Septic Tanks May be Contaminating Freshwater Lakes and Resorts with Fecal Matter

First Posted: Aug 05, 2015 10:06 AM EDT

Septic tanks may actually be contaminating Michigan's waters. Scientists have uncovered freshwater contamination that stems from septic systems.

"All along, we have presumed that on-site wastewater disposal systems, such as septic tanks, were working," said Joan Rose, one of the researchers, in a news release. "But in this study, sample after sample, bacterial concentrations were highest where there were higher numbers of septic systems in the watershed area."

Until now, researchers assumed that soil could filter human sewage and that this worked as a natural treatment system. Discharge-to-soil methods, which is a simple hold dug in the ground under an outhouse, had been used for many years. Unfortunately, it seems as if these systems do not help with E. coli and other pathogens.

"For years we have been seeing the effects of fecal pollution, but we haven't known where it is coming from," said Rose. "Pollution sources scattered in an area-called non-point-have historically been a significant challenge in managing water quality."

The researchers used source-tracking markers in order to sample 64 river systems in Michigan for contamination. This revealed that these water sources were contaminated by septic tanks.

"This study has important implications on the understanding of relationships between land use, water quality and human health as we go forward," said Rose. "Better methods will improve management decisions for locating, constructing and maintaining on-site wastewater treatment systems. It's financially imperative that we get it right."

It's crucial to take steps to avoid contamination. Resort areas near lakes all across the United States rely heavily on septic tanks for human sewage, which means that steps need to be taken to avoid fecal matter in bodies of fresh water.

The findings are published in the journal Proceedings of the National Academy of Sciences.

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