FIO-River Road Dike Final SEA-EIR Addendum w Appendices_June 2021.pdf

FINAL

SUPPLEMENTAL ENVIRONMENTAL ASSESSMENT

ENVIRONMENTAL IMPACT REPORT ADDENDUM

FOR

SANTA ANA RIVER MAINSTEM PROJECT, PRADO DAM

SEPARABLE ELEMENT: RIVER ROAD DIKE

RIVERSIDE COUNTY, CALIFORNIA

(State Clearinghouse No. 1997071087)

PREPARED BY:

U.S. ARMY CORPS OF ENGINEERS

SOUTH PACIFIC DIVISION

LOS ANGELES DISTRICT

JUNE 2021

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FINDING OF NO SIGNIFICANT IMPACT

SANTA ANA RIVER MAINSTEM PROJECT

PRADO DAM SEPARABLE ELEMENT: RIVER ROAD DIKE

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. The Final Supplemental Environmental Assessment (SEA), dated June 2021, is for proposed modifications to the River Road Dike (RRD), a feature of the Santa Ana River Mainstem Project located in the Prado Dam Reservoir in the Riverside County, California.

The Corps has prepared this SEA to address modifications to the original design of River Road Dike, last presented in the 2001 Supplemental Environmental Impact Statement, to better align with current residential developments and roadways. The 2001 design protected farmlands and residential properties that have since been redeveloped and raised above the 566 feet elevation line. This SEA complies with the National Environmental Policy Act (NEPA) (42 USC 4321 et seq.), the Council on Environmental Quality regulations published at 40 CFR Part 1500 et seq., and the Corps’ NEPA regulations published at 33 CFR Part 230.

The Final SEA, incorporated herein by reference, evaluates two alternatives. The No Action Alternative, also known as Alternative 2: 2001 Design Alternative, is defined as constructing the River Road Dike embankment and floodwall according to the plan presented in the 2001 SEIS.

The 2001 Design location and design details differ from the Proposed Action. The Proposed Action, also known as Alternative 1, proposes design modifications for the River Road Dike. The Proposed Action Alternative is the recommended plan and includes:

• Constructing an 1,859-foot-long compacted earth fill dike with a maximum height of 18 feet with an average height of approximately 8 feet above existing grade, consisting of approximately 30,000 cubic yards of compacted fill. The crest width at the top of the dike would be 21 feet wide and sides would slope at 2.25H:1V. Both the landward-facing and reservoir sides of the dike would be armored with 18-inch-thick riprap with a 12-inch-thick layer of bedding. The dike would also be equipped with a 15-foot-wide asphalt paved road at the crest, and aggregate base course access roads along the landward and reservoir facing toes of the dike.

• Extensive site grading for a culvert, and open concrete and riprap channels to ensure positive drainage off-site. The 755 linear feet concrete-lined channel collects water from existing development on the land side of the dike and directs it to the two gated 48-inch RCP culverts that pass through the dike and over a 245 linear feet lined riprap channel.

• A secant pile wall consisting of four-foot diameter poured concrete piles, 75 feet in depth and approximately 267 feet in length, will be constructed parallel to the existing residential concrete wall at the south tie-in of the dike and will be flushed to the proposed dike elevation 567 feet to protect an existing sewer line in place.

For both alternatives, the potential effects were evaluated, as appropriate. A summary assessment of the potential effects of the recommended plan are listed in Table S-1:

Table S-1: Summary of Potential Effects of the Recommended Plan

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

All practicable and appropriate means to avoid or minimize adverse environmental effects were analyzed and incorporated into the recommended plan, which include the environmental commitments listed in Section 5 of the Final SEA. Of particular importance is the Corps’ environmental commitment to restore native vegetation of temporarily and permanently impacted habitat including within stream channel areas.

Public review of the draft SEA was completed on January 8, 2021. Comments were received from the Riverside County Water Conservation and Flood Control District and the City of Eastvale. All comments submitted during the public review period were responded to in the Final SEA. Copies of all comments received and responses to those comments are located in Appendix I of the Final SEA.

Subsequent to the publication of the draft SEA, the Corps modified the Proposed Action Alternative with the addition of the secant pile wall to protect-in-place an existing sewer line within the project site. The temporary construction easement has also been modified to include the entire 3.93-acre mitigation area. In addition, the 15-foot vegetation free zone has been extended to a maximum of 50 feet and would be established from each toe of the dike where a minor revision to the operation, maintenance, repair, replacement and rehabilitation (OMRRR) requirement has also been addressed. The landward side slope and 50-foot vegetation free zone (except for the 15-foot access roads within this area) would be planted with low-growing grasses. The disturbed areas outside of the 50-foot zone and the borrow area would be seeded or planted with native shrubs, forbs, and grasses. These modifications are included in the Final SEA.

The Corps provided applicable resource agencies updated information regarding project modifications subsequent to circulation of the draft SEA. The outcomes of consultation and approval processes described below are reflective of the recommended plan as described in the Final SEA.

Pursuant to section 7 of the Endangered Species Act of 1973, as amended, the Corps determined that the recommended plan will have no effect on federally listed species or their designated critical habitat.

