2017-03-23_HYDROLOGY - M2008080 - Laserfiche WebLink

Home Browse Search

Journey Ventures Pit SWSP Page 2 of 6 March 21, 2017 reservoir through the construction of a slurry wall around the mining area. The surface area of the reservoir at the completion of mining is expected to be between 33 acres to 38 acres. In accordance with the letter dated April 30, 2010 (copy attached) from the Colorado Division of Reclamation, Mining, and Safety (“DRMS”), all sand and gravel mining operators must comply with the requirements of the Colorado Reclamation Act and the Mineral Rules and Regulations for the protection of water resources. The April 30, 2010 letter from DRMS requires that you provide information to DRMS to demonstrate you can replace long term injurious stream depletions that result from mining related exposure of ground water. The DRMS letter identifies four approaches to satisfy this requirement. In accordance with approach nos. 1 and 3, of the DRMS April 30, 2010 letter the Applicant obtained a bond for $487,550 through the DRMS for phases 1, 2, 7 and 11a of this site to assure that depletions from groundwater evaporation do not occur in the unforeseen event, or events, that would lead to the abandonment of the Pit. Depletions The anticipated net depletions for this SWSP are 61.78 acre-feet. A total of 2.15 acres of water surface is exposed at the site in settling/recharge ponds for wash water and a sump for pumping water to the batch plant. Gross annual evaporation at the gravel pit location is estimated to be 46.0 inches per year and the monthly distribution is as depicted on the 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 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 the attached Table 1 and using the estimated exposed water surface area of 2.15 acres, the total annual stream depletion resulting from the exposure of groundwater is estimated to be 6.89 acre-feet. You have provided a monthly breakdown of the annual depletions, which include 6.89 acre- feet of net evaporative loss, 22.81 acre-feet of water lost with the mined product (which represents 775,000 tons of mined product), 4.08 acre-feet of water used for dust control (based on an estimated maximum amount of 4,000 gallons per day), and 28.0 acre-feet of water usage at the batch plant (Table 2). The IDS AWAS stream depletion model was used to determine the lagged depletions from evaporation and operational losses to the South Platte River. The model in the previous SWSP used the SDF effective mode, with a stream depletion factor (“SDF”) of 120 obtained from Plate-6 of Hydrogeologic characteristics of the valley-fill aquifer in the Greeley reach of the South Platte River valley, Colorado (Hurr and Schneider, 1973, USGS Open-File Report: 73-124). As requested in the previous SWSP the IDS AWAS model was modified to use the alluvial aquifer option. 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 due to mining operations during the SWSP period are shown in Table 3 and are estimated to total 39.14 acre-feet during this approval period.