2023-04-17_HYDROLOGY - M2003016 - Laserfiche WebLink

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Heit Pit Substitute Water Supply Plan Page 2 of 5 April 17, 2023 the Heit Sand and Gravel Mine during the period of this SWSP will be replaced by fully consumable water released from the City and County of Broomfield. In accordance with the letter dated April 30, 2010 from the Colorado Division of Reclamation, Mining, and Safety ("DRMS"), all sand and gravel mining operators must comply with the requirements of the Colorado Reclamation Act and the Mineral Rules and Regulations for the protection of water resources. The attached April 30, 2010 letter from DRMS required that the applicant provide information to DRMS to demonstrate you can replace long term injurious stream depletions that result from mining related exposure of ground water. The DRMS letter identified four approaches to satisfy this requirement. A surety reduction was approved on March 23, 2010 by DRMS reducing the bond by $110,614 - representing the remaining 20% of the construction bond that was posted for the slurry wall. The remaining bond of $197,280 remains in place to cover the remainder of the reclamation plan. With the slurry wall installed and approved by DWR as meeting the State Engineers lining criteria for gravel pit, the Heit Mine is in compliance with the State Engineer's requirements pursuant to section 37-90-137(11). Depletions The Applicant estimates that currently there are up to 5.95 acres of groundwater surface exposed at the Heit Pit within the lined area. Net evaporative depletions were calculated using a gross annual evaporation of 44 inches from the exposed water surface, with a credit of 12.99 inches for effective precipitation based on data obtained from the Western Regional Climate Center (period of 1950-2000) and the monthly gross evaporation rate distribution factors from the State Engineer's General Guidelines for Substitute Water Supply Plans for Sand and Gravel Pits. Evaporative depletions were assumed to be zero for the months of December and January based on the mean temperatures below 32°F from the Fort Lupton and Brighton Weather Stations temperature data (period of 1950-2000). The net depletion of groundwater due to evaporation from the 5.95 acres of water exposed at the site, assuming ice cover, was calculated to be 16.3 acre-feet, as shown on attached Table 1. While no evaporative depletions were projected for the months during which ice cover was assumed, the Applicant shall replace the net evaporation depletions from the exposed groundwater surface area that may occur during the assumed ice-covered period (the months of January and December) for any time that the pit is not completely covered by ice. Computation of the net evaporation during any time that the pit is not completely covered by ice shall be determined as the pro-rata amount of the monthly gross evaporation rate distribution amount identified in the State Engineer's General Guidelines for Substitute Supply Plans for Sand and Gravel Pits, subtracting the pro-rata amount of the effective precipitation for that period. For this SWSP period, 3 acre-feet per year of exposed water from inside the approved slurry wall will be used for dust suppression under as shown on attached Table 2. No processing will occur on site and since the pit is lined, no depletions will occur from water lost from mined product or aggregate washing. Therefore, total depletions are 19.3 acre-feet. Since all depletions occur within the slurry liner, depletions are instantaneous. Since the Applicant proposes a 10% contingency, the replacement obligation under this SWSP is 21.2 acre-feet, as shown on attached Table 3.