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Mr. Mike Schaffner <br /> July 26,2018—TR-101 PAR <br /> Page 2 <br /> and Dam Construction, Rules 4.2.5.1 and 2 to determine if existing and/or upgraded <br /> embankments require Dam Safety oversight and provide a summary in your response for each <br /> EMP reviewed. <br /> 3) ECOSA Toe Berm: The evaluation indicates CC&V believes the ECOSA toe berm should not <br /> be classified as an EMP. The Division disagrees for two reasons: 1)the potential for stormwater <br /> runoff from the ECOSA to have metals and low pH is significant based on water quality results <br /> from the ECOSA seep, and 2)runoff from the west side of the SGOSA is captured by DC-EMP- <br /> 8b which reports to EMP-8b which is an EMP with a required design storage capacity of two <br /> times the 10-year, 24-hour storm runoff volume. Please reclassify the ECOSA toe berm as an <br /> EMP and provide the necessary design upgrades to the ECOSA toe berm to satisfy the two times <br /> the 10-year runoff volume criteria. <br /> 4) Geotextile use: Section 4.2 discusses using 8-ounce non-woven geotextile underlayment for <br /> riprap-lined channels. The Division's engineer's experience with riprap on non-woven geotextile <br /> is that on longitudinal slopes greater than about 10 to 12 percent, design peak flows wash the <br /> riprap right off the geotextile. In order to avoid maintenance after storms approaching the design <br /> storm, the Division recommends (but does not require at this time) using a granular filter under <br /> riprap for longitudinal slopes greater than 10 percent. <br /> 5) Closing Remarks: Section 5.0 attempts to summarize necessary upgrades to ponds, diversion <br /> channels and spillways, but is somewhat confusing. For example, channel DC-EMP8a appears <br /> to be a newly required channel, but implies there upgrades necessary related to capacity and <br /> riprap. If this channel does not exist, as indicated in Table 3.1, why are there concerns with <br /> capacity and riprap. Also the use of the word "absent" is confusing. For example, channel DC- <br /> EMP18N is followed by "absent", yet Table 3.1 indicates it exists. Please provide a more <br /> thorough summary of what specific (e.g., non-existent channel requires full design; riprap not <br /> present,but necessary;pond inlet protection not present,but necessary; etc.), if any upgrades are <br /> necessary for each structure. <br /> 6) Drawings 050 and 200: Previous EMP upgrades have led to violations related to affecting area <br /> outside the affected area boundary (specifically EMP 9a). As the current permit boundary is <br /> coincident with the affected area boundary, please include the Amendment 12 permit boundary <br /> on Drawings 050 and 200. <br /> If you have any questions or need further information,please contact me at(303)866-3567 x8169. <br /> Sincerel <br /> Timoth A. Cazier,P.E. <br /> Environmental Protection Specialist <br /> ec: Michael Cunningham, DRMS <br /> Amy Eschberger, DRMS <br /> Elliott Russell, DRMS <br /> DRMS file <br /> Meg Burt, CC&V <br /> Justin Bills, CC&V <br /> v\v\min\tc1\_cc&v\m-1980-244 cc-v\tr-101 stmwtr mgt evakm-80-2444101par-2018-07-26 docx <br />