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IP—RZ, <br /> GAVIN NEWSOM <br /> GOVERNOR <br /> C0.LI i0 R LI I• JAIREo NFELD <br /> SECRETARRY FOR <br /> Water Boards ENVIRONMENTAL PROTECTION <br /> Central Valley Regional Water Quality Control Board <br /> 29 December 2020 <br /> Heorot Power Holdings <br /> Attn: Barbara Guiltinan <br /> 575 Broadway <br /> New York, New York 10012 <br /> ADDITIONAL SITE ASSESSMENT REPORT REVIEW, FORMER SAN JOAQUIN <br /> COGENERATION, 17200 MURPHY PARKWAY, LATHROP, SAN JOAQUIN COUNTY <br /> Staff of the Central Valley Regional Water Quality Control Board (Central Valley Water <br /> Board) have reviewed the 21 October 2020 Additional Site Assessment Report (Report) for <br /> the Former San Joaquin Cogeneration Facility (SJCF) located at 17200 Murphy Parkway in <br /> Lathrop, San Joaquin County (Site), prepared on your behalf by AdvancedGeo, Inc. (AGI). <br /> The objective of the investigation was to define the limits of soil impacted with <br /> polychlorinated biphenyls (PCBs) and total petroleum hydrocarbons (TPH) and to further <br /> delineate the limits of the North Waste Cell and South Waste Cell. <br /> Background <br /> Pilkington North America (PNA) operated a plant at 17100 Murphy Parkway, which is <br /> situated immediately east of the site. The former PNA facility contained unpermitted <br /> landfill cells that resulted in discharge of wastes, including dioxin/furan compounds, <br /> PCBs and petroleum hydrocarbons to soil. Two primary waste cells reported as the <br /> North Waste Cell and South Waste Cell were reportedly assessed and remediated on <br /> the Pilkington property up to what was thought to be the boundary of the cogeneration <br /> plant. At the time of remediation, the property boundary was estimated and not <br /> established by licensed surveyors. <br /> In March and April 2019, AGI conducted a soil and groundwater investigation, <br /> documented in the 15 May 2019 Site Assessment Report. A total of 43 direct-push soil <br /> borings (131 through B43) were advanced across the Site to define and evaluate the <br /> extent and characteristics of the North and South landfill cells that were thought to <br /> extend onto Site property, the former facility footprint, as well as underlying groundwater <br /> characteristics. The objective of the borings was to locate and identify unpermitted <br /> landfilled waste buried in the area as well as to determine if historical property uses <br /> adversely affected subsurface conditions at the Site. Monitoring wells MW-1 through <br /> MW-4 were installed to evaluate groundwater flow conditions. A total of 58 soil and <br /> waste samples and 10 groundwater samples were collected and analyzed during the <br /> site assessment. A summary of the results are as follows: <br /> • The Site consists of sand and silty sand near the surface grade to approximately <br /> 14 feet below ground surface (bgs) underlain by 1 to 6 inches of clay in most <br /> KARL E. L.ONGLEY SCD, P.E., CHAIR I PATRICK PULUPA, ESQ., EXECUTIVE OFFICER <br /> 11020 Sun Center Drive#200, Rancho Cordova, CA 95670 1 www.waterboards.ca.gov/centralvalley <br />