W912PL21B0004_FIO-6-SupplementalEnvironmentalAssessmentPhaseII2021.pdf

SANTA ANA RIVER MAINSTEM PROJECT:

ALCOA DIKE - PHASE II

County of Riverside, California

FINAL

SUPPLEMENTAL ENVIRONMENTAL ASSESSMENT

AND

ENVIRONMENTAL IMPACT REPORT ADDENDUM

LEAD AGENCY:

U.S. Army Corps of Engineers

915 Wilshire Boulevard, Suite 930 Los Angeles, California 90017

May 2021 https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&ved=2ahUKEwjN9KejwrjnAhWyJzQIHZxMDToQjRx6BAgBEAQ&url=https://en.wikipedia.org/wiki/United_States_Army_Corps_of_Engineers&psig=AOvVaw1fHI4n7TTggq9epgx5ljfK&ust=1580926986285444

This page is intentionally left blank.

FINDING OF NO SIGNIFICANT IMPACT

ALCOA EMBANKMENT – PHASE II PROJECT

RIVERSIDE COUNTY, CALIFORNIA

The U.S. Army Corps of Engineers, Los Angeles District (Corps) has conducted an environmental analysis in accordance with the National Environmental Policy Act of 1969, as amended (NEPA), for proposed modifications and refinements to Phase II of the Alcoa Dike project, a feature of the Prado Dam Separable Element of the Santa Ana River Mainstem Project (SARMP). The Supplemental Environmental Assessment (SEA), dated May 2021, addresses modifications and refinements to the dike design along with associated road and utility modifications, and addresses inclusion of a segment of regional bicycle and equestrian trail within the project as a betterment, with an out grant to be issued to Riverside County. This SEA has been prepared by the Corps as a supplement to the Final Supplemental Environmental Impact Statement (SEIS) for Prado Basin and Vicinity, dated November 2001 and to the August 2018 Final SEA. Phase I construction was initiated in 2019.

The proposed modifications to the Alcoa Dike features include: Construction of one additional 48-inch drainage structure extending through the main dike embankment;

extension of the dike an additional 170 feet in length along Temescal Wash to tie into Lincoln Avenue; and extending the flood wall at Auburndale by 26 feet for a total length of 176 feet of flood wall and a 36 foot wide swing floodgate; an increase in the length of the dike alignment at the Lincoln Avenue tie-in adjacent to Temescal Wash;

construction of one culvert comprised of four concrete boxes, each seven (7) feet by four (4) feet, extending through the Rincon Street roadway embankment between Pond I and II; redesign of the concrete v-ditch to an earthen contoured drainage ditch from Pond IA to Pond I; and a new borrow site and haul route were established for Phase II construction activities. Additionally, the drainage channel from the main dike to Temescal Wash near Auburndale Street described in the 2018 Final SEA/EIR Addendum was removed and will be replaced with a single culvert consisting of four reinforced concrete boxes (each 7’ by 4’) extending through the Rincon roadway embankments, and a concrete drainage swale. Minor revisions to the operation, maintenance, repair, replacement and rehabilitation (OMRRR) requirement have also been addressed, such as continuation of maintenance roads along the 170-foot dike extension, and maintaining a maximum 50-foot instead of a 15-foot vegetation-free zone (VFZ) from the toe of the dike on each side. Roadway realignments of Rincon Street to cross the dike at grade and Butterfield Connector to connect to Rincon Street on the reservoir side of the dike would be performed; and a portion of Auburndale Street would be restored with slight grading improvements so water will drain away from where the gate crosses the road. The finished ground next to Auburndale Street would be hydroseeded. New or amended out grants would be issued by the Corps’ Real Estate Division for such roadways where required. The Proposed Action also evaluates out grants for construction, operation and maintenance of a segment of the proposed Santa

Ana River Trail (SART) within and immediately adjacent to the project footprint, and for replacement and protection of the Santa Ana Watershed Project Authority’s (SAWPA’s) utility Brine Line. This SEA provides NEPA compliance to support the real estate actions of providing a right-of-entry for this work to occur. All areas to be temporarily impacted during construction will be reseeded with a native plant palette upon completion of construction activities. The Proposed Action is detailed in Section 2.0 of the SEA.

The Final SEA, incorporated herein by reference, evaluates two alternatives: The No Action Alternative (i.e., the Previously Approved Design Alternative), under which construction of the second phase of Alcoa Dike as described in the 2018 Final SEA would occur, with no modifications or additions as described in this SEA; and the Proposed Action, in which the proposed design modifications and refinements to the feature and associated roadways and utilities and increase in the VFZ, along with the identified real estate actions for the SART, would be implemented.

Construction of Phase II is scheduled to begin in September 2021 and would continue for approximately twenty-four (24) months.

An electronic public Draft SEA, prepared jointly with an EIR Addendum by Orange County Flood Control District, was made available on the Los Angeles District homepage and was distributed to known interested parties in December 2020, with a request for comments from December 14, 2020 to January 14, 2021. Comments received on that public Draft are included in Appendix B of the SEA, along with the Corps’ response. None of the comments received changed the description of the Proposed Action or the analysis contained in the SEA.

