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CONSULTING CIVIL & li'fl TER RESOURCES ENGINEERING LLC <br />Ramsay M McDermid, P.E., Principal <br />9420 West Tennessce Avenue <br />Lakewood, Colorado USA 80226-4105 <br />Phone (303) 728-1580 Fax (303) 728-1577 Mobile (303) 903fi698 <br />medermid n comcast.net <br />To: Maureen Jacoby. Banks and Gesso <br />From: Mike McDermid___~ <br />Date: February 21, 2005 cc: <br />Subject: King Mountain Gravel LLC. Permit No. M-1978-314. CN-O1 <br />Response to Adequacy Review #2 questions and comments letter dated February 8. 2005 <br />from the Colorado DMG <br />Comment No. 7 under Rule 6.4.5 Exhibit E. -Reclamation Plan, regarding surface water <br />drainage aspects of the 184 acre pit (now 172 acres). <br />1. The NRCS (formerly SCS) Method was used to estimate runoff volumes resulting <br />from precipitation falling on the pit and on the small tributary area. The method <br />uses the parameters of catchment azea, precipitation depth, soil type and land use <br />to determine the depth of precipitation reporting to runoff. The soil type and land <br />use parameters are combined into a Curve Number for use in computing runoff. <br />2. The re-configured pit encompasses 172 acres located on Five Pine Mesa. The <br />mesa is bounded by incised drainages containing intermittent and perennial <br />streams. The pit will capture precipitation falling directly on the pit, as well as <br />runoff from approximately 40 acres of land tributary to the pit on the west side. <br />Precipitation falling on the tributary area will be lost to evapotranspiration, <br />infiltration and surface runoff. Precipitation falling in the pit, and surface runoff <br />from the tributary area, will either be lost to evapotranspiration and infiltration in <br />the porous pit bottom, or flow overland to one of three sumps located on the <br />easterly extremities of the pit. <br />3. The soils on the mesa aze classified as the Fourmile-Tellura Complex - 1-8% <br />Slopes. The soil parent material is glacial alluvium; the soils are well drained and <br />runoff is slow to medium. The soils on the slopes and bottom of the pit will be <br />sands and gravels with few fines having a high infiltration rate. <br />4. Based on this description, the hydrologic soil group applicable to the tributary <br />area soils is Hydrologic Soil Group B -Soils having an infiltration rate of 0.15 to <br />0.30 inches per hour. The pit bottom sands and gravels were assigned to <br />Hydrologic Soil Group A -Soils having an infiltration rate of 0.30 to 0.45 inches <br />per hour. <br />