E7-23029. United States Section; Notice of Availability of a Final Environmental Assessment and Final Finding of No Significant Impact for Improvements to the Main and North Floodways Levee System in the Lower Rio Grande Flood Control Project, ...

AGENCY:

United States Section, International Boundary and Water Commission, United States and Mexico.

ACTION:

Notice of Availability of Final Environmental Assessment (EA) and Final Finding of No Significant Impact (FONSI).

SUMMARY:

Pursuant to Section 102(2)(c) of the National Environmental Policy Act (NEPA) of 1969, the Council on Environmental Quality Final Regulations (40 CFR parts 1500 through 1508), and the United States Section, International Boundary and Water Commission's (USIBWC) Operational Procedures for Implementing Section 102 of NEPA, published in the Federal Register September 2, 1981, (46 FR 44083); the USIBWC hereby gives notice of availability of the Final Environmental Assessment and FONSI for Improvements to the Main and North Floodways Levee System, in the Lower Rio Grande Flood Control Project, located in Hidalgo, Cameron and Willacy Counties, Texas.

FOR FURTHER INFORMATION CONTACT:

Daniel Borunda, Environmental Protection Specialist, Environmental Management Division, United States Section, International Boundary and Water Commission; 4171 N. Mesa, C-100; El Paso, Texas 79902. Telephone: [phone]; e-mail: [e-mail].

DATES:

The Final EA and FONSI will be available November 30, 2007.

SUPPLEMENTARY INFORMATION:

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, Sess. I Ch. 561 (H.R. 6453), approved August 19, 1935 (49 Stat. 660), and codified at 22 U.S.C. 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.

The USIBWC, in cooperation with the Texas Parks and Wildlife Department, prepared this EA for the proposed action to improve flood control along sections of the Main and North Floodways Levee System located in Hidalgo, Cameron, and Willacy Counties, Texas. This levee system is part of the LRGFCP that extends approximately 180 miles from the Town of Peñitas in south Texas to the Gulf of Mexico. The Main and North Floodway Levee system extends approximately 75 levee miles, downstream from Anzalduas Dam, and extending near the town of Mercedes to the Laguna Madre northwest of Arroyo City, Texas.

Proposed Action

Alternatives to the Proposed Action

The Proposed Action would increase the flood containment capacity of the Main and North Floodways Levee System by raising the elevation of a number of levee segments for improved flood protection. Fill material would be added to the existing levee to bring height to its original design specifications, or to meet a 2 feet freeboard design criterion. Typical height increases in improvement areas would be less than 1 foot and would not require expansion of the existing levee footprint.

In some locations, up to 2 feet of fill material would be placed on top of the levee, extending the levee footprint up to a maximum of 12 feet from the current toe of the levee. This expansion would take place along the approximately 20 foot service corridor currently utilized for levee maintenance, inside the maintained floodway, and entirely within the flood control project right-of-way. In some instances, adjustment in levee slope would be made to eliminate the need for levee footprint expansion, when required due to engineering considerations or for protection of biological or cultural resources. The need for excavation outside the levee structure is not anticipated.

Summary of Findings

Pursuant to NEPA guidance (40 Code of Federal Regulations 1500-1508), the President's Council on Environmental Quality issued regulations for NEPA implementation which included provisions for both the content and procedural aspects of the required Environmental Assessment. The USIBWC completed an EA of the potential environmental consequences of raising the Main and North Floodways Levee System to meet current requirements for flood control. 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 would retain the current configuration of the Main and North Floodways 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 Rio Grande flooding under severe storm events, with associated risks to personal safety and property.

Proposed Action

Biological Resources

Improvements to the levee system require placement of fill material that would affect grassed areas at levee footprint expansion locations. All expansion would take place along the current levee service corridor, limiting vegetation removal to invasive-species grasslands; this grass cover is expected to be rapidly re-established after project completion.

No significant effects are anticipated on wildlife habitat in the vicinity of the levee system, including potential habitat for threatened and endangered species. While approximately 17 percent of levee system is adjacent to natural resources conservation areas, only a small fraction would fall within levee improvement areas. In areas requiring levee footprint expansion, no woodland communities would be impacted; impacts on vegetation would be limited to non-native grasslands along the levee, of very limited value as wildlife habitat. No wetlands are located within the potential levee expansion area.

Cultural Resources

Improvements to the Main and North Floodways Levee System are not expected to adversely affect known archaeological or historical resources. Typically, placement of fill material over the existing levee would not expand the levee footprint; when levee footprint expansion is needed, expansion would take place within the service corridor currently used for levee maintenance. High-Probability Areas (HPAs) identified along the levee system would be located outside the improvement areas, with minor exceptions. In areas where HPAs are located near improvement areas, the need for footprint expansion would be eliminated by adjusting levee slope to retain current location of the toe of the levee.

Cultural resources located in the general vicinity of the levee system include historic age structures. Potential historic-age resources near the levee system would not be affected because most of those resources are located outside of the floodway, and away from potential levee footprint expansion areas. Only irrigation canals and minor irrigation structures, such as weir gates and standpipes, are located within or near the levee service corridor where footprint expansion would take place; irrigation canals and nearly all irrigation structures would be retained in their current condition.

Water Resources

Improvements to the levee system would increase flood containment capacity to control the design flood event with a negligible increase in water surface elevation. Levee footprint expansion would not affect water resources.

Land Use

Footprint levee expansion, where required, would take place completely within the existing floodway and along the levee service corridor. No urban or agricultural lands would be affected. Impacts to natural resources conservation areas would be limited to grassland areas.

Community Resources

In terms of socioeconomic resources, the influx of federal funds into Hidalgo, Cameron, and Willacy Counties from the levee improvement project would have a positive but minor local economic impact. The impact would 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. A moderate increase in utilization of public roads would be required during construction; a temporary increase in access road use would be required for equipment mobilization to staging areas.

Environmental Health Issues

Estimated air emissions of five criteria pollutants during construction represent less than 1.1 percent of the annual emissions inventory of Hidalgo, Cameron, and Willacy Counties. There would 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 Main and North Floodway Levee Project area, and none would affect, or be affected, by the levee improvement project.

Best Management Practices

When warranted due to engineering considerations, or for protection of biological or cultural resources, the need for levee footprint expansion would be eliminated by levee slope adjustment. Best management practices during construction would 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 and dust.

To protect vegetation cover, both the modified levee and construction corridor would be re-vegetated with native herbaceous species. To protect wildlife, construction activities would be scheduled to occur, to the extent possible, outside the March to August bird migratory season.

Availability

Single hard copies of the Final Environmental Assessment and Finding of No Significant Impact may be obtained by request at the above address. Electronic copies may also be obtained from the USIBWC Home Page at http://www.ibwc.state.gov.

Dated: November 20, 2007.

Allen Thomas,

Attorney Advisor.