Effects of Septic Fields on Sylvan Lake Water Quality and Public Health

The 2005 study of the watershed by AXYS Environmental included investigations of the nutrient and bacteriological impacts of shoreline properties on near-shore water quality. The goals were in part to determine if that source of nutrient loading of the lake might contribute to blue-green algae growth and to detect if added bacteria might be of public health concern.

Two important AXYS 2005 (15 MB download) conclusions are:

1. The Phosphorus and Nitrogen nutrient loading of the lake from septic field seepage were estimated to be less than 9% and 3% respectively of the total P and N nutrients discharged into the lake at that time. Most of the nutrient load enters the lake in the tributary flows that carry nutrients and contaminants off the land into the lake.

Since 2005 more septic fields have been replaced with holding tanks and containment is improved so releases to the lake presumably have been reduced substantially.

2. Two surveys (1988 and 2004) of bacteriological contamination in the near-shore zones that might be affected by septic field seepage determined that water samples met health standards on those dates. The AXYS 2005 authors concluded that more bacterial contamination likely entered the lake in tributaries than in septic field seepage.

The importance of these facts for lakefront communities is that the risk to Sylvan Lake caused by septic field contamination as assumed by some may be too high. Therefore the benefit/cost ratio of the proposed sanitary servicing project described in other related SLWSS News posts is likely lower than imagined.

In addition, management of sewage by property owners has changed since 2004. Containment and handling has been improved and seepage into the lake surely has been reduced substantially since then.

 

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