Pursuant to Section 106 of the National Historic Preservation Act of 1966, as amended, the Corps determined that the recommended plan would have no historic properties affected. The Corps received a concurrence letter from the State Historic Preservation Office on April 16, 2021. The letter is included in Appendix H of the Final SEA. In the event that previously unknown cultural resources are discovered during the project, all ground disturbing activities shall cease until the Corps has met the requirement of 36 CFR 800.13 regarding post-review discoveries.

The project is subject to compliance with section 404 of the Clean Water Act. The discharge of fill material associated with the recommended plan has been found to be compliant with the section 404(b)(1) Guidelines (40 CFR 230). The 404(b)(1) Guidelines evaluation is found in Appendix D of the Final SEA.

An amended water quality certification pursuant to section 401 of the Clean Water Act was received from the Santa Ana Regional Water Quality Control Board (SARWQCB) on January 25, 2021. All conditions of the water quality certification have been incorporated into the Final SEA and shall be implemented in order to minimize adverse impacts to water quality. Since the project description was subsequently updated to include a maximum of 50 feet instead of a 15-foot vegetation free zone, which resulted in an additional 0.04 acres of impact to Waters of the U.S. for a total of 0.68-acre impact area, the Corps conducted additional coordination with SARWQCB staff and confirmed that no change or amendment to the Water Quality Certification is required at this time, and no additional offsetting measures would be required. A Project

Modification Report was prepared and sent to the SARWQCB to document this minor change in the project description. The 401 Certification, Project Modification Report, and email correspondence with the SARWQCB are included in Appendix E of the Final SEA.

The recommended plan emissions considered heavy duty construction equipment and commuter vehicles for all phases of construction during the project duration. Daily (pounds per day) and yearly (tons per year) emissions for the proposed project were calculated for the air quality analysis determination. Implementation of best management practices (BMPs) and environmental commitments during construction would avoid, reduce, and minimize impacts to air quality. Emissions generated by the proposed project are expected to be temporary and would be below the applicability rates. Thus, emissions from the proposed action would conform to the SIP. The Corps has determined that the proposed project is in compliance with the Clean Air Act, and that a conformity determination is not required for the recommended plan. The proposed project meets the requirements of Section 176(c) of the Clean Air Act.

All applicable environmental laws, executive orders, regulations and local government plans were considered in evaluation of alternatives and coordination with appropriate agencies and officials has been completed as documented in Sections 6 and 7 of the Final SEA. 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 recommended plan 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

17 June 2021 i

TABLE OF CONTENTS

1 PROJECT OVERVIEW

1.1 Authority and Background

1.2 Project Location

1.3 Previously Prepared Documents

1.4 Agency and Public Input

1.5 Objectives and Purpose and Need

2 PROJECT ALTERNATIVES

2.1 Alternative 1: Proposed Action

2.2 Alternative 2: 2001 Design

3 AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

3.1 Air Quality

3.2 Biological Resources

3.3 Recreation

3.4 Water Resources and Hydrology

3.5 Earth Resources

3.6 Cultural Resources

3.7 Land Use

3.8 Aesthetics

3.9 Noise

3.10 Socioeconomics & Environmental Justice

3.11 Transportation

3.12 Public Health and Safety

3.13 Public Services and Utilities

4 CUMULATIVE IMPACTS

4.1 Air Quality

4.2 Biological Resources

4.3 Recreation

4.4 Water Resources and Hydrology

4.5 Earth Resources

4.6 Cultural Resources

4.7 Land Use

4.8 Aesthetics

ii

4.9 Noise

4.10 Socioeconomics and Environmental Justice

4.11 Transportation

4.12 Public Health and Safety

4.13 Public Services and Utilities

5 ENVIRONMENTAL COMMITMENTS

5.1 Air Quality

5.2 Biological Resources

5.3 Recreation

5.4 Water Resources and Hydrology

5.5 Earth Resources

5.6 Cultural Resources

5.7 Land Use

5.8 Aesthetics

5.9 Noise

5.10 Socioeconomics and Environmental Justice

5.11 Transportation

5.12 Public Health and Safety

5.13 Public Services and Utilities

6 ENVIRONMENTAL COMPLIANCE

6.1 Federal Laws and Regulations

6.2 State Laws and Regulations

6.3 Local Laws and Regulations

7 AGENCY COORDINATION

8 PREPARERS AND REVIEWERS

9 CONCLUSION

10 REFERENCES

11 ACRONYMS AND ABBREVIATIONS

iii

Figures

Figure 1. Regional Project Location

Figure 2. Project footprint

Figure 3. Location of dike and floodwall in 2001 Design relative to the Proposed Action

Figure 4. Proposed River Road Dike construction design

Figure 5. Plan view of the Secant Pile Wall

Figure 6. 2001 Design Borrow Area 2 (yellow polygon with hash lines) and haul routes (blue line)

Figure 7. Special status species occurrence records and critical habitat

Figure 8. Temporary and Permanent Impacts to Vegetation from the Proposed Project

