2021-10-29_HYDROLOGY - M2014043 - Laserfiche WebLink

Home Browse Search

October 29, 2021 Page 2 of 3 prior to January 1, 1981 as a result of open mining of sand and gravel ("pre-81 areas"), regardless of whether mining continued after December 31, 1980. Based on the information provided, this office recognized a total of 6.8 acres at the Frey Hatchery Pit as having been exposed prior to January 1, 1981. Per our "General Guidelines for Substitute Water Supply Plans for Sand and Gravel Pits" updated April 1, 2011, pre-81 areas are tied to the physical location at which the groundwater was exposed prior to January 1, 1981. The applicant provided a map on September 19, 2017 showing the specific location of the 6.8 acres of pre-81 area. The 6.8 acres includes a 6.5 acre pond in the northwest corner of the permit area and a 0.3 acre pond located to the south of the 6.5 acre pond (Figure 2). Figure 2 also includes a 1.1 acre pond located to the south of the 6.5 acre pond, however the 1.1 acre pond was backfilled, therefore there is no remaining pre-81 exemption for evaporation for this 1.1 acre site. The credits for the pre-81 areas are tied to the locations identified on said map and may not be re -allocated to other areas of ground water exposure within the gravel pit boundary. Any pre-81 area that is backfilled will lose the pre-81 exemption should it be excavated in the future. Additionally, the backfilling of a pre-81 area does not create a credit to be used elsewhere. According to the SWSP request no groundwater is exposed at this site outside of the pre-81 area. In accordance with the letter dated April 30, 2010 (copy attached) 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 April 30, 2010 letter from DRMS requires that you provide information to DRMS to demonstrate you can 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, you have indicated that a bond has been obtained for $809,500 through the DRMS for lining of this site to assure that depletions from groundwater evaporation do not occur in the unforeseen event or events that would lead to the abandonment of the Pit. Depletions The projected depletions for the period of this SWSP amendment consist of water removed in the mined product and dust suppression. Water is lost with the mined product removed from the mine site. The Applicant projected that they will produce 765,000 tons of gravel for the period of April 2021 through March 2022, 805,000 tons of gravel for the period of April 2022 through March 2023 and 75,000 tons of gravel in April 2023. Gravel mined will be in a dewatered state and will be washed on site. The material excavated is estimated to be one-half above and one-half below the ground water table. Assuming a 4 percent loss for product mined below the ground water table and a 2 percent loss for the product mined above the ground water table and washed onsite the groundwater lost with the mined product during this period is estimated at 3 percent by weight. The water lost with the mined product is projected to total 16.89 acre-feet for the period of April 2021 through March 2022, 17.77 acre-feet for the period of April 2022 through March 2023 and 1.66 acre-feet for April 2023. In order to assure that the depletions from water lost in mined product does not exceed the estimated amount, the Applicant must separately track the amount of product mined above and below the ground water table and separately track the depletions from each. Water for gravel washing and dust control will be provided by water pumped from the pit. The estimated water used for dust suppression totals 1.0 acre-foot per year.