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Mr. Allen Weaver, Mine Engineer -4- March 30, 1994 <br />Energy Fuels Mining Company <br />4. Watershed diversion ditch 1 maintenance and design. <br />Evidence of erosion exists in Section B of Watershed Diversion 1. During our <br />meeting we discussed several options for erosion control of the steep section located <br />above the powerline light use road. Discussed options included: <br />a. Channelize the existing gully from the outlet of ditch section A downslope to the <br />powerline light use road, and install energy dissipating structures, silt traps, and <br />riprap as necessary to control erosion; or <br />b. Extend Section A of Diversion 1 approximately 20 feet further west to outlet to <br />the natural drainage that currently defines section C of Diversion 1 below the <br />powerline light use road. Submit demonstrations that the natural drainage will <br />safely pass runoff from the 100-year, 24-hour precipitation event. <br />Riprap has been dumped on the outslope of the road embankment of the powerline <br />light use road at the location where Watershed Diversion 1 crosses the light use <br />road. This riprap has been dumped in a manner that disrupts the cross section of the <br />channel. Paragraph 4 of page 425 R, revised May 1993, of the permit, describes the <br />triangular channel that was to be lined with riprap (D50 = 6 inches) where <br />Watershed Diversion 1 crossed the powerline light use road. Maintenance is needed <br />at the location where Diversion 1 crosses the light use road and on the outslope of <br />the road embankment to ensure that Diversion 1 safely pass the design storm event. <br />Contradictions exist in the permit concerning Watershed Diversion 1. A data table on <br />page 358Rd lists Drainage Structures, Return Periods, and Precipitation amounts for <br />the 100-year and 10-year events. This table states that Watershed Diversion 1 has <br />three sections. Section A and B are designed for the 100-year, 24-hour precipitation <br />event, but Section C, located down channel from sections A and B, is designed for <br />the 10-year, 24-hour event. The current copy of Map 12, certified by <br />P.G. Corser, P.E., June 24, 1993, supports this data table in that this copy of <br />Map 12 shows three sections of Watershed Diversion 1. On page 425R, however, <br />Watershed Diversion 1 is described as having four sections, with Sections A, B, and <br />C being designed to convey the 100-year, 24-hour precipitation event, and <br />Section D, located down channel of sections A, B, and C, being designed for the 10- <br />year, 24-hour event. The labeling of Watershed Diversion 1 needs to be consistent <br />to avoid confusion. Please describe whether Watershed Division 1 will have three <br />sections or four sections and revise the corresponding permit section accordingly. <br />Rule 4.09.2(7) states that sediment control structures designed to divert runoff from <br />entering onto the coal refuse pile must be designed to safely pass runoff from the <br />100-year, 24-hour precipitation event. Watershed Diversion 1 Sections A, B, and C <br />have been designed in accordance with Rule 4.09.2(7), but Section D, which <br />conveys flow from Sections A, B, and C around the sediment pond before <br />discharging to the natural stream channel, has only been designed to pass runoff <br />from the 10-year, 24-hour event. The Division believes that such designs are <br />contradictory to prudent engineering practices. <br />