03_Final Mission EA 200702.pdf

Final Environmental Assessment Improvements to the Mission and

Common Levee Systems

Lead Agency:

United States Section, International Boundary and

Water Commission El Paso, Texas

Technical Support:

Parsons Austin, Texas

February 2007

Cooperating Agency:

Texas Parks and Wildlife Department

COVER SHEET

ENVIRONMENTAL ASSESSMENT

AND

FINDING OF NO SIGNIFICANT IMPACT

IMPROVEMENTS TO THE

MISSION AND COMMON LEVEE SYSTEMS

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

Cooperating Agency: Texas Parks and Wildlife Department

Proposed Action: Raising approximately 17 miles of the Mission and Common Levee Systems to meet current requirements for flood control.

Report Designation: Environmental Assessment

Abstract:

The USIBWC is considering raising the 12.0-mile Mission Levee System and the 5.3-mile Common Levee System to meet current flood control requirements. The proposed action would increase the height of the levee up to 8 feet depending on location. The height increase would also result in expansion of the levee footprint by lateral extension of the structure. Levee footprint increases for both the Mission and Common Levee systems would occur within the USIBWC right-of-way and extend primarily toward the riverside of the existing levee. Along sections of the Mission Levee System, structural improvements such as slurry walls may be required in segments with seepage potential. In an approximate 1-mile reach, a mechanically stabilized earth structure would be built along the existing levee crown to avoid footprint extension beyond the existing right-of-way easements. A number of natural resources management areas are located near or adjacent to the levee system, including units of the Lower Rio Grande Valley National Wildlife Refuge System and the Bentsen-Rio Grande Valley State Park.

The Environmental Assessment 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 Environmental Assessment.

ENVIRONMENTAL ASSESSMENT

IMPROVEMENTS TO THE MISSION AND COMMON LEVEE SYSTEMS

Lead Agency:

UNITED STATES SECTION,

INTERNATIONAL BOUNDARY AND WATER COMMISSION

UNITED STATES AND MEXICO

Cooperating Agency:

TEXAS PARKS AND

WILDLIFE DEPARTMENT

Technical Support:

Parsons

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

USIBWC Contract IBM04D0002, Task Order IBM05T0022

FEBRUARY 2007

Mission and Common Levee Systems Environmental Assessment Contents i USIBWC

TABLE OF CONTENTS

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

1.3 Scope of the Environmental Review................................................................................. 1-3

1.4 Environmental Coordination and Compliance Analysis.................................................... 1-4

1.5 Organization of the Environmental Assessment............................................................... 1-6

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

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

2.1.1 Mission Levee System ............................................................................................ 2-1

2.1.2 Common Levee System.......................................................................................... 2-5

2.2 Proposed Action................................................................................................................ 2-6

2.2.1 Mission Levee System ............................................................................................ 2-7

2.2.2 Common Levee System.......................................................................................... 2-9

2.3 Alternatives Considered and Eliminated from Detailed study........................................... 2-9

2.4 Other Actions With Potential Cumulative Impacts ............................................................ 2-9

2.5 Summary Comparison of Environmental Consequences of the Alternatives................. 2-10

2.5.1 Mission Levee System .......................................................................................... 2-10

2.5.2 Common Levee System........................................................................................ 2-11

SECTION 3 AFFECTED ENVIRONMENT ...................................................................................3-1

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

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

3.1.2 Wildlife..................................................................................................................... 3-4

3.1.3 Threatened and Endangered Species .................................................................... 3-5

3.1.4 Wetlands and Aquatic Habitat................................................................................. 3-8

3.2 Cultural Resources ......................................................................................................... 3-10

3.2.1 Previous Cultural Resources Studies ................................................................... 3-10

3.2.2 Historical and Prehistoric Cultural Resources....................................................... 3-20

3.2.3 Architectural and Engineering Resources............................................................. 3-22

3.3 Water Resources ............................................................................................................ 3-24

3.3.1 Regional Flood Control ......................................................................................... 3-24

3.3.2 Water Flow ............................................................................................................ 3-27

3.4 Land Use......................................................................................................................... 3-28

3.4.1 Mission Levee System .......................................................................................... 3-28

3.4.2 Common Levee System........................................................................................ 3-29

3.5 Community Resources.................................................................................................... 3-29

3.5.1 Socioeconomics .................................................................................................... 3-29

3.5.2 Environmental Justice ........................................................................................... 3-31

3.5.3 Transportation ....................................................................................................... 3-31 ii USIBWC

3.6 Environmental Health...................................................................................................... 3-32

3.6.1 Air Quality.............................................................................................................. 3-32

