2015-02-04_HYDROLOGY - M2005059 - Laserfiche WebLink

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Nelson Mining Resource SWSP Page 2 of 8 February 3, 2015 exposed water surface, with a credit of 9.73 inches for effective precipitation (based on an average annual precipitation of 13.88 inches for the Longmont 2 ESE weather station). The anticipated net depletions for this plan are estimated at 23.73 acre -feet for up to 7.25 acres of water surface exposed at the site. You have provided a monthly breakdown of the annual depletions made up of 17.69 acre - feet per year of evaporative loss, 1.50 acre -feet per year of water used and consumed for dust control, and 4.21 acre -feet of water lost with the mined product (which represents 143,000 tons of mined product). The IDS Alluvial Water Accounting System (AWAS) analytical stream depletion model, which uses the Glover method, was used to calculate the lagged depletions to St. Vrain Creek. You have provided a monthly breakdown of the "annual depletions at this site in your attached Table AI1.3. The following parameters were used in the model: transmissivity (T) = 157,000 gallons per day per foot; specific yield (SY) = 0.2, the distance (X) from the centroid of the exposed ground water surface to the creek = 2,476 feet, and the distance (W) from the aquifer boundary through the well to the creek channel = 2,126 feet. The total lagged depletions were determined to be 3.5 for November and December 2014 and 23.73 for 2015. Replacements The proposed source of replacement for this pit is the historical consumptive use ( "HCU ") from the dry-up of 30 acres of land historically irrigated with 0.434 shares of Last Chance Ditch previously used for irrigation of the mined property. There are 20 outstanding shares in the Last Chance Ditch Company, a mutual ditch company. The Last Chance Ditch (WDID 0500589) headgate is located on Saint Vrain Creek. The water right was adjudicated on June 2, 1882 in Civil Action No. CA6009 with appropriation dates from March 15, 1872, with a decreed diversion rate of 94.94 cfs. Irrigation has ceased on the Nelson Pit site due to the mining operation and groundwater lakes. The landowner, Harold Nelson, originally owned 1 and 5 /9th share (1.55 shares) of the outstanding 20 shares of the Last Chance Ditch. In the 1990's Mr. Nelson sold 1/18th of a share, leaving 1.5 shares under his ownership. As requested by the previous SWSP the Applicant performed a new HCU based on ownership of 1.55 shares from 1950 to 1993 and 1.5 shares from 1994 to 2005. The subject Last Chance Ditch shares were historically used for irrigation on the Nelson Pit mining site. The historical use of the irrigation supply was quantified using the average monthly diversion from 1950 through 2005. The total irrigated crop acreage varied from 101 acres (1950 -1965) to 121 acres (1966 -1990) to 72 acres (1993- 2005). Aerial photos from 1950, 1992 and 2004 were provided in the HCU analysis. According to the 1950 aerial photos the irrigated acreage claimed on the east side of the Nelson Farm (12.28 acres) do not appear to have been irrigated but appear to have been sub - irrigated. Also, according to the 1992 aerial photo the Applicant is claiming 13.34 acres and 25.35 acres (on the east side of the Nelson Farm) that do not appear to have been irrigated but more like sub - irrigated. The claimed irrigated acreage in the HCU analysis is accepted for the purpose of this SWSP. However, by the next renewal request the Applicant must demonstrate that the acres claimed in the HCU analysis located on the east side of the Nelson Farm (specifically 12.28 acres in the 1950 and 13.34 acres and 25.35 acres in the 1992) have been irrigated with water from the Last Chance Ditch and they were not sub - irrigated by a different source of water. Otherwise these acres should be excluded from the HCU analysis.