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levels have stabilized, depth to water measurements will be made at each borehole and the top-of-casing elevations will be surveyed to an arbitrary datum. The surveyed top-of-casing elevations and depth to water level measurements will be made to an accuracy of 0.01 foot. These measurements will provide information regarding groundwater flow direction and gradient. After the depth to water level measurements are completed, the well screen and casing will be removed from each borehole and the boreholes will be backfilled with neat cement grout containing 5% powdered bentonite from the total depth of the borehole to the ground surface. The cement grout will either be pumped or tremied into the boreholes. Soil samples collected during this site investigation will be analyzed by a State of California-certified laboratory (Chromalab, San Ramon) for total petroleum hydrocarbons as gasoline (TPH-G) by EPA method 5030/8015,total petroleum hydrocarbons as diesel (TPH-D) by EPA method 3550/8015, total oil and grease (TOG) by standard method 5520 D&F, and benzene, toluene, ethylbenzene and xylenes (BTEX) by EPA method 8020. Groundwater samples will be analyzed for TPH-G by EPA method 5030/8015, TPH-D by EPA method 3510/8015, TOG by standard method 5520 B&F or EPA method 418.1, and BTEX by EPA method 602. MONITORING WELL INSTALLATION As previously stated, one groundwater monitoring well will be drilled and installed at a location adjacent to the reboiler and associated discharge line (Figure 2). The purpose of this well is to monitor groundwater quality in the vicinity of the discharge line. The following procedures will be followed during monitoring well installation. Borehole Advancement The borehole will be drilled and sampled to a depth of 10 to 15 feet below the top of the aquifer (--20-25 feet below ground surface) provided a continuous aquitard is not encountered. If an aquitard (i.e., a stiff clay layer) is encountered below the water table and is found not to contain elevated levels of petroleum hydrocarbons using field screening methods (e.g., PID meter), then the vertical continuity of this clay layer will be verified by sampling and advancing the borehole 41h feet. If the clay layer is found to be greater than 41h feet thick, the clay will be considered a continuous confining layer and the borehole will be plugged with bentonite or grout to the top of the clay. The monitoring well will be completed in the portion of the saturated zone overlying the clay layer. If the clay layer is found to be less than 41h feet thick, the clay will be considered a localized clay lens and the borehole will be advanced to the designed depth. Well Construction Procedures Two-inch diameter, Schedule 40 PVC casing and screen will be used to complete the groundwater monitoring well (see Figure 3, Typical Monitoring Well Construction Details). The proper lengths of screen and blank casing will be steam-cleaned and threaded above ground prior to lowering inside the hollow-stem cca/9-30-92/8913a/JAWP13 9