J.05_EA_Final_Arroyo_Colorado.pdf

Environmental Assessment Improvements to the

Arroyo Colorado North Levee Project

Lead Agency:

United States Section, International Boundary and

Water Commission El Paso, Texas

June 2009

ENVIRONMENTAL ASSESSMENT

IMPROVEMENTS TO THE

ARROYO COLORADO FLOODWAY

IN HIDALGO AND CAMERON COUNTIES

Lead Agency:

UNITED STATES SECTION,

INTERNATIONAL BOUNDARY AND WATER COMMISSION

UNITED STATES AND MEXICO

Technical Support:

Parsons

8000 Centre Park Dr., Suite 200 Austin, Texas 78754

USIBWC Contract IBM04D0002, Task Order IBM09T0016

JUNE 2009

COVER SHEET

ENVIRONMENTAL ASSESSMENT

AND

FINDING OF NO SIGNIFICANT IMPACT

FLOOD CONTROL IMPROVEMENTS TO THE

ARROYO COLORADO FLOODWAY

Lead Agency: United States Section, International Boundary and Water Commission

Proposed Action: Raising approximately 11 miles of levee along the Divisor Dike and Arroyo Colorado Floodway (ACF) beginning at Divisor Dike near the juncture point of the ACF and the North Floodway.

Report Designation: Environmental Assessment (EA)

Abstract: The United States Section, International Boundary and Water Commission (USIBWC) is considering raising levee segments along the Arroyo Colorado starting at the Divisor Dike near the juncture point of the Arroyo Colorado and the North Floodway in Hidalgo County and ending at White Ranch Road in Cameron County, Texas. The Arroyo Colorado was divided into two reaches for planning purposes. Levee rehabilitation would take place on the north side of the Arroyo Colorado levee sections from Divisor Dike to approximately levee mile 7.0 (near the Hidalgo/Cameron county line) (6.9 miles) and from west of Santa Maria Road (FM 2556), through the Willacy Canal area, to White Ranch Road (4.1 miles). Approximately 84 percent of the two reaches would not require fill material to be placed on top of the levee; therefore, no extension of the levee footprint would be required.

The proposed action would increase the height of the levee up to 2 feet for approximately

8.6 percent of the 11-mile segment. Approximately 4 percent of the levee height would be increased from 2 to 4 feet, and approximately 2.4 percent would be increased from 4 to 6 feet.

Moderately higher increases (greater than 6 feet) would be needed in small levee segments accounting for less than 1.2 percent of the total length.

The EA assesses potential environmental impacts of the proposed action and the no action alternative. Potential impacts on natural, cultural, and other resources were evaluated, and mitigation measures were incorporated into the proposed action. A Finding of No Significant Impact was issued for the proposed action based on a review of the facts and analyses contained in the EA.

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lmprovements to the Arroyo Colorado Floodway Environmental Assessment Finding of No Significant Impact

FINDING OF NO SIGNIFICANT IMPACT

Flood Control lmprovements to the Arroyo Colorado

LEAD AGENCY: United States Section, International Boundary and Water Commission, United States and Mexico (USIBWC).

BACKGROUND

The USIBWC is authorized to construct, operate, and maintain any project or works projected by the United States of America on the Lower Rio Grande Flood Control Project (LRGFCP) as authorized by the Act of the 74th Congress, Sec. I Ch. 561 (H.R. 6453), approved August 19, 1935 (49 Stat. 660), and codified at 22 USC Section 277, 277a, 277b, 277c, and Acts amendatory thereof and supplementary thereto. The LRGFCP was constructed to protect urban, suburban, and highly developed irrigated farmland along the Rio Grande Delta in the United States and Mexico.

An interior floodway system is a component of the LRGFCP of the Arroyo Colorado Floodway (ACF) that conducts floodwater diverted from the Rio Grande to the Laguna Madre in the Gulf of Mexico. Diverted water enters a Main Floodway that branches near Mercedes, Texas into a North Floodway, south branch, and the ACF. The USIBWC prepared this Environmental Assessment (EA) for the proposed action to improve flood control and flood containment capacity along the Divisor Dike and ACF.

The Arroyo Colorado is an ancient distributary of the Rio Grande, and it serves as drainage for crop irrigation, municipal wastewater returns, and as a floodway during periods of heavy precipitation in the lower Rio Grande Valley. The beginning of this project is a 2.1-mile Divisor Dike near the juncture point of the Arroyo Colorado and the North Floodway in Hidalgo County, extending a total of 6.9 miles to the Willacy Canal. The remaining segment is

4.0 miles from the Willacy Canal ending at White Ranch Road in Cameron County, Texas.

PROPOSED ACTION

The proposed action will improve flood control along the Divisor Dike and ACF. The project begins at Divisor Dike near the juncture point of the Arroyo Colorado and the North Floodway in Hidalgo County to approximately levee mile 7.0 near the Hidalgo/Cameron county line, and from west of Santa Maria Road (FM 225 1) through Willacy Canal area to White Ranch Road in Cameron County. The proposed levee rehabilitation improvements consist of: 1) raising the top-of-levee elevation; 2) conducting geotechnical investigations and testing to determine the type and extent of any required remediation improvements due to slope stability, seepage, levee settlement; and 3) modifying, if necessary, hardware or structures located along the levee reaches. Any structure modifications would comply with the Texas Historical Commission recommendations.

