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;.:'. �z2 r y.. �-' astir' - .r. "`-.:� ,., '""-' "` `.'•..`�',y.*^ "--.- - <br /> ,w <br /> r <br /> PRESENT CONDITIONS <br /> EHCON Associates began evaluation of the recovery system at this site in <br /> October 1485. The investigation included an evaluation of the hydraulic <br /> functioning of the recovery system and an assessment of the current <br /> �- extent of hydrocarbon contamination. The prime purpose of the hydraulic <br /> evaluation is to determine the area of influence of the recovery well to <br /> ensure the capture of gasoline product beneath the site. <br /> The hydraulic evaluation of the site involved (1) deactivation of the <br /> system, then monitoring the recovery for a week, and (2) monitoring of <br /> water levels during reactivation of the recovery system and observing <br /> the drawdown response in the water table. Hydrogeologic parameters <br /> including transmissivity of the aquifer, flow rates, and cone of depres- <br /> sion were estimated from this data. <br /> During the system reactivation, monitoring showed ali site wells were <br /> affected within two hours by pumping at 16 gpm in,the extraction well. <br /> _. Drawdowns ranged from 2.26 feet in the recovery well to .02 foot in <br /> E-12, 110 feet from the pumping well. The data collected from the <br /> evaluation was used to estimate some hydraulic parameters. - An average <br /> transmissivity of approximately 7,000 gallons per day per foot (gpd/ft) <br /> was calculated from the drawdown and recovery of water levels during <br /> deactivation and reactivation of the system. From this transmissivity, <br /> an average ground-water velocity of 1 to 2 feet/day towards the recovery ` <br /> ti well was estimated based on the observed gradient (see Appendix C for <br /> transmissivity calculations). <br /> Contour maps developed from liquid levels measured while the recovery <br /> system was operating (Figure 6) and while the system was deactivated for <br /> one week (Figure 7), demonstrate the influence of the extraction well. <br /> The zone of pumping influence extends approximately 110 feet from the <br /> extraction well. The capture zone encompasses all the area beneath the <br /> service station as shown by the cone of depression in Figure 6. The <br /> majority of lost product is believed to be within this zone due to flat <br /> ground-water gradients and low velocity. <br /> PJD 438-22.04 8 <br /> `,` EMCM Associates <br />