ARCHIVED REPORTS_XR0008259 CASE 2

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12/02 '02 TUE 09 15 FAX 19259469968 ERNWEST WC X1005 Mr Harlin Knoll 15 June 1999 Page 4 • Total petroleum hydrocarbons as gasoline (TPH-g) by United States Environmental Protection Agency (USEPA) method 8015M, • Benzene, toluene,ethylbenzene and xylenes (BTEX)by USEPA method 8020,and • Fuel oxygenates by USEPA method 8260M A trip blank was submitted with the samples each day that soil samples were collected for Quality Assurance/Quality Control (QA/QC) purposes Ground Water Investigation ERM installed three permanent monitoring wells (MW-1 through MW-3) at the site in the locations shown on Figure 2 Monitoring well locations were selected to characterize ground water impacts based on previous investigation results and to collect elevation data for ground water flow evaluation The wells were installed using a truck-mounted, hallow-stem auger drilling rig Each monitoring well was constructed with a 15-foot section of 2-inch-diameter,Schedule 40 polyvinyl chloride (PVC) screen with 10- slot (0 010-inch) openings The screen was connected to 2-inch PVC riser pipe extended to the ground surface Each well was screened from approximately 50 to 35 feet bgs. Clean coarse quartz sand was placed around the well screens to serve as a filter pack,extending approximately 1 foot above the top of the screen A 1-foot-thick layer of hydrated bentonite pellets was placed above the sand pack to serve as a seal. The remainder of the borehole was filled with a bentonite grout mixture to approximately 1 foot bgs All wells were completed with a flush-mounted, steel protective cover in a concrete base The top of the base was sloped to drain surface water away from the monitoring well Airtight locked lids were placed on the well risers to prevent surface water from infiltrating into the well bores Monitoring well installation was performed under monitoring well permit#015626 issued by San Joaquin County Construction details for each well are included in Appendix A