3_140R2021Q0086_Atch_1_CAP_T0605500304.PDF

Corrective Action Plan Former Putah Creek Resort Lake Berryessa, California

Prepared for:

United States Bureau of Reclamation

Mid-Pacific Region Regional Office

Division of Acquisition Services

Order No. R15PX00826

April 7, 2017

Submitted by:

April 7, 2017

Ms. Vera Fischer Central Valley RWQCB 11020 Sun Center Drive, Suite #200 Rancho Cordova, CA 95670-6114

Re: Corrective Action Plan Former Putah Creek Resort Lake Berryessa, California

Dear Ms. Fischer, On behalf of the United States Bureau of Reclamation, Sierra West Consultants, Inc. is pleased to submit the enclosed Corrective Action Plan for the Former Putah Creek Resort on Lake Berryessa in Napa County California. This submittal is in accordance with the Central Valley Regional Water Quality Control Board’s letter dated November 18, 2016.

If you have any questions, please contact Mr. Michael Biever with the Bureau of Reclamation at 916-989- 7170 or mbiever@usbr.gov.

Sincerely, Jeffrey C. Bensch, P.E. Brian Whalen, P.G.

Principal Engineer Project Geologist

Cc: Michael Biever, USBR Peter Funkhouser, USBR, Lake Berryessa Field Office jbens Jeff Signature jbens PE NoSignature swc Signature - Blue i

Table of Contents Corrective Action Plan

Former Putah Creek Resort UST Site

1.0 Introduction

2.0 Site Background Information

2.1 Site Location and Description

2.2 Site History

2.3 Site Geology and Hydrogeology

2.4 Conceptual Site Model

2.5 Hydrocarbon Mass Estimate

3.0 Pilot Study Results

3.1 Bench-Scale Testing

3.2 SVE/AS Field Test

3.2.1 Pilot Test SVE Extraction and AS Injection Times

3.2.2 Vapor Extraction Monitoring

3.2.3 Influence on Surrounding Wells

3.2.4 Estimated Mass Removal

3.3 Groundwater Performance Monitoring

3.4 Evaluation of Remedial Alternatives

4.0 Corrective Action Plan

4.1 System Design and Permitting

4.2 Well Installations

4.2.1 Pre-Field Activities

4.2.2 Drilling and Well Construction

4.2.3 Development and Surveying

4.2.4 Waste Characterization and Disposal

4.3 SVE/AS System Installation

4.3.1 SVE/AS Equipment

4.3.2 SVE/AS Operations Approach

4.3.3 Permits

4.3.4 Power Supply

4.3.5 Vapor Performance Monitoring

4.3.6 SVE/AS System Maintenance

4.2.7 Waste Characterization and Disposal

4.4 Groundwater Performance Monitoring

4.5 Budget for Implementation

4.6 Regulatory Compliance

4.7 Draft Fact Sheet

4.8 Schedule

5.0 References

ii

Figures

Figure 1 Vicinity Map Figure 2 Site Plan Figure 3 Cross Section of Pilot Study Area Figure 4 Pilot Test Configuration Figure 5 Influent Vapor Concentration vs. Time Figure 6 SVE/AS Well Layout Figure 7 SVE/AS Well Layout with ROI Figure 8 Remediation Well Construction Details Figure 9 SVE/AS Piping Layout

Tables

Table 1 SVE System Operating Parameters Table 2 Groundwater Performance Monitoring Results – Constituents of Concern Table 3 Groundwater Performance Monitoring Results – Biodegradation Parameters Table 4 Proposed Well Construction Details

Appendices

Appendix A Figures from 4Q16 Monitoring Report Appendix B Cross Sections and Analytical Results from 2010 Investigation Appendix C Boring Logs Appendix D Hydrocarbon Mass Estimates Appendix E Draft Fact Sheet and Distribution List

1.0 Introduction

This Corrective Action Plan (CAP) has been prepared for the Former Putah Creek Resort Underground Storage Tank (UST) site located at 7600 Knoxville Road in Napa County, California (Site). The Site location is shown on Figure 1. USTs at the Site have been removed and gasoline related constituents are present in subsurface soils and groundwater. Cleanup of these impacts is needed to achieve regulatory approval and allow for future economic development of the property.

Pilot study activities were performed during 2016, and included: redeveloping existing wells, installing one remediation test well, drilling four soil borings and collecting samples along the Lake Berryessa shoreline, performing bench-scale laboratory tests using site soils and groundwater, and performing a five-day pilot test using soil vapor extraction and air-sparging (SVE/AS) technologies. These activities were performed consistent with Sierra West’s Pilot Study Work Plan dated August 27, 2015, and Pilot Study Work Plan – Addendum for Shoreline Soil Borings (Work Plan Addendum) dated January 28, 2016; as well as with the Central Valley Regional Water Quality Control Board’s (RWQCB) response letters dated October 23, 2015 and February 25, 2016, respectively.

Pilot study results were favorable, and the Pilot Study Summary Report was submitted to the RWQCB on July 1, 2016 (Summary Report). The Summary Report contained an evaluation of remedial alternatives, and based on anticipated costs and effectiveness, SVE/AS was selected as the preferred remedial alternative.

Sierra West recommended preparing this CAP for implementation of SVE/AS, and the RWQCB concurred with the recommendation in their response letter dated November 18, 2016.

This CAP presents the following:

Site background information is presented in Section 2.0;

Pilot study results are summarized in Section 3.0; and, The CAP is presented in Section 4.0.

