2020-11-24_HYDROLOGY - M2008082 - Laserfiche WebLink

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Ready Mix Concrete Substitute Water Supply Plan Page 3 of 9 November 24, 2020 Depletions Evaporation The projected depletions for Stages 1, 2, 4, 5, 6A, 6B, and 6C/6D result from evaporation, water washed for the mined product, water lost in mined product, dust control, water for reservoir construction at Stage 4, and the refill of Stage 2. The Applicant proposes to replace evaporation from exposed groundwater at the Morton-Holton site based upon evaporation atlases in NOAA Technical Report NWS 33 and the State Engineer's Office ("SEO") monthly distribution factors for sites below 6,500 feet, as shown in attached Table 1. Gross annual evaporation at these gravel pit locations is estimated to be 44.27 inches per year. 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, which was estimated based on the data from the Fort Lupton 2SE (ID 3027, record 1950-1976) and Brighton 1 NE (ID 950, record 1976-2014) NOAA weather stations. The net evaporation rate for the exposed water surface is estimated to be 2.92 acre-feet/acre for 2021, as shown on Table 1. Total evaporation is 7.25 acre feet for October through December 2020 and 67.1 acre-feet for 2021, as shown on attached Table 2, column 1. The projected maximum exposed groundwater surface area at each stage is described below. • Stage 1 - As described above the exposed groundwater surface area in the southern portion of Stage 1 currently exposes 11 acres and is not expected to change for this SWSP period. • Stage 2 - Stage 2 currently exposes 5 acres of groundwater and will be filled to a depth of 15 feet and expose 10 acres beginning in January 2021 which is not expected to change for the remainder of the SWSP period. • Stage 3 - Stage 3 was backfilled with overburden from other stages at the end of 2019 and therefore there is no permanent surface area or first fill depletions. There are no remaining lagged depletions at this stage. • Stage 4 - RMCC constructed a slurry wall around Stage 4. The groundwater surface area at Stage 4 is currently 0.2 acres which is not expected to change for this SWSP period. Stage 4 will continue to be dewatered throughout the period of this SWSP. • Stage 5 - As of October 2020, 0.2 acres of groundwater was exposed in Stage 5 which will be increased to 1 acre in November 2020 and is not expected to change for the remainder of this SWSP period. • Stage 6A - Mining at Stage 6A is completed. The exposed groundwater surface area is 0.1 acres and is not expected to change for this SWSP period. Stage 6A will remain dewatered throughout the SWSP approval period. • Stage 6B - As of October 2020, 0.5 acres of groundwater was exposed in Stage 6B which will be decreased to 0.2 acres in January 2021 which is not expected to change for the remainder of this SWSP period. Stage 6B will continued to be dewatered throughout the period of this SWSP. • Stage 6C/6D - Mining at Stage 6C/6D will continue. The exposed groundwater surface area is currently 0.5 acre and is not expected to change for this SWSP period. Stage 6C/6D will be dewatered throughout the period of this SWSP. The total exposed groundwater surface area for all stages is expected to be 17.5 acres in October 2020, 18.3 acres in November and December 2020, and 23 acres for all of 2021. The projected