Figure 9. Existing vegetation within the Proposed Action Area

Figure 10. Disturbed riparian vegetation in the site

Figure 11. Ruderal vegetation within the site

Figure 12. Non-native riparian vegetation in the site

Figure 13. Vegetation and Cover Types within the 50-foot Vegetation-Free Zone

Figure 14. Location of proposed riparian mitigation site

Figure 15. Non-wetland waters of the U.S

Figure 16. Land use types surrounding the proposed River Road project site

Figure 17. City of Eastvale Zoning Designations

Figure 18. Map of final dike alignment and closest known HTRW

Figure 19. Utilities located near the southeast corner of the project footprint

Tables

Table 3-1 Federal Attainment Status Designation for the South Coast Air Basin (SCAB)

Table 3-2 Comparison of Proposed Project Daily Construction Emissions to SCAQMD

Table 3-3 Comparison of Proposed Project Annual Construction Emissions to

Table 3-4 Comparison of Proposed Project Daily O&M Emissions to SCAQMD Lbs/Day

Table 3-5 Comparison of Proposed Project Annual O&M Emissions to General Conformity de minimus

Thresholds

Table 3-6 Acres of affected riparian vegetation and proposed mitigation efforts

Table 3-7 Vegetation and Cover Types in Acres within the 15’ and 50’ Vegetation-Free Zone

Table 3-8 Jurisdictional Impacts

Table 3-9 Typical Noise Levels for Construction Equipment

Table 3-10 Demographic data for the city of Eastvale and Riverside County iv

Table 3-11 Environmental Justice Populations Data

Table 3-12 Annual Average Daily Traffic on Selected Roadways in the Project Area

Table 4-1 Projects within five miles of the proposed River Road Dike project site

Appendices

Appendix A - Construction Equipment List Appendix B - CalEEMod for Construction and O&M Appendix C - Geotechnical - HTRW Survey report Appendix D - 404(b)1 Evaluation Appendix E - 401 Certification Appendix F - Environmental Justice Screen Report Appendix G - Mail Distribution List Appendix H - SHPO Consultation Appendix I - Comment Letters/Response to Comments

River Road Dike SEA/EIR Addendum – June 2021 1 Project Overview

1 PROJECT OVERVIEW

This Supplemental Environmental Assessment/Environmental Impact Report (SEA/EIR) Addendum has been prepared by the U.S. Army Corps of Engineers (Corps) as a supplement to the Final Supplemental Environmental Impact Statement (SEIS) and Environmental Impact Report (EIR) for Prado Basin and Vicinity, Including Reach 9 and Stabilization of the Bluff Toe at Norco Bluffs, dated November 2001. The 2001 SEIS/EIR identified a number of protective dikes and embankments in the Prado basin necessary to provide protection to nearby residential developments, businesses and infrastructure from a proposed expansion of the reservoir. This expansion is part of the Prado Separable Element of a comprehensive flood risk management project (the Santa Ana River Mainstem Project or SARMP) that extends throughout much of the Santa Ana River watershed. One of the protective features described in the 2001 SEIS/EIR is the River Road Dike, which is the focus of this SEA/EIR Addendum. Design modifications have been developed by the Corps’ Engineering Division. Construction of the dike is scheduled to begin in the summer 2021 and would continue for approximately twenty (20) months. It is possible that the proposed project would be built in stages, with multiple start dates and construction periods for various sections of the proposed project depending on land acquisition and utility relocations schedule, environmental windows and weather delays. Clearing and grubbing activities will occur outside of the bird nesting season. Construction phasing may result in an extension of the overall project duration, i.e.

beyond the approximate duration of twenty months.

The Corps is the lead agency under the National Environmental Policy Act (NEPA) and the lead agency under California Environmental Quality Act (CEQA) is the Orange County Flood Control District (OCFCD).

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 would consider the information in this document along with other information that may be presented during the NEPA/CEQA process. As identified in the Prado and Vicinity SEIS/SIER (2001) and this SEA/SEIR Addendum, these agencies may include:

• California Department of Fish and Wildlife (CDFW)

• Santa Ana Regional Water Quality Control Board (RWQCB)

• U.S. Fish and Wildlife Service (USFWS)

• City of Eastvale

• Riverside County Flood Control and Water Conservation District

This SEA/EIR Addendum describes the proposed modifications to the dike design and location and analyzes potential environmental impacts associated with its construction due to the design modifications and changed conditions. This document has been prepared pursuant to NEPA (42 United States Code 4321 et seq.), Council on Environmental Quality regulations published at 40 Code of Federal Regulations (CFR) Part 1500, et seq., other environmental laws, Executive Orders, Corps regulations, CEQA (Public Resources Code Section 21000, et seq.) and the State of California CEQA Guidelines (California Code of Regulations [CCR], Title 14, Section 15000, et seq.). This document complies under the old NEPA regulations (prior to July 2020 NEPA updates) as this is the continuation of the original project with a few minor modifications to the original design.

1.1 Authority and Background

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). It originally 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 term referred in most cases to the 190-year flood event. Construction of the SARMP commenced in fiscal year 1989.

