2014-08-12_HYDROLOGY - M1978056 - Laserfiche WebLink

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Cheryl Signs, P.E. Page 3 Durham Combined SWSP August 12, 2014 exposed prior to 1981 is shown on the attached map (outlined in purple and numbered 1 through 11). The exception to the requirement to replace evaporative depletions for the pre- 1981 area is tied to the location identified on the map and may not be applied to other areas of ground water exposure within the gravel pit permit boundary. Although some of the pre-1981 ponds identified in the map are currently dry because of the dewatering operations at the site, if the dewatering stops the original pre-1981 ponds will fill, once filled the pre-1981 area will be consistent with the attached map. In previous SWSP approvals, phreatophyte credit for pasture grass was credited to this plan, which was based on the 6-feet depth to ground water, pending better site-specific information. Since the Applicant did not provide site-specific information regarding the depth to the ground water table at this location, no credit for phreatophyte is allowed in this SWSP until the depth to the ground water can be established. Therefore for the purpose of this SWSP the net evaporation from the 15.0 acres was determined based on an effective precipitation credit of 70 percent from the average precipitation and does not use any phreatophyte credit as shown on Table 6 Column (5). Computation of evaporation at the Durham Pit site was also reduced during the ice covered period. You have assumed the ice covered period to occur during the months of January and December, based on the average temperatures of 26.0°F for January and 27.4°F for December; taken from the Greeley weather station (053533). Operational losses at the Durham Pit also include the Feit Well (Permit No. 76867-F, WDID 0304999) which is used for the concrete batch plant owned by VCI, but located on the Feit Gravel Pit site. Well permit no. 76867-F limits the average annual amount of ground water to 3.23 acre-feet. However under the proposed amendment of this SWSP, it is projected that 14.52 acre-feet per year will be used in batch plant operations which include an allowance of 0.01 acre-feet per month for domestic use. The Applicant will be required to obtain a new well permit pursuant to §37-90-137(2), C.R.S. for Feit Well prior to pumping the projected pumping of 14.52 acre-feet. The monthly depletions of the Durham Pit and the Feit Well are included in "Table 6 Durham Pit Demand" and "Table 2 Feit Well Demand." Western Sugar Pit The currently exposed groundwater at this site totals 25 acres. Gross evaporation is estimated to be 42.12 inches per year. With an annual effective precipitation amount of 9.99 inches per year the net annual evaporation is estimated to be approximately 2.68 acre-feet per acre (32.13 inches). Computation of evaporation under this SWSP was also reduced during the ice covered period. You have assumed the ice covered period to occur during the months of January and December, based on the average temperatures of 26.0°F for January and 27.4°F for December; taken from the Greeley weather station (053533). The monthly depletions of the Western Sugar Pit are included in "Table 4 Western Segar Demand". Dakolios Pit The original SWSP approved on April 15, 2013 included losses associated with a 1-acre pond. No changes were identified in this SWSP amendment. Computation of evaporation from the 1-acre pond was reduced during the ice covered period. You have assumed the ice covered period to occur during the months of January, February and December, based on the average temperatures of 27.0°F for January, 30.8° for February and 28.8°F for December; taken from the Longmont weather station. For the purpose of this SWSP, the Applicant shall replace the net evaporation depletions from the exposed ground water surface area at the three sites that may occur during the assumed ice covered period for each site for any time that the pits are not completely covered by ice. Computation of the net evaporation during any time that the ponds are not completely covered by ice shall be determined as the