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p tb <br />NOV C-97-1~l-ATTACHMENT <br />CRDA_2 <br />1. Near the end of Terrace Bench Drain #4, just above the <br />juncture with East Collection Ditch, water overtopped the <br />terrace drain, eroded a gully 4' deep, 5' wide, and lo' long <br />through the toe of the bare refuse slope. A segment of the <br />East Collection Ditch a short distance below the blowout <br />filled in with refuse sediment and the ditch overflowed. A <br />rilled flow path 8-10 feet wide, with individual rills 4-6 <br />inches deep extended down the undisturbed hillslope <br />approximately 150 feet to an ephemeral drainage. Avery minor <br />amount of coaly debris had been deposited along the flow path. <br />A 60 foot segment of the perimeter ditch beginning <br />approximately 50 feet below the junction with the #4 bench <br />terrace drain was largely filled in with refuse sediment. <br />2. CRDA-2 Upland Permanent Diversion Ditch breached at a point <br />approximately 150 yards from the western terminus of the <br />ditch, where the ditch crosses a dry wash. The ditch at this <br />location had filled in with sediment from the dry wash and <br />overtopped, resulting in upland drainage flowing onto the <br />refuse. Debris path indicates that the water flowed across a <br />compacted corner of the active refuse bench and then down the <br />access road ditch, with no apparent adverse consequences. A <br />50 to 100 foot segment of the permanent diversion in the <br />vicinity of the breach needs to be cleaned out and restored to - <br />design capacity. <br />CRDA-1 - <br />3. An overflow of the Northwest Collection Ditch occurred in a <br />low gradient segment of the ditch a short distance below the <br />junction with_Bench #2 terrace drain. Trie ditch at this <br />location filled in with refuse sediment and overtopped. Out <br />of ditch flow occurred across undisturbed ground for a short -- <br />distance, leaving a surface skim of fine coaly material in <br />some areas; no erosion. Flow re-entered a lower section of <br />the ditch and was conveyed to the sediment pond. <br />4. Drainage from the rough graded active bench of CRDA-1 caused <br />erosion of the bare refuse outslope in several areas along the <br />southeast outslope of Bench #4. This in turn resulted in <br />blockage of the Bench #3 terrace drain in the vicinity of the <br />sharp turn at the southeast corner of the pile, which was <br />largely filled in by sediment along a 150' segent. <br />Overtopping of the #3 Bench drain resulted in minor rilling <br />(2-4 inch rills) within a 10 foot wide flow path down the <br />revegetated outslope below the terrace drain. <br />5 Terrace Drain #3 had also been filled in with sediment <br />approximately 50 feet from its junction with the Southeast <br />