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Transit Mix Concrete Co. <br /> DRMS COMMENTS - Tim Cazier - Adequacy Review of Stormwater <br /> Management <br /> 1. Page G-16, section c, Drainage Discussion. The narrative states "Once this water is diverted <br /> back to Little Turkey Creek, Transit Mix will fully mitigate any possible impacts to the <br /> hydrological system." Please explain how Transit Mix will mitigate hydrologic impacts after <br /> flows are diverted back to Little Turkey Creek. <br /> Response: The text in Exhibit G has been revised to clarify this statement. The impacts to <br /> the hydrologic system are minimized by diverting flows back into Little Turkey Creek. <br /> The outlet plates on the sediment detention basins control the discharge rates so that stream <br /> flows are similar to pre-mine stream flows. <br /> 2. Page G-19, Table G-4. Please provide rationale as to how the CN of 63 was determined as <br /> "Fir/Pine" is not an option in TR-55 curve number tables. <br /> Response: Exhibit G of the permit text discusses the rationale for selecting the curve <br /> number for the Fir/Pine forest. "As there are no values for Fir/Pine forests representative <br /> of the western portion of the site, it was assumed that Oak-Aspen community would be <br /> similar. Based on a D-type soil for the fir/pine forests, a curve number of 63 was assigned <br /> to all undisturbed subwatersheds for the western portion of the site." <br /> 3. Page G-21, Ditch CWD-1/MegaDitch. The "prefabricated channel material" is planned for <br /> conveying unimpacted drainage from detention basin P-DET-1. The Division has some limited <br /> experience with this product suggesting it may require frequent maintenance which may not be <br /> accomplished with heavy equipment. Additionally, there appears to be steep sections (30 to 40 <br /> percent grades) for this channel shown on Figure G-8a (and subsequent Exhibit G figures). <br /> Please provide the following: <br /> a. Means of access and maintenance for this relatively remote diversion channel, and <br /> b. SmartDitch's limits on channel gradient (for successful installation), and hydraulic shear stress <br /> capacity for the proposed HDPE material. <br /> Response: The Smart Ditch will be installed adjacent to fines stockpile F1 and can be <br /> accessed via the stockpile benches for several years after the installation of the channel. <br /> Any material defects or installation issues will be realized during this time period. <br /> Following regrading and reclamation of the stockpile, the channel can be accessed using <br /> tracked equipment should any maintenance be necessary. <br /> Smart Ditch can be installed on the steep slopes specified for this project, but additional <br /> anchoring is required. The hydraulic shear stress capacity is only limited by the tensile <br /> strength of the HDPE material (approximately 3,000 psi). Transit Mix will continue to <br /> work with Smart Ditch engineering and technical staff to refine the ditch system and <br /> anchoring designs for installation purposes. <br /> 4. Page G-22, Table G-5, Slopes. Ditches DD-1 and F1-1 list slopes a 1.2% and 1.0%, <br /> respectively. Figure G-8a shows segments of DD-1 may be as steep as 40% and Figure G13 <br /> Hitch Rack Ranch Quarry(M-2017-049) <br /> Response to Comments—March 9,2018 <br />