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TkRPPER MINING INC TEL~303-824-4632 <br />TRAPPER <br />Rpr 23 96 10 26 No .001 P.O1 <br />III IIIIIIIIIIIII III <br />t~C. <br />April 23, 1996 <br />FAX DELIVERY <br />Mr. Joe Dudash <br />Environmental Protection Specialist <br />Colorado Division of Minerals & Geology <br />1313 Sherman Street, Room 215 <br />Denver. CO 80203 <br />Dear Joe: <br />Re;;;:: tipper rntngi)(oc:. crmitNo.;G. 1-010;x':':': ' . <br />n::. <br />,: , . -.;~Itepa~rPlan; and';Schedule.for Grouae:PondpSpilhvays~,:, !`; (<: ;:; .::~~;' '::';..,;;:.: : ':'::'.?:':r;.<: ;::' <br />Please accept this letter as our response to your letter of March 21,1996 concerning a repair plan <br />and schedule for the Grouse #1 and #2 ponds spillway outfalls. <br />EXPLANATION FOR EROSION <br />Concerning your question as to why the erosion occurred on the spillway outfalls, our investiga- <br />tion led us to the following conclusions: <br />Hieh Peak Flows. Although the flow recorder at NPDES discharge point O15 (Grouse <br />Pond #2 spillway flume) was not operational at the time peak flows occurred in Grouse <br />drainage in late February (the stilling well was still frozen), we were able to roughly <br />approximate a peak flow for the Grouse Ponds by noting the high water mark on the spill- <br />way flume. This mark represented a peak flow of approximately 1,450 GPM. [Note: the <br />highest observed flow was 745 GPM, noted by Larry Henderson on 2/22/96.] This calcu- <br />lated flow of 1450 GPM represents a very high runoff, well above the peak flows normally <br />observed with spring runoff. <br />2. Immature Vegetation Establishment. Due to the recent construction of Grouse Ponds #1 <br />and #2 spillway outfalls, vegetation was still in the early development stage and thus did not <br />provide as much erosion protection as would have been expected from a more mature stand <br />of vegetation. <br />3. Erosion Control Materials. Excelsior Blanket erosion control mats were used on both <br />Grouse ponds spillway outfalls, In the pest, this method of erosion protection has proven <br />very successful with almost no exceptions. <br />At the Grouse Pond #2 outfall the Excelsior Blanket mate were effective in controlling ero- <br />sion. The slight erosion at Grouse #2 was well beyond the actual spillway, occurring at the <br />spot where Excelsior Blankets terminated, near the end of the spillway outfall. <br />P.0. Box 187 Craig, Colorado 81626 (303) 824-4401 <br />