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lI <br />Mr. Bob Condon <br />Two Rivers Rock Pit (M-02-052) <br />March 27, 2009 <br />Page 2 <br />Due to the fact that the site is set back from the river, a stream depletion model was used to <br />determine the lagged depletions to the Big Thompson River. The following parameters were! used in <br />the model: transmissivity (T) = 10,000 gallons per day per foot, specific yield (SY) = 0.2 (which is <br />typical for an alluvial aquifer), the distance of the exposed ground water to the river=1000 feet. <br />Based on the indicated values, an SDF value of 20 days was computed. Thus, the lagged <br />evaporative losses for this approval period are 3.55 acre-feet. According to the terms of the <br />previous SWSP approval, the Applicant was required to provide a comparison of estimated lagged <br />depletions using both the SDF option and the alluvial aquifer option in the Alluvial Water Accounting <br />System ("AWAS") model that was developed by the IDS Group at Colorado State University. Based <br />on the information provided, the lagged evaporative depletions from the pit using AWAS model were <br />determined to be relatively close to the lagged evaporative depletions from the pit using the SDF <br />option. Therefore for the purpose of this SWSP either option is acceptable in calculating thE3 lagged <br />depletions from the Two Rivers Rock Pit. <br />Replacement <br />The proposed source of replacement water for this pit is a lease of excess recharge <br />accretions from the Milliken. Milliken has filed for a plan for augmentation in Division 1, Water Court <br />.in case no. 2002CW339. In accordance with Section 37-92-308(4), C.R.S., on January 26, 2009, the <br />State Engineer's Office approved a substitute water supply plan ("SWSP") forthe Town. Milliken has <br />generated excess recharge accretions credits pursuant to the above-described SWSP. A Copy of <br />the water lease agreement for 2009 was submitted to this office with this SWSP request and is <br />attached to this letter. The amount of water leased from Milliken is 10.57 acre-feet, therefore in the <br />event that WETCO intends to start mining during the period of this SWSP the additional <br />replacement water can be used to cover the additional depletions from the pit. The monthly <br />breakdown of the lagged evaporative losses and replacement requirements are found on the <br />attached Table 1. <br />Conditions of Approval <br />I hereby approve the proposed substitute water supply plan in accordance with §37-90- <br />137(11), C.R.S., subject to the following conditions: <br />1. This plan shall be valid for the period of January 1, 2009 through December 31, 2009, unless <br />otherwise revoked or modified. If this plan will not be made absolute by a water court action <br />by the plan's expiration date, a renewal request must be submitted to this office with the <br />statutory fee (currently $217) no later than November 15, 2009. <br />2. Well permit no. 64772-F was obtained in accordance with Section §37-90-137(2) and (11), <br />C.R.S., for the proposed use and exposed pond surface area of the gravel pit. <br />3. The maximum surface area of the groundwater exposed at this site during the term of this <br />plan shall not exceed 1.5 acres, resulting in a total evaporative loss of 3.91 acre-feet. <br />4. Total consumption at the pit(s) must not exceed the aforementioned amount unless an <br />amendment is made to this plan.