E6-17680. United States Section; Notice of Availability of a Draft Final Environmental Assessment and Finding of No Significant Impact for Improvements to the Mission and Common Levee Systems, in the Lower Rio Grande Flood Control Project, Located ...

AGENCY:

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

ACTION:

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

SUMMARY:

Pursuant to Section 102(2)(c) of the National Environmental Policy Act of 1969; the Council on Environmental Quality Final Regulations (40 CFR parts 1500 through 1508); and the United States Section's Operational Procedures for Implementing Section 102 of NEPA, published in the Federal Register September 2, 1981, (46 FR 44083); the United States Section hereby gives notice that the Draft Environmental Assessment and Finding of No Significant Impact for Improvements to the Mission and Common Levee Systems, in the Lower Rio Grande Flood Control Project, located in Hidalgo County, Texas are available.

FOR FURTHER INFORMATION CONTACT:

Gilbert G. Anaya, Supervisory 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].

Supplemental 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 TPWD, prepared this Draft Environmental Assessment (Draft EA) for the proposed action of raising the Mission and Common Levee Systems located in Hidalgo County, Texas to improve flood control. These two adjacent 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 Mission Levee extends approximately 12 miles along the Rio Grande, downstream from the Town of Peñitas. The Common Levee System, approximately 5.3 miles long, consists of the Common Levee and Anzalduas Dike, which connects the Common Levee to Anzalduas Dam.

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. Height increases between 2 and 6 feet are typically needed to reach the design freeboard value throughout the Mission Levee System. 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 increase in levee height will also expand the levee footprint by lateral extension of the structure.

Along with the increase in levee height, structural improvements will also be required for levee segments throughout the downstream reach of the Mission Levee and the Common Levee System where seepage is a potential problem. These improvements will consist of either a slurry cutoff barrier or a riverside impermeable liner.

Alternatives to the Proposed Action

A No Action Alternative was evaluated for the Mission and Common Levee Systems. This alternative will retain the existing configuration of the two systems, 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 National Environmental Policy Act (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 Mission and Common Levee Systems 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.

Mission 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 Mission 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 Mission Levee corridor would affect plant communities through excavation and fill activities. Impacts would occur on the levee sidewalls where fill will be added, and within the expanded levee footprint area. Potential acreage removed and impacts to four vegetation communities identified along the Mission Levee project area are as follows: (1) removal of up to 34.2 acres of mesquite-acacia woodland, in various stages of succession, along the levee corridor, (approximately 19 percent of thorn woodland located within the levee right-of-way); (2) removal of up to 77.5 acres of herbaceous vegetation along the levee corridor; impacts would be short-term as herbaceous vegetation would be rapidly re-established and is represented primarily by Bufflegrass, an invasive species; (3) up to 1.1 acres of wetlands/riparian communities will be modified along an irrigation intake channel; these communities are represented primarily by phragmites—arundo emergent and semi-emergent plants; and (4) minimum removal of agricultural lands is anticipated, less than 0.5 acre.

Thorn woodlands and wetlands along the Mission levee corridor provide the best quality wildlife habitat. Some wildlife species may utilize these areas as transit corridors, but that usage is likely limited. Natural resource areas with quality wildlife habitat adjacent to the riverside of the Mission Levee system occupy approximately 33 percent of the 12.1 miles total length, as follows: 2.4 miles along the Lower Rio Grande Valley (LRGV) National Wildlife Refuge; 1.3 miles along the Bentsen-Rio Grande Valley State Park; and 0.3 mile along the Chihuahua Woods Preserve. Based on regional distribution, 26 Threatened and Endangered (T&E) species habitat could be found in the project area. Improvements to the existing levee system are not likely to affect those habitats. Consultation with TPWD and the U.S. Fish & Wildlife Service (USFWS) will be conducted to schedule construction activities to minimize potential impacts on those species and their habitat.

