Final Environmental Impact Statement Minidoka Dam Spillway Replacement Minidoka Project, Idaho U.S. Department of the Interior Bureau of Reclamation Pacific Northwest Region Snake River Area Office Boise, Idaho August 2010 U.S. DEPARTMENT OF THE INTERIOR The mission of the Department of the Interior is to protect and provide access to our Nation’s natural and cultural heritage and honor our trust responsibilities to Indian tribes and our commitments to island communities. MISSION OF THE BUREAU OF RECLAMATION The mission of the Bureau of Reclamation is to manage, develop, and protect water and related resources in an environmentally and economically sound manner in the interest of the American public. Final Environmental Impact Statement Minidoka Dam Spillway Replacement Minidoka County, Idaho Lead Agency: For further information contact: U.S. Department of the Interior Allyn Meuleman Bureau of Reclamation Snake River Area Office Pacific Northwest Region 230 Collins Road Boise, ID 83702-4520 (208) 383-2258 Cooperating Agencies: U.S. Department of the Interior U.S. Department of Agriculture U.S. Fish and Wildlife Service Rural Development Idaho Fish and Wildlife Office Idaho State Office Community Facilities Program Washington, D.C. Abstract: This Final Environmental Impact Statement (Final EIS) examines alternatives to correcting structural problems at the Minidoka Dam Spillway and associated facilities on Lake Walcott, Idaho. Alternatives considered in the Draft EIS are the No Action, as required under the National Environmental Policy Act; total replacement of the spillway and headgate structures; and replacement of just the spillway. Total replacement of the spillway and headgate structures is the preferred alternative. Proposed changes in operations following construction are also discussed. In addition, certain public activities became restricted per 43 CFR Part 423 Public Conduct on Bureau of Reclamation Facilities, Lands, and Waterbodies which became effective on October 1, 2008. The Final EIS identifies special use areas to be designated under each of the action alternatives that would open areas currently closed for public use. Designation of special use areas would again allow traditional uses that are appropriate for this area, but are not currently allowed under the new rules and regulations. The Final EIS was prepared in compliance with the National Environmental Policy Act. It also provides the public review required under Executive Orders 11988 (Floodplain Management) and 11990 (Protection of Wetlands) and the National Historic Preservation Act. Results of compliance per Secretarial Order 3175 (Indian Trust Resources), Executive Order 13007 (Sacred Sites), the Fish and Wildlife Coordination Act and the Endangered Species Act of 1973 (for construction) are included in the evaluations contained in this Draft EIS. A Record of Decision (ROD) identifying Reclamation’s decision on which alternative to implement is anticipated in late September. Final Environmental Impact Statement Minidoka Dam Spillway Replacement Minidoka Project, Idaho U.S. Department of the Interior Bureau of Reclamation Pacific Northwest Region Snake River Area Office Boise, Idaho August 2010 Managing Water in the West Minidoka Dam Spillway Replacement l Cana de Si Project Area th or N in a M LAKE WALCOTT μ (! Acequia Reclamation Lands Minidoka Dam Lake Walcott State Park al Minidoka National BCan Wildlife Refuge ?° ACanal Can a l Cities ide th S B2 Canal ai n Sou M Interstate Highway Roads 00.50.25 11.52 Miles Neither the authors, Reclamation, or any other party involved in preparing the material and data displayed here warrant or represent that the information is in every Rupert respect complete and accurate, and are not held responsible for errors or omissions. Filename: MDSR_ForEIS_1007083.mxd Drawn by: G. Young/J. Jones Date: Aug. 7, 2009 W A S H I N G ?± T O N MONTANA IDAHO W Y O M Area of Detail I O Idaho Boise N R Falls ^_ !( G E !"`$ G American !( MountainHome Falls Pocatello O _!"$ !( Rupert !( N Burley !( !"^$ TwinFalls !( !( !"_$ !( Milner _!"$ !"