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2021 Groundwater Monitoring Report www.arcadis.com 2021 Holcim FINAL GWMR 3 triggered by the disposal of CKD into previously mined sections of the site and the potential for leachate from CKD to adversely impact ambient groundwater quality for existing and reasonably potential future uses. In 2004, all requirements from the DRMS’s adequacy reviews were fulfilled with the submittal of the final quarter of data for monitoring well MW-10 (BBL 2004). The data from the groundwater monitoring program was provided to the DRMS for use in establishing ambient groundwater concentrations and a parameter list for future monitoring. Holcim was to initiate annual groundwater monitoring per the GMP (BBL 2002) once the ambient groundwater concentrations and parameter list were established by the DRMS. The DRMS responded to the BBL (2004) report as part of a December 2007 site inspection. As a result of the site inspection, Holcim performed a site-wide monitoring event in March 2008. Subsequent to that monitoring event and based on further discussions with the DRMS, Holcim prepared several revisions to the GMP (BBL 2002), which are discussed in Sections 1.3.2 through 1.3.5. 1.3.2 November 21, 2008 Groundwater Monitoring Plan A revised GMP, dated November 21, 2008 (Holcim 2008), proposed the following activities:  Install one new monitoring well (MW-13) located hydraulically downgradient of the CKD disposal area.  Perform annual monitoring of new monitoring well MW-13, plus existing monitoring wells MW-7 and MW-12.  Abandon monitoring wells MW-6, MW-8, and MW-10, which were no longer usable and/or no longer serve any purpose in the monitoring program. 1.3.3 February 17, 2009 Groundwater Monitoring Plan A revised GMP, dated February 17, 2009 (Holcim 2009, and Appendix A), proposed numeric protection levels (NPLs) for downgradient monitoring well MW-7, based upon the highest historical analyte concentrations (see Section 3.2). The revised GMP (Appendix A) and the NPLs were approved by the DRMS on February 24, 2009 (DRMS 2009, Appendix A), with the condition that well MW-13 be monitored for five successive quarters to establish NPLs for that well. The DRMS approval letter stipulated that if two or more analytical parameters in monitoring well MW-7 exceed their respective compliance standards by more than 10 percent, semi-annual sampling for those parameters would be required. In April 2009, Holcim retained Arcadis to install a new groundwater monitoring well (MW-13) downgradient of the quarry operations and to abandon three groundwater monitoring wells that were no longer in service. The field activities performed as part of the groundwater monitoring well installation and abandonments are discussed in the Final April 2009 Groundwater Monitoring Report (Arcadis 2009). Following installation in April 2009, MW-13 was sampled quarterly for five consecutive quarters at the request of the DRMS to determine appropriate parameters and establish NPLs for the well. Analytical results are presented in the March 2010 Groundwater Monitoring Report (Arcadis 2010). Subsequently, MW-13 was added to the annual groundwater monitoring program in March 2011.