2025-09-18_HYDROLOGY - M1999034 - Laserfiche WebLink

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Holcim South Platte Combined SWSP September 18, 2025 Plan IDs 3614, 4773, 3624, 4772, 4616, 3437, 3376, 3650, 3668, 5475, 5829, &t 6243 Page 16 of 37 recharge credits for any water delivered to the Lighthouse Cove Pond prior to the date of the water commissioner's approval. The expected volume of water available for diversion into the Lighthouse Cove Pond for the subject 1.5 shares is 187.79 acre-feet per year. This figure represents the pro-rata average headgate diversion less a 10% ditch loss. The pro-rata historical consumptive use credit for the 1.5 shares is estimated to total 91.65 acre-feet for this plan period and the pro-rata return flow obligation for the 1.5 shares is estimated to be 132.56 acre-feet. The Lighthouse Cove Pond (formerly Groom Addition Pit, DRMS Permit no. M-1983-099) is an existing gravel pit pond that is subject to a written augmentation agreement with the Water Users Association of District No. 6. Pursuant to section 37-90-137(11)(b), C.R.S., and case no. 2009CW49, a gravel pit operator or property owner does need to replace water lost through evaporation in excess of the augmentation amount in the written agreement, provided that the operator continually complied with the provisions of the written agreement. The written agreement, dated May 24, 1983, transferred 0.736 shares of the Smith 6t Emmons Ditch Company to the Water Users Association of District No. 6 for the replacement of evaporation associated with 55 acres of exposed groundwater. The delivery of water to recharge in the pond is not anticipated to increase the surface area of the pond or create additional evaporative depletions beyond those attributable to the groundwater exposed to the atmosphere in connection with the extraction of sand and gravel by open mining, therefore the Applicant is not required to consider evaporative depletions of water delivered to the Lighthouse Cove Pond for recharge. The lagged accretions from the Lighthouse Cove Pond were estimated by the Applicant's consultant using the AWAS stream depletion model with the following parameters: • Distance from the recharge pond centroid to the river (X) = 3,450 ft • Alluvial aquifer width (W) 9,300 ft • Specific yield (S) = 0.2 • Transmissivity (T) =50,000 (gpd/ft) The lagged accretions to the confluence of the St. Vrain Creek and Boulder Creek are projected to total 58.66 acre-feet during this plan period based on the Applicant's projected delivery of 0.5 acre-feet of Smith 6t Emmons water per day or the monthly volumetric limit, whichever was less, for the period of May 1-October 31. After accounting for return flow obligations, net recharge credit was projected to total 10.80 acre-feet for this plan period.