The Most Common Mistake When Evaluating Onsite Systems for Real Estate Transactions

Not inspecting the entire system and relying on only the view through a vent will often result in misdiagnosing system failure

The Most Common Mistake When Evaluating Onsite Systems for Real Estate Transactions

A lot of people evaluate existing onsite systems for real estate transactions. The methods used vary in number equal to those performing the evaluations. 

I spent almost six years with four other industry professionals writing a curriculum on how to teach best practices for evaluating existing systems, for the purposes of accuracy and uniformity. We then had the curriculum (a large three-ring binder) peer reviewed by many leading industry professionals, from academics to installers and regulators. 

The No. 1 mistake I see constantly made by those evaluating existing systems is the same mistake I have watched several county inspectors make. I saw too many systems be prematurely replaced due to a flawed method of evaluation. These prematurely replaced systems easily had five to 10 years of life left in them, they weren’t nearing failure. This flawed method is still used by many to this day. 

This incorrect method is too simple: Pulling up to a site; looking in the vent; if there is water in the vent calling it failing.

Talk about grinding my gears. So I watched as county inspectors dropped pebbles in vents and if they heard a splash their letter said (I’m paraphrasing here): “Run for the hills this system is in bad shape.” If they did not hear a splash, their letter said (paraphrasing again): “Maybe start to run for the hills.”  It was clear to me that they were most interested in covering themselves. And back in those days they would not even remove the manhole cover because, I was told,  “…they are too heavy for us to lift…” 

But after repeatedly seeing this happen, and seeing too many systems be replaced that were in perfectly good operating condition, I knew something had to be done. I went back to several systems and took a spotlight and looked closely down the vent at the water, something the inspectors did not do. What became immediately apparent was a lot of the vents that were being used as the sole method of evaluating the systems were installed on the top of distribution boxes. Distribution boxes will have water in them and are not indicative of the saturation level (if any) of the distribution cell. Please read and internalize the previous sentence.

This made me so very angry, and that’s when I helped found the committee of WOWRA that worked on writing curriculum for accuracy and uniformity. 

What is a distribution box?

At least in my neck of the woods, distribution boxes were used in onsite systems on the inlet end and outlet end of the distribution cell in the 1970s and ’80s (and still in some systems today), the same way we use PVC headers or manifolds today.  When I need to explain what a distribution box is to customers I say, think of an underground garbage can made of concrete. Holes for pipes to connect are near the top of the distribution box. So when water flows into the distribution box, the water will never have a way to get out; they will always have water in them to about the bottom of the pipes leading into them. 

So I received a call from an older couple, frantic because they were on month seven of pumping their system monthly and adding an expensive additive each month because their pumper told them that the 22 inches of water in their vent meant the system was on its very last legs. After seven expensive months of pumping and additives, they wanted a second opinion because the level of water was still 22 inches in the vent. 

As soon as I heard the 22 inches I knew exactly what I was going to find there. I showed up with my trusty Milwaukee Tool M18 spotlight and looked in the vent. It could have only been more obvious that I was looking at the top of a distribution box if there was a neon arrow pointing into the vent that said ‘distribution box.’ I described to them that this was normal and why, and when I had them look in the vent, they could even tell it was a distribution box. I explained how that level will always be 22 inches, no matter how much pumping they do or additives they use.

Now, don’t get me wrong. If the vent is actually a pipe in the distribution cell (see image B, below) and not in a distribution box (D-box), then the level of the water in the pipe is an indication of the ponded water level in the system. However, if you are looking into a distribution box, seeing water is not a negative issue. 

And what if there is water in a vent that is not in a D-box? I always tell people that’s where I want to see the water; it’s supposed to be underground. Seeing water when we are stepping through puddles of it on the surface is a failed system, not water several feet below the ground. 

I was lucky enough to see onsite guru and soils expert Jerry Tyler speak many times. He once said that (I’m paraphrasing here): When a system has a biomat across the entire bottom of the system, and ponding has begun to occur across the entire footprint of the distribution cell, the system is not functioning at its highest efficiency. Once biomat covers the entire bottom, now you are using the entire footprint to treat the water

I always say, evaluate the system in its entirety, then look in the vent to corroborate what you already know. I also say that the vent is 5% of what I want to know.

Too many people use the vent as their sole method of evaluating a system, and that is wrong — especially when they are not aware of the different system construction methods discussed here. 

Water in a vent is not indicating a failed system. Our state has five definitions of a failed system. Not only do they not mention water in a vent, they don’t even mention vents. Vents were actually removed from our state code for a while. When I asked why, I was told ‘we took them out because they don’t do anything.’ While vents were reintroduced into our code years later, there still is no requirement for them (other than pump tanks and holding tanks), the code merely mentions how to install them if you do.

To attend a system evaluation four-afternoon class online in November look for evaluator certification at   

About the author
Todd Stair is vice president of Herr Construction Inc., with 34 years’ experience designing, installing, repairing, replacing and evaluating septic and mound systems in southeast Wisconsin. He is the author of The Book on Septics and Mounds and a former president of the Wisconsin Onsite Water Recycling Association.  


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