2.0 Site Background Information

This section reviews the Site location and history, describes geologic and hydrogeologic conditions, and presents the extent of constituent impacts at the Site. Information regarding the Site’s history has been guided by the Former Putah Creek Resort, Lake Berryessa, California, Semi-Annual Monitoring Report, Fourth Quarter 2016 Monitoring Event as prepared by the Bureau of Reclamation, dated January 17, 2017 (4Q16 Monitoring Report). Selected figures from the 4Q16 Monitoring Report are included in Appendix A.

2.1 Site Location and Description

The Site is located on the western shore of Lake Berryessa, approximately 35 miles northeast of the City of Napa (Figure 1). The Site is situated on a small peninsula that is bordered on the east and west by Lake Berryessa, and on the north by the Putah Creek inlet to the lake. The main constituents of concern (COC) at the Site are total petroleum hydrocarbons as gasoline (TPHg), benzene, toluene, ethylbenzene, and total xylenes (BTEX), and methyl tertiary butyl ether (MTBE). A Site Plan showing the locations of wells and other Site features is included as Figure 2.

2.2 Site History

The following is a brief description of the Site’s history, including remediation activities:

September 1990 - According to Napa County records, on September 4, 1990, approximately 760 gallons of unleaded gasoline were released from a UST due to a leaking pipe.

May 1993 - An initial investigation determined that petroleum hydrocarbons had impacted soil and groundwater beneath the Site.

April 1995 - Two 8,000-gallon USTs were removed from the Site on April 4, 1995. Approximately 4,000 cubic yards of hydrocarbon impacted soils were excavated, stockpiled, and aerated on-Site. Following aeration, the stockpiled soil was then graded and compacted on the western side of Knoxville Road.

January 1999 - October 2001 - Monitoring wells were installed at the Site. Initial monitoring wells installed detected TPHg in groundwater ranging up to 340,000 micrograms per liter (μg/L).

April 2002 - April 2004 - An ozone injection system consisting of 13 fine-bubble sparge wells was installed.

The sparge wells were installed along the southern shoreline of the peninsula as a barrier system, where dissolved phase impacts threatened to discharge to the lake. After beginning operation of the ozone system, elevated system pressures were observed that indicated clogging, that was attributed to precipitation of iron onto the sparge points. The ozone system operated for less than one year due to ongoing difficulties, and the sparge wells were subsequently destroyed in 2004.

September 2003 - An Interim Remedial Action Plan was completed on September 30, 2003 that proposed a groundwater extraction and treatment (GET) system. The design flow rate was four to seven gallons per minute (gpm).

April 2004 - August 2008 - A GET system was installed in 2004, and operated during two distinct periods.

From April 2004 to January 2006, the GET system treated water from four wells. From March 2007 to August 2008, the GET system treated water from seven wells. Operation of the GET system was discontinued during the fourth quarter of 2008 because the extraction rate had decreased to less than one gpm. Minimal groundwater recharge was attributed to drought conditions, and the underlying fractured shale and siltstone units inhibiting effective transmissivity of the groundwater.

July 2009 - The RWQCB submitted Cleanup and Abatement Order No. R5-2009-0704, and Monitoring and Reporting Order R5-2009-0819 to the Bureau of Reclamation during July of 2009. The Bureau of Reclamation established a groundwater monitoring program and is currently complying with the Monitoring and Reporting Order.

August 2010 - The Site was further characterized during August 2010. This effort involved drilling 27 borings to depths ranging from 25 to 45 feet and installing five new monitoring wells (MW-16, 17, 18, 19, and 20). The purpose of the additional characterization was to sample and analyze soil, and to delineate the extent of COCs in groundwater and soil to the north, east and south of the site. Soil cuttings from the borings were described and geophysical well logs were used (natural gamma ray, caliper, short and long induction resistivity logs) to characterize the soil. This effort indicated that petroleum constituents in the soil were primarily located a few feet above the groundwater, and more specifically, no shallow impacts were found underneath structures formerly present at the site. Cross sections and analytical results from the 2010 investigation are included as Appendix B.

July 2011 - November 2012 - ACCORD Engineering, Inc. conducted a dual phase extraction (DPE) pilot study to assess the effectiveness and ability of DPE technology to remediate residual hydrocarbon impacts from soil and groundwater at the Site. Results of the DPE pilot test were described in the 2011-2012 Dual Phase Extraction Pilot Test Study and Treatment Report (Accord Engineering, 2012) (DPE Report). During the pilot test, the effective radius of influence was estimated to be 17 feet, and more than 1,100 pounds of petroleum hydrocarbon mass were extracted. It was determined, however, that DPE was not a cost-effective long-term remedy for the Site, and monitored natural attenuation was recommended as the preferred remedy.

The DPE Report also included a Human Health Risk Assessment (HHRA) (Enviro-Tox Services, Inc., 2012). The HHRA presented a Conceptual Site Model that included incomplete exposure pathways for ingestion, dermal contact, and indoor air. Inhalation of soil vapors through outdoor air exposure to recreational visitors was determined to be the only complete exposure pathway. Using the COC concentrations present in 2012, the calculated exposure risks were acceptable.

May 2014 - Present - The RWQCB issued a letter on May 2, 2014 comparing Site conditions to the Low- Threat Closure Policy. It was determined that existing concentrations were elevated, the plume length was excessive, and Lake Berryessa was too close for the Site to qualify under the Low-Threat Closure Policy.

The RWQCB stated: “Active remediation is needed to reduce contaminant mass and concentrations and to move this Site towards a finding of No Further Action Required”. This directive did not preclude future use of the Low-Threat Closure Policy as a means to closure.

