WORK PLANS - Laserfiche WebLink

Home Browse Search

T e INTRODUCTION On behalf of Phillips 66 Company (Phillips 66), ATC Group Services LLC (ATC) doing business as Atlas Technical (Atlas) is submitting this well destruction workplan describing proposed activities and methodology for the destruction of groundwater monitoring and remediation wells associated with Former Thrifty Oil Co.Station No.172/Phillips 66 Site No.5449 located at 7647 Pacific Avenue in Stockton, California (Figures 1 and 2). In correspondence dated July 15, 2022, the Central Valley Regional Water Quality Control Board(RWQCB)indicated the site is ready for case closure and directed proper destruction of the remaining remediation and monitoring wells (Attachment 1). This workplan was prepared as a requirement to apply for a Well Destruction Permit with the San Joaquin County Environmental Health Department(SJCEHD).The scope of work is described in detail below. SITE BACKGROUND The site was formerly a Thrifty Oil Co. service station. The station and its facilities have been decommissioned and the property has been redeveloped into a 7-11 convenience store. Phillips 66 has completed a legal agreement with Thrifty Oil Co. (Thrifty) to assume environmental management responsibilities including groundwater monitoring and remediation system operation, effective April 7, 2010 through No Further Action. The San Joaquin County Environmental Health Department (SJCEHD) was informed of this transition, and has indicated, as there are no Unauthorized Release Reports for this location listing Phillips 66, it must continue to consider Thrifty as a responsible party of record and included them on outgoing correspondence. However, by means of the agreements between the two companies, Phillips 66 will be responding to agency directives for this site. PREVIOUS ASSESSMENTS From May 23 through June 6, 1991, SSB Environmental Consultants, Inc. (SSB) installed four groundwater monitoring wells (MW-1 through MW-4). Two monitoring wells were located adjacent to the underground storage tanks (USTs), and two monitoring wells were installed near the pump islands. Groundwater was encountered at 58 feet below ground surface (bgs) and the monitoring wells were installed to depths of 76 to 80 feet bgs. Laboratory analysis of a soil sample collected at a depth of 20 feet from well MW-2 indicated the highest concentrations of total petroleum hydrocarbons (TPH, also reported as total purgeable petroleum hydrocarbons TPPH), and benzene at 380 milligrams per kilogram (mg/kg) and 33 mg/kg, respectively. Laboratory analysis of groundwater samples collected ranged from 36.4 micrograms per liter(µg/L)to 5,270 µg/L benzene in wells MW-4 and MW-2,respectively(SSB, 1991). On April 22, 1994, Thrifty installed three vadose zone wells (VWA, VWB, and VWC) to depths of 35, 48, and 45 feet bgs, respectively. Thrifty also installed two groundwater monitoring wells (MW-7 and MW-8) to 56 feet bgs and 58 feet bgs, respectively. Laboratory analysis of soil samples detected TPH concentrations up to 21,000 mg/kg, and benzene concentrations up to 36 mg/kg. Laboratory analysis of groundwater samples detected 5,500 µg/L TPH and 830 µg/L benzene in MW-7, and 130,000 µg/L TPH and 7,200 µg/L benzene in MW-8. Thrifty investigated the OPW vault area near MW-8. The vault was approximately 10 inches in diameter and covered what appeared to be a sewer line clean-out. A 24-inch diameter hole was excavated adjacent to the OPW vault and a cast iron pipe that appeared to be a sewer line,and was encountered at approximately 3 feet bgs.The pipe was connected to the OPW pipe opening, but was not conclusively identified as a sewer line (Thrifty, 1994). 1 1 P a g e