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3246 East Fremont Street, Stockton, California September 16, 1993 Chevron USA Products Company Page 4 Nineteen soil samples from soil borings MW-4 and MW-5 and one soil pile composite were selected for ' laboratory analysis. Samples selected for analysis Include the 15 feet BG through 75 feet BG samples from MWA and the 5, 20, 40, 50, 70 and 75 feet BG samples from MW-5. Each sample was analyzed ' for benzene, toluene, ethylbenzene and xylenes (BTEX), and TPH-G by Environmental Protection Agency (EPA) 5030/8020/modified 8015. In addition, four soil samples were collected approximately 5 feet BG beneath the former product line trenches and analyzed for BTEX and TPH-G (Figure 2). 3.5 GROUNDWATER MONITORING WELL INSTALLATION One groundwater monitoring well was installed in each soil boring. The monitoring wells were ' constructed of 2-inch diameter, schedule 40 PVC casing with flush threads, and 0.020-inch-slot well screen. The well screen was installed from a depth of approximately 85 feet to a depth of 60 feet BG in each well. A sand filter was placed around the well screen to a height of approximately 2 feet above the top of the screen. The wells were completed with a bentonite and neat-cement seal, to grade. The wellhead was protected by a locking cap and a traffic-rated street box with a watertight bolted lid. Well construction details are presented in the drill logs (Appendix B). MW-4 and MW-5 were professionally surveyed for horizontal position and elevation above mean sea level using the previously established ' benchmark for the on-site monitoring well network (Appendix C). ' 3.6 MONITORING WELL DEVELOPMENT ' Monitoring wells MW-4 and MW-5 were developed to remove fine-grained sediments from the well and filter pack. Approximately three well volumes were extracted from each well by this method. This technique develops an even sand filter pack, removes fines, and rehabilitates the borehole sides. The ' fines are drawn from the well by the bailer until the well water is visibly clear. The development water was retained on site in a DOT-approved 55-gallon drum pending proper disposal. ' 3.7 GROUNDWATER MONITORING ' On June 28, 1993, Groundwater Technology personnel gauged the depth to the water table in each accessible monitoring well on site. 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. Wells EA-1 through EA-3 were dry and wells EA-4 and EA-5 could not be located. GROUNDWATER 3e65eaa.Rgr TECHNOLOGY