Groundwater / Surface Water Interactions

Surface water, particularly urban streams, is often contaminated by chemicals and pathogens. Pathogens are disease-causing organisms such as bacteria that can cause illnesses, even at low concentrations. Potential pathogen sources for surface water include septic tanks, public wastewater treatment plant effluent, leaking sewage collection systems and other nonpoint and point sources of pollution. Groundwater is also vulnerable to pathogens from surface sources where rapid infiltration or limited filtration capacity occurs. The extent of pathogens in groundwater from nonpoint sources, and specifically pathogen persistence, concentrations and modes of transport, has not been fully investigated.

The Examination of Groundwater/Surface Water Interactions and Potential Contamination Sources project is the first phase of an investigation of the pathogen risk to human health where public and private alluvial aquifer wells are used as a drinking water source. The project is investigating pathogens in groundwater adjacent to surface water bodies that are identified as being, or suspected as being contaminated by pathogens, and will be used as a case study of the linkage of pathogens in surface or near-surface sources, surface runoff and streams, to impacts on groundwater.

The Texas Commission on Environmental Quality (TCEQ) has identified high concentrations of bacteria and possibly related parameters of high nitrates and low dissolved oxygen in the study area of Colorado River Segment No. 1428. Within this area, project members are identifying surface sources of (potential) pathogen contamination and collecting groundwater quality and flow data to determine if surface sources or degraded river water quality are affecting groundwater quality.

This reconnaissance study is focusing on public or private wells in the alluvial aquifer along the river segment where pathogens originating from the stream, surface runoff from grazing land, or application of manures or sludges have occurred. It is focusing on potential sites of highest risk based on density of onsite wastewater treatment systems, groundwater chemistry and areas the TCEQ Water Supply Division has identified with potential impacts.

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