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<br />Mathews, Dan
<br />From: Mathews, Dan
<br />Sent: Monday, July 22, 2002 12:57 PM
<br />To: Gorham, Kent; Dudash, Joe; Boulay, Mike; Walker, Byron
<br />Cc: Brown, Sandy; Berry, David
<br />Subject: drainage issues at Deserado Refuse Disposal Areas
<br />Kent, Joe, Mike and Byron
<br />I would like to request your input regarding some refuse area drainage design issues at Deserado. The Deserado refuse
<br />areas are in rolling sagebrush country northeast of Rangely. Currently, there are three refuse "sub-areas", RP-1 which is
<br />fully reclaimed, RP-2/3/4 which is active, nearing completion, and RP-5, which is active, in early stage of development.
<br />Each refuse sub-area is contained within a small (20 to 40 acre), bowl shaped watershed, that drains gently to the north.
<br />The pile final designs are basically crowned mounds, with 20% to 25%outslopes, without terraces or benches. RP-1 was
<br />reclaimed in the early 1990's. It appears to be stable, with no erosion and more or less blends into the surrounding terrain.
<br />The two active piles were initiated during the early 1990's, althouth Pile RP-5 has been used only sporadically until the last
<br />year.
<br />The three piles share the basic features described, but there are some differences with respect to detailed designs. The
<br />questions I have are focused on RP-5, which is at an early stage of construction, such that some basic design
<br />modifications would still be feasible. During initial site development a sediment pond was constructed immediately to the
<br />north of the refuse site, at the lower end of the watershed. A permanent, 100 year design ditch with riprap and vegetated
<br />segments was constructed just below the ridge crests along the perimeters of the watershed, concurrent with sediment
<br />pond construction. Design was such that the toe of the refuse pile side slopes would drain into these permanent design
<br />ditches.
<br />During early phases of pile construction, the pile was used intermittently, and refuse was spread in a thin veneer
<br />throughout the entire footprint of the pile area. The perimeter ditches along the sides of the watershed were at a higher
<br />elevation than the refuse, such that runoff across the compacted refuse generally was to the north, with drainage entering
<br />the sediment pond without any conveyance by design ditches. Some erosion resulted in the vicinity of the sediment pond
<br />inlet. As use of the refuse pile increased this year, the operator began building the pile up in lifts, and a toe was
<br />established along the western perimeter of the pile. Contrary to my interpretation of the approved design, the toe was at a
<br />substantially lower elevation than the perimeter ditch, such that drainage off the western outslopes of the pile would flow to
<br />the north and ultimately into the sediment pond, without entering the design perimeter ditch.
<br />I expressed my concern and ultimately issued an NOV. Operator's arguments, as I understand them include:
<br />"The approved design with toe draining into ditch was for final pile configuration, we would have gotten around to
<br />establishing the toe of the pile higher up on the slopes, to drain into the ditch, eventually."
<br />"It would be illogical to route the bare refuse drainage through the permanent ditches designed for the final reclaimed
<br />configuration, since vegetated sections and riprap would be covered over by refuse material and torn out during
<br />maintenance work."
<br />"What are you worried about, the disturbance is totally contained within the small watershed and everything is routed into
<br />the Sediment Pond?"
<br />My thoughts are that operator probably has a point regarding problems with routing operational drainage through the
<br />permanent ditches, but the pile design should probably from the beginning have specified requirements for interim ditches
<br />to convey refuse runoff into the pond, without erosion or ponding along the toe of the fill. Otherwise, it would seem that the
<br />the requirements of 4.09.2(7), would not be met during construction of the pile. Comments/Suggestions?
<br />Another question I have regards Rule 4.09.2(5) "Drainage shall not be directed over the outslope of the fill,"
<br />At most mines of which I am aware, refuse fills are constructed using a series of benches, beginning at the lowest point in
<br />the watershed and progressing upward, with the outer portion of each succeeding bench retained as a terrace that drains
<br />to a perimeter ditch. But not at Deserado. They don't use benches or terrace drains. Given the mounded design of the
<br />final pile, drainage is by necessity "over the outslope". During construction, the high amount of runoff from the long,
<br />compacted refuse areas results in significant erosion from the pile outslopes, which the operator periodically repairs.
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