|
Mud Creek Pit -Reclamation Permit Application -112 (C) Exhibits Page 29 of 67
<br />4. Changes to drainage basins caused by operations on site:
<br />There will be no significant and permanent changes in watershed boundaries caused by operations on site. As
<br />discussed in the reclamation plan, final (post-reclamation) contours will change the divide and therefore existing
<br />watershed boundaries between Mud Creek and its unnamed tributary, but since this is a tributary, there will be no
<br />large change.
<br />Other than disturbances in vegetation, area exposed to erosion, and evaporation, the only significant
<br />change in drainage basin characteristics is the blocking of potential surface flows from pit and working areas during
<br />the life of the pit and after reclamation, resulting in increased infiltration into the surficial deposits. There will be minor
<br />and temporary changes to Mancos River drainage, but the impact will be minimal, as less than 0.001 % of the total
<br />basin wilt be blocked from discharging at any one time during mining and reclamation operations.
<br />5. Aquifers and watersheds in this area:
<br />The only recognized aquifer in the area is the Morrison Formation, approximately 2000 feet below surface; the
<br />alluvial aquifer associated with Mud Creek is not recognized by the state as a significant source of water, but may be
<br />useable for water for plant and pit operations. There may be isolated water tables at the top of the Mancos Shale
<br />below the Quaternary terrace deposits being mined. Based on depths of existing wells in the area, there are no
<br />bedrock formations used as aquifers in the area which will be mined which would be affected by the mining of the
<br />sand and gravel. The overburden (soil) and the sand and gravel are not significant aquifers in this area13. Based on
<br />the location and depth of other known wells in the area, the mining activities proposed will have no reasonable
<br />potential for any adverse impact. There will be no blasting at this site.
<br />6. Prevention and mitigation actions:
<br />As discussed above, the permit area is more than 500 feet away, and the affected areas more than 1000 feet, from
<br />Mud Creek, and located well outside the 100-year floodplain. Potential wetland areas (natural or manmade) are not
<br />being mined. There will be no surface discharge of storm water which has come in contact with exposed stripped
<br />areas, mining areas, or stockpiles of extracted materials, waste materials, or topsoil. As necessary, storm water
<br />pollution prevention and management actions, including erosion and sedimentation control, will be implemented as
<br />required by the Colorado Discharge Permit System storm water general permit for which coverage has been
<br />obtained for this site (prior to beginning mining). This meets the requirement for an NPDES permit and covers
<br />dewatering and process (wash) water as well as storm water, and application has been made for coverage. Since
<br />surface water flow will instead infiltrate into the terrace alluvial deposits at the edge of pits and reclaimed areas and is
<br />presumed to flow into Mud Creek as subsurface flows, no net impact on river flow is anticipated. Overall design of the
<br />pit was done to plan for a minimum impact on surface and ground water. Pre-mining return flow of irrigation water
<br />will be essentially unchanged except for irrigation water applied to the property itself, which will now be subsurface
<br />rather than potential surface flow.
<br />7. Project water requirements:
<br />Water use for extracting and processing aggregates from the pit will be low, amounting to 13.9 acre-feet per year
<br />under worst case conditions. This water will come from the temporary industrial use of agricultural water from
<br />existing water rights for the property, primarily shares in MWCD. Based on data available on historic irrigation of the
<br />property, approximately 100 acres was irrigated.14 Assuming an irrigation season of 120 days, the two shares of
<br />Boss Ditch water equal 69.5 acre-feet, and the MWCD shares are 85 ac-ft, for a total of 154.5 acre-feet, or 1.55 acre-
<br />feet per acre (18.6 inches per year). Since, during actual mining operations, a minimum of 18.3 acres normally
<br />irrigated will be disturbed and not require irrigation, an estimated minimum of 28.4 acre-feet of water will be available
<br />for pit and plant operations each year, assuming all other areas are irrigated (including reclaimed areas), which is
<br />more than twice estimated maximum annual requirements.
<br />The general location and configuration of the site increase the likelihood that water is necessary for dust control on
<br />working areas and roads. Use of dust control chemicals will reduce water use on site. If materials are washed, water
<br />will be recycled, reducing use and discharge, as well as protect water quality. For evaluation purposes, based on the
<br />t3 Per conversations with Soil Conservation District personnel.
<br />~4 Per Environmental Assessment, Mancos Valley Salinity Study, 2007, US Bureau of Reclamation.
<br />McStone Aggregates, LLC 15 FEB 2008 ©WASTELINE, INC 2008 PN 5006.1-4(009)
<br />
|