For all alternatives, the potential effects were evaluated, as appropriate. A summary assessment of the potential effects of the Proposed Action are listed in Table-1 below:

Table-1: Summary of Potential Effects of the Proposed Action (including proposed minimization and avoidance measures)

Insignificant effects Insignificant effects as a result of mitigation

Resource unaffected by action

Aesthetics ☒ ☐ ☐ Air quality ☒ ☐ ☐ Aquatic resources/wetlands ☒ ☐ ☐ Invasive species ☒ ☐ ☐ Fish and wildlife habitat ☐ ☒ ☐ Threatened/Endangered species/critical habitat

Historic properties ☒ ☐ ☐ Other cultural resources ☒ ☐ ☐

Insignificant effects

Insignificant effects as a result of mitigation

Resource unaffected by action

Floodplains ☒ ☐ ☐ Hazardous, toxic & radioactive waste ☐ ☐ ☒ Hydrology ☒ ☐ ☐ Land use ☒ ☐ ☐ Navigation ☐ ☐ ☒ Noise ☒ ☐ ☐ Public infrastructure ☒ ☐ ☐ Recreation ☐ ☒ ☐ Socio-economics ☒ ☐ ☐ Soils ☒ ☐ ☐ Tribal trust resources ☐ ☐ ☒ Water quality ☒ ☐ ☐ Climate change ☐ ☐ ☒

Avoidance and minimization measures to be implemented as part of the Proposed Action are included in the SEA in Section 6.0. With the implementation of these measures, all potential impacts to environmental and human resources in and adjacent to the project area would be less than significant.

The Proposed Action will not result in additional effects to federally listed species that occur in the vicinity (including but not limited to endangered least bell's vireo (Vireo bellii pusillus), California gnatcatcher (Polioptila californica), and yellow-billed cuckoo (Coccyzus americanus; cuckoo)) or their designated critical habitats from those previously assessed for the Alcoa Dike project. Effects from the overall Alcoa Dike project were assessed in the U.S. Fish and Wildlife Service’s (FWS) letter dated August 23, 2018, concerning Reinitiation of Formal Section 7 Consultation on the Santa Ana River Mainstem Flood Control Project at the Alcoa Dike. The Proposed Action is in compliance with the Endangered Species Act of 1973, as amended (16 USC§ 1531, et seq). The FWS concurred that no additional consultation was required for the Phase II modifications or to address the SART.

The impacts to potential Waters of the United States (WOUS) remain consistent with the Clean Water Act section 404(b)(1) Evaluation prepared as part of the 2018 SEA and in the project’s Clean Water Act section 401 Water Quality Certification (WQC) obtained April 11, 2019. Implementation of the Alcoa Dike project feature, including the Proposed Action, is resulting in 2.03 acres of permanent impacts to the WOUS. The project remains in compliance with the Clean Water Act.

The Proposed Action would result in a total of 0.75 acre of new temporary impacts to non-native upland grassland in addition to 1.83 acres of new temporary and 0.01 acre of new permanent impacts to existing riparian vegetation through vegetation clearing and ground-disturbing activities within the expanded project area. Of these impacts, 1.5 acres of temporary impacts and 0.02 acres of permanent impacts to native riparian vegetation would be a result of the Santa Ana River Trail out grant. The Proposed Action will also temporarily impact 50.5 acres of agricultural lands in the borrow area and will permanently impact 4.53 acres of native riparian habitat along W Rincon Street, that was previous considered to be a temporary impact. These additional impacts are attributed to design refinements associated with raising Rincon Street to match the elevation of the proposed dike and other road modifications. While the Draft SEA/EIR Addendum assumed that a 15-foot Vegetation Free Zone (VFZ) would be maintained and did not identify or describe the requirement for a 50-foot VFZ, the impact acreages presented in that document reflected the worst-case scenario of a permanent impact of

100.7 acres for the 50-foot VFZ.

To offset the temporary and permanent effects of Alcoa Dike and roadway re-alignment elements of the Proposed Action on riparian habitat and WOUS, the Corps will conduct onsite and offsite restoration activities in accordance with 401 WQC requirements and Phase I and Phase II SEA commitments. SART impacts will be restored within the trail’s temporary construction easement by the trail proponent (Riverside County). No additional impacts will occur, and no offsets will be required as a result of the SAWPA brine line protection.

The Proposed Action also remains consistent with the overall project's existing programmatic agreement (PA) prepared under the National Historic Preservation Act.

Pursuant to Section 106 of the National Historic Preservation Act of 1966, as amended, a PA was executed for the SARMP in 1993 by the Corps, State Historic Preservation Officer (SHPO), and the Advisory Council on Historic Preservation. The PA details the procedures to be followed for each feature of the project. Under the Proposed Action, no additional consultation is required for the dike and associated utility relocations and protections or roadway modifications. One cultural resource was identified within the dike construction footprint (CA-RIV-5521) and seven cultural resources were identified within the borrow area, (CA-RIV-4727, CA-RIV-4728, CA-RIV-5253, CA-RIV-7136, CA- RIV-5573, CA-RIV-7676, and CA-RIV-7679). All eight cultural resources have been determined to be not eligible for the National Register of Historic Places through a consensus determination with the SHPO. The Proposed Action would not affect any significant cultural resources.

While the Alcoa dike and the associated utility relocations, protections and roadway modifications are covered by the SARMP PA, the SART is a separate undertaking under the National Historic Preservation Act. In 2017, the Corps consulted with the SHPO on the creation of nine (9) miles of the SART, a segment of which is addressed in the SEA. The Corps found that the creation of the trail would result in no adverse effect to historic properties and the SHPO concurred via letter dated July 26, 2017.

Based on the analyses in the SEA, implementation of the Proposed Action would result in short term and long-term, insignificant impacts to environmental resources including, but not limited to, biological resources, air quality, recreation, and water quality. All applicable laws, executive orders, regulations, were considered in evaluation of alternatives. Based on the Final SEA, the reviews by other Federal, State and local agencies, and the review by my staff, it is my determination that the Proposed Action would not have a significant effect on the quality of the human environment; therefore, preparation of an Environmental Impact Statement is not required.

