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~~~ Mr. Brent Anderson Page Three February 6, 1991 approximately 300 feet long be constructed to replace the culvert as shown on Figure 2, Lower Pit 5 & Access Road -Proposed Drainage Configuration. Channel design calculations and a description of design methodology are presented in Attachment 2 to the Bond Release Request Responses. ,ll In order to maintain access for the light use road which presently crosses Culvert 5-3, pj o ~ low gradient (4H:1~ access ramps will be incorporated in the engineered channel ~!J`~~ ~` segment at the crossing Location. Exposed sideslopes at the vehicular crossing will be ~~'~`' t2~(c~ armored as appropriate to minimize erosion. x,033 FEATURE 5 The existing contour ditch which intercepts and routes runoff from the northeast end of the Pit 5 reclaimed area to the Pit 5 access road ditch is excessively steep as -~,,,~ °" ~"~, described in the previous letter report (ACZ Inc., 10/1/90). As a result, the contour ;~ ^ ~ Ut ditch and the downgradient access road ditch show evidence of progressive 't a r'"e downcutting and erosion. As recommended in the previously referenced report and ~ e ~° shown on Figure 2, Lower Pit 5 ~ Access Road -Proposed Drainage Configuration, itv~ ~~"'~ is proposed that the contour ditch be relocated to reduce overall gradient to 1-2 ~d~~t° percent and the existing ditch be reclaimed by regrading and revegetating the ditch ¢\`~~+`~' area. The relocated contour ditch will be approximatey the same size and configuration as the existing ditch and will be revegetated by broadcast seeding upon completion. FEATURE 4 As described' in the previous report (ACZ, 10/1 /90) on the Pit 5 area, there is some rill and gully erosion on and along the sides of the Pit 5 access road. The most significant erosion occurs below the junction of the existing contour ditch described in the preceding section. Erosion becomes relatively severe near the inlet of Culvert 5-4. Minor rill and gully erosion on the road surtace can be addressed by regrading the road surface to eliminate flow channels, eliminating the ditch on the east side of the road and sloping the road to the west, installation of water bars or swales across the road at intervals of 70-100 feet, and revegetation of the road surface. In order to effectively address the more significant erosion on the west side of the access road, it is proposed that eroded areas be backfilled and the entire ditch be regraded to the design configuration detailed in Attachment 2 to the Bond Release Request Responses. Existing erosion of the west ditch is a reflection of high