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Response to Adequacy Review Comments Coulson Excavating Company, Inc. - Bonser Gravel Pit - The following sections were also added to Exhibit L: Item 6 "Sediment Settling Reservov", Item 8 "Construction Quality Assurance Costs", Item 9 "Mobilization and Demobilization of Equipment", and Item 10 "Indirect Costs". In addition, Item 3 "Topsoil Preparation" has been amended to reflect the separate costs of disking and seeding. - The cost estimates for Items 6, 9, and 10 were adapted from a previous 112 application for the Boyd Gravel Pit, Loveland Ready Mix, Inc. These cost estimates are assumed to be acceptable due to the fact that the 112 application for the Boyd Gravel Pit has been approved. The specialist assigned to the Boyd Gravel Pit was Tomas A. Schreiner. Please Note: Reclamation costs are revised to reflect the proposed change in post-mining use. 5. Comments Regarding the March 13, 2001 Memo From Allen Sorenson I . Possible Flooding Impacts • The 100-yr floodplain, adapted from FIRM data, has been added to Exhibit C. A ] 0-yr floodplain (Army Corp of Engineers 1977) boundary has also been added to Exhibit C. • Referring to the mine plan in Exhibit D, stockpile locations have been changed to surround the entire permit boundary by the fmalization of aggregate extraction. The location of these stockpiles will serve to facilitate backfilling during reclamation and mitigate Flooding of the pit. The stockpiles are constructed by driving scrapers along the soil and dumping they loads as they pass over the crest. This method of stockpile construction creates stockpiles that are relatively competent. It is felt that when the stockpiles are vegetated, they will act as a competent levee. If floodwaters do enter the pit, they are expected to do so as placid backwaters and serve to decrease overall stream energy in the area. • Floodwaters are expected to flow in an east northeasterly d'vection, with a velocity of 4 ft/sec fora I % chance Flood event (Army Corp of Engineers 1977). The 1977 Army Corps of Engineers study calculated I % chance floodwater elevations to reach an elevation of approximately 4856 ft in the area. • Please see Exhibit D "On and Off-Site Protection From the 100 Year Flood" for complete details. 2. Issues Related to the Proposed Pit Liner a) A plan to key the reservoir liner is added to Exhibit E, "Construction Procedure". b) Documentation of the water table is provided in Exhibit G.