On June 6, 2014 the RWQCB issued review comments on the HHRA. The RWQCB indicated that groundwater underlying the Site does have a beneficial use, although the current ingestion pathway is incomplete. The RWQCB stated, “All groundwater is designated as having beneficial use for domestic and municipal water supply in the Central Valley Water Quality Plan”, and “concentrations of benzene and MTBE …are in direct contact with the public drinking water resource of Lake Berryessa. The drinking water standards for these chemicals are 1 ug/L and 13 ug/L respectively”. This letter also avoided numerical groundwater cleanup goals when the RWQCB stated, “cleanup should be conducted to remove as much mass as technically feasible from this Site”.

On December 9, 2014 the Bureau of Reclamation met with the RWQCB to discuss remediation activities at the Site. Following this meeting, the RWQCB issued a letter on December 31, 2014 requiring:

- Submission of a Pilot Test Work Plan for in-situ treatment options;

- Completion of approved pilot test and submission of the results;

- Submission of a Feasibility Study (FS) Report and Corrective Action Plan (CAP) selecting the most cost effective remedial strategy;

- Implementation of the CAP.

On August 27, 2015, Sierra West submitted the Pilot Study Work Plan (Work Plan) to the RWQCB. The Work Plan recommended installing one double-completion air-sparge well (AS-1A/1B), collecting samples for a bench-scale study, and performing a five-day SVE/AS field test. In their letter dated October 23, 2015, the RWQCB conditionally approved the Work Plan, and also provided a directive to collect grab groundwater samples along the Lake Berryessa shoreline to laterally and vertically delineate the extent of hydrocarbon impacts.

On January 28, 2016, Sierra West submitted the Pilot Study Work Plan – Addendum for Shoreline Soil Borings (Work Plan Addendum) to the RWQCB. The Work Plan Addendum proposed advancing four soil borings along the shoreline (B-28 through B-31), and collecting depth discrete groundwater samples at 10, 20, and 30 feet below ground surface (bgs). The RWQCB provided conditional approval of the Work Plan Addendum in their letter dated February 26, 2016. Drilling of B-28 through B-31 and installation of AS- 1A/1B was performed on March 28 through 30, 2016, consistent with the Work Plan and Work Plan Addendum, and in accordance with directives provided by the RWQCB. Results from the drilling activities were described in the Supplemental Site Assessment Report, submitted to the RWQCB on June 14, 2016.

The SVE/AS pilot test was conducted in May 2016. SVE was applied to well MW-14, while periodic air sparging was performed on dual completion AS-1A/1B. Significant quantities of petroleum hydrocarbons were extracted and treated during the pilot study using SVE/AS. Performance monitoring groundwater samples were collected before and after the pilot study, and indicate that the pilot test activities mobilized petroleum hydrocarbons bound to subsurface soils. Pressure and vacuum monitoring conducted through the pilot study indicate that significant interconnectivity exists through subsurface lithology. Additionally, results from the bench-scale test show that the addition of oxygen to subsurface soils and groundwater is an effective means of contaminant mass removal.

Pilot test results were submitted to the RWQCB in the Pilot Study Summary Report, dated July 1, 2016 (Summary Report). The Summary Report described well redevelopment, bench-scale testing, and SVE/AS performance data. The Summary Report also presented an evaluation of potential remedial alternatives, and concluded with a recommendation that SVE/AS be the preferred alternative. In their letter dated November 18, 2016, the RWQCB concurred with Sierra West’s recommendation to prepare a Corrective Action Plan (CAP) to implement SVE/AS at the Site.

2.3 Site Geology and Hydrogeology

The geology of the Lake Berryessa region is structurally complex, containing folded and faulted sedimentary rock, mélange, ophiolite, and volcanics. Subsurface lithology at the Site consists of fractured and folded sedimentary rock with complex soil geology. The depth to siltstone and claystone units, and the thickness of the overburden varies across the Site. In previously drilled wells and borings at the site, fractured shale or mudstone has been encountered at depths ranging from less than 10 feet to greater than 30 feet bgs.

Outcrops of mudstone, sandy claystone, sandstone, and conglomerate along the beach directly south of the old concessionaire store have been encountered. Boring logs from previous site investigations are included as Appendix C.

It was previously reported that rocks near the former Putah Creek Resort concessionaire area have been folded into a southeast-plunging anticline, with an axis trending approximately N15°W under the location of the former restaurant, and with beds dipping away from the anticline axis to the northeast (Accord Engineering, 2011). Geology observed in the vicinity of wells used in the pilot-test (MW-14, MW-16, AS- 1A/1B, and MW-14) are consistent with the presence of the previously reported anticline axis. A cross section showing well construction details and geology in the pilot study area is included as Figure 3.

Groundwater at the Site shows a strong correlation with fluctuations in the surrounding lake’s water level.

Historically, water levels in the monitoring wells at the site have ranged from 2 feet to over 25 feet bgs. The general groundwater flow at the site is to the south, towards the lake shoreline. Groundwater elevation contour maps from the 4Q16 Monitoring Report are included in Appendix A.

2.4 Conceptual Site Model

The impacted area of the Site is along approximately 300-feet of Lake Berryessa shoreline at the Putah Canyon Recreation Area campground site (Appendix A). The shallow geology consists of silts, clayey silts, fractured shale, or mudstone that limit permeability. Significant TPHg, BTEX, and MTBE impacts are present in the groundwater and likely within soils at the groundwater interface (smear zone).

Sensitive receptors are potential future uses of the groundwater and potential migration of impacts into Lake Berryessa. Future groundwater uses are unlikely next to the lake, and no impacts have been observed in the lake. No buildings are present in the vicinity of the impacts, and as such, there are no indoor air exposure pathways. Future building construction in the area is unlikely because of the steep terrain and proximity to the Lake Berryessa shoreline. Potential exposure to soil gas vapors and dermal contact would be limited to possible excavation or well drilling construction activities.

