2017-06-26_HYDROLOGY - M1980244 - Laserfiche WebLink

Home Browse Search

Executive Summary Colorado Division of Reclamation, Mining and Safety (DRMS) has requested that Cripple Creek & Victor Gold Mining Company (CC&V) submit a review of the currently approved groundwater monitoring plan and available site groundwater monitoring data to demonstrate that CC&V is in compliance with Regulation No. 41's requirements. In the following demonstration of compliance with Regulation 41, CC&V has also provided an analysis of the mine-site conditions to support previously-approved, site- specific groundwater numeric protection limits (NPL) for Squaw Gulch, Arequa Gulch, Vindicator Valley, Poverty Gulch, Wilson Creek, and Grassy Valley. The analysis indicates that groundwater in Arequa Gulch, Poverty Gulch and Vindicator Valley has been impacted by historic mining activities within these drainages. Groundwater in Squaw Gulch is hypothesized to reflect very long-term natural elevations in dissolved constituents that resulted from diatreme groundwater discharge via Squaw Gulch prior to drainage tunnel construction, as well as historic mining. Wilson Creek and Grassy Valley groundwater sampled at designated compliance points has not been impacted, and represents the natural groundwater chemistry in those drainages. 1. Introduction In December of 2016, DRMS issued a request to CC&V for Demonstration of Compliance with WQCC Regulation No. 41 —The Basic Standards for Groundwater. The request required that CC&V provide a review of the current approved groundwater monitoring plan and available site groundwater monitoring data against the Interim Narrative Standard requirements. These Interim Narrative Standard Requirements are presented below. DRMS indicated that: "The 'Interim Narrative Standard' in 41.5(C)(6)(b)(i) below[in the letter] is applicable to all groundwater, to which standards have not already been assigned in the state... Until such time as use classifications and numerical standards are adopted for the groundwater on a site-specific basis throughout the state, and subject to the provisions of subsection (ii) below[in the letter], groundwater quality shall be maintained for each parameter at whichever of the following 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"' In Regulation 41, the Water Quality Control Commission stated its intent about the application of the Interim Narrative Standard by implementing agencies including the DRMS: iii. In applying this narrative standard, the Commission intends that agencies with authority to implement this standard will exercise their best professional judgment as to what constitutes adequate information to determine or estimate existing ambient quality, taking into account the location, sampling date, and quality of all available data. Data generated subsequent to January 31, 1994, shall be presumed to be 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 subsequent to that date. If available information is not adequate to otherwise determine or estimate existing ambient quality as of January 31, 1994, such groundwater quality for each parameter shall be assumed to be no worse that the most stringent level provided for in Tables 1 through 4 of"The Basic Standards for Ground Water," unless the Commission has adopted alternative numerical standards for a given specific area. In essence, if CC&V has sufficient water quality data to determine or estimate the existing ambient quality as of 31 January 1994, those data will be used to establish the NPL. If data are not adequate to determine or estimate the water quality as of 31 January 1994, item B above applies; the"most stringent criteria" have been assumed to be the criteria for domestic drinking water. DRMS notes: "If an operator wishes to propose a groundwater standard less restrictive than those contained in 'The Basic Standards for Ground Water' tables, it will be the operator's burden to sufficiently demonstrate to DRMS that their circumstances meet at least one of the two conditions outlined below[in the letter], thereby allowing DRMS to apply a less restrictive standard, and still fully implement the requirements of Regulation No. 41."