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Improvements to the Amyo Colorado Floodway

The top elevation of the levee-raising improvements will be to provide containment of flood flows with a minimum freeboard of 3 feet for water surface elevations as calculated in the USIBWC 2003 Hydraulic Model for the LRGFCP. Raising the levee from the centerline of the levee is assumed for analyses, but raising the levee on the riverside of the levee is possible where right-of-way (ROW) is a constraint.

Fill material from commercial sources will be added to the existing levee to bring flood containment to its original design specifications. The proposed action will increase the height of the levee up to 2 feet for approximately 8.6 percent of the 1 1 -mile segment. Approximately 4 percent of the levee height will be increased from two to 4 feet, and approximately

2.4 percent will be increased from four to 6 feet. The existing levee is a raised trapezoidal compacted-earth structure with a crown width of 16 feet, a typical height ranging from 10 to 15 feet, and approximately 3:l side slope ratio (horizontal run : vertical rise). For a typical levee cross-section at the ACF that will require additional fill material the levee footprint will be expanded at a 1 :6 ratio (crown height: footprint length). The lateral expansion could be equally divided between the riverside and landside (centered expansion) or entirely on one side (offset expansion). Moderately higher increases will be needed in a small segment that accounts for less than 1.2 percent of the total length. In areas where existing topography is too steep to allow levee expansion, construction solutions, including armored banks (riprap) or retaining walls will be used.

Footprint expansion, when required, will take place inside the maintained floodway, and entirely within the USIBWC ROW. In some instances, adjustment in levee slope will be made to eliminate the need for levee footprint expansion when required due to construction constraints or for protection of biological or cultural resources. Construction constraints include; the presence of irrigation drains or canals as well as structural features abutting or built into the levee along some reaches of the levee system, or urban development in the immediate vicinity of the levee system. The need for excavation outside the levee structure is not anticipated.

ALTERNATIVES TO THE PROPOSED ACTION

A no action alternative was evaluated for the ACF levee system. This alternative will retain the existing configuration of the system, as designed over 30 years ago, and the current level of protection currently associated with this system. Under severe storm events, current containment capacity may be insufficient to fully control Rio Grande flooding, including risks to personal safety and potential property damage.

SUMMARY OF FINDINGS

Pursuant to the National Environmental Policy Act (NEPA) guidance (40 Code of Federal Regulations 1500- 1508), The President's Council on Environmental Quality issued regulations for implementing NEPA, which included provisions for both the content and procedural aspects of the required EA. The USIBWC completed an EA of the potential environmental consequences of raising the ACF levee system to meet current requirements for flood control.

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Improvements to the Arroyo Colorado Floodway

The EA, which supports this Finding of No Significant Impact, evaluated the proposed action and no action alternative.

LEVEE SYSTEM EVALUATION

No Action Alternative

The no action alternative was evaluated as the single alternative action to the proposed action.

The no action alternative will retain the current configuration of the ACF levee system, with no impacts to biological and cultural resources, water resources, land use, soil, community resources, or environmental health issues. In terms of flood protection, however, current containment capacity under the no action alternative may be insufficient to fully control Rio Grande flooding under severe storm events, including associated risks to personal safety and property.

Proposed Action

Biological Resources

Biological resources near the levee systems are dominated by agricultural fields, rangelands, and non-native grasslands. There are some woody species along the margins of the Arroyo Colorado, drainage ditches from irrigation fields, and adjacent to borrow pits. The 160-foot wide biological survey corridor, centered on the existing levee, includes approximately 221 acres, primarily composed of non-native grasslands dominated by buffelgrass and king ranch bluestem or rangelands.

The proposed action will raise the levee using a centered expansion, except in areas south of La Feria reservoir, where an offset expansion will be utilized. The proposed levee expansion will remove non-native grasslands on the levee slopes and adjacent areas. Native grasses will be planted at the completion of the project. The levee expansion will not occur in wooded areas.

There are wetlands near the proposed levee expansion, and less than one-half acre of non-jilrisdictional wetlands will be affected by the levee expansion. No habitats used by federally or state-listed threatened or endangered species will be impacted by the levee expansion.

In areas adjacent to sensitive areas such as water bodies, levee expansion may be altered to an offset expansion toward the riverside of the levee to avoid affecting sensitive resources. In areas where the existing topography is too steep to allow levee expansion, construction solutions, including armored banks (riprap), will prevent erosion of the levee slopes. The construction solutions will not affect sensitive habitats, including wooded areas, habitats for threatened and endangered species, or jurisdictional wetlands.

Cultural Resources

Improvements to the ACF levee system may adversely affect prehistoric and historic archaeological resources. Some areas adjacent to the toe of the levee contain intact archaeological resources. Adverse effects to archaeological resources may occur from the use of heavy equipment during levee construction that could disturb surface or shallowly buried

FONSI - Page 3 deposits. Adverse effects may also occur to archaeological deposits that will be buried by the addition of the fill material on the surface above them. Alternatively, levee footprint expansion may protect archaeological resources by capping with fill material, preserving those resources in place.