2.5 Hydrocarbon Mass Estimate

Hydrocarbon mass estimates have been completed to quantify TPHg mass in soil and groundwater. Figures and tables used to approximate TPHg mass are presented in Appendix D. Hydrocarbon mass estimates for soil are based on analytical results from the 2010 investigation. As shown in the cross sections and data tables included in Appendix C, TPHg impacts to soils have been divided into a shallow interval (0’ to 25’) and a deep interval (25’ to 45’). Hydrocarbon mass estimates for groundwater are based on analytical results from the monitoring event performed during the second quarter of 2016 (Appendix A).

TPHg impacts to soil in the shallow interval (0’ to 25’) are primarily located in the source area, and have an estimated areal extent of 4,800 square feet (ft2). Source area soils are relatively clean from ground surface to 15 feet bgs, therefore the shallow interval of TPHg impacts to soil is estimated to be from approximately 15 to 25 feet bgs, having a thickness of 10 feet. Using an area of 4,800 ft2, a thickness of 10 feet, and average constituent concentrations from the 2010 soil borings, the estimated mass of TPHg in shallow soils is approximately 3,700 pounds.

TPHg impacts to soil in the deep interval (25’ to 45’) are more widespread than shallow impacts, having migrated away from the source area. The areal extent of TPHg impacts in deep soils is 25,300 ft2. The majority of TPHg impacted soils in the deep interval are from approximately 25 to 40 feet bgs, having a thickness of 15 feet. Using an area of 25,300 ft2, a thickness of 15 feet, and analytical data from the 2010 soil borings, the estimated mass of TPHg in deep soils is approximately 32,600 pounds.

Given the Site’s proximity to Lake Berryessa, groundwater levels have a historically wide range of fluctuation. In source area monitoring wells, the depth to groundwater typically ranges between 10 and 25 feet bgs. TPHg was observed in several source area borings at depths extending to 40 and 45 feet bgs. As such, the zone of TPHg impacts to groundwater is estimated to be from 15 to 45 feet, having a thickness of 30 feet. The areal extent of TPHg impacts to groundwater is approximately 36,700 ft2. Concentrations of TPHg from wells sampled during the second quarter 2016 groundwater monitoring event were averaged to calculate constituent mass in groundwater. Also, an average porosity of 35% for these soils is used for estimating purposes. Based on these factors, the remaining mass of TPHg in groundwater was calculated to be approximately 2,000 pounds.

3.0 Pilot Study Results

Pilot study activities were conducted during the spring and summer of 2016, consistent with the Work Plan and Work Plan Addendum, and included: drilling remediation well AS-1A/1B and soil borings B-28 through B-31; redeveloping all of the Site monitoring and remediation wells; bench-scale testing;

groundwater performance monitoring; and, a 5-day SVE/AS pilot test. The pilot test results were presented in the Pilot Study Summary Report (Sierra West, July 1, 2016) and accepted by the RWQCB in their letter dated November 18, 2016. Selected activities and findings from pilot study activities are summarized in the following sections.

3.1 Bench-Scale Testing

As reported in the Pilot Study Summary Report, a bench-scale test was performed to evaluate the effectiveness of in-situ bioremediation using Site soils and groundwater. Reactors containing Site soils and groundwater were set up and sampled after 14 and 28 days. The water samples were analyzed for TPHg, BTEX, MTBE, dissolved oxygen, ORP, and pH. Results of the bench-scale test are summarized in the following table:

Summary of Bench-Scale Testing Results

Analyte (µg/L, unless noted otherwise)

Nitrogen Control Sterile Control Oxygen – 10% Oxygen – 20%

Day 14 Day 28 Day 14 Day 28 Day 14 Day 28 Day 14 Day 28

TPHg 46,000 39,000 51,000 47,000 27,000 8,900 36,000 1,000

MTBE 1,400 1,400 1,400 1,300 1,400 1,300 1,400 790

Benzene 14,000 13,000 15,000 14,000 9,700 240 9,900 19 Toluene 5,100 3,800 7,500 6,600 1,400 9.1 4,300 13 Ethylbenzene < 100 < 40 800 630 < 50 < 5.0 67 < 0.50 m,p-Xylenes 4,700 3,500 4,400 3,700 2,500 1,400 3,900 31 o-Xylene 2,000 1,700 1,900 1,600 1,400 1,200 1,800 22 Diss. O2 (mg/L) 1.2 1.2 8.0 8.2 1.6 2.0 5.4 5.5 ORP (mV) 48 30 120 102 66 76 119 145 pH (unitless) 7.33 7.29 7.30 7.42 7.25 7.26 7.26 7.23

As shown in the table above, no significant reductions in constituent concentrations were observed in the Nitrogen Control or Sterile Control reactors. Significant reductions, however, were observed in the reactors where oxygen was applied. TPHg and BTEX concentrations were substantially reduced in the Oxygen-10% reactors, while MTBE was not affected. TPHg, BTEX, and MTBE were significantly reduced in the Oxygen-20% reactors. These results indicate that oxygen addition by air sparging is a viable remedy for treating hydrocarbon impacts at the Site.

3.2 SVE/AS Field Test

The SVE/AS pilot test was conducted between May 11 and May 16, 2016. SVE was applied to well MW- 14, while periodic air sparging was performed on dual completion AS-1A/1B. During SVE and air sparging activities, nearby wells DPE-8, MW-8, MW-9, MW-16, and DPE-8 were monitored to observe changes in pressure, vacuum, and depth to water. The locations of wells used during the pilot test are shown on Figure 4.

