2011-04-29_HYDROLOGY - M2001005 - Laserfiche WebLink

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Heidi Frey February 4, 2011 Page 3 Based upon the proposed mining operation, Transit Mix plans to deplete no more than approximately 78.31 ac-ft in 2011 and 88.74 ac-ft in 2012. REPLACEMENT SOURCES Depletions associated with the mining operation are replaced using irrigation credits from the Lester- Attebery Ditch and water releases from Twin Lakes Reservoir. Historical Irrigation Water Credits The Lester-Attebery Ditch historical irrigation credit analysis was presented in our previous SWSP renewal request. A summary of the analysis results is presented in Table 2. The calculated HCU for the Grisenti parcel was approximately 220.88 ac-ft per year (2.47 ac-ft/ac). Historical irrigation practices caused depletions during the irrigation season and accretions to the river the rest of the year, as shown in Table 2. The Grisenti Pit mining area is entirely within Grisenti's historically irrigated acreage, and as part of Transit Mix's agreement with Grisenti, irrigation credits from the mined farm land are used to offset a portion of the depletions associated with the mining operation. To-date, mining operations have removed approximately 45.4 acres of the 89.4 acres of historically irrigated land. Therefore, the pro-rata historical stream depletion credit available to Transit Mix is approximately 112.17 ac-ft per year (123.59 ac-ft of credit during the irrigation months from April through October and a return flow obligation of 11.42 ac-ft for the rest of the year). Twin Lakes Reservoir Table 3 summarizes the total depletions associated with the mining operation. After applying credits from up to 112.17 ac-ft per year of historical depletion, we are conservatively projecting that Transit Mix will need to replace 31.13 ac-ft of wintertime depletions in 2011 and 32.73 ac-ft in 2012. This includes replacing depletions from evaporation as well as replacing winter irrigation return flows. Transit Mix owns 60 shares of Twin Lakes Reservoir water. A copy of their share certificate was included with the previous SWSP renewal request. A transit loss of 0.07 percent per mile is assessed for downstream delivery from this reservoir. Based upon a measured distance of 111.6 miles between Twin Lakes Reservoir and the Grisenti site, the total transit loss associated with Transit Mix's 60 shares is about 7.81 % of their entitlement. Under this conservative depletion analysis, Transit Mix will require Twin Lakes releases totaling approximately 31.13 ac-ft in 2011 and 32.73 ac-ft in 2012, as shown in Table 3. As of November 1, 2010, Transit Mix had 61.63 ac-ft in their Twin Lakes account, more than twice the volume required for replacements under this plan. OPERATION OF PLAN In accordance with Senate Bill 120, the proposed Substitute Water Supply Plan for Transit Mix Concrete's planned Grisenti Gravel Pit accounts for and replaces in quantity and timing all mining depletions and evaporative losses associated with this plan. Depletions from the pit are summarized in Table 1 and will not exceed 78.31 ac-ft in 2011 and 88.74 ac-ft in 2012. Depletions under this plan are