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5431 Grant Line Road, Banta, California April 7, 1994 Chevron USA Products Company Page 4 under chain-of-custody manifest to Superior Precision Analytical, Inc (Superior), in San Francisco, California The field geologist maintained a complete log of the materials encountered during drilling using the Unified Soil Classification System (Appendix B) Seven of the twelve soil samples from the soil borings were selected for analysis Each sample was analyzed for benzene, toluene, ethylbenzene and xylenes (BTEX), total petroleum hydrocarbons-as-gasoline (fPH-G), and total petroleum hydrocarbons-as-diesel (f PH-D) by w Environmental Protection Agency (EPA) methods 5030/8020/moddied 8015 34 Temporary Groundwater Monitoring Well Installation Temporary monitoring wells TW-1 and TW-2 were installed in borings located to the northwest and southeast (respectively) of the former underground tank pit (Figure 2) The monitoring wells were constructed of 2-inch-diameter, schedule 40 PVC casing with flush threads, and 0 020-inch-slot well screen Well screen for both wells was installed from 10 to 15 feet below grade A sand filter pack was added from the bottom of the borehole to 1 foot above the well screen The wells were secured by a locking, expandable well cap, cones, and barricades until the wells were sampled on January 6, 1994 Well construction details are presented in the drill logs attached in Appendix B Following installation, both temporary wells were surveyed to an arbitrary bench mark for both horizontal and vertical control (Appendix C) On January 5, 1994, the temporary wells were developed using a PVC bailer Approximately four well volumes of water was extracted from each well to remove fine-grained sediment and insure an even sand filter pack Groundwater was purged from the wells by bailer until the well water became visibly clear (Appendix D) All water generated during sampling and development was stored on site in Department of Transportation (DOT)-approved 55-gallon drums pending disposal 3.5 Groundwater Monitoring On January 6, 1994, depth to water in both temporary monitoring wells and the existing well was gauged from top-of-casing to determine the static water level and thickness of separate-phase hydrocarbons (SP), if present Water levels were measured using an ORS Environmental Equipment INTERFACE . PROBET"" Well Monitoring System, consisting of a dual optical sensor and electrical conductivity probe, that distinguishes between water and petroleum products GROUNDWATER 4894EAR RFrr1—JTECHNOLA)GY