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At C December 13,2016 Page 2 of 8 INTRODUCTION On behalf of Phillips 66 Company (Phillips 66), ATC Group Services LLC (ATC) is submitting this groundwater delineation workplan for Former 76 Station No. 11190 located at 1206 East March Lane in Stockton, California, at the request of the Regional Water Quality Control Board (RWQCB) in correspondence dated October 5, 2016. The site description, a summary of previous assessments, and the proposed groundwater investigation scope are included below. SITE DESCRIPTION The site is the location of an operating convenience store and service station. The facility is bounded on the north by March Lane and on the east by West Lane. Above-ground structures at the site consist of a single-story, convenience store building and a car wash structure. Three 10,000-gallon underground storage tanks(USTs) containing unleaded gasoline are located north and west of the building. Six product dispenser islands are centrally located on the property. Pertinent site features are shown on the site plan included as Figure 2. PREVIOUS ASSESSMENTS In April 1987, Kaprealian Engineering, Inc. (KEI) observed the removal of one waste-oil UST. No visible damage to the UST was observed and the native soil sample collected at a depth of 10 feet from the tank pit showed no detectable levels of total petroleum hydrocarbons as diesel (TPHd), volatile organic compounds (VOCs), and oil and grease. In 1988, an unauthorized release report was filed with the San Joaquin County Public Health Service (SJCPHS) on the basis of two USTs that failed pressure tests along with a cracked impact housing in the diesel dispenser. International Technology Corporation (IT)conducted a preliminary site investigation in June 1991. Two soil borings were advanced near the former pump islands and the former UST complex to a depth of 20 feet below ground surface (bgs). A third boring was advanced to 45 feet bgs east of the former UST complex. Groundwater was not encountered in the soil borings. Soil samples were analyzed for total petroleum hydrocarbons as gasoline (TPHg), TPHd, and benzene, toluene, ethyl-benzene, and total-xylenes (BTEX). Although samples collected from the soil borings reported non-detectable(ND) levels for all of the analytes, IT noted that"due to the nature of the site's coarse grained soils any hydrocarbons may have migrated vertically instead of laterally' (IT, 1991). Four USTs and associated piping were removed from the site in October 1991. The USTs were single-wall fiberglass tanks used to store leaded and unleaded gasoline and diesel. IT reported that the tanks appeared to be intact and no petroleum odor or staining was noted in the underlying soils; however, a San Joaquin County Inspection Report dated October 30, 1991, indicated a "strong hydrocarbon odor in pea gravel backfill." An oil/water separator located east of the former UST complex was also removed during excavation activities. Approximately 1,200 tons of soil from the UST excavation and the pipeline stockpiles and 25 cubic yards of soil from the oil/water separator excavation stockpile were transported to the BFI Landfill in Livermore, California. New tanks and piping were installed in November 1991 (IT, 1992). A San Joaquin County Public Health Services (SJCPHS) letter received on August 28, 1992, documented the completion of site investigation and remedial activities.