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Heit Pit Substitute Water Supply Plan Page 2 of 5 <br /> April 25, 2024 <br /> In accordance with the letter dated April 30, 2010 from the Colorado Division of Reclamation, Mining, and <br /> Safety ("DRMS"), all sand and gravel mining operators must comply with the requirements of the Colorado <br /> Reclamation Act and the Mineral Rules and Regulations for the protection of water resources. The attached <br /> April 30, 2010 letter from DRMS required that the Applicant provide information to DRMS to demonstrate <br /> you can replace long term injurious stream depletions that result from mining related exposure of ground <br /> water. The DRMS letter identified four approaches to satisfy this requirement. As of March 6, 2023, the <br /> Applicant has been released from their bond to ensure backfilling of the pit or lining of the pit since it is <br /> operated by a municipality. With the slurry wall installed and approved by DWR as meeting the 1999 SEO <br /> Guidelines for lining criteria for gravel pit, the Heit Mine is in compliance with the State Engineer's <br /> requirements pursuant to section 37-90-137(11). <br /> Depletions <br /> The Applicant estimates that currently there are up to 5.95 acres of groundwater surface exposed at the <br /> Heit Pit within the lined area. Net evaporative depletions were calculated using a gross annual evaporation <br /> of 44 inches from the exposed water surface, with a credit of 9.09 inches for effective precipitation based <br /> on data obtained from the Western Regional Climate Center (period of 1950-2000) and the monthly gross <br /> evaporation rate distribution factors from the State Engineer's General Guidelines for Substitute Water <br /> Supply Plans for Sand and Gravel Pits. Evaporative depletions were assumed to be zero for the months of <br /> December and January based on the mean temperatures below 32°F from the Fort Lupton and Brighton <br /> Weather Stations temperature data (period of 1950-2000). The net depletion of groundwater due to <br /> evaporation from the 5.95 acres of water exposed at the site, assuming ice cover, was calculated to be <br /> 16.3 acre-feet, as shown on attached Table 1. <br /> While no evaporative depletions were projected for the months during which ice cover was assumed, the <br /> Applicant shall replace the net evaporation depletions from the exposed groundwater surface area that <br /> may occur during the assumed ice-covered period (the months of January and December) for any time that <br /> the pit is not completely covered by ice. Computation of the net evaporation during any time that the pit <br /> is not completely covered by ice shall be determined as the pro-rata amount of the monthly gross <br /> evaporation rate distribution amount identified in the State Engineer's General Guidelines for Substitute <br /> Supply Plans for Sand and Gravel Pits, subtracting the pro-rata amount of the effective precipitation for <br /> that period. <br /> For this SWSP period, 3 acre-feet per year of exposed water from inside the approved slurry wall will be <br /> used for dust suppression under as shown on attached Table 2. No processing will occur on site and since <br /> the pit is lined, no depletions will occur from water lost from mined product or aggregate washing. <br /> Therefore, total depletions are 19.3 acre-feet. <br /> Since all depletions occur within the slurry liner, depletions are instantaneous for purposes of this SWSP. <br /> The Applicant is proposing a 10%contingency, therefore the replacement obligation under this SWSP is 21.2 <br /> acre-feet, as shown on attached Table 3. <br /> Replacements <br /> The proposed source of replacement water for the Heit Pit is fully consumable effluent from the City and <br /> County of Broomfield. The replacement water will be released from Broomfield's wastewater treatment <br /> plant (WDID 0201021), which is located on Big Dry Creek approximately 28.1 miles upstream from the Heit <br /> Sand and Gravel Mine. Of the 28.1 acre-feet of replacement water from Broomfield, approximately 14.05% <br /> will be lost during transit, based on a transit loss of 0.5% per mile for the 28.1 miles from the Broomfield <br /> wastewater treatment plant to the Heit Sand and Gravel Mine. The amount of Broomfield replacement <br /> water that reaches the Heit Sand and Gravel Mine, accounting for transit loss, is 24.7 acre-feet, as shown <br /> on Table 4, which is sufficient to cover the projected evaporative and operational depletions for this plan <br />