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<br /> <br />COLINA ORO MOLINO, INC. <br />GOLD HII.L MILL, BOULDER COUNTY, COLORADO OCT ~ ~ X997 <br />FII.E NO.: M-94-117 <br />RESPONSE TO CORRECTIVE ACTION NO. 1 ,~ , ,:,r~~;•r~ <br />MLRB MEETING OF SEPTEMBER 24, 1997 <br />ISSUE: <br />At the MLRB meeting of September 24, 1997, COM, Inc. was ordered to implement the <br />following corrective action: <br />"1) Submit verification that the spray evaporative system meets the capacity as <br />designed by Richard Fox and approved by the Division no later than October 15, <br />1997." <br />RESPONSE: <br />1. The files for the permittee were reviewed at the offices of the DMG, and the pertinent <br />correspondence listed below were obtained. <br />2. The "capacity as designed by Richard Fox" appears to be addressed in a letter dated <br />March 17, 1996. Paragraph 4 of that letter gives two examples, with different <br />assumptions about evaporation loss and wind drift loss, which provide the estimated <br />times to evaporate 20,000 gallons through a spray evaporation system recirculating <br />250 gallons per minute (gpm). The estimated evaporation rate "capacity" (gpm) is not <br />given, there any no "design" details, and there is no justification as to why 20,000 <br />gallons or 250 gpm were chosen for the examples. <br />3. In a letter dated March 18, 1996 the DMG took the two examples from the Fox <br />March 171etter, and performed a calculation which concluded "...the Gold Hill Mill <br />tailing pond should be able to dispose of between 5 and 10.7 gpm of water by <br />evaporation". Nowhere in the DMG letter does it say that the "design" by Fox was <br />approved. <br />4. Based on the above correspondence, it appears that COM, Inc. is being asked by the <br />DMG to "verif}~' that the spray evaporation system will "dispose of between 5 and <br />10.7 gpm by evaporation". <br />5. According to records maintained by the operator of the existing evaporation system <br />approximately 2 inches of pond water were evaporated over 24 hours on October 10, <br />1997. According to a January 9, 1996 letter from Fox, 1 inch of pond water is equal <br />to approximately 11,600 gallons. Therefore, the existing system is evaporating <br />approximately 23,200 gallons over 24 hours, or about 16 gpm. This estimate could be <br />reduced approximately 1 gpm to account for pan evaporation, thereby leaving an <br />approximate 15 gpm net evaporation rate. <br />6. Since the existing system is estimated to evaporate 15 gpm, COM Inc. has complied <br />with the 5 to 10.7 gpm "capacity" requved by the DMG. <br />10/15/97 <br />