Binational Study Regarding the Presence of Toxic Substances in the Rio Grande/Rio Bravo and its Tributaries Along the Boundary Portion Between the United States and Mexico -
Phase 3 Proposal

In February 1992, Mexico and the United States issued the first stage of the Integrated Environmental Plan for the Mexican-U.S. Border Area (First Stage:1992-1994; the subsequent plan is now called US-Mexico Border XXI Program). This plan set the stage for the two countries to work jointly in identifying and solving problems along the International border. On November 13, 1992, the United States and Mexican Sections of the International Boundary and Water Commission (IBWC) approved Minute No. 289, titled "Observation of the Quality of the Waters Along the United States-Mexico Border." This agreement resulted in the first phase of the Rio Grande/Rio Bravo Toxics Substance Study (RGTSS). These studies have been a binational multi-phase and multi-agency effort to characterize the extent of toxic contamination of the Rio Grande/Rio Bravo and its tributaries.

The original study was prompted by a widely held belief that the river was being contaminated by toxic substances originating from industrial and agricultural sources near the border. This concern has intensified in recent years with the increasing number of industrial facilities within the border region. While revealing some evidence of contamination from toxic substances, review of prior studies yielded limited information and failed to provide any environmental assessment.

The overall objective of the multi-phase study was to determine if the suspected contamination of the Rio Grande/Rio Bravo by toxic substances was, in fact, occurring. This objective was accomplished by the analysis of a full spectrum of chemical analytes in order to detect their presence and evaluate their impact on fish and other aquatic organisms living in the river.

Problem Definition:

Due to the variety of activities occurring in the Rio Grande/Río Bravo basin, it is difficult to pinpoint exact sources of a particular contaminant. Phases 1 and 2 of the RGTSS were intended to be a starting point and not an answer to all of the water quality issues facing the Rio Grande/Río Bravo. Concerns identified in the multiple phases of this study have assisted in focusing resources on those sites and those contaminants most likely to impair water quality.

Project Description:

The proposed project will focus on the El Paso/Ciudad Juárez-Big Bend National Park reach. This reach extends upstream from the El Paso/Ciudad Juárez metropolitan area and includes the area upstream and downstream of the Río Conchos confluence with the Rio Grande/Río Bravo. Phase 2 Site Ranking Classification identified the portion of the reach from El Paso/Ciudad Juárez to Presidio/Ojinaga as a high potential risk for toxic substance effects. A moderate potential for toxic substance effects was identified at Big Bend National Park-Santa Elena Canyon. The primary goals of this project are to:

• Verify the results from Phase 1 and Phase 2 with more intensive monitoring at fewer sites; better define problems.
• Determine the stressors that have the greatest effects on aquatic communities and human health.
• Perform multivariate analyses using habitat, land use, physical/chemical, and biological data in order to determine stressors at the sites.
• Perform upstream/downstream assessments of paired stations and make comparisons among stations of heavily urbanized/high impairment, limited urban/agricultural/moderate impairment, and natural/limited agriculture/limited impairment.

The data will be used to set priorities for wastewater treatment upgrades, nonpoint source best management practices and other potential mitigation practices.

Partners:

The Texas Natural Resource Conservation Commission (TNRCC), United States Environmental Protection Agency (USEPA), International Boundary and Water Commission- United States/Mexican Sections (IBWC), Comision Nacional del Agua (CNA), United States Park Service (Department of Interior) and the United States Geological Survey (Department of Interior).

SUMMARY OF PHASE 3 DATA COLLECTION COMPONENTS

STUDY AREA

The proposed stations are located upstream and downstream of three very distinct areas. El Paso/Ciudad Juárez and Presidio/Ojinaga both represent sources of stressors on the Big Bend National Park area, an important and valued shared natural resource. This reach of the Rio Grande/Río Bravo offers a unique opportunity to assess a variety of factors over these three areas including: habitat alteration, land use, water/sediment quality, flow variations and biological communities. These components can be brought together to identify key stressors on each of these areas.

TROPHIC LEVEL BIOACCUMULATION OF METALS AND SELECTED PESTICIDES (Aquatic Community Health)

Based on data from Phase 1 and 2, metals were the most common contaminant found in water and sediment. The most common pesticides found were DDE and chlordane. Algae (if present), benthic macroinvertebrates (herbivores and predators), minnows (prey species) and large fish species (predators and forage species) will be analyzed for metals and the selected pesticides to determine if bioaccumulation is occurring.

WATER

Samples (routine chemical) are needed to further assess elevated salinity. This was identified as a potential stressor in Phase 2, especially in Presidio/Ojinaga and Big Bend National Park. In Phase 2, the highest chloride concentrations were found in the El Paso/Ciudad Juárez-Big Bend National Park reach. Dissolved metals in water will also be collected. Organics in water, not found in this reach, will not be collected. Field data will also be collected.

SEDIMENT

Single composite sediment samples collected in Phase 1 and 2 indicated the presence of metals at all sites. These samples were all collected in a single general area at the sample station. In Phase 3, we would like to collect replicate samples over a broader sample area. Sediment samples will be analyzed for metals, selected pesticides, and conventionals.

FLOW

Instantaneous flows will be calculated at the time of sample collection. Analysis of historical flow data will be analyzed as part of the USGS habitat assessment.

BIOLOGICAL COMMUNITY

Benthic macroinvertebrate, fish and possibly plankton communities will be sampled in Phase 3.

EDIBLE FISH TISSUE (Human Health)

The edible portion of fish tissue will be analyzed for metals and selected pesticides in an attempt to further define potential human health issues.

TOXICITY

Samples for toxicity in water and sediment will be collected. Significant effects of water on water fleas were observed downstream of Presidio and at Santa Elena Canyon. Toxic effects of sediment on fathead minnows was found downstream of El Paso/Ciudad Juárez. Samples are needed to verify, especially in Presidio/Ojinaga and Big Bend National Park, if these occurences were anomalies or chronic problems.

HABITAT ASSESSMENT

Intensive habitat assessments will be done on Phase 3 sites. This information will be used primarily in a multivariate analysis along with land use, biological and physical/chemical data. This will allow for comparisons between stations and to define potential stressors.

Tasks to be completed by the USGS on a Reach Scale will include the following (as proposed by Bruce Moring to TNRCC Border Environmental Assessment Team (in part); funded by the Clean Rivers Program and USGS):

Establish a reach representative of the biological sampling area

Longitudinal survey and mapping of reach

• Map reach from upstream to downstream boundary including channel features, point bars, islands, snags, undercut banks, and other channel features.
• Map reach using laser-surveying system with a total station.
• Map reach at intervals equal to the high-bank to high-bank width (i.e. floodplain terrace).

Cross-sectional surveys at four transects

• Conduct cross-sectional surveys at four transects that represent the most changes in channel shape/form (i.e., at bends and riffles); conducted from high-bank to high-bank at regular intervals and/or each break in slope.
• Determine bank slope, bank height, bank width, and ratios for each cross-section.

In-channel assessments

• Velocity, depth, and substrate characterization at thalweg and points equidistant back to each water edge.

Point-quarter vegetation assessment

• Conduct point-quarter analysis of woody (or other) vegetation on each bank at each transect.
• Species composition; dominance and diversity.

Scoring/characterization of bank features

• Score bank stability based on vegetative coverage; presence/absence and type of bank erosion.
• Characterize bank type based on shape (linear, concave or convex).

Measures of flow variability

• Establish reach at or in close proximity to a gaging station (if possible).
• Determine comparable period of record of discharge for all sites (>10 years); mean monthly discharge per site; coefficient of variation of monthly discharge over period of record; frequency of zero flows; ratio of mean annual to discharge area; and differentials for maximum and minimum monthlies.

Habitat assessment will be done at the six (6) proposed Phase 3 sites. The proposed stations are all on the mainstem. USGS has agreed to do a total of ten (10) sites. The remaining four are open for discussion. Additional habitat assessment at sites located on the Pecos and Devils Rivers is possible. In addition, rapid bioassessment protocols for habitat assessment will be conducted at each station at the time of sample collection.

The habitat work is to be done by study participants but may not correspond to the biological, chemical data collection field trip. The work is planned for late July/early August and must be completed before August 31, 1997. This work has an added benefit in that it will also train United States and Mexican personnel how to use USGS/NAWQA habitat assessment techniques.

MULTIVARIATE DATA ANALYSIS

Habitat, land use, physical/chemical, and biological data will be used to do a multivariate analysis of the sites using Phase 1, 2 and 3 data. This is a key way to determine stressors with the greatest affect on the aquatic community and human health. In general, the multivariate analysis will consist of an (1) upstream/ downstream assessment of paired stations, and (2) comparison of stations from heavily urbanized/high impairment to limited urban/agricultural/moderate impairment to natural/limited agriculture/limited impairment.

1997 Phase of the Binational Rio Grande/Río Bravo Toxic Substance Study

Proposed Stations and Parameters

*Biological Community-benthic, fish, plankton-may be done in different combinations depending on availability at a site.

Proposed time frame for the water, sediment and biological data collection field trip -one week long trip in late July. We are planning to do one (1) station/day. We would like to set a date as soon as possible.

**USGS habitat work will be done independently of the water, sediment and biological data collection trip. This will require the assistance of study participants. The time needed to do the habitat assessments is one (1) station/day