Septic tanks aren't keeping poo out of rivers and lakes

August 3, 2015
In the largest watershed study of its kind, MSU researchers samples 64 rivers in Michigan for human fecal bacteria. Credit: MSU

The notion that septic tanks prevent fecal bacteria from seeping into rivers and lakes simply doesn't hold water, says a new Michigan State University study.

Water expert Joan Rose and her team of water detectives have discovered freshwater contamination stemming from . Appearing in the Proceedings of the National Academy of Sciences, the study is the largest watershed study of its kind to date, and provides a basis for evaluating and health implications and the impact of septic systems on watersheds.

"All along, we have presumed that on-site wastewater disposal systems, such as , were working," said Rose, Homer Nowlin Chair in water research. "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, it was assumed that the soil could filter human sewage, and that it works as a natural treatment system. Discharge-to-soil methods, a simple hole dug in the ground under an outhouse, for example, have been used for many years. Unfortunately, these systems do not keep E. coli and other pathogens from water supplies, Rose said.

"For years we have been seeing the effects of fecal pollution, but we haven't known where it is coming from," she said. "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, a novel method Rose calls "CSI (Crime Scene Investigation) for water," to sample 64 river systems in Michigan for E. coli and the human B-theta. Advances in source-tracking allow water scientists to track down the origin of non-point pollution more accurately than ever before.

Michigan, Florida and South Carolina, as well as resort areas near lakes all across the United States, rely heavily on septic tanks for . Though each state regulates septic tanks differently, more needs to be done in order to ensure humans are not contaminating surface waters by using septic tanks.

Continuing to use long-trusted methods of waste disposal systems may come at a hefty price, added Rose. The Environmental Protection Agency's latest survey for capitol improvement identifies the need to invest $298 billion over the next 20 years on wastewater and stormwater infrastructure to meet the Clean Water Act public safety goals of swimmable and fishable waters.

"This study has important implications on the understanding of relationships between land use, water quality and human health as we go forward," she said. "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."

Explore further: Scientist studies septic systems' effect on water quality

More information: PNAS

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4.5 / 5 (2) Aug 03, 2015
Did anyone ever think that burying or seeping sewage into the ground would make it disappear?
Only when populations were small and septic systems far apart did the idea seem reasonably safe.
not rated yet Aug 03, 2015
Nothing new about septic tanks near water fronts - contaminating the water. Soil characteristics and fluctuating water tables all contribute to the effectiveness - or lack of with septic tanks. Up until a few decades ago many waterfront communities allowed direct discharge of sewer lines into rivers. I grew up in Jacksonville, FL and one our favorite entertainments was shooting floating condoms in the creeks that ran into Trout River. Older water front homes in many areas have extremely poorly designed and maintained septic tanks and sewer systems. There are many water front communities that still allow sewage overloads to be discharged into water sheds and of course floods generally overflow sewage treatment plants and treatment lagoons. Septic tanks are often blamed for poor watershed quality as a leverage to expand municipal sewage treatment. That's good if municipal system keeps their sewage out of the watershed.
not rated yet Aug 04, 2015
Consider that septic tank effluent is good algae food, mixed properly of course it will produce enough biodiesel for the car per household used in photo-bioreactors to grow the algae, recent harvest techniques using EMF reduce costs to trivial vs centrifuges for micro-algae.

In a city effluent is worth a whopping 2-gal/person/day above the USA's needs for all transportation fuels ... just sayin' all it needs is more work on soot emissions.

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