2012-10-04_HYDROLOGY - M1977439 - Laserfiche WebLink

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Richard T. Rains, P.H. Partners Combined SWSP — Amendment #1 October 1, 2012 Page 2 of 5 In accordance with the letter dated April 30, 2010 (copy attached) from the Colorado Division of Reclamation, Mining, and Safety ( "DRMS "), all sand and gravel mining operators must comply with the requirements of the Colorado Reclamation Act and the Mineral Rules and Regulations for the protection of water resources. To prevent long term injurious stream depletions that result from mining related exposure of ground water, future operations will include constructing slurry walls around each of the five ponds to construct water storage reservoirs. The Partners have a pending application for a conditional water right for these future reservoirs in water court case no. 2000CW251. The owners and operators of the mining site are municipal entities and thus a bond to cover the cost of lining or backfilling the pits is not required. Depletions The construction of a slurry wall around Treiber A will require approximately 20 acre -feet of water which will be consumed in mixing the bentonite slurry mix. This water will come from Treiber B (ground water lake) and is considered 100% consumptive. Evaporation for each of the five lakes covered under this SWSP was calculated in the previous SWSP for this site. Treiber B and Lamb A, B & C will not change as a result of this amendment. However, with the dewatering of Treiber A starting in October 2012, the evaporation for this lake has been proportionately reduced in October and November 2012 and starting December 2012 ground water evaporation at this lake will cease occurring as the lake will be in a dewatered state and a slurry wall will have been installed and undergoing testing. See Table 4 for the monthly breakdown of the unlagged depletions. The monthly evaporative depletions to the Cache la Poudre River were lagged from the pit site using the AWAS program developed by the IDS Group at Colorado State University. The parameters used in the model were an estimated distance from the exposed water surface area to the river (X) of 744 feet (representing the average distance from the centroid to the river), an estimated distance from the site to the no flow aquifer boundary (W, measured perpendicular to the point of impact) of 6,500 feet, an aquifer transmissivity (T) of 160,000 gallons per day per foot, and a specific yield (S) of 0.2. The depletions associated with the 20 acre -feet of water consumed in the slurry wall mixing process was lagged with the same parameters as above with the exception of the distance from the exposed water surface (X). The 20 acre -feet of water will come only from Treibe B lake whose centroid is 640 feet from the Poudre river and thus X was set to 640 feet. The new lagged stream depletions taking into account the dewatering and slurry wall installation equal 297.33 acre -feet in 2012, and 208.59 acre -feet in 2013. See Table 5 for the monthly breakdown of the lagged depletions. Should the slurry wall fail, or construction is delayed and Treiber A is allowed to refill with ground water, this SWSP will no longer be valid and another amendment must be submitted to this office. Replacement All replacement sources listed in the May 11, 2011 SWSP remain a part of this plan. This amendment includes an additional replacement supply in the East Larimer County Water Distrcit (ELCO). ELCO is one of the Tri- Districts thus a lease is not required. ELCO recently decreed its municipal return flows in Case No. 09CW282 on June 29, 2012. Their accounting was approved by the Division Office on August 23, 2012. The reusable municipal return flows accrue to the Poudre River primarily at either the Fort Collins Waste Water Treatment Plants