2012-10-15_REVISION - M1977211 (2)

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Mr. Mac Shafer October 15, 2012 3) Please provide a typical design for the proposed diversions and French Drain. No design details were provided with the application. Page 3 Under topsoil application, the operator states, "The applicant will apply the salvaged topsoil from the site and donated topsoil from the public on disturbed areas affected by the layback project". 4) Please provide the location and possible source and quantity of the donated topsoil in the facilities map. 5) What measures will be taken to ensure noxious weeds will not be imported with any donated topsoil? 6.4.7 Exhibit F- Reclamation Plan Map Please provide the reclamation plan map in accordance with Rule 6.4.6 (a) which shall include the following, "The expected physical appearance of the area of the affected land, correlated to the proposed mining and reclamation timetables. The map must show proposed topography of the area with contour lines of sufficient detail to portray the direction and rate of slope of all reclaimed lands ". 6.4.7 Exhibit G - Water Information Under Surface Water, the operator states, "Surface water will be affected in various ways but as much as possible surface water will be diverted around the operation, or treated in depressions on the site or passed through the sediment pond. Control of sediment and flow volumes will be accomplished through the storm water management control features. These facilities were described in Technical Revision 7, approved in early 1994. To control flow volumes, rates, and sediment discharge, a series of sediment basins and energy dissipation drop structures are used. These structures control the outflow volumes and are designed around a 10 -year 24 -hour storm event. It is likely that storms larger than this will be controlled to some extent, but sediment loads and volumes from larger storms will probably exceed the capability of the system to provide full control ". 1) Given the site's potential for erosion to occur on steep slopes, the Division recommends upgrading the structure designs to at least a 25 -year, 24 -hour event. All diversion structures that are redesigned to handle velocities in excess of 5 feet per second must be armored with appropriately sized riprap. Please provide a detailed updated storm water design for the facility. 2) The Division recommends placing an upland diversion to limit flows and seeps into the fracture zone of the quarry during mining and reclamation activities. Under ground water, the operator states, " The EXAP boring project was initiated on August 7, 2011, using air percussion drilling (Appendix 41, Exponent report). The goal of three wells within the H -area pit was to intersect the underlying Sawatch Sandstone; the northern EXAP -1 did not reach the Sawatch at 67' (7046.46') while EXAP -2 contacted it at 62'(7053.89') and EXAP -3 were unable to reach it at 70'(7075.3). All these wells had water in them the day after the drilling, with two northern wells having water levels within 7 -8' of the surface, and EXAP -3 having water within 40' of the surface suggesting intersection with confined aquifer. Exponent (2011) observed that 40 of 2144 GW levels were within a few feet of surface from coffined groundwater conditions ". The 3