2018-05-11_REVISION - M1977493 (2)

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Water Quality Monitoring Plan Climax Molybdenum Company Version R4 Permit No. M-1977-493 5.0 NPLS, DATA ANALYSIS AND REPORTING This section describes the methodology used to establish numeric protection levels (NPLs) at POC wells: ARwell and ARK-MW-001 D in the Arkansas River Watershed; EVMW-3S, EVMW-3D, and EV-MW-004 in the Eagle River Watershed; and GW#2 and TM-MW-002D in the Tenmile Creek Watershed. Also presented are the data analysis and reporting procedures for the POC wells and internal monitoring locations, other than those established above either Eagle Park or Clinton Reservoirs. Section 6 addresses data evaluation requirements for monitoring sites above Eagle Park and Clinton Reservoirs. 5.1 Numeric Protection Levels (NPLs) for POC Wells Colorado Revised Statute (C.R.S.) 25-8-202(7) and the December 14, 2010 Memorandum of Agreement (MOA) between CDPHE,WQCC, and DRMS clarify that the WQCC is the entity solely responsible to adopt water quality standards and classifications for state waters. The WQCC has not established classified uses for groundwater at or near Climax for which standards specific to the area have been adopted, therefore the Interim Narrative Standard under the CBSG is applicable for POC wells at Climax. The MOA provides that DRMS will establish points of compliance for discharges to groundwater and must provide reasonable assurance to the WQCD and WQCC that compliance with the Colorado Revised Statute (C.R.S.) 25-8- 202(7) has been obtained by using the groundwater standards and classifications established by WQCC as the basis for setting enforceable performance limits, adopting rules and regulations to establish points of compliance for discharges to state waters other than point source discharges to surface water, and other requirements as included in the MOA. The Interim Narrative Statewide Standard (CBSG Section 41.5(C)(6)(b)(i)) provides that "ground-water quality shall be maintained for each parameter at whichever of the following levels is least restrictive: (A) existing ambient quality as of January 31, 1994, or (B) that quality that meets the most stringent criteria set forth in Tables 1 through 4 of [CBSG]". As described in both TR-18 and TR-24, the DRMS-approved EPP adopted NPLs for two wells (ARwell and GW#2) using both the CBSG tables and existing ambient quality. This WQMP (TR-27) replaces those NPLs and establishes new NPLs at all of the existing POC wells identified in Section 5.0 above. Establishing NPLs for manganese in the Arkansas and Eagle River Basins will be addressed following the process involving the WQCD and WQCC described in Section 1.0. Section 4 describes the approach followed in evaluating baseline monitoring data and other information in order to identify the indicator parameters used for establishing NPLs at the various POC locations. Analytes on the indicator parameter lists are those that have been demonstrated as being associated with mining related sources at the Site, are most indicative of changes in water quality, and have a reasonable potential to exceed the applicable groundwater quality standards (the CBSG tables) and thus are appropriate for establishing NPLs pursuant to Rule 3.1.7. Compliance with NPLs set at levels equal to the most stringent criteria from CBSG Tables for the indicator parameters allows DRMS to provide assurance as to compliance with the Interim Narrative Standard. Each watershed at Climax has a minimum of two POC wells. One to monitor shallow, alluvial groundwater conditions and one to monitor deeper, bedrock groundwater conditions. The established NPLs are described below for each of the watersheds. The data analysis approach to be used in evaluating routine monitoring data against the NPLs is described in Section 5.2. EPP—Appendix C May 2018 22