2019-12-18_HYDROLOGY - M1998013 - Laserfiche WebLink

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Shores Substitute Water Supply Plan December 18, 2019 Page 2 of 7 to satisfy this requirement. In accordance with approach nos. 1 and 3, you have obtained a bond for $888,677.00 through DRMS for lining or backfilling of the exposed ground water. This is a reduction from the previous bond, which is based on the approval of the five lined reservoirs. Depletions Currently 11 acres of ground water surface is exposed at the Shores Pit within the silt pond and 3.5 acres of water is exposed surrounding Pond E. The depletion of groundwater due to evaporation from the 11 acre silt pond is calculated to be 28.82 acre-feet and from the 3.5 acres of open water surface is calculated to be 9.17 acre-feet during this SWSP period. Net evaporative depletions were calculated using a gross annual evaporation of 42 inches from the exposed water surface, with an annual credit of 10.56 inches for effective precipitation. The effective precipitation was calculated as 70% of the average precipitation from the Longmont weather station during 1967 through 1996, which is 15.08 inches. Ground water from the 11 acre silt pond is used for dust control and concrete batching. The Applicant estimates that 1.66 acre-feet of water per year will be used for dust control. Approximately 105,000 cubic yards of concrete will be batched onsite during this plan period at a depletion of 40 gallons per cubic yard, resulting in a water requirement of 12.89 acre-feet. The plant utilizes a water tap for the concrete batching at a rate of 4 million gallons per year, or 12.27 acre-feet during this plan period. Therefore the resulting annual net depletion from concrete batching is 1.64 acre-feet. The water supplied by the Central Weld County Water District shall be metered along with the total water used for onsite concrete batching to aid in calculating the actual depletions owed. The data from both metered sources shall be included in the accounting provided to the Division Engineer. According to the SWSP request all mining during this plan period has ceased, though the applicant anticipates moving the mining operation to the north when an approved DRMS permit is obtained. The net evaporation and operation depletions associated with the Shores pit are estimated to be 42.93 acre-feet, as shown in the attached Table 5. Dewatering of the site commenced in February 1999 at a rate of 300 gallons per minute and had remained constant during mining of cells A, B, C, and D. For modeling purposes dewatering was stopped on December 2006 which is the year the slurry walls for the three cells were completed. Dewatering from Pond E has ceased. The dewatering from Pond E has been recharged in the Pond E recharge area, shown on attached Figure 1 and returned back to the Saint Vrain River. The SWSP accounts for the net depletions at the river that occur due to the past dewatering operations. During this SWSP period lagged depletions from past dewatering at the site total 47.24 acre-feet and accretions from past recharge of dewatering water are projected to total 40.35 acre-feet, for a net depletion to the river of 6.89 acre-feet. The net depletion is shown in attached Table 6b. The depletions were lagged to Saint Vrain Creek using a Glover analysis and the following parameters where (T) is transmissivity, (Sy) is Specific Yield, (W) is the distance from the stream to the no-flow boundary and (X) is the distance from the point of depletion to the river. Table 1- Glover aquifer parameters for the mining operation Operations X W T Sy All mining depletions (1998-2007) 51409 101000 72,300 0.2 Evaporation, Concrete, dust suppression and 6,488 101000 72,300 0.2 settling pond evap.(2008-2017) Dewatering depletions (1998-2006) 4,507 101000 72,300 0.2