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M-2002-120 Bernhardt SWSP Approval Page 2 of 6 November 29, 2023 An alluvial well has been constructed to provide water for concrete batching. This well was constructed under permit no. 60729-F (WDID 0405678) and is located outside the boundaries of the existing slurry wall. The SWSP request does not seek to pump water from this well during the plan period. Well no. 60729-F has not been used for concrete batching since 2008 and all lagged depletions from previous pumping from the well have already impacted the stream. A flow meter has been installed on the well, as is required by condition of approval #9 on well permit no. 60729-F, and the meter is currently in compliance with the South Platte Well Measurement Rules. Depletions The depletions that result from the mining operation during this SWSP period are water used for dust control and evaporation. The mining operation, including aggregate washing, occurs within the approved liner of the slurry walls, therefore no water lost with the mined product is accounted for in the SWSP. Additionally, based on the analysis previously performed by the Applicant, there are no lagged depletions from past dewatering operations that will accrue to the river during this plan period. While the liners for Cells 3 and 4 require repair and new modified liner tests, the Applicant proposes to continuously dewater these cells back to the river until the repairs can be made at the locations shown on attached Figure 2. Evaporative Depletions The plan proposes to expose 4.98 acres of groundwater at the Bernhardt Pit within the settling ponds. 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. Evaporative depletions were calculated using a gross annual evaporation of 43.86 inches (based on the NOAA Technical Report NWS 33) with a credit of 9.29 inches for effective precipitation (based on an average annual precipitation of 13.27 inches for the Longmont weather station). Evaporative losses are 2.88 acre-feet/acre, or 14.34 acre-feet for this SWSP period as shown on attached Table 1. Operational Depletions Consumptive use of groundwater from the Bernhardt Pit consists of 0.18 acre-feet/month for on-site dust control, or 2.16 acre-feet for this SWSP period as shown on attached Table 1. Water from dust control is obtained from the settling pond. Lagged Depletions The total consumptive use at this site during this plan period is 16.50 acre-feet (see attached Table 1). The depletions from evaporation and operational losses were lagged to the stream using a Glover analysis assuming a distance (X) from the centroid of the exposed ground water surface to the stream of 715 feet, a distance (W) to the impermeable boundary of 2,976 feet, a transmissivity (T) of 100,000 gpd/ft, and a specific yield (S) of 0.2. The total lagged depletions are 16.41 acre-feet for this SWSP period as shown on attached Tables 2 and 3. Depletions from mining operations at the Bernhardt site will impact the Big Thompson River upstream of the Evanstown Ditch (WDID 0400517). Dewatering Since the liner in Ponds 3 and 4 was damaged, dewatering of Ponds 3 and 4 will produce delayed depletions to the stream system. As long as the pits are continuously dewatered at a relatively constant rate, the water returned to the stream system should be adequate to offset the depletions attributable to the dewatering operation. Dewatering operations must be measured by totalizing flow meters that can