Twenty-one wetlands and open water areas that met criteria as jurisdictional waters of the United States were identified within the Mission Levee right-of-way (ROW). None of these wetlands will be directly impacted by the levee expansion project. A single wetlands area, located outside the current levee ROW but within the potential levee expansion area, will be impacted by construction activities at the new levee crossing at the Peñitas Pumping Plant intake channel. Construction activities may remove approximately 1 acre from wetlands that flank the irrigation intake channel.

Cultural Resources. According to a preliminary cultural resources evaluation conducted in support of the EA preparation, improvements to the Mission Levee System have a potential to impact historic archaeological materials at six locations, as well as a known prehistoric archaeological resource (41HG143). No areas considered to be high probability for the occurrence of unknown prehistoric archaeological sites were identified in previous studies or during the current archival research. However, areas of historic occupation sometimes contain a prehistoric component and should also be considered as possible locations for prehistoric archaeological sites because European settlers also considered prehistorically utilized landform surfaces (stable surfaces) as desirable living surfaces. Four historic-age resources exist within the current Mission Levee ROW and are engineering elements of the levee system. These resources will likely be redesigned to some extent by proposed modifications to the levee, or may undergo a moderate visual impact by encroachment of the expanded levee footprint. One additional historical resource, the La Lomita Chapel, is located near the Mission Levee project within a National Register of Historic Places District, but outside the potential effects area.

Water Resources. Improvements to the levee system will increase flood containment capacity to control the design flood event as evaluated by hydraulic modeling. A minimum change in floodwater surface elevation, less than 1 inch, is anticipated as a result of the levee height increase for the Mission Levee System. Levee footprint expansion will not affect water bodies with exception of the new crossing at the Peñitas Pumping Plant intake channel.

Land Use. The approximate 113-acre expansion of the Mission Levee will impact mostly herbaceous vegetation dominated by invasive species (approximately 78 acres). Up to 34 acres of thorn woodland, a higher quality habitat, will also be removed. Removal of agricultural lands will be limited to 0.5 acre. Construction impacts along sections of the Riverside Subdivision of Madero will be temporarily affected by construction activities.

Community Resources. Improvements to the Mission Levee System, individually or in combination with the Common Levee System, represent an influx of federal funds into Hidalgo County and will have a positive local economic impact; however, the benefit will be limited to the construction period and represents less than 0.2 percent of the annual county employment, income, and sales values. No adverse impacts to disproportionately high minority and low-income populations were identified. Minimum utilization of public roads during construction is anticipated; a temporary increase in access road use will be required for equipment mobilization to staging areas.

Environmental Health Issues. Improvements to the Mission Levee System represent less than 1 percent of the Hidalgo County annual emissions inventory for five air criteria pollutants. Moderate increases in ambient noise levels will result from excavation and fill activities, with no transient or long-term exposures above threshold values for adverse impacts. No waste storage or disposal sites were identified within the expanded Mission Levee footprint and its vicinity.

Indirect Impacts. No significant indirect impacts of the Mission Levee Improvements were identified.

Best Management Practices and Mitigation. Engineering design measures will include optimization of the levee expansion alignment to the extent possible to avoid impact to sensitive vegetation and natural resources management areas, including Bentsen-Rio Grande Valley State Park and the LRGV National Wildlife Refuge. Mitigation for cultural resources, as required, will be coordinated between the Texas Historic Commission and the USIBWC. Levee expansion will be rerouted across the Edinburg irrigation intake channel to protect the historic-age Peñitas pumping station. Prior to construction, site surveys will determine the type (herbaceous or woody) vegetation to be removed and separation between construction corridor(s) and boundaries of wetlands.

During construction, best management practices (BMP) include development of a storm water pollution prevention plan to minimize impacts of receiving waters, including use of sediment barriers and soil wetting to minimize erosion. To the extent possible, construction activities will be scheduled to occur outside the migratory bird nesting season.

Following construction, expanded levees and the construction corridor will be promptly revegetated using native herbaceous or wooded indigenous species, as agreed with the natural resources management agency where the corridor is located. The USIBWC, in coordination with the USFWS, is developing approximately 30 acres of new wetlands as mitigation for levee improvements throughout the LRGFCP.