Architectural resources may be adversely affected by levee height increases or by expansion of the levee footprint. Potential effects include vibration and ground disturbance from the use of heavy equipment during construction. Design for levee improvements is primarily considering avoidance of the structures as much as possible. However, if structures have to be removed or modified, USIBWC will consult with the Texas Historical Commission (THC) to determine the appropriate level of documentation prior to any modification. In addition to documentation, mitigation of impacts to cultural resources may include their replacement with "in-kind" structures that will look and operate the same. The increased height of the levee is not expected to change the flow of water to or from architectural resources in the floodway or farm fields flanking the levee. Native American resources may be affected by the levee improvements;

consultation with the Native American tribes will assist in identifying resources or concerns regarding the project.

Under NEPA, there will be no significant impacts (i.e., "unresolvable" adverse effects under the National Historic Preservation Act PHPA]) to cultural resources because all cultural resources will be identified and evaluated for National Register of Historic Places (NRHP) eligibility. Any impacts to National Register of Historic Places-eligible resources will be mitigated prior to implementation of levee height increases, footprint expansion, or other structural modifications, in consultation with the Texas Historical Commission (THC) and Native American Tribes.

Water Resources

Flood control improvements to the ACF will increase flood containment capacity to control the design flood event with a negligible increase in water surface elevation. Levee footprint expansion will not affect water bodies.

Land Use

Footprint levee expansion, where required, will take place completely within the existing ROW. No urban or agricultural lands will be affected.

Soil

Improvement activity contributing to soil disturbance will include geotechnical investigations and adding soil to the top and sides of the levee. Levee fill material will come from local commercial sources and not from borrow areas in the floodplain. The disturbance of soil will occur within areas where soil has been disturbed and modified by prior levee construction and maintenance activities. Therefore, alteration of soil previously unassociated with the existing levee will not occur.

Community Resources

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In terms of socioeconomic resources, the influx of federal funds into Hidalgo and Cameron Counties from the flood control improvement area will have a positive but minor local economic impact. The impact will be limited to the construction period, and represent less than 1 percent of the annual county employment, income, and sales values. No adverse impacts to disproportionately high minority and low-income populations were identified for construction activities. Moderate utilization of public roads will be required during construction; a temporary increase in access road use will be required for equipment mobilization to staging areas.

Environmental Health Issues

Estimated air emissions of five criteria pollutants during construction will be discontinuous and represent less than 0.1 3 percent of the annual emissions inventory within the air quality control region of Hidalgo, Cameron, and Willacy Counties. There will be a moderate increase in ambient noise levels due to construction activities. No long-term and regular exposure is expected above noise threshold values. A database search indicated that no waste storage and disposal sites were within the proposed ACF levee improvement area, and none will affect, or be affected by, the levee improvement project.

Best Management Practices

When warranted due to engineering considerations, or for protection of biological resources, the need for levee footprint expansion will be eliminated by levee slope adjustment. Best management practices during construction will include development of a storm water pollution prevention plan to avoid impacts to receiving waters, and use of sediment barriers and soil wetting to minimize erosion.

To protect vegetation cover, the embankment improvement areas will be re-vegetated with native herbaceous species. To protect wildlife, construction activities will be scheduled to occur, to the extent possible, outside the March to August bird migratory season.

DECISION

Based on my review of the facts and analyses contained in the Environmental Assessment, I conclude that implementation of the proposed action to improve the ACF levee system will not have a significant impact. Accordingly, requirements of the National Environmental Policy Act and regulations promulgated by the Council on Environmental Quality are fulfilled and an environmental impact statement is not required.

C.W. Ruth, Commissioner International Boundary and Water Commission, United States Section

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Environmental Assessment

IMPROVEMENTS TO THE

ARROYO COLORADO FLOODWAY

IN HIDALGO AND CAMERON COUNTIES

LEAD AGENCY:

UNITED STATES SECTION,

INTERNATIONAL BOUNDARY AND WATER COMMISSION

UNITED STATES AND MEXICO

TECHNICAL SUPPORT:

Parsons

8000 Centre Park Dr., Suite 200 Austin, Texas 78754

USIBWC Contract IBM04D0002, Task Order IBM09T0016

JUNE 2009

Environmental Assessment Contents i USIBWC

CONTENTS

List of Tables ........................................................................................................................iii List of Figures ........................................................................................................................ iv Acronyms and Abbreviations.................................................................................................. v

SECTION 1 PURPOSE OF AND NEED FOR THE PROPOSED ACTION .................1-1

1.1 Purpose of and Need for Action ..................................................................................1-1

1.2 USIBWC Authority .....................................................................................................1-1

1.3 Scope of the Environmental Review ...........................................................................1-1

1.4 Environmental Coordination and Compliance Analysis .............................................1-3

SECTION 2 DESCRIPTION OF PROPOSED ACTION.................................................2-1

2.1 Levee System Description...........................................................................................2-1

2.2 Proposed Action ..........................................................................................................2-1

