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2 3 UNDERGROUND STORAGE TANK REMOVAL ' On May 11, 1988 American Moulding and Millworks contracted Stockton Service Station to remove, decontaminate and dispose of the 10,000 gallon diesel UST west of the maintenance shop, and ' the 500 gallon waste oil UST to the east of the shop This work was carried out under the direction of the San Joaquin County Public Health Service Complete records of the work plans and tank removal ' operation were not available, however, all available documentation regarding the UST removals and subsequent soil sampling are attached in Appendix C ' At the time the tanks were removed, the product lines from the 10,000 gallon diesel tank remained in place Unfortunately,this was not discovered until a representative from San Joaquin County ' contacted American Moulding and Millwork in January 1991, after the remedial actions to excavate the impacted soil were completed The application to remove the product lines and close UST according to San Joaquin County regulations is described below in Section 2 6 2 4 FEASIBILITY STUDY/REMEDIAL ACTION PLAN ' In April 1988, AFPC contracted Dames & Moore to review existing data and perform a supplemental site investigation in the maintenance shop area Dames & Moore received approval from San Joaquin Public Health Services-Environmental Health Department (PHS-EHD) for their proposed investigation The additional characterization included eighteen additional soil borings to a depth of ' approximately 45 feet bgs (Figure 2 1), the results of which are summarized in Appendix D At each boring location, soil samples were collected at five foot intervals between a depth of 10 feet to 40 feet ' bgs In July 1988, Dames & Moore completed the Feasibility Study/Remedial Action Plan (FS/RAP) containing a risk assessment, and the results of the additional soil sampling and analysis The FS/RAP was reviewed by PHS-EHD and was conditionally approved on November 3, 1988 The PHS-EHD ' comments were addressed by Dames & Moore on November 28, 1988 ' A total of 108 soil samples including 5 blind duplicates were analyzed for TPH/D (EPA Method 8015) Five soil samples were analyzed for polynuclear aromatic hydrocarbons (EPA Method 8010) Analytical results reported TPH/D concentrations at depths between 10 and 35 feet (Appendix D) Soils at the east and west end of the maintenance shop were found to be impacted, and the largest area impacted was generally in the south eastern corner of the maintenance shop Soil TPH ' concentrations ranged from 27 ppm to 28,000 ppm, with She highest concentrations occurring to the west of the maintenance shop at a depth of approximately 10 to 20 feet bgs (Appendix D) ' On June 13 and 15, 1988, Dames & Moore collected groundwater samples from the three JHKA monitoring wells The samples were analyzed for polynuclear aromatic hydrocarbons (EPA Method 6P) < L' SAC36046 14, I L) 5