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Work Plan For a Limited Subsurface Investigation — Former Chevron Service Station #9-5775 Nnvemher 11 1999 Task 2. Well Installation GR will drill four on-site soil borings (SB -2 through SB -5), install three off-site and one on-site groundwater monitoring wells (MW -5 through MW -8), and install two on-site vapor extraction wells (VE -1 and VE -2) at the locations shown on Figures 2 and 3. Drilling and well construction will be performed by a licensed California well driller. A GR geologist will monitor the drilling activities and prepare a log of each boring. The four groundwater monitoring wells will be drilled to approximately 75 feet below ground surface (bgs) with 8 -inch diameter hollow -stem augers. The groundwater monitoring wells will be constructed with 2 -inch diameter Schedule 40 polyvinyl chloride (PVC) well casing and 0.02 - inch machine slotted well screen. The three off-site wells will be constructed with 20 feet of screen, extending from approximately 55 to 75 feet bgs. The one on-site well will be constructed �V " Z with 5 feet of screen, extending from approximately 70 to 75 feet bgs. The actual screen interval will depend on the groundwater depth and lithologic conditions encountered during drilling. Proposed groundwater monitoring well construction details are shown on Figures 4 and 5. The two on-site vapor extraction wells will be drilled to approximately 35 feet and 55 feet bgs with 10 -inch diameter hollow -stem augers. The vapor extraction wells will be constructed with 4 -inch diameter Schedule 40 PVC well casing and 0.02 -inch machine slotted well screen. Each well will be constructed with 15 feet of screen, extending from approximately 20 to 35 feet bgs, and 40 to 55 feet bgs. The actual screen interval will depend on the lithologic conditions encountered during drilling. Proposed vapor extraction well details are shown on Figures 6 and 7. The four soil borings will be drilled to just above groundwater (approximately 55 feet bgs) with 8 -inch diameter hollow -stem augers. Upon completing soil sample collection, the borings will be backfilled to ground surface with neat cement with 5% bentonite. If high levels of volatile organic compounds are detected in any boring using a photoionization detector (PID), that boring will be completed as a vapor extraction well. The boring will be enlarged using 10 -inch diameter hollow -stem augers. The vapor extraction well will be constructed with 4 -inch diameter Schedule 40 PVC well casing and 0.02 -inch machine slotted well screen. The length and depth of well screen will depend on the lithologic conditions encountered in the boring. The vapor extraction wells will be completed similar to the details shown in Figures 6 and 7. Soil samples for description and possible chemical analysis will be obtained from the boring at five-foot intervals, as a minimum. Soil samples will be collected with a split -spoon sampler fitted with clean brass sample rings. The actual number of samples submitted for chemical analysis will depend on site conditions and field screening data. At a minimum, one soil sample from the capillary fringe in each boring will be submitted for chemical analysis as described in Task 5. Soil from each sampled interval will be screened in the field for the presence of volatile organic compounds using a photoionization detector (PID). These data will be collected for reconnaissance purposes only, and will not be used as verification of the presence or absence of petroleum hydrocarbons. 346408.06