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reclaimed blocks proposed for the SL -13 bond release application. Historical data from the <br />backfill wells indicate leachate forms in the spoil /ash backfill. This leachate is high in <br />dissolved solids (TDS), mainly sulfates, and is alkaline. TDS concentrations appear to peak <br />around 4,000 mg/l. This concentration may continue for several hundred years, as predicted <br />for the Seneca II Mine in Routt County, Colorado (USGS Water- Resources Investigations <br />Report 92- 4187). The alkalinity (pH near 7) appears to have prevented significant <br />mobilization of metals in the spoil /ash backfill The elevations of water levels in the bedrock <br />wells are higher than the highest elevations to which leachate levels can be expected to rise in <br />spoil/ash backfill; therefore, significant invasion of the bedrock units by leachate is unlikely. <br />Spoil/ash leachate has not been detected in the downgradient bedrock monitoring wells <br />(witness the minimal variation in TDS concentrations in well GP -5, between 1,000 and 1,300 <br />mg/1); although ground water flow velocities in the bedrock units may be too slow for <br />leachate to have reached the farthest downgradient wells. <br />Surface Water Impacts <br />Within the area of the proposed SL -13 bond release, surface water flows through seven <br />different watersheds. This includes discharges through eight active NPDES outfalls. The <br />eight active discharge points are all covered under NPDES Permit CO- 0032115 and are in <br />the following gulches: Deer, No Name, East Pyeatt, Grouse, Sage, Oak, West Flume, and <br />Middle Flume. Of these, surface water consistently discharges only through No Name and <br />East Pyeatt Gulches. The remaining discharge points seldom if ever record surface water <br />runoff. Throughout the sampling history of these discharge points, no violations of CO- <br />0032115 standards have occurred. Furthermore, recent Division reviews of AHRs (from <br />2001 to 2010) and 2011 DMRs indicate that there have been no significant water quality <br />problems at these discharge points. <br />No known spoil springs appear to be present on any of the reclaimed lands proposed for bond <br />release in SL -13. Furthermore, per the surface water quality data in the 2010 Trapper Mine <br />AHR, the only NPDES site that shows indications of groundwater affiliated constituents (for <br />example, TDS) is NPDES 001 in Johnson Gulch, and none of the SL -13 areas are within this <br />drainage. <br />Compliance with Basic Standards for Ground Water <br />The absence of leachate plume development in the bedrock units indicates that for bedrock <br />units in and adjacent to the bond release area, the mine operator is in compliance with the <br />Colorado Water Quality Control Commission's Basic Standards for Ground Water (Rule 41). <br />Any ground water in alluvial deposits in the bond release area meets the classification of <br />Limited Use and Quality because the alluvial water is of such small volume in these thin, <br />laterally discontinuous deposits that it is not currently used and is unlikely to be used in the <br />future. The Basic Standards for Ground Water have no water quality standards for the <br />Limited Use and Quality classification. <br />Recent Division reviews of AHRs (from 2001 to 2010) indicate that there have been no <br />significant ground water quality problems in the monitored formations. <br />Trapper Mine <br />Phase III Bond Release (SL -13) <br />Page 11 March 27, 2012 <br />