes and not system leakage. Likewise, leak-detection compounds are utilized during the entire sampling process to confirm the integrity of the sample.

4.6 QA/QC SAMPLING PROCEDURES

The following field sampling quality assurance (QA)/quality control (QC) procedures will be observed for collecting soil and groundwater samples:

• One equipment blank per day will be collected by running deionized water through the DPT inner rod and/or HSA.

• One trip blank per cooler prepared by the laboratory will accompany the samples to the Site and back to the lab.

• One duplicate will be collected from a groundwater sample and submitted for analysis.

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4.7 INVESTIGATION-DERIVED WASTE MANAGEMENT

All soils and fluids generated from this field effort will be stored in Department of Transportation (DOT)-rated 55-gallon steel or polycarbonate drums with removable lids. It is anticipated that ten

(10) drums will be sufficient for the activities described in this Work Plan. Drum labels will identify contents as Non-Hazardous Waste Pending Classification. Labels will also indicate the project name, date, borehole(s), contents (soil or water), and anticipated chemical contaminants. All drums will be temporarily stored in a location designated by the CMD and FSM Group. The contractor will arrange for characterization and disposal of waste soil and fluids.

All drill cuttings will likely be classified as non-hazardous. Laboratory reports will be required for waste characterization prior to disposal.

4.8 BORING LOCATIONS SURVEY

Well locations and top-of-casing will be surveyed by a California-licensed Land Surveyor. The survey data will be reported in North American Datum of 1983 (NAD 83) and North American Vertical Datum of 1988 (NAVD 88). The well survey data will be submitted electronically and in hard copy for GeoTracker submittal requirements with a new site map.

5 REPORTING

Upon completion of field activities and waste disposal, a final Additional Site Investigation Report containing sample coordinate locations, field documentation, initial groundwater and soil gas sample results, laboratory analytical results, depth to water, well construction information (as applicable), Site maps, investigative derived waste handling and disposal documentation including waste manifests, and boring logs will be submitted. The report will be reviewed and stamped by a California-registered Professional Geologist or Professional Engineer and submitted to the Regional Water Board.

Quarterly groundwater monitoring results for FMS-MW10 will be reported in the annual monitoring report for FMS Stockton and submitted to the Regional Water Board.

5.1 PHOTOGRAPHS AND DOCUMENTATION OF ALL FIELD ACTIVITIES

While conducting field activities as described in this Work Plan, the contractor will obtain photographs and document work, as appropriate, at key stages throughout the project.

5.2 GEOTRACKER UPLOAD

Upon completion of the field work and laboratory analyses, boring logs, well completion data, laboratory data, groundwater levels, and the Additional Site Investigation Report will be uploaded into GeoTracker for regulatory review.

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6 REFERENCES

Department of Toxic Substances Control (DTSC) 2015. Active Soil Gas Investigations Advisory, July.

ECM 2014. Final Summary Letter Report for Additional Groundwater and Membrane Interface

Probe (MIP) Investigation, California Military Department Stockton Field Maintenance Shop #24, Stockton, California. April.

_____. 2015. Final Remedial Action Completion Report (RACR) For In-situ Chemical Injection (ISCO), California Military Department Stockton Field Maintenance Shop #24, Stockton, California. 30 September, 2015.

_____. 2015b. Final Summary Letter Report, Soil Boring, PDB Groundwater Sampling, and 30- Day Post Injection Groundwater Monitoring, California Military Department Stockton Field Maintenance Shop #24, Stockton, California. 13 November, 2015.

_____. 2016a. Final Summary Letter Report, 90-Day ISCO Post-Injection Groundwater Monitoring, California Military Department Stockton Field Maintenance Shop #24, Stockton, California. 26 January, 2016.

_____. 2016b. Vapor Energy Generator / In-situ Chemical Oxidation Remedial Work Plan, California Military Department Stockton Field Maintenance Shop #24, Stockton, California.

4 October, 2016.

_____. 2018. Final Remedial Action Completion Report (RACR) For In-situ Chemical Injection (ISCO) and Vapor Energy Generation (VEG), California Military Department Stockton Field Maintenance Shop #24, Stockton, California. 28 February, 2018.

_____. 2020a. 2019 Second Semiannual Groundwater and Soil Gas Monitoring Report and 2019 Annual Report. 18 March.

_____. 2020b. 2020 First Semiannual Groundwater and Soil Gas Monitoring Report. 26 August.

_____. 2021a. 2020 Second Semiannual Groundwater and Soil Gas Monitoring Report and 2020

Annual Report. 2 March.

_____. 2021b. 2021 First Semiannual Groundwater and Soil Gas Monitoring Report. 15 June.

OTIE 2012. Treatability Study Report and Feasibility Evaluation for in-situ Petroleum Hydrocarbon

Remediati…