_$ NEVADA UTAH Page intentionally left blank. EXECUTIVE SUMMARY MINIDOKA DAM SPILLWAY REPLACEMENT FINAL ENVIRONMENTAL IMPACT STATEMENT EXECUTIVE SUMMARY The Proposed Action The Bureau of Reclamation (Reclamation) is proposing to correct structural problems at the Minidoka Dam spillway and canal headworks on Lake Walcott, Idaho. The existing spillway and canal headworks are showing considerable signs of degradation. Following construction, Reclamation proposes to modify current operations to increase power production since the reservoir can be held at a higher level during the winter. In addition to correcting the structural problems of the existing spillway and canal headworks, Reclamation is also proposing to designate Special Use Areas at the project site in accordance with 43 CFR Part 423 Regulations, Public Conduct on Bureau of Reclamation Facilities, Lands, and Waterbodies. These Special Use Areas will define what public uses are allowed in close proximity to the dam, spillway, and other facilities. Purpose and Need for Action The purpose of the Proposed Action is to prevent structural failure of the Minidoka Dam spillway and canal headworks (proposed action area). After 103 years of continual use, the 2,237-foot-long concrete spillway has reached the end of its functional lifespan. The concrete that forms the spillway crest and stoplog structure piers has suffered extensive deterioration at numerous locations. Additionally, previous ice damage to the overflow section of the spillway requires that the reservoir water level be dropped each winter. The headworks at the North Side Canal and South Side Canal also show serious concrete deterioration similar to the spillway conditions. The current conditions of the Minidoka Dam spillway and headworks present increasingly difficult reliability and maintenance problems. Reclamation must be able to continue to meet its contractual obligations for water delivery, power generation, and commitments to provide flow augmentation water under the Nez Perce Settlement Agreement and the Endangered Species Act (ESA). A partial or complete failure of the spillway or canal headworks could threaten Reclamation’s ability to meet those obligations. Minidoka Dam Spillway Replacement Final EIS – August 2010 Executive Summary S 1 Alternatives Currently, in accordance with 43 CFR Part 423 Regulations, Public Conduct Rules on Bureau of Reclamation Facilities, Lands, and Waterbodies, certain public activities are restricted on Reclamation lands, facilities, and waterbodies. Specifically, Subpart C, Section 423.36 Swimming, states in part that, (a) You may swim, wade, snorkel, scuba dive, raft, or tube at your own risk in Reclamation waters, except: (1) Within 300 yards of dams, powerplants, pumping plants, spillways, stilling basins, gates, intake structures, and outlet works. In addition, Section 423.37 Winter Activities, states in part that, (b) You must not ice skate, ice fish, or ice sail within 300 yards of dams, powerplants, pumping plants, spillways, stilling basins, gates, intake structures, or outlet works. The 43 CFR Part 423 rules and regulations restrict certain historic recreational uses on Reclamation lands, facilities, and waterbodies associated with the proposed action area. In order to allow traditional uses that are appropriate but are not currently allowed, Reclamation has determined that it would be in the best public interest to identify Special Use Areas for some of these traditional uses as provided under the rules and regulations. Therefore, Reclamation will restrict uses which affect public safety. Alternatives Alternative Formulation To address the deterioration and potential structural failure of the spillway and associated structures, Reclamation began an alternative formulation process in March of 2000 with the preparation of an appraisal-level design that analyzed two different options for buttressing the existing spillway crest and providing new gated spillway sections. Since 2000, Reclamation has evaluated several technical conceptual designs and options to address spillway replacement. Much of the early effort was devoted to identifying specific engineering elements and combinations that would meet this objective. A Value Planning Study was completed in January 2002 that considered 15 options for spillway replacement. Three options were eliminated due to feasibility or cost; twelve options were considered feasible and carried forward for further study. In 2003, an Appraisal Study was completed that investigated the two most favorable options from the 2002 Value Planning Study: (1) complete replacement of the spillway with a new concrete overflow section and a set of 12 new radial gates; and (2) complete replacement of the spillway with a combination of overflow sections and rubber dam sections. Both options were considered feasible with Option 1 being considered as the most cost-effective solution. Executive Summary S 2 Minidoka Dam Spillway Replacement Final EIS – August 2010 Alternatives A Realignment Study was completed in 2006 that considered three different alignments for the spillway. The goal of this study was to shorten the overall length of the spillway; and thereby, reducing costs. A Value Engineering Study, completed in June 2008, resulted in 16 different options or combination of options being considered. The study team included staff and experts from Reclamation as well as representatives from the irrigation districts.