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May 16,2001 7Additional nty Motor Poowacility .. ssessment Workplanump PH smlentSforC he additionPHS has alsite work deroval to use the scribed bed n this twoSkpOa$474) used during the Task 3: Drilling and Soil/Groundwater Sampling Initial and step-out borings will be advanced using a truck-mounted drill rig equipped with 8-inch outside diameter (OD) hollow stem augers to uppermost groundwater (approximately 40 — 50 feet bgs). One initial boring (B-8) will be advanced to 100 feet bgs for vertical delineation purposes. Proposed boring locations are shown in Figure 2. Soil samples will be collected from each boring at five-foot intervals and/or where changes in lithology are observed. A TEM geologist, trained and supervised by a California Registered Geologist, will describe soil samples using the Unified Soil Classification System (USCS). The geologist will use a Photoionization Detector(PID) to screen the soil samples in the field for the presence of volatile organic compounds (VOC's) and to select soil samples for laboratory analyses. Samples retained for laboratory analysis will be collected in 1%-inch diameter by 6-inch long steel sleeves capped with Teflon lined polyethylene caps, properly labeled and immediately delivered to the on-site mobile laboratory under chain-of-custody protocol. Groundwater samples will be collected from each boring using a hydropunch sampler lowered through the auger string and advanced past the augers at static water level. This will minimize the likelihood of a "false positive" detection resulting from the augers dragging contaminated soil from shallow layers. The collected sample will be transferred from the hydropunch sampler to the appropriate laboratory supplied sample containers. Samples collected for VOC analyses will have their respective containers filled completely with a convex meniscus so as to eliminate any trapped air or headspace. The collected groundwater samples will be properly labeled and immediately delivered to the on-site mobile laboratory under chain-of-custody protocol. The drilling and sampling equipment will decontaminated between each sampling interval and between boring locations to minimize the possibility of cross-contamination. Soil cuttings and decontamination water will be stored in Department of Transportation (DOT)-approved 55-gallon drums until waste characterization profiling can be completed. Task 3A: Monitoring Well Installation Three (3) of the eight (8) soil borings will be converted in to groundwater monitoring wells. The borings to be converted will be selected on the basis of soil and groundwater analytical results obtained from the on-site mobile laboratory. Locations and rationale for monitoring wells would be reported verbally and via correspondence to the SJCPHS for their approval. The selected borings will be over-drilled using 10-inch OD hollow stem auger to a depth of approximately 60 feet bgs. Groundwater at the SITE is approximately 44 feet bgs as last measured in December 2000. The wells shall be constructed of flush-jointed, threaded, 4-inch, Schedule 40 PVC slotted screen (0.020) and blank casing. The wells will be screened from 30 feet bgs to 60 feet bgs. Blank casing will be used to construct the upper 30 feet of the wells. A filter pack consisting of No. 3 sand will be placed approximately three (3) feet above the top of the screened interval. The wells will then be surged approximately 15 minutes to allow the filter pack to settle. The annular seal shall consist of a three(3) foot thick hydrated bentonite chip seal placed directly above the filter pack. The remaining annular space shall be backfilled with Type 1-11 Portland cement to approximately two (2) feet bgs. The upper two (2) feet of each well shall consist of a traffic-rated well box cemented to existing surface grade. Page 3 of 5