I’ve been a certified soil tester in the state of Wisconsin for 34 years. I am not a soil scientist; I’m not half the soils expert that some of my colleagues and peers are. But I’ve performed a lot of soil tests, attended (and still attend) many clinics and classes, and trained soil testers, some who are now way better at soil testing already than I ever was.
Yet, this week I made a huge, (personally) thrilling soil discovery that really altered how I see soil testing. It was an extremely unique situation. When I explain, many of you will just say "Yeah, we’ve known this for a long time. Welcome to the club of understanding basic hydrogeology," but this blew me away.
Let me set the stage. I’ve said in a previous article it concerns me that some onsite installers use the term “perc test." Are there really places that still merely pour water in the ground and measure how fast it moves? I hope not, for health’s sake. The reason is that knowing how fast water moved doesn’t tell us if the water was moving through creviced bedrock untreated to an aquifer. The speed of the water in a perc test does not tell us if seasonally fluctuating groundwater would adversely impact a system if installed subsurface at that location. Perc tests utilize small holes compared to the excavations used for morphological testing.
Thankfully, we’ve moved on to morphological evaluations where soil testers are trained to determine structure and loading rates, and look for redox features and other limiting factors that would adversely affect the effluent being treated in the soil. The holes used here, larger than perc holes, are in many cases excavations large enough for the soil tester to see the entire profile on each side of the excavations and examine each horizon within that profile.
A soil test was performed for a commercial project. One half of the large area tested was considered mound soil as high chroma (red) redox was observed shallow. The other half passed for an inground system, as limiting factors were not observed until quite deep or not at all.
It was determined based on the size of the commercial system and the area it required that because the entire tested area would be utilized, the system was going to be sized for a mound system.
Immediately after the permit was issued for the mound, I received a call from a county inspector who said he was driving by the site and the site appeared to have been disturbed. The installer called me out to visit him at the site as he too said there was site disturbance and wanted me to meet him at the site.
I was absolutely not prepared for what we found, but it was one of those learning experiences I wish everybody could have.
We all know that mound systems use the in situ “A” or topsoil layer as one of the treatment layers within the mound system, and consequently there can be no impact to the surface within the proposed mound footprint.
I always put in writing to my customers that the mound area and 15 feet downslope must be protected from any vehicle traffic, stripping, filling and compaction. Should any of these occur to the mound area it would no longer be considered a viable site for a system, and in many cases could be the difference between the lot being buildable or not.
Upon arrival at the site, I was absolutely stunned by what I saw. The area the mound system was designed to go was now an excavation of at least three-quarters of an acre and 17 feet deep. The builder needed a borrow pit and boy, did they dig one. Unfortunately the borrow pit was right where the mound was supposed to go. To say this was one of the largest excavations I had ever seen is an understatement; it was huge.
I visited the site with a co-worker who is also a soil tester. We stood at the edge of the excavation almost speechless for a few minutes, the silence interspersed with a few colorful phrases. Your first thought when you see this is, “well obviously the mound area is no longer a mound area…”
Remember I said previous soil testing had shown areas suited for a mound vs. areas with no limiting factor, indicating those areas could be approved for inground systems.
I also mentioned earlier that the old perc tests utilized small holes. When we moved to morphological descriptions of the soil profiles and horizons, the excavations were larger, giving us a better view to observe far more detail in the soil. But the view we were looking at took the obvious description of what was happening in the soil below the surface to an entirely new magnitude. The county inspector met us, and I said we were lucky to see this very rare view of the soil, and joked that every soil test should be a half-acre hole 17 feet deep.
Some patterns in the soil on the wall faces and bottom began to emerge. I could see high chroma patches of redox along the bottom that looked like red waves due to how it was excavated. The detail you could see in the wall profiles was amazing — the different textures, patterns and colors told a much more detailed story than what we typically see standing in a 3-foot wide hole probing at it with our screwdrivers. As soil testers we were seeing a way more complete picture of what we were really working with here. There was no water nor moisture in the excavation.
Giant patches of redox were extremely apparent along the bottom of the walls. We measured down to the redox from the surface and determined the upper limit of the redox to be 10.5 feet deep. We consulted with the county inspector and determined a depth to limiting factor and depth for an in-ground system design, if there was enough square footage of area left that had not been excavated.
It’s difficult in a short article to explain how much was unveiled that gave us a much more nuanced understanding of what was happening at the site then we could tell from the typical soil test excavations. What the previous soil test found, how in one localized area the soil appeared to be suitable for a mound on one half and an in-ground system on the other, was strikingly apparent.
I mentioned (repeatedly) to the others with me that day how lucky we were to get this extremely rare view of the soil beneath the surface in this kind of amazing detail.
About the author
Todd Stair is owner and president of Herr Septic and Sewer, Inc., with over 35 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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