PERMFILE126519 - Laserfiche WebLink

Home Browse Search

Exhibit Page 25 4. Changes to drainage basins caused by operations on site: There will be no significant and permanent changes in watershed boundaries caused by operations on site. As discussed in the reclamation plan, final (post-reclamation) contours will maintain existing watershed boundaries. Once ponds are full to capacity, discharge will equal intake from surface runoff, with evaporation losses made up by Home Ditch flows. Other than disturbances in vegetation, area exposed to erosion, and evaporation, the only significant change in drainage basin characteristics is the temporary blocking of potential surface flows from pit and working areas during the life of the pit. There will be minor and temporary changes to Dolores River drainage, but the impact will be minimal, as less than 0.1 % of the total basin of the drainage will be blocked from discharging at any one time during mining and reclamation operations. 5. Aquifers and watersheds in this area: The only recognized aquifer in the area is the alluvial aquifer associated with the Dolores River. Based on depths of existing wells in the area, there are no bedrock formations used as aquifers in the area which will be mined which would be affected by the mining of the sand and gravel. The bedrock in this portion of the valley is the Westwater Canyon Sandstone Member of the Mortison Formation, generally not considered a significant aquifer. The overburden (soil) and the sand and gravel may be considered part of the alluvial aquifer associated with the Dolores River and are considered significant aquifers in this areas, and will be protected by the method of mining and actions as discussed below and in the surface water management plan. Based on the location and depth of other known wells in the area, and the analysis of well drawdown potential (below), the mining activities proposed will have no reasonable potential for any adverse impact. There will be no blasting at this site. REPORT OF WELL DRAWDOWN POTENTIAL SUMMARY: There is no significant impact to water levels in any domestic wells in the vicinity of the proposed pit, based on the assumptions stated. Overall drawdown underworst-case conditions is less than 2 feet. This is a smaller fluctuation than normally experienced during the course of a normal year. In addition, the need for dewatering will be limited to a relatively small period of the I'rfe of the pit, primarily during the operating seasons of the last 2.5 years of extraction. The anticipated worst-case drawdown will also be mitigated by returning dewatering flows to the river above the nearest domestic wells. Assumptions and data: 1. Worst case will be assumed, both to ensure that worst conditions are identified and to simplify analysis. 2. Entire pit open to 20 feet below original ground level. 3. Pit is 660 feet wide,1410 feet long, perimeter 4107 feet. 4. Sump is 40 feet from pit wal1,125 feet wide, 250 feet long, perimeter 750 feet. 5. Normal water table at 5 feet below surface (based on well data). Pit drawdown will therefore be 15 feet from normal. 6. Depth of aquifer 126 feet and thickness of aquifer (Y)121 feet (data from well 132252A). (Calculations will also be done assuming a depth of 65 and thickness of 60 feet.) 7. Aquifer flow is parallel to river Flow. However, forworst-case situation, it is assumed that there is no recharge of the aquifer between the pit and the wells from the river. 8. Steady-state (equilibrium) conditions. 9. Includes seepage from river (200 feet distant) at pit but not at wells. 10. Includes seepage from Home Ditch at pit. (Actually, Home Ditch will either be shut down along the actualR pit or will be lined/piped during the period of mining.) ~C%V~qr 11. Level, unconfined aquifer (spatially homogeneous & isotropic hydraulic conductivity). N s Per conversations with Soil Conservation District personnel. Four States Aggregates, LLC Application for Permit: Line Camp Pit M-2001-001 AR 2 17001 o~ ~~ ~8'bn cf~ Fed Oryi 15 MAR 200 $ Geo o9y FSA-LCP-D2-001