In 2001, the Corps submitted 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 pursuant to Section 309(a) of WRDA of 1996, which required the Corps to review the Prado Dam feature, a component 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 reservoir storage capacity from 217,000 acre-feet to 362,000 acre-feet and to enable the release of 30,000 cubic feet per second (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 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 River Road Dike is a feature of the Prado Dam separable element. The River Road Dike was analyzed in the 2001 LRR and SEIS/EIR for the purpose of providing flood risk protection to the public and privately owned properties in the project area.

1.2 Project Location

The proposed River Road Dike project is located in the city of Eastvale, east of Hellman Avenue between Shoreham Street and River Road, within Riverside County, California (Figure 1).

Figure 1. Regional Project Location

The proposed modifications for River Road Dike consists of a compacted earth fill dike, approximately 1,859 feet in length. At the south end, the dike would abut the existing raised ground of the residential tract (Tract No. 31961) in a nearly east-west direction. The dike would then turn north across a tributary drainage to Mill Creek and former dairy land and then turn west and parallel the southern edge of residential tracts (Tract No. 30905 and Tract 29997), ending just west of Port Arthur Drive (Figure 2). A concrete channel would be constructed in the southeastern corner of the site to allow drainage into Mill Creek. The concrete channel will be extended 755 linear feet to the two proposed 48" culverts. An additional proposed 245 liner feet lined riprap channel west of the dike will connect to the concrete channel on the landward side.

Figure 2. Project footprint

1.3 Previously Prepared Documents

The environmental impacts of the SARMP have been evaluated in several documents since the initial SARMP study commenced in the 1970s. Below is a partial list of environmental documents that have been completed for the SARMP and may be referenced throughout this SEA/EIR Addendum.

• 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.

• Santa Ana River Mainstem including Santiago Creek Phase II General Design Memorandum and Supplemental Environmental Impact Statement (GDM/SEIS), United States Army Corps of Engineers, Los Angeles District, 1988.

• Prado Basin and Vicinity, Including Reach 9 and Stabilization of the Bluff Toe at Norco Bluffs SEIS/Environmental Impact Report (EIR), United States Army Corps of Engineers, Los Angeles District, 2001.

1.4 Agency and Public Input

This document was made available for public review and comment for a period of thirty (30) days, beginning December 8, 2020 through January 8, 2021. Notification of availability of the draft for public review was made on the Corps website, social media post, as well as mail distribution to interested parties (Appendix G). The Corps received comment letters from the Riverside County Flood Control and Water Conservation District (RCFC&WCD) and the city of Eastvale. Comments letters and responses to comments are located in Appendix I.

1.5 Objectives and Purpose and Need

The federal objective of the SARMP is to provide flood risk management within the Santa Ana River watershed. The SARMP ranges over the counties of San Bernardino, Riverside, and Orange in an area that includes residences, thousands of businesses and other structures. Over two million people populate this area. River Road Dike is one of the last remaining features of Prado Basin separable element of the SARMP to be implemented. Other remaining features include Alcoa Dike Phase 1 and Auxiliary Embankment Phase 2 (both currently under construction), Alcoa Phase 2, Norco Bluffs, Prado Spillway modifications including a tie-in to the Auxiliary Embankment, minor modifications to other existing structures, and continued habitat restoration and mitigation management. Other features of SARMP remain to be constructed or completed in the Santa Ana River below Prado Dam and in Santiago Creek.

The River Road Dike was approved as part of the LRR and SEIS/EIR as a value-engineering solution to reduce otherwise-required land acquisition for the Prado Dam Separable Element.

Statement of Need Operation of the Prado Dam for flood risk management once the spillway raise is complete will inundate lands up to elevation 566 feet in the absence of constructed features that otherwise allow for basin operation.

Statement of Purpose Completion of the proposed design modification of River Road Dike would better align with residential developments and roadways that have since been redeveloped with the residential developments raised above the 566 feet elevation line. The overall purpose of the project, however, is to allow for full operation of the Prado Dam after the completion of the spillway raise.

2 PROJECT ALTERNATIVES

Two alternatives will be considered for environmental analysis in this document.

Alternative 1: Proposed Action

Alternative 2: 2001 Design Alternative, also known as the Previously Approved Design Alternative, which is defined as constructing the River Road Dike embankment and floodwall exactly according to the plan presented in the 2001 SEIS/EIR. Note that the location and design details differ from the Proposed Action (Figure 3). Since 2001, residential developments (housing tract #29997) were constructed above the 566’ elevation. The 2001 dike footprint would therefore be infeasible as it would overlap with and run along many new residential communities built since 2001 in the cities of Eastvale and Norco. This alternative is the No Action Alternative.

Table 2-1 below presents a summary of changes between the Proposed Action and the 2001 Design.

Table 2-1. Summary of changes between the 2001 Design and the Proposed Action.

2001 Design Proposed Action

Lo ca tio n

The 2001 Design included two features: a dike and a flood wall.

The dike would be constructed on the westerly side of Hall Road, north of River Road.

The floodwall would be constructed within Norco’s public road right-of-way, along the westerly side of River Road at Bluff Street.

