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PARSONS 1 INTRODUCTION On behalf of Remediation Management Services Company, Parsons has prepared this Plume Delineation Work Plan for additional site activities at the former Atlantic Richfield Company(ARCO)service station no. 00595 located at 6100 North Highway 99 in Stockton, California (referred to as the "Site;" Figure 1). This work plan has been prepared in response to a letter from Central Valley Regional Water Quality Control Board (CVRWQCB), dated May 14, 2020. In their letter, CVRWQCB noted that in the last round of groundwater monitoring at the Site (i.e., quarter 4, 2019) had the highest concentrations of methyl tert- butyl ether (MTBE) and tert-butyl alcohol (TBA) detected at MW-13 since the well was installed in 2016. Further, as there are no wells to the south of MW-13,the extent of the petroleum release in groundwater to the south of MW-13 has not been delineated. CVRWQCB requested that the lateral extent of the petroleum release in groundwater be delineated to the south of monitoring well MW-13. To address this request, Parsons is proposing the following activities: (1) advance three borings to groundwater south/southwest of MW-13 (Figure 2); (2) collect grab groundwater samples from each boring and analyze the samples for MTBE, TBA, GRO (gasoline range organics), BTEX (benzene, toluene, ethylbenzene, and total xylenes), 1,2-dichloroethane (1,2-DCA), and naphthalene; and (3) install a monitoring well at the southernmost boring where all analytes are non-detect. The proposed activities are detailed in Section 3. 2 SITE DESCRIPTION AND HISTORY The site is an unpaved vacant lot located on the southeastern corner of the intersection of Hammer Lane and Frontage Road in Stockton, California (Figures 1 and 2). The site operated as a commercial fueling facility(gas station) from 1959 to 2005.There are three known previous underground storage tank (UST) removals/infrastructure upgrades at the Site: 1) in 1987, one 280-gallon used oil UST was removed; 2) in 1999, the product lines/dispenser islands were upgraded; and 3) the station was demolished between December 29, 2005 and January 3, 2006 and three 12,000-gallon gasoline USTs, two dispenser islands, and associated product lines were removed (Arcadis 2016). The site is located in a commercial area and is zoned C-FS (Freeway Service Commercial). A vacant lot is located to the north of the Site. A Weinerschnitzel restaurant is located to the west of the Site. A restaurant and a used car sales lot are located southwest of the Site. An orchard extends from the northeast to the south of the Site (Arcadis 2016). Site investigations began in 1999 when petroleum hydrocarbon-impacted soil was noted during excavation activities associated with product line and dispenser upgrades. Groundwater monitoring activities began on a quarterly basis in 2000 (Arcadis 2016). Currently, there are 11 shallow zone monitoring wells and six deep zone monitoring wells on and adjacent to the Site (Figure 2). According to the United States Geological Survey, the elevation of the Site is approximately 33 ft above mean sea level (amsl). The closest open bodies of water are irrigation canals, with one located approximately 450 feet to the south of the Site and another located approximately 650 feet to the east of the Site. 1