Folsom Dam Modification Project_Approach Channel Final EIS_EIR

346 Pages·2012·6.81 MB·English

Folsom Dam Modification Project, Approach Channel SEIS/EIR
December 2012

FOLSOM DAM MODIFICATION PROJECT
APPROACH CHANNEL

FINAL SUPPLEMENTAL
ENVIRONMENTAL IMPACT STATEMENT/
ENVIRONMENTAL IMPACT REPORT

DECEMBER 2012

State Clearinghouse SCH # 2012072039
Folsom Dam Modification Project, Approach Channel SEIS/EIR
December 2012

FOLSOM DAM SAFETY AND FLOOD DAMAGE REDUCTION
FOLSOM DAM JOINT FEDERAL PROJECT

FOLSOM DAM MODIFICATION PROJECT
APPROACH CHANNEL

SUPPLEMENTAL ENVIRONMENTAL IMPACT STATEMENT/
ENVIRONMENTAL IMPACT REPORT

December 2012

Type of Statement: Final Supplemental Environmental Impact Statement/Environmental
Impact Report (SEIS/EIR)

Lead Federal Agency: U.S. Army Corps of Engineers, Sacramento District

Lead State Agency: State of California Central Valley Flood Protection Board
(CVFPB)

Abstract: This Final SEIS/EIR has been prepared by the U.S. Army Corps of Engineers (Corps)
and the Central Valley Flood Protection Board, the non-Federal sponsor, for the proposed
construction of the approach channel of the Folsom Dam auxiliary spillway. The document
supplements the Final EIS/EIR and Record of Decision completed in 2007 for the Folsom Dam
Safety and Flood Damage Reduction Project by providing new and additional information on the
design and means to construct the auxiliary spillway approach channel which was not completely
defined at the time of publication. The 2007 EIS/EIR stated that the design of the approach
channel would be determined in the Corps’ pre-construction, engineering, and design phase and,
as needed, supplemental NEPA/CEQA documentation would be prepared. The Final SEIS/EIR
evaluates the direct, indirect, and cumulative environmental effects of alternative plans for the
approach channel. Mitigation measures are identified to avoid, minimize, and compensate for
resource impacts. Most potential adverse effects would be either short term, or would be
avoided or reduced using best management practices. Public and agency comments that were
received during the DSEIS/EIR comment period are addressed in this FSEIS/EIR.

Public Review and Comment: The final public review period is scheduled for December 28,
2012, and the official closing date for receipt of comments on the final SEIS/EIR will be January
28, 2012. Comments received will be considered in the Record of Decision (ROD). For further
information, please contact the U.S. Army Corps of Engineers at the following address: U.S.
Army Corps of Engineers, Sacramento District; Attn: Mr. Todd Plain, Public Affairs Office;
1325 J Street; Sacramento, California 95814-2922, or by e-mail: [email protected].
Folsom Dam Modification Project, Approach Channel SEIS/EIR
December 2012
Folsom Dam Modification Project, Approach Channel SEIS/EIR
December 2012

EXECUTIVE SUMMARY

ES.1 PURPOSE OF THE SEIS/EIR

This Supplemental Environmental Impact Statement/Environmental Impact Report
(SEIS/EIR) has been prepared for the Folsom Dam Modification Project, Approach Channel.
The SEIS/EIR is a supplement to the 2007 Final EIS/EIR for the Folsom Dam Safety and Flood
Damage Reduction Project (FEIS/EIR), prepared by the U.S. Bureau of Reclamation. This
project is also known as the Folsom Joint Federal Project (Folsom JFP). The Folsom JFP is a
cooperative effort between the U.S. Army Corps of Engineers (Corps), the U.S. Bureau of
Reclamation (USBR), the State of California Central Valley Flood Protection Board (CVFPB),
and the Sacramento Area Flood Control Agency (SAFCA).

This SEIS/EIR examines the impacts of proposed construction of the approach channel of
the “Gated Auxiliary Spillway Alternative” identified as the preferred alternative in the March
2007 FEIS/EIR; and as the Selected Alternative in the Record of Decision (ROD) approved on
May 3, 2007. The FEIS/EIR stated that the design of the spillway approach channel would be
determined in the Corps’ pre-construction, engineering, and design phase and if needed,
supplemental National Environmental Policy Act (NEPA)/California Environmental Quality Act
(CEQA) documentation would be prepared. The implementing regulations of the NEPA at 40
CFR 1502.9(c) provide that a lead Federal agency must prepare a supplemental EIS if (1) the
agency makes substantial changes in the proposed action that are relevant to the environmental
concerns, or (2) there are significant new circumstances or information relevant to environmental
concerns and bearing on the proposed action or its impacts. The SEIS/EIR for the approach
channel complies with this implementing regulation of NEPA. A draft SEIS/EIR was prepared
for public review during the period of July 25 through September 10, 2012. The comments
resulting from this review have been addressed within the document.