The Proposed Action includes a dike. The dike would be located in a 70-acre site just southeast of the intersection of Hellman Avenue and Shoreham Street in the city of Eastvale. The property is owned by

OCFCD.

Si ze

The dike would be approximately 4,500 linear feet and would range in height from 7 to 14 feet for a short distance.

The floodwall would be 6 feet high.

The proposed dike would be approximately 1,859 total linear feet of earthen dike. Dike height would range from 5 to 16 feet above existing grade.

A secant pile wall consisting of four-foot diameter poured concrete piles, seventy-five foot in depth and approximately 267’ in length, will be constructed parallel to the existing residential concrete wall at the south tie-in of the dike and will be flushed to the proposed dike elevation 567’ to protect an existing sewer line in place.

De si gn

The proposed floodwall will be an “L-wall” design and will replace an existing buff colored reinforced masonry block wall.

The dike would have 2.25:1 horizontal-to-vertical side (H:V) slopes and would vary in width from about 19 feet to 98 feet.

The crest width at the top of the dike would be approximately 21 feet wide with 2.25:1 H:V side slopes on each side of the dike.

Ac ce ss A 13 to 16 feet wide maintenance road would be located on top of the proposed dike and another on the outer side.

The dike would be equipped with 15-foot-wide asphalt paved road at the crest and aggregate base course access roads along both the landward and the reservoir facing toes of the dike.

2001 Design Proposed Action

Dr ai na ge

Seven 36-inch diameter reinforced concrete drain pipes would ensure proper drainage for the watershed draining toward the dike.

There would be extensive site grading. Two 48-inch culverts and open concrete channels on the landward side of the dike and a lined riprap channel west of the dike would be constructed to ensure positive drainage to Mill Creek.

Su rf ac e

M at er ia ls The dike would be covered with 18-inch layer riprap on the reservoir facing side above a sheet of filter fabric to provide protection from wave action. The landward facing side would be hydroseeded with grasses.

The dike would be armored with 18-inch-thick riprap with 12-inch-thick bedding on both the landward and reservoir-facing sides.

Fi ll

M at er ia ls

A total of 50,225 cubic yards of earth would be excavated from an adjacent parcel to be used as compacted fill in the dike. In addition, 81,571 tons of riprap would be imported to the project for placement on the basin side of the dike.

Dike construction would include excavation of approximately 36,000 cubic yards of suitable soil from the onsite borrow site then hauling and placing compacted fill within the limits and grades indicated in the dike description. Dike construction also includes placement of 18-inch-thick riprap with 12-inch maximum stone size over a 12-inch-thick layer of bedding material. The placement limits of the riprap would be three feet below existing grade to the crest of the dike.

Ve ge ta tio n- Fr ee Z on e

-- Maintain a 50-foot Vegetation Free Zone (VFZ) from the toe of the dike to comply with levee safety certification requirements

River Road Dike SEA/EIR Addendum – June 2021 2 Project Alternatives

No Construction Alternative

The No Construction Alternative was addressed in the 2001 SEIS/EIR, along with the previously approved design. The No Construction Alternative would not meet the purpose and need and is not carried forward in this document.

Figure 3. Location of dike and floodwall in 2001 Design relative to the Proposed Action.

2.1 Alternative 1: Proposed Action

Figure 4. Proposed River Road Dike construction design

Dike Design

The proposed modification for River Road Dike is a 1,859-foot long compacted earth fill dike (Figure 4).

The dike would have a maximum height of 18 feet with an average height of approximately 8 feet above existing grade. The dike would consist of approximately 30,000 cubic yards of compacted fill. The crest width at the top of the dike would be 21 feet wide and sides would slope at 2.25 horizontal feet to one vertical foot on each side of the dike (2.25H:1V). Both the landward-facing and reservoir sides of the dike would be armored with 18-inch thick riprap with a 12-inch thick layer of bedding.

The dike would also be equipped with 15-foot wide asphalt paved road at the crest, and aggregate base course access roads along the landward and reservoir facing toes of the dike. There will be extensive site grading, a culvert and open concrete channels to ensure positive drainage off-site. The concrete-lined channels collect water from existing development on the land side of the dike and directs it to the two 48-inch reinforced concrete pipe (RCP) culverts that pass through the dike. The RCP culverts will be gated and allow the ponding area on the land side of the dike to drain to the reservoir side of the dike through and over a 245-ft long riprap-lined channel.

A secant pile wall consisting of four-foot diameter poured concrete piles, seventy-five foot in depth and approximately 267 feet in length, will be constructed parallel to the existing residential concrete wall at the south tie-in of the dike and will be flushed to the proposed dike elevation 567’ to protect the Jurupa Community Services District (JCSD) 42-inch RCP sewer line in place (Figure 5).

Figure 5. Plan view of the Secant Pile Wall

Staging Area

The staging area is located in the northwest corner, approximately 1,000 feet southeast of the intersection of Hellman Avenue and Shoreham Street (Figure 4). The staging area would be used for storage of construction equipment and materials. The staging area would be cleared and grubbed prior to project construction and it would be restored with native upland vegetation upon completion.

