Laserfiche WebLink
<br />degraded water quality. Water found in adjacent old mine <br />workings is degraded (TDS, 10,509 mg/1, and SAR, 27). If <br />water of this quality discharged to the stream/alluvial <br />aquifer system at the same rate as maximum groundwater inflow <br />to the mine workings, the resulting water quality in the <br />stream under low flow conditions would be a TDS concentration <br />of 698 mg/1, and an SAR of 4. Water of this quality has a <br />moderate salinity hazard and a low sodium hazard. It is <br />suitable for irrigation. <br />Other possible effects would not be expected to be <br />significant. Increased runoff and erosion from the surface <br />disturbances associated with the mine would be routed to a <br />sediment pond. Water released from the pond would have low <br />sediment concentrations, but in some instances might be <br />erosive. In this case, however, surface flows are infrequent <br />and the amount of water to be released on a continuous basis <br />is small (less than 0.17 cfs) and should not cause signifi- <br />cant downstream erosion. The pond contains 1.24 acre-feet of <br />dead storage, but this would normally be filled with water <br />from the underground workings so the pond would not decrease <br />surface flow from the site. <br />3. Summary and Findings <br />The Division has examined the probable hydrologic consequences <br />due to mining operations for the groundwater and surface water <br />systems at the Red Canyon Mine. The Division finds that <br />underground mining at the Red Canyon Mine will not have a <br />significant impact on these water systems. The mine will take <br />the necessary measures to ensure that mining will not affect the <br />hydrologic regime (2 .07.6 (2)(c)). <br />IV. Topsoil <br />No topsoil was salvaged during construction of the mine due to the fact <br />the majority of the disturbance took place before topsoil salvage was a <br />requirement under Colorado law. However, overburden materials were <br />approved and used as replacement for a topsoil medium. The resulting <br />plant growth medium is the best available at the site. This <br />determination is based on physical and chemical analyses approved by the <br />Division (4.06.2(9)(a)). <br />The overburden approved as non-toxic cover at Red Canyon was clayey and <br />moderately saline (Table 2.04.9(1)(b)-4: Site No. 0-6 and 0-7), with one <br />EC value of 5.6 (0-7) . SAR values were very low and pH ranged from <br />moderately acidic (4.6) to slightly alkaline (8.0). The material was <br />judged conditionally suitable for non-toxic refuse cover (see also C.S.U. <br />soils analytical evaluation, Figure 2.04.9(1)(d)-1) if acidic materials <br />are neutralized. This material was replaced to a depth of four feet over <br />the underground development waste pile. On site overburden was used as <br />a substitute for topsoil on other portions of the disturbed area. <br />23 <br />