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Investigation of Groundwater Quality Near the Underground Workings <br />Groundwater quality near the underground workings was monitored to evaluate the <br />ambient groundwater quality. The investigation also attempted to evaluate the <br />persistence of any mining- related effects to groundwater downgradient from the <br />underground mine workings. However, this information was not obtained in the <br />investigation as a result of the proximity of the underground monitoring wells in <br />relation to the mine dewatering system. <br />Groundwater quality standards in Colorado are set forth by the Colorado Department <br />of Public Health and Environment (CDPHE) Regulation 41, The Basic Standards for <br />Ground Water (BSGW) (5 CCR 1002 -41). Regulatory jurisdiction for implementation <br />of the BSGW at active metal mines in Colorado is delegated to DRMS as set forth by <br />Memorandum of Agreement For the Implementation of SB181 Amendments to the Colorado <br />Water Quality Control Act Pertaining to the Regulation of Metal Mines (CDPHE 2010). The <br />BSGW define ambient groundwater quality as the quality that was present on January <br />31, 1994. The BSGW also provide the following: <br />"In applying this interim narrative standard, the Commission intends that <br />agencies with authority to implement this standard will exercise their best <br />professional judgment as to what constitutes adequate information to <br />determine or estimate existing ambient quality...Data generated subsequent <br />to January 31, 1994, shall be presumed to be representative of existing <br />quality as of January 31, 1994, if there have been no new or increased sources <br />of groundwater contamination initiated in the area in question subsequent to <br />that date..." (41 .5[ C]f 6](b]f iii]) <br />Ambient groundwater quality is defined similarly in HRMMR 1.1(5): <br />"Ambient Groundwater Quality" for mining operations permitted prior to <br />January 31, 1994, Ambient Groundwater quality shall mean the quality of the <br />groundwater at the mine site as of 1994. For mining operations permitted on <br />or after January 31, 1994, ambient groundwater shall mean the quality of <br />groundwater at the time of submittal of the permit operation. In establishing <br />ambient groundwater quality, an Operator or Applicant shall use available or <br />collected groundwater data sufficient to characterize the site's ambient <br />groundwater quality and submit such information in a form suitable to the <br />Office. <br />The Sunday Mines Group has been in existence since the mid 1950s, and the vast <br />majority of underground mine development occurred prior to 1994. Although some <br />additional mining has been done at the Sunday Mines Group since 1994, neither the <br />type of mining activities conducted nor the geochemical characteristics of the ore and <br />development rock has changed appreciably. It is unlikely that current groundwater <br />quality is significantly different than conditions on January 31, 1994. Therefore, the <br />groundwater quality measured in this investigation is thought to best represent <br />ambient conditions at the Sunday Mines Group. <br />C \Users\cwoodward\ Desktop \ Sundays \FINAL • Environmental Protection Plan Sunday Mines Revised January 2012 docz <br />Section 8 <br />Groundwater Quality <br />8 -2 <br />