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3.0 MONITORING PROCEDURES Groundwater monitoring took place on August 25. Upon arrival at the site, Upgradient personnel opened the wells and allowed them to equalize with air pressure. Approximately 15 minutes after opening,the depth to groundwater was measured with a Solinst water level meter. The witer depths are shown in Table 1 and Appendix B. A two-stage submersible pump was then used to purge the wells of standing water, which was deposited in a 55-gallon drum. During purging, the temperature, pH, and conductivity o F the water were measured at 3 to 5-gallon intervals with a Corning Checkmate meter until these parameters stabilized (see Appendix B). To prevent cross-contamination, the pump was washed in a TSP solution between wells. The water samples were collected with a disposable plastic bailer and placed in 40-m1 vials. The vials were labeled and logged and placed in a cooled ice chest. 4.0 RESULTS 4.11 Depth to Groundwater and Groundwater Gradient When the wells were monitored in May, the depth to groundwater was approximately 6 feet. Since then, the static water level has dropped to 9 feet, but remains several feet above the well screen. The data in Table 1 were used to contour the piezometric surface and interpret the groundwater flow direction, which are illustrated in Figure 3. The piezometric surface now slopes almost due north at a gradient of 0.0025 ft/ft. Although the gradient is identical to the gradient during the first quarter, the direction differs by more than 90 degrees. Since monitoring began in 1994, the gradient has shifted from east, to southwest, to north. Previously, we suspected that the change n gradient was due to a rise of the static water level into the low-permeability clay that overlies the ;first water- bearing zone at the site. However,the large variation in groundwater flow direction indicated by the present gradient suggests that other factors are at work. 4.2 Laboratory Results As in the past, a gasoline odor was noticeable in all wells when they were purged. Gasoline and BTEX compounds were detected in all three wells, but at much lower concentrations than in previous monitoring events (Table 2). This could be due to some natural attenuation of the contaminants, to lateral spreading and dilution of the plume, to adsorption of the hydrocarbons onto soil particles as the water table has dropped, or to some other mechanism. 3