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Work Plan for Additional Assessment Lr ARCO Facility No.2186 Stockton.California Page 2 the USTs, proceeded along the western edge of the site and connected the USTs to two dispenser islands located north of the station building. In August 1999 IT conducted a soil and groundwater assessment consisting of two on-site CPT borings (CPT-2 and CPT-3) located at the eastern edge of the site and one off-site CPT boring(CPT- 1) located to the north of the site. Benzene and methyl tertiary butyl ether(MTBE) were detected in water samples collected from CPT-2. Low residual concentrations of total petroleum hydrocarbons as gasoline, benzene, toluene, ethyl benzene, and total xylenes in soil remain at depths of 31 to 56 feet below ground surface. The highest detected dissolved petroleum hydrocarbon concentrations have historically occurred in well MW-1. Since the initial soil and groundwater investigation, conducted in September 1995, the groundwater elevation has risen from approximately 58 feet bgs to approximately 34 to 35 feet bgs (June 2000 quarterly sampling event). The groundwater flow at the subject has been generally to the northeast to east-northeast. ADDITIONAL WELL SURVEY INFORMATION A water well survey was conducted by Pinnacle Environmental Solutions, a division of EMCON, which they reportedly identified one water well within %a mile of the site (Pinnacle, April 15, 1999). This well was reported as a municipal well, owned by the City of Stockton and located approximately 1100 feet north of the site. ARCO contracted the IT Group to conduct a well survey identifying water supply wells in the vicinity of most ARCO facilities in northern California. The results of their survey for the subject site were available in June 2000. Appendix A presents the survey results and includes an area map showing the location of both the ARCO site and the municipal wells. The survey identified three wells within 2,000 feet of the site. Two wells were designated as agricultural and reported as being located approximately 400 and 900 feet from the ARCO site. The third well was reported as being approximately 1,800 feet from the site and in the same direction from the site (northwest) as the well located 400 feet from the site. Delta field verified the locations of the three water wells and contacted the owner/operator of the wells to obtain information regarding the construction and operation of each well. The wells reported as being approximately 400 and 900 feet from the site in the IT Group survey was accurate. The wells are owned by the City of Stockton and operated by the Department of Parks and Recreation. Based on conversations with representatives with the Parks and Recreation, both wells are used to provide water for maintaining the lawns and grounds of Oak Park. Delta was able to obtain the well logs from the City of Stockton; copies are included in Appendix A. The well's operational data, such as yield and operating frequency could not be obtained at this time. The well that was reported to be 1,800 feet from the site was field verified and is located on the property of St. Luke's Church. The location appears to correspond with the location and owner identified in the Pinnacle survey; however, the Pinnacle survey reported three wells at this location and Delta was