Laserfiche WebLink
lnformalion to Su000rl Denison BLMEn11/ronmenfalAssessmenl Remand <br />Denison SundayMhes Group <br />previously approved portions of the mines is warranted. BLM should <br />provide additional information and clarification regarding this comment. <br />Comment 4 Groulyd Xaler.4ffecled6y Uldelgl The existing mine workings <br />intercept ground water at some distance from the outcrop and mine entry. Mine <br />workings, including ventilation air shafts, have brought considerable fresh <br />air into contact with the mineralized zone(s), and ground water. Normal <br />anoxic conditions within the mine have changed with the introduction of <br />atmospheric oxygen during mining. Its availability to the ore minerals <br />and other non- re reduced minerals in the mineralized zone(s) may have <br />resulted in the metal ions and other components becoming soluble into the <br />groundwater creating possible ground water quality issues and additional <br />sampling is necessary to verify the actual condition of the groundwater. A <br />preliminary ground water study is provided in an initial form (Hydrologic <br />Evaluation of the Sunday Mines Group San Miguel Colorado, CDMInc, <br />May 2009) and shows likely aquifers of concern, water table elevations, <br />and water intercept localities within the mine workings. In general, data <br />is sparse to non - existent in between workings and is difficult to interpret <br />with respect to regional groundwater flow and rate. However, local data <br />density near mine workings and vent hole shafts is such that flow direction <br />can be inferred, specifically near the southwest edge of the Sunday Mine <br />workings. It appears that a cone of depression, possibly due to previous <br />mine de- watering, has caused flow to occur from beyond the mine <br />workings in the SE toward the center of the Sunday mine workings. Water <br />surface elevation of 5413 ' was measured for the S -8 shaft near the SW <br />edge of the workings, and the surface elevation decreases to 5398' at S -4 <br />(15 feet vertically over a 675 feet horizontal distance, bearing nearly due <br />north). Almost the entire inter -shaft horizontal distance is transected with <br />mine workings, but few workings occur up gradient from the S -8 shaft. It <br />is likely that the water chemistry changes between the 2 sample points are <br />affected by the presence of the mine openings and the ore body. Water <br />quality data from 4120 and 4121109 at these locations indicate that as <br />water flows down gradient from S -8 at the edge of the Sunday mine <br />workings into the mine center area at S -4, significant increases occur to <br />several ions, metals and radionuclides (potassium; IDS, aluminum; <br />arsenic; boron; iron; selenium; uranium; vanadium; gross alpha; gross <br />beta). The significance of this potential loading is unknown in the <br />context of background water quality in mineralized zones at the mine area, <br />and data is lacking with respect to rates, regional flow and any potential <br />for chemical equilibration over time and distance. Although the <br />drawdown cone will keep contaminants from migrating away from the site <br />in the short term, once flow regime returns to regional gradient this will <br />no longer be the case, and there may be potential for groundwater <br />contamination. Sorption reaction rates and flow velocity and transport of <br />uranium may or may not minimize this effect, depending on the particular <br />rates that are occurring. Detailed hydrologic study including monitoring <br />Final Sunday Mines BLM Remand Letter.doc <br />