WORK PLANS - Laserfiche WebLink

Home Browse Search

Mr. Brattain October 19, 2020 Page 3 additional monitoring wells were installed in the prospective extraction area in the downgradient area to assess performance of the Final Remedy and the ISCO system was modified to increase extraction and injection rates. Towards the end of Phase 2, two new extraction wells (GEW-34A and GEW-3513) were installed in the core of the plume at 503 Benjamin Holt Avenue to enhance COC mass removal from groundwater. The new extraction wells commenced operation in October 2019. In addition, three vessels containing ion-exchange (IX) resin for contingent treatment of hexavalent chromium (Cr[VI]), a byproduct of ISCO were also installed. The IX system is currently not in operation as the existing treatment train continues to meet the Cr(VI) discharge limits under the National Pollutant Discharge Elimination System(NPDES)permit. Phase 3 of the Final Remedy (also referred to as Phase 3 recirculation) commenced operation in January 2020 with the conclusion of ISCO injections and subsequent decommissioning of the ISCO mixing and dosing equipment at the groundwater extraction and treatment system(GWETS) compound. Phase 3 of the Final Remedy will continue groundwater recirculation to distribute residual oxidant in the groundwater to enhance treatment, enhance COC mass removal through additional extraction at mid-plume and, at the plume margin and prevent further downgradient migration of ISCO byproducts, as needed. Phase 3 recirculation is expected to continue operating for five years. The performance of the Final Remedy is monitored under the WDR-MRP whereas overall performance of the groundwater remedy for the Site is monitored under the GWMP. With the conclusion of Phase 1 and Phase 2 of the Final Remedy, page 5 of the WDR-MRP states that: " The groundwater monitoring program for Phase 3 will initially follow the same scope and schedule as the Phase 2 groundwater monitoring program and may later be adjusted, as appropriate". In addition,page 9 of the WDR-MRP states that the Annual Report should include: "if desired, a proposal and rationale for any revisions to the groundwater sampling plan frequency and/or list of analytes." The WDR-MRP at the time of drafting, anticipated continued changes to the monitoring program during implementation of Phase 3 though it was not specific as to the scope or the process for making these modifications. With Phase 3 of the Final Remedy approximately 1 year into operation, groundwater monitoring at the same frequency as developed for Phase 1 and Phase 2 does not provide appropriate benefit for remedial performance monitoring. Therefore, changes to engineers I scientists I innovators