83 FR 64335 - Notice of Availability of the Draft Environmental Impact Statement for the Dam Safety Modification Study for the Cherry Creek Project, Arapahoe County, Colorado

DEPARTMENT OF DEFENSE
Department of the Army; Army Corps of Engineers

Federal Register Volume 83, Issue 240 (December 14, 2018)

The U.S. Army Corps of Engineers (Corps) has made available for public review and comment the Draft Environmental Impact Statement (Draft 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 being conducted in accordance with Corps policy as described in Engineering Regulation 1110-2-1156 ``Safety of Dams--Policy and Procedures.''

[Federal Register Volume 83, Number 240 (Friday, December 14, 2018)]
[Notices]
[Pages 64335-64337]
From the Federal Register Online  [www.thefederalregister.org]
[FR Doc No: 2018-27115]


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DEPARTMENT OF DEFENSE

Department of the Army; Army Corps of Engineers


Notice of Availability of the Draft Environmental Impact 
Statement for the Dam Safety Modification Study for the Cherry Creek 
Project, Arapahoe County, Colorado

AGENCY: Department of the Army, U.S. Army Corps of Engineers, DoD.

ACTION: Notice of availability.

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SUMMARY: The U.S. Army Corps of Engineers (Corps) has made available 
for public review and comment the Draft Environmental Impact Statement 
(Draft 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

[[Page 64336]]

actions will be identified through a Dam Safety Modification Study 
being conducted in accordance with Corps policy as described in 
Engineering Regulation 1110-2-1156 ``Safety of Dams--Policy and 
Procedures.''

DATES: The public comment period on the Draft EIS begins on December 
12, 2018 and will last 45 days. Submit written comments on the Draft 
EIS on or before January 28, 2019.

ADDRESSES: Send written comments, requests to be added to the mailing 
list, or requests for sign language interpretation for the hearing 
impaired or other special assistance needs to U.S. Army Corps of 
Engineers Omaha District, ATTN: CENWO-PMA-C, ATTN: Cherry Creek DSMS, 
1616 Capitol Avenue, Omaha, NE 68102-4901; or email to [email protected].

FOR FURTHER INFORMATION CONTACT: Mr. John Palensky, U.S. Army Corps of 
Engineers, 1616 Capitol Ave., Omaha, NE 68102, or 
[email protected].

SUPPLEMENTARY INFORMATION: The Corps is issuing this notice pursuant to 
section 102(2)(c) of the National Environmental Policy Act of 1969 
(NEPA), as amended, 42 U.S.C. 4321 et seq.; the Council on 
Environmental Quality's (CEQ) regulations for implementing the 
procedural provisions of NEPA, 43 CFR parts 1500 through 1508; the 
Department of the Interior's NEPA regulations, 43 CFR part 46.
    The Corps published a Notice of Intent (NOI) to prepare the Draft 
EIS in the Federal Register on December 17, 2013. Public scoping 
meetings to share information and to allow the public to provide oral 
or written comments were held near Cherry Creek Dam on January 22, 2015 
at the Cherry Creek High School and on January 24, 2015 at the Campus 
Middle School. Three public scoping meetings were held (September 20, 
21 and 22, 2016) in the vicinities of the 3 potential impact areas of 
the Cherry Creek project, the Cherry Creek Presbyterian Church, 
Virginia Village Library, and the Aurora Municipal Center. The Corps is 
planning an additional public on December 12, 2018 at the Lake House at 
Cherry Creek, Greenwood Village, Colorado to present the Draft EA and 
seek additional input from the agencies, utility companies and other 
stakeholders.
    Background Information. The Cherry Creek Dam and Reservoir Project 
is located in western Arapahoe County, Colorado southeast of the city 
of Denver. The project consists of a main dam embankment, outlet works, 
and an emergency side-channel spillway. The 14,300-foot-long embankment 
holds approximately 270,000 acre-feet of water at the top of the dam. 
Cherry Creek Dam and Reservoir is operated as a system with the 
Chatfield and Bear Creek projects. Chatfield Dam is located on the 
South Platte River approximately 15 miles upstream of the South 
Platte's confluence with Cherry Creek in downtown Denver. Bear Creek 
Dam is located on Bear Creek, which flows into the South Platte River 
approximately seven miles upstream of the South Platte's confluence 
with Cherry Creek. The tri-lakes system is operated to minimize flows 
at the Denver gauge on the South Platte River in downtown Denver, CO.
    The dam was screened in 2005 using the Screening Portfolio Risk 
Assessment (SPRA). As a result of that analysis, an Issue Evaluation 
Study (IES) was completed in 2011. The most significant failure mode 
identified during the IES was overtopping and failure of the embankment 
during extreme floods. Combined with the extremely high consequences, 
primarily due to the project location upstream of the Denver 
metropolitan area, the dam was found to pose an unacceptable risk to 
the public.
    A Dam Safety Modification Study (DSMS) was started in 2013. The 
purpose of the DSMS is to identify and recommend a risk management plan 
that reduces risks posed by Cherry Creek Dam. The recommended plan is 
the No Action Alternative. Federal costs of implementation for this 
alternative are zero. In some instances, the justification can be made 
that tolerating structures with high consequences from a failure is in 
the interest of society. In the case of Cherry Creek Dam, the 
probability of failure is very low, individual risk is more than two 
orders of magnitude below the USACE threshold, the risk posed by the 
project meets the principle of equity as described in ER 1110-2-1156, 
and the benefits provided by the dam to society justify continued 
federal investment in this project by the federal government. Risks at 
the dam are being properly monitored by USACE and state of the practice 
actions are being taken, including improvements to the USACE warning 
issuance time and improvements to emergency planning and preparedness 
by downstream local emergency management agencies.
    During the DSMS, the Omaha District initiated a Water Control Plan 
(WCP) Modification Study in accordance with ER 1110-2-240, Water 
Control Management and ER 1110-2-1156, Safety of Dams, Policy and 
Procedures. The purpose of the study was to reduce the potential risk 
of failure of Cherry Creek Dam during extreme floods by releasing more 
water from the outlet works at the dam while limiting exposure to 
potential downstream damages. The study proposed using a pool elevation 
trigger. The modification to the WCP was approved in April 2017.
    Another factor that reduced overtopping risk in the Future without 
Action Condition (FWAC) is the restoration of the spillway capacity. 
The spillway is located on the right side of the embankment and is 
configured to spill water into the adjacent Sand Creek basin, which 
flows into the South Platte River in Commerce City north of downtown 
Denver. Over time soil has accumulated on the bed of the spillway 
channel resulting in an increase in the spillway crest elevation of 
approximately 12.5 feet. The spillway crest will be returned back to 
its design elevation through the maintenance program. A draft 
Environmental Assessment to evaluate the potential environmental and 
social effects of the Cherry Creek Spillway Project is currently being 
prepared under the Operation and Maintenance (O&M) program. Conducting 
the spillway project under the O&M program will allow the issue to be 
addressed as a matter of required maintenance as opposed to a dam 
modification via the Dam Safety program. A contract for the spillway 
excavation work is planned for 2019 and anticipated to take 12 to 18 
months. The costs for returning the spillway to the design 
configuration are about $11 million.
    The Draft EIS document was produced to look at environmental 
impacts from implementing potential risk reduction alternatives. While 
the focus of the DSMS concerns tolerable risk, risk of life loss, etc., 
the focus of this Draft EIS is not to evaluate impacts of dam failure, 
but to compare direct, indirect, and cumulative effects of implementing 
any of the alternatives that address risk.
    This notice announces the availability of the Draft EIS and begins 
a 45-day public comment period on the range of alternatives and effects 
analysis. Analysis in the Draft EIS will support a decision on the 
selection of an alternative. The Draft EIS can be accessed at: http://www.nwo.usace.army.mil/Missions/Civil-Works/Planning/Project-Reports/. 
The Corps is serving as the lead Federal agency for the NEPA analysis 
process and preparation of the Draft EIS. No Cooperating Agencies were 
established for this study.
    Project Alternatives. The purpose of the Cherry Creek DSMS is to 
identify