Haul Roads

A vehicle ingress and egress entry point to the site would be located on Hellman Avenue, approximately 300 feet south of the intersection of Hellman Avenue and Shoreham Street (Figure 4). Construction traffic would only affect civilian traffic when entering and exiting the ingress and egress location. Traffic control would be provided at the ingress and egress location.

Construction Phasing

It is anticipated that River Road Dike will be constructed in three major phases: 1) site preparation, 2) construction of the dike and 3) grading for interior drainage, site access and hydroseeding.

1) Site Preparation Site preparation consists of clearing and grubbing, stripping, and dike foundation excavation.

Clearing and grubbing activities include removing and disposing of objects that may obstruct work performed in the project area. This includes felling, trimming and cutting of trees and other vegetation into sections for removal as well as removing and disposing of any existing structures that may impede work. Stripping consists of removal of the top 12 inches of soil within the grading limits of the project. Dike foundation excavation includes removing unsuitable soil within the footprint of the dike. Removal limits can range from three to six feet deep.

2) Dike Construction Construction of the dike will consist of placing suitable compacted fill and riprap. Dike construction will include excavation of approximately 36,000 cubic yards of suitable soil from the onsite borrow site (as shown in Figure 4) then hauling and placing compacted fill within the limits and grades indicated in the dike description. Dike construction also includes placement of riprap with 12-inch maximum stone size over 12-inch thick layer of bedding material on the reservoir side slope of the dike. The placement limits of the riprap will be three feet below existing grade to the crest of the dike.

The proposed dike would reduce the flood storage of the Prado Basin by 115.2 acre-feet, or 0.04 percent of the total future volume of the facility (292,026 acre-feet) compared to the 2001 design. Use of the proposed borrow area would restore a portion of this lost reservoir capacity by excavating approximately 36,000 cubic yards from this onsite borrow site area. The Corps Hydraulics and Hydrology Section (H&H) has determined that the loss of volume created by River Road Dike construction, and all other planned dikes and dikes already in place, with respect to the overall available project storage needs, is negligible.

3) Site Grading and Hydroseeding Interior drainage grading, site access, and hydroseeding will consist of grading the project site to promote positive drainage, constructing access roads to provide access to major project features, and hydroseeding to restore native vegetation throughout the project site. Site grading activities include placing and moving soil in a matter that will promote positive drainage throughout the site to Mill Creek. Slopes indicated for the site grading are generally a minimum of one percent to prevent ponding of water within the site. Proposed access roads at the toe of the dike will be graded at a higher elevation to ensure water is directed away from the dike. A 15-foot paved road will be constructed on the crest of the dike. Six-inch-thick by 15-foot wide aggregate base course access roads will be constructed on the landward and reservoir side toes of the dike to provide access to major project features. A maximum 50-foot vegetation free zone would be established from each toe of the dike. The landward side slope and 50-foot vegetation free zone (except for the 15-foot access roads within this area) would be planted with low-growing grasses. The disturbed areas outside of the 50-foot zone and the borrow area would be seeded or planted with native shrubs, forbs and grasses to compensate for adverse effects of construction on the land.

Construction Equipment

Construction equipment would include a combination of concrete pumpers, water trucks, waste trucks, haul trucks, dump trucks, scrapers, loaders, dozers, cranes, back hoes, soil compactors, rollers, graders, vegetation chippers, and excavators.

Construction Schedule

Construction is expected to begin in the summer of 2021 for an approximate duration of 20 months.

Clearing and grubbing is proposed to be completed outside of the bird breeding season to avoid impacts to nesting birds. If needed, sound walls would be constructed prior to March 1 of each year. Funding constraints, weather delays, and other issues could potentially move the construction completion timeline beyond the 20-month duration into late 2023.

Daily construction would normally occur between 7:00 a.m. and 6:00 p.m., Monday through Friday, although additional hours or Saturday work may occasionally be permitted for specific activities. The construction contractor would need to obtain a variance from local noise ordinances if needed in those circumstances.

Water Source

The construction contractor would determine and acquire a water source for construction of the proposed project. The most likely source is from the Jurupa Community Services District (JCSD). City of Eastvale requires the use of reclaimed water for construction purposes and will not authorize temporary potable water meters to existing fire hydrants for construction activities.

Source of Material

The embankment would be constructed using riprap imported from a local quarry. For the purposes of this analysis, it is assumed that the nearest quarry would be used. Fill material for construction would be borrowed from the onsite borrow area as shown in Figure 4.

Disposal Sites

Construction of the Proposed Action would produce organic, inorganic, and unsuitable construction materials which must be disposed of in the manner and areas specified so that the proposed project site would be restored after completion of construction. Organic materials, trees, shrubs, and abandoned timber structures, would be disposed of by hauling to a local commercial site. Topsoil containing organic material may be stockpiled and spread on embankment slopes or borrow areas as a part of site restoration. Disposal of these materials by burning or burying at the proposed project site would not be permitted. Inorganic materials would include, but are not limited to, broken concrete, rubble, asphaltic concrete, metal, and other types of construction materials. These materials would also be taken to a commercial landfill.

Dewatering

If dewatering is necessary, the construction contractor would be responsible for obtaining and complying with a dewatering permit from the Santa Ana Regional Water Quality Control Board.

