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Please demonstrate how the proposed mitigation structures will limit the differential head between <br />each of the above mentioned mine cells, to ensure the lateral berms will not erode. <br />2.) Page SE8 of the Stability Analysis states a HECRAS model was used to analyze the rate of flow for the <br />various inflow/outflow structures during different stages of a flood event. In order to verify the <br />adequacy of the design of the inflow/outflow structures please submit the results of the HECRAS model <br />as well as the inputs used for the model with an explanation how the inputs were derived. <br />3.) According to the plan, the inflow/outflow channel's will be excavated to a depth of two feet. Please <br />clarify where the two foot excavation will be keyed off? For example, the channel should be excavated <br />two feet below the top of the pit bank and then excavated at the same elevation from the top of the pit <br />bank to the river. It should not be excavated just two feet uniformly across the land surface between <br />the pits and the river. <br />4.) For each of the inflow/outflow structure for each mining cell using the unit hydrograph for a 100-year <br />flood event, please submit tables that compare the river water elevation and the pit water elevation. <br />Please time the tables so the water level for the river and the pit are displayed for every 15 minutes <br />during the flood event. If this exercise does not demonstrate that the cells are filled with flood water <br />prior to overtopping of the riverbank, the inflow/outflow structures must 'be re-designed to achieve that <br />goal. <br />5.) Please commit to grading and armoring the pit-side embankment at the inflow point of the mining <br />cells as soon as possible after mining is complete. <br />6.) Please provide the seed mix that will be planted in the inflow/outflow channel. This should include <br />the names of the native species and the pounds of live seed per acre that will be used. Also, this <br />channel will be prone to erosion until native grass has begun to establish. Please commit to planting a <br />fast growing cover crop in the channel and specify the species of grass that will be utilized. <br />This concludes the Division's review of the inflow/outflow structures proposed for flood mitigation at <br />the Parsons Mine. Please remember that the decision date for this application is January 27th, 2009. If <br />there are still unresolved issues when the decision date arrives and no extension has been requested, <br />the application will be denied. If you have any questions, please contact me at (303) 866-3567 ext. <br />8120. <br />Sincerely, <br />Jared Ebert <br />Environmental Protection Specialist <br />Cc: Anne Best Johnson, Lafarge West, Inc. <br />Tony Waldron, DRMS <br />Eric Scott, DRMS