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<br />• item 5: continued <br />If inflow into the pond does not meet effluent <br />limitations (this is unlikely since, due to mostly <br />groundwater inflow, the pond, MB-5 has never been out <br />of compliance) the valve will be operated manually, <br />i.e. it will be closed, chemical treatment will occur <br />and after sufficient tifie has elapsed for clarification <br />to occur, the pond will be manually dewatered in a <br />minimum time. <br />~_J <br />Item 6: A small concrete headwall approximately 2 ft x 2 ft <br />will be constructed at the inlet end of the pipe. This <br />headwall will prevent seepage and provide anchorage for <br />the 8 inch diameter cast iron canal gate. The pipe <br />trench will be thoroughly compacted to prevent seepage. <br />There will be no contingency plan for controlling <br />groundwater inflow into the pond. Since the past 9 to <br />5 years have been very "wet" years it is reasonable to <br />assume that groundwater inflow will be controllable <br />with the dewatering device as explained in item 5. <br />However, if groundwater inflow increases significantly, <br />since groundwater quality has in the past always met <br />effluent limitations, Sediment Pond MB-5 could simply <br />be rapidly dewatered on a frequent or as needed basis <br />to maintain 10 year, 24 hour storage capacity. The <br />dewatering device in the full open position can flora <br />540 GPM with no static head which would empty the 10 <br />year, 24 hour storage volume of 0.17 acre-ft in 1.7 <br />hours. <br />Item 7: The emergency spillway is simply being relocated. It <br />will be constructed using the same design and materials <br />as the original spillway previously approved by the <br />Division. Rip-rap, fill, etc. will be reused to the <br />extent possible. If fill is needed it will be imported <br />from the WELL borrow area. If additional rip-rap is <br />required it will frost likely be hauled from local <br />gravel pits by truck. <br />Item 8: The function of the dewatering pipe is described in <br />Item 5. The valve gate will be near the pond bank and <br />if necessary, a small walkway will be constructed for <br />easy access. The valve is a cast iron canal gate and <br />will be located, as shown on attachment G - Pond <br />sections, just above the 1008 sediment storage level as <br />required by the Colorado regulations. <br /> <br />