2.3 Alternatives Considered and Eliminated from Detailed study ....................................2-5

2.4 Other Actions With Potential Cumulative Impacts .....................................................2-5

2.5 Summary Comparison of Environmental Consequences of the Alternatives .............2-5

2.5.1 No Action Alternative ........................................................................................2-5

2.5.2 Proposed Action ...............................................................................................2-14

SECTION 3 AFFECTED ENVIRONMENT AND POTENTIAL ENVIRONMENTAL

CONSEQUENCES.....................................................................................3-1

3.1 Biological Resources ...................................................................................................3-1

3.1.1 Vegetation...........................................................................................................3-1

3.1.2 Wildlife...............................................................................................................3-3

3.1.3 Threatened and Endangered Species ..................................................................3-4

3.1.4 Wetlands and Aquatic Habitat............................................................................3-6

3.2 Cultural Resources.......................................................................................................3-7

3.2.1 Previously Identified Cultural Resources within the ACF Improvement

Area ....................................................................................................................3-8

3.2.2 Architectural Resources......................................................................................3-9

3.2.3 Native American Resources .............................................................................3-13

3.3 Water Resources........................................................................................................3-14

3.3.1 Regional Flood Control ....................................................................................3-14

3.3.2 Water Flow .......................................................................................................3-15

3.3.3 Water Quality ...................................................................................................3-15

3.4 Land Use....................................................................................................................3-16

3.4.1 Natural Resources Management Areas ............................................................3-16 ii USIBWC

3.4.2 Agricultural Land .............................................................................................3-16

3.4.3 Urban Areas......................................................................................................3-17

3.5 Soil.............................................................................................................................3-17

3.6 Community Resources...............................................................................................3-18

3.6.1 Socioeconomics ................................................................................................3-18

3.6.2 Environmental Justice ......................................................................................3-22

3.6.3 Transportation...................................................................................................3-23

3.7 Environmental Health................................................................................................3-24

3.7.1 Air Quality........................................................................................................3-25

3.7.2 Noise.................................................................................................................3-27

3.7.3 Hazardous Materials and Waste Management .................................................3-28

3.8 Indirect and Cumulative Impacts...............................................................................3-30 SECTION 4 BEST MANAGEMENT PRACTICES..........................................................4-1

4.1 Engineering Measures .................................................................................................4-1

4.2 Natural Resources........................................................................................................4-1

4.3 Cultural Resources.......................................................................................................4-5

SECTION 5 ENVIRONMENTAL COMPLIANCE AND COORDINATION...............5-1

5.1 Public Review of Draft EA..........................................................................................5-1

5.2 List of Contributors .....................................................................................................5-4

SECTION 6 REFERENCES ................................................................................................6-1

APPENDICES

Appendix A Comment Letters on the Draft EA iii USIBWC

LIST OF TABLES

Table 1.1 Summary of Environmental Coordination and Compliance ................................1-4 Table 2.1 ACF Levee System Improvement Summary........................................................2-4 Table 2.2 Summary of Environmental Impacts of Proptosed Improvements to the Arroyo

Colorado Floodway ............................................................................................2-14 Table 3.1 Architectural Resources in the Area of Potential Effect ....................................3-10 Table 3.2 Native American Groups Identified for the ACF Improvement Area................3-13 Table 3.3 Population Growth in Cameron and Hidalgo Counties Adjacent to the Arroyo

Colorado Floodway ............................................................................................3-19 Table 3.4 Percentage of Minority Populations and Poverty Rates in the Arroyo Colorado

Floodway Levee Area.........................................................................................3-19 Table 3.5 Estimated Total Employment for Cameron and Hidalgo Counties....................3-20 Table 3.6 Potential Economic Impacts Improvements to the Arroyo Colorado Floodway

Levee System for Hidalgo County .....................................................................3-21 Table 3.7 Potential Economic Impacts Improvements to the Arroyo Colorado Floodway

Levee System for Cameron County ...................................................................3-22 Table 3.8 Air Emissions for Improvements to the Arroyo Colorado Floodway Levee

System ................................................................................................................3-26 Table 3.9 Summary Search Report for the Arroyo Colorado Floodway Levee System, McAllen, Texas Vicinity ....................................................................................3-29 Table 3.10 Cumulative Impacts............................................................................................3-30 Table 4.1 List of Grasses, Forbs and Vines suitable for Re-vegetation (TPWD list) .........4-3 Table 5.1 Distribution List for the Environmental Assessment ...........................................5-2 Table 5.2 Preparers of the Environmental Assessment and Technical Studies....................5-4 Table 5.3 Technical Review of the Environmental Assessment ..........................................5-4 iv USIBWC

LIST OF FIGURES

Figure 2.1 Arroyo Colorado Floodway Levee System Location Map...................................2-7 Figure 2.2 Levee Miles 0 – 2 .................................................................................................2-8 Figure 2.3 Levee Miles 2 – 4 .................................................................................................2-9 Figure 2.4 Levee Miles 4 – 6 ...............................................................................................2-10 Figure 2.5 Levee Miles 6 – 8 ...............................................................................................2-11 Figure 2.6 Levee Miles 8 – 11 .............................................................................................2-12 Figure 2.7 Levee Miles 11 – 12 ...........................................................................................2-13 Figure 3.1 Proposed Modifications to Structures on and under the Arroyo Colorado North

