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Ei)vi'*ropn)ei)t, C. <br />LARRY E. O'BRIAN 7985 VANCE DRIVE, SUITE 205A <br />FOUNDER ARVADA, COLORADO 80003 <br />STEVAN L. O'BRIAN 303- 423 -7297 <br />PRESIDENT FAX 303 - 423 -7599 <br />February 19, 2015 t/ <br />DIVISION OF RECLAMAI ION <br />MININGAND SAFETY <br />Mr. Tyler O'Donnell <br />Division of Reclamation, Mining & Safety <br />1313 Sherman St., Suite 215 <br />Denver, CO 80215 <br />Dear Tyler; <br />RE: Albert Frei and Sons, Inc. M— /6777 ---S2j& <br />Worthing Pit - - _ <br />Technical Revision 04 - Adequacy Response #2 ./ <br />On behalf of my client Albert Frei and Sons, Inc., I am responding to your second <br />adequacy review letter dated January 16, 2015. I have included your review points that <br />need to be addressed in the order presented so the questions and answers will be in the <br />some document for easy reference. <br />3) In review of the design submitted DRMS believes that this design does not provide a <br />long -term solution. DRMS believes that there is high potential for the open channel to: fill in <br />with silt, become clogged with vegetation and the soil walls of the 1H:1V open channel to <br />slump off and restrict flow. Please provide a groundwater mounding mitigation plan that will <br />have a lower likelihood of failure as described above. The design must demonstrate <br />long -term success. <br />This design has not been finalized at this time, this means that the elevations of the <br />trench may change if needed as construction continues. Attached is a sketch map showing <br />the trench divided into 3 sections to better describe what will happen when the trench is <br />completed. Section 1 is the yellow line is the newly constructed out -fall trench, Section 2 <br />is the old Slough area, blue line and Section 3 is the southern end and area that contains <br />the head of the trench, green line. <br />The plan is designed to assure this is a long term fix to the groundwater mounding <br />problem by sloping the groundwater trench, from the southwest end to the river so it has <br />a negative grade. This will keep the water flowing from start to end. The trench bottom <br />will be wide enough to allow adequate carrying capacity to keep a positive flow along its <br />