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5 <br /> Groundwater Extraction (Optional) <br /> The decision as to whether or not groundwater extraction is needed to remediate the site will <br /> be based on data collected during the first 6 months to 1 year of sparging and vapor extraction. <br /> If required, groundwater may be extracted from TEX-1 and from monitoring wells ATR-2, <br /> ATR-4, and ATR-5. The purposes of pumping from these wells will be to: <br /> +' 1. Keep the water table from rising as a result of vapor extraction so that vapors can be <br /> withdrawn from the hydrocarbon-affected soil 1 to 2 feet above the current water table. <br /> 2. Lower the water table in order to expose more vadose zone. <br /> 3. Recover and treat hydrocarbon-affected groundwater from these wells. <br /> Pumping rates at wells ATR-2, ATR-4, and ATR-5 are expected to be on the order of 0 to <br /> 2 gpm, and at TEX-1, 10 to 15 gpm . The actual pumping rates will vary depending on water <br /> elevations in specific wells and the actual performance of TEX-1. <br /> Figure 6 shows the anticipated capture zone achieved by pumping from TEX-1 at 10 gpm <br /> and ATR-2, 4, and 5 at 1 gpm. These results were obtained using the analytical groundwater , <br /> flow model "Quickflow" (by Geraghty & Miller, Inc.). The model input parameters used in the <br /> analysis are as follows: <br /> ( Hydraulic conductivity - 60 ft/day <br /> Hydraulic gradient = 0.002 <br /> Aquifer thickness = 23 feet <br /> Average flow direction = N45E <br /> These parameters have been previously reported in quarterly reports and in the t <br /> "Supplemental Site Investigation Report," dated March 5, 1991, (BC) for this site. <br /> The extraction system is not expected to have a significant impact on the regional hydraulic <br /> gradient. <br /> Groundwater Treatment <br /> s <br /> All extraction wells will be plumbed to the treatment area by PVC piping placed below <br /> ground. Extracted groundwater will be treated by three 1,000-pound GAC units connected in <br /> series, located in the treatment area as shown on Figure 2. <br /> Discharge and Permits <br /> Treated groundwater is proposed to be discharged into the City of Tracy (City) storm drain <br /> system. Piping from the treatment area to this storm drain located on Tracy Boulevard will be <br /> installed underground, as shown on Figure 2. <br /> ' 44 03r9S—N740YAMORM7403-0I.R-1 <br /> QMS-MWO <br />