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Mr. Brattain October 19, 2020 Page 4 the monitoring program are warranted at this time. Changes to the monitoring program are expected to continue to evolve with progress of the remedy and therefore, additional changes will be proposed in the future. As part of these changes, several historical monitoring wells at the Site that fall outside of the current remedial footprint and have not been used historically are proposed to be destroyed. During a 15 October 2020 teleconference between Bill Brattain (CVRWQCB), the Trustee and Srinivasa Varadhan (Geosyntec) to discuss the monitoring reduction request, it was determined that while the current WDR-MRP anticipated and allows for flexibility in making changes to the monitoring plan, the Notice of Applicability(NOA) limits the applicability of the current MRP to Phases 1 and 2 of the Final Remedy(page 2 of the NOA dated 20 January 2016). Consequentially, the current MRP does not specifically cover monitoring requirements for Phase 3 of the Final Remedy. With Phase 3 already in progress and not comprising of ISCO injections, the existing Phase 1 and 2 monitoring plan is deemed not applicable moving forward. Therefore, potential pathways to modify the MRP specific to Phase 3 were explored during the discussion. A more likely option for resolving the WDR-MRP coverage issue described herein is to rescind the current WDR-MRP and draft a new WDR-MRP for Phase 3 and subsequent activities at the Site. The new WDR-MRP would include provisions to modify the monitoring frequency and analyte list with the progress of the remedy. In addition,the WDR-MRP would include provisions for implementing contingent actions,if warranted. Finally,it is our understanding that the Sitewide GWMP will remain as is and modifications to the GWMP can be requested through the annual groundwater monitoring reports for the Site, independent of the WDR-MRP. The following sections present the approach and data evaluation conducted in support of this determination to reduce the monitoring frequency,analyte list,and modify the monitoring network for the Site. Approach This section presents the approach employed to support our request for modifications to the current monitoring programs. As part of this evaluation,historical COC,permanganate and Cr(VI) data for select locations being proposed for monitoring reduction were compiled. The data were subject to statistical analysis using the Environmental Sampling Trend Analysis Tool (ESTAT), a proprietary Geosyntec program that utilizes statistical methodology identical to the Air Force Center for Engineering in engineers I scientists I innovators