DATE Julie A. Balten

Colonel, U.S. Army Commander and District Engineer i

Table of Contents

1 INTRODUCTION

1.1 Introduction

1.2 Project Location

1.3 Project Authority

1.4 Previously prepared documents

2 PROPOSED ACTION AND ALTERNATIVES

2.1 Objectives, Purpose and Need

2.2 Comparison of Previously Approved Design and Proposed Action

2.3 Alternatives Evaluated and Eliminated

2.4 Project Alternatives (Alternatives Considered for Environmental Analysis)

2.4.1 Previously Approved Design Alternative

2.4.2 Proposed Action

2.4.3 Staging Areas, Haul Routes, and Construction Activities

2.4.4 Utilities

2.4.5 Future Operation, Maintenance, Repair, Replacement and Rehabilitation

3 AFFECTED ENVIRONMENT

3.1 Air Quality

3.2 Biological Resources

3.2.1 General Setting

3.2.2 Vegetation

3.2.3 Special-Status Plant Species

3.2.4 Jurisdictional Habitats

3.2.5 Wildlife

3.3 Water Resources and Hydrology

3.3.1 General Setting

3.3.2 Temescal Wash and Santa Ana River

3.3.3 Groundwater

3.4 Earth Resources

3.4.1 Geology and Soils

3.4.2 Seismicity and Faulting

3.5 Land Use

3.6 Aesthetics

3.7 Recreation

3.8 Noise

3.8.1 Noise Environment in the Proposed Project Area

3.8.2 Sensitive Receptors in the Proposed Project Area

3.9 Socioeconomics

3.9.1 Housing

3.9.2 Employment and Income

3.9.3 Ethnicity

3.10 Transportation

3.11 Safety and hazards

ii

3.12 Cultural Resources

3.13 Public Services and Utilities

3.13.1 Public Services

3.13.2 Utilities and Service Systems

3.14 CERCLA Hazardous Substances and Other Pollutants

4 ENVIRONMENTAL CONSEQUNCES

4.1 Air Quality

4.1.1 Proposed Action

4.1.2 Previously Approved Design Alternative

4.2 Biological Resources

4.2.1 Proposed Action

4.2.2 Previously Approved Design Alternative

4.3 Water Resources and Hydrology

4.3.1 Proposed Action

4.3.2 Previously Approved Design Alternative

4.4 Earth Resources

4.4.1 Proposed Action

4.4.2 Previously Approved Design Alternative

4.5 Land Use

4.5.1 Proposed Action

4.5.2 Previously Approved Design Alternative

4.6 Aesthetics

4.6.1 Proposed Action

4.6.2 Previously Approved Design Alternative

4.7 Recreation

4.7.1 Proposed Action

4.7.2 Previously Approved Design Alternative

4.8 Noise

4.8.1 Proposed Action

4.8.2 Previously Approved Design Alternative

4.9 Socioeconomics

4.9.1 Proposed Action

4.9.2 Previously Approved Design Alternative

4.10 Transportation

4.10.1 Proposed Action

4.10.2 Previously Approved Design Alternative

4.11 Safety and hazards

4.11.1 Proposed Action

4.11.2 Previously Approved Design Alternative

4.12 Cultural Resources

4.12.1 Proposed Action

4.12.2 Previously Approved Design Alternative

4.13 Public Services and Utilities

4.13.1 Proposed Action

4.13.2 Previously Approved Design Alternative

iii

5 CUMULATIVE IMPACTS

5.1 Introduction

5.2 Analysis of Cumulative Impacts

5.2.1 Air Quality

5.2.2 Biological Resources

5.2.3 Water Resources and Hydrology

5.2.4 Earth Resources

5.2.5 Land Use

5.2.6 Aesthetics

5.2.7 Recreation

5.2.8 Noise

5.2.9 Socioeconomics

5.2.10 Transportation

5.2.11 Safety and Hazards

5.2.12 Cultural Resources

5.2.13 Public Services and Utilities

6 ENVIRONMENTAL COMMITIMENTS

6.1 6.1 Environmental Commitments

6.1.1 Air Quality

6.1.2 Biological Resources

6.1.3 Water Resources and Hydrology

6.1.4 Land Use

6.1.5 Noise

6.1.6 Cultural Resources

7 COMPLIANCE WITH ENVIRONMENTAL REQUIREMENTS

7.1 7.1 Relevant Federal, State, and Local Statutes, Laws, and Guidelines

7.1.1 Federal Laws and Regulations

7.2 State Regulations

7.2.1 Air Quality

7.2.2 Biological Resources

7.3 Local Regulations

7.3.1 Air Quality

7.3.2 Biological Resources

7.3.3 Noise

8 AGENCY COORDINATION

9 LIST OF PREPARERS AND REVIEWERS

10 CONCLUSION

11 REFERENCES

iv

LIST OF APPENDICES

APPENDIX A: CULTURAL RESOURCES DOCUMENTATION

APPENDIX B: DISTRIBUTION MAILING LIST

APPENDIX C: RESPONSE TO COMMENTS

LIST OF FIGURES

Figure 1 Project Location Figure 2 Project Vicinity Map Figure 3 Existing and Proposed Perimeter Dikes in Project Vicinity Figure 4 Flood Risk Management Areas due to Proposed Project Figure 5 Showing the location of the ponds and the remaining pond Ia Figure 6 Showing the 15’ Vs. 50’ Vegetation Free Zone (VFZ) constructed in Phase II project Figure 7 Project Site Plan Figure 8 Phase II Alcoa Dike Project Design Figure 9 Phase I vs. Phase II Project Footprint Figure 10 Phase I vs. Phase II Vegetation Communities Figure 11 Jurisdictional Waters and Wetland within the Proposed Project Area Figure 12 Least Bell’s Vireo and Critical Habitat Occurrence Figure 13 Coastal California Gnatcatcher Occurrence Figure 14 Impact to existing mitigation site from Alcoa Dike and SART alignment Figure 15 Change in Permanent and Temporary Impact Areas (Phase I vs. Phase II) Figure 16 Change in Vegetation Community Impact Areas (Phase I vs. Phase II) Figure 17 Wildlife Movement Corridors along Temescal Creek Figure 18 Phase II Proposed Sound Wall Figure 19 Shows drainage facilities and basins designed to control runoff behind the Dikes as a result of the local SPF (standard project flood) v

