Laserfiche WebLink
%6 <br />P.O. Box 187 <br />December 8, 2016 <br />EMAILED <br />TRAPPER MINING INC. <br />Craig, Colorado 81626 <br />Ms. Tabetha Lynch <br />Environmental Protection Specialist <br />Colorado Division of Reclamation, Mining and Safety <br />1313 Sherman Street, Room 215 <br />Denver, CO 80203 <br />nic <br />Jeffy.and Deal Diversion <br />xAdequacy Reespa>lw #1 <br />Dear Ms. Lynch: <br />Please accept this letter as our response to the adequacy review letter of November 3, 2016. <br />(970)824-4401 <br />Division Comment. The Division must review all variables used to derive the structure outputs <br />with the Deacon/Jef fay Diversion. Based on the Division's review, all variables appear <br />adequate for the diversion. However, the use of Curve Numbers (CN) 66, 72, and 63 to represent <br />the ground conditions to derive the model output does not reflect the current Trapper Mine Plan. <br />The Division believes that although the curve numbers utilized in the SEDCAD model may reflect <br />the current on -the -ground conditions, they do not reflect the worst case scenario when <br />determining if the Deacon/Jeffway Diversion is adequately designed. The Division believes that a <br />curve number of 86 is the appropriate CN when modeling this Diversion. Please provide the <br />Division with a revised Deacon/Jeff vay Diversion design that reflects a variable CN of 86, or <br />provide justification as to the use of the proposed curve numbers of 66, 72, and 63 within the <br />currently approved mine plan. <br />Trapper Response: The current design of the diversion ditch in relation to the stripped areas <br />ahead of mining is adequate for the foreseeable future. Trapper anticipates the needed sediment <br />control structures will be in place before any further disturbance is required above the diversion <br />ditch. At that time the ditch will become unnecessary. If further pit advancement is necessary <br />before ponds are in place, the adequacy of the current diversion will be re-evaluated and modified <br />as needed. At such time a revised design will be submitted to the division. The attached <br />demonstration by Tom Paulson shows his calculations for each watershed and the Curve Number <br />utilized in the current SEDCAD Model. <br />