3.6.2 Noise ..................................................................................................................... 3-33

3.6.3 Hazardous and Toxic Waste ................................................................................. 3-34

SECTION 4 ENVIRONMENTAL CONSEQUENCES ....................................................................4-1

4.1 Biological Resources ........................................................................................................ 4-1

4.1.1 Vegetation ............................................................................................................... 4-1

4.1.2 Wildlife..................................................................................................................... 4-3

4.1.3 Threatened and Endangered Species .................................................................... 4-4

4.1.4 Jurisdictional Wetlands and Aquatic Habitat........................................................... 4-6

4.2 Cultural Resources ......................................................................................................... 4-10

4.2.1 Historic and Prehistoric Cultural Resources ......................................................... 4-10

4.2.2 Architectural and Engineering Resources............................................................. 4-11

4.3 Water Resources ............................................................................................................ 4-12

4.3.1 Flood Control......................................................................................................... 4-12

4.3.2 Water Flow ............................................................................................................ 4-13

4.4 Land Use......................................................................................................................... 4-13

4.5 Community Resources.................................................................................................... 4-15

4.5.1 Socioeconomics .................................................................................................... 4-15

4.5.2 Environmental Justice ........................................................................................... 4-16

4.5.3 Transportation ....................................................................................................... 4-17

4.6 Environmental Health...................................................................................................... 4-18

4.6.1 Air Quality.............................................................................................................. 4-18

4.6.2 Noise ..................................................................................................................... 4-19

4.6.3 Hazardous and Toxic Waste ................................................................................. 4-20

4.7 Indirect and Cumulative Effects ...................................................................................... 4-20

SECTION 5 BEST MANAGEMENT PRACTICES AND MITIGATION ACTIONS............................5-1

5.1 Engineering Measures ...................................................................................................... 5-1

5.1.1 Best Management Practices ................................................................................... 5-1

5.1.2 Engineering Design Measures................................................................................ 5-1

5.2 Natural Resources ............................................................................................................ 5-2

5.2.1 Best Management Practices ................................................................................... 5-2

5.2.2 Mitigation Measures ................................................................................................ 5-3

5.3 Cultural Resources ........................................................................................................... 5-7

5.3.1 Best Management Practices ................................................................................... 5-7

5.3.2 Mitigation Measures ................................................................................................ 5-7

SECTION 6 ENVIRONMENTAL COMPLIANCE AND COORDINATION .......................................6-1

6.1 Consultation Process ........................................................................................................ 6-1

6.1.1 Cooperating Agency Support .................................................................................. 6-1 iii USIBWC

6.1.2 Identification of Potential Impacts and Issues......................................................... 6-1

6.1.3 Comments on Draft EA ........................................................................................... 6-3

6.2 Persons and Agencies Consulted..................................................................................... 6-4

6.3 List of Contributors............................................................................................................ 6-5

SECTION 7 REFERENCES................................................................................................................. 7-1

APPENDICES

Appendix A Detailed Maps of Levee Alignment, Right-of-Way and Potential Expansion Area

Appendix B Environmental Assessment Consultation and Comments

LIST OF TABLES

Table 1.1 Summary of Environmental Coordination and Compliance............................................. 1-5

Table 3.1 Acreages of Plant Communities along Levee ROW and Expansion Area ...................... 3-4

Table 3.2 Threatened and Endangered Species Habitat Potentially Occurring within the Levee Corridor ............................................................................................................................ 3-6

Table 3.3 Wetlands within Mission Levee ROW.............................................................................. 3-8

Table 3.4 Mission Levee Current Freeboard and Potential Height Increase ................................ 3-25

Table 3.5 Current Freeboard of the Common Levee/Anzalduas Dike and Potential Height Increase ....................................................................................................................................... 3-27

Table 3.6 Racial Composition of Hidalgo County .......................................................................... 3-30

Table 3.7 Hidalgo County Income Data......................................................................................... 3-31

Table 3.8 Summary Search Report for the Mission Levee System............................................... 3-35

Table 3.9 Summary Search Report for the Common Levee System ............................................ 3-36

Table 4.1 Impacts to Vegetation within Mission and Common Levee System Corridors .................. 4-2

Table 4.2 Vegetation Removal by Natural Resources Managing Organization for Riverside Expansion Scenario......................................................................................................... 4-2

Table 4.3 Potential Impacts of Mission and Common Levee Improvements on Federally Listed Threatened and Endangered Species............................................................................. 4-5

Table 4.4 Potential Impacts on Wetlands within Mission Levee ROW............................................ 4-7