The SEIS/EIR describes changes to the project and/or conditions in the project area that
have occurred since the 2007 FEIS/EIR. While it builds upon and incorporates work already
completed as part of the project development process, it does not reproduce in full the prior 2007
FEIS/EIR and ROD documentation. Instead, it incorporates information from those documents
by reference, where applicable. The 2007 FEIS/EIR and ROD can be reviewed at:
http://www.usbr.gov/mp/nepa/nepa_projdetails.cfm?Project_ID=1808

ES.2 PROJECT AREA

The project area is located in the city of Folsom at Folsom Dam, approximately 20 miles
northeast of Sacramento (Figure ES-1) in Sacramento County. The new auxiliary spillway is
located on the left abutment of the main dam, immediately downstream of the left wing dam.
Current access to the site is via Folsom Lake Crossing to an overlook site at approximately 480
feet in elevation. The approach channel for the auxiliary spillway is expected to extend
ES-1
Folsom Dam Modification Project, Approach Channel SEIS/EIR
December 2012

approximately 1,100 feet upstream of the concrete control structure. Currently, this area consists
of a natural rock plug, which is currently acting as a natural dam between the reservoir and the
excavation areas for the gated control Structure and spillway chute.

In this document, the project area consists of the ongoing auxiliary spillway construction
area; the footprint of the approach channel; a spur dike and transload facility; the existing project
haul routes; the existing disposal areas at the Mormon Island Auxiliary Dam (MIAD) and Dike
7; the proposed disposal areas at Dike 8 and in-reservoir, and the existing staging areas at the
Folsom Overlook and Folsom Prison sites. The project area is shown on the map in Figure ES-2.

ES.3 BACKGROUND AND NEED FOR ACTION

The current spillway and outlets at the Folsom facility do not have sufficient discharge
capacity for managing the predicted probable maximum flood (PMF) and lesser flood event
inflows above a 100-year event (an event that has a 1% chance of occurring in any given year).
Structural modifications associated with the Folsom JFP are proposed to address increasing
discharge capability and/or increasing storage during extreme flood events above the 200-year
event level. The new auxiliary spillway is a major feature that will address the need to safely
pass part or the entire PMF event. A hydraulic analysis was completed for the new auxiliary
spillway and is included in the PACR (Corps 2007).

In 2007, the Corps completed the Post Authorization Change Report (PACR) for the
Folsom Modifications and Folsom Dam Raise Projects. This report recommended authorization
of two refined projects: (1) the Folsom JFP and (2) the Folsom Dam Raise. In 2007, the U.S.
Bureau of Reclamation (USBR) also completed the FEIS/EIR for the Folsom JFP. This
FEIS/EIR addressed alternative measures for implementing both USBR’s dam safety and
security obligations, as well as the Corps’ flood damage reduction structural modifications at the
Folsom facility. The Corps was a cooperating Federal agency in the preparation of this
FEIS/EIR.

The refined Folsom JFP, as described in the Corps’ PACR and USBR’s FEIS/EIR was
later authorized under the Water Resources Development Act of 2007. Construction of the
Folsom JFP was initiated by USBR in the fall of 2007, with USBR acting as the lead agency for
the first two phases of construction. The new auxiliary spillway will address the need to safely
pass part of or the entire PMF event. Increasing the discharge capability and increasing storage
will potentially achieve the goal of a greater than 200-year flood protection objective (USBR
2006).

