Restrictive Soil Layer

FYI - The soil in many areas of the United States have a restrictive layer. The restrictive layer means a layer of soil that stops or impedes the vertical movement of water, air, and growth of plant roots. It has different names depending on how it was formed, such as hardpan, claypan, fragