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�LI Mr Kyle Christie May 15, 1995 Page 2 Results and Discussion The general groundwater flow direction beneath the site on March 8, 1995, was to the northeast under a hydraulic gradient of approximately 0 005 (Figure 1) The cone of depression centered around the groundwater extraction well (R) can be attributed to the operation of the groundwater extraction system at the site. Since groundwater monitoring began in 1989, the general groundwater flow direction has been to the northeast at this site The hydraulic gradient measured this quarter is slightly steeper than previously measured gradients Summaries of depth-to-water measurements and calculated groundwater elevations are presented in Table 1 Table 2 lists historical groundwater flow directions and hydraulic gradients for this site Depth-to-water on March 8, 1995 ranged from 12 55 in well PR-2 to 15.25 in well E-11. Since the last quarterly monitoring event (December 8, 1994), water-level elevations in all monitoring wells except E-6 and MW-2 have increased an average of 2.42 feet. Water-level data collected from wells E-6 and MW-2 were not used in Figure i because the well casings elevations were altered during the incorporation of these wells into the soil vapor extraction and air sparging system EMCON's data are based on the altered well casings. The well casing for these wells will be resurveyed in the second quarter of 1995. Benzene concentrations this quarter ranged from non-detectable in wells E-7, E-12, PR-1, PR-2, BHD-2, MW-1, MW-3, and MW-4, to 3,000 micrograms per liter (pg/1) in well E-5 These concentrations are within the range of previously reported values, with the exception of wells E-2, E-6, E-9, and MW-2. Benzene concentrations in well E-2, E-6, and E-9 are lower than previously reported values, but are higher than previous values in MW-2. TPH-G concentrations ranged from non-detectable in wells E-7, PR-1, PR-2, BHD-2, MW-1, MW-3, and MW-4, to 94,000 pg/l in well E-3 These concentrations are consistent with previous values, with the exception of wells E-3, E-6, and MW-2 TPH-G concentrations in wells E-3, E-6, and MW-2 are higher than previously reported values. The detection limit for benzene is 0 5 pg/l and for TPH-G is 50 pg/l. 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. The hydrocarbon concentrations detected in BHD-I are thought to be attributed to the Chevron station across the street from the ARCO site. Chevron's well MW-1 is located approximately 30 feet to the north of well BHD-1 and near Chevron's former underground storage tank location. Samples from Chevron's MW-1 have generally contained similar TPH-G and BTEX concentrations to those in BHD-1 • Use or disclosure of data contained on this sheet is subject to the restriction specified at the beginning of this document 2060,REP0RTSV ST95QTR.RPT