2009-04-01_HYDROLOGY - M1980149 - Laserfiche WebLink

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Rachel Kullman March 25, 2009 According to the information provided by the applicant, the County will continue to dewater the 9.9-acre cell during this plan period. The total exposed surface area for the 9.9-acre cell is one acre in the dewatering trench. The county also intended to line the 30.5-acre cell in 2009, but lining has been delayed. It is anticipated that lining will occur over the next two years. The 30.5-acre cell will continue to be dewatered until lining is complete. The total exposed water surface associated with this cell is 0.37 acres in the dewatering trench. Currently 70.1 acres of surface acreage is exposed at the Hokestra Pit site, and approximately 1.37 acres are exposed in the dewatering trenches. Of the 70.1 acres of exposed surface, 56 acres were exposed after December 31, 1980 and 14.1 acres were exposed prior to January 1, 1981. Due to a change in administration of evaporation from ground water exposed to the atmosphere prior to 1981, pre-1981 credits will no longer be allowed for gravel pits which exposed ground water to the atmosphere prior to 1981 and were actively mined on or after January 1, 1981. Accordingly, evaporative depletions for such gravel pits will need to be replaced from the entire surface area of the ground water exposed in the pits. Therefore, no evaporation credit will be claimed in this SWSP for the 14.1 acres exposed prior to January 1, 1981. 'Weld County will irrigate approximately 0.15 acres of blue grass and 5.5 acres of native grass around the reclaimed pond at the Weld County Service Center, which is a reduction from the irrigated acres at this site from previous plans. Weld County conducted a field survey on February 7,'-2,008 acid„reported 0.15 acres of blue grass and 5.5 acres of native grass. This area will be irrigatedusing water pumped from the lake during the growing season. According to a Modified Blaney-Criddle analysis the potential crop consumptive use for the 0.15 acres of blue grass is 0.30 acre-feet and the potential crop consumptive use for the 5.5 acres of native grass is 9.35 acre-feet. Since the irrigation occurs directly around the reclaimed pond, the plan assumes that the return flows will return to the river in the same timing as the depletions. Consumptive use from the evaporation of this site during this plan period is 183.54 acre- feet from 71.47 acres of exposed surface area. The total consumption at this site from evaporation and irrigation is 193.19 acre-feet. The depletions from evaporation losses were lagged to the stream using a Glover analysis and assuming a distance to the stream of 250 feet, distance to the impermeable boundary of 6,600 feet, transmissivity of 50,000 gal/day/ft and specific yield of 0.2. The depletions from irrigation were also lagged to the stream using a Glover analysis and assuming a distance to the stream of 800 feet, distance to the impermeable boundary of 6,600 feet, transmissivity of 50,000 gpd/ft and specific yield of 0.2. The attached Table 4 provides a monthly schedule of lagged actual depletions to the river system, together with a schedule of replacement requirements. This SWSP accounts for actual depletions determined to accrue to the stream system during this plan period. The total lagged stream depletions from mining operations and irrigation is 191.87 acre-feet. REPLACEMENTS The sources of replacement water are 3.75 Rural Ditch shares owned by Weld County, storage of excess credits in Varra's 112 Pit, fully consumable water leased from SVLH, and fully consumable water leased from Greeley. The 3.75 shares of the Rural Ditch will be used directly to replace depletions between May and September. This plan proposes to store excess river credits attributable to the 3.75 shares of Rural Ditch. The excess river credits which accrue to the stream system in June, July and August