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<br />July 8, 2003 <br />To: Larry Oehler // <br />From: James Dillie~u~ / <br />Re: Review of Bear Creek Re-alignment Plans, Portland Plant, M-1977-344 <br />As requested, I reviewed the revised Bear Creek re-alignment plans for the referenced mine site. <br />Following are my comments and requests: <br />1) The operator should submit more information regarding how the berms will be <br />compacted. The operator illustrates berm dimensions, slope gradients and key-in <br />information on Figure 9 but does not explain how the material will be compacted. <br />2) Hydrologic data (for the 100 year event) shows: <br />A) Highway 50 culvert system on Bear Creek will not fully convey runoff. <br />Floodwater is projected to overtop the highway (a CDOT problem). According to <br />the submitted hydrologic analyses, the relocated creek is adequately designed to <br />convey floodwaters except that the proposed terminus culverts will not totally <br />convey the projected 100-year event so the flow is expected to overtop the access <br />road and, most likely, wash out the roadbed. Once the site is reclaimed, this will <br />no longer be a problem because the access road and culverts are to be removed. <br />B) Floodwater flows are expected to overtop both temporary access crossings. Long <br />term, the temporary crossings will be removed so no overtopping problem will <br />exist after the site is reclaimed. However, if the area floods while the mine is still <br />active, and a temporary crossing is washed out, the culverts and roadbed material <br />will need to be replaced. <br />3) Energy dissipation structure -did the operator evaluate the need for a filter layer? If a <br />filter layer is necessary, what are the limits of the filter material with respect to both the <br />base and riprap material? How far does the riprap layer extend below the culvert outlet? <br />What flow velocity did the operator use to determine the size of the riprap material? Will <br />the riprap structure remain after the site is reclaimed? <br />4) Is the operator required to re-vegetate the banks and bed of the relocated creek? If not, I <br />would suggest re-seeding the excavated creek so it will remain stable (less erosion) during <br />times of high runoff. <br />Overall, the revised relocated creek is adequately designed to handle runoff from most storm <br />events. The designed gradient is mostly gentle to mild throughout the entire reach of the <br />relocated channel. More than likely, since the groundwater inflow from the east will be <br />minimized or totally eliminated, flow within the new creek will be intermittent, at best. <br />If you wish, just send a copy of this memo to the operator rather than re-writing the requests for <br />additional information. <br />Need anything else? <br />cc: Harry Posey (e-mail) <br />