2010-11-09_REVISION - C1981019 (2)

Home Browse Search

COMMENT RESPONSE FOR TR-87, ADDRESSING OCTOBER 14, 2010 CDRMS COMMENTS Rule 2.05.4 - Reclamation Plan In the 2009 reclamation blocks in the East Pit and West Pit, Colowyo used surface roughening (cross- ripping) and contour ditches with good success. Based on discussions with the Division, Colowyo has revised page 2.05-30, which addresses the commitment to perform additional reclamation practices in. the East Pit reclamation areas. Basically, Colowyo has committed to the use of surface roughening, including cross-ripping, and the use of contour furrows to help reduce surface runoff and sheet flow. On revised page 2.05-30, Colowyo states that they will use "contour furrows approximately 4-6 inches deep and 20- 25 inches wide... spaced approximately 10-75 feet apart" depending on the slope. Although the description provided in the text is very specific regarding the use of contour furrows, the Division would like clarification whether Colowyo intends to use contour furrows or contour ditches on the reclamation, as they are two very different reclamation practices. Additionally, the Division does not believe that the use of contour furrows and surface roughening alone will be enough to adequately control the runoff and sheet flow that will be present in the reclaimed East Pit. Please clarify/confirm whether Colowyo intends to use contour furrows in the East Pit reclamation and whether Colowyo intends to also use contour ditches in the East Pit reclamation. If Colowyo does, in fact, plan to use contour furrows, please include a description of how Colowyo plans to construct the furrows, from an equipment stand point. If Colowyo plans to use contour ditches in the East Pit reclamation, please include a description of the general construction practices that will be used for the contour ditches. Please update revised page 2.05-30 as necessary. Response: Colowyo does not intend to use contour furrows as a means of surface roughening and agrees with the Division in their belief that the use of contour furrows and surface roughening alone will not be enough to adequately control runoff and sheet flow that will be present in the East Pit reclamation. Colowyo does, however, plan on implementing several contour ditches after all regrade, topsoil and seed work is complete. Each contour ditch will be surveyed and staked on contour at a grade of 1 %. In the past, Colowyo has utilized a D6 dozer to cut and maintain each contour ditch approximately three feet deep. Colowyo will continue to use this method of construction as the D6 is the most effective piece of equipment available to Colowyo for the given task. Colowyo has updated page 2.05-30 to reflect its current and future practices and implementation of contour ditches rather than contour furrows. Rule 2.10 - Maps and Plans 2. Based on the meeting with the Division conducted on 13 October 2010, Colowyo intends to modify the design of the stock tanks so they sit slightly outside of the post-mining channel. Water will be diverted from the post-mining channel, into the stock tank, then back into the post-mining channel. The plan as depicted on Map 12 - Hydrology, South Area, shows these stock tanks in the middle of the post-mining channels. Please modify Map 12 to show the exact location of the stock tanks, as discussed in the 13 October 2010 meeting. Please also modify all of the figures included in the SEDCAD modeling for the Prospect Pond to show the exact location of the stock tanks. The map and figures should also contain the routing detail of the runoff from the post-mining channel, into the stock tank, then back into the post-mining channel. Response: As requested, Map 12 and Figures Exh. 7-14R-1 through 6 have been revised to show the exact locations of the stock tanks. A new Figure Exh.7-14R-8 has been included to show the routing details of the ditch inlet from the post-mining channels and the outlet return back to those channels. Colowyo Coal Company, L.P. • 5731 State Highway 13 • Meeker, CO 81641 T + 1 970 824 1578 • F +1 970 824 1598 • http://prospect.riotinto.org/irj/portal