2010-03-05_HYDROLOGY - M1996050 - Laserfiche WebLink

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Mr. Forest Leaf, P.E. February 22, 2010 Page 2 For 2010, you have estimated the operational and evaporation losses to be 17.21 acre- feet based on am.exposed ground water surface area of 3.7 acres. There is no dewatering associated with the mining operation. The pit is located greater than 100 feet from the South Platte River and the resulting depletions have been lagged to account for the delayed effects on the river system. The IDS AWAS stream depletion model was used to determine the lagged depletions to the South Platte River. The following parameters were used in the model: transmissivity (T) = 390,000 gallons per day per foot, specific yield (SY) = 0.2, the distance from the South Platte River to the edge of the alluvium = 12,707 feet, and the distance from the centroid of the exposed surface water areas to the South Platte River is approximately 1,804 feet. Based on the above, the lagged stream depletions are estimated to be 16.80 acre-feet from January 1, 2010 through December 31, 2010. The monthly lagged stream depletions are shown in the attached Table 3. According to the "General Guidelines for Substitute Water Supply Plans for Sand and Gravel Pits", water consumption by the mining operation will also include water removed from the tributary stream system by the "first fill" of the gravel pit. The "first fill" is the water that fills the gravel pit and occupies the volume previously occupied by the removed sand and gravel. For the.Reese-Logan Pit, the "first fill" was estimated based on 16,500 tons of aggregate -production for 2010 multiplied by the percentage gravel matrix (65% assuming a porosity of 35% and a density, of the material of 120 lb/cubic-foot) and then subtracting the volume of water lost with the mined,product for "Not Washed" gravel. Based on the above, the water removed by the "first fill" was determined to be 3.62 acre-feet for 2010. You have provided a monthly breakdown of the maximum annual depletions totaling 12.28 acre-feet of evaporative loss from a maximum of 3.7 acres of exposed ground water, 0.83 acre-feet of water loss due to dust suppression, and 0.49 acre-feet of water loss associated with the extraction of an estimated 16,500 tons of aggregate from below the water table for 2010. No phreatophyte credit has been applied to this plan. A summary of the monthly operational and evaporative depletions is shown in the attached Table 2. Replacements The Applicant proposes to provide replacement water for the actual operational depletions by a lease agreement with NSID. The source of water from NSID will be excess recharge credits in accordance with the decree in case no. 1996CW1034. A copy of the 2009 lease for replacements with the NSID was provided to the State Engineer's Office ("SEO") with the SWSP request. For the September 2009 through December 2009 period, a total of 5.58 acre-feet of replacement water was leased from NSID. For 2010, a total of 17 acre-feet of replacement water was leased from NSID. A copy of the leases for 2009 and 2010 are attached to this plan. To assure that depletions from groundwater evaporation do not occur in the unforeseen event, or events, ,that would lead to the abandonment of the pit, one share of the Schneider Ditch is committed jo be used to cover groundwater evaporation in case of abandonment. The one share of the., Schneider Ditch has an estimated 30 acre-feet of historical net stream depletions. This substitute water supply plan may be revoked at any time should it be determined that the one share of the Schneider Ditch will be insufficient to make replacements for the Reese-Logan Pit site.