Levee and Divisor Dike......................................................................................3-12

Environmental Assessment Acronyms and Abbreviations v USIBWC

ACRONYMS AND ABBREVIATIONS

ACF Arroyo Colorado Floodway APE area of potential effect

AQCR air quality control region CFR Code of Federal Regulations dbA A-weighted sound level in decibels DNL day-night average sound level

EA environmental assessment EO executive order

GIS geographic information system HAER Historic American Engineering Record IBWC International Boundary and Water Commission

LRGFCP Lower Rio Grande Flood Control Project LRGV Lower Rio Grande Valley

MxIBWC Mexican Section, International Boundary and Water Commission NAAQS National Ambient Air Quality Standards

NEPA National Environmental Policy Act NHPA National Historic Preservation Act NLCD National Land-Cover Database NRHP National Register of Historic Places NRCS Natural Resources Conservation Service O&M operation and maintenance PEIS Programmatic Environmental Impact Statement ROW right-of-way

SHPO state historic preservation office T&E threatened and endangered THC Texas Historical Commission

TPWD Texas Parks and Wildlife Department USACE U.S. Army Corps of Engineers USEPA U.S. Environmental Protection Agency

USIBWC United States Section, International Boundary and Water Commission

Environmental Assessment Acronyms and Abbreviations vi USIBWC

Environmental Assessment Purpose of and Need for the Proposed Action

1-1 USIBWC

SECTION 1

PURPOSE OF AND NEED FOR THE PROPOSED ACTION

This section discusses the purpose of and need for the proposed action; the authority of the United States Section, International Boundary and Water Commission (USIBWC) to conduct the project as part of its mission; the scope of the environmental review; a summary of environmental compliance requirements; and the organization of this document.

1.1 PURPOSE OF AND NEED FOR ACTION

The ACF is a component of the Lower Rio Grande Flood Control Project (LRGFCP) that conducts floodwater diverted from the Rio Grande to the Laguna Madre in the Gulf of Mexico.

The proposed action would include levee system improvements to address the 100-year flood protection criteria established by the Federal Emergency Management Administration.

The Divisor Dike and the two portions of the north ACF levee system would be raised by adding fill material to the existing levee to bring flood control to its original design specifications, or to meet a 3-foot freeboard design criterion. The proposed action is described in detail in Subsection 2.2.

1.2 USIBWC AUTHORITY

The International Boundary and Water Commission (IBWC), which before 1944 was known as the International Boundary Commission, was created by the Convention of 1889, and consists of a (USIBWC and a Mexican Section (MxIBWC). The IBWC was established to apply the rights and obligations the Governments of the United States and Mexico assumed under the numerous boundary and water treaties and related agreements. Application of the rights and obligations are accomplished in a way that benefits the social and economic welfare of the people on both sides of the boundary and improves relations between the two countries.

The mission of the USIBWC covers the proposed raising of the ACF levee system.

1.3 SCOPE OF THE ENVIRONMENTAL REVIEW

Federal agencies are required to take into consideration the environmental consequences of proposed and alternative actions in the decision-making process under the National Environmental Policy Act (NEPA) of 1969, as amended. The President’s Council on Environmental Quality issued regulations to implement NEPA that include provisions for both the content and procedural aspects of the required environmental analysis. In 1978, the Council on Environmental Quality issued regulations implementing the process (40 Code of Federal Regulations [CFR] 1500-1508).

The USIBWC regulations for implementing NEPA are specified in Operational Procedures for Implementing Section 102 of the National Environmental Policy Act of 1969, Other Laws Pertaining to Specifics Aspects of the Environment and Applicable Executive Orders (46 FR 44083, September 2, 1981; Appendix 501-A).

1-2 USIBWC

This EA identifies and evaluates potential environmental consequences that may result from implementation of the proposed action and No Action alternative. It also characterizes the affected environment and describes, when required, mitigation measures to prevent or minimize impacts to environmental resources.

Analysis of environmental resources for the affected environment and environmental consequences was based on a potential impact corridor around the existing ACF levee system.

Analyses of environmental consequences also include potential indirect impacts adjacent to the levee corridor and the region, depending on the resource and its relationship to the proposed action and alternatives. Reference values for air quality, cultural resources, socioeconomics, and environmental justice are evaluated on a regional basis (county level).

Results of field biological surveys of terrestrial and aquatic natural resources and cultural resources, including archaeological sites, architectural resources, and Traditional Cultural Properties, were incorporated into the EA. Findings of these studies were used to document baseline conditions for biological resources, cultural resources, wetlands, and waste storage and disposal. The report also documents potential performance of the levee system based on hydraulic model simulations, and an evaluation of environmental compliance requirements and coordination activities.

Environmental impacts associated with the proposed flood control improvements described in this EA were tiered from the 2008 Final Programmatic Environmental Impact Statement (PEIS) (USIBWC 2008), as per 40 CFR 1502.20. Recent published information is used for impact analyses based for the time period covered during construction and subsequent flood control improvement conditions. Potential environmental consequences of the ACF levee system for each resource area are discussed separately in this EA.