3.2.1 Pilot Test SVE Extraction and AS Injection Times

The SVE system operated for 24 hours and then temporarily shut down to test the air sparge system.

Following air sparge testing, SVE and AS operated for 3 days with air injection into AS-1A and AS-1B for 5 minutes each hour.

3.2.2 Vapor Extraction Monitoring

Laboratory analyses and direct field measurements were used to monitor constituent concentrations in extracted vapors. Field readings measured volatile organic compound (VOC) concentrations in parts per million by volume (ppmv) using a Horiba organic vapor analyzer. SVE/AS system operating parameters are shown on Table 1, and a trend graph showing influent VOC concentrations versus time is included as Figure 5.

Laboratory data and VOC measurements indicated that substantial hydrocarbon mass was extracted from MW-14 throughout the pilot test event. VOC concentrations decreased throughout the first day of the pilot test, when the SVE system operated by itself. This is typical of SVE operation as the initial soil gas pore volume is extracted, the constituent volatilization rate is less than the air flow rate, and concentrations decrease. VOC concentrations showed an increasing trend throughout the remainder of the pilot test after starting the AS system.

3.2.3 Influence on Surrounding Wells

SVE operations induced vacuums of 8.8 inches of water (in.H2O) in AS-1B and limited vacuums in DPE-8 at 0.02 in.H2O, while no vacuum was observed in any of the other neighboring wells.

Air sparging was applied to AS-1A/1B and wellhead pressure and depth to water measurements were collected from neighboring wells DPE-8, MW-8, MW-9, MW-14, and MW-16. Initially, air was applied to the vadose zone through AS-1A. A relatively low wellhead pressure was created for a very high flow rate, indicating that the Site geology is conducive to air sparging. The wellhead pressures in nearby MW-14 and MW-16 increased slightly indicating a communication between these wells. No measureable increases were observed in the other wells.

Subsequently, air was applied to the saturated zone through AS-1B at approximately the same pressure and flow rate. The wellhead pressures in nearby MW-14 and MW-16 quickly exceeded 10 psi, the upper limit of the pressure gauges. This substantial pressure indicates significant communication between these wells. No noticeable increases were observed in the other wells.

Given that vacuum influence was observed in AS-1B when extracting from MW-14, and pressure influence was observed in MW-14 and MW-16 when injecting into AS-1B, it is apparent that communication exists in the fractured siltstone and claystone units beneath the Site.

A minor increase in pressure was observed in MW-14 and MW-16 while injecting into AS-1A, indicating that communication exists in the fine-grained overburden soils. While air sparging into the overburden soils is anticipated to be effective in treating hydrocarbon impacts, the effective radius of influence appears to be much greater in lower fractured rock units.

3.2.4 Estimated Mass Removal

Laboratory data and field VOC measurements indicate that substantial hydrocarbon mass was extracted from MW-14 throughout the pilot test. In 24 hours of SVE system operations, VOC concentrations decreased in the extracted vapors, while an estimated 5.6 pounds of hydrocarbon mass were extracted. With the AS applied for the remainder of the test, significantly higher VOC concentrations were observed and the rate of hydrocarbon mass removal increased to approximately 24 pounds per day.

3.3 Groundwater Performance Monitoring

Three groundwater performance monitoring events were performed as part of the pilot test: prior to the test, at the end of the five-day test, and approximately three weeks following the end of the test. Groundwater performance monitoring analytical results for constituents of concern are summarized in Table 2.

Concentrations of TPHg, BTEX constituents, MTBE, and naphthalene generally increased in each of the performance monitoring observation wells after SVE and air sparging were implemented at the Site. The greatest increase in constituent concentrations was observed in MW-14, where concentrations increased substantially from levels that were previously near or below laboratory detection limits, and similar increases were also observed in MW-8 and MW-19. Constituent concentrations in MW-4, MW-16, and DPE-8 were already elevated prior to performing the pilot test, but still increased substantially after the test was complete.

Concentrations of fuel oxygenates DIPE, ETBE, TAME and TBA, as well as 1,2-DCA were not observed above laboratory detection limits either before or after the pilot test.

Groundwater performance monitoring analytical results for biodegradation parameters are summarized in Table 3. Performance monitoring results generally indicate that aerobic biodegradation is occurring at the Site. Consistent with expectations, the lowest dissolved oxygen concentrations were observed near MW-4, where the greatest hydrocarbon impacts are present. Low dissolved oxygen concentrations indicate that the oxygen is being consumed by naturally occurring microbes, and that aerobic biodegradation processes are happening. Aerobic biodegradation in the vicinity of MW-4 is also supported by the observation of high concentrations of manganese, carbon dioxide, and alkalinity, where carbon dioxide from microbial degradation dissolves minerals in Site soils, resulting in higher alkalinity values. Additionally, the ORP in each well was measured to be positive, ranging from 200-400 millivolts (mV), as is needed for the aerobic degradation of hydrocarbons.

Performance monitoring results generally show that SVE and air sparging are effective means of hydrocarbon removal at the Site. Pilot-test operations mobilized significant hydrocarbon mass, temporarily increasing concentrations in wells near where SVE and air sparging were applied. As demonstrated by the pilot-test data, SVE is an effective method of removing these hydrocarbons, and the rate of removal increased following the addition of air sparging. Significant hydrocarbon concentrations still remain at the Site. However, groundwater chemistry analytical results indicate that aerobic biodegradation is occurring, and it is anticipated that these processes can be accelerated by the addition of oxygen via air sparging.

