2023-11-17_HYDROLOGY - M2016030 - Laserfiche WebLink

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2023-2024 Valley's Edge Resource Substitute Water Supply Plan Renewal Page 2 of 6 November 16, 2023 protection of water resources. The April 30, 2010 letter from DRMS requires that the Applicant provide information to DRMS to demonstrate the ability to replace long term injurious stream depletions that result from mining related exposure of groundwater. The DRMS letter identifies four approaches to satisfy this requirement. In accordance with approach nos. 1 and 3, the Applicant has obtained a bond for$873,550 through the DRMS for complete reclamation of the site which, according to the DRMS permit, will require a complete backfill of the site. Depletions The projected depletions for the period of this SWSP impact the South Platte River below Brighton, CO and consist of net evaporation from exposed groundwater surface area, dust control, and water retained in removed product. No dewatering will occur during this period. Evaporation The Applicant proposes to replace evaporation from exposed groundwater at the site based upon evaporation atlases in NOAA Technical Report NWS 33 and the precipitation at the Brighton station, as shown in attached Table 1. Gross annual evaporation at the gravel pit location is estimated to be 45.00 inches peryear. 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 effective precipitation (14.04 inches) was estimated based on the data from the Brighton NOAA weather station. The exposed surface is currently 16.2 acres but is anticipated to decrease to 14.6 acres by September2024. Therefore, the net evaporation from the exposed water surface is 45.61 acre-feet for this SWSP approval period. Dust Control The Applicant estimates that the water used for dust control will be 2.28 acre-feet for this SWSP approval period as shown on attached Table 1. Mined Product The Applicant does not anticipate any further significant mining at this point; however some remaining product is anticipated to be recovered. Based on a recovery of 40,000 tons above the groundwater table (2% retained in product) and 10,000 tons below the groundwater table (40/6 retained in product), the water retained in removed product will be 0.88 acre-feet for this SWSP approval period as shown on attached Table 1. Therefore, the total consumptive use is 48.77 acre-feet during this SWSP approval period as shown on attached Table 1. Lagged Depletions A Glover analysis using the IDS AWAS stream depletion model was used to determine the lagged depletions to the South Platte River. The aquifer characteristics used in the model for the depletions are: transmissivity (T) = 70,000 gallons per day per foot, specific yield (SY) = 0.2, the distance from the centroid of the site to the stream (X) =5,700 feet, and the location of the parallel impermeable boundary from the stream or aquifer width (W) = 7,900 feet. Lagged depletions are 53.68 acre-feet for this SWSP approval period. Total depletions and replacements are summarized in Table 1, attached. Depletions from this operation will accrue to the South Platte River in the SE '/a of the NW '/a of Section 19, Township 1 North, Range 66 West, 6ch P.M. For purposes of this SWSP, the depletions