The following terminology is used in this document.

• Riverside/Landside, riverside refers to the side of the levee closest to the Arroyo Colorado, and landside refers to the side of the levee away from the Arroyo Colorado.

• Existing levee footprint, this is the footprint of the levee without any improvements or changes. For the purposes of this report, the existing levee footprint is assumed to be 88 feet from landside toe of the levee to riverside toe of the levee.

• Survey Corridor, the land on both sides of the levee included in visual surveys and verified with aerial imagery

• Construction Corridor, the area of the levee identified as having deficiencies, where fill would be added to the top of the levee a height defined by modeling and surveys to provide adequate flood control. The Construction Corridor also includes areas where staging of equipment and/or materials will occur. The Construction Corridor is assumed to be a 100-foot buffer from the centerline of the levee.

1-3 USIBWC

• Levee Expansion Area, the area within the construction corridor where the footprint of the levee will be expanded beyond the existing footprint.

• Area of Potential Effect, the area where cultural resources may occur and may be affected by construction activities.

1.4 ENVIRONMENTAL COORDINATION AND COMPLIANCE ANALYSIS

Table 1.1 is a summary of regulatory and/or permitting requirements potentially applicable to improvements under consideration, potential compliance issues, and anticipated level of environmental coordination.

1-4 USIBWC

Table 1.1 Summary of Environmental Coordination and Compliance Agency or

Organization Regulation or Issue Level of USIBWC Coordination

Biological Resources

U.S. Fish and Wildlife Service

(USFWS)

Endangered Species Act of 1973 (Public Law 93-205) and amendments of 1988 (Public Law 100-478)

Section 7 of the Act requires formal consultation if significant adverse impacts to federally listed threatened and endangered species and migratory birds could occur.

Texas Parks and Wildlife Department

(TPWD)

Chapters 67 and 68 of the TPWD Code, and Section 65.171-

65.184 of the Texas Administrative Code

Coordination with Wildlife Division concerning potential impacts of the levee-raising project to wildlife.

Coordination with State Parks Division concerning potential impacts on park tracts.

Cultural Resources

State Historic Preservation Office (SHPO) - Texas Historical Commission (THC)

National Historic Preservation Act (NHPA) of 1966, as amended (16 United States Code [USC] 470 et seq.)

American Indian Religious Freedom Act (AIRFA), 1978 Native American Graves Protection and Repatriation Act

(NAGPRA) 1990

Ensure compliance with NHPA, AIRFA and

NAGPRA.

The THC may suggest conditions and mitigation measures following review of the Draft EA.

Water Resources

U.S. Army Corps of Engineers

(USACE)

Section 10 of the Rivers and Harbors Act of 1899 Section 404 of the Clean Water Act (33 USC 1344)

Permit application if waters of the United States are affected. Mitigation plan and permit application for potential impacts to wetlands.

Texas Commission on Environmental Quality (TCEQ)

Section 401 of the Clean Water Act (33 USC 1344);

Section 26.040 of Texas Water Code

Section 401 Certification: conditions and mitigation measures may be stipulated for the 401 permit; coordination is typically a function of the USACE permitting process.

United States Environmental Protection Agency

(USEPA)

Section 402 of the Clean Water Act Section 404 of the Clean Water Act

Requirements for National Pollutant Discharge Elimination System construction permit and Storm Water Pollution Prevention Plan preparation.

Section 404 Certification; coordination is typically a function of the USACE permitting process.

Other Issues Natural Resources Conservation Service (NRCS)

Farmland Protection Policy Act Determination that no unique or prime farmland would be affected by the federal project.

Irrigation Districts Modifications to intake channel and construction along irrigation canals

Mercedes Districts in Hidalgo County; La Feria, Adams Garden, and Harlingen Irrigation Districts in Cameron County: levee construction along the Arroyo Floodway.

Environmental Assessment Description of Proposed Action

2-1 USIBWC

SECTION 2

DESCRIPTION OF PROPOSED ACTION

This section presents a description of the proposed action for improvements of the ACF levee system. An overview of the ACF levee system is presented in Figures 2.1 to 2.7. The Biological Resources Report (USIBWC 2009) prepared in support of this EA presents detailed maps of levee alignment, potential levee improvement areas, and land use in the levee system vicinity.

2.1 LEVEE SYSTEM DESCRIPTION

The Arroyo Colorado, that drains to the Laguna Madre, is an ancient distributary of the Rio Grande, and it serves as drainage for crop irrigation, municipal wastewater returns, and as a floodway during periods of heavy precipitation in the lower Rio Grande Valley. The ACF is part of the LRGFCP, which was constructed to protect urban, suburban, and highly developed irrigated farmlands in the Rio Grande delta from floods in both the United States and Mexico.

The proposed levee rehabilitation project includes 2.1 miles of the Divisor Dike, and the upper

8.9 miles of the Arroyo Colorado north levee that contain areas of rich farm and citrus land near the municipalities of Mercedes and La Feria, Texas.

Levee floodway system descriptions for the LRGFCP, including the Main and North Floodways and the ACF, are described in detail in the 2008 Final PEIS (USIBWC 2008).