3.4 Evaluation of Remedial Alternatives

Three remedial alternatives were evaluated prior to the pilot study: in-situ bioremediation with ORC; in-situ chemical oxidation with ozone sparging; and, in-situ SVE/AS. SVE/AS was recommended as the preferred remedial alternative in the Summary Report, and the RWQCB concurred with Sierra West’s recommendation in their response letter dated November 18, 2016. The pilot study confirmed the viability and effectiveness of SVE/AS as a remediation technology at the Site. The CAP for implementation of SVE/AS at the Site is provided in Section 4.0.

4.0 Corrective Action Plan

Petroleum hydrocarbons and fuel additives are the primary constituents of concern in soil and groundwater at the Site. The most significant impacts are found in the immediate vicinity of the former USTs, beneath the former general store and video arcade buildings. Due to the complex subsurface geology, the distribution of constituent impacts is heterogeneous and varies both laterally and vertically. During an investigation performed in 2010, soil borings BH-1 through BH-27 were drilled and collected data showed that the greatest impacts were generally found 20 to 30 feet below ground surface (bgs) in the groundwater smear zone, but that deeper impacts were also present.

Data from the 2010 investigation, recent groundwater monitoring data (Appendix A), results from the 2011 DPE pilot study, and the 2016 SVE/AS pilot study (Section 3.0) were used to develop the proposed SVE/AS system layout. As shown on Figures 6 and 7, a network of SVE and AS wells with overlapping radii of influence is proposed to treat hydrocarbon impacts at the site. The locations of the SVE and AS wells are based on the known distribution of constituent impacts and the topography of the site. The network of wells consists of:

22 SVE wells: existing wells DPE-1 through DPE-8 from the 2011 DPE pilot study; existing well MW-14 from the 2016 SVE pilot study; and, 13 new SVE wells (SVE-1 through SVE-13).

21 AS wells: existing double-completion well AS-1A/1B from the 2016 SVE pilot study, and 20 new AS wells (AS-2 through AS-21). Due to the observation of deeper impacts in the 2010 investigation, some of the proposed air sparge wells will be completed with upper and lower zones (AS-7A/7B, AS-8A/8B, AS-14A/14B, AS-16A/16B, AS-17A/17B, and AS-20A/20B).

Anticipated well construction details for each of the new proposed wells are summarized in Table 4 and shown on Figure 8. The proposed construction details are based on the observed lithology in nearby wells borings, but encountered conditions may be different due to the heterogeneous nature of subsurface conditions at the site. The actual well construction may be modified based on the lithology and contaminant impacts encountered while drilling.

4.1 System Design and Permitting

Final designs of the layout shown in Figure 9, with the SVE and AS equipment installations and power supply will be prepared and presented in the Final Remediation Plan. Drawings and specifications will be suitable for permitting, bidding, contracting, and construction purposes. Procurement of drilling contractors, general contractors, remediation equipment supplies, and controls equipment suppliers is also included in this task.

4.2 Well Installations

Consistent with the other wells and borings at the Site, the proposed SVE and AS wells will be drilled and installed using hollow-stem auger drilling equipment.

4.2.1 Pre-Field Activities

Well drilling permits are required by the Napa County Department of Public Works (NCDPW), and utility locates are required prior to conducting field work. A Site health and safety plan is required for the proposed scope of work. The selected drilling contractor will be required to have a California C-57 drilling license, and have an independent health and safety plan prior to performing the work.

4.2.2 Drilling and Well Construction

SVE-1 through SVE-13, and AS-2 through AS-21 will be installed using hollow-stem auger drilling methods, in accordance with the details shown on Figure 8. Soil samples from each boring will be collected at 5-foot intervals using a California split-spoon sampler, and the cuttings will be observed during drilling operations. Soils will be logged using the Unified Soils Classification System (USCS) visual and manual methods and Munsell soil color charts. Additionally, a photo-ionization detector (PID) equipped with a 10.6 electron volt lamp will be used to field-screen soils for volatile organic compounds (VOCs).

SVE-1 through SVE-13 will be constructed using 2-inch diameter schedule 80 PVC casing, with a 15-foot length of 0.020-inch machine slotted screen. The remainder of each SVE well will be constructed with blank PVC riser casing. A filter pack of #3 sand will be emplaced around the screened interval, and will extend approximately two feet above the top of the screen. A three foot thick bentonite transition seal will be placed above the filter pack, followed by cement grout in the remaining annular space to near ground surface.

AS-2 through AS-21 will be constructed using 1-inch diameter schedule 80 PVC casing, with a 4-foot length of 0.020-inch machine slotted screen. The remainder of each AS well will be constructed with blank PVC riser casing. A filter pack of #3 sand will be emplaced around the screened interval, and will extend approximately one foot above and one foot below each screen. A three foot thick bentonite transition seal will be placed above the filter pack, followed be cement grout in the remaining annular space to near ground surface.

Given that several of the proposed remediation wells are located near the Lake Berryessa shoreline, each remediation well will be constructed as an above-ground stove-pipe completion, with a concrete pad measuring approximately two feet by two feet. The top of each well will be completed with a threaded PVC female adapter and a threaded male PVC plug, to facilitate future use of the wells for extraction or injection.

4.2.3 Development and Surveying

Approximately 48 to 72 hours following installation, SVE-1 through SVE-13 and AS-2 through AS-21 will be developed by surging over the length of the screened interval and then purging. Each well will be developed until pH, electrical conductivity, temperature, and turbidity have stabilized. Generally, a minimum of 10 casing volumes are necessary for water quality parameters to stabilize. Given the site’s location near the Lake Berryessa shoreline, water levels at the site can have seasonal fluctuations of 15 feet or greater. Adding clean water to shallow wells may be necessary if development is performed while water levels are low and wells dewater during development.