LIST OF TABLES

Table 2-1 Differences between Previously Approved 2001 and 2018 Dike Designs and the Dike Design is adopted Table 2-2 Differences between Preferred SCE Replacement and Alternative SCE Replacement Table 3-1 Recreation Facilities and Amenities in Project Vicinity Table 3-2 Demographic Data for the City of Corona Table 3-3 Annual Average Daily Traffic on Selected Roadways in the Proposed Project Area Table 3-4 Utility and Service Providers by Jurisdiction Table 4-1 Comparison of Proposed Project Daily Construction Emissions to Table 4-2 Comparison of Proposed Project Annual Construction Emissions to General Conformity

Applicability Rates and GHG annual emissions Table 4-3 Comparison of Proposed Project Daily OMRRR Emissions to SCAQMD Lbs/Day Table 4-4 Comparison of Proposed Project Annual OMRRR Emissions to General Conformity

Applicability Rates and GHG annual emissions Table 4-5 Impacted Cover Types Phase II Expanded Footprint Table 4-6 Change in Permanent/Temporary Impact Areas (2018 Final SEA/EIR Addendum Design

Alternative vs. Proposed Action (Phase I vs. Phase II) Table 4-7 Changes in Impacts to Riparian Vegetation Table 4-8 Additional Mitigation Acreages (Phase I vs. Phase II) Table 4-9 Additional Impacts Resulting from the SART – to be offset by trail proponents within the temporary impact area and immediate vicinity Table 4-10 Permanent Impacts to Biological Resource from the 50 feet VFZ Table 4-11 Additional Impacts to Jurisdictional Wetlands/Waters in Phase II Footprint Table 4-12 Impacts to Jurisdictional Wetlands/Waters (2018 Final SEA/EIR Addendum Table 4-13 Typical Noise Levels for Construction Equipment Table 5-1 Cumulative Projects in the Phase II Proposed Project Activity Area Table 6-1 Original Mitigation Commitment from 1988 Supplemental Environmental Impact Statement and 2018 Final SEA/EIR Addendum vi

This page is intentionally left blank.

SEA/EIR Addendum – Alcoa Dike Phase II May 2021 1 Introduction

1 INTRODUCTION

1.1 Introduction

This Supplemental Environmental Assessment and Environmental Impact Report Addendum (SEA/EIR Addendum) for the Alcoa Dike Phase II portion of the Prado Separable Element of the Santa Ana River Mainstem Flood Control Project (SARMP), has been prepared jointly by the U.S. Army Corps of Engineers (Corps) and Orange County Flood Control District (OCFCD) as a supplement to the Final Supplemental Environmental Impact Statement (SEIS) and EIR for Prado Basin and Vicinity, dated November 2001 (2001 Final SEIS/EIR). This SEA/EIR Addendum also supplements the August 2018 Alcoa Dike Final SEA/EIR Addendum (2018 Final SEA/EIR Addendum). The 2018 Final SEA/EIR Addendum addressed the initial clearing and Dike construction within the project area, but due to insufficient design information at the time, it did not fully address all elements including road realignments and some utility relocations. The Phase I construction was initiated in 2019. A contract for Phase II construction is anticipated to be awarded in 2021. This SEA/EIR Addendum includes more detail about associated road and utility modifications, addresses minor design modifications to the Dike structure, and addresses inclusion of a segment of a regional bike trail and equestrian trail as a project betterment This document complies with requirements of the National Environmental Policy Act (NEPA) and the California Environmental Quality Act (CEQA) This document complies under the old NEPA regulations as this is the continuation of the original project with a few minor modifications to the original design. The Corps is the lead agency for compliance with NEPA, and the OCFCD, the non-federal sponsor for the Prado Dam separable element, is the lead agency for compliance with CEQA. The OCFCD will be responsible for operation, maintenance, repair, replacement, and rehabilitation of the Dike. Other agencies (i.e., cooperating, responsible, and trustee agencies) that may use this SEA/EIR Addendum in the decision making or permit process related to the Alcoa Dike Phase II construction will consider the information in this document along with other information that may be presented during the NEPA/CEQA process.

Other responsible and trustee agencies were identified in the 2001 Final SEIS/EIR and 2018 Final SEA/EIR Addendum, and are listed again as follows:

• California Department of Fish and Wildlife (previously California Department of Fish and Game)

• Santa Ana Regional Water Quality Control Board

• Riverside County

• Southern California Edison

• Santa Ana Watershed Project Authority

• United States Fish and Wildlife Service

• California Department of Parks and Recreation

• City of Corona, and

• Orange County Water District.

This SEA/EIR Addendum is necessary to document and evaluate the impacts of design refinements on environmental resources, and to document any changed conditions in the project area compared to the 2018 Final SEA/EIR Addendum. This SEA/EIR Addendum addresses design modifications for Alcoa Dike Phase II construction, as well as adjustments to roadways and utility relocations. Phase II construction will complete the portion of the Dike not constructed in Phase I, generally in the vicinity of road crossings including the south Lincoln tie-in near Butterfield Drive and the portions of the Dike crossing Rincon Street and Auburndale Street. Phase II construction will also incorporate design changes that have occurred subsequent to completion of the Phase I construction, as well as work requiring outgrants and outgrant modifications for other utilities, roadways, and the Santa Ana River Trail (SART).