Sections of the interior floodway system were identified by hydraulic modeling as priority areas to improve flood containment. The hydraulic evaluation indicated that an increase in levee height, up to 4-feet, would be needed in a number of sections of the ACF to meet design criteria for flood protection (USIBWC 2003a). The section of the ACF evaluated in this EA runs primarily through agricultural areas. Urban development in the section of the ACF evaluated in this EA is primarily limited to portions of Mercedes and La Feria, Texas. No residential developments are allowed within the floodway.

2.2 PROPOSED ACTION

Levee assessment and potential rehabilitation will occur on the north levee. The upper reach of the project area extends from the Divisor Dike to the Willacy Canal (6.9 miles) and from the Willacy Canal to White Ranch Road (4.1 miles). There is a reach between levee miles 7 and 8 where the levee road is on high ground (See Figure 2.5), and no levee is present and no levee will be constructed in this reach. This reach (0.75 miles) is not included in the 11-mile levee assessment reported in this EA.

The proposed action would improve flood control and increase flood containment capacity along the Divisor Dike and ACF beginning at Divisor Dike near the juncture point of the Arroyo Colorado and the North Floodway in Hidalgo County and ending at White Ranch Road, Cameron County, Texas. The proposed levee rehabilitation improvements consist of: 1) raising the top-of-levee elevation; 2) conducting geotechnical investigations and testing to determine the type and extent of any required remediation improvements due to slope stability, 2-2 USIBWC seepage, levee settlement, and any other geotechnical issues that may cause levee failure; and

3) modifying, if necessary, hardware or structures located along the levee reaches. Any structure modifications would be in compliance with the Texas Historical Commission recommendations. The top elevation of the levee-raising improvements would be to provide containment of flood flows with a minimum freeboard of 3 feet for water surface elevations as calculated in the USIBWC 2003 Hydraulic Model for the LRGFCP (USIBWC 2003a). Raising the levee from the centerline of the levee is assumed for analyses, except for the areas south of La Feria reservoir. Due to the proximity of the reservoir to the existing levee, construction and levee expansion would be offset to the riverside of the levee.

The existing levee is a raised trapezoidal compacted-earth structure with a crown width of 16 feet, a typical height ranging from 10 to 15 feet, and an approximate 3:1 side slope ratio (units of horizontal run in feet per foot of vertical rise). The levee crown is an unpaved service road with restricted public access. The existing levee footprint typically ranges from 70 to 100 feet, depending on location. A typical levee cross-section is shown in the diagram below.

Levee assessment and potential levee rehabilitation will occur on the ACF north levee.

The upper reach of the project area extends from the Divisor Dike to approximately levee mile

7.0 (near the Hidalgo/Cameron country line) (6.9 miles total). The entire upper reach falls within Hidalgo County. Downstream of the upper reach is a short segment (0.75 miles) of high ground where there is no levee and no levee will be constructed. The lower reach extends from west of Santa Maria Road (FM 2556), through the Willacy Canal area to White Ranch Road (4.1 miles). The lower reach is further divided into two sections: the area extending from the high ground west of FM 2556, adjacent to La Feria reservoir to FM 800 (approximately 2.3 miles), and the easternmost end of the project area, extending from FM 800 to White Ranch Road (approximately 1.8 miles). The entire lower reach falls with Cameron County.

The proposed action would increase flood containment capacity by raising elevation of a number of levee segments for improved flood control. Fill material from commercial sources would be added to the existing levee to bring flood control to its original design specifications, or to meet a 3-foot freeboard design criterion. There are commercial sand pits within the ACF floodway, but these will not be utilized to obtain fill material

Addition of fill material would be place on top of the levee, extending the footprint beyond the toe of the existing levee. Levee footprint expansion would occur within the maintained floodway and within the USIBWC right-of-way (ROW). For a typical levee cross-section with height increases of up to 4 feet, the levee footprint would be expanded by 24 feet, 12 feet on either side of the levee. The need for excavation outside the levee structure is not anticipated.

3:1 SLOPE

16 ft

88 ft

12 ft

2-3 USIBWC

Figures 2.2 to 2.7 present an overview of the Arroyo Colorado levee systems that would undergo levee rehabilitation. The proposed action would raise the levee in areas where modeling indicates that the existing levee is insufficient to provide adequate flood control.

With the exceptions described below, most of the levee expansion will be centered, extending the footprint the same width on each side of the levee (Table 2.1).

Along the boundary of the La Feria reservoir, a centered expansion is not possible.

Adjacent to the La Feria reservoir, any levee expansion will occur within the floodway, toward the riverside of the levee. The areas for the offset expansion are shown in Table 2.1.

At the most downstream end of the project area, there is no levee, but the “levee road” is on high ground. Hydraulic modeling indicates several segments of the levee road will have to be raised. As shown in Table 2.1, most of the levee expansion in the downstream end will be a centered expansion. In one reach (approximately 424 feet), the hydraulic modeling indicates that up to 8 feet of fill will be required to obtain adequate flood control. At this location, lateral extension is not possible to the landside of the levee road due to the proximity of a borrow pit, nor into the floodway due to the steep topography. Construction of a flood retaining wall may be used to avoid lateral expansion, or increasing the levee slope and use riprap armoring to prevent erosion.

