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S •` 19 June 2000 AGE-NC Project No 96-0232 Page 29 of 35 9 2 2 Feasibility Studies Ground water extraction should have a moderate to high feasibility for the Flag City site Ground water extraction is generally not a desirable method for remediation, however this technology is useful for hydraulic control to prevent spreading of the contaminant plume and to capture MTBE-impacted groundwater MTBE is highly soluble and therefore does not readily adhere to soil Based on the limited area of vadose zone at the site, the majority of adsorbed petroleum-impact is already submerged beneath the water table Therefore, MTBE adhered to soil should dissolve and could be addressed with ground water extraction On 03 April 2000,interim ground water extraction was initiated at the site by pumping ground water from EW-1 at a rate of 2 GPM, grab ground water samples have been collected on a weekly basis since 05 Apn12000 at the discharge from EW-1 Dissolved MTBE was detected in initial samples at concentrations of 1,800 gg/l,thereafter, consecutive MTBE decreases were observed from 1,600 µg/1 to 350 µg11 over a two month period (Table 9) Based on ten ground water monitoring events recorded at the site between July 1996 and March 2000, ground water gradient has been observed as relatively flat at the site ranging between 0 001 and 0 01 Based on the low historical groundwater gradient, minimal extraction wells and minimal pumping influence (draw-down) would be necessary to implement on-site hydraulic control 9 2 3 Duration Experience has shown that ground water extraction systems operating on similar sites of magnitude typically will operate for several years During this time, pumps and other equipment may need replacement several times A minimal treatment period of 24 to 36 months is estimated for the site 9 2 4 Cost Ground water extraction is usually a very costly method of remediation, treatment is highly dependant upon the type of dissolved hydrocarbons in the ground water Costs for installation of a ground water well extraction system typically range from $10,000 to $20,000, based upon the number and total depth of wells Once groundwater is extracted,the contaminated water will require disposal (i a on-site discharge into municipal sewer/storm drain system or transportation to off-site wastewater treatment facility) If discharging into a municipal sewer/storm drain system is selected, then an on-site treatment (i e activated carbon and/or air stripping) will be necessary prior to discharging Advanced GwEw.ironmental,Inc