2018-06-28_HYDROLOGY - M2008082 - Laserfiche WebLink

Home Browse Search

Ms. Jennifer S. Lindahl Page 4 of 9 June 28, 2018 0.8 acre-feet/month for September-October, and 0.5 acre-feet/month for November-December, as shown in Table 2, column 5. RMCC will dewater Stage 6A, Stage 3 until it is backfilled, and Stage 4 in order to mine the gravel. The projected dewatering pumping volume is shown in Table 2, column 6. A berm between Stage 6A and 6B was constructed to allow storage to occur only within Stage 6B. Water was diverted into storage at Stage 6B under free river conditions. As mentioned above water was stored in Stage 6B to a depth of 12 feet above the bottom elevation of Stage 6B, with a surface area of approximately 5 acres, under free river conditions. The total consumptive use at the site for the remaining SWSP period is 123.6 acre-feet (from evaporation, water lost with the mined product and dust control. The dewatering pumping volume to be discharged to Big Dry Creek during the period of this SWSP amendment is estimated at 9,155 acre-feet, as shown on the attached Table 2. The IDS AWAS stream depletion model was used to determine the lagged depletions from dewatering, evaporation and operational losses at the Morton-Holton Lakes site to Big Dry Creek and the South Platte River, using the following Glover parameters: • specific yield = 0.2 • transmissivity = 150,000 gpd/ft based upon pumping test data in Colorado Ground Water Circular No. 11 • distance from centroid of the Stage 1 mining area to Big Dry Creek = 300 feet • distance from centroid of the Stage 2 mining area to Big Dry Creek = 1,150 feet • distance from centroid of the Stage 6A mining area to the South Platte River = 1,360 feet • distance from centroid of the Stage 6B mining area to the South Platte River = 1,720 feet • distance from centroid of the Stage 3 mining area to South Platte River = 700 feet • distance from centroid of the Stage 4 mining area to South Platte River = 1,000 feet • distance from Big Dry Creek to alluvial boundary = 7,250 feet for Stage 1 and 2, and 8,557 feet for Stage 6A, 8,680 feet for Stage 6B, 7,830 feet for Stage 3, and 8,400 feet for Stage 4, based upon CDSS South Platte River alluvial aquifer boundary mapping Based upon this analysis, 95 percent of the depletions accrue to the stream within 5 months for Stage 1, within 14 month for Stage 2, within 19 months for Stage 6A, within 22 months for Stage 6B, within 11 months for Stage 3, and within 16 month at Stage 4. Normalized lagged factors were developed to determine the timing of lagged depletions to the stream as summarized in the table below: