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Geologkot technics/ac. Page 10 Groundwater Monitoring Report Project No.750.2 April 1,2005 Date Influent (ppm)i Eff luent(ppm)l eciency(%)2 01/04/05 83 21 99.75 01/17/05 86 32 99.63 02/22/05 80 25 99.69 03/17/05 56 41 99.93 Averages= 76.251 20.51 99.73 i Influent and Effluent from Laboratory Analytical Data 2 Efficiency percentage calculated as Effluent/Influent 4.2 Mass Removal Mass removal calculations are completed utilizing the results of weekly OVM readings and monthly laboratory analyses of the SVE system influent and effluent. These calculations are presented in Table 5 in Appendix A. As of March 30, 2005, the system has removed an estimated cumulative total of 336 gallons or 637 pounds of TPH-G. Mass emission calculations are completed utilizing the results of weekly OVM readings and monthly laboratory analyses of the SVE system influent and effluent. These calculations are presented in Table 6 in Appendix A. As of March 30, 2005, the system has emitted an estimated cumulative mass of 84 pounds. At no time did the SVE emit more than 1.8 pounds in a 24-hour period. The historical average emissions are estimated at 0.532 pounds per day. 5.0 FINDINGS & RECOMMENDATIONS Findings The results of the groundwater sample analyses show the following: • All groundwater-monitoring wells were non-detect above laboratory reporting limits for all analyzed constituents. • Vertical groundwater gradient was calculated for the event of February 16, 2005, and was found to be insignificant. o The magnitude of the vertical gradient has decreased significantly from the initial values measured in 2001. o Fifteen of the past seventeen monitoring events show a downward trend to groundwater flow. o The downward vertical gradients are typically equal too or less than the horizontal groundwater gradients. • Oxidation-Reduction Potential measurements are positive for all the wells. This suggests that the volume of contaminants leaching into groundwater has been stopped and that biodegradation of the contaminants is at a rate sufficient to mitigate the residual BTEX/TPH-G plume in the area around the source without depleting the oxygen. V 1.ui