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i <br /> ; f ASSOCIATESON%TC <br /> I N C . <br /> �s <br /> sampled monitoring wells MW-1, MW-2 and MW-3. Analytical results of the soil and <br /> groundwater samples collected indicated elevated concentrations of petroleum hydrocarbons were <br /> present in the soil and groundwater downgradient of the former gasoline UST locations. <br /> On September 24 and October 2, 1996, Smith Technology conducted an additional subsurface <br /> investigation at the site. A total of 9 soil borings were advanced to depths up to 15 feet below <br /> ground surface. Soil, soil vapor, and groundwater samples were collected from the borings. <br /> Analytical results of the soil and groundwater samples collected indicated the general extent of <br /> total petroleum hydrocarbons as gasoline (TPHg), benzene, toluene, ethylbenzene, and xylenes <br /> (BTEX), and methyl tertiary butyl ether (MTBE) in soil and groundwater under the site. <br /> Analytical results for geochemical parameters in soil and groundwater indicated bioremediation is <br /> occurring in the plume of petroleum hydrocarbons in groundwater beneath the site. Analytical <br /> results of soil vapor samples indicated the availability of oxygen, carbon dioxide, nitrogen and <br /> methane in the vadose zone. Also, results of laboratory geophysical testing on soil samples from <br /> the site indicated that the potential receptor on-site, the water supply well, would not be affected <br /> by the plume of petroleum hydrocarbons in groundwater within the next 20 years, in the worst <br /> case. <br /> GROUNDWATER SAMPLING AND GRADIENT EVALUATION <br /> ATC personnel performed the latest quarterly groundwater monitoring of monitoring wells on <br /> March 30, 1998. Field work consisted of measuring depth-to-water levels in all wells and <br /> collecting groundwater samples from all wells and submitting groundwater samples for laboratory <br /> analysis. <br /> Water level measurements were collected from groundwater monitoring wells MW-1, MW-2, and <br /> MW-3. The depth to water ranged from 6.58 to 8.07 feet below top of well casing elevation. <br /> Groundwater elevations have increased an average of 0.61 feet since December 31, 1997. The <br /> water level data were used to develop the groundwater elevation contour map (Figure 2). <br /> Assuming that horizontal isotropic conditions prevail, groundwater in the uppermost aquifer <br /> beneath the site flowed in a north-northwest direction. The average hydraulic gradient on March <br /> 30, 1998 was calculated to be 0.003 ft/ft or about 17 feet/mile. The data indicates a groundwater <br /> gradient that is consistent with the gradient last quarter. A summary of groundwater monitoring <br /> data is presented in Table 1. Groundwater elevations are referenced to feet above mean sea level. <br /> Groundwater samples were collected from monitoring wells MW-1, MW-2, and MW-3. Prior to <br /> collection of groundwater samples a minimum of three well casing volumes were purged. The <br /> depth-to-water, pH, electrical conductivity, and temperature were measured and allowed to <br /> stabilize before groundwater samples were collected. Samples were then collected from each well <br /> using disposable bailers. Purge water was contained in 55-gallon DOT approved drums. Purge <br /> water from monitoring well MW-1 from the previous sampling event did not contain detectable <br /> concentrations of petroleum hydrocarbons and was discharged to the ground surface. <br /> Groundwater well purge and sample logs are provided in Appendix A. <br /> w:1951221Reports\1QMR1998.doc 2 <br />