2012-12-26_HYDROLOGY - M2003091 - Laserfiche WebLink

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Mr. Heintz & Ms. Wynne Duckworth SWSP December 24, 2012 Page3of7 depletion. The depletions will be lagged using the same AWAS parameters as the evaporation and mining operations depletions. Dewatering is projected to occur at a constant rate of 1,000 gpm, or approximately 135 acre -feet per month. Table 2 presents a dewatering schedule that assumes 35 acre -feet is able to be diverted into the LCP and the remaining 100 acre -feet is pumped back to the river on a monthly basis. For the approval period this equals 420 acre -feet that is dewatered and immediately recharged at the LCP such that the lagged depletions are offset by the lagged recharge credits. This operation will create 1,200 acre -feet of dewatering credits and 160.71 acre -feet of lagged depletions, for a yearly total of 1,039.29 acre -feet of dewatering credit. Actual dewatering volumes will be metered and lagged depletions /credits will be based off of actual use. Replacements This plan provides three replacement sources that can be used during this plan period and are dewatering credits, Rural Ditch shares, and excess accretions from MMM's South Platte Combined Replacement Plan. The credit associated with dewatering is described in the previous section and is expected to generate 1,039.29 acre -feet of credits during the approval year at a month rate as shown on Table 2. Credits for dewatering are only applicable during the month they generate and unused credits cannot be rolled over into future months. Table 3 provides the anticipated replacement schedule for the plan period and shows that the dewater credits alone are sufficient to provide replacement during this plan approval period. However, the Rural Ditch shares and excess accretions from MMM's combined SWSP can be used as described below. Rural Ditch (WD1D ..0600551) Shares MMM owns two shares in the Rural Ditch that were historically used on the Heaton property for irrigation. The Heaton property is north of the Duckworth pit and is the current site of Heaton Reservoir (WDID 0504089). These shares were previously apart of Case No. 01CW194 to be changed from irrigation to augmentation and other uses associated with Lafarge's (MMM's predecessor) sand and gravel operations. This case was dismissed without prejudice on April 5, 2011 before going to trial at the request of Lafarge because the credit sought would not adequately meet the needs of Lafarge's operation and new mining properties along the lower St. Vrain or the South Platte River, which could use the consumptive use credit, had not been identified. An engineering report (see November 12, 2010 letter attached) was completed for Case no. 01CW194 and presents the historical consumptive use analysis for these two shares. This report is the basis for the historical consumptive use analysis for this SWSP. These two shares were also part of the Heaton Property Batch Plant SWSP (WDID 0502523). This SWSP provided that these two shares may be used at the Duckworth Pit but would require a separate SWSP prior to use. That batch plant is not currently in operation, and will not be in operation for the duration of this SWSP. According to the engineering report, the average annual ditch diversions attributable to MMM's two shares is 204.2 acre -feet per year. An assumed 20% ditch loss assessed on the diversions provides an average annual farm headgate delivery of 163.4 acre -feet per year. The historic return flow obligations which must be maintained and are equal to 73.3 acre -feet. Return flow obligations can be made by bypassing water through Heaton Reservoir or through the Smith & Emmons Ditch waste way. The shares will be delivered when in priority from April through September and shall not exceed the maximum monthly values given in Table 7 of the engineering report. Table 8 of the report provides the depletion and return flow factors attributable to the two shares.