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Trying out the New Onsite Wastewater Treatment System Assessment Tool

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Through funding from U.S. EPA, a team at the Illinois State Water Survey with the help of NOWRA and RCAP developed the new Onsite Wastewater Treatment System assessment tool (OWTS tool). The OWTS tool was created as a companion to the Well Assessment Tool, which has been utilized by RCAP’s Technical Assistance Providers (TAPs) and other health professionals to help people across the nation evaluate their private wells.

The OWTS tool allows the assessor to collect contact information, landscape and geology details, and general information about the system and house. There is a checklist for site observations as well as miscellaneous questions to make sure you fully understand how the system is being used.

Once the OWTS tool was finalized, Steve Wilson and Sallie Dolan from our team headed out to perform some OWTS and well assessments. The first stop was close by in Piatt County. The homeowners have only lived in the house for a year and a half, so they were curious to learn as much as they can about the well and OWTS. 

The well was of good construction and had no obvious issues. It did have to be shocked with chlorine prior to them moving in, so we recommended they have the water tested for bacteria, nitrates, and that they have a broad panel test done. The home has a water softener and charcoal filter, but the homeowners did not know why they were added to the system. Identifying what metals, minerals, etc. are in the water will help them understand why they have these components.

The OWTS is in the backyard which slopes to a floodplain of the small drainage ditch/creek that runs along the northside of the property. It consists of a Delta Whitewater aerobic tank with chlorinator. The discharge pipe delivers the effluent into the creek floodplain. The homeowners have planted native wetland plants in the area which helps prevent water from standing and beautifies the area.

The 50-gallon tank had to be pumped within the first six months of them living in the home. The homeowners switched to septic-friendly toilet paper and learned the dos and don’ts of what goes into the system, yet it needed to be pumped again less than a year later. The previous owners reported that they never had a similar problem.

Three bedrooms and a family room are in the walk-out basement. Sallie’s theory is that moving trucks drove across the pipe while accessing the walk-out basement during move in. This would have caused the pipe to break and allow sediment to flow into the tank. We are hoping to be on-site when the system is scoped to see if this theory is correct.

The second home we visited was to our east in Vermilion County. The homeowner explained that a “wetland” had formed at the edge of his property which was full of leopard frogs. When we pulled up driving directions on Google maps, we knew that there was an issue with the system. The satellite image clearly showed the outline of a septic tank with lush, green grass growing in three lines while the rest of the yard was brown and dry. The homeowner had already acquired the sewage permit, and the as-built drawing matched up perfectly with the lines on the Google maps image.

The assessment revealed that the homeowner had built a two-bedroom addition to the house soon after it was purchased, taking it from a four-bedroom home to a six-bedroom one. Both homeowners work from home most days, they have three children who live at home, and older children who visit frequently. The “wetland” was an area of lower elevation just beyond the drain field where water from the system was pooling. We recommended that an OWTS installer who is registered with the local health department be contacted to determine if the system is now undersized for its current use. 

At first, the well log for this property could not be located. Luckily, the manager of the well and sewage programs at the local health department knew the site and was able to find the log for us. The well was a bored well with a buried slab. A 6-inch casing was placed from 12 inches above the surface to 28 feet deep, and then a 4-foot well was bored from 28 to 52 feet. According to the well log, it is topped with 28 feet of clay, which helps protect the well from surface water contamination. We also recommended that the soil be sloped around the well head to help protect it. Annual testing for coliform and nitrates is highly advised as they are indicators of potential contamination.

In both cases the assessment did its job to help identify areas of concern with the onsite wastewater treatment systems. The homeowners are more informed and can now take the next steps to contact a professional pumper/installer to help correct any issues found. 

The OWTS and well assessment tools can be found on our sister site,

If you would like an assessment done on your well and/or OWTS, contact your local RCAP office.

If you would like more in-depth information from Steve and Sally on how these tools work, check out the Conducting Private Well and Onsite Wastewater System Assessments webinar recording

What's New in our Document Library: Fall 2018

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Every day, staff members at search the internet to find events, resources and tools that have the potential to make a water operator's job easier and more effective. Here is a selection of our most recently-entered resources of interest to small system operators. 

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Cyanobacteria/Harmful Algal Blooms

Emergency Response

Financial Management


Non-community Systems



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Water Security