A well survey will be performed by a California licensed surveyor to measure and record the top-of-casing elevations relative to mean sea level within 0.01-foot accuracy, and horizontal coordinates to sub-meter accuracy. Surveying will be conducted consistent with GeoTracker requirements.

4.2.4 Waste Characterization and Disposal

Soil cuttings from drilling will be stored on-site in 55-gallon drums, or in a Department of Transportation rated roll-off bin. Groundwater displaced during well installation, and generated during well development will be stored in separate containers. Soil and groundwater samples will be collected from the drums for waste characterization, and will be sampled for TPHg, BTEX, MTBE, and total lead. Upon receipt of analytical results, the soil and groundwater will be removed from the site and transported to an appropriate disposal facility according to applicable protocols.

4.3 SVE/AS System Installation

Following installation of the remediation wells, the SVE/AS equipment will be installed and connected to the wells. Conveyance piping between the SVE/AS equipment and the remediation wells is shown on Figure 9.

4.3.1 SVE/AS Equipment

An air compressor capable of delivering 185 cubic feet per minute (cfm) at 100 psi, will be used for air sparging. A blower with an approximate capacity of 250 cfm and 25 inches mercury (In.Hg) vacuum will be used to induce a vacuum in unsaturated soils and extract impacted soil vapors. The vapors will be drawn through an air/water separator (knockout tank) to remove water prior to the blower. Extracted vapor will then be treated by a thermal oxidizer, where VOCs are destroyed by combustion, prior to discharge to the atmosphere. The collected water will be transported off-Site for disposal in accordance with local, state, and federal regulations.

SVE/AS equipment will be connected to the wells via aboveground piping (Figure 9). Two manifold pipelines will be used to connect the SVE wells and AS point to their respective blower. 2-inch and 1-inch schedule 80 PVC piping will be used to connect each of the SVE extraction and AS injection wells to their respective manifolds. Solenoid valves will be installed on each connector pipe, and will be used to control extraction and injection to individual SVE/AS wells. Solenoid valves will be connected to a central controls system.

The former aboveground storage tank (AST) concrete pad is anticipated to be used to support some of the SVE/AS equipment. Additionally, a temporary security fence surrounding the remediation equipment will be necessary to prevent theft or vandalism.

4.3.2 SVE/AS Operations Approach

The SVE/AS system will operate continuously for a period of approximately one to two years. It is anticipated that SVE/AS wells will be operated in clusters of several wells at a time, and that SVE/AS will be applied to well clusters in rotating groups.

4.3.3 Permits

A permit to construct and a permit to operate will be obtained from the Bay Area Air Quality Management District (BAAQMD) for the SVE treatment systems. An electrical permit from the Napa County Building Division will be required for connecting the SVE/AS equipment to the power supply.

4.3.4 Power Supply

An existing power pole is located at the Site, in the vicinity of DPE-5 and the former USTs. The electrical supply to this power pole is no longer active, however the line is still connected to the electrical grid surrounding Lake Berryessa. Power will need to be restored to this location to supply electricity to the remediation equipment. To restore power, it will be necessary to coordinate with the local electricity provider, Pacific Gas & Electric (PG&E). After obtaining an approved electrical permit from the Napa County Building Division, PG&E will install a meter on the power pole and provide electrical service to the Site.

4.3.5 Vapor Performance Monitoring

Influent and effluent vapor wills be periodically monitored for VOCs and constituents of concern to evaluate remedial performance and comply with BAAQMD permit requirements. Influent vapors will be monitored using a PID to measure VOCs, and influent and effluent vapor samples will be collected into Tedlar bags for laboratory analysis.

Vapor samples for laboratory analysis will be collected on a monthly basis to comply with BAAQMD permit requirements. These samples will be collected during monthly operations and maintenance (O&M) site visits. Influent and effluent VOC readings, as measured by a PID, will also be collected during monthly O&M site visits.

4.3.6 SVE/AS System Maintenance

Routine O&M is necessary to ensure that the SVE/AS system operates as intended. Following system startup, it is anticipated that daily visits will be necessary for the first week of operation. During these daily visits, SVE and AS will be applied to individual remediation wells, and pressure and vacuum measurements will be collected at neighboring observation wells. Based on these initial measurements, optimal compressor and blower settings for each well will be established for use throughout the duration of SVE/AS implementation.

Following the initial system startup, routine O&M site visits will be performed on a weekly frequency, with extra system maintenance activities being performed on monthly, quarterly, semi-annual, and annual frequencies. Routine O&M activities will include, but not be limited to: adding grease or oil to SVE/AS system components, exercising system valves, measuring influent and effluent VOC concentrations, measuring system parameters such as pressures and flow rates, and inspecting the system for other maintenance needs. System operating parameters will be recorded on field sheets, and included in in remedial status reports.

4.2.7 Waste Characterization and Disposal

Water vapor from the influent vapor stream will be collected in the knockout tank, and then pumped into a secondary temporary storage tank pending disposal. Prior to transport and disposal, the knockout water will be tested for site constituents for profiling purposes.