Table 4.5 Potential Economic Impacts Improvements to the Mission Levee System................... 4-15

Table 4.6 Potential Economic Impacts Improvements to the Common Levee System................. 4-16

Table 4.7 Air Emissions for Improvements to the Mission and Common Levee Systems............ 4-18

Table 5.1 Hidalgo County Native Indigenous Grasses, Forbs, Vines, Shrub and Trees ............... 5-4

Table 6.1 Preparers of the Environmental Assessment and Technical Studies ............................. 6-5

Table 6.2 Technical Review of the Environmental Assessment...................................................... 6-5 iv USIBWC

LIST OF FIGURES

Figure 1.1 Project Location Map....................................................................................................... 1-2

Figure 2.1 Mission Levee System Location Map.............................................................................. 2-2

Figure 2.2 Common Levee System Location Map............................................................................ 2-3

Figure 3.1 Wetlands Location Map – Mission Levee System........................................................... 3-9

Figure 3.2 Cultural Resources in Mission Project Miles 0 to 3 ....................................................... 3-11

Figure 3.3 Cultural Resources in Mission Project Miles 3 to 6 ....................................................... 3-12

Figure 3.4 Cultural Resources in Mission Project Miles 6 to 9 ....................................................... 3-13

Figure 3.5 Cultural Resources in Mission Project Miles 9 to 12 ..................................................... 3-14

Figure 3.6 Cultural Resources in the Upstream Reach of the Common Levee ............................. 3-15

Figure 3.7 Cultural Resources in the Downstream Reach of the Common Levee......................... 3-16

Figure 3.8 Location of Site 41HG143 Showing Ongoing Landfill Activity ....................................... 3-17

Figure 3.9 Locations of Major and Minor Engineering Structures along the Mission and Common Levee Systems ....................................................................................... 3-23

Figure 4.1 Cross-Sectional Areas of Wetlands Separation from Levee Expansion Area................ 4-8

Environmental Assessment Acronyms and Abbreviations v USIBWC

ACRONYMS AND ABBREVIATIONS

amsl above mean sea level

AQCR air quality control region AST aboveground storage tank BMP best management practices

CERCLIS Comprehensive Environmental Response, Compensation, and Liability Information System

CFR Code of Federal Regulations cfs cubic feet per second dbA A-weighted sound level in decibels DNL day-night average sound level

EA environmental assessment EIS environmental impact statement

ERNS Emergency Response Notification System of Spills FM farm-to-market

GENS generator of hazardous waste HPA high probability area

IBWC International Boundary and Water Commission LGGROUP LopezGarcia Group

LRGFCP Lower Rio Grande Flood Control Project LRGV Lower Rio Grande Valley MSE mechanically stabilized earth

NAAQS National Ambient Air Quality Standards NABA North American Butterfly Association

MxIBWC Mexican Section, International Boundary and Water Commission NEPA National Environmental Policy Act

NPL National Priority List NRCS Natural Resources Conservation Service RCRA Resource Conservation and Recovery Act ROW right-of-way

SWP3 storm water pollution prevention plan T&E threatened and endangered

TCEQ Texas Commission on Environmental Quality TPWD Texas Parks and Wildlife Department

TSD transport, storage, and disposal USACE U.S. Army Corps of Engineers USEPA U.S. Environmental Protection Agency USFWS U.S. Fish and Wildlife Service

USGS U.S. Geological Survey USIBWC United States Section, International Boundary and Water Commission

UST underground storage tank

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 USIBWC, in cooperation with the Texas Parks and Wildlife Department (TPWD), prepared this Draft Environmental Assessment (EA) for the proposed action of raising the Mission and Common Levee Systems located in Hidalgo County, Texas. These two adjacent levee systems are part of the Lower Rio Grande Flood Control Project (LRGFCP) that extends approximately 180 miles from the Town of Peñitas in south Texas to the Gulf of Mexico.

The USIBWC identified the Mission and Common Levee Systems as priority areas for improved flood containment. The Mission Levee extends 12.1 miles along the Rio Grande, downstream from the Town of Peñitas. The Common Levee System, 5.2 long, consists of the Common Levee and Anzalduas Dike, which connects the levee to Anzalduas Dam. The need for levee improvements was determined from hydraulic modeling results indicating that typical height increases of up to 8 feet would be required to meet current design criteria for flood protection along the Mission and Common Levee Systems (USIBWC 2003a).

In addition to the flood containment evaluation, the Engineer Research and Development Center of the U.S. Army Corps of Engineers (USACE) was commissioned by the USIBWC to assess structural integrity of the entire LRGFCP levee system (USACE 2003). The assessment identified a need for structural improvements along a number of segments of the Mission and Common Levee Systems where seepage control would likely be required.

