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<br /> <br />Mr. Harold E. Aare II - 2 - June 6, 1989 <br />connected underwater. The latter (No. 21 has the advantage that no <br />engineering design is required to ensure that flood flow events can pass <br />through the lake and out the spillway. The former (No. 1) requires that <br />floods be able to pass through the culvert and, more than likely, also <br />over the forebay embankment during large floods. Without going through a <br />formal engineering design to size the culvert, the Division suggests you <br />consider using option No. 2. Of course, the design you have proposed <br />with a lake and no forebay will also work. <br />If you agree with our recommendation, the forebay embankment should be <br />constructed with 3 horizontal to one vertical sideslopes (3:1) on both <br />upstream and downstream faces, 5 foot top width, submerged 1 foot below <br />e.Kpected waterline, and provide a forebay area of about one-fifth the <br />lake area Sor 314 acre). If you choose to include a forebay in the lake, <br />please commit to these design parameters and also include a revised <br />E;chibit F or simply a sketch map which shows the location of the forebay. <br />2. The processing of gravel extracted from the lake is proposed to be washed <br />and screened: <br />a. What will you do with the settled mud? Will it be used as topsoil, <br />or if not, where will it be placed? <br />6. Screening may require a fugitive dust emissions permit be obtained <br />from the Air Pollution Control Division of the Colorado Department <br />of Health. Please address whether a permit will be required or not. <br />3. The mine plan states that after processing the product will be <br />transported by truck to 18061 Teller County Highway ~1 for stock pi lino <br />and resale. Please note that the area of this stockpile location, <br />because it is functionally associated with the mining operation, must be <br />included within the permit area. Please submit a map which shows this <br />area. Also, please describe the area (in acres) which encompasses the <br />stockpile area. <br />4. The plan says the area is fed by springs. It appears, however that the <br />lake will be filled primarily by the streamflow backed up by the lake <br />em~ankment. Because the lake is larger than two (2) surface acres in <br />size, you will need to demonstrate to the State Engineer that water <br />rights have been obtained, or otherwise transferred, to provide for the <br />evaporative loss created by the lake surface. A copy of this adequacy <br />letter is bein_q provided to the State Engineer's office in this respect. <br />Please respond as to your intention in this regard. <br />5. Included with the application was a "Notice of Intent to i<onstruct a <br />Non-Jurisdictional Water Impoundment." A principal spillway of 24 inch <br />culvert (gated) will create a lake depth of eight (8) feet. A vertical <br />dis>tance of one (1) foot between normal lake level and the bottom of the <br />emergency spillway channel is described. The emergency spillway will be <br />fifty (50) feet wide and four (4) feet deep before the embankment is <br />overtopped during a flood. The emergency spillway will be riorapped as <br />shown on Exhibit E. This design appears to be more than adequate to <br />safely pass large flood events, but no quantitative estimates have been <br />