4.4 Groundwater Performance Monitoring

Groundwater monitoring at the site is currently performed on a semi-annual frequency, with sampling events occurring during the second and fourth quarters. During the second quarter event, only monitoring wells with historically elevated constituent concentrations are sampled. During the fourth quarter event, all of the monitoring wells are sampled, with the exception of MW-13 where constituent concentrations have never been observed. Also during the fourth quarter monitoring events, two samples are collected from Lake Berryessa. Samples collected during groundwater monitoring are analyzed for:

TPHg by EPA Method 8015M;

BTEX, MTBE, DIPE, ETBE, TAME, TBA, 1,2-DCA, and naphthalene by EPA Method 8260B.

Increased monitoring frequency is necessary to evaluate the effectiveness of SVE/AS. Following installation of the new remediation wells but prior to implementation of SVE/AS, a baseline monitoring event will be performed. Following startup of the SVE/AS system, additional groundwater monitoring events will be performed during the first and third quarters to evaluate remedial progress.

The baseline monitoring event, and events performed during the first, second, and third quarters will consist of sampling MW-1 through MW-12 and MW-14 through MW-19. Samples collected during these events will be analyzed for the constituents of concern listed above. No changes to the fourth quarter monitoring event are proposed. After active remediation has commenced, operation of the SVE/AS system should be paused for approximately 24 hours prior to performing monitoring events.

It is anticipated that the SVE/AS system will operate for approximately two years. After shutdown of the SVE/AS system, groundwater rebound monitoring will be performed. It is anticipated that groundwater rebound monitoring will be performed on a semi-annual frequency.

4.5 Budget for Implementation

The anticipated budget for implementation of SVE/AS at the site is $820,000. This budget estimate assumes the following tasks and their associated budgets:

Task 1 – System Design and Permitting This task includes preparing a Final Remediation Plan (FRP) with design drawings and specifications for permitting and contracting purposes. The FRP should also include a health and safety plan (HASP), updated schedule, and refined estimated budget. Task 1 also includes acquiring the BAAQMD emissions permit, NCDPW drilling permits, and the Napa County building permit (electrical), and coordinating with PG&E to restore electricity to the power pole located near DPE-5. Procurement of drilling contractors, general contractors, remediation equipment suppliers, and controls equipment suppliers is also included in this task.

A budget of $16,000 is estimated for permitting and electrical connection fees. Permit fees amounts are based on information gathered from their respective agency websites. A budget of $34,000 is estimated for document preparation, subcontractor procurement, and permit application preparation and oversight. The total estimated budget for Task 1 is $50,000.

Task 2 – Well Installation This task includes drilling and installing 13 SVE wells and 20 AS wells. Oversight will be performed by a licensed professional geologist, and drilling will be performed by a California C-57 licensed drilling contractor. Following drilling, the newly installed wells will be developed and surveyed. Investigation derived waste from drilling operations will be characterized and disposed of. Following drilling activities, a well installation report will be prepared and submitted to the RWQCB.

A budget of $90,000 is estimated for drilling, development, surveying, and waste disposal subcontractors. A budget of $40,000 is estimated for oversight and reporting. The total estimated budget for Task 2 is $130,000.

Task 3 – SVE/AS System Installation This task includes installing the SVE blower and AS air compressor, above-ground conveyance piping between the SVE/AS equipment and the wellheads, system controls and solenoid valves, and connecting the equipment to the nearby PG&E power supply.

A budget of $65,000 is estimated for initial installation of remediation equipment, including system controls, conveyance piping, temporary fencing, and electrical hookup. Subcontractor estimates are based on correspondence with equipment suppliers, and previous remediation projects with similar scopes. A budget of $35,000 is estimated for subcontractor coordination and for oversight during system installation. The total estimated budget for Task 3 is $100,000.

Task 4 – SVE/AS System Operation This task includes daily oversight of the system for the first two weeks of operation, routine O&M site visits on a weekly basis for two years of operation, with more significant maintenance occurring on a monthly frequency. Quarterly remediation status reports including the monthly emissions testing results for the BAAQMD are also included in this task.

A budget of $270,000 is estimated for operation of the SVE/AS system for 24 months. Operation costs include monthly electric bills, monthly vapor sampling analytical costs, annual permitting fees, and monthly remediation equipment leasing fees paid to the supplier. The remediation contractor is anticipated to perform minor O&M events on a weekly basis. Subcontractor costs are estimated based on correspondence with equipment suppliers, while electrical and permitting costs are based on previous remediation projects with similar scopes. A budget of $130,000 is estimated for reporting to the BAAQMD, and for monthly O&M site visits. The total estimated budget for Task 4 is $400,000.

Task 5 – Groundwater Performance Monitoring This task includes performing one baseline monitoring event, and four semi-annual groundwater performance monitoring events to be performed during the first and third quarters during two years of anticipated system operation. Each groundwater performance monitoring event will include sampling 19 monitoring wells, and collecting two samples from Lake Berryessa, with groundwater samples being analyzed for site constituents of concern and biodegradation parameters.

Each groundwater performance monitoring event has an estimated budget of $12,000. The total estimated budget to complete the baseline and four semi-annual events under Task 5 is $60,000.

Task 6 – Routine Groundwater Monitoring This task includes performing four semi-annual groundwater monitoring events to be conducted during the second and fourth quarters over an anticipated two-year operating period. These routine monitoring events are similar in scope to the performance monitoring events described in Task 5, but include additional analyses and reporting requirements to comply with Monitoring and Reporting Order R5-2012-0800.

Historically, routine groundwater monitoring during the second and fourth quarters has been performed by the Bureau of Reclamation. Following the implementation of SVE/AS at the Site, it is anticipated that these monitoring events will be performed by the remediation contractor. Given the increased analytical and reporting requirements, the estimated budget for each routine groundwater monitoring event is greater than the cost for each performance monitoring event.

Each routine groundwater monitoring event has an estimated budget of $20,000.