2016-02-01_HYDROLOGY - M1977439 - Laserfiche WebLink

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Upper Poudre Combined SWSP Page 3 of ii January 28, 2016 Pursuant to § 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. This SWSP recognizes a total of 100.0 acres at the Home Office Pit as being pre-81 exposure. Of the 100 acres, 22.1 acres are within Lamb Lake A as reflected in the Partners Combined SWSP for their portion of the Home Office Pit. Therefore, for MMM's SWSP, 77.9 acres are recognized as being pre-81. 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 with the exception for areas whose reallocation was approved by the State Engineer prior to January 1, 2011. Previous SWSPs (prior to January 1, 2011) approved the pre-81 area without specific mention of its location. Therefore, the State Engineer's Office allowed the pre-81 area to be re-allocated and memorialized under the May 11, 2011 SWSP approval. The applicant provided a map (Figure 1) showing the specific location of the pre-81 area (including the 22.1 acres of ground water exposed in Lamb Lake A). The credits for the pre-81 area are tied to the location identified on Figure 1 and may not be re- allocated to other areas of ground water exposure within the gravel pit boundary. Evaporative depletions were calculated using a gross annual evaporation of 38 inches, with a credit of 10.56 inches for effective precipitation (based on an average annual precipitation of 15.08 inches for Fort Collins weather station 053005, Western Regional Climate Center). You have estimated that there are a total of 240.9 acres of exposed ground water surface within the permit boundary of the Home Office Pit. Of this amount, 100 acres are considered to be pre-81 and do not require replacement and 125.2 acres are included in the Partners Combined SWSP (note that this amount includes 37.8 acres associated with Treiber Pond A, which has been lined), leaving depletions from 15.7 acres which must be replaced under this SWSP. The 15.7-acre pond is known as the Curry Pit. MMM expects to start mining the northernmost area of the Home Office Pit beginning in December 2016. The dewatering trench will be 5 feet wide and approximately 2,500 feet long which will expose a total of 0.29 acres. Therefore a total of 15.99 acres will be exposed at the Home Office Pit site beginning December 2016. You have estimated the total surface area of ground water exposed in the North Taft Hill Expansion Site as 3.05 acres for this plan period in 2.45-acre pond located in the SW corner of the site and a dewatering trench approximately 5 feet wide and 5,250 feet long (0.60 acres). You have stated that no ground water will be exposed at the Overland Ponds Site during this plan period since all cells within this site have been lined. The evaporation losses under this combined plan were reduced during the ice covered period. You have assumed the ice covered period occurs from December through February, based on the average temperatures of 29.04°F for December, 27.59°F for January and 30.61 °F for February; taken from the Fort Collins weather station (053005) using available data for the period of 1893-2012. The ice covered periods may be used to reduce the amount of evaporative losses that need to be replaced; however, for the purpose of this SWSP, the Applicant shall replace the net evaporation depletions from the exposed ground water surface area that may occur during the assumed ice covered periods (January, February, and December 2016) for any time that the pits are not completely covered by ice. Computation of the net evaporation during any time that the pits are 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.