Laserfiche WebLink
SDH -3 Dewatering Treatment System <br />General Notes on Design, Operation and <br />SedCAD Analysis <br />The SDH -3 Dewatering System area (see Map 140 and 143) was analyzed using SedCAD to evaluate the <br />area when subjected to 10 -year and 100 -year, 24-hour design storm events. Due to the lack of ability for <br />SedCAD to directly incorporate base flow conditions, i.e. D -seam discharge, SWS #4 was added to the <br />structures representing the ponds. Starting at the upper pond SWS-4 was sized to produce a peak <br />discharge of 350 gpm. Subsequently, the same was done for the middle and lower ponds such that the <br />peak discharges were at 350 gpm through each pond. Then the other SWS's were added to reflect actual <br />storm water runoff. <br />Several items should to be pointed out concerning the design and model. <br />1. Modeling represents worst case conditions immediately following construction. <br />2. Routing was ignored in the SedCAD model. Actual peak flows are expected to be lower than those <br />presented due to the longer flow distances and associated delays in flow caused by the upstream <br />ponds and channels. <br />3. Since the sediment load and settling characteristics of the mine discharge water could be variable <br />a conservative educated estimate of the retention pond requirements was made. Operational <br />observations indicate that our current pond is slightly undersized. Bench scale tests indicate that <br />the retention time provided by the pond expansion will be more than adequate to treat the <br />discharge. <br />4. The first pond in the series is intended to accumulate the vast majority of the sediment from the <br />mine discharge. Periodic sediment removal will be facilitated by temporarily diverting mine flow <br />directly to the second pond while the first pond is dewatered and sediment removed. <br />Two soil types are indicated by the soil surveys. Turley is a fine sandy loam, hydrologic soil group B, and <br />K factor 0.29. Moyerson is a stony clay loam, hydrologic soil group D, and K factor 0.32. <br />The native site is a sagebrush grassland in fair to good condition. "Fair" was used in the curve number <br />selection to remain conservative. Where two HSGs occur in the same SWS a composite CN and K factor <br />were used. <br />Minor Revision #166 (10/2015) <br />