Common Levee System Proposed Action and Alternatives

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 Common Levee System, with no impacts to biological and cultural resources, land use, and soil, community resources, or environmental health. 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. The Common Levee System corridor runs primarily through agricultural areas. Approximately 1 mile of the total length of the 5.2-mile levee system runs along two units of the LRGV National Wildlife Refuge. No thorn woodland will be removed along the levee expansion, while 3.9 acres of low density woodland will be removed along Anzalduas Dike. The 3.9 acres along the Anzalduas Dike represent 10 percent of the total area of thorn woodland within the Common Levee System (including both the Common Levee and the Anzalduas Dike areas). A single wetlands/open water area located within the Common Levee ROW is located outside the 100-foot buffer area for the proposed levee expansion, and will not be affected by construction activities. Removal of T&E species habitat, including woodland habitat suitable for the ocelot, would be minimal along the Common Levee System corridor. For other species whose habitat is potentially present near the levee corridor, construction activities will be scheduled to minimize impacts to those species and their habitat.

Cultural Resources. No areas of high probability for the occurrence of unknown prehistoric archaeological sites have been reported along the Common Levee System, and none were identified during the current archival research conducted in preparation of the EA. Preliminary investigations indicate that two historic-age resources exist within the current Mission Levee ROW and are engineering elements of the levee system. These resources will undergo minor modifications at the levee tie-ins, or may undergo a moderate visual impact by the encroachment of the expanded levee footprint.

Water Resources. The Common Levee System was evaluated with the updated hydraulic model to determine if changes to water surface elevations will be affected by the proposed improvements to the levee system. As in the case of the Mission Levee System, a minimum change in floodwater surface elevation, less than 1 inch, is anticipated as a result of the levee height increase.

Land Use. The proposed expansion of the Common Levee System will occur entirely within the ROW. No urban development is located near the proposed levee expansion area. The expansion will remove approximately 62 acres of herbaceous vegetation along the Common Levee and approximately 6 acres of herbaceous vegetation along the Anzalduas Dike. Alignment of the levee expansion will be adjusted to minimize removal of established wooded vegetation along the Gabrielson and Cottam Units of the LRGV National Wildlife Refuge. Anzalduas Dam County Park, where Anzalduas Dike is located, will be temporarily affected during project construction. No impacts to agricultural lands are anticipated.

Community Resources. Improvements to the Common Levee System, individually or in combination with the Mission Levee System, represent an influx of federal funds into Hidalgo County that will have a positive local economic impact; however, the benefit will be limited to the construction period and represents less than 0.2 percent of the annual county employment, income, and sales values. No adverse impacts to disproportionately high minority and low-income populations were identified. Minimum utilization of public roads during construction is anticipated; a temporary increase in use of the access road will be required for equipment mobilization to staging areas.

Environmental Health Issues. Construction of the Common Levee System represents less than 1 percent of the Hidalgo County annual emissions inventory for five air criteria pollutants. Moderate increases in ambient noise levels will result from excavation and fill activities, with no transient or long-term exposures above threshold values for adverse impacts. No waste storage or disposal sites were identified within the expanded levee footprint and its vicinity.

Best Management Practices and Mitigation. Engineering design measures will include optimization of the levee expansion alignment to the extent possible to avoid impact to sensitive vegetation and natural resources management areas within the LRGV National Wildlife Area. Mitigation for cultural resources, as required, will be coordinated between the Texas Historic Commission and the USIBWC. During construction, BMPs include development of a storm water pollution prevention plan to minimize impacts of receiving waters, including use of sediment barriers and soil wetting to minimize erosion. Following construction, expanded levees and the construction corridor will be promptly revegetated using native herbaceous indigenous species.

Availability

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 www.ibwc.state.gov.

Dated: October 17, 2006.

Susan Daniel,

General Counsel.