Proposed design refinements and related actions for work not undertaken as part of or associated with 2018 construction include:

• Construction of Lincoln Avenue tie-in adjacent to Temescal Wash extending the Dike an additional approximate 170 feet in length;

• Construction of one additional 48-inch drainage structures extending through the main Dike embankment;

• An increase in the length of the Dike alignment at the Lincoln Avenue tie-in adjacent to Temescal Wash;

• Construction of one culvert comprised of four (4) concrete boxes, each seven (7) feet by

(4) four feet, extending through the Rincon Street roadway embankment between Pond I and II;

• Redesign of the concrete v-ditch to an earthen contoured drainage ditch from Pond IA to Pond I;

• Extending the flood wall at Auburndale by 26 feet for a total length of 176 feet of flood wall and a 36-foot-wide swing floodgate;

• Vegetation Free Zone (VFZ) width of fifty (50) feet to comply with levee safety certification requirements;

• A new borrow site and haul route were established for Phase II construction activities;

• Work during Phase II is also proposed to include the following roadway modifications, for Lands, Easements, Rights-of-Way, and Relocations (LERR) obligations and/or at non-project cost and includes outgrant modifications and/or new outgrants by the Corps’ Real Estate Division: Roadway re-alignment of Rincon Street to cross the Dike at grade;

• A portion of Auburndale Street would be restored with slight grading improvements so water will drain away from where the gate crosses the road. The finished ground next to Auburndale Street would be hydroseeded; and

• Butterfield Connector realignment to connect to Rincon Street on the reservoir side of the Dike.

Furthermore, other activities would be accommodated within and adjacent to the proposed new alignments of Rincon Road and Butterfield Drive:

• A segment of the proposed SART would be accommodated within and adjacent to the proposed new alignments of Rincon Road and Butterfield Drive. Right-of-way authorization from the Corps would be required for the construction, operation, and maintenance of the SART by Riverside County. The SART would be extended through a Corps mitigation site along Butterfield Drive up to Temescal Wash. The bike path segment (varying 14 to 16-foot-wide multi-use path) would be immediately adjacent to the road, while an equestrian trail would be offset but roughly parallel to that same alignment (10-foot-wide decomposed granite (DG) trail);

• The temporary replacement and protection of a segment of the Inland Empire Brine Line by the Santa Ana Watershed Project Authority, to enable the Brine Line to withstand the additional load where it crosses under project features. Right-of-way authorization from the Corps would be required;

• Related action: The replacement of Southern California Edison transmission, distribution, and telecom poles/circuits by the owner, disclosed below; and

1.2 Project Location

The Alcoa Dike project area is located in the city of Corona, Riverside County (Figure 1, Project Location), adjacent to Temescal Creek. The Phase I and Phase II features occur along the southeastern perimeter of Prado Basin (Figure 2). Alcoa Dike is one of several perimeter Dikes or embankments that are being constructed around the Prado Basin as part of SARMP (Figure 3), as documented in the 2001 SEIS/EIR. The Alcoa Dike project is located south of the Corona National Housing Tract Dike, east of the Corona Sewage Treatment Plant Dike, and would cross over Butterfield Dive, Rincon Street, and Auburndale Street. The feature was originally named for the Alcoa aluminum plant that at one time was located in this area of the basin. While that plant no longer exists in this location, the flood risk reduction that would be provided by this feature is still needed for other developments and private property in the area.

Figure 1 Project Location

1.3 Project Authority

The SARMP is located along a 75-mile reach of the Santa Ana River in Orange, Riverside, and San Bernardino Counties, California. The SARMP is a comprehensive flood risk management system that was authorized for construction by Section 401(a) of the Water Resources Development Act (WRDA) of 1986.

The recommended plan for the SARMP is contained in the Phase I General Design Memorandum (GDM) for the SARMP (Corps 1980) and included eight elements, which were subsequently reevaluated in the Phase II GDM (Corps 1988). The Phase II GDM modified the SARMP by redefining the authorized SARMP features and clarifying that the Standard Project Flood (SPF) term referred in most cases to the 190-year flood event. Construction of the SARMP commenced in fiscal year 1989.

In 2001, the Corps prepared an SEIS/EIR that addressed additional and modified features or elements in the vicinity of Prado Dam. The Corps also prepared a Limited Reevaluation Report (LRR) entitled Prado Dam Separable Element, Prado Basin & Vicinity, including Stabilization of Bluff Toe at Norco Bluffs Santa Ana River Basin, California, dated September 2001. This report was prepared pursuant to Section 309(a) of WRDA of 1996, which required the Corps to “review” the Prado Dam feature, a component feature of the SARMP. The LRR was approved by the Director of Civil Works on August 16, 2002. The LRR recognized, consistent with the Phase I GDM and Phase II GDM, that the purpose of the proposed Prado Dam improvements was to increase the reservoir storage capacity from 217,000 acre-feet to 362,000 acre-feet and to be able to release 30,000 cfs flows from Prado Dam into the downstream channels. In accordance with the determination in the LRR to construct Prado Dam as a separable element, the Prado Dam component was removed from the definition of the project in the Local Cooperation Agreement (LCA) by a second modification to the LCA dated February 24, 2003. A Project Cooperation Agreement for the Prado Dam feature as a separable element was signed on February 11, 2003, with OCFCD as the non-Federal sponsor.

The specific feature of the Prado Basin and Vicinity addressed by this SEA/EIR Addendum is the Alcoa Dike project.

1.4 Previously prepared documents

Below is a list of the relevant environmental documents that have been completed for SARMP.

Throughout the analysis of this SEA/EIR Addendum, the following documents may be referenced:

• Limited Reevaluation Report (LRR/SEIS). Prado Dam Separable Element, Prado Basin & Vicinity, including Stabilization of Bluff Toe at Norco Bluffs Santa Ana River Basin, California. 2001.

• Final Supplemental Environmental Assessment (SEA) and Environmental Impact Report (EIR) Addendum for the Phase I Alcoa Dike portion of the Santa Ana River Mainstem Flood Control Project (SARMP), 2018.

• Formal Section 7 Consultation, Biological Opinion (BO) on the Santa Ana River Mainstem Flood Control Project at the Alcoa Dike, Corona Riverside California, FWS-WRIV-08B0408-18F1350, dated August 23, 2018.

