2018-11-01_REVISION - C1981019 (2)

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Zach Trujillo Page 2 November 1, 2018 The MOA states that: The WQCC [Water Quality Control Commission] is to remain solely responsible for the adoption of water quality standards and classifications for state waters. Each implementing agency is to apply these water quality standards and classifications adopted by the WQCC through their own programs after consultation with the WQCC and the WQCD [Water Quality Control Division]. Groundwater which has been classified by the WQCC is described in Regulation 42 - SITE-SPECIFIC WATER QUALITY CLASSIFICATIONS AND STANDARDS FOR GROUND WATER [2]. Section 42.3 of that document gives the index of classified areas, and shows that only two sites in Moffat and Rio Blanco counties have classified groundwater: the town of Meeker and the Oil and Gas fields of Northern Moffat County (which lie northwest of Craig). All groundwater at the Colowyo Mine is, therefore, unclassified. Standards for unclassified groundwater are specified in 41.5(C)(6)(a) of Regulation 41: The “Interim Narrative Standard” … is applicable to all ground water, to which standards have not already been assigned in the state, with the exception of those areas where the total dissolved solids (TDS) are equal to or exceed 10,000 mg/l Since monitoring data shows that TDS is generally well below 10,000 mg/L, and site specific standards have not been adopted, the applicable water quality standard for groundwater at the Colowyo Mine is the Interim Narrative Standard. As stated in 41.5(C)(6)(b)(i), the Interim Narrative Standard requires that water quality: …shall be maintained for each parameter at whichever of the following levels is less restrictive: (A) Existing ambient quality as of January 31, 1994, or (B) That quality which meets the most stringent criteria set forth in Tables 1 through 4 of “The Basic Standards for Ground Water.” As an implementing agency, DRMS has some discretion in the determination of “existing ambient quality”, including the use of data generated more recently than January 31, 1994. In most cases baseline monitoring data should be adequate for the purpose. (Note that even if the classification as “Limited Use and Quality” were valid, the following statement from section 2.0 of the AECOM report, which discusses applicable water quality standards, would still be false: According to the Colorado Water Quality Control Commission, groundwater standards do not apply to water deemed to be of “Limited Use and Quality” …since the Interim Narrative Standard would still apply, as discussed in 41.5 of [1]: The standards specified in subsections A and C apply to all State ground waters, unless alternative site-specific standards have been adopted for a specified area)