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. :. _ ..• ~ .23.:The.drainage Swale to be constructed along the western edge of the affected land .. : . <br />.. :. .is intended to operate much the same as the surface diversion presently in place - <br />have operated for the past number of years, only more effective. The shallow <br />diversion stmcture will move surface flow originating from historic mine <br />operations above, intense storm events, or snow melt southwazds towazds the <br />southwestern comer of the affected land. At a point approximately aligned with ' <br />the present location of the lower pit, the ground directly above and slightly south <br />of the pit naturally creates a drainage control that presently directs surface flows <br />downwards towazds the lower pit. Colorado Marble intends to utilize this <br />condition that has effectively diverted surface nm-off the past 100 years . The <br />following response to the Division's questions: <br />The diversion ditch system as well as the highwall bench co~guration will be <br />stepped down via short ramps no steeper than 3:1 at intervals from app. 300' to <br />app. 100' along the length of highwall. The gradient is steeper at the north end of <br />the affected land than the southern end. The ditch and highwall benches with <br />their individual ditch configuration for drainage of the bench top will be <br />connected by short, steeper mns of ditch mm~ing along side the ramped zone at <br />no greater slope than 15%, allowing for machine access for maintenance and exit <br />areas for wildlife that may wander into the benchlhighwall configuration. The <br />bench ramps will be constmcted to not exceed 30' in height from one level (I %) <br />run to the next along the ditch bench run and the ramps will be oBeset firm the <br />bench above and below to break the visual line of the bench/ramp system and <br />minimize any one area of ramp construction along a vertical line. This technique <br />will tend to break up the overall linear appearance of t]re bench/lrighwall system <br />from its tendency to appear as a long horizontal nm as depicted on the plan view <br />map. As the difference in grade as measured on the plan view map reflects, there <br />may be 18-201eveling adjustments from the extreme southern end of the highwall <br />system to the extreme northern end at the maximum extent of highwall <br />development. <br />The anticipated flows to be diverted in the ditch at the top of the highwall <br />configuration is estimated at between 5 and 50 gpm based on observance of the <br />existing surface water flows during 2005 and 2006, although 2006 flow rates aze <br />very low with exception of short term storm events. <br />The.cross section of the west diversion ditch will be included in this mailing. The <br />ditch will be a simple "v" type ditch cut with bulldozer to 3' depth and 8' in width <br />with steeper (1: i) slope on downslope of hill side and lower slope (3:1) on uphill <br />side of ditch cut. The ditch will be seeded and mulched with permanent seed mix <br />to promote re-vegetation as soon as possible after installation. The ditch will be <br />left as a permanent feature after mining ceases due to its purpose of mitigating <br />overland flow over the highwall bench system in the future. <br />The diversion of the ditch flow into the lower pit is an integral piece of logic <br />regazding on site environmental control. For one, the diversion of surface water <br />