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<br /> Each of the wells was constructed with 0.020-inch slotted casing. Figure 2 in the attached report
<br /> includes drilling locations while Appendix A contains boring logs and well construction details.
<br /> Soil samples collected during the drilling of each of the wells were submitted to an analytical laboratory.
<br /> Where possible, capillary fringe samples were submitted, although shallower soil samples were also
<br /> analyzed. All samples were analyzed for gasoline and benzene, toluene, ethylbenzene, and xylenes
<br /> (BTEX). Although the sample collected from MW-8 at a depth of 75 feet bgs contained trace
<br /> concentrations of hydrocarbons (0.064 ppb benzene, 0.005 ppb toluene, and 0.007 ppb xylenes), none of
<br /> the other soil samples contained detectable concentrations of hydrocarbons. Table 2 in the attached
<br /> report summarizes analytical results and laboratory reports are included as Appendix D.
<br /> On July 19, 1996, samples were collected from MW-1 through MW-9 by a representative of SECOR.
<br /> MW-10 was sampled on August 1, 1996. Prior to purging, the depth to water in each well was measured
<br /> to evaluate elevation, flow direction, gradient, and free product thickness. As noted in the attached
<br /> report, groundwater with a southwesterly flow direction and a gradient of 0.03 ft./ft. were encountered in
<br /> the wells at depths of 67.7 feet to 84.07 feet below ground surface. Free product was not encountered in
<br /> any of the wells. The locations of the wells are identified on Figure 2 of the attached report.
<br /> Since the previous sampling event, groundwater elevation decreased in MW-3 by 0.07 feet and
<br /> increased in wells MW-1, MW-2, and MW-4 by 0.15 feet to 0.33 feet, resulting in an overall average
<br /> increase in groundwater elevation of 0.18 feet across the site. Groundwater flow direction changed from
<br /> southeast to southwest and gradient decreased from 0.15 ft./ft. 0.03 ft./ft. The variations in groundwater
<br /> elevation, flow direction, and gradient could be a result of additional data points provided by the new
<br /> wells, or they could be due to seasonal variation. Table 1 in the attached report summarizes all
<br /> groundwater elevation data collected to date.
<br /> Analyses identified elevated concentrations of hydrocarbons in the samples collected from MW-1
<br /> (13,600 ppb gasoline, 1,130 ppb benzene, 4,100 ppb toluene, 482 ppm ethylbenzene, and 2,710 ppb
<br /> xylenes), MW-3 (2,700 ppb gasoline, 288 ppb benzene, 242 ppb toluene, 133 ppm ethylbenzene, and
<br /> 280 ppb xylenes), and MW-6 (1,370 ppb gasoline, 142 ppb benzene, 292 ppb toluene, 81 ppm
<br /> ethylbenzene, and 495 ppb xylenes). Trace concentrations of hydrocarbons were found in the samples
<br /> collected from MW-4 (83.5 ppb gasoline, and 1.4 ppb benzene), MW-5 (64 ppb gasoline, 15.3 ppb
<br /> benzene, 0.7 ppb toluene, 2.5 ppm ethylbenzene, and 1.4 ppb xylenes), MW-8 (5.8 ppb benzene and 1.0
<br /> ppb xylenes), and MW-9 (1.4 ppb benzene). Hydrocarbons were not present at detectable
<br /> concentrations ins the samples collected from MW-2, MW-7, and MW-10. Table 3 in the attached report
<br /> summarizes groundwater analytical data and laboratory reports are included as Appendix D.
<br /> Conclusions
<br /> Based on the results of the site investigation it appears as though soil impacts remain limited to the
<br /> immediate vicinity of the former tank system. Although low concentrations of hydrocarbons appear to be
<br /> migrating offsite to the east (MW-8, sidegradient) and west (MW-5, sidegradient), groundwater impacts
<br /> appear to be fairly well defined in except to the northwest (MW-6, upgradient).
<br /> Since the May 1996 quarterly sampling event hydrocarbon concentrations decreased in MW-2 and MW-4
<br /> and increased in MW-1 and MW-3; however, the changes were not very great in any of the wells. The
<br /> observed fluctuations in hydrocarbon concentrations may be a result of a changes in groundwater
<br /> elevation; however, not enough data has been collected to evaluate their significance. Additional
<br /> groundwater data will be collected to further evaluate the extent of the dissolved hydrocarbon plume.
<br /> I
<br /> Future Site Activities
<br /> The results of the most recent site investigation suggest that the extent of impacted soil has been
<br /> defined in all directions, while the extent of groundwater impacts is fairly well defined except to the i
<br /> northeast (upgradient) of the former tank system. Because the extent of impacts is nearly defined, and it
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