2015-11-25_HYDROLOGY - M2008080 - Laserfiche WebLink

Home Browse Search

Paul Weiss, P.E. Page 2 Journey Ventures Pit Amendment November 17, 2015 Depletions The anticipated net evaporation depletions for this SWSP amendment are 0.55 acre-feet from May 2015 through March 2016. The original SWSP approval letter dated May 19, 2015 indicates that 0.12 acres of water surface will be exposed at the site in a dewatering trench (1,151 feet long x 3 feet wide) and a 50 foot diameter dewatering sump. The total proposed exposed ground water surface area will increase from 0.12 acres to 0.36 acres to account for the evaporation of the silt pond and the recharge pond. 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. Table 1 shows the gross and net evaporation losses at the Journey Venture Pit for the period of April 2015 through March 2016 showing the increase in surface area beginning in October 2015. You have provided an updated monthly breakdown of the annual depletions, which include 0.55 acre-feet of net evaporative loss, 7.36 acre-feet of water lost with the mined product (which represents 250,000 tons of mined product), 2.26 acre-feet of water used for dust control (based on an estimated maximum amount of 4,000 gallons per day), and 4.10 acre-feet of water usage at the batch plant (Table 2). The original SWSP estimated 4.48 acre-feet of water used for dust control (based on an estimated maximum amount of 4,000 gallons per day), and 7.67 acre-feet of water usage at the batch plant. The operational losses amounts in this SWSP amendment are based on the actual usage through September 2015 and projected usage from October 2015 through March 2016. The IDS AWAS stream depletion model was used to determine the lagged depletions from dewatering, evaporation and operational losses to the South Platte River. The model was used in 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). The total lagged depletions for the period of this SWSP amendment equal to 6.87 acre-feet (Table 3). Since this is an amendment to the original SWSP, the stream depletion analysis using the SDF option in the IDS AWAS is still accepted, however any renewal request of this SWSP must justify the use of the SDF or use the alluvial aquifer option in the IDS AWAS. Dewatering Dewatering began in October and is expected to continue up to the completion of the slurry wall, estimated to be April 2016. Dewatering water that is pumped to the silt pond and the recharge pond will be assumed to return to the stream in the same timing as the dewatering depletions. Dewatering is projected to occur at a rate of 1,000 gpm (135 acre-feet per month), with a total capacity of 4,000 gpm (540 acre-feet) from the dewatering sump to the silt pond and recharge pond. The configuration of the recharge pond within the pit at the southeast corner (as shown in Figure 1) will not allow for recharge to the river to the north if any portion of the slurry wall other than the eastern wall, southern wall, and western wall south of the slurry wall are completed. If the Applicant advances slurry wall construction beyond these allowed areas, they must move the recharge pond to a different location where recharge is not impeded. The new location must be approved by the State and Division Engineer's Offices.