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f;r A S S O C I A T E S I N C . ?, In Jul 1999 ATC conducted a groundwater extraction test. The aquifer test was conducted over Y � g q a 24-hour period by extracting groundwater at a constant rate from well MW-4. The test was performed to determine the aquifer properties and the radius of influence for groundwater pumping. The groundwater pumping rate during the pilot test, as measured by the flow meter, averaged approximately 3 gallons per minute (gpm)for the first half of the test and 5.5 gpm for the second half M of the test. The collected data were analyzed using AQTESOLVTm groundwater modeling software and a recovery test analysis. The observed maximum drawdown in each of the four observation wells during the test was plotted against the distance of each well from well MW-4. Based on the observed data, the radius of influence for groundwater extraction at the site is greater than 50 feet. Observation well MW- 1 is located approximately 46 feet from pumping well MW-4 and the groundwater elevation dropped about 1.7 feet in this well. Observation wells MW-2, MW-3, and MW-5 are each located approximately 55 feet from pumping well MW-4 and the groundwater elevation dropped 1 about 0.7 feet in each of these wells. In general, a small radius of influence is expected for pumping in an unconfined aquifer. The Cooper-Jacob type-curve solution for an unconfined aquifer was used to estimate aquifer eters. The obtained results for the story using the Cooper-Jacob a coefficient Param g g solution were a little lower than expected for an unconfined aquifer. The storage coefficients for unconfined aquifers are typically between 0.01 and 0.3, while those for confined aquifers are typically between 0.00005 and 0.005 (Driscoll page 210, 1986). The average storage coefficient calculated using the Cooper-Jacob solution was 0.0015. Although the storage coefficients were lower than expected, <_ this method was considered appropriate for the site conditions. The average hydraulic conductivity values (0.001 meters per second [m/s]) calculated fall within e_-r =:r the average range for fine to coarse sand (1 to 10'S m/s) (Driscoll page 74, 1986). Using this hydraulic conductivity, an average groundwater velocity can be calculated. Based on an average groundwater gradient of 0.0077, the average groundwater velocity is approximately 1.66 meters/day or almost 2,000 feet per year. This is an average velocity but is not necessarily �I,' representative of the movement of the TPHd plume because it does not take into consideration effectsavec=ion ispersion;a_r anis ropic and/or non us geology. The plume of TPHd appears to be migrating at a much slower rate as the elevated concentrations historically detected in well MW4 have not been observed in hydraulically downgradient wells MW2 and MW3 since monitoring began in 1989. 4.2.2 Petroleum Hydrocarbons in Groundwater Total Petroleum Hydrocarbons as diesel have historically have been detected in the greatest concentrations at monitoring which is adjacent to the former UST. This monitoring g well MW4� J g w:162574.021repor \closure-smith.doc 5 2