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Frey Hatchery Pit, M2014-043 Page 2 of 6 December 11, 2017 Pursuant to S 37-90-137(11)(b), C.R.S. and 2009CW49, a gravel pit operator or property owner does not need to replace depletions that occur due to evaporation from ground water exposed 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 area are tied to the location 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. 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 ground water. 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 consist of net evaporation from exposed ground water surface area, water removed in the mined product, dust suppression, and dewatering. The SWSP anticipates that a total of 1.0 acre of water surface will be exposed at the site in dewatering trenches during the first two years of operation. The Applicant proposed to replace evaporation from exposed ground water at the site based upon evaporation atlases in NOAA Technical Report NWS 33 and the SEO monthly distribution factors for sites below 6,500 feet. Gross annual evaporation at the gravel pit location is estimated to be 43.00 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 Brighton NOAA weather station. The net evaporation from the exposed water surface area is 2.75 acre-feet per year. In addition to the evaporation, water is lost with the mined product removed from the mine site. The Applicant projected that they will produce 750,000 tons of gravel each year for the first two years of operation. 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 ground water 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 14.68 acre-feet for the first year of operation and 11.04 acre-feet for the second year of operation. 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.