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Mr Chuck Carmel September 3 1993 Page 2 Analytical results are summarized in Table 3 (Exhibit D) The complete laboratory report for the April 1993 sampling is presented in Exhibit E Figure 2 shows BTEX and TPH-G concentrations for each well sampled Discussion The general groundwater flow direction is to the northeast under a hydraulic gradient of 0 003 Water-level elevations have increased an average of 1 84 feet since the last quarterly monitoring (January 27, 1993) The TPH-G and BTEX concentrations detected in the samples collected this quarter are generally consistent with and within the range of previously reported results, however, the level of one or more of these constituents is higher than previously detected in wells E-2,E-4, E-5, and E-6 The samples from ott-site wells PR-1, PR-2, and BHD-2 did not contain detectable concentrations of hydrocarbons indicating that oft-site migration is being contained by the groundwater extraction system The hydrocarbon concentrations detected in BHD-1 are thought to be attributed to the Chevron station across the street trom the ARCO site Groundwater Extraction System ., A free product recovery system was installed at this site about 1984 After the free product was recovered, the system was modified for use as a groundwater extraction system and operated periodically from 1986 to 1991. The extracted groundwater was (and still is) discharged directly to the city of Stockton sanitary sewer system Additional modifications were made to improve the system in 1991, and it has been operating nearly continuously since June 1991 From June 1991 to September 1991, the system was operated at approximately 10 gallons per minute (gpm) In September 1991, the pumping rate was reduced to approximately 5 gpm because too large of an area was being influenced at a pumping rate of 10 gpm From September 1991 to January 1993, the pumping rate slowly decreased to approximately 2 5 gpm due to fungal growth clogging the system At the end of January 1993, the pumping rate was increased to approximately 5 5 gpm Since start-up in 1991, the system has extracted approximately 4 5 million gallons of water and has removed approximately 28 pounds of TPH, or 4 5 gallons During this quarter (second quarter 1993), the system operated at an average flow rate of approximately 4 gpm A summary of the groundwater extraction system data is shown in Table 1 The current groundwater extraction and monitoring program will be continued through 1993 Additionally, a soil vapor extraction system is currently being designed Use or disclosure of data contained on this sheet is subject to the restriction specified at the beginning of this document Brown and Caldwell 7453V2EPORT5\2ND93QTR RPT Cc,nsultants