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Mr. Chuck Carmel March 17, 1993 • Page'2 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 2 97 feet since the last quarterly monitoring (October 1992). The TPH-G and BETX 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-4, E-6, and E-11. The samples from off-site wells PR-1, PR-2, and BHD-2 did not contain detectable concentrations of hydrocarbons, indicating that off-site nugration is bung 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 from the ARCO site Groundwater Extraction System A product recovery system was installed at this site around 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 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. From November 1992 through January 1993, a total of approximately 210,000 gallons of groundwater were extracted from beneath the site. Based on the concentrations of BETX and TPH-G in the extracted groundwater, the following estimates of hydrocarbon removal can be made. Pounds removed Month B E T X TPH-G November 1992 0.0006 0.0009 <0.0006 0,009 012 December 1992 <0.0006 0 0012 0.0003 0 036 054 January 1993 0.03 1-0.0030 1 0.0006 0.054 057 The current groundwater extraction and monitoring program will be continued through 1993. Additionally, a soil vapor extraction system is currently being designed. grown and Caldwell -7453stEP0W isrY3QTR.itFr Consultants