Concerns about water quality on Isle of Palms first emerged in the late 1990s, when elevated fecal coliform levels were detected in drainage ditches. In 2000, city council paused a proposed septic tank ordinance after residents and officials questioned whether the contamination came from human waste or from animals. Without clear evidence, council chose to pursue scientific testing. With support from the South Carolina Department of Health and Environmental Control (DHEC), IOP initiated a federally funded water quality study.
PHASE I (2002)
DHEC sampled 15 locations across the island, including drainage outfalls and open water areas. All samples were analyzed for fecal coliform, and select locations were also tested for nutrients such as nitrogen and phosphorus.
PHASE II (2002-2003)
Follow-up testing focused on areas with higher contamination. Advanced DNA analysis was used to determine whether fecal coliform came from human or animal sources.
KEY FINDINGS:
- Human-source contamination was limited and localized, primarily near the Forest Trail outfall
- Human waste accounted for only about 20% of fecal coliform at that site
- Less than 10% of samples from open waters showed human sources
- Approximately 70% of contamination was traced to domestic and wild animals
- Based on these results, human sewage issues were ruled out.
RENEWED TESTING (2024–2025)
Over time, increased housing development with septic systems, stronger storms and frequent flooding renewed concerns about water quality. In response, the city’s Environmental Advisory Committee (EAC) initiated a new baseline study in 2024.
2024 BASELINE STORMWATER STUDY
During a rain event, eight stormwater outfalls across the island were sampled and tested for a variety of contaminants, including fecal coliform.
RESULTS:
Three outfalls showed elevated “levels of concern:”*
- 25th Avenue – extremely high nitrogen levels, suggesting runoff pollution
- 36th Avenue/Forest Trail – elevated nitrogen, phosphorus and suspended solids
- Myrtle Avenue – elevated phosphorus and sediment
This study established a new baseline for additional testing.
DNA TESTING OF HIGH-CONCERN AREAS (2025)
To determine whether human waste was contributing to contamination, the city conducted targeted DNA testing at the three highest-concern residential outfalls.
Samples were collected under both dry-weather and rain-event conditions and screened for E. coli. When bacteria levels were high enough, DNA testing was performed to identify sources.
RESULTS:
- DNA analysis detected dog waste only>/li>
- No human-source E. coli was found in any sample, including during heavy rainfall
- The likely sources were domestic pets, wild animals or a combination of both
WHAT THE STUDIES SHOW
- Two comprehensive testing efforts — conducted more than 20 years apart — reached the same conclusion:
- Human waste was not found in outfalls on Isle of Palms
- Animal waste, primarily from dogs, is the main source of fecal contamination
WHAT THE STUDIES SHOW
The EAC plans to retest island outfalls in two years to evaluate changes following a pet waste education and cleanup initiative with Doody Calls planned for 2026.
Additional attention will be given to marsh health, recognizing the importance of these ecosystems to the island’s environmental well-being.
Protecting water quality is a shared responsibility. Cleaning up after pets can make a measurable difference.
*“Level of concern” refers to contaminant concentrations exceeding recommended environmental guidelines.
By Laura Lovins – IOP Environmental Advisory Committee Chair
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