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4 0. PREVIOUS SUBSURFACE INVESTIGATION ' The following is a summary of previous investigations at the site of the unauthorized release of fuel products to the subsurface ' • April 1999- Six soil borings (P-1 through P-6)were advanced at the site to assess the lateral and vertical extent of petroleum-impacted soil and ground water A total of 17 soil samples and five ground water samples were collected during the investigation and were submitted for laboratory analysis TPH-g and total petroleum hydrocarbons quantified as diesel(TPH-d) were detected in analyzed soil samples at concentrations as high as 390 mg/kg, dissolved TPH-g and TPH-d were detected in grab ground water samples at concentrations ranging as high as 310,000 micrograms per liter(µg11) BTEX compounds were detected in selected soil samples and grab ground water samples at concentrations as high as 51 mg/kg and 48,000 ' gg/l,respectively MTBE,TAME and TBA were detected in selected soil samples and grab ground water samples at concentrations as high as 0 36 mg/kg and 310,000 µg/1 Results of the April 1999 investigation were reported in Preliminary Investigation and Evaluation ' Report (PIER) dated 11 June 1999 prepared by AGE • June 2000-Ground water monitoring wells MW-1,MW-2,MW-3,MW-4 and MW-5 were installed on- and off-site to assess the lateral and vertical extent of petroleum-impacted soil ' and ground water A total of seventeen soil samples were collected during drilling activities and submitted to a DHS-certified laboratory for analysis for TPH-g,BTEX,MTBE,ETBE, TAME, RIPE, TBA, 1,2-DCA, EDB, methanol and ethanol TPH-g was detected in soil ' samples collected from borings MW-1, MW-2 and MW-4 at concentrations as high as 85 mg/kg, BTEX compounds were detected in soil samples collected from MW-1,MW-2 and ' MW-4 at concentrations as high as 6 7 mg/kg, MTBE and TAME were detected in soil samples collected from MSV-1, MW-2 and MW-3 at concentrations ranging as high as 110 mg/kg No other fuel components were detected by laboratory analysis Results of the June ' 2000 investigation were reported in Quarterly Report - Third Quarter 2000 dated 20 September 2000 prepared by AGE • August and September 2000-AGE conducted a sensitive receptor survey to locate potential vertical conduits within a 2,000 foot radius of the site The results of the sensitive receptor survey located a municipal water well (City of Manteca Well No 4) located approximately 1,900 feet northwest of the site near and a second municipal water well (City of Manteca ' Well No 5) located approximately 1,500 feet south of the site Results of the investigation were reported in Sensitive Receptor Survey dated 08 September 2000 prepared by AGE • December 2000-Four soil borings(P-7„P-8,P-9 and P-10)were advanced on-site utilizing cone penetrometer testing (CPT) technology to characterize the geological and hydro- geological framework and to assess preferential migration pathways Based on soil composition data obtained from the CPT soil borings,cross sections C-C' and D-D' (Figures 3 and 4)were constructed depicting the general subsurface soil composition on-and off-site Based on the CPT soil characteristics data,AGE identified fourpotential hydrogeologic units ' informally identified as"First Water Zone"(located 15 to 47 feet bsg),"Second Water Zone" M (located 58 to 92 feet bsg), "Third Water Zone" (located 102 to 115 feet bsg) and"Primary Aquifer Zone" (located 128 to 150 feet bsg) Significant fuel component and chlorinated l Advanced GeoEaviroamentai,Inc , I 1 I I