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

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Technical Memorandum Arcadis U.S., Inc., 735 Tank Farm Road, Suite 150, San Luis Obispo, California, 805 706 2805, www.arcadis.com Technical Memorandum 11-04-2022 1/4 SUBJECT TO Response to October 19, 2022, Water Board Letter Daniel S. Kippen DATE November 4, 2022 On behalf of Forward, Inc., Arcadis U.S., Inc. (Arcadis) has prepared this Technical Memorandum for the Forward Landfill (Forward, Inc.), 9999 S. Austin Road, Manteca, California. This memo presents a technical justification and responses to the Central Valley Regional Water Quality Control Board (Water Board) questions regarding the interim groundwater remediation approach for areas north of the landfill. In a letter dated October 19, 2022, the Water Board presented the following four questions, and the responses are summarized below. Water Board Question 1: Please provide the field notes, the well development logs, and the sieve analysis data from the screen interval for EW-1. Response: Attached to this letter are the boring, well construction, well development log, sieve analysis results for soil samples collected from the screen interval, and hydraulic testing field forms for extraction well CDCR-EW-1. Water Board Question 2: Section 3.c) of CAO R5-2017-0703 requires, in part, that “[t]he extraction wells shall be located near the center of plume mass and must be able to contain and treat the VOCs, create an inward gradient of the groundwater table, measured from existing monitoring wells within the plume, in all zones affected by the release.” Please describe how Forward will e xtract contamination from the various zones impacted by the plume. Response: Section 3.c) of Clean-up and Abatement Order (CAO) R5-2017-0703 requires an interim groundwater plume remediation system that includes “the installation of additional groundwater extraction wells to remediate areas north of the landfill where the discharger identified total volatile organic compound (VOC) concentr ations in groundwater exceeding 25 µg/l.” At the onset of 2022 the sole groundwater data point north of the landfill with total VOC concentrations exceeding 25 micrograms per liter (µg/l) was the shallow water bearing zone monitoring well location AMW-22S on the California Department of Corrections and Rehabilitation (CDCR) property; therefore, this monitoring well location represented the center of plume mass to be contained and treated to maintain compliance with the CAO. In a letter submitted to Mr. Kippen on February 16, 2022, Forward recommended additional assessment activities be conducted on the CDCR property before the installation of a groundwater plume remediation system to provide sufficient data for extraction well placement. In the interests of expediting the interim remedy, however, the Water Board directed Forward to revise their workplan and begin installation of the remediation system prior to collecting additional assessment data. In response to this directive, Forward submitted the Revised CDCR Site Investigation and Remedial Design Workplan Addendum to the Water Board on March 7, 2022. The Water Board provided comments on this revised workplan on March 24, 2022. In accordance with the approved March Work Plan, Arcadis and their subcontrac tors installed CDCR-EW-1, a 6- inch diameter extraction well screened in the shallow water bearing zone beneath the CDCR property, in an attempt to capture the >25 µg/l shallow zone plume mass in the vicinity of AMW -22S (approximately 140 feet northeast of the extraction well location). Hydraulic testing of CDCR-EW-1, which included a step test and 12-hr constant rate test, indicated the shallow zone extraction well is not capable of capturing the plume mass in the vicinity of AMW-22S. The maximum sustainable flow rate was approximately 0.5 gallons per minute (gpm) with approximately 7.9 feet of drawdown in the extraction well. Furthermore, the extraction well was not capable of