2008-05-14_HYDROLOGY - M1980149 - Laserfiche WebLink

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Steve Nguyen May 14, 2008 lining is complete. The total exposed water surface associated with this cell is 0.37 acres in the dewatering trench. Currently 70.86 acres of surface acreage is exposed at the Hokestra site, including 70.1 acres outside of the currently mined area and approximately 0.76 acres exposed in the dewatering trenches. Of the 70.86 acres of exposed surface, 56.76 acres were exposed after December 31, 1980 and 14.1 acres were 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, 2008 and reported 0.15 acres of blue grass and 5.5 acres of native grass. This area will be irrigated using water pumped from the lake during the growing season. According to a Modified Blaney-Griddle 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 operation of this site consists of 4.4 acre-feet of water lost in product (4% moisture of 150,000 tons of raw material), 1.2 acre-feet for on-site dust control and 145.76 acre-feet of evaporation from 56.76 acres of lake surface exposed after December 31, 1980. The total consumption at this site from mining operations and irrigation is 161 acre-feet. The depletions from evaporation and operational 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 5 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 162.43 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 and fully consumable water leased from SVLH. Weld County has obtained a lease from SVLH for 22.0 acre-feet and a copy of the lease is attached to this letter. The amount leased from the SVLH includes a transit loss of 0.25% per mile for the 12 miles between the pit location and the discharge point for the SVLH water. 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 will be stored in the Varra Pit No. 112, which lies directly to the south of the Hokestra Property and across the Rural Ditch. It is estimated that 81.9 acre-feet of excess credits will be available for storage during this plan period. According to the reservoir operations model for the 112 Pit, the water placed in the 112 pit will incur an evaporative loss of 5% or 3.9 acre-feet. The 112 Pit has access to a ditch headgate, which will be used to deliver the excess river credits to the lined reservoir for storage. The stored water will be released from the pit to cover depletions from the site as shown in attached Table No. 5.