• Upstream Dam Alternatives Supplemental EIR, United States Army Corps of Engineers, Los Angeles District, 1985.

• Phase II General Design Memorandum for the Santa Ana River Mainstem Project. 1988.

• Phase I General Design Memorandum and Supplemental EIR, United States Army Corps of Engineers, Los Angeles District, 1980.

• Survey Report and EIR, United States Army Corps of Engineers, Los Angeles District, 1975.

Figure 2 Project Vicinity Map

Figure 3 Existing and Proposed Perimeter Dikes in Project Vicinity

SR-71

May 2021 2 Proposed Action and Alternatives

2 PROPOSED ACTION AND ALTERNATIVES

2.1 Objectives, Purpose and Need

The federal objective of water and related land resources project planning is to contribute to national economic development (NED). Such contributions are considered increases in the net value of the national output of goods and services expressed in monetary units. These contributions are to be consistent with the protection of the nation’s environment, pursuant to applicable executive orders and other federal planning programs, including the consideration of state and local concerns. The NED objective of the approved SARMP is to provide flood risk management for portions of Orange, Riverside, and San Bernardino Counties, while maximizing contributions to NED.

The Alcoa Dike feature is part of the Prado Dam separable element of the SARMP. The feature was analyzed in the 1988 Phase II GDM/SEIS and the design was further revised in the 2001 Final SEIS/EIR and the 2018 Final SEA/EIR Addendum. During completion of the feature’s Plans and Specifications, the design of the Phase II Alcoa Dike embankment (Proposed Action or proposed project) was further refined. The main objective of the Proposed Action would be the same as the originally approved Alcoa Dike embankment, which is to reduce the flood risk and thereby protect the lives and properties of public and privately owned development in the project area.

Statement of Need

Due to the planned increase in height of Prado Dam to provide additional flood risk reduction to the surrounding communities, all properties located between elevation 556 feet and elevation 566 feet behind the Dam would be within the expanded flood pool of the basin, subject to inundation (Figure 4 Flood Risk Management Areas due to Proposed Project). The figure shows the difference between 556 ft contour (blue) and 566 ft contour (pink) for flood risk associated with raising the dam spillway (566 ft contour increased area is designed to protect). Inundation of the basin area requires land acquisition and utility/facility replacements in the absence of a structural feature to prevent inundation of the area. In the subject area, heavily used roadways such as Rincon Road and Auburndale would be subject to removal or replacement in the absence of a structural feature.

Design refinements and other changes are needed to the temporary and permanent construction footprint since the 2018 Final SEA/EIR Addendum. Modification to the design was deemed necessary to avoid environmental, cost, and timing consequences for flood risk management purposes. The Corps is also responding to a request from Riverside County for inclusion of a segment of the multipurpose trail known as the SART.

Statement of Purpose

The purpose of the Proposed Action is to provide protection from predicted future inundation associated with the planned increased height of the Prado Dam spillway that would otherwise extend up to the 566-ft pool elevation in the project area, address requests for road modification and utility outgrants to comport with the Alcoa Dike design, and to address the request for inclusion of the Riverside County’s segment of the SART.

Figure 4 Flood Risk Management Areas due to Proposed Project

2.2 Comparison of Previously Approved Design and Proposed Action A comparison of the Previously Approved Design and the Proposed Action is shown below in Table 2-1.

Table 2-1 Differences between Previously Approved 2001 and 2018 Dike Designs and the Dike Design, if Proposed Action is adopted

Previously Approved Design as Described in the 2001 Final

SEIS/EIR

Previously Approved Design as Described in the 2018 Final SEA/EIR

Addendum

Proposed Action Modification and Refinements for SEA/EIR Addendum – Alcoa Dike Phase II

Approximately 5,550 ft of bank protection. (project feature).

Approximately 7,530 ft of bank protection; minor design changes to embankment include height increase of

1.5 ft to 3 ft (project feature).

Approximately 4,700 ft of this bank protection was completed during Phase I construction..

Construction of the remaining 3000 ft of the previously approved bank protection, plus an additional 170 ft (for a total Dike length of approximately 7,700 ft) would be constructed during Phase II, extending the alignment of the Dike to tie into Lincoln Avenue closer to Temescal Wash (project feature).

Ponding area for interior drainage behind the Dike located at the northwest corner of the intersection of Rincon Street and Auburndale Street (project feature).

Three additional ponding areas or detention basins (total of four) with a total storage volume of 83.3 acre-feet for interior drainage behind the Dike (project feature). Three of the four ponding areas (detention basins) were built during Phase I construction.

Construction of the remaining basin (1a), as shown in figure 5, would be built during Phase II construction. The Proposed Action would not change the number, design or total storage volume of these project features.

Two 48-inch drainage structures added extending through the main Dike embankment (total of three), one culvert with 4 reinforced concrete boxes (7’ by 4’), extending through the Rincon roadway embankments between Pond I and II, and a concrete drainage swale from Pond IA to Pond I (project feature).

Two proposed 48-inch drainage structures extending through the main Dike embankment, two other culverts extending through roadway embankments, a concrete v-ditch and 48 inch drainage pipe to Temescal Creek, a drainage channel from the main Dike to Temescal Wash adjacent to and east of Auburndale Street, and a drainage channel from the main Dike to Temescal Wash adjacent to and west of Lincoln Street (project feature). One of the two drainage structures was built during Phase I construction.

As part of Phase II construction as proposed, the other drainage structure described in the 2018 Final SEA/EIR Addendum and one additional 48-inch drainage structure extending through the main Dike embankment would be constructed, for a total of three 48-inch drainage structures. The drainage channel from the main Dike to Temescal Wash adjacent to and east of Auburndale Street described in the 2018 Final SEA/EIR Addendum and built during Phase I would be removed and replaced/modified with the construction of one culvert with 4 reinforced concrete boxes (7’ by 4’), extending through the Rincon roadway embankments between Pond I and II, and a concrete drainage swale from Pond IA to Pond I (project feature).