Future Operation and Maintenance

Future operation and maintenance, including routine inspections and minor repairs, of the embankment and its associated project features would be required after construction is completed and conducted by OCFCD. The following activities would occur:

• Routine and special inspection and patrol with pickup trucks and sport utility vehicles weekly to daily during flood season, and weekly to monthly during the non-flood season;

• Mobilizing dump trucks to haul stones and using hydraulic excavators to place stones along eroded areas of the embankment to protect and reinforce the dike as necessary during floods;

• Periodic weeding and patching stone and aggregate base course maintenance roads along the landward and reservoir facing toes of the dike;

• Rodent control;

• Periodic mending of fencing and painting metal gates;

• Maintenance of hydroseeded and mitigation restoration areas. This includes periodic mowing, weeding or other maintenance of the 50 ft VFZ to prevent encroachment of deep-rooted or high growing vegetation that could interfere with inspection, maintenance or integrity of the dike structure.

Environmental Commitments/Avoidance and Minimization Measures During Construction

Due to the limited nature of construction disturbance, the activities of the Proposed Action are not expected to cause any long term adverse environmental effects. Environmental commitments and best management practices from the 2001 SEIS/EIR along with new commitments, as summarized in Section 5 of this document, would be implemented for the proposed action to ensure that potential construction-related effects are either avoided or minimized.

2.2 Alternative 2: 2001 Design

2001 Design: Floodwall

The previously approved floodwall would be constructed within Norco’s public road right-of-way, along the westerly side of River Road (Figure 3). In addition to the wall, a flowage easement would be required for approximately half of the parcel located at the southeast corner of River Road and Bluff Street.

There are six homes along the previously approved River Road floodwall. All six are above 566-ft elevation, but the backyards are not. The purpose of the floodwall is to prevent reservoir water from flooding property below 566-ft that would otherwise be required to be acquired. Each of these properties is on approximately half acre lots with no permanent structures below 566-ft elevation.

The proposed floodwall would be a 6-ft high “L-wall” design and would replace an existing buff-colored reinforced masonry block wall. The proposed wall would be pattern stamped and colored to resemble the existing wall. The floodwall would be placed at the right-of-way line between residential homes and River Road. The footing, for the wall, would be as much as 12-ft wide on the flood side of the wall. There is approximately 12-ft between the existing masonry wall and the existing curb and gutter along River Road. The area between the masonry wall and curb and gutter is currently earthen and serves as a footpath. When the proposed wall footing is complete, it would serve as a sidewalk along this area.

2001 Design: Dike

The previously approved dike would be approximately 4,500 feet in length and would range in height from 7 to 14 feet (Figure 3). It would generally follow the perimeter of the parcels to be protected (refer to 2001 SEIS/EIR Appendix D) and as such, would diverge somewhat from the 566-ft elevation contour.

The dike would have 2.25:1 (H:V) slopes and would vary in width from 6 to 30 meters.

A 12 to 15-ft wide maintenance road would be located on top of the proposed dike and another on the outer side. Seven 36-inch diameter reinforced concrete drain pipes would ensure proper drainage for the watershed draining toward the dike. On the side facing towards Prado Basin, the dike would be covered with an 18-inch layer riprap above a sheet of filter fabric to provide protection from wave action. The slope facing outward away from the basin would be hydroseeded with grasses. The total footprint of the dike encompasses approximately 5.93 acres.

A total of 50,225 cubic meters of earth would be excavated from an adjacent parcel to be used as compacted fill in the dike. In addition, 8,157 tons of riprap would be imported to the project for placement on the basin side of the dike. Other materials to be imported include 91-cm diameter reinforced concrete pipe for drains, 19,400 square meters of geotextile, 7,100 square meters of filter cloth, and 8,989 linear feet of chain link fence.

The dike would reduce the flood storage of the Prado Basin by 307 acre-feet, or 0.11 percent of the total future volume of the facility (292,026 acre-feet) as evaluated in a 1995 Value Engineering Study.

Replacement of the lost volume would include excavating approximately 453,000 cubic meters (366 acre-feet) from a site identified in Appendix D of the 2001 SEIS/EIR. After the 1995 study, a significant amount of residential development occurred in the area. A majority of the residential developments were raised above 566' therefore significantly changing the existing conditions. OCFCD prepared a supplemental study in 2010 to document changes in scope and performed a volume calculation based off of the 2015 reservoir survey. As determined with the reduction in scope under the current plan (Alternative 1), loss volume capacity was determined to be negligible and therefore would not be replaced. OMRRR actions under the 2001 Design Alternative would be the same as those identified under the Proposed Action Alternative in section 2.1-1.

Implementation of this alternative would require the use of a borrow area and haul routes different from the Proposed Action. As identified in the 2001 SEIS/EIR, the fill material is anticipated to be obtained from the northern portion of the Prado Basin, referred to as Borrow Area No. 2, which is located at the confluence of Mill Creek and Chino Creek near the southern terminus of Cucamonga Avenue (Figure 6). Haul routes to transport fill to the project site would be north along Cucamonga Ave, east on Chino Corona Road and south on Hellman Ave.

