2014-01-28_HYDROLOGY - M2003091 - Laserfiche WebLink

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Mr. Heintz & Ms. Wynne Duckworth SWSP January 27, 2014 Page 2 of 7 inches for effective precipitation which is 70% of the average annual precipitation based on Longmont 2, CO (ID #5116) NOAA weather station. Based on a projected exposed acreage of 0.88 acres from November through January and 1.15 acres from February through October, the total net evaporative depletion will be 2.86 acre -feet for this plan period, shown on Table 1. The Applicant has estimated that 6.24 acre -feet of water will be used for dust suppression at the site and will occur during the months of aggregate production. Mining is expected to occur in the months of March through September of 2014 with a total amount mined of 599,000 tons. The aggregate will be crushed, not washed and mined in a dewatered state. Pursuant to paragraph 13 of the General Guidelines for Substitute Water Supply Plans for Sand and Gravel Pit (April 2, 2011), a 2% moisture content by weight is charged as a ground water diversion. Therefore, 8.81 acre -feet of water is expected to be consumed from the aggregate production during this approval period. The Alluvial Water Accounting System ( "AWAS ") model was used with the alluvial aquifer boundary condition option to lag depletions to Boulder Creek. The following parameters were used in the model: transmissivity (T) = 35,000 gallons per day per foot, distance (X) from the centroid of the surface of the exposed ground water to the river = 4,400 feet, distance (W) from the aquifer boundary through the exposed ground water to the river channel = 8,800 feet, and specific yield (SY) = 0.2. The location of the stream depletion is assumed to be perpendicular to the river. The lagged depletions due to evaporation and mining operations during the SWSP period are shown in Table 1 and are estimated to total 5.53 acre -feet during this approval period. Dewatering The Applicant will dewater the site to allow for dry mining operations using collection ditches that will surround the pit. This water will either be pumped directly to two unlined silt ponds in the northwest corner of the Duckworth Property as shown in attached Figure 2, pumped to the Lighthouse Cove Pond to the north, or pumped to the Smith and Emmons Ditch to be transported back to Boulder Creek. Dewatering water that is pumped to the silt ponds will be assumed to return to the stream in the same timing as the dewatering depletions. Dewatering water may also be used as part of the dust control operations which is considered 100% consumptive. Dewatering shall be metered so as to account for water delivered to the silt ponds, Lighthouse Cove Pond, the Smith and Emmons Ditch, or to dust control operations. The Lighthouse Cove Pond ( "LCP ") is an unlined ground water pond (well) owned by the Lighthouse Cove Development. This pond was created from sand and gravel operations under DRMS permit no. M- 1983 -099 and was known as the Groom Addition. DRMS released this pit in 1993. A pre -1989 augmentation agreement between the gravel pit operator and the District 6 Water Users Association provides for replacement of evaporation from the LCP. Given the size of the pond and the rate of dewatering, the dewatering operation is not expected to increase the exposed surface area of the pond by any measureable amount. The LCP is approximately the same distance from Boulder Creek as is the Duckworth site and therefore any lagged depletions associated with dewatering that is discharged into the LCP is assumed to be offset by the lagged recharge credits generated by the same operation. This SWSP does not confer on Applicant the right to use facilities or structures not owned by it. MMM has stated they are in the process of obtaining permission from Lighthouse Cove Development to use their pond and they shall not divert any water to that pond until the appropriate legal arrangements are made. Any dewatering water placed into LCP cannot be used for irrigation or any other purpose by Lighthouse Cove Development or others, and must be allowed to accrete to the stream. The provision in the SWSP allowing LCP to be used as a recharge pond may not be continued in SWSP renewals should it be determined by the water commissioner or