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Field team flags possible septic leak as likely source of Centerville 'CN10' E. coli hotspot
Summary
The student stream team identified a CN10 hot spot in Centerville Creek with upstream E. coli averages far above other nearby sites and presented a provisional hypothesis that an underground septic leak may be the source; they emphasized this is tentative and requires additional testing.
During the Lakeshore Water Summit presentation, field coordinator Karen Bergen described a persistent CN10 hot spot in Centerville Creek where weekly samples showed unusually high E. coli readings. After ruling out algae mats and an upstream farm (Klasig's) as sources, the team reported average E. coli levels across the three sub-sites: residential site average 830.35 CFU, bridge 923.1 CFU, and the upstream site 1,422.7 CFU. Based on the spatial pattern and downstream transport observations, the team advanced a working hypothesis that a leaking underground septic system near the upstream site could be contributing to the spikes.
Bergen stressed the tentative nature of the claim: "This is a hypothesis. Please don't go cold calling anybody," she said, and urged targeted follow-up rather than public accusation. The presenters said no visible septic tank was found on the property during field visits and noted underground tanks can leak when old or corroded.
What the team did and did not find: the team explained they performed QA/QC comparisons and additional localized sampling (outfall, bridge, residential sub-sites) and that the outfall—fed from a tile line—showed lower nutrient and E. coli readings than upstream sites, suggesting the source originates near the residential convergence. They noted that E. coli peaks moved downstream before settling at the upstream testing site in follow-up weeks, a pattern that informed their spatial inference.
Next steps recommended by the presenters include targeted pathogen-source tracking, septic-system inspections coordinated with property owners and health officials, and repeated sampling focused on the suspected origin. They emphasized follow-up testing and additional evidence are required before any public action.
Quotations: "We believe it could potentially be a septic tank leak, but this is a great area to carry over for next year to do some more testing," Karen Bergen said. "Please don't go cold calling anybody," she added.
Implication: the finding points to a specific, testable local source that county public-health, landowners and watershed managers can investigate, rather than an unspecified regional contributor.
