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During storms of approximately 100 year return frequency, water will initially enter the lake through <br />u <br />r 1 <br />LJ <br />• <br />the spillway, which is 2.0 feet lower than the top of dam. As the storm grows, water will overtop the <br />embankment and flow into the lake, which may have a water elevation of 5 feet lower than the top of <br />dam. The normal water level is approximately 9 feet lower than the top of dam but since water will be <br />entering from the drainage basin as well as the spillway, the expected level at overtopping should only <br />be 5 feet from the top. Erosion should not be a concern since a) at least 12" of good soil will have been <br />placed on all parts of the embankment which will be vegetated aggressively, b) the inside slopes of the <br />dam are 3H:1V, which, when vegetated should reduce erosion, c) if any rills develop in this 5' drop, <br />the underlying material is river rock of D50 of approximately 1.0 feet, which will further reduce ero- <br />Sion and d) if any rills develop, they can be repaired after the storm ebbs. This maintenance should be <br />wnsidered normal for a storm of such magnitude. It is extremely unlikely that, with the above items in <br />place, a 100 year event could cause the river to capture the lake. <br />8. Water Information. Rights and Aut?mentation <br />All water rights issues such as augmentation for this operation, dust control, NPDES permit, is pre- <br />sented in Exhibit G -Water Information. <br />9. Mining Timetable <br />Two timetables are presented: one for ongoing harvesting from the river and the other for one time <br />lake excavation in the spring of 2002. The current lease with the landowner allows for 20 years of river <br />mining from March of 2001. The following timetable is a best estimate of the sequence of operations <br />for the life of the mine: <br />River Oration Timetable (Takes into account that site is pre-law and already built) <br />Task # Description Time Needed <br />1 Harvest gravel in environmentally acceptable way from river <br />for 6 week period of low flow flows each year 20 yrs <br />2 Regrade river channel to grade stated in mining plan 0.5 month <br />3 Replace topsoil on those portions of mine area to be restored to <br />agricultural use 0.5 months <br />4 Reseed agricultural portion of site 0.25 months <br />5 Move ail portable equipment offsite 0.25 months <br />Thomas Pit 2/02 <br />Total: 20 years and 1.5 months <br />22 <br />