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I to 78 feet bgs in borings MW-7 and MW-8 . A 2/12 sand filter was placed around the well screen to a height of approximately Pack feet above the top of the screen. Hydrated bentonite was placed to a height of approximately 2 feet above the top of the sand filter pack and the remaining annular space was filled to the ground surface with a cement/bentonite slurry. The well head is protected by a locking cap and a traffic-rated utility box with a water- tight, bolted lid. Well construction details are included with the logs of borings, presented in Appendix A. E 3 .4 Monitoring Well Development and Sampling � I On September 25, 1994 Sierra Environmental (Sierra) of Quincy, California developed monitoring wells MW-7 and MW-8 by surging and t� bailing. Prior to well development, the field technician used a bailer to collect groundwater samples for subjective analysis of petroleum hydrocarbon sheen or free product. Development water was placed into 55-gallon drums and stored on-site pending receipt of laboratory analytical results and proper disposal. Well purge logs and field monitoring data are presented in Appendix B. On September 26, 1994 Sierra personnel measured depth-to-water in monitoring wells MW-1 through MW-8 using a conductivity probe and collected groundwater samples from monitoring wells MW-6, MW-7 and MW-8. No evidence of free phase petroleum hydrocarbons was detected in monitoring wells MW-6 through MW-8. Groundwater was not present in monitoring wells MW-1 through MW-5. Purge water f generated during groundwater sampling was placed into 55-gallon drums and stored on-site pending receipt of laboratory analytical results and proper disposal. MCA will submit a separate waste disposal plan for groundwater generated during previous sampling events and for groundwater generated during this investigation. r G P 4.0 SITE CONDITIONS 4 . 1 Geology and Hydrogeology Sediments encountered during drilling of on-site boring MW-7 r consisted of clay, silt, sandy silt, silty sand, sandy silty gravel, and sand. The section encountered during drilling of off- site boring MW-8 consisted of clay, silt, sandy silt, and sand. Groundwater was first encountered during drilling at a depth of approximately 65 - 70 feet bgs. The materials above the saturated zone are largely silty and clayey. A sandy zone was encountered in both borings at approximately 55 -6o feet. Descriptions of the materials encountered are shown on the boring logs. The sediments logged in the two recent borings are consistent with the recent alluvium and Pleistocene victor Formation alluvial r 5 6