2023-05-18_HYDROLOGY - M2008080 - Laserfiche WebLink

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Journey Ventures Pit SWSP Page 2 of 5 May 18, 2023 Depletions A total of 1.653 acres of water surface area is estimated to be exposed at the site within the boundaries of the slurry wall being a combination of groundwater and precipitation. Gross annual evaporation at the gravel pit location is estimated to be 46.0 inches per year, and the monthly distribution is as shown on attached Table 1. Net evaporation is defined as gross evaporation less the consumptive use of water by vegetation that naturally occurred at the site prior to construction of the pit. The historical consumptive use by vegetation was assumed to be equal to the effective precipitation, which was estimated based on the data from the Kersey weather station. The net evaporation for the exposed water surface is 38.4 inches per year, with a monthly distribution as shown on attached Table 1. Using the estimated exposed water surface area of 1.653 acres, the total annual stream depletion resulting from the exposure of water is estimated to be 5.29 acre-feet. You have provided a monthly breakdown of the depletions during this plan period, which include 5.29 acre- feet of net evaporative loss and 6.25 acre-feet of water consumed for dust control, for a total depletion of 11.54 acre-feet, as shown on attached Table 3. Water used for dust control will be pumped from water discharge to the settling pond from within the slurry wall. The Applicant must measure all water diverted for dust control and replace all depletions resulting from such diversions. The IDS AWAS stream depletion model, using the alluvial aquifer option, was used to determine the lagged depletions to the South Platte River from past mining operations. The following parameters were used in the model: transmissivity (T) = 100,000 gallons per day per foot, distance (X) from the centroid of the surface of the exposed ground water to the river = 4,766 feet, distance (W) from the aquifer boundary through the exposed ground water to the river channel = 9,500 feet, and specific yield (SY) = 0.2. The lagged depletions during this plan period due to past mining operations total 9.31 acre-feet, as shown in attached Table 3. Since all depletions during this plan period will occur within the boundaries of the slurry wall, the Applicant has assumed that such depletions are instantaneous. Therefore the total depletions during this plan period are estimated to total 20.85 acre-feet, as shown in attached Table 3, which include the lagged depletions from pre April 2022 operations. Dewatering Dewatering began in October 2015. Dewatering water was historically discharged to the silt pond and the settling pond and was assumed to return to the stream in the same timing as the dewatering depletions. During this plan period dewatering may only occur within the boundaries of the slurry wall and such water must be discharged to the slough that runs back to the river, unless prior approval for a different discharge location is first approved by the water commissioner. Replacements The operator proposes to provide replacement for this pit using fully consumable water leased from the Central Colorado Water Conservancy District ("CCWCD"). A copy of the lease agreement with CCWCD for up to 23.15 acre-feet for one year from April 1, 2023 through March 31, 2024 was provided to this office with the SWSP request and is attached to this letter. The leased water includes additional water to cover transit losses, based on a transit loss of 0.5 percent per mile. Water will be released from the Geisert Pit, located along the Poudre River in Greeley and approximately 6.8 miles upstream from the Journey Ventures Pit. The Ogilvy Ditch headgate on the Cache la Poudre River is a potential summer dry-up point that is located between Geisert Pit and the location of the Journey Venture Pit depletion point, in the SE '/a of Section 7, Township 5 North, Range 64 West of the 6th P.M. Central has a bypass structure at the Ogilvy Ditch headgate to pass augmentation flows by the Ogilvy at