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Requirements for fill generated outside the approved permit area (MLRB Rule 3.1.5 (9)) <br />are addressed below. <br />Final Groundwater Lake Stability The stormwater channel outlet is illustrated on the <br />attached plan map, Reclamation Plan ;Map Revisions.. The invert of the stormwater <br />channel entering the groundwater lake will be at or near the anticipated normal lake water <br />surface elevation of 4669 feet above mean sea level (amsl). The stormwater channel. will <br />be armored for erosion protection from ,the proposed box culvert under F Street to the <br />channel outlet. The armoring will also extend past the stormwater channel outlet and <br />cover the lake bank and. shoreline to the toe of the slope. Armoring material will,be <br />composed of riprap, concrete mattress, erosion fabric, or other appropriately designed <br />erosion protection material. <br />It is anticipated 'that flows entering- the .site through the stormwater channel will reach <br />800 cubic feet per. second (cfs) during the 100-year storm event. The stormwater channel <br />outlet will be sized-to ensure that flows from the 100-year event can be delivered to the <br />groundwater lake. as designed. Sufficient sizing of the channel outlet and the armoring <br />described above will prevent significant erosion of the stormwater channel and the lake <br />banks and shoreline during major storm events. It is estimated that an inflow of this . <br />magnitude would raise, the groundwater lake elevation. approximately 2.5 feet. Freeboard <br />for the anticipated groundwater lake is more than sufficient to contain the estimated rise <br />in lake surface during this type of major storm event.. In addition, because the existing" <br />reclamation plan includes the creation of 3H:1V slopes.for the lake.banks and shorelines <br />that will be stabilized with vegetation,, -the temporary rise in lake elevation is not likely to <br />cause excessive bank erosion. <br />Following a major storm event, surface flows out-of the_lake and groundwater infiltration <br />are expected to gradually return .the lake surface elevation to its normal.' anticipated <br />elevation of 4669 feet amsl. A historic channel near the northeast corner of the' <br />groundwater lake runs under the -Colorado and Southern Railroad Bridge and connects <br />the lake,to the.Cache la Poudre River. The invert of the. channel is' at an elevation of- <br />approximately 4670 feet amsl and, therefore, the channel -would convey flows to the <br />Cache la Poudre River if the lake elevation increased significantly: Existing rock and <br />vegetation alongthe channel banks provide annoring to protect against erosion.. During <br />the 100-year stormwater event and associated rise in lake elevation, temporary flows out <br />of the lake are estimated to be. 150 cfs. Flows of this magnitude would not be expected to <br />cause' significant erosion ,in. the historic channel: <br />As stated above, final reclamation for the site will contain two lakes. The two lakes are <br />separated by high ground left in place because of .an underground pipeline. The, <br />reclamation plan includes. a culvert through the higher ground that separates the lakes; <br />potentially connecting the 'eastern. lake with the western lake.. However, the proposed <br />invert of the culvert is at 4675 feet amsl. It is not expected that the water surface <br />elevation of the eastern .lake would ever reach 4675 feet amsl and, therefore, it is not <br />likely that water from the eastern lake could enter the western lake.