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i 0 antea'group Work Plan for Monitoring Well Installations SECTION 1.0: INTRODUCTION On behalf of BP Products North America, Inc. (BP), Antea'Group has prepared this Work Plan for Monitoring Well Installations in response to correspondence dated May 28, 2019,from the Central Valley Regional Water Quality Control Board (CVRWQCB) to the owners of Former ARCO Service Station No. 0559 at 2085 E. Main Street, Stockton, California (the Site; Figure 1 and Appendix A). In the letter, the CVRWQCB requested a soil and groundwater investigation to evaluate the origin and extent of impacts in monitoring well MW-3. The monitoring well was installed adjacent to the Site as part of the underground storage tank(UST) investigation for the American Medical Response West(AMRW) property located southwest of the Site at 2060 E. Main Street, Stockton, California. Antea Group proposes installing five monitoring wells (MW-1, MW-2, and MW-4 through MW-6) to evaluate potential petroleum hydrocarbon impacts to soil and groundwater beneath and down gradient of the Site, and to determine if the Site is responsible for the petroleum related impacts in monitoring well MW-3. SECTION 2.0: SITE DESCRIPTION The Site is located at the northwest corner of the intersection of E. Main Street and E. Lafayette Street in Stockton, California, Assessor parcel number(APN) 153-102-100-000 (Figure 2).The Site is currently an active, self-serve car wash. According to Spectrum Environmental, Inc.'s July 14, 2015, Phase 1 Environmental Site Assessment Report for AMRW, available on GeoTracker, the Site served as an Atlantic Richfield Corporation (ARCO)fueling facility from 1940 to 1965. According to historical building permits from the City of Stockton and other documents located by the CVRWQCB, ARCO owned and operated a commercial fueling facility at the Site from 1952 to 1973. The City of Stockton issued a building permit for the car wash on May 13, 1974. A Sanborn fire insurance map from 1950 shows a general layout of the former oil and gas service station (Appendix B; Spectrum, 2015). SECTION 2.1: SITE GEOLOGY AND HYDROGEOLOGY Antea Group referred to AMRW reports for boring logs MW-3 and B6 to summarize subsurface conditions beneath the Site. Shallow soil was not logged in MW-3 and B6 until 15 feet and 30 feet below ground surface (bgs), respectively. Soils observed in MW-3 on the eastern side of the Site consisted of a dense silt at 15 feet bgs, silty sand at 20 feet bgs, silt at 30 feet bgs, and a very stiff clay was encountered from 40 feet bgs to 60 feet bgs. No samples were collected at 25, 35, 45, or 55 feet bgs (AdvancedGeo, 2017a). In boring B6, located to the southwest side of the Site, silty sand was encountered from 30 feet to 54 feet bgs (AdvancedGeo, 2018a). Antea Group referred to data from AMRW monitoring well MW-3 to summarize groundwater characteristics beneath the Site. Groundwater was initially encountered at a depth of 41.74 feet bgs in March 2017 (AdvancedGeo, 2017b).The groundwater table rose during the subsequent quarterly monitoring events, and depth to water was measured at 34.85 feet bgs in May 2018 (AdvancedGeo, 2018b).The screen interval for MW-3 is 45 to 60 feet bgs. Based on AMRW monitoring data, groundwater flow is to the northeast. McLeod Lake is the nearest surface water feature, located about 1.6 miles west of the Site. SECTION 3.0: REGULATORY STATUS On February 11, 2019,the CVRWQCB sent a letter to the owners of the Site requesting an Environmental Assessment and documenting the CVRWQCB had assigned the Site case#392006. In the letter, the CVRWQCB asserts that the Site's historical operations could have resulted in a UST release that degraded groundwater quality. XINOGEN* 1 us.anteagroup.com