[[Page 64337]]

and recommend a risk management plan that addresses risk of life loss 
and significant economic, social, and environmental damages associated 
with a potential failure of Cherry Creek Dam. In addition to the No 
Action Alternative, Alternatives 2F (raise dam 7.1 feet and spillway to 
elevation 5610.5 from original design of 5599.8 feet NAVD88 to prevent 
overtopping) and 3B (dam raise of 6.2 feet and no spillway raise) were 
evaluated in the final array of alternatives.
    Dam Raise Alternative 3B consists of the FWAC spillway and a dam 
raise to contain the PMF. A dam raise height for this alternative is 
6.2 feet and the crest width was assumed to be approximately 38 feet to 
allow reconstruction of the crest road using current road design 
standards. Various methods for raising the dam were considered, 
including an earth raise, reinforced concrete wall, and mechanically 
stabilized earth. The most efficient method of raise depends on several 
factors including the height of raise, crest width, availability of on-
site materials, and steepness of embankment side slopes. Earth/rock 
fill raises compete well for raises below 4 to 5 feet if the crest 
width can be minimized. Reinforced Concrete (RC) wall raises are 
clearly more cost effective for larger raises and when a wide crest is 
required to allow construction of a crest road that meets modern 
standards of construction, therefore, the dam would be raised using an 
RC wall if Alternative 3B is implemented.
    Dam Raise Alternative 2F consists of a RC wall dam raise of 7.1 
feet and a spillway raise to crest elevation 5610.5 feet NAVD88 to 
prevent overtopping during the PMF. This spillway crest elevation of 
5610.5 feet was chosen to minimize non-breach flows in the spillway 
impact area. As with Alternative 3B the dam would be raised using an RC 
wall and the crest width would be approximately 38 feet to allow 
reconstruction of the crest road using current road design standards.
    The Draft EIS evaluates the potential effects on the human 
environment associated with each of the alternatives. Issues addressed 
include: Land use and vegetation, social and economic conditions, 
recreation, water resources, air quality, noise, and environmental 
justice.
    Schedule. The public comment period will begin December 12, 2018. 
Comments on the Draft EIS must be received by January 28, 2019. The 
Corps will consider and respond to all comments received on the Draft 
EIS when preparing the Final EIS. The Corps expects to issue the Final 
EIS in the summer of 2019, at which time a Notice of Availability will 
be published in the Federal Register.
    The public meeting date or location may change based on inclement 
weather or exceptional circumstances. If the meeting date or location 
is changed, the Corps will issue a press release and post it on the web 
at http://www.nwo.usace.army.mil/Media/News-Releases/ to announce the 
updated meeting details.
    Public Disclosure Statement. If you wish to comment, you may mail 
or email your comments as indicated under the ADDRESSES section of this 
notice. Before including your address, phone number, email address, or 
any other personal identifying information in your comment, you should 
be aware that your entire comment--including your personal identifying 
information--may be made available to the public at any time. While you 
can request in your comment for us to withhold your personal 
identifying information from public review, we cannot guarantee that we 
will be able to do so.

Brenda S. Bowen,
Army Federal Register Liaison Officer.
[FR Doc. 2018-27115 Filed 12-13-18; 8:45 am]
 BILLING CODE 3720-58-P