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,. . , Mr. John Horton -4- September 30, 1987 Upon completion of the work above, we will complete appropriate evaluations to develop a financial program for the project in accordance with the requirements of the ewCB. The financial program may include such work as allocating project costs to each of the project purposes identified during earlier portions of the work program, analysis of the costs allocated to each purpose, derivation of revenues to pay the reimbursable project costs, and a payout schedule showing each major item of income and expense, principal and interest payment on construction funding for each year of the repayment period. In accordance with the requirements of the ewCB, and emergency operating reserve will be included in the financial program development. Discussion of Alternative Modification Schemes The Cucharas No.5 dam was constructed in the early 1900's. Many concrete-faced rockfill dams constructed prior to the early 1960's have experienced large deformations, leakage and piping problems similar to those which occured with the Cucharas No. 5 dam. Subsequently, a variety of improved design and construction methods have been implemented which have significantly improved the performance of concrete-faced rockfill dams. Some of the improved design and construction methods include 1) compacting rockfill materials, 2) constructing graded filter/drainage systems behind the concrete facing, 3) special excavation and treatments for foundation bedrock contacts, and 4) revisions to traditional toe slab, perimeter joint and facing slab details. It shall be the intent of these feasibility level evaluations to consider implementing these new design and construction methods into the existing structure to the extent possible. Our feasibility evaluations will include such considerations as 1) removal and replacement of the upper 60 to 80 feet of the dam with compacted rockfill and 2) construction of a filter/drain system behind a new concrete facing. Consideration will also be given to modifying the existing upstream and downstream slopes of the dam to enhance overall stability. In addition, our feasibility evaluations will include consideration of hydrologic and hydraulic issues associated with the existing spillway structure. Our previous studies have indicated that the existing spillway cannot safely pass a probable Maximum Flood event. Howeve,r, results of our "Incremental Damage Assessment" resulted in a provisional acceptance by the Colorado State Engi~eers Office of the existing spillway configuration. The feasibility evaluations will consider borrow from the spillway cha,~nel in order to increase its flood routing capacity. <t> GEarECHNlCAL E:S'GINEERS INC.