Laserfiche WebLink
Ms. Kim Frick <br />November 12, 2010 <br />Page 2 <br />In accordance with the letter dated April 30, 2010 (copy attached) from the <br />Colorado Division of Reclamation, Mining, and Safety ("DRMS"), all sand and gravel <br />mining operators must comply with the requirements of the Colorado Reclamation Act <br />and the Mineral Rules and Regulations for the protection of water resources. The April <br />30, 2010 letter from DRMS requires that you provide information to DRMS to demonstrate <br />you can replace long term injurious stream depletions that result from mining related <br />exposure of ground water. The DRMS letter identifies four approaches to satisfy this <br />requirement. For the Derr Pit, it is our understanding that approach no. 1 or no. 3 will be <br />utilized as evidenced by the Applicant's proposal to obtain a bond in the amount of <br />$1,362,889 prior to the exposure of ground water at the Derr Pit. Prior to the exposure of <br />ground water at this site, the Applicant is required to provide proof to this office (the <br />Division of Water Resources) that such a bond has been obtained and the requirements <br />of the April 30, 2010 letter from DRMS have been satisfied. <br />Depletions <br />This SWSP describes the proposed water uses from October 1, 2010 through <br />September 30, 2012 for this proposed new pit. The total consumptive use of ground water at <br />the Derr Pit (including evaporative and operational losses) is estimated to be 84.19 acre-feet. <br />You have provided a monthly breakdown of the annual depletions totaling 19.84 acre-feet of <br />'evaporative loss from 6.8 acres of exposed surface area, 2.00 acre-feet of water used, and <br />consumed for dust control, 7.36 acre-feet of water lost with the mined product (250,000 tons of <br />aggregate), and 54.99 acre-feet of water removed by the "first fill". The average precipitation <br />from the Greeley UNC weather station for the years 1967 to 2009 was used to determine the <br />net consumptive use from evaporation. The average precipitation for this time period is 14.2 <br />inches. No phreatophyte credit has been applied to this SWSP. <br />Water consumption by the mining operation will also include water removed from the <br />tributary stream system by the "first fill" of the gravel pit. The "first fill" is the water that fills the <br />gravel pit and occupies the volume previously occupied by the removed sand and gravel. For <br />the Derr Pit, the "first fill" was estimated based on 250,000 tons of aggregate production for <br />2010 multiplied by the percentage gravel matrix (68% assuming a porosity of 32% and a <br />density of the material of 1.69 tons/cubic-yard) and then subtracting the volume of water lost <br />with the mined product. Based on the above, the water removed by the "first fill" was <br />determined to be 54.99 acre-feet. <br />A stream depletion model was used to determine the lagged depletions to the Cache La <br />Poudre River. The following parameters were used in the model: harmonic transmissivity (T) _ <br />76,056 gallons per day per foot, specific yield (SY) = 0.2, the distance of the exposed ground <br />water to the river X = 2,124 feet, and the location of the parallel impermeable boundary was <br />estimated to be 14,115 feet from the stream. Because this is a new proposed mining operation, <br />no ground water was exposed at this location prior to January 1, 1981. The stream depletion <br />model shows that the Applicant must replace 41.01 acre-feet for the period of October 2010 <br />through September 2011 and 64.25 acre-feet from October 2011 through September 2012. For <br />the purposes of this SWSP, the distance of the exposed ground water to the river ("X") is <br />accepted; however, should the Applicant seek to renew this SWSP, the Applicant must <br />calculate the depletions with the X value measured from the centroid of the ground water <br />pond.