Laserfiche WebLink
1/23/2019 State.co.us Executive Branch Mail-Fwd:Twentymile Coal, LLC,TR16-84 TA4 Responses <br /> 1. Please provide additional design detail for the Cascade at the inlet of the system, including the <br /> peak flow volume, rational for stone sizing, identification of vortex stones which are in the text of the <br /> diagram but not labelled. <br /> a. It appears to DRMS that weep holes may be needed, particularly at the <br /> discharge end of the cascade structure. Please explain why these are not <br /> necessary or consider modifying the design. <br /> b. Please provide a description and update diagram showing how the inlet pipe <br /> and cascade are being anchored into the drainage, so that neither water moving <br /> through the pipe or precipitation will compromise the function of the cascade. <br /> Response: All system components are designed for a peak system flow of 375gpm (0.84 cfs). No vortex stones <br /> are included in the drawing, given the relatively small flows. Detail 1 mentions the term but that is a general <br /> reference to other stone types as well. Only footer and crest stones are shown in the diagram. No weep holes are <br /> necessary given the relatively small size of the structure and that the system is open to soil on all sides and no <br /> significant retention of water is expected below the grouted rip-rap. <br /> The inlet pipe will be a short, exposed section of the buried water transfer pipeline which will have grouted footer <br /> stones on either side, with the end of the pipe resting on the cascade crest stone. As shown in the detail drawing <br /> (Drawing C-11 — Sheet 15 of 15), the cascade system will be keyed into the slope at the top and bottom, with a <br /> geotextile base, graded rock bedding, and sized footer stones, which overlap on their downgradient edge for <br /> support. The cascade system will be surface grouted both to provide additional support and to minimize <br /> infiltration and maintenance. System flow will be as noted above, and precipitation flows will be minimal, with <br /> essentially all runoff, except direct precipitation on the system, being captured and diverted by the north and <br /> south diversion ditches. The system design (stone sizing, etc.) is very conservative given the low design flow. <br /> Best regards, <br /> Jerry <br /> Jerry M. Nettleton <br /> Manager Environmental Affairs <br /> Twentymile Coal, LLC <br /> 29515 RCR27 <br /> Oak Creek, Colorado 80467 <br /> Office Phone: 970.870.27121Cell: 970.761.0125 <br /> jnettletonpeabodyenergy,com <br /> https://mail.google.com/mail/b/AN5OxKOKJ ROCsWaEnKNoaNi le8rnVdY8EGJbj5W5_to7gHAFsFyx/u/O?ik=deb7fOcd20&view=pt&search=all&permthi... 3/4 <br />