Figure 1.1 presents an overview of the project area in south Texas. Levee miles along each system are numbered starting from their upstream reach: from the Town of Peñitas for the Mission System, and from Anzalduas Dam for the Common Levee System.

MEXICO

TEXAS

PEÑITAS

MISSION

ABRAM

R IO G

R

A

N

DE

MADERO

MISSION LEVEE SYSTEM

COMMON LEVEE SYSTEM

Mile 9

Mile 8 Mile 7

Mile 6

Mile 5

Mile 4

Mile 3

Mile 2

Mile 1

Mile 0

Mile 12

Mile 11

Mile 10

Mile 5Mile 4

Mile 3 Mile 2

Mile 1

Mile 0

MEXICO

Texas

Tamaulipas

Project Location

UNITED STATES

T e x a s

O k l a h o m a

N e w M e x i c o

Mission and Common Levee Systems Figure 1.1- Project Location Map

J:\744\744778_Mission Levee EA\6A_Levee Analysis\mxd\bothLevees_location_lettersize.mxd - 5/12/2006 @ 3:57:18 PM

Scale = 1 : 78,000

0 4,000 8,000 12,000 16,0002,000 Feet

0 1 2 30.5 Miles

1-3 USIBWC

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 United States Section (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 has five components, the third of which covers the proposed raising of the Mission and Common Levee Systems:

• Regulation and conservation of waters of the Rio Grande for use by the United States and Mexico through joint construction, operation, and maintenance of international storage dams and reservoirs and plants for generating hydroelectric energy at the dams, and regulation of the Colorado River waters allocated to Mexico;

• Distribution of waters of the Rio Grande and the Colorado River between the two countries;

• Protection of land along the Rio Grande from floods through levee and floodway projects, and solution of border sanitation and other border water quality problems;

• Preservation of the Rio Grande and Colorado River as the international boundary; and

• Demarcation of the land boundary.

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). These federal regulations establish both the administrative process and substantive scope of the environmental impact evaluation designed to ensure that deciding authorities have a proper understanding of the potential environmental consequences of a contemplated course of action. The Council on Environmental Quality regulations requires that an EA:

• Briefly provide evidence and analysis to determine whether the proposed action might have significant effects that would require preparation of an environmental impact

1-4 USIBWC

statement (EIS). If analysis determines that the environmental effects would not be significant, a Finding of No Significant Impact is prepared;

• Facilitate the preparation of an EIS, when required; or

• Aid an agency’s compliance with NEPA when no EIS is necessary.

This EA identifies and evaluates the 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. The following resource areas are analyzed for potential environmental consequences: biological resources; cultural resources; water resources; land use; and community resources (socioeconomics, environmental justice, and transportation). Environmental health issues are also evaluated (air quality, noise, and hazardous and toxic waste).

Analyses of environmental resources for the affected environment and environmental consequences are based on a potential impact corridor around the existing Mission and Common Levee Systems, and the proposed area for partial rerouting of the levee system across the Edinburg intake channel (at Project Mile 0.6 of the Mission 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 studies conducted in support of the EA preparation were reported in the document Technical Support Studies for the Environmental Assessment of Flood Control Improvements to the Mission and Common Levee Systems (Parsons 2006). 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. A copy of the Technical Support Studies report was previously provided in CD format with the Draft EA.

The most recent information is used for the impact analyses. Impacts are considered for the time period covered under the construction period and subsequent flood control improvement conditions. Potential environmental consequences of the Mission and Common Levee Systems for each resource area evaluated are discussed separately in Section 4 of this

EA.

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.

1-5 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) FWS Coordination Act (916 USC 661, et seq.)

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

Consultation with USFWS regarding impacts on various units of the LRGV National Wildlife Refuge adjacent to the levee systems.

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 Mission Levee: Bentsen-Rio Grande Valley State Park

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.

The Nature Conservancy

Mission Levee: Chihuahua Woodlands Preserve

Coordination concerning potential impacts on Chihuahua Woodlands Preserve.

North American Butterfly Association

(NABA)

Mission Levee: NABA International Butterfly Park

Coordination concerning potential impacts on future development areas of the International Butterfly Park.

Cultural Resources Texas Historic Commission

(THC)

National Historic Preservation Act of 1966, as amended (16 USC 470, et seq.)

Compliance with Section 106 requirements for potential impacts to archaeological and historic resources.

Water Resources

U.S. Army Corps of Engineers

(USACE)

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

Permit application for crossing the intake channel of the Peñitas Pumping Plant.

