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Environmental Protection Plan, Schwartzwalder Mine 15-2 <br />• and design for bedrock monitoring wells is provided in Section 15(c) and an approximate timeline for <br />engineering studies, evaluation, DRMS review, and construction is provided in Section 15(d). <br />During the interim period while long-term sustainable mitigation measures are evaluated, selected, and <br />designed, short-term measures have been implemented for protection of human health and the environment. <br />Water treatment was initiated on July 2, 2010. The 50-gpm treatment system which operated from July 2 <br />to July 31 is described in Section 15(b)(i). The 100-gpm treatment system is described in Section 15(b)(ii). <br />(a) Description of Constituents of Concern and Sources <br />As described in Section 9(b)(ii), uranium is the primary constituent of concern (COCs) in alluvial <br />groundwater. On average, uranium concentrations exceed Colorado groundwater standards by a factor of <br />about 40. Concentrations of other metals are generally below analytical detection limits, with the exception <br />of molybdenum and zinc. Colorado adopted a groundwater standard for molybdenum in 2008. There are <br />no applicable surface water standards or drinking water standards for molybdenum. Three of nine alluvial <br />groundwater wells exceed the current molybdenum groundwater standard (0.035 mg/L) by a factor of about <br />1.5, and have shown decreasing trends over time. Zinc concentrations are below the Colorado groundwater <br />standard of 5 mg/L. Radium-226 is below the 5 pCi/L groundwater standard in all groundwater monitoring <br />locations except at Sump 1. No trend of increasing radium-226 has been observed at this location. A <br />gamma survey of the site indicated a small, localized zone of elevated gamma emission in the vicinity of <br />Sump 1, which is probably related to the source of elevated radium-226 in groundwater at this particular <br />location. TDS increases with distance downgradient in the alluvium, but remains low to moderate, <br />averaging 170 mg/L in upgradient well MW00, increasing to about 380 mg/L in the vicinity of the mine. <br />Uranium concentrations show a general trend of increasing concentrations from upgradient well MW00 to <br />downgradient well MW12. Uranium concentrations in alluvial wells generally increase from <br />. upstream/upgradient to downstream/downgradient29. Proximity to Ralston Creek also affects water quality, <br />with wells located closer to the creek (e.g. MW2) having lower uranium concentrations than distal wells. <br />(i) Source of Chemical Loading <br />The primary source of uranium and molybdenum in alluvial groundwater is the fill material, based on <br />several lines of evidence as described in Section 9(b)(ii). Groundwater mixing calculations suggest that <br />flooded mine workings could theoretically contribute a small amount (no more than 0.8% based on <br />uranium, or no more than 8% based on calcium) of flow and therefore may contribute a small fraction of <br />chemical loading to the alluvium and fill, as described in Section 9(b)(ii).1. However, molybdenum <br />concentrations have been consistently decreasing at alluvial groundwater monitoring locations since the <br />late 1990's, suggesting that the mine pool, which is significantly elevated in both uranium and <br />molybdenum, is unlikely to be a source of any additional chemical loading to alluvial groundwater. <br />The waste rock dumps do not affect water quality in Ralston Creek, according to a November 2008 <br />electrical conductivity (E.C.) survey of the creek and over a decade of surface water monitoring results <br />from Stations above and below the waste rock dumps. However, it is unclear whether water quality in <br />alluvial well MW-0 is affected by the East Waste Rock Dump or by other sources in the alluvium. <br />Uranium concentrations in MW-0 peaked at 0.98 mg/L in 2003 during surface reclamation operations, and <br />have declined to their present levels of about 0.3 mg/L. No consistent trend of increasing uranium <br />concentrations has been observed in the well, and radium concentrations are currently at the lowest <br />concentrations observed in 10 years of monitoring. <br />• 29 The order of increasing uranium concentrations in wells is as follows: MW-00 (lowest uranium concentrations), MW2, MW-1, <br />MW-0, MW-9, MW-7, MW-6, MW-12 (highest uranium concentrations). <br />4109C.100731 Whetstone Associates 6