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6.2.1.1.2 Extraction Wells <br /> At least one large-diameter well (12 or 24 inches) would be necessary to recover <br /> groundwater at adequate flow rates to remove the contaminated water. The existing 4-inch <br /> well (MW-1) is screened only within the upper 5 feet of the saturated zone, and even hand <br /> bailing during quarterly monitoring activities exceeds the well yield. It would therefore not <br /> be suitable for sustained pumping, even at a flow rate of 1 gallon per minute. All of the <br /> other monitoring wells are either screened above the water table or are 2-inch diameter <br /> wells and are located too far from the center of the contamination plume. An extraction well <br /> near MW-1 and piped to the carbon filters would be necessary. <br />' 6.2.1.1.3 Disposal <br /> Following treatment, the water could be discharged to the storm sewer under a National <br /> ' Pollution Discharge Elimination System (NPDES) permit or to the sanitary sewer under a <br /> special exemption by the City of Lodi. Discharge to the storm sewer would require <br /> ' installation of piping from the extraction well to the nearest storm drain, which is located <br /> on Lodi Avenue. A sanitary sewer line runs down the alley behind the site, and it would <br /> therefore be more cost-effective to discharge to the sanitary sewer. <br /> ' An alternative would be re-injection of treated water into the aquifer via injection wells. <br /> This method would require a Waste Discharge permit from the Central Valley Regional <br /> Water Quality Control Board. Monitoring wells MW-6 and MW-7 could be used for <br /> injection, because they are up-gradient of the contamination plume and would increase the <br /> flow rate of contaminated groundwater from MW-4 and MW-3 to the extraction well. <br /> ' 6.2.1.1.4 Duration <br /> ' Experience has shown that all systems involving groundwater extraction require much more <br /> time than would be anticipated from aquifer tests and calculations of groundwater discharge <br /> rates, and seldom achieve regulatory goals for groundwater clean-up. Systems typically <br /> ' operate for several years. During this time, pumps and carbon filters may need replacement <br /> several times. This equipment is expensive. The primary utility of pump-and-treat systems <br /> is in preventing migration of contaminated groundwater, which has not been a problem at <br /> this site. <br /> ' 6.2.1.2 Disposal <br /> A second variation of pump-and-treat systems is transport and disposal at a licensed <br /> hazardous waste facility. This method suffers from many of the problems of carbon filtration, <br /> ' -and can be even more expensive when concentrations of contaminants are relatively low and <br /> large volumes of water must be disposed. <br /> Ombgical Audu s.rv�..luc. <br /> A&A PARl1-78-"I 47 34 <br /> 1 <br />