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 NPDES 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.

U.S. Customs and Border Patrol Levee Road Usage Coordination during construction activities.

1-6 USIBWC

Agency or Organization

Regulation or Issue Level of USIBWC Coordination

City of Mission

Mission Levee: Military Road expansion.

Mission Levee; La Lomita Chapel Historical Park

Compliance of expansion plans with updated flood control requirements.

Coordination for construction work in the park vicinity.

Hidalgo County Anzalduas Dike:

Anzalduas Dam County Park Coordination for construction work along the park.

Irrigation Districts

Mission Levee:

Modifications to intake channel and construction along irrigation canals

Hidalgo County Irrigation District No. One: changes to intake channel in front of the Peñitas Pumping Plant.

United Irrigation District of Hidalgo County: levee construction along an approximately 3-mile segment of the Mission Main Canal.

Hidalgo County Irrigation District No. 19: levee construction along a 1.7-mile segment of the Granjeno Canal.

1.5 ORGANIZATION OF THE ENVIRONMENTAL ASSESSMENT

This Environmental Assessment is composed of the following sections:

Section 1 identifies the purpose of and need for the Proposed Action, defines the scope of the environmental review, and provides an environmental coordination and compliance analysis.

Section 2 describes the Proposed Action and No Action Alternative, and summarizes potential environmental impacts.

Section 3 presents information on the affected environment, providing a basis for analyzing the impacts of the Proposed Action.

Section 4 analyzes the environmental consequences of the flood control improvements of the Mission and Common Levee Systems.

Section 5 describes best management practices for construction and potential mitigation actions.

Section 6 describes the consultation process and lists persons and agencies consulted, and contributors to the EA preparation.

Section 7 is a list of cited references and source documents relevant to preparation of the

EA.

Support documentation includes detailed maps of levee alignment, right-of-way, and potential expansion area (Appendix A) and environmental assessment consultation and review comments (Appendix B).

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 Mission Levee System and Common Levee System. A summary of potential environmental impacts, subsequently discussed in Section 4, is provided at the end of Section 2. An overview of the Mission and Common Levee Systems is presented in Figures 2.1 and 2.2, respectively.

2.1 LEVEE SYSTEM DESCRIPTION

The Mission Levee extends approximately 12 miles south of the City of Mission, from the Town of Peñitas to its junction with the Banker/Main Floodway (U.S. interior floodway).

The Common Levee System encompasses the Common Levee and Anzalduas Dike. The Common Levee extends approximately 4.5 miles along the Banker/Main Floodway to its junction with the River Levee segment surrounding the City of Hidalgo. Anzalduas Dike is an approximate 0.7 mile segment that extends from the north end of Anzalduas Dam to the upstream end of the Common Levee.

The Mission and Common Levee Systems are part of the LRGFCP that extends approximately 180 miles from the Town of Peñitas in south Texas to the Gulf of Mexico. The LRGFCP was constructed to protect urban, suburban, and highly developed irrigated farm lands in the Rio Grande delta from floods, in both the United States and Mexico. The LRGFCP includes 102 miles of grass-covered earthen structures along the United States margin of the Rio Grande and Anzalduas Diversion Dam. The dam diverts floodwaters into a United States interior floodway system (Banker/Main Floodway) flanked by 168 miles of levees. A second dam, Retamal Diversion Dam, routes Rio Grande floodwaters into Mexico’s interior floodway.

The distance between the United States and Mexican levees along the Rio Grande ranges from approximately 400 feet to 3 miles.

2.1.1 Mission Levee System

The Mission Levee System is illustrated in Figure 2.1. More detailed information is presented in 2-mile segments in Appendix A (Figures A1 through A6). The Mission Levee extends approximately 12 miles south of the City of Mission, from the Town of Peñitas (Mile 0.0) to its junction with the Banker Floodway (U.S. Interior floodway). The levee right-of-way (ROW) runs primarily through agricultural areas. Two irrigation canals border approximately 5 miles of the levee, on the landside: the Mission Main Canal (Project Miles 5.3 to 8.3), and the Granjeno Canal (Project Miles 10.2 to 12). The following wildlife management areas are located along the levee ROW or its vicinity:

• The Abram West, Abram East, La Parida Banco, El Morillo Banco, and Madero Units of the U.S. Fish and Wildlife Service (USFWS) Lower Rio Grande Valley (LRGV) National Wildlife Refuge.

