2020-03-16_INSPECTION - M1974069

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14.5 Mariana Butte Pit Net Evaporation: The Mariana Butte Pit includes ground water exposed to the atmosphere from mining operations which occurred both before and after January 1, 1981. Mining operations are complete at the Mariana Butte Pit. The total surface area of exposed groundwater in the Mariana Butte Pit is 5.51 acres. 14.5.1 2.7 acres of ground water surface area were exposed to the atmosphere by mining the Mariana Butte Pit prior to January 1, 1981, and therefore the evaporative depletions from the 2.7 acres of exposed ground water surface area do not require replacement pursuant to C.R.S. § 37-90-137(11)(6). 14.5.2 2.81 acres of ground water surface area were exposed to the atmosphere by mining the Mariana Butte Pit subsequent to December 31, 1980, resulting in net evaporation averaging 6.22 acre feet per year(gross evaporation less historic natural depletions)as shown on Exhibit E. 15. Timing of depletions: Due to the timing of evaporation, and the lagging effects of the aquifer,the net evaporation depletions to the river will be distributed through the year using the following method and parameters: 15.1 The monthly net evaporative depletions from each Gravel Pit that require replacement shall be lagged to the Big Thompson River using the Glover Method and the AWAS Glover alluvial aquifer model. The AWAS model is based on the Glover Stream Depletion Method, and requires the definition of several aquifer and stream parameters, including the distance from the gravel pit to the impacted stream (X), the width of the aquifer on the side of the river where the gravel pit is located (W), the harmonic transmissivity of the aquifer(T), and the storage coefficient(S). Data from a local pump test were used to establish the aquifer parameters (a transmissivity of 50,000 gallons per day per foot and a storage coefficient to 0.2). The X, W, T and storage coefficient parameters are shown in the following table: Gravel Pit X(ft) W(ft) S T(GPD/ft) Larimer Pit 200 1,550 0.2 50,000 Baer Pit 500 1,550 0.2 50,000 Mariana Butte Pit 1,500 1,550 0.2 50,000 15.2 Larimer Pits: On January 1 of each year or more frequently as required by the Division Engineer, but no more than a total of four times each year, while mining operations are ongoing, LRM shall determine the total current exposed surface area, and calculate actual out of priority net evaporative depletions pursuant to Paragraph 14.2. Out of priority net evaporative depletions shall be replaced pursuant to the lagging pattern that shall be calculated according to the parameters for the Larimer Pits set forth in Paragraph 15.1 which are also included in the monthly accounting. In the event that a total of 52.9 acres of ground water surface area are exposed at Larimer Pits 13, 14, 15, 18 and 20,the maximum out of priority net evaporative depletions shall be replaced pursuant to the lagging pattern set forth in column 10 of Exhibit C. 7 of 14