Coastal Services Center

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Identifying Non-Point Sources of Fecal Coliform

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Fecal coliform bacteria can cause beaches and shellfish beds to close. Coastal managers in South Carolina are testing thermal infrared radiometer (TIR) imagery to see if this technology can help identify leaking septic tanks near the shoreline, a common source of fecal coliform.

The Project: Identifying Sources of Fecal Coliform Bacteria in Charleston, S.C.

Fecal coliforms in fresh and marine waters may indicate the presence of bacteria that can cause typhoid, dysentery, hepatitis A, and cholera. Drinking water and recreational lakes, rivers, ponds, estuaries, and ocean waters are therefore often monitored for fecal coliform contamination. Leaking septic tanks, sewer malfunction, contaminated storm drains, and storm water runoff are some of the many possible sources of this bacterial pollution.

Increased fecal coliform levels near shellfish beds can lead to shellfish bed closures. Shellfish are sensitive to fecal coliform contamination because filter-feeding organisms such as oysters, clams, and mussels can accumulate bacteria, protozoa, and viruses. The bacteria concentrated in the shellfish by this method of feeding are not harmful to the shellfish, but can be harmful to people that consume the shellfish.

To prevent further shellfish bed closures and improve the condition of restricted or closed beds, coastal managers need to know exactly where the septic system leaks and other illicit discharges are located. FLIR, a type of thermal infrared imaging, can help identify contaminated seeps by detecting differences in water temperature and thereby providing coastal managers with smaller focus areas from which to obtain water samples and conduct investigations.

Determining Information Using Forward Looking Infrared (FLIR) Imagery

Red arrows point to warmer liquid entering a water body, a cue that a septic system might have failed.

Through the Coastal Nonpoint Program, the S.C. Department of Health and Environmental Control (SCDHEC) funded a pilot project to determine if FLIR imagery is an effective method for identifying sources of fecal coliform bacteria that cause shellfish bed closures. SCDHEC's coastal management and shellfish management staff identified shellfish beds that were restricted or closed because of elevated fecal coliform levels. From the list of restricted or closed beds, specific shellfish bed areas were selected for the project where failing septic systems were believed to be a primary contributing factor. Once the project area was chosen, thermal infrared images were collected using a Mitsubishi 600 imaging system.

Flights were conducted during the winter, when the liquid from a leaking septic system or other illicit discharge is warm in comparison with the colder surface waters of a creek or river. Also, flying during winter months minimizes interference from leaf cover. The goal was to focus shellfish bed monitoring and water quality sampling efforts, reducing the time and money that would have been necessary to locate these possible leakages on foot.

Thermal infrared imaging is also successfully used in North Carolina and Arkansas to detect "hot spots" where failing septic systems, leaking sewer systems, and other illicit discharges are contributing to elevated fecal coliform levels.

The Result

By determining the location of possible leaks, this imagery can provide shellfish managers with a smaller focus area from which to obtain water samples and conduct investigations. This, in turn, cuts down on the time and costs expended as part of shoreline surveys to detect high levels of fecal coliform. SCDHEC staff is currently conducting ground-truthing and water quality analysis based on the results of this pilot project and will produce a final report comparing the findings of the thermal infrared study with the field verifications.

For More Information

For more information you may contact the Coastal Nonpoint Program Coordinator or the Trident District Shellfish Manager at the South Carolina Department of Health and Environmental Control.

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