Landfill

PEÑITAS

MISSION

Edinburg Intake Channel

ABRAM

Mission Canal Intake Channel

Banker Floodway

RIO GRANDE

Bentsen - Rio Grande Valley State Park

Granjeno Canal

Mission Canal

Military Road alongMission Inlet Closure

MADERONABA International Butterfly Park

Mile 9Mile 8Mile 7

Mile 6

Mile 5

Mile 4

Mile 3

Mile 2

Mile 1

Mile 0

Mile 12

Mile 11

Mile 10

Mile 9.5

Mile 8.5

Mile 7.5

Mile 6.5

Mile 5.5

Mile 4.5

Mile 3.5

Mile 2.5

Mile 1.5

Mile 0.5

Mile 11.5

Mile 10.5

MEXICO

TEXAS

McAllenMcAllen

BrownsvilleBrownsville

Mission Levee System Figure 2.1 - Location Map

J:\744\744778_Mission Levee EA\6A_Levee Analysis\mxd\location_map.mxd - 12/22/2006 @ 9:17:22 AM

Environmental Assessment International Boundary and Water Commission

United States Section

Scale = 1 : 45,000 0 2,500 5,000 7,500 10,0001,250

Feet

0 0.5 1 1.5 20.25 Miles

Mile Markers Existing Levee Footprint USFWS National Wildlife Refuge The Nature Conservancy Preserve TPWD State Park

Lower Rio Grande Valley National Wildlife Refuge

(Gabrielson Unit)

Lower Rio Grande Valley National Wildlife Refuge

(Cottam Unit)

Banker Floodway Anzalduas Dike Common Levee

Mile 5 Mile 4

Mile 3

Mile 2

Mile 1

Mile 0 Mile 4.5

Mile 3.5

Mile 2.5

Mile 1.5

Mile 0.5

MEXICO

TEXAS

McAllenMcAllen

BrownsvilleBrownsville

J:\744\744778_Mission Levee EA\6A_Levee Analysis\mxd\location_map_common_levee.mxd - 5/12/2006 @ 4:04:26 PM

Environmental Assessment International Boundary and Water Commission

United States Section

Scale =

0 1,300 2,600 3,900 5,200650 Feet

0 0.25 0.5 0.75 10.125 Miles

Mile Markers

Existing Levee Footprint

USFWS National Wildlife Refuge

Anzalduas County Park

Common Levee System Figure 2.2 - Location Map1:22,000

2-4 USIBWC

• Three tracts recently incorporated by the TPWD into the Bentsen-Rio Grande Valley State Park that are located within, or adjacent to, the levee ROW.

• One tract on the riverside of the levee acquired by the Nature Conservancy is part of the Chihuahua Woods Preserve.

• A land parcel largely used in agriculture, acquired by the North American Butterfly Association (NABA) for additional development of the International Butterfly Park.

NABA is a membership-base, not-for-profit organization working to increase conservation of butterflies in the United States, Mexico, and Canada.

Urban development in the vicinity of the Mission Levee System is primarily limited to the unincorporated towns of Peñitas, Abram, and Madero. Nearly all residential areas are located near the levee landside with the single exception of the Chimney Park trailer/RV park in Madero, located along the riverside of the levee at Project Miles 10.1 to 10.4. No residential developments are located, or allowed, within the levee system ROW.

The existing levee is a raised trapezoidal compacted-earth structure with a crown width of 16 feet, a typical height ranging from 6 to 10 feet, and an approximate 3:1 side slope ratio (units of horizontal run in feet per foot of vertical rise). The existing levee footprint ranges from 50 to 80 feet, depending on location. A typical levee cross-section is shown in the diagram below.

The levee crown is an unpaved service road with restricted public access throughout most of the Mission Levee System. In the downstream reach, part of the levee crown is a public road that includes a segment of Military Road along the Mission Inlet Closure (Project Miles 8.3 to 9.1). The levee crosses the intake channels of the Edinburg Canal and the Mission Main Canal. Across the Edinburg intake channel, the levee structure is replaced by a concrete retaining wall attached to the Peñitas Pumping Plant of the Hidalgo County Irrigation District No. One (Project Mile 0.6). The levee structure is complemented by a concrete retaining wall at the crossing of the Mission Main Canal of the United Irrigation District of Hidalgo County (Project Mile 5.3).

8 ft

64 ft

16 ft

3:1 Slope

2-5 USIBWC

2.1.2 Common Levee System

Figure 2.2 illustrates the Common Levee and Anzalduas Dike components of the Common Levee System. More detailed information is presented in Appendix A (Figures A7 and A8). Similar to the previously described Mission Levee geometry, the Common Levee System is a raised trapezoidal, compacted-earth structure with a typical height from 8 to 10 feet, and an approximate 3:1 side slope ratio (units of horizontal run in feet per foot of vertical rise). The existing levee footprint ranges from 60 to 80 feet, depending on location.

