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. ~ Hydro~lamics Incorporated ~~~1\ 19039 E. Plaza Drive P.O. Box 1327 HydroDynamics ; Parker, CO 80134 \~~~~ Voice: (303) 841-0377 FAX: (303) 841.6386 January 6, 2000 Ms. Lori Potter Kelly/Haglund/Gaznsey & Kahn 1441 Eighteenth Street, Suite 300 Denver, CO 80202-1225 RE: Comments on DMG's December 22, Project No. 9974-01 Dear Ms. Potter: 1999 Reply to HDI's November 8, 1999 Letter t ~, We have reviewed DNIG's comments as submitted to your office by Ivlr.,b2r*.~r~TJ~llie and. aze providing the fo4owing responses. 1. / Mr. Dillie's Fourth Paragraph It is stated that "The runoff in Red Creek is not collected, or retained, in the sedimentation pond." This is the first time we have been informed that flows ' Red Creek are routed around the sedimentation pond. No documents on file with DMG indica .e this situation. We are curious as to whether runoff from a northeast Red Creek tributary that flows through the quarry is also routed aoound the sedimentation pond. When we reviewed 1960 through 1993 aerial photographs ofithe quarry, we discovered that Red Creek has been forced northward away from its historic chjlnnel by placement of fill material. Thus, what appeazs to be a historic Flow path today is actually a new channel created within the last 30 years by the quarry operation. ~ Mr. Dillie's Fifth Paragraph We doubt whether the observed "scouring" would have been as significant if the quarry was not in existence. The 6/4/99 DMG inspection report noted eroded banks and increased stream width. Such conditions more than likely occurred due to placement (and subsequent erosion) of fill material used when the original historic Red Creek channel was moved. If any runoff from the quarry entered into Red Creek via overland flow or through the breached sediment pond, it would have conveyed sediment downstream. This is very evident since quarry material nearly filled the small pond immediately north of Mr. Heck's property. The statement that "...the Division has no evidence that any sediment load even left the mined site." is very misleading. According to the 6/4/99 inspection report, it appears the DMG did not conduct any offsite inspection to substantiate such a statement. Mr. Dillie's Siath Paragraph We appreciate Mr. Dillie's explanation on a "constructed basin." What is unclear is whether there is more than one "swale area near the active mining site" and whether these are total containment systems. Also, we have not found any information in the regulations that indicate for what frequency storm event such facilities are designed. Water Resources Hydrologists • Engineers • Planners