Future Operation and Maintenance

Future operation and maintenance actions under the 2001 Design Alternative would be the same as those identified in the Proposed Action Alternative above.

Figure 6. 2001 Design Borrow Area 2 (yellow polygon with hash lines) and haul routes (blue line)

River Road Dike SEA/EIR Addendum – June 2021 3 Affected Environment and _____________________________________________________________Environmental Consequences

3 AFFECTED ENVIRONMENT AND ENVIRONMENTAL

CONSEQUENCES

This section summarizes the existing condition of the physical and human environment within the area of potential effects surrounding the project site. It also provides an assessment of potential impacts to the environment. Impacts on environmental resources were originally identified and mitigated for in the 2001 Final SEIS/EIR. Additional or different impacts resulting from the proposed modifications are identified herein and are addressed accordingly. Construction-related environmental commitments from the 2001 Final SEIS/EIR, additional environmental commitments developed for the Proposed Action project design features and best management practices (BMPs) have been incorporated into the project description of each alternative to avoid and/or reduce potential impacts. The finding or conclusion of level of significance following each resource category assumes that appropriate measures will be applied. A full list of environmental commitments that are applicable to the River Road Dike feature can be found in Chapter 5 of this document.

3.1 Air Quality

Air quality conditions in the proposed project area are similar to those described in other Corps environmental documents prepared for Prado Basin features, including the 2017 SEA/EIR Addendum for the Auxiliary Embankment and Floodwall Phase 2 project, the 2013 California Institution for Women’s Dike SEA/EIR Addendum, and the 2018 Alcoa Dike SEA/EIR Addendum. The Corps’ 2001 SEIS/EIR is also a reference for air quality in the proposed project area, and it documented anticipated air quality impacts from construction of all Prado Basin and Vicinity projects. These reports are hereby incorporated by reference, as per 40 CFR 1502.21.

3.1.1 Existing Conditions

The proposed project area is entirely within the Prado Flood Control Basin’s Mill Creek drainage area, which is part of the larger Prado Dam Reservoir basin area, and is located in the central part of the South Coast Air Basin (SCAB) of California, an approximate 6,600 square mile (mi²) area encompassing Orange County and the non-desert portions of Los Angeles, Riverside, and San Bernardino counties. SCAB is bounded by the Pacific Ocean to the west and the San Gabriel, San Bernardino, and San Jacinto Mountains to the north and east. Air quality in the SCAB is regulated by federal, state, and regional control authorities, including the U.S. Environmental Protection Agency (EPA); the California Air Resources Board (ARB), which is part of the California Environmental Protection Agency (Cal EPA); the South Coast Air Quality Management District (SCAQMD) and the Southern California Association of Governments (SCAG).

Regional Air Quality Air pollutant emissions in the SCAB are generated from stationary, mobile, and natural sources.

Stationary sources can be divided into two major subcategories: point and area sources. Point sources occur at an identified location and usually are associated with manufacturing and industry. Examples are boilers or combustion equipment that produce electricity or generate heat. Area sources are distributed widely and produce many small emissions. Examples of area sources include residential and commercial water heaters, painting operations, portable generators, lawn mowers, agricultural fields, landfills, and consumer products such as barbeque lighter fluid and hair spray. Construction activities that create fugitive dust such as excavation and grading also contribute to area source emissions. Mobile sources refer to emissions from on- and off-road motor vehicles, including tailpipe and evaporative emissions.

On-road sources may be operated legally on roadways and highways. Off-road sources include aircraft, trains, and construction equipment. Mobile sources account for the majority of the air pollutant emissions within the air basin. Air pollutants also can be generated by natural sources such as when fine dust particles are pulled off the ground surface and suspended in the air during high winds.

To protect the public health and welfare, the federal government has identified common air pollutants (also known as “criteria air pollutants”) and established ambient air quality standards for these pollutants through the Federal Clean Air Act and the California Clean Air Act. The six air pollutants for which Federal standards have been promulgated and that are most relevant to air quality planning and regulation in the air basins include ozone (O3), carbon monoxide (CO), sulfur dioxide (SO2), nitrogen dioxide (NO2), lead (Pb) and suspended particulate matter (PM). PM comes in a range of sizes and PM emissions are regulated in two size classes: Particulates up to 10 microns in diameter (PM10) and particulates up to 2.5 microns in diameter (PM2.5). PM10 and PM2.5 are so small that they can enter the lungs and cause serious health problems.

Air pollutants are classified as primary or secondary pollutants. Primary pollutants are emitted directly into the atmosphere and include carbon monoxide, nitrogen dioxide, particulate matter, sulfur dioxide, and lead. Ozone is considered a secondary pollutant because it is formed through a photochemical reaction in the atmosphere with volatile organic compound (VOC) and nitric oxide in the presence of sunlight.

While ambient air quality standards have been developed specifically for O3 and NOX, there is no National Ambient Air Quality Standard (NAAQS) for VOCs. VOCs include many compounds of carbon.

There are certain classes of carbon compounds that are not VOCs, including: carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates, ammonium carbonate, and…