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Keeping It Blue: Old septic systems pose a threat to water quality
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Keeping It Blue

Keeping It Blue: Old septic systems pose a threat to water quality


When looking for pollution sources to our waterways, we often look at our landscape and see obvious sources right in front of us. What we often don’t see is below-ground pollution sources.

Septic systems or “Private Onsite Wastewater Treatment Systems” are designed to take sewage and disburse it on the land to slowly infiltrate through the soil and into the groundwater. When designed and functioning correctly, they are effective at treating domestic wastewater. When not designed properly or failing, they will discharge nutrients, bacteria and other contaminants into ground and surface water.

The U.S. EPA has identified septic systems as one of the top five sources of pollutants in surface water bodies.

The average lifespan of a septic system is 30 years. Many of the systems around Geneva Lake pre-date the first rules that regulated systems in the 1970s. Many are original systems, meaning they are more than 50 years old, and no longer working properly. Those installed between 1970 and 1980 are “iffy” at best. After 1980, new state laws required better design and installation, making them more likely to still be functioning properly.

Within the Geneva Lake watershed, approximately 25% of existing septic systems were installed prior to 1970.

The key to a functioning system is good soil. Particularly on Geneva Lake’s south side, soils tend to be saturated with groundwater. This means wastewater can infiltrate groundwater directly without first being filtered through soil. Groundwater is the source of water for the lake and for drinking water. So even if a third of these systems were installed in poor soils, the amount of wastewater being discharged to the lake could be significant.

To understand how pollution occurs, it is important to understand how a system is designed to function. The system design starts with a soil test. The soil test determines the texture and porosity of the soil.

Prior to 1980, systems were installed based on a “perc” (or percolation test). The soil tester would dig a hole in the ground a few feet deep and pour water into the hole. If the water infiltrated at a certain rate, the property “perc-ed” and therefore was buildable. We later learned this was a poor way of judging soils. A “perc” test done on a dry day in late August could easily produce very different results than on a cool wet day in April.

Today, the soil test involves three large borings. The soil tester will then review and report the soil profile through an official soil evaluation report. This then determines the kind of system the site will handle. A common system type, when the soil has good absorption qualities, is the conventional seepage system. If soils are poor or there is high groundwater found during testing, some other system, such as a mound or holding tank, will be required.

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With the conventional system, the infiltration area and the system size is determined by soil absorption rate and design flow, which is based on the number of bedrooms. A common misconception is that systems serving seasonal homes can be smaller, because they are used less often, or that they can be overloaded on the weekend, because they will “catch up” during the week. It does not work this way. The infiltration area is designed for a maximum daily load of effluent. Once that load is met, the pores in the soil will become saturated and the system will no longer work. The system will fail much sooner when this occurs.

Obvious signs of system failure include saturation on the surface, areas of greener grass even in dry times, an obvious discharge of wastewater on the ground or effluent seeping out of the side of the mound system. Some people believe that if their toilets flush fine and sinks drain normally, their system is fine. This is not always the case.

When we talk about water quality, we often discuss phosphorous. Phosphorous is a major contributor to algae blooms, but nitrogen is a less discussed culprit. One pound of phosphorous creates 500 pounds of algae, but seven pounds of nitrogen can do the same. Septic systems are not designed to filter out nitrogen. The average human produces 11 pounds of nitrogen waste a year. The typical septic system discharges 20 pounds of nitrogen to the groundwater each year. Though the discharge to groundwater may not be an immediate discharge to the lake, if a septic system does not filter it properly, the phosphorus and nitrogen will eventually flow there. The improperly treated sewage can also contribute to high E-coli counts at beaches and make people and animals sick.

You can limit discharge of nutrients from your septic system by first knowing the kind of septic system you have, and the approximate year it was installed. If the system is older than 1980, it is not code-compliant. If it is older than 1970, it is very likely failing. If your neighbors are replacing their systems with holding tanks or mound systems, you have high groundwater in your area and your system is likely discharging directly to groundwater.

If your system was installed before 1980, you need to install a new septic system to protect Geneva Lake and all the people and wildlife who use it. In some cases, there are government programs and loans to help you pay for this.

Limit water use in your household to the design flow of the system. The plumbing code assigns a daily design load of 75 gallons per person per day. If permitted after 1980, a three-bedroom home has a septic system designed to accommodate six people per day. If you plan to have a big group on the weekend, hold off on laundry for a few days before or after. Also limit the use of the dishwasher during these times.

The law requires you to have your system reviewed, if you add bedrooms. Be sure to obtain the proper permits from the building inspector and the Walworth County Sanitation Officer in the Land Use and Resource Management Department.

Take care of your septic system to ensure it is not contributing to pollution in Geneva Lake. If not, we will all pay the price in terms of a lake that is overloaded with phosphorus and nitrogen creating an environment for algae blooms that limit recreational use for all of us and future generations.

“Keeping It Blue” is written by Geneva Lake Task Force members to inform and educate the public about water quality and other issues impacting Geneva Lake and how the public can help to address them. Comments and questions can be sent to

Shannon Haydin is deputy director of Walworth County Land use and Resource Management and a member of the Geneva Lake Task Force.

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