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I16 September 1997 . • AGE-NC Project No 95-0139 Page 3 of 5 3 0. FINDINGS ' 3 1 GROUND WATER GRADIENT AND DIRECTION r> The elevation of ground water in each well was calculated by subtracting the ground water depth from the surveyed casing elevation (Table 4) Depth to ground water at the site ranged from 9 28 to 11 78 feet below the tops of the well casings Between January and July 1997, ground water elevation decreased an average of 1 28 feet at the site ' The ground watenflow direction was calculated to be N 39° E with a gradient of 0 0053 ft/ft This represents a 37 degree change in flow direction and an increased gradient since the January 1997 monitoring event Current groundwater elevation contours are Illustrated on Figure 3 3 2 LABORATORY ANALYSIS OF GROUND WATER SAMPLES - TPH-g and TPH-d were detected in MW-1 at concentrations of 1,200 and 910 arts per billion (ppb, _ p reported as -micrograms per liter), respectively BTE&X were also detected in MW-1 at ' concentrations ranging from 0 95 ppb (toluene) to 74 ppb (xylenes) MTBE was detected in MW-2 at a concentration of 29 ppb MTBE was confirmed at a concentration of 24 ppm by EPA method 8260 No other petioleum hydrocarbons were detected during the July 1997 sampling event The analytical results of the ground water samples are summarized in Table 2 The laboratory report (MAI I D Nos 78299 - 78302) and chain-of-custody form are included in Appendix B 3 3 REVIEW OF HISTORIC CHROMATOGRAMS Indications of MTBE were not present on the chromatograms for the samples collected in March, June or Septembei 1994 Detection limits were estimated at 10 ppb Indications of MTBE were ' noted on the chromatogram for the sample collected from MW-2 in January 1996, at an unspecified concentration Indications of trace concentrations of MTBE were noted for the sample collected from _ h MW-3 in January 1996 Indications of MTBE were not noted for the January 1996 samples collected ' from MW-I or MW-4 Letters from WEST laboratories are included in Appendix C ti 3 4 MASS OF REMAINING HYDROCARBONS Approximately 530 cubic yards of impacted soil was estimated to be in place north of the former USTs location Based on average concentrations of TPH-g of 120 ppm, approximately 72 9 kg, or s � ' 25 7 gallons of gasoline remain Based on an average concentration of TPH-d of 25 ppin, '} Adianced CeoEnvironmental,Inc 1