2017-06-26_HYDROLOGY - M1980244 - Laserfiche WebLink

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The first narrow circumstance and authority for DRMS to apply a groundwater quality standard that is less restrictive than the Table Value Standard at a Point of Compliance exists when a mine operator provides DRMS with adequate documentation and data to determine, to the satisfaction of DRMS, that the existing ambient groundwater quality on January 31, 1994, was above the Table Value Standard. Only two of the drainages under review have analytical data prior to 31 January 1994: Grassy Valley(two samples) and Wilson Creek(six samples). In this situation, the DRMS letter asserted: "The second narrow circumstance and authority for DRMS to apply a groundwater quality standard less restrictive than the Table Value Standard at a Point of Compliance exists when an operator provides DRMS with data generated after January 31, 1994 which exceeds Table Value Standards and can also demonstrate that no new or increased sources of groundwater contamination in the area in question have been initiated since January 31, 1994, and therefore ambient conditions exceeded Table Value Standards prior to January 31, 1994. The only other way a DRMS permitted site may allowably exceed the standards set by the Interim Narrative Standards would be for the permittee/applicant to obtain site-specific exemption or variance from WQCC [Water Quality Control Commission] through a rulemaking process." The interpretation in DRMS's letter is inconsistent with the language of Regulation 41. Section 41.5(C)(6)(b)(iii) requires the DRMS to exercise its best professional judgment to determine what constitutes adequate information to determine or estimate existing ambient quality. This requires consideration of all data. The regulation then creates a presumption that data after January 31, 1994 are representative of existing quality as of January 31, 1994, if the available information indicates that there have been no new or increased sources of groundwater contamination initiated in the area in question after that date. The regulation does not create a "narrow circumstance" for consideration of data after January 31, 1994; instead, it directs DRMS to weigh all the data but to apply a presumption that the data are representative of conditions before January 31, 1994, if the required conditions are met. In December 2016, CC&V proposed NPL for seven compliance monitoring points. (CC&V, 2016, Table 2-1). The proposed NPL are given in Table 1, and the locations of the drainages are shown in Figure 1. Table 1: Proposed NPL (CC&V, 2016)and domestic well standards (t is total, d is dissolved, WCMW 3 and 6 are in the Wilson Creek drainage). Drainage Sulfate(t) pH Manganese (d) Zinc(d) WAD CN m /L m /L m /L m /L Are qua Gulch 1070 6 -9 8.1 2 0.2 Grassy Valley 250 6-9 1 2 0.2 Vindicator Valley 800 6.5—8.5 4 2 0.2 WCMW 3 250 6-9 0.5 2 0.2 WCMW 6 250 6-9 0.5 2 0.2 Squaw Gulch 1070 6.5—8.5 8.1 2 0.2 Poverty Gulch 1070 6—8.5 8.1 2 0.2 Domestic Wells 250 6.5—8.5 0.05 5 0.2 Below is an analysis of the data and recommendations for additional work in support of the proposed NPL. WAD CN is not discussed because it has not approached the 0.2 mg/L standard in any of the drainages.