2011-08-08_REVISION - M1977493 (36)

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• • Water Quality Monitoring Plan Climax Molybdenum Company Version: R1 Permit No. M- 1977 -493 4.0 SELECTION OF MONITORING PARAMETERS AND NUMERIC • PROTECTION LEVELS (NPLS) This monitoring program is intended to provide data for (1) demonstrating that EPP requirements are being met, and (2) evaluating changes in water quality that may be related to mining and milling operations at the site. It also provides a process for identifying when changes may be occurring so that appropriate actions can be taken to prevent adverse off-site impacts. 4.1 Monitoring Parameters 4.1.1 POC Groundwater Monitoring The list of analytical parameters to be monitored has been developed based on a review of available baseline data from the existing groundwater monitoring network, an evaluation of the monitoring requirements under the Site's existing CDPS permit, and a review of the Colorado Water Quality Control Commission Basic Standards for Groundwater; 5 CCR 1002 -41 (CBSG). Numeric Protection Levels for groundwater at existing POC locations are established below to protect existing and reasonably potential future uses of groundwater. The Colorado Water Quality Control Commission (WQCC) has not established classified uses for groundwater at or near the Site for which standards specific to the area have been adopted. DBMS Hard Rock Metal Mining Rule (HRMMR) 3.1.7(2)(c), recommends the use of the groundwater quality table values in the CBSG as a guide for establishing numeric protection limits or permit conditions. In situations where ambient groundwater exceeds groundwater table values, the rule recommends establishing permit conditions to protect existing and reasonably potential future uses against further lowering of groundwater quality. The Interim Narrative Statewide Standard (CBSG Section 41.5(C)(6)(b)(i)) states that groundwater quality shall be maintained for each parameter at the least restrictive of existing ambient quality as of January 31, 1994 or the table values in the CBGS. Under the previous (1995) groundwater monitoring program, groundwater samples have been analyzed for the following constituents: pH, conductivity, TDS, hardness, sulfate, total cyanide, chloride, and dissolved metals (cadmium, calcium, copper, iron, magnesium, manganese, molybdenum, lead, silver, and zinc). Based on a review of the data from the existing monitoring network, calcium, chloride, cyanide, magnesium and silver are eliminated from further monitoring. While data are available for calcium, chloride, magnesium, and silver these parameters were not specifically identified as primary constituents in the 1995 Groundwater Monitoring Plan and the ongoing collection of this data is not considered necessary to detect potential impacts to water quality. In the case of calcium and magnesium, although detected in the groundwater samples, there are no potentially applicable groundwater or surface standards for these analytes. Cyanide and silver have been detected in groundwater infrequently at very low concentrations near the detection limit, and chloride concentrations observed are well below the secondary drinking water standard of 250 mg /I. The parameters listed in the CDPS permit are appropriate for consideration in developing a parameter list for this Water Quality Monitoring Plan because they reflect the results of a comprehensive review of water quality data and reflect the reasonable potential analysis conducted by the WQCD in the administration of the discharge permit. Of the monitored parameters under the CDPS discharge permit for which numeric discharge limits apply, arsenic, cadmium, copper, iron, lead, manganese, mercury, selenium, and zinc have been assigned EPP — Appendix C August, 2011 11