COMPLIANCE INFO_EW-5 INSTALL PERMIT PACKAGE 2/14/25

Home Browse Search

Mr. Kippen November 4, 2022 www.arcadis.com Technical Memorandum 11-04-2022 3/4 for plume mass capture to be achieved. The volumes were compared to lithological and hydraulic assessments performed at the Forward landfill point of compliance (POC), on groundwater monitoring well AMW-19BR screened in the intermediate water bearing zone and on groundw ater extraction well EW-1 screened in the shallow water bearing zone. The desktop calculations indicate that capture of the plume mass with total VOC concentrations >25 µg/L can be achieved with three extraction wells installed in the intermediate zone extracting a combined 150 gpm. These will be positioned to hydraulically capture the plume mass in the shallow water bearing zone by inducing a downwar d vertical hydraulic gradient to the intermediate zone in area(s) where plume migration has already occurred . This will restrict additional downgradient migration. Upgrades and optimization efforts to the POC groundwater extraction system have created a clean waterfront that is currently moving through the aquifer, in accordance with CAO requirement in Section 5 C) iii). The upgrades included the installation of an additional groundwater extraction well (EW -5), groundwater monitoring wells (AMW- 37 and AMW-38), as well as groundwater monitoring wells placed immediately downgradient of the POC capture zone (AMW- 40S/40M, AMW-41S/41M, AMW-42S/42M and AMW-43S/43M) installed to monitor and assess the effectiveness of the POC groundwater capture system. These downgradient monitoring wells indicate COC concentrations are below laboratory detection levels and document the clean waterfront. Also, groundwater monitoring wells further downgradient of the POC have been indicating stable or declining COC concentrations, as t he migration of the clean waterfront, and earlier POC capture optimization efforts, are reflected downgradient. The VOC concentrations in the monitoring locations downgradient of the POC are typically either stable or have decreasing trends that will meet the water quality objectives for this basin in a reasonable timeframe. The final design of the groundwater remedy will be based on the results of hydraulic testing from the intermediate water bearing zone on the CDCR property after the installation of the additional proposed extraction wells. Water Board Question 4: Will Forward generate a disposal plan or engineered solution for disposal related to operation of the extraction well(s) that will be installed? We anticipate Forward could simply resubmit a design for a second system that is identical to the existing system. No engineering would be needed except for electrical, conveyance of the water, and siting of the system . Response: The current disposal plan for the operation of the interim remedial system and associated extraction wells to address the center of plume mass on the CDCR property will be to convey the treated water south of the CDCR to the permitted infiltration basin currently being utilized by the existing POC treatment system. This approach will streamline the engineering effort required to finalize system design and installation . Sincerely, Arcadis U.S., Inc. Drew Feucht Shawn Roberts. PhD, CHg Principal Scientist Senior Geologist