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Mr Chuck Carmel September 6, 1994 Page 2 Results The general groundwater flow beneath the site on May 20, 1994, was to the northeast under an average hydraulic gradient of 0 001 (Figure 1) A summary of depth-to-water measurements and calculated groundwater elevations is presented in Table 1 Table 2 lists past and present groundwater flow directions and hydraulic gradients for this site Analytical results of groundwater samples are summarized in Table 3 The complete laboratory report for the sampling event is presented in Exhibit A Figure 2 shows TPH-G and BTEX concentrations for this sampling event Benzene concentrations ranged from nondetectable in several wells to 590 micrograms per liter (pg/1) in ATR-4 TPH-G concentrations ranged from nondetectable in several wells to 8,100 pg/1 in well ATR-4 The detection limits for benzene, toluene, and ethylbenzene are 0 3 pg/l, for xylenes is 0 5 pg/l, and for TPH-G is 50 pg/1 Approximately 0 29 feet of free product was measured in ATR-8 and a trace of free product was observed in ATR-3 Discussion Water-level elevations decreased an average of 012 feet across the site since February 18, 1994 Water levels in all wells declined slightly (an average of 0 12 feet) The northeasterly groundwater flow direction and the hydraulic gradient(0 00 1) are consistent with previously reported data BTEX constituents detected in the samples taken on May 20, 1994, from wells ATR-7, ATR-9, ATR-10, ATR-11, and ATR-12 were at concentrations less than 0 5 pg/1 Well ATR- 1 detected slightly higher BTEX concentrations than the detection limits for the second quarter in a row BTEX and TPH-G concentrations are generally consistent with previous results in wells ATR-2, ATR-4, and ATR-5, except the TPH-G concentration in well ATR-4 which rose significantly from 950 pg/i on February, 18, 1994 to 8,100 pg/1 on May 20, 1994 Wells ATR-8 and ATR-3 were not sampled due to the presence of free product, 0 29 feet in ATR-8 and a trace in ATR-3 ATR-6 was inaccessible and not sampled ARCO is preparing a work plan for the installation of air sparge and soil vapor extraction wells at this site The work plan will be submitted to the County and Regional Board Upon approval of the work plan by the County, drilling permits will be secured and drilling will be scheduled These wells will become part of the remediation system currently being designed for the site The remediation system will be installed in autumn of 1994 • Use or disclosure of data contained on this sheet is subject to the restriction specified at the beginning of this document 12641REPORTSW4D94Q7RAPT