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1� Additional Assessment Report 4 Chevron USA Products Company, 2405 Airport Way Stockton, California September 23, 1994 sealed with aluminum foil, capped, taped, labeled, placed on ice in an insulated container and delivered under chain-of-custody manifest to GTEL Environmental Laboratories (GTEL) in Concord, California The field geologist maintained a complete log of the materials encountered during drilling using the Unified Soil Classification System (Appendix B) Six of the 13 soil samples collected from the soil boring were selected for analysis Each sample was analyzed for benzene,toluene, ethylbenzene and xylenes (BTEX),and total petroleum hydrocarbons-as- gasoline (TPH-G) by Environmental Protection Agency (EPA) methods 8020/modified 8015 34 Groundwater Monitoring Well Installation/Surveying/Development One monitoring well was installed at the location shown on Figure 2 The monitoring well was constructed of 2-inch-diameter, schedule 40 polyvinylchloride (PVC) casing with flush threads, and 0 020-inch-slot well screen Well screen for the well was installed from 45 to 65 feet BGS The well annulus was filled with a sand filter pack from the bottom of the borehole to 1 foot above the top of the well screen The annulus was sealed with 2 feet of bentonite on top of the sand and a portland cement grout to 1 foot BGS The well was finished to grade with a traffic-rated, watertight street box set in concrete, and protected with a locking, expandable well cap Well construction details are presented on the drill log attached in Appendix B The new well was professionally surveyed for horizontal position relative to the existing well network and elevation relative to mean sea level datum (Appendix C) On June 3, 1994, MW-4 and MW-5 were developed by surging and bailing to remove fine-grained sediments from the well casing and filter pack MW-4 was developed to remove any sediment which may have been introduced into the well when the wellhead was damaged and subsequently repaired Water was removed from the wells until visibly clear All development water was transferred to a DOT- approved purge water trader and transported to the Chevron refinery in Richmond, California for recycling 3 5 Groundwater Monitoring/Sampling All site related wells were gauged from top-of-casing to determine the static water level and thickness of separate-phase hydrocarbons (SP), if present The depth to water was measured using an ORS Environmental Equipment iNTERFACE PROBE® Well Monitoring System, consisting of a dual optical sensor and electrical conductivity probe that distinguishes between water and petroleum products Monitoring wells MW-1 through MW-4 were sampled after purging on July 8, 1994 (MW-5 was sampled on August 22 1994) Field data sheets with pH, conductivity, and temperature readings recorded prior 5038SUM RPT 14' GROUNDWATER TECHNOLOGY