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~. Richard D. Lamm Governor III IIIIIIIIIIIIIIII DEPARTMENT OF NATURAL RESOURCES Davitl H. Getches, Execulrve Director MINED LAND RECLAMATION DIVISION DAVID C. SHELTON, Director January 14, 1986 Mr. Vern Pfannenstiel Peabody Coal Company 10375 East Harvard Avenue, Suite 400 Denver, Colorado 80231 Re: Response to NOV C-85-081, Seneca II Mine - File No. C-80-005 Dear Vern: I apo]ogize for the length of time it has taken me to respond to the above referenced letter. I have several comments on the material presented; some we have already discussed during telephone conversations and after the assessment conference. 1. As we have discussed, the Wadge Impoundment is of sufficient size to hold the 10 yr-24 hr storm and 110.6 at-ft of sediment. Peabody presented calculations for an annual sedimentation rate of 10.2 ac-ft/yr but did not exp]ain how this number was reached. Some explanation should be presented. Using 10.2 ac-ft/year, since pond construction available storage has been depleted by 54.4 ac-f t. The remaining storage will be depleted in 11.4 years. While this is a few years away, I strongly recommend Peabody re-evaluate their sediment yield calculations for this area to show that these figures are conservative. This will eliminate the need for pond surveys in the future to show that cleanout is or is not necessary. This can be done as part of the 5 year permit renewal. 2. My calculations show a slight deviation from the ones presented by Peabody for the shop area pond. Sediment levels for this pond do not require cleanout at present, however, my calculations show 1.56 ac-ft of storage remaining before the 60 percent level is reached. Please evaluate and correct if necessary. Peabody may want to re-evaluate annual sediment yield calculations for this pond also. 3. For the southeast pond my calculations again show a slight deviation from Peabody's. Please evaluate and correct if necessary. The l0yr-24 hr storm will most likely be passed without using the emergency spillway. Peabody should do a flood routing to verify this. Sediment yield calculations may also need revising. 4. Finally, Peabody proposes to implement a sediment level monitoring schedule of every 3 years. Familiarity with the mine site requires the Division to impose a monitoring schedule of once a year 423 Ceniennia! Building, 7313 Sherman Street Denver, Colorado 80203 Tel. (303) 866-3567