The Folsom JFP auxiliary spillway is being constructed by both USBR and the Corps in
five phases, plus a commissioning and transfer phase. The five phases are (1) initial spillway
excavation, (2) spillway excavation, (3) gated control structure, (4) lower spillway, stilling basin,
and excavation and lining of the upstream approach to control structure, (5) site restoration.
Phases 1 and 2 were completed in 2011. Phase 3 is currently under construction by the Corps.
Phases 4 and 5 are currently under design. The expected completion of the project is October
2017. Figure ES-4 shows an aerial photograph of the project area.
ES-2
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ES 1 -Project Vicinity Map
Approach Channel SEIS/ EIR
US Army Corps December 2012
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ES-3
Auxiliary Spillway
-- Chute & Stilling Basin
-- Control Structure
- - Coffer Dam
- cutoff Wall
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Folsom Dam Modification Project,
•· ES - 2 Project Area Map Approach Channel SEIS/ EIR
U$ Army Corp$
of Enginear& December 2012
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ES-4
LEGEND
-- Control Structure
- Cutoff Wall
- CofferDam
Approach Channel
m--n & Auxiliary Spillway
Existing Overlook
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Folsom Dam Modification Project,
• ES 3- Construction Footprints of Alternatives 2 and 3 Approach Channel SEIS/ EIR
US Army Corps
of Engineer$ December 2012
SatA..,.IItO Olltritt

ES-5
Folsom Dam Modification Project, Approach Channel SEIS/EIR
December 2012

Figure ES-4. Aerial View of Project Area and Folsom Dam.

The 2007 FEIS/EIR stated that the design of the approach channel would be determined
in the Corps’ pre-construction, engineering, and design phase and, if needed, supplemental
NEPA/CEQA documentation would be prepared. This final SEIS/EIR provides this
supplemental documentation and evaluates the direct, indirect, and cumulative environmental
effects of alternative plans for the approach channel and identifies mitigation measures to avoid,
minimize, and compensate for impacts.

ES.4 ALTERNATIVES

Documentation of the plan formulation process associated with the overall Folsom Dam
Modification Project can be found in the Corps’ 2007 Post Authorization Change Report for the
American River Watershed Project, Folsom Dam Modifications and Folsom Dam Raise.
Concurrently, USBR prepared the 2007 EIS/EIR, a programmatic document to which this
supplemental EIS/EIR is tiered (USBR 2007a). The 2007 EIS/EIR contains the overarching
analysis of this multi-phased project, followed by supplemental NEPA documents focusing on
the design refinements of each project phase. Specific approach channel design assessment was
intended for later NEPA and CEQA analyses that are conducted within this EIS/EIR.

Potential design alternatives were identified for assessment of engineering,
environmental, and cost considerations. The two alternatives chosen included a small cofferdam
and a cutoff wall. These structures could accommodate approach channel construction in
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Folsom Dam Modification Project, Approach Channel SEIS/EIR
December 2012

partially dry conditions, and stabilize the shoreline in compliance with dam safety standards
throughout excavation of the existing shoreline. Assessment of construction safety and
scheduling to optimize total construction time was a primary factor in the evaluation of
alternatives. The cutoff wall or cofferdam would serve as a dam to restrain reservoir water from
the construction area until the control structure is functional and the approach channel can be
flooded.

ES.4.1 Alternative 1 – No Action

Under Alternative 1, the Corps would not participate in the construction of the approach
channel to the auxiliary spillway. Since the approach channel is an essential feature to the
overall function of the spillway, dam safety and flood damage reduction improvements to the
Sacramento area would not be implemented, and enhanced public safety would not be realized as
detailed in the 2007 FEIS/EIR (USBR 2007a).

ES.4.2 Alternative 2 – Cutoff Wall

Alternative 2 consists of excavation of the approach channel using a cutoff wall to serve
as a temporary dam during excavation The proposed action would also construct an adjacent
spur dike, which would channel flood flows to the auxiliary spillway. This alternative would
include:

 Installation of a 1,000-foot-long concrete secant pile cutoff wall between the rock plug
and the control structure.
 Placement of fill material along the east side of the rock plug to maintain the 80-foot-
wide haul road connection to the spillway.
 Excavation of an approximate 1,100-foot-long approach channel at the upstream side of
the auxiliary spillway and control structure.
 Installation of the approach channel concrete slab and walls.
 Construction of a spur dike in the reservoir adjacent to the approach channel.
 Stockpiling and disposal of excavated material at one of five proposed potential disposal
sites (MIAD, Dike 7, Dike 8, spur dike, and in-reservoir).
 Construction of a transload facility consisting of up to a 2,000-foot-long rock ramp into
the reservoir near Dike 7 for barge unloading of dredge material.
 Staging of contractor materials and equipment at the spillway excavation site, Folsom
Overlook, Dike 7, Folsom Prison, and MIAD locations (Figure ES-2).
 Temporary installation of a concrete-producing batch plant and/or rock crusher at the
spillway excavation site, Folsom Overlook, Folsom Prison, or MIAD locations.

ES-7