Percolation (Perc) Test - Clay Soil

[ME27272727]

With all of the alternative septic systems available today, is there ever a risk that a site is completely unbuildable due to poor soil permeability, or is the risk just associated with added cost of having to provide an alternative, more expensive system than a conventional subsurface system? For example, clay soil that is very slow perc rate, will a modified raised bed with sand or mound system typically always suffice?

I know every site is specific, just trying to get an idea of how often a clay site is deemed completely unbuildable.

 

[dik]

Depending on the clay... percolation test times can nearly be forever... might want to consider a raised bed or an alternative septic system...

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So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[TigerGuy]

In rural areas with extensive clays, they often use a surface lagoon, instead of septic system. Just like a septic tank, the lagoon needs to have sludge removed periodically.

Theoretically, you could build a septic system over a completely impermeable layer, but as dik indicates it would need to be one of the many alternative system designs in use today.

 

[EdStainless]

Around here (SE WI) they don't accept a perc anymore.
If you are building or replacing, they want to visually examine the soil.
They will tell the contractor where to dig and how deep for the examination.
Many of the systems here are raised mound, sort of a midway solution.
If you are over real tight clay, then there is a lot of work to be done.
U of Minn has done a lot of research on this subject.

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P.E. Metallurgy, consulting work welcomed

 

[phamENG]

Coastal Virginia here - everyone is on alternative now in my area. Clay starts about 6" below grade and is at list 8ft thick (then you're in sandy clay, not much better. My well point is 100' down) . Essentially impermeable. When we bought 8 years ago the old tank was being filled by groundwater back flow from the drain field after they pumped it.

Seller had to install an alternative system that treats and then discharges to a raised mound. From there it goes straight to a surface ditch.

Only places I could see being unbuildable for this would be a site adjacent to a particularly sensitive ecosystem, but even then there are systems that can practically turn the effluent to potable water. $ $ $ $ $, but possible.

 

[bimr]

Too general of a topic. Yes, it is possible that some sites may be small to be buildable. Among other things, it will depend on how many people, how may square feet, the topography, the effluent limit, the depth to groundwater, and how much does the builder want to spend.

 

[ME27272727]

Thanks for the responses. So if I understand correctly, on a large lot (20+acres) without ecologically restricted area / wells, where nearby homes are on tight clay with modified raised bed septic systems, it's very likely I should be able to build somewhere on the site with an alternative system. I'm just trying to gauge the risk of buying a lot with quick closing and without perc test contingency.

 

[phamENG]

I'd say the risk is huge. 20 acres without doing due diligence? That would be foolish. (And just because everyone else in the market is doing foolish things doesn't mean it's not foolish to do it with them. Something about lemmings and cliffs...)

 

[EdStainless]

Contact the local authority, here that is the county.
They have very detailed maps and tell you what is being used near by.
Here on 1 acre lots we have to pump and inspect every 3 years, no exceptions.
If you live near a lake it is an annual requirement.

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P.E. Metallurgy, consulting work welcomed