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Notice of Availability of a Draft Environmental Assessment and Finding of No Significant Impact for Improvements to the Lateral A/Retamal Dike Levee System, in the Lower Rio Grande Flood Control Project, located in Hidalgo County, TX

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


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


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 that the Draft Environmental Assessment and FONSI for Improvements to the Lateral A/Retamal Dike Levee System, in the Lower Rio Grande Flood Control Project, located in Hidalgo County, Texas, are available.

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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: (915) 832-4767; e-mail:

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Comments on the Draft EA and Draft FONSI will be accepted through February 5, 2007.

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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 U.S. Fish and Wildlife Service (USFWS), prepared this Draft Environmental Assessment (Draft EA) for the proposed action of raising the Lateral A/Retamal Dike Levee System located in Hidalgo County, Texas to improve flood control. 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 Lateral A/Retamal Dike Levee System extends approximately 14 miles, from the Carlson Settling Basin to Retamal Diversion Dam.

Proposed Action

The Proposed Action would increase the flood containment capacity of the Lateral A/Retamal Dike System to meet the 3-foot freeboard design criterion for flood protection. Throughout the approximately 11.5-mile Lateral A segment, height increases between 1.5 and 4 feet are typically needed to reach the design freeboard value. For the 3.5-mile Retamal Dike segment, typical increases in levee height range from 0 to 2 feet. The increase in levee height will result in an expansion to the levee footprint by lateral extension of the structure. Structural improvements, such as a slurry cutoff barrier or a riverside impermeable liner, may be required for some levee segments where seepage is a potential problem.

Alternatives to the Proposed Action

A No Action Alternative was evaluated for the Lateral A/Retamal Dike 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, with risks to personal safety and potential property damage.

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 Lateral A/Retamal Dike 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. Start Printed Page 798

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 Lateral A/Retamal Dike 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 Lateral A/Retamal Dike Levee would require vegetation removal. The approximate removal is 151 acres of herbaceous vegetation, 3 acres of Mesquite-Acacia woodland, and 8 acres of Texas Ebony-Anacua forest. Given its small extent, woodland removal would have a minimum impact on wildlife habitat. No significant effects are anticipated for any of the 25 threatened and endangered species with potential habitat near the right-of-way (ROW). None of 17 wetlands located within the ROW are located within the construction corridor and would be impacted by the potential levee expansion. Indirect impacts to wetlands near the corridor will be avoided, as required, by modification of the levee expansion alignment.

Cultural Resources

Improvements to the Lateral A/Retamal Levee system may adversely affect known archaeological resources, by mechanical excavation or by burial under the expanded levee footprint. Resources potentially affected include nine areas with a high probability to contain historic or prehistoric archaeological materials, and two known archaeological sites. Historic-age resources would also be affected, primarily structures associated with irrigation canals along the levee. These resources are the levee, canals, weir gates, standpipes, bridges, and residential structures. Several of the historic-age resources identified are located landside of the levee, across irrigation canals, and will not be adversely affected or minimally affected.

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 bodies.

Land Use

The expansion would take place almost completely within the ROW. Removal of approximately 3 acres of woodlands from natural resources management areas would be required. Levee expansion would affect less than 1 acre of active agricultural areas. Two irrigation canals along the levee would be temporarily affected by construction activities. There is a minimum potential for impacts on urban areas since no residential developments are located near the levee.

Community Resources

In terms of socioeconomic resources, the influx of federal funds into Hidalgo County from the levee improvement would have a positive local economic impact limited to the construction period; the impact would 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 is 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 0.7 percent of the Hidalgo County annual emissions inventory. There would be a moderate increase in ambient noise levels due to excavation and fill activities. No long-term and regular exposure is expected above noise threshold values. A database search identified no waste storage or disposal sites within the expanded levee footprint and its vicinity.

Best Management Practices and Mitigation

Engineering design measures will be used, including optimization of the levee expansion alignment to avoid impacts on wooded vegetation, wetlands, and other natural resources. Riverside expansion will be used for a majority of the Lateral A/Retamal Dike Levee System. During construction, best management practices will include development of a storm water pollution prevention plan to minimize impacts of receiving waters, and use of sediment barriers and soil wetting to minimize erosion.

To protect vegetation, the construction corridor may be re-vegetated with herbaceous or woody vegetation, as agreed with the natural resources management organization where the corridor is located. Final surveys prior to the start of the project would determine the types and amounts of vegetation to be removed, and separation between construction corridor and boundaries of wetlands. To protect wildlife, construction activities will be scheduled to occur, to the extent possible, outside the bird migratory season.

If buried cultural materials are encountered during construction, work would cease and notification given to the State Historic Preservation Officer. Mitigation actions recommended by the Texas Historical Commission (THC) for potential impacts to historical or archaeological resources will be specified in a Memorandum of Agreement between THC and the USIBWC.


Single hard copies of the Draft 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

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Dated: December 29, 2006.

Allen Thomas,

Attorney Advisor.

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[FR Doc. E7-46 Filed 1-5-07; 8:45 am]