-- Two 15-foot maintenance access roads -one on each side along the toe of the embankment (project feature).

Under the Proposed Action, the two 15-ft maintenance access roads would be extended along the

Described in the 2001 Final

SEIS/EIR

Described in the 2018 Final SEA/EIR

Addendum

Proposed Action Modification and Refinements for SEA/EIR Addendum – Alcoa Dike Phase II additional 170 ft of embankment -one on each side along the toe of the embankment (project feature).

Raising of Auburndale Road (sponsor road relocation) to match the top elevation of proposed Dike.

Horizontal swing floodgate at Auburndale Road and reinforced concrete floodwall on each side of the floodgate (project feature). Not completed, will be constructed in Phase

II.

Construction of the previously proposed horizontal swing floodgate at Auburndale Street and reinforced concrete floodwall on each side of the floodgate. In design of Phase II, the floodwall was extended 26 ft, resulting in a total length of 176 ft of floodwall and a 36 ft wide swing floodgate (no change) (project feature).

-- Raising of Rincon Street to match the elevation of the proposed Dike, and road modification to Rincon Street to meet current design standards. (sponsor road relocation). Not completed, will be constructed in Phase II.

Final design for the raising of Rincon Street to match the elevation of the proposed Dike and road modification to Rincon Street did not change from the original design and were incorporated to meet current design standards as previously described in the 2018 Final SEA/EIR Addendum (no change) (sponsor road relocation).

-- Road realignment of Butterfield Drive (City of Corona paid element – not a project feature or project-required relocation). Not completed, will be constructed in Phase II.

Road realignment of Butterfield Drive did not change from the original design and would be constructed as previously described in the 2018 Final SEA/EIR Addendum (no change) (City of Corona paid element, outgrant).

VFZ shall be limited to 15 ft native grasses in compliance with Corps Dam and Levee Safety Regulations

Modification to the VFZ width from 15 ft to 50 ft to comply with levee safety certification requirements.

Santa Ana Watershed Project Authority (SAWPA) utility Brine Line replacement and protection (outgrant from the Corps).

SART segment installation located within the existing footprint of the Phase II Alcoa Dike, (Betterment, outgrant from the Corps).

The replacement of Southern California Edison transmission, distribution, and telecom poles/circuits at owner cost, new (Related Action)

Figure 5 Showing the location of the ponds and the remaining pond Ia to be constructed in Phase II project.

2.3 Alternatives Evaluated and Eliminated

No Construction Alternative

The Alcoa Dike embankment as originally designed was approved for construction in the record of decision for the 2001 Final SEIS/EIR and in the Finding of No Significant Impact in the 2018 Final SEA/EIR Addendum, and continues to be a required project feature to allow for operation of Prado Dam subsequent to raising of the spillway height. Thus, not constructing this flood control improvement feature would not meet the project purpose and need. Therefore, the No Construction alternative has been removed from consideration and is not carried forward for further analysis.

2.4 Project Alternatives (Alternatives Considered for Environmental Analysis) Two alternatives have been carried forward for this SEA/EIR Addendum. Also refer to 2018 Final SEA/EIR Addendum for detailed analysis. These alternatives are:

• Previously Approved (2018) Design Alternative, i.e. the No Action Alternative.

• Proposed Action

2.4.1 Previously Approved Design Alternative

The Previously Approved Design Alternative is defined as constructing the Alcoa Dike embankment according to the plan presented by the Corps in the 2018 Final SEA/EIR Addendum. The proposed Dike would reduce flood risk to the infrastructure, and private and public developments located just outside of the existing rights-of-way in the southeastern part of the Prado reservoir. The entire parcel (plus other privately owned development) is located within the proposed expanded Prado Basin reservoir inundation limit at elevation 566 foot. Studies indicate that it would be more economical to construct a Dike between the reservoir and these properties than to acquire these properties for flood control purposes.

Operation, maintenance, repair, replacement and rehabilitation (OMRRR) actions under this Previously Approved Design Alternative will continue to be the same as identified in the 2018 Final SEA/EIR Addendum, Proposed Action Alternative, sub-section 2.5. Proposed design refinements would not be made, and the Corps would need to prepare separate NEPA documentation to support any Real Estate decisions regarding utility relocations or trail construction. Any previously permitted removals/replacements for roads and utilities in the project footprint continue to be the owner’s responsibility to maintain (with or without the proposed changes).

2.4.2 Proposed Action

The Proposed Action is similar to the Previously Approved Design Alternative and associated local sponsor real estate actions, including road and utility modifications, except for the changes identified in Table 2-1 above. This SEA/EIR Addendum addresses design modifications for construction, including adjustments to roadway and utility replacements. This SEA/EIR Addendum also evaluates outgrants and outgrant modifications for other utilities, roadways, and the SART.

Road Realignments: As with the Previously Approved Design Alternative, the Proposed Action would be located on federal land within the city of Corona in Riverside County and would be adjacent to the existing Smith Avenue and Rincon Street. The alignment of the proposed Dike was adjusted from the 2001 alignment as previously described in the 2018 Final SEA/EIR Addendum to minimize impacts on existing facilities such as streets, utilities, percolation ponds, and other industrial and commercial development. Despite the adjustments, the proposed Dike would also have to cross over Rincon Street, Butterfield Drive and Auburndale Street. Both the 2018 Final SEA/EIR Addendum and this SEA/EIR Addendum design included modifications to incorporate a floodgate at Auburndale Street that would eliminate the need to reconstruct Auburndale Street, but Rincon Street would be modified to cross the Dike at grade. As described in the 2018 Final SEA/EIR Addendum the reservoir side of the roadway slopes would be protected with 15 inches of stone over 12 inches of bedding. For Proposed Action, the alignment further extends in the northerly direction, across Butterfield Drive, approximately 1,800 feet on to Corps owned property until it crosses Rincon Street. The alignment continues in the easterly direction parallel to Temescal Wash for approximately 2,200 feet on land owned in fee by the City of Corona. (Figure 4). The Butterfield Connector roadway will be realigned to connect to Rincon Street on the reservoir side of the Dike to match the elevation of the proposed Dike. The road modification to Rincon Street did not change from the original design and was incorporated to meet current design standards as previously described in the 2018 Final SEA/EIR Addendum.

