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C A M B R I A <br /> 31 ppm. This investigation is described in the October 9, 1990 Environmental Assessment <br /> Status Report written by Groundwater Technology, Inc. (GTI) of West Sacramento, <br /> California. <br /> In May 1989, GTI drilled four vertical soil borings and one angle soil boring onsite. During <br /> May 1989, February 1990, April 1990, and May 1990, GTI installed seven onsite <br /> groundwater monitoring wells and four offsite monitoring wells. Maximum concentrations <br /> detected in soil from these borings were 2,500 ppm TPHg and 11 ppm benzene. These <br /> activities are also summarized in GTI's October 9, 1990 Environmental Assessment Status <br /> Report. <br /> In April 1992, GTI installed four soil vapor extraction (SVE) wells and conducted an SVE <br /> pilot test. These results are described in GTI's September 16, 1992 Sau»nrury Report of Soil <br /> Vapor Extraction Test Sampling Activities. <br /> In September 1993, GTI installed five offsite groundwater monitoring wells. Soil from these <br /> borings contained TPHg at concentrations up to 3.7 ppm and benzene at concentrations up <br /> to 0.23 ppm. This investigation is documented in GTI's December 16, 1993 Summary <br /> Report of Drilling Activities. <br /> Separate phase hydrocarbons (SPH) have historically been detected in well MW-1, but no <br /> measurable SPH has been observed since March 1993. From May 1989 to December 1989, <br /> approximately 45 gallons of SPH were recovered from well MW-1. An SVE test was <br /> conducted in June 1992, and the SVE system began operation in August 1995. SECOR <br /> International, Inc. of Huntington Beach, California detail this in their September 12, 1996 <br /> Soil Vapor Extraction System Installation and Start-up Report. Between January 1996 and <br /> March 1998, the SVE system removed approximately 6,250 pounds of TPHg. The SVE <br /> system was shut down March 9, 1998 due to declining influent concentrations and rising <br /> groundwater depth. <br /> Quarterly groundwater monitoring and sampling have been performed at this site since <br /> May 1989. Currently, depth to groundwater ranges from approximately 19 to 22 fbg. <br /> Since 1992, groundwater has risen approximately 20 feet. Groundwater flow direction at this <br /> site has been variable, but is generally to the north or northeast. <br /> 241-1399 2 <br />