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v %TC i r: A S S O C I A T E S I N C samples were collected from the borings. On July 21, 1995, Smith Technology developed and sampled monitoring wells MW-1, MW-2 and MW-3. Analytical results of the soil and groundwater samples collected indicated elevated concentrations of petroleum hydrocarbons were present in the soil and groundwater downgradient of the former gasoline UST locations. On September 24 and October 2, 1996, Smith Technology conducted an additional subsurface investigation at the site. A total of 9 soil borings were advanced to depths up to 15 feet below ground surface. Soil, soil vapor, and groundwater samples were collected from the borings. Analytical results of the soil and groundwater samples indicated the general extent of total petroleum hydrocarbons as gasoline (TPHg), benzene, toluene, ethylbenzene, and xylenes (BTEX), and methyl tertiary butyl ether (MTBE) in soil and groundwater under the site. Analytical results for geochemical parameters in soil and groundwater indicated bioremediation is occurring in the plume of petroleum hydrocarbons in groundwater beneath the site. Analytical results of soil vapor samples indicated the availability of oxygen, carbon dioxide, nitrogen and methane in the vadose zone. Also, results of laboratory geophysical testing on soil samples from the site indicated that the potential receptor on-site, the water supply well, would not be affected by the plume of petroleum hydrocarbons in groundwater within the next 20 years, in. the worst case. GROUNDWATER SAMPLING AND GRADIENT EVALUATION ATC personnel performed the latest quarterly groundwater monitoring of monitoring wells on June 25, 1998. Field work consisted of measuring depth-to-water levels .in all wells, collecting groundwater samples from all wells, and submitting groundwater samples for laboratory analysis. Water level measurements were collected from groundwater monitoring wells MW-1, MW-2, and MW-3. The depth to water ranged from 6.44 to 7.93 feet below top of well casing elevation. Groundwater elevations have increased an average of 0.14 feet since March 30, 1998. The water level data were used to develop the groundwater elevation contour map (Figure 2). Assuming that horizontal isotropic conditions prevail, groundwater in the uppermost aquifer beneath the site flowed in a north-northwest direction. The average hydraulic gradient on June 25, 1998 was calculated to be 0.003 ft/ft or about 17 feet/mile. The data indicates a groundwater gradient that is consistent with the gradient observed last quarter. A summary of groundwater monitoring data is presented in Table 1. Groundwater elevations are referenced to feet above mean sea level. Groundwater samples were collected from monitoring wells MW-1, MW-2, and MW-3. Prior to collection of groundwater samples a minimum of three well casing volumes were purged. The depth-to-water, pH, electrical conductivity, and temperature were measured and allowed to stabilize before groundwater samples were collected. Samples were then collected from each well using disposable bailers. Purge water was contained in 55-gallon DOT approved drums. Purge water from monitoring well MW-1 from the previous sampling event did not contain detectable "'A178Wreportsl2gmr199 H.doc 2