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t. CHAPTER 3 SOIL EXCAVATION PROCEEDINGS OCEEDINGS AT THE KENT'S OIL FACILITY IN STOCKTON, CALIFORNIA Brown and Caldwell (BC) was retained by Sheldon Oil Company (Sheldon) in January 1993, to oversee the remediation of the petroleum hydrocarbon affected soil previously identified in the area of the former underground storage tank (UST). Aprotek, operating within G.R. Kause Construction and Engineering (Kause) was an environmental contractor hired by Sheldon in 1993 to perform additional excavation and remediation work at the Kent's Oil facility (Site). Aprotek prepared a work plan for the excavation and bioremediation of an additional 1000 cubic yards 4 of petroleum hydrocarbon affected soil and, on behalf of Sheldon, submitted the work plan to the San Joaquin County Public Health Services Department (County) for approval. The Aprotek work plan. is .included as Attachment A. Work plan approval was obtained from the County } r verbally by Aprotek, and Aprotek began conducting the additional excavation of visually affected soil in April 1993. Following the removal of approximately 2000 cubic yards of additional material, the excavation was halted because it was determined that the affected area was greater than expected when the scope of work was prepared and approved. In May,1993,BC prepared a work plan to drill five soil borings, construct four temporary groundwater monitoring wells, and collect soil and groundwater samples for laboratory analysis f to evaluate the extent of hydrocarbons in the soil and/or groundwater. The BC work plan and ' the County's letter approving it are included in Attachment B of this report. The objective of the BC work was to identify the lateral and vertical extent of petroleum hydrocarbons in the soil in the vicinity of the former UST location. BC drilled five soil borings 07W1,TW2,TW3,TW4, and SB 10) to depths ranging from 71.5 to 85 feet below ground surface (bgs) between May 11 ► and 14, 1993. The locations of the five soil borings relative to the existing excavation are r illustrated on Figure 3-1. l Soil and groundwater sampling procedures followed during this investigation, as well as f 4 results of the laboratory analyses of soil and groundwater samples, were summarized and fi presented in BC's letter report to the County dated July 27, 1993, included in the report as Attachment C. To summarize that report, soil affected by petroleum hydrocarbons was visually identified at the ground surface near boring TW2 and at a depth of 43 feet bgs in boring TW4. Soil samples were collected at 5-foot intervals from four of the five borings. Only one soil ' sample was collected from boring TW4 at a depth of 45 feet bgs, immediately beneath an area visually identified as being affected by petroleum hydrocarbons. Soil samples were submitted to Western Envn iromental Science and Technology (WEST), a State of California certified analytical laboratory, for analysis of benzene, toluene, ethylbenzene and total xylene isomers (BTEX) following Environmental Protection Agency (EPA) Method 8020, and total petroleum { Use or disclosure of data contained on this sheet is subject to the restriction specified at the beginning of this document. E1J22A3�\7GO3itEPOR1S1U:.4T-0ILC1.0 Qms-nnoo f