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Exploratory borings MW-12 and MW-13 were drilled using 8-inch-diameter ' hollow-stem auger drilling equipment. Boring B92-1 was drilled using 6-inch- diameter hollow-stem auger drilling equipment. Soil samples were collected at 5-foot intervals in advance of the auger bit with a modified-California ' split-spoon sampler containing stainless steel liners. These samples were collected for geologic interpretation and chemical analysis. Representative soil samples from each sampling interval were sealed in stainless steel liners with Teflon tape and plastic end caps, and placed on ice pending selection for chemical analysis. Before drilling each boring, the augers were steam cleaned to prevent cross contamination. The sampling equipment ' was cleaned between sampling events with a trisodium phosphate solution. Soil samples were screened in the field by performing visual, olfactory, and ' head-space analysis using a portable photoionization detector (PID). Samples not preserved for chemical analysis were extruded from the liners and logged according to the Unified Soil Classification System (USCS) by ' an EMCON Associates geologist. This work was supervised by a California- certified engineering geologist. Auger-return material was stored on site pending receipt of analytical data to determine the proper disposal method. ' The exploratory boring logs are presented in Appendix C. Visual and olfactory evidence of petroleum hydrocarbon impact were not detected in the soil samples collected from borings MW-12 and B92-1. However,the soil samples from boring MW-13 showed visual, olfactory, and PID evidence of petroleum hydrocarbons from the depth of the bottom of ' the excavation to just above first-encountered ground water. Exploratory soil boring B92-1 was sealed from the bottom of the boring to the surface with cement bentonite grout, and borings MW-12 and MW-13 were converted to ' ground-water monitoring wells. 3.2 Monitoring Well Installation Borings MW-12 and MW-13 were advanced approximately 6.5 feet beyond first-encountered ground water and converted to ground-water monitoring ' wells by installing 2-inch-diameter polyvinyl chloride casing with approximately 14 feet of 0.020-inch machine-slotted screen. For each well, a sand filter pack was placed in the annular space to approximately 2 feet above the top of the screen. A 2-foot-thick bentonite seal was placed over the top of the sand pack, and a cement bentonite grout was pumped from the top of the bentonite to within 1.5 feet of the ground surface through a tremmie pipe. A locking well cap and a traffic-rated vault box set in concrete were installed at the surface to protect each well and to prevent unauthorized access. Well construction details are presented in Appendix C. p1010f9010f900020.1 ag 3 - 2 Rev. 0 December 15, 1992