Drainage and Dike Modifications: Under the Proposed Action, Phase II construction consists of construction of the remaining drainage structure and detention basin as described in the 2018 Final SEA/EIR Addendum, with one additional 48-inch drainage structure proposed to extend through the main Dike embankment, for a total of three 48-inch drainage structures (Figure 5).

Three of the four ponding areas (detention basins) described in the 2018 Final SEA/EIR Addendum were built during Phase I construction. Construction of the final remaining basin (1a) would be built during Phase II construction. The length of the Dike alignment at the Lincoln Avenue tie-in adjacent to Temescal Wash would increase, extending the Dike an additional approximate 170 feet in length. The previously proposed reinforced concrete floodwall on each side of the floodgate at Auburndale Street would be extended by 26 feet, resulting in a total length of 176 feet of floodwall and a 36 feet wide swing floodgate. The drainage channel from the main Dike to Temescal Wash adjacent to and east of Auburndale Street described in the 2018 Final SEA/EIR Addendum built during Phase I will be removed and replaced/modified with the construction of one culvert with 4 reinforced concrete boxes (7’ by 4’), extending through the Rincon roadway embankments between Pond I and II, and a concrete drainage swale from Pond Ia to Pond I. The proposed project modifications also include extension of the two 15-foot maintenance access roads along the additional approximate 170 foot of embankment toe on each side to tie into Lincoln Avenue close to Temescal Wash, and a drainage swale to Temescal Wash adjacent to and west of Lincoln Avenue to provide interior drainage behind the Alcoa Dike.

Temporary detours would be provided as necessary during construction.

Reinforced concrete boxes and an earthen drainage swale are proposed under the Rincon Street roadway embankment to replace the concrete v-ditch and a 48-inch drainage pipe that were described in the 2018 Final SEA/EIR Addendum. The earthen drainage swale would flow adjacent to and east of Auburndale Street and adjacent to and west of Lincoln Avenue that would drain water to Temescal Wash. The dimensions of the swale would include a 3-ft (foot) trapezoidal channel with 15-inch (in) thick riprap over 12-in. thick bedding, 10-ft trapezoidal channel with 15-in thick riprap over 12-in thick bedding, and 10-ft trapezoidal earthen channel.

A maximum 50-foot VFZ would extend out from the toe of the Dike on each side. This zone includes the 15-ft wide paved maintenance roads and an additional 35-foot area that would be planted with low growing, native grasses and maintained free of other vegetation in compliance with Corps Dam and Levee Safety Regulations as shown in the figure 6 below. Other areas disturbed by construction outside of the 50-foot zone would be seeded or planted with native shrubs and grasses.

Figure 6 Showing the 15’ Vs. 50’ Vegetation Free Zone (VFZ) constructed in Phase II project.

SAWPA Inland Empire Brine Line (Outgrant): Alcoa Dike Phase II crosses the SAWPA Inland Empire Brine Line at two intersections, the California Rehabilitation Center lateral line (15 in /1 in) along Auburndale Street and the Brine Line Reach IV (3 in) parallel to Butterfield Drive. The proposed Brine Line Protection activities along Auburndale Street include removal of 80 linear ft. of existing Vitrified Clay Pipe / Ductile Iron Pipe, one manhole and one gate valve, and 75 linear ft. of new 18 in. High Density Polyethylene (HDPE) pipe along the same alignment and elevation as the existing pipe. This will require the construction of one manhole at the downstream end of the pipe segment being replaced and furnishing and installation of a new gate valve along the same alignment. No bypass would be required considering the line is inactive.

Temporary dewatering may include two (2) wellheads, discharge piping and water treatment equipment if necessary, to meet discharge requirements. In addition, the Proposed Action parallel to Butterfield Drive would involve removal of 430 linear ft of existing reinforced concrete pipe (RCP) and furnish and install 411 linear feet of new 48-in HDPE pipe along the same alignment and elevation as the existing pipe. Two additional new manholes at the upstream and downstream ends of the pipe segment being replaced would also be added along the same alignment. A temporary bypass of flow is required and consists of two (2) pumps and bypass piping. Temporary dewatering may include three (3) wellheads, discharge piping, and water treatment equipment if necessary, to meet discharge requirements.

SART (Outgrant and Betterment): A portion of the proposed SART would be located within the existing footprint of the Phase II Alcoa Dike consisting of a 12-ft-wide asphalt bike trail and a 12-foot-wide DG Hiker Equestrian Trail. Most of the trail construction for this segment would be built by the Alcoa Dike construction contractor through a Betterment Agreement. The trail proponent (Riverside County) would construct remaining features. This SEA/EIR Addendum provides NEPA compliance for the proposed construction of the trail and the action of issuing an outgrant for operation and maintenance of this trail segment; additional NEPA documentation would be prepared for other Prado Basin trail segments. Riverside County Parks and Recreation would maintain the trail per the outgrant. The trail passes through the Temporary Construction Easement (TCE) between the Alcoa Dike and the proposed Butterfield Connector and turns south at the terminus of Rincon Road and Butterfield Drive (Figure 8). The proposed SART would include 3H:1V fill slopes to meet existing ground. A 2,900-foot long “connector” segment of bike and equestrian trails would extend north of the Dike, along the edge of a Corps mitigation site that was restored to offset impacts of various SARMP features. Construction of the trail would begin after completion of the proposed Alcoa Dike.