2012-07-16_HYDROLOGY - M1977036 - Laserfiche WebLink

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Ms. Kristina Wynne Page 2 Greeley 35th Ave /Iverson Combined SWSP July 16, 2012 Depletions 3e Ave Pit The depletions that result from the mining operation at the Greeley 351h Avenue Pit are evaporation from exposed surface area, water lost in mined product, dust control used at both 35th Ave Pit and Iverson Pit, and water used in concrete production. Evaporation of exposed ground water at the site will create depletions to the South Platte River. 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 ( "pre -81 ") as a result of open mining of sand and gravel, regardless of whether mining continued after December 31, 1980 ( "post -80 ").The total exposed groundwater area at this site remains at 74.8 acres, of which 26.3 acres are considered post -80 and require augmentation for its evaporation. According to the information from the previous plan, a total of 52 acres of groundwater was exposed within the Greeley 35th Avenue Pit reclamation permit boundary prior to January 1, 1981. Of the pre -81 exposed areas, 3.5 acres are currently being dewatered and are not included in the 74.8 total acres of exposed groundwater at this site. The area exposed prior to 1981 is shown on the attached map (Figure 2). The credits for the pre -1981 area are tied to the location identified on the map and may not be re- allocated to other areas of ground water exposure within the gravel pit permit boundary. Gross evaporation at 35th Ave Pit is estimated to be 43.8 inches, or 3.65 feet per NOAA Technical Report NWS 33 with an effective precipitation amount of 14.35 inches, or 1.2 feet per year based upon Greeley UNC, CO (ID #3553) NOAA weather station for the timer period of 1967 -2010. The total annual net evaporation is then 2.42 feet per year. For the SWSP request period, the total net evaporation projected to occur from 35th Ave pit's 26.3 acres of post -80 ground water exposure is 73.98 acre -feet. The applicant projects mining 66,350 tons of washed aggregate and 295,900 tons of crushed (not washed) aggregate during the SWSP request period. The washed material is assessed a 4% water loss by weight and the not washed material is assessed a 2% water loss by weight for a total water loss of 6.30 acre -feet during the SWSP request period. The applicant also projects a dust control water loss of 24.87 acre -feet which covers 16.20 acre -feet to be used at the 35th Ave Pit and 8.67 acre -feet to be trucked and used at the Iverson Pit. MMM also owns and operates a concrete batching plant on site. The Applicant projects a total of 8.82 acre -feet of water loss from concrete batching operations during the SWSP request period. In all, 35th Ave Pit is expected to have a water loss of 113.98 acre -feet over the SWSP request period. The 35th Avenue Pit depletions must be lagged back to the Cache La Poudre River as depletions from the site do not occur instantaneously. A stream depletion model using the Glover method was used to calculate the lagged depletions to the Cache La Poudre River. The following parameters were used in the model: transmissivity (T) = 120,000 gallons per day per foot, specific yield (SY) = 0.2, the distance from the Cache La Poudre River to the edge of the alluvium = 5,000 feet, and the distance from the centroid of the pit to the Cache La Poudre River = 1,500 feet. The total lagged mining depletions during the SWSP period is 128.41 acre - feet. This total includes lagged depletions from past mining operations that hit the river during this approval period. The total lagged depletions include the 8.82 acre -feet used for concrete production from well permit no. 47856 -F. See Table 2 for the monthly breakdown of depletions at 35th Ave Pit.