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r, i PES Environmental, Inc. mr. Jeff Werner February 12, 1991 Page 2 casing, The results of the investigation indicated that petroleum hydrocarbons were present in subsurface soil (concentrations up to 214.5 parts per million tppm] total petroleum hydrocarbons [TPH� as gasoline, 7,67 ppm benzene, 37.9 ppm toluene. 29.9 ppm ethylbenzene, and 111 pptn xylenes) and in groundwater (concentrations up to 46.2 ppm TP14 as gasnline, 0.74 ppm benzene. 0.624 ppm toluene, and 1.75 ppm xylenes). In February 1986, Brown and Caldwell (B&C), retained by GLDM to further define the vertical and lateral extent of hydrocarbon contaminaduri, drilled five E 1)hP troleuml i through GL-5) and collected soil samples for chemical analysis (P hydrocarbons were not detected in soil samples from boreholes GL-1 and GL-4; low concentrations of petroleum hydrocarbons (<25 ppm TPH as gasoline, and <2 ppm 6 r e, toluene, et benzenhylbenzene,and xylenes) were found in borehole GL-5, and relatively elevated concentrations (up to 240 ppm TPH as gasoline. up to 10 ppm toluene, and up to 32 Ppm xylenes)were found in boreholes GL-2 and GL-3. s MW-5 to a depth of approximately 60 feet bgs and collected In July 1986, B&�' drilled Well soil and groundwater samples for chemical anaiysis (Plate 1). Well MW-5 was cormp t with 30 feet of 2-inch diameter 0.020 slotted PVC casing and 30 feet of 2-inch diameter PVC blank,casing. Petroleum hydrocarbons were detected in sol! (concentrations es to 17 ppm benzene, 36 ppm toluene, and 97 ppm xylenes) and [,104 ppm TPH as gasoline, m benzene, 0.1 ppm groundwater(concentrations up to 11 ppm TPH as gasoline. 0.12 pp toluene, and 0.28 ppm xylenes) samples collected from Well MW-5, 1 onal Water Quality Control Board, Central Valley Region In March 1990, the California Regi s (RWQCB) issued Cleanup and Abatement Order No. 90-702. The Order required: (1) t definition of the extent of petroleum hydrocarbon affected groundwater. (2) submission of a s problem assessment report, (3) performance of quarterly groundwater moni[oring and reporting, and (4) submission and implementation of a final remedial plan. This work pian addresses items 1, 3, and 4. g S. With the In May 1990, B&C redeveloped and sampled Wells MW-1 through MW- :E exception of Well NEW-2, groundwater samples from these wells contained petroleum ihvdrocarbons. In June and July 1990, B&C drilled Wells MW-6 through MW-9 and C ollected soil and groundwater samples for chemical analysts (Plate 1). These wells we30 re drilled to a depth of approximately 70 feet bgs and were completed with approximately feet of 2-inch diameter 0.020-slotted PVC casing and approximately 40 feet of 2-inch diameter PVC blank casing. Low concentrations of petroleum hydrloc es Were detected TPH as gasoline, and <0.5 ppm benzene. toluene, ethylbenzene, and xy soil samples from Wells MW-6 through MW-8; relatively higher concentrations (up to 100 lr m toluene. and 2.1 ppm PPM TPH as gasoline, and up to 5.3 ppm ethylbenzene. 2.1 pp ] xvlenes) were detected in soil samples from Well MW-9. Groundwater samples collected in r- July 1990 from Wells MW-6 through MW-9 contained petroleum hydrocarbons (up to Z.3 E