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

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WELL INSTALLATION AND INTERIM REMEDIAL ACTION REPORT www.arcadis.com FINAL_Forward CHCF (CDCR) Well Installation Report_10182024 25 8 Summary Groundwater extraction (two wells) and monitoring wells (four wells) were installed at the CDCR property as part of the remedial scope to address the requirement in CAO R5-2017-0703 (RWQCB 2017), Item 3c, for an IRA to address the VOC plume mass beneath the CDCR property. All field activities were performed by, or under the direct supervision of, Arcadis field staff, in accordance with the Work Plan (Arcadis 2023a). Drilling log interpretation indicated the presence of variable thicknesses of permeable materials, which thin towards the east of the CDCR remedial area. This geological feature appeared to at least partially control groundwater flow and plume migration in the area, with the groundwater plume indicated towards the north- northeast and then towards the northeast. The thinning of permeable materials towards the east required relocation of extraction well CDCR-EW-3 approximately 300 feet to the west, to position it at a location with greater permeable thickness, and more optimal for plume control. Groundwater capture assessment of the TVOC plume with concentrations of 25 µg/L or greater at the CDCR property was performed using the results from hydraulic testing on the extraction wells. With combined extraction from CDCR-EW-2, 3, and 4, adequate capture of the 25 ug/L TVOC plume at the CDCR Property was not indicated to be achieved. Therefore, an additional extraction well is proposed to be installed approximately 70 feet to the northeast of monitoring well AMW-50M. The proposed extraction well is anticipated to sustainably pump at a similar rate and with comparable capture to extraction well CDCR-EW-3. The maximum extraction capacity for four wells is predicted at approximately 140 gpm and was calculated to achieve capture of the TVOC plume with concentrations of 25 µg/L or greater. At this combined extraction rate, the capture parabolas for the wells are indicated to overlap such that a lower extraction rate might still achieve full TVOC plume capture. Well extraction rate and capture balancing would be performed upon startup of the remedial system. Groundwater extraction with ex-situ treatment and disposal will be used as the IRA to treat the TVOC plume beneath the CDCR property and to create hydraulic control to mitigate potential migration of the plume, to address item 3c of the CAO R5-2017-0703 (RWQCB 2017). Arcadis requests review and approval of this document within 30 days in order to proceed with design, permitting, and procurement efforts associated with this system. Once this document is approved, system startup/shakedown activities are expec ted to occur within six months, given permitting and long-lead procurement items. System construction, including As-Built Drawings, and startup/shakedown activities will be documented in a forthcoming Construction Completion Report. Following system startup activities, r outine O&M will be completed after startup activities occur and O&M activities and data will be reported quarterly.