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Corrective Action Plan <br /> table. Exposing the impacted soil zone is the single most important function of the proposed <br /> groundwater extraction process. Secondary, yet also necessary, benefits of groundwater <br /> extraction include controlling migration of impacted groundwater away from the source and the <br /> removal of the most severely hydrocarbon-impacted groundwater from the subsurface. <br /> (Normallyperforming a soil vapor treatability study and aquifer pump testing would be standard <br /> operating procedures. OST is proposing to forego both of these tests for the following reasons: <br /> ' Present conditions at this site preclude meaningful preliminary SVE testing. The horizon most <br /> impacted by gasoline constituents lies in the interval from-10 feet to 20 feet bgs. The <br /> groundwater table is presently near its recorded highest elevation at 15 feet bgs. The capillary <br /> fringe area likely extends several feet above the water table. Therefore, the impacted soil horizon <br /> is either at a high level of saturation or is completely saturated. Saturated soils have no gas <br /> 1 permeability. Gas permeability of the soil will be restored through dewatering of the impacted <br /> area by the groundwater co-extraction process and the additional removal of interstitial water <br /> (from the soil pores) by evaporation during the SVE process. Throughout the duration of <br /> remediation at the site, soil vacuum studies will be conducted to confirm radius of influence and <br /> other parameters necessary to evaluate the effectiveness of the SVE process. Recorded soil <br /> characteristics at the site and DST's considerable experience in applying SVE to these kinds of <br /> ' soils is sufficient for the design of an effective SVE system. Furthermore the system will be <br /> designed to provide flexibility for easy upgrade if this is found to be necessary. <br /> Aquifer pump testing is considered unnecessary and not cost-effective. There is sufficient <br /> understanding of the hydrogeologic characteristics at the site from the careful review of the rates <br /> ' of water table drawdown and recovery recorded during well development and during purging <br /> for groundwater sampling. The groundwater treatment system proposed by OST will <br /> accommodate a rate ofgroundwater extraction far greater than that which will be experienced <br /> ' during remediation. The true test of the effects of the groundwater extraction process will be the <br /> actual data recorded over the first weeks of operation. As for the SVE process, the system is <br /> designed for maximum flexibility for upgrade if considered necessary) <br /> 5.1 Groundwater/SVE Co-Extraction Wells <br /> To implement the groundwater extraction/SVE system,OST proposes the installation of four new <br /> extraction wells at the locations proposed on the Remediation Site Map, Figure 5. The wells will <br /> consist of 4-41/2-inch-diameter casing installed within a 12-inch-diameter boring. The wells will W <br /> ' be completed to a depth of 30 feet bgs, with the botto installe casixlaei - <br /> blank. The wells will be perforated in the interval from 10 feet bgs to 20 feet bgs except for co- <br /> extraction well EW-1, located at the source, which will be perforated in the interval from 5 feet <br /> ' to the bottom. It is noteworthy that each .extraction well will have.an (existing) companion . <br /> monitoring well which will allow better understanding and control of the water situation at each <br /> location and the site in general. <br /> r � a- <br /> 701-1-2.cap OST Page 10 <br />