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Also of interest to this investigation was the removal of a 6,000 gallon gasoline tank (Tank 3) from along the north wall of the shop building and a 12,000 gallon aviation fuel tank (Tank 4) ' from the northwest corner of the shop building While the results of soil sampling from beneath each tank indicated that no volatile hydrocarbons were present in the sort, extractable hydrocarbons were inexplicably found A sample from the west end of Tank 3 allegedly contained 50 mg/Kg while a sample from the south end of Tank 4 contained 70 mg/Kg A ' review of available records does not indicate why extractable hydrocarbons were found at these locations nor if there was a possibilIt y-of-sample-mismanagement or analytical error ' 1.2 Hydrology The site is located in the south central portion of the San Joaquin County Groundwater Basin ' At the time of the remedial excavation project in April 1987, the water table was approximately 28 feet below grade as observed during the we same ing. However, based on water level measureme�n s�cotl r i ugus ,—groundwater rs currently 48 to 49 feet below ground ' surface (see Table 2) Based on these measurements, groundwater flow is to the north-northwest at the site (Figure 3) On a regional basis, according to the SJCFCD, publication, "Elevation of Water in Wells, Spring 1993", groundwater flows to the northeast in the vicinity of the site ' TABLE 2 9U17 Groundwater Elevations 8 +Gl ILocation Elevation Depth to Water Water Table (Top of Casing) (Feet) Elevation Feet MSL Feet MSL MW-1 2093 4797 -2704 ' MW-2 213 4794 -26.90 MW-3 2107 4824 -2687 1.3 Scope of Work ' The scope of the field investigation was originally proposed by WESTON in a Work Plan dated February 14, 1994 Review and comment by the EHD led to a Revised Work Plan dated April 18, 1994 which adjusted the locations of MW-1 and MW-2 slightly and altered certain soil sampling procedures The modified work plan included the completion of four soil bonngs, the collection of two Hydropunch groundwater samples and installation of three monitor wells ' 2.0 SUMMARY OF FIELD ACTIVITIES WESTON installed three monitor wells and completed four soil borings between July 26 and July 29, 1994 Five soil samples were collected in brass sleeves from each of two soil borings I (SB-1 and SB-2) located as shown on Figure 2 near the former spray oil tank site and submitted for analysis of total petroleum hydrocarbons as diesel (TPH-D) and benzene, toluene, ethylbenzene and xylene (BTEX) Soil samples were also collected in brass sleeves at two depths (8 and 12 feet below grade) from each hydropunch boring (HP-1 and HP-2) located near the former gasoline (Tank 3) and aviation fuel tank (Tank 4) sites and analyzed for TPH-D and TPH-G Only the number of soil samples originally scheduled in the work plan were submitted for laboratory analysis as field screening results did not warrant the analysis of additional samples S'MXR"S\SICMvcDI SM 4 kon M