Department of the Army, U.S. Army Corps of Engineers; DoD.
Notice of intent.
Pursuant to the National Environmental Policy Act of 1969, as amended, the U.S. Army Corps of Engineers, Omaha District (Corps) intends to prepare a draft Environmental Impact Statement (EIS) for the federal action to remediate dam safety concerns at Cherry Creek Dam. The dam safety concerns are primarily related to a hydrologic deficiency resulting from an extreme precipitation event and the large population that could be affected by such an event. Cherry Creek Dam and Lake is located on Cherry Creek, 11.4 miles upstream of its confluence with the South Platte River, in Aurora, Colorado (southeast Denver metropolitan area). The remediation actions will be identified through a Dam Safety Modification Study (DSMS) being conducted in accordance with Corps policy as described in Engineering Regulation 1110-2-1156 “Safety of Dams—Policy and Procedures.”
Omaha District Corps of Engineers, 1616 Capitol Ave, Omaha, NE 68102-4926 (Attn: Margaret Oldham CENWO-PAO).
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FOR FURTHER INFORMATION CONTACT:
Current and archival information regarding Cherry Creek Dam may be obtained by contacting the Omaha District. The point of contact is Margaret Oldham, Phone: (402) 995-2416; email: Margaret.E.Oldham@usace.army.mil. Questions or comments regarding the upcoming studies at Cherry Creek Dam should also be directed to Ms. Oldham.
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1. Background Information. The Cherry Creek Dam project was authorized in the 1940s for the primary purpose of protecting the city of Denver against floods from Cherry Creek. The dam is located in a densely populated area and provides flood protection to over 200,000 people. Starting in 2005, the Corps sought to better categorize the risk at all of its dams. Risk considers both the probability and consequences of a dam failure. Cherry Creek Dam received an elevated risk rating primarily because of the hydraulic deficiency resulting from an extreme precipitation event and the large population which is protected by the dam. Estimation of extreme precipitation events is based on the Probable Maximum Precipitation (PMP) for a given location. A PMP is an extremely rare event and is defined as the maximum amount of precipitation that could occur if all meteorological elements were optimal to allow a perfect environment for forming precipitation. The resulting stream flow from a PMP is a flood defined as the Probable Maximum Flood (PMF).
Multiple past studies have indicated that Cherry Creek may not be able to adequately pass a PMF event. Hydrologic deficiency issues associated with Cherry Creek Dam were initially brought to light in 1970 after the National Weather Service (NWS) completed a site-specific PMP study of the upper South Platte River basin for the design of Chatfield Dam (a nearby dam on the South Platte River). Applying the 1970 PMP criteria to the Cherry Creek basin resulted in a larger stream flow than used in the project's original design and indicated the dam had a potential hydrologic deficiency. Since 1970, the NWS and the Corps have completed several PMP and PMF estimates including a Cherry Creek basin, site-specific PMP study completed by the NWS in 1995. Applying the current estimate of the PMF, which is also based on the 1995 PMP study, Cherry Creek Dam has a hydrologic deficiency even if the pool elevation at the start of the PMF was at normal operating levels.
Because of the risk rating, Omaha District completed an Issue Evaluation Study (IES) in 2011 to further evaluate Cherry Creek Dam's safety issues and corresponding risk. The IES findings were presented to a Senior Oversight Group (SOG) appointed by the Corps' Headquarters. The SOG reviewed the IES and confirmed the risk rating for the dam. Omaha District was directed to proceed into a DSMS, which is currently under way, with the task of defining in detail the risk associated with the Cherry Creek Dam's safety issues and assessing possible options for mitigating the risk. Those options may include federal actions which will be the subject of the EIS.
2. Remediation Alternatives. The draft EIS will address an array of remediation alternatives that could reduce the risk of life loss, extensive downstream damage, functional loss of the project, and the loss of all project benefits. The nature and extent of the remediation alternatives will be determined based on the results of on-going engineering studies, public and agency input during the scoping period, and preparation of the draft EIS.
3. Issues To Be Addressed. The draft EIS will address environmental issues concerning the remediation alternatives proposed. Issues will be identified based on public input during the scoping process and during preparation of the draft EIS. Environmental issues initially identified as potentially significant include, but are not limited to: hydrology and water quality, noise and vibration, air quality, socioeconomics, water supply, land use, recreation, visual and aesthetic resources, traffic and transportation, historical and cultural resources, vegetation and wildlife, special status species, and fisheries.
4. Public Involvement. Public scoping meetings will be held in 2014 at specific locations to be announced within the local Cherry Creek Dam project area. The purpose of the public scoping meetings will be to present information to the public regarding the array of remediation alternatives that may be addressed in the draft EIS, receive public comments, and solicit input regarding dam safety issues, remediation alternatives to consider, and environmental issues of concern to the public. These meetings are intended to initiate the process to involve concerned individuals, and local, state, and federal agencies. The public scoping meeting place, date, and time will be advertised in advance in local newspapers, and meeting announcement letters will be sent to interested parties.Start Printed Page 76289
5. Availability of the Draft EIS. The Corps intends to issue the draft EIS in the 2015/2016 time frame. The Corps will announce availability of the draft EIS in the Federal Register and other media, and will provide the public, organizations, and agencies with an opportunity to submit comments to be addressed in the final EIS.
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Dated: December 4, 2013.
Project Manager, U.S. Army Corps of Engineers.
[FR Doc. 2013-29984 Filed 12-16-13; 8:45 am]
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