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channel or spillways are required at this site. Per good workman like practice, sediment from the <br />operation is to be controlled, and controlled dominantly through the use of vegetative cover for non - <br />traveled surfaces, and using the historic gutters, drains, and small sediment collection areas already in <br />place for sediments. The engineers deem these controls to be adequate for the proper protection of the <br />environment. We are currently in discussions with CDPHE, and will assemble a document specifically <br />relating to storm water. <br />We do have a question in regards to comment 4b,ii. The velocity head is normally expressed in the <br />terms of the first equation shown. The second equation appears to make the assumption that the head <br />in this instance is reduced by a factor of two for any given velocity, or that the specific energy of the <br />fluid acting is less than it really is. It is not immediately apparent how this modification in formula <br />directly equates to free board, other than the calculated results leading to a smaller channel design. <br />Why is this paragraph worded this way? <br />A general review of the engineer characteristics of the site are as follows: <br />Natural Resources Conservation Service (NRCS) Technical Release No 55 is a tool for estimating peak <br />runoff and volumes for watersheds and drainage basins. It is an improvement of some of the original <br />work that was done in the 1960's and 1970's that culminated in the Colorado Water Conservation Board <br />Technical Manual No. 1, published in 1976. At that time, this was the bible for estimating storm water <br />runoff and flows for this area. It is unfortunate that some of the Front Range counties did not pay more <br />attention, as the lessons contained within it are still to be learned. <br />After careful thought, it can be concluded that the historic 3 -acre disturbed area located on the side of <br />a hill above the town of Cripple Creek is not of sufficient size or configuration that the peak flow or <br />volume calculations created by Technical Release No 50 would be useful or meaningful. However, we <br />can borrow some useful information contained in the work that can be relevant for this site. <br />Going back to the USDOC numbers, the 100 -year 24 -hour event is estimated to be 3.5 inches of <br />precipitation. From the site - specific data, the soils are composed of coarse grained materials <br />characterized as "gravely and gravely sandy loams. Technical Release No. 55 produces a Runoff Curve <br />Number (RCN) of 42 for the grassed areas and an estimated average number of 60 for the disturbed <br />areas including road surfaces. The number for a hypothetical ore pile would depend on the size of the <br />material and the configuration of the pile. There would be conditions that the ore would be anticipated <br />to retain the entire amount of precipitation and other conditions that could result in nearly zero percent <br />retention. From a design standpoint, the most conservative design would assume that the material <br />would have no retention. Thus, the simplest design would include a 3.5 -inch high (plus safety factor) <br />berm around the pile. The accumulated water within that berm would then be allowed to evaporate in <br />the dry Cripple Creek climate. Continuing with the method, we can then predict the amount of <br />precipitation that will permeate into the soils. Infiltration and evaporation (etc.), into the grassed areas <br />would be anticipated to be over 3 inches leaving only 0.5 inches as runoff. Infiltration into the road <br />areas would be anticipated to in be 1.8 inches, leaving a calculated run -off value of 1.7 inches. As an <br />example, a hypothetical area having dimensions of 20 feet by 20 feet would be anticipated to produce <br />4 <br />