2008-09-09_REVISION - C1982056 (2)

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Binns, Janet From: Binns, Janet Sent: Tuesday, September 09, 2008 3:37 PM To: jnettleton@peabodyenergy.com Subject: TR-61 Factor of Safety Good afternoon Jerry, I have been in discussions with Tom Kaldenbach and Dan Hernandez throughout the day to assure that all of the items initially identified in the Division's August 30, 2007 adequacy have all been adequately resolved. As I had discussed with you earlier today, the last unresolved items from the Division' 8/30/2007 adequacy letter, and the second adequacy letter, dated 10/22/2007, were: #15: Rule 4.05.9(8)(a) requires impoundments that meet the size criteria of 30 CFR 77.216(a) OR that meet the Class B or Class C criteria for dams in USDA NRCS Technical Release No. 60 OR that are located where failure would be expected to cause loss of life or serious property damage to have both a minimum factor of safety of 1.5 for normal pool with steady state seepage saturation conditions AND a seismic safety factor of at least 1.2 or higher to ensure stability. TCC revised the design of the pond since the static factor of safety was provided in the NWCC evaluation, dated 8/06/2007. Please provide a stability demonstration that indicates a safety factor of at least 1.5 for a normal pool with steady state seepage saturation conditions, AND a seismic safety factor of at least 1.2 (Rule 4.05.9(8)) for the revised design. The design changes still result in a pond meeting the criteria of 30 CFR 77.216(a). I will forward your response to Marcia for her review. #30: Rule 4.05.2(4) exempts disturbances caused by sediment ponds, ditches, treatment facilities, and associated roads from Rule 4.05.2(3). Areas that were proposed outside of the impoundment footprint were subsequently addressed and approved by MR-228. This item is resolved. #37: This item is the same question as #15. This question was apparently asked twice. So the response to #15 shall resolve #37 as well. #38: This was resolve by the fact that #37 applies. #38 originally was asked if the conditions of #37 did not apply, then conditions of #38 were valid. Since #37 applies, #38 is eliminated. #42: The revised design would result in a 10 ft. head of water at the maximum. The Division finds that the hydraulic head would be approximately 4.3 psi. This would be minimal and the Division is not concerned about impacts to the groundwater if the pond is constructed as designed. This item is resolved. Thank you, Jerry, I am trying to assure that all these loose ends are wrapped up as quickly as possible. Janet Binns Environmental Protection Specialist II Colorado Division of Reclamation, Mining and Saftey (303) 866-4944 9/10/2008