88 ft 12 ft max expansion

12 ft max expansion up to 4 ft height increase

2-4 USIBWC

Table 2.1 ACF Levee System Improvement Summary

Needed Increase in Levee Height

Approximate Length (miles)

Percent of Length

Expansion Alignment

Area of Impact (acres)

Comments

UPPER REACH (Divisor Dike to approximately levee mile 7.0) (total 6.9 miles)

Not required 6.4 58.1 n/a n/a No changes to existing levee up to 2 feet 0.3 3.1 centered 0.2 (1) 0 to 6 ft footprint expansion on each side of the levee (2)

2 to 4 feet 0.2 1.7 centered 6 to 12 ft footprint expansion on each side of the levee

4 to 6 feet 0.004 [23 feet] 0.04 centered

0.6 (3)

12 to 18 ft footprint expansion on each side of the levee

LOWER REACH

From FM 2556 to FM 300 (Adjacent to La Feria Reservoir) (total 2.3 miles)

Not required 1.8 16.2 n/a n/a No changes to existing levee up to 2 feet 0.3 2.5 offset to riverside 0.2 0 to 6 ft footprint expansion on each side of the levee (2)

2 to 4 feet 0.06 [326 feet] 0.6 offset to riverside 0.7 6 to 12 ft footprint expansion, entirely to riverside

4 to 6 feet 0.1 [711 feet] 1.2 offset to riverside 1.3 12 to 18 ft footprint expansion entirely to riverside

6 to 8 feet 0.05 [259 feet] 0.4 offset into floodway side 0.4 36 to 48 ft footprint expansion, entirely to riverside

From FM 300 to White Ranch Road (Downstream end of Project Area) (total 1.8 miles) Not required 1.0 9.4 n/a n/a No changes to existing levee up to 2 feet 0.3 3 centered 0.2 0 to 6 ft footprint expansion on each side of the levee (2)

2 to 4 feet 0.2 [994 feet] 1.7 centered 0.6 6 to 12 ft footprint expansion on each side of the levee

4 to 6 feet 0.1 [659 feet] 1.1 centered 0.5 12 to 18 ft footprint expansion on each side of the levee

6 to 8 feet 0.08 (424 feet) 0.7 centered n/a

New levee on top of existing road, no footprint expansion due to steep topography in area

Total 11.0 100 4.7

(1) Height increases of up to 2 feet may require footprint expansion, and it is assumed that expansion will be on average 3 feet on either side of the levee (total of 6 feet).

(2) Depending on specific conditions in areas where up to 2 feet of fill may be added to the top of the levee, the levee slopes may be adjusted to reduce footprint expansion.

(3) For the upper reach, the area of impact calculation is combined for the two height increases, because the 4 to 6 foot height increase is a short length.

2-5 USIBWC

Any staging areas for heavy equipment or soil storage needed for construction activities associated with the proposed action would be located outside the USIBWC ROW and Area of Potential Effect (APE). Vehicles would access the project area by means of existing levee access or farm roads. No new haul roads would be constructed. The majority of work to raise the levee would occur on top of the existing levee. Belly dump trucks would carry commercially obtained fill material to the top of the levee. Areas requiring placement of fill material on the sides of the embankments would be accessed from the top of the levee road and spread over the embankments until the desired thickness has been reached. After releasing a load of fill, a motorgrader would follow behind to compact fill to the required height. After increasing the height of the levee and extending the footprint, where necessary, the easement area adjacent to the levee, up to 35 feet on either side, would also be subject to compaction.

2.3 ALTERNATIVES CONSIDERED AND ELIMINATED FROM DETAILED STUDY

Levee expansion beyond the current flood control project ROW was ruled out as a viable, or needed, option for levee improvements.

2.4 OTHER ACTIONS WITH POTENTIAL CUMULATIVE IMPACTS

Complete environmental impact analysis of the alternatives must consider cumulative impacts due to other actions. The USIBWC reviewed a number of reasonably foreseeable actions with potential cumulative effects. Two projects were identified along the ACF levee system.

• Construction work for the Main and North Floodway levee improvements project would occur at the same time as the Arroyo Colorado levee improvement project.

• Geotechnical work would be conducted along the 11-mile project area to assess the ability of the levee to safely contain flood flows in the Rio Grande.

Subsection 3.8 provides an assessment of cumulative effects of the Main and North Floodway levee improvements project, in conjunction with the proposed action.

2.5 SUMMARY COMPARISON OF ENVIRONMENTAL CONSEQUENCES OF THE

ALTERNATIVES

2.5.1 No Action Alternative

The no action alternative would retain the current configuration of ACF levee system with no impacts to biological and cultural resources, land use, community resources, or environmental health issues. In terms of flood protection, however, current containment capacity under the no action alternative may be insufficient to fully control flooding within the interior floodway system under severe storm events, with associated risks to personal safety and property.

2-6 USIBWC

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0 1 2 Miles¹

!. Levee Mile Markers North Levee Centerline Highway Major Road Arroyo Colorado Floodway North Floodway

Levee Deficiency (feet) < 2 2 - 4 4 - 6 6 - 8 counties

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