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Mr. Maurice Benson <br /> March 12, 2009 <br /> Page 2 <br /> shut down for both planned and unplanned periods, totaling 9 hours and 16 <br /> hours, respectively, during the 30-day test. The two extraction wells are located <br /> approximately 170 feet apart, with EW056A screened from 30-40 feet below <br /> ground surface (bgs) and EW055B screened from 87-102 feet bgs. EW056A <br /> produced approximately 10 gallons per minute (gpm) under steady state <br /> conditions with EW055B operating at approximately 75 gpm. The hydrologic <br /> units between the two screen intervals are unconfined with data showing <br /> hydraulic communication. Despite the apparent hydraulic influence from the two <br /> concurrently operating EWs, the report does not discuss the influence the wells <br /> could have on each other and potential effects on the mass removal tests #1 and <br /> #2. Specifically, operating two extraction wells screened in different hydrologic <br /> units in an unconfined aquifer in relative close proximity would affect each <br /> extraction well's potential radius of influence with competing hydraulic gradients <br /> and should be discussed in all applicable sections of the report. <br /> 2. The Dieldrin Mass Removal Test Pump Report in Appendix B concludes that <br /> dieldrin colloids less than 0.45 pm in diameter cannot migrate farther than 12 feet <br /> under the influence of a pumping well, with dieldrin larger than 0.45 pm only able <br /> to migrate 6 feet under the influence of a pumping well. These conclusions are <br /> primarily based on the two Hydropunch(D samples taken 6 feet from the EW056A <br /> and the two performance monitoring wells, LM190A and LM191A, located <br /> approximately twelve (12) feet away according to Figure 2-2. The feasibility <br /> study did not conduct any groundwater sampling for dieldrin colloidal mass <br /> farther than twelve (12) feet from EW056A to determine these conditions and <br /> should be amended to encompass a discussion of these uncertainties. <br /> 3. Page 4-1, Contaminant Properties, fourth paragraph; Based on the following <br /> factors: the NWC dieldrin plume has migrated over 200 feet in the last 16 years <br /> since injection at wells IW001, IW002, and IW003; EW056A results showed that <br /> all thirty-six (36) — (18 filtered/18 unfiltered) groundwater samples collected both <br /> pre, during and post pumping, contained dieldrin; EW056A performance <br /> monitoring wells both filtered and unfiltered showed steady dieldrin <br /> concentrations as the aquifer pump tests proceeded with increasing dieldrin <br /> concentrations towards the end the test; and, the highest concentrations of <br /> dieldrin in the northwest corner Were collected from EW056A effluent. Based on <br /> these results alone it appears that the dieldrin mass in the saturated zone is not <br /> as immobile as originally perceived based on literature. Additionally, while <br /> dieldrin has an affinity for organic carbon, the soil colloids present with the <br /> dieldrin mass were never analyzed to determine content and type. Knowing the <br /> nature and composition of the colloids would help better determine the true <br />