2008-04-07_REVISION - M1980149 (3)

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_ - ~~ ~~ v% Applegate / ,- z; Group, ~~~. Apri13, 2008 ~ ~~ii~~ V Colorado Department of Natural Resources APR a 7 ~oo~ / ' . .Division of Reclamation, Mining, and Safety Attn: Ms. Erica Crosby Division of ~teciamation, 1313 Sherman Street, Room 215 Mining and Safiety ~. Denver, Colorado 80203 RE: Adequacy Review Comments #2; Weld County; Hokestra Pit; M-80-149 / Dear Ms. Crosby: This letter is provided in response to the adequacy review comments dated March 10, 2008. Thank you for taking the time .to review our responses. We appreciate your time and effort regarding this project and feel that we have adequately addressed your concerns. 1. A map showing all adjacent land owners has been provided. Adjacent landowners were also added to Exhibit C-1. 2. The application has been revised to reflect the approved (AR-04) permit boundary acreage of 172 acres.. 3. The stability analysis indicates that the slopes of reservoir III and 1V which will be surrounded by a slurry wall will be stable. The XSTABL model assumed the following. • The slurry wall will be minimum of 12 feet from the reservoir embankment. • Gaslines are located outside of the slurry wall. • ~ The slurry-wall does not infringe upon the easements for the existing gaslines. • Reservoir slopes are at a 4:1 and are native sand and gravel. ' • The material properties for the shale bedrock-were taken from on-site tests. The sand and ~~ gravel properties are from the Bureau of Reclamxation's "Design of Sma11 Dams", Third Edition, 1987. These properties are shown in the table accompanying the answer to comment 5 in this letter. The model was run in both a rapid draw down condition and a static condition. The model showed .that the reservoir side slopes were stable.. A factor of safety of 1.74 was. generated in the rapid. drawdown scenario. The static scenario produced a slough failure with at a factor of safety of 2.83. Neither failure plane impacted the slurry wall. The gaslines will be outside of the slurry wall, and therefore their stability was also not affected. The results of this analysis are attached. During construction where-the slurry wall crosses the gaslines, the County will have crossing agreements with the gasline companies and supply copies of those agreements to the DRMS before construction of the slurry wall begins.. _ 1499 West 120th Avenue, Suite 200 - (303) 452-661.1 • Fax {303) 452-2759 Denver, Colorado 80234-2759 www.applegategroup.com