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S.,i <br /> cw4gkal7edmicstxc. Page 6 <br /> Groundwater Monitoring Report <br /> Project No.425.2 <br /> August 6,2004 <br /> ` • All three of the domestic wells were non-detect for this monitoring event. <br /> • Dissolved Oxygen measurements are all on the low end of the scale, ranging between <br /> 0.04 and 2.6 ppm. <br /> • Oxidation-Reduction Potential (ORP) measurements are all negative (Table 4) and <br /> corroborating with the low DO values. <br /> 4.0 CONCLUSIONS AND RECOMMENDATIONS <br /> The following conclusions have been drawn regarding the status of the plume at this site and <br /> recommendations for future work: <br /> Conclusions <br /> 1. The water table groundwater gradient historically flowed in a northerly direction at about <br /> 0.0020 ft/ft prior to May 1998. <br /> 2. The intermediate depth groundwater has flowed easterly, with three shifts to southeast <br /> during September 2000, September 2001 and December 2002. The northerly flow <br /> direction during the December 3, 2001 event was anomalous. The gradient is currently <br /> N890E at 0.0025 ft/ft. <br /> 3. The dominance of upward vertical flow of groundwater may be the primary reason the <br /> contaminants have not impacted the drinking water aquifer. <br /> 4. Increased TPH-G concentrations in MW-5 suggest the plume may be spreading laterally <br /> to the west. <br /> ` 5. Petroleum hydrocarbon concentrations in the groundwater at the site fluctuate with each <br /> monitoring event. The residual contamination in soil, up gradient of MW-2, remains a <br /> significant source of impact to the groundwater plume. <br /> 6. The deeper groundwater plume is defined vertically since MW-102 and MW-202 remain <br /> non-detect for contaminants, indicating that the contamination is not moving deeper into <br /> ` the aquifer. <br /> 7. The groundwater plume is not defined to the northeast or to the west. It may not be <br /> feasible to perform further definition to the west, but the northeast direction is available <br /> for well installation. <br /> 8. The three domestic wells sampled remain non-detect for all analyzed constituents, <br /> indicating that the drinking water aquifer has not been impacted. <br /> Recommendations <br /> The following recommendations are made: <br /> 1. Continue quarterly groundwater monitoring events. <br /> 2. Prepare a work plan for the bench-scale test. <br /> 3. Further define the down gradient extent of the groundwater plume northeast of the site. <br /> Install one monitoring well near MW-8 as shown in Figure 9. The MW-108 will be in the <br /> second zone about 10' screen in the course grained unit. <br /> L <br />