Arroyo BST

Problem/Need Statement

The Arroyo Colorado Watershed is located in the Lower Rio Grande Valley of South Texas and flows through the middle of Hidalgo and Cameron counties. The lower 16 miles of the Arroyo Colorado is the boundary between Cameron and Willacy counties. The Arroyo Colorado drainage area is a subwatershed of the Nueces-Rio Grande Coastal Basin, also known as the Lower Laguna Madre Watershed. The streams of the Nueces-Rio Grande Coastal Basin, including the Arroyo Colorado, drain to the Laguna Madre, which is considered to be one of the most productive hypersaline lagoon systems in the world. The Lower Rio Grande Valley comprises the northern part of the Rio Grande Delta, a broad fluviodeltaic plain laid down over tens of thousands of years by the ancestral Rio Grande. Just as the Rio Grande is the major source of freshwater for the Lower Rio Grande Valley, the Arroyo Colorado serves as the main drainage stream for this area of Texas.

The Arroyo Colorado currently has low dissolved oxygen levels within the tidal segment, not meeting the aquatic life use designated by the State of Texas and described in the Water Quality Standards. This has been the case for every 303(d) list prepared by the state since 1996. In addition, bacteria has always been a parameter of concern and as of 2006, the Arroyo became impaired due to high bacteria levels. There are many challenges associated with restoring water quality in the Arroyo Colorado Watershed. The watershed is one of the most productive agricultural areas in the State; however, it also has one of the fastest growing populations of any region in the state as well, which increases the threat for bacterial impairments.

Surface water irrigation on consumptive crops is widely used. This bacteria impairment not only poses a human health threat through contact recreation but also potentially through consuming food that is grown with this water.

Previous work conducted in this area has laid the ground work and produced outcomes that will be incorporated into this effort. Specifically, the TSSWCB funded project (06-10) entitled Arroyo Colorado Agricultural Nonpoint Source Assessment utilized the SWAT model to simulate flow and nutrient loadings to the Arroyo Colorado. These data provide critical flow and nutrient information that will aid in the development of BMPs to address bacteria and nutrient loadings and develop estimated load reductions that will be incorporated into the revision of the Arroyo Colorado Watershed Protection Plan (WPP). Additionally, other efforts are ongoing with a range of focus from sustaining the partnership to educating landowners on available financial incentive programs to implement agricultural BMPs.

TCEQ is funding a project to revise the Arroyo Colorado WPP. Initially written with implementation scheduled through 2015, the Arroyo Colorado WPP focused primarily on nutrients, but through adaptive management, the bacteria impairment has become an issue stakeholders are prepared to address in the next phase of the plan.

Although data collected through these projects tend to justify the currently listed impairment, this data remains limited and additional data is needed to accurately calculate bacteria loading rates and the most likely sources of bacterial contamination. The needs for a bolstered data set and comprehensive data analysis arise as management options are considered. Without adequate data, uncertainty increases in properly identifying the sources of contamination in the watershed while comprehensive data analysis is needed to hone in on potential sources of water pollutants. Collecting 12 months of additional water quality and streamflow data along with input from local stakeholders will provide much needed information that will enable more accurate watershed pollutant source assessments and the revision of a focused and effective Arroyo Colorado WPP.

General Project Description

Through this project, a water quality monitoring regime will be employed that will help decision makers make appropriate recommendations for addressing the bacteria impairment in the revision of the Arroyo Colorado WPP. Monthly sampling will be conducted at 12 sampling sites as identified in the WPP. UTB will conduct water sampling, measure field parameters (pH, temperature, conductivity, and dissolved oxygen), and deliver samples to the NELAP-accredited Brownsville Public Utilities Board Analytical Laboratory for enumeration of E. coli and Enterococcus. Data will be stored in a database maintained by UTB containing field and lab analysis data. UTB will manage and prepare data consistent with the TCEQ Data Management Reference Guide (DMRG) for submittal to TSSWCB (through TWRI) and subsequent transmittal to TCEQ for inclusion in Surface Water Quality Monitoring Information System (SWQMIS).

TWRI will conduct a source survey to identify possible sources of bacteria in the watershed. Based on this assessment, TWRI, in consultation with UTSPH, will collect 200 known source fecal samples and ship them to UTSPH according to established protocols for processing and inclusion in the Texas E. coli BST Library. Further, Brownsville PUB Analytical Laboratory will prepare water samples for transport to UTSPH for BST analysis. To assess and identify different sources contributing to bacterial loadings, UTSPH will conduct library-dependent BST and analyze E. coli isolates using the ERIC-PCR and RiboPrinting combination method. Results of the source survey, assessment of bacterial levels at each site, and BST results will be presented to the Arroyo Colorado Watershed Partnership (ACWP) for incorporation into the WPP.

Funding Source

Funding provided by the Texas Commission on Environmental Quality as part of a Clean Water Act Section 319(h) Grant.