Laserfiche WebLink
Corrects e 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 /> (Normally performing a soil vapor treatability study and aquifer pump testing would be standar d <br /> operating pi ocedures 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 Ices 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 /> 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 OST'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 car eful review of the rates <br /> of water table drawdown and recovery recorded dui ing 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 far 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 4-4%z-inch-diameter casing installed within a 12-inch-diameter boring The wells will <br /> be completed to a depth of 30 feet bgs, with the bottom five feet of the installed casing being <br /> bla-4. 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 ,Nell 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 /> OST <br /> 701-1-2 cap Page 10 <br />