Groundwater / Surface Water Interactions

Project Work Plan

Surface water, particularly urban streams, is often found to be contaminated with both chemical contaminants and pathogens. Potential pathogens include viruses, protozoa (e.g. Cryptosporidium, Giardia), and bacteria. Potential sources of these pathogens include faulty on-site sewage facilities (OSSFs), outfalls from publicly owned waste water treatment works, and leaking sewage collection systems. It is not uncommon for health warnings to be issued informing the public to avoid direct contact with stream water, especially immediately after storm events that flush contaminants off of surface areas and into streams. Groundwater is also vulnerable to pathogen contamination from surface sources where rapid infiltration or limited filtration capacity occurs. However, investigations of the extent of pathogens in groundwater as a result of nonpoint sources and specifically pathogen persistence, concentrations, and modes of transport or removal in groundwater are limited.

This proposed reconnaissance study will investigate pathogen occurrence in groundwater as a case study of the linkage of pathogens in surface or near-surface sources, surface runoff, and streams to impacts on groundwater. This study is Phase I of a two-phase study and will complete the following tasks:

  1. Complete the Project Administration and Public Outreach objectives for both phases of the project, except where Phase II extends beyond the completion of Phase I.
  2. Complete the Groundwater/Surface Water interactions studies objective, including the existing data study, reconnaissance study, and interactions report.
  3. Complete the Delineation of Potential Contamination Sources Study and Report.
  4. Prepare the water quality monitoring objectives, water quality monitoring plan, and data quality objectives for use in preparation of the Quality Assurance Project Plan (QAPP).

The subsequent phase(s) of this project will be conducted under the Section 604(b) Grant.

The intent of the investigation is to collect data on the occurrence of pathogens in groundwater adjacent to surface water bodies that have been identified as being impacted with or suspected to have been impacted with pathogens. Segment No. 1428, Colorado River below Town Lake, has been identified by the Texas Commission on Environmental Quality (TCEQ) as having high concentrations of bacteria and possibly related parameters of high nitrates and low dissolved oxygen. This river segment will serve as the area of investigation. Within this area, surface sources of (potential) pathogen contamination will be identified and groundwater quality and flow data will be collected to examine: 1) if surface sources or; 2) degraded river water quality are impacting groundwater quality. The focus of the investigative work will be on public or private wells in the zone of the aquifer nearby the river segment where pathogens originating from the stream, surface runoff from grazing land, or areas where land application of manures or sludge have occurred. This reconnaissance study will focus on potential sites of highest risk based on (1) density of OSSFs, (2) groundwater chemistry, and (3) areas the TCEQ Water Supply Division has identified with potential impacts.

Groundwater sampling sites and protocols will be developed for different depths within the aquifer and at different locations near t he river in order to assess the presence or absence of pathogens along differing lengths of flow paths within the aquifer. Because water quantity and quality are impacted by flow regimes, low and high flow regimes will be considered in the timing of sample collection. Wells with detailed information on water inputs, fracture locations from downhole camera surveys, tracer tests, geophysical logging information, and long term groundwater level and groundwater chemistry data will be selected, where possible. Installation of site-specific groundwater monitoring and sampling wells may be necessary but will be determined following the initial reconnaissance of the study area and assessment of the available sampling points or data files. Groundwater chemistry data will be acquired and assessment of the available sampling points or data files. Groundwater chemistry data will be acquired to evaluate variations in groundwater residence times. Water samples will be analyzed for total fecal coliforms and E. coli. If the results of these tests are positive, then polymerase chain reaction (PCR) analyses for selected pathogens (e.g., protozoa and viruses) will be conducted. PCR methods will also be conducted on a representative set of coliform negative samples to evaluate the usefulness of the coliform test as a surrogate for fecal viruses. Additionally, water flow and water chemistry data will be collected to assess flow pathways for the pathogens.

This study will be carried out by researchers from the Bureau of Economic Geology (BEG) at the University of Texas (UT) and its subcontractors.

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