Fecal Coliforms Increase in a Storm Drain Fed Pond After Rain Events

Veronica J. Albrecht


Cannon Hill Park Pond (CHPP), Spokane, WA is a residential pond that has historically been maintained by the continuous input of potable water (~14 million gallons/year, City of Spokane Water Quality Report Cannon Hill). In 2010, as part of the Lincoln Street Spokane Urban Runoff Greenways Ecosystem project, a vegetated bio-filtration cell (storm garden) was designed to capture and filter storm water and direct its flow to CHPP via a storm drain. It was meant to mitigate storm water and sanitary sewage overflow during storm events and contribute to CHPP water levels (estimated 315,000 gallons/typical year). While the City of Spokane has conducted some chemical analyses of CHPP, they have yet to conduct any fecal coliform (fc) testing. We were interested in comparing fc levels in CHPP to levels recommended by the Washington State Department of Ecology(WA-DOE) and in determining if fc levels increased with rain events due to the storm water input from the storm drain. To address our questions, we used a membrane filtration method and cultured filters on mFC agar to identify fc bacteria. We sampled three different pond sites: directly in front of the storm drain, from the potable water spigot, and an off-shore point >10m from the storm drain. We sampled CHPP weekly for 15 weeks (10 non-rain events, 5 rain events) and determined that fc levels at the storm drain and at the off-shore site, exceeded WA-DOE levels (10% samples exceed 400 fc/100 ml). Additionally, we found that during rain events there was a significant increase in fc detected at the storm drain p=0.007, but not at the off-shore site, p=0.13. We never detected fecal coliforms in our potable water samples.


Fecal Coliforms, Rain Water, Washington

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