Anzalduas Dike

Anzalduas Dike, the upstream reach of the levee system, is an approximate 0.7-mile segment that extends from the north end of Anzalduas Dam to the dike junction with the Common Levee at the Banker weir. The entire length of Anzalduas Dike is adjacent to Anzalduas Dam County Park, operated and maintained by Hidalgo County. Most of the park land was acquired by the USIBWC as part of the flood control project and subsequently leased to the County for operation.

Common Levee

The Common Levee extends approximately 4.5 miles along the Banker/Main Floodway (Project Mile 0.7) to its junction with the River Levee segment surrounding the City of Hidalgo (Project Mile 5.2). This levee system serves as both the River Levee and the Banker/Main Floodway Levee.

The Common Levee ROW runs mainly through agricultural areas. There are no irrigation canals or residential developments on either side of the Common Levee. Parcels owned in fee by the USIBWC occupy the Banker Floodway that extends from the Banker Weir (Project Mile 0.7) to Rincon Road (Project Mile 2.6). On the riverside, this reach of the levee is almost entirely flanked by the Gabrielson and Cottam Units of the LRGV National Wildlife Refuge.

Downstream from Rincon Road (Project Mile 2.6), the floodway is referred to as the Main Floodway. Within the Main Floodway, parcels in which the USIBWC has flowage easements are privately owned. These parcels serve as flood easements used for annual crop agriculture where building of permanent structures, or development of woody vegetation, are not allowed. On the downstream reach of the Common Levee, outside the Main Floodway, agricultural parcels occupy most of the land (Project Miles 2.6 to 5.1).

2-6 USIBWC

2.2 PROPOSED ACTION

The Proposed Action would increase flood containment capacity of the Mission and Common Levee Systems to meet the 3-foot freeboard design criterion for flood protection.

Throughout the Mission Levee System, height increases between 2 and 6 feet are typically needed to reach the design freeboard value. For the Common Levee, typical increases in levee height range from 3 to 8 feet, and for the Anzalduas Dike, from 0 to 4 feet.

The proposed increase in levee height would also expand the levee footprint by lateral extension of the structure. For a typical cross-sectional area (8-foot elevation, 3:1 slope, and 16-foot crown), a 6-foot increase in levee height would result in a 36-foot offset increase in footprint. In this example, a current width value of 64 feet would expand to 100 feet as a result of the increased levee height. A typical cross-sectional area of the expanded levee is shown in the diagram below.

Expansion corridor width is commonly measured as the distance from the current levee centerline to the toe of the expanded levee. In the previous example, the distance from centerline to the toe is 32 feet for the existing levee, and 50 feet for the expanded levee (32 feet current distance to the toe plus an 18-foot expansion).

Along with the increase in levee height, structural improvements would also be required for levee segments throughout an approximate 7.5-mile reach of the Mission Levee System where seepage is a potential problem (downstream of Project Mile 4.7). Structural improvements are also likely required for the Common Levee. These improvements would consist of either a slurry cutoff barrier or a riverside impermeable liner. The slurry barrier would be installed at a closed trench on the riverside toe of the expanded levee. The impermeable liner would be buried to a specified depth (18-30 inches) along the levee slope, and from some distance from the riverside toe to above the riverside shoulder of the levee.

8 ft

6 ft

18 ft 24 ft

16 ft

3:1 Slope

Existing Levee

Increased Height and Footprint

2-7 USIBWC

2.2.1 Mission Levee System

Levee Alignment

While the centered levee expansion previously described is commonly used, an offset expansion is used when required due to insufficient ROW availability or existing infrastructure.

This offset expansion would take place entirely on the landside of the levee or the riverside, as allowed by the available ROW. Landside expansion, away from the river, is the preferred engineering option because it maximizes the containment capacity of the flood control system.

A typical expansion is illustrated below for a cross-sectional area at Project Mile 3.608 where the required increase in levee elevation is 4.42 feet. The height increase would extend the levee riverside toe to an approximate 73-foot distance from the current centerline from a current value of 40 feet. Taking into account a temporary 12-foot access corridor that would be required during construction, the potential direct impact corridor at that location would be 85 feet from centerline. The diagram below also indicates a minimum 40-foot separation between the expanded levee toe and the edge of wetlands present at that location, as determined during field surveys.

Landside expansion is the preferred engineering option throughout more than half of the Mission Levee System. For approximately 5 miles of the flood control system, however, riverside expansion would be required due to the presence of irrigation canals on the landside of the levee. These canals extend from Project Miles 5.3 to 8.3 (Mission Main Canal), and from Project Miles 10.2 to 12 (Granjeno Canal).

Crossing of the Edinburg Irrigation Intake Channel

The existing levee system crosses the Edinburg irrigation intake channel at Project Mile 0.6. At this location, a concrete floodwall attached to the Peñitas Pumping Plant is used instead of the compacted-earth levee structure. For the increase in levee height, the Peñitas Pumping Plant, a potential historical site, would not be modified by the project. Levee

SECTION 3.608 (Elevation Increase 4.42 ft.)

-160-140-120-100-80-60-40-20020406080100120140160

Riverside Distance from Current Centerline (feet)

E le va tio n (F ee t)

Wetlands' Edge

Levee Expansion

2-8 USIBWC

expansion would be accomplished by construction of a new crossing, using an earthen embankment similar to that used in the remaining levee system. The embankment, placed away from the pumping plant, would provide a new roadway for traffic crossing over the channel. To maintain the operability of the pumping plant, the new embankment would be built over intake pipes with a diameter similar to those of the pumping plant intake. This crossing of the intake channel, which would be approximately 500 feet long, is the only segment of the improved Mission Levee requiring construction outside the current ROW.

Military Road Expansion

A segment of Military Road runs along Project Miles 8.3 to 9.1 of the levee system (the Mission Inlet Closure). Military Road expansion is a project currently being implemented by the City of Mission and Hidalgo County as a separate project from the levee improvement by the USIBWC. This road project, in agreement with the USIBWC, has been designed to meet height requirements of the Mission Levee flood control system.

Madero Reach of the Levee System

An approximate 0.5-mile segment of the Mission Levee System, from Project Miles 10.0 to 10.5, runs along a trailer/RV park on the riverside of Madero. Along this reach, the narrow ROW available restricts lateral expansion of the levee. As an alternative, the current levee alignment and footprint would be retained by building a mechanically stabilized earth (MSE) structure to increase levee height and obtain the required flood containment capability. The MSE is a raised structure composed of compacted earth reinforced with concrete face panels and placed along the existing levee crown. The top of the existing levee would be excavated to a maximum depth of 4 feet to accommodate the structure base. The excavation depth would decrease as the structure height decreases, but a minimum of 1 foot of excavation would be required to tie the new construction to the impervious core of the existing levee. The diagram below illustrates a conceptual cross-sectional area of an MSE structure for a 6-foot increase in levee height.

6 ft

24 ft

16 ft

3:1 Slope

Mechanically Stabilized

Earth Structure

Existing Levee

2-9 USIBWC

2.2.2 Common Levee System

Levee footprint increases for the Common Levee/Anzalduas Dike would occur entirely within the ROW. Footprint expansion outside the Banker/Main Floodway is the preferred option to maximize its flood containment capacity. This alignment would be partially modified when warranted to minimize footprint expansion impacts to the Gabrielson and Cottam Units of the LRGV National Wildlife Refuge and other established wooded vegetation.

2.3 ALTERNATIVES CONSIDERED AND ELIMINATED FROM DETAILED STUDY

Raising the floodwall in place at the Peñitas Pumping Plant was considered to increase flood containment at that location. The alternative was removed from consideration because it would disrupt pumping plant operations and impact a potential historical structure. Continuing the levee across the intake channel was determined to be a better option to continue plant operations and provide a roadway for traffic crossing over the channel.

2.4 OTHER ACTIONS WITH POTENTIAL CUMULATIVE IMPACTS

Complete environmental impact analysis of the alternatives must consider cumulative impacts due to other actions. A cumulative impact, as defined by the Council on Environmental Quality (40 CFR 1508.7), is the “...impact on the environment which results from the incremental impact of the action when added to other past, present, and reasonably foreseeable future actions. Cumulative impacts will be evaluated, regardless of which agency (federal or non-federal) or person undertakes such actions. Cumulative impacts can result from individually minor but collectively significant actions taking place over a period of time.” The USIBWC reviewed a number of reasonably foreseeable actions with potential cumulative effects. Two projects were identified along the Mission Levee System, and none for the Common Levee System.

• Military Road Expansion. The City of Mission will expand the Military Road segment along the Mission Inlet closure, from a two-lane to a four-lane roadway. Since this project has been coordinated with the USIBWC, this segment of Military Road will be raised to match the increased levee elevation required for flood protection.

• Anzalduas International Bridge: The City of McAllen, in cooperation with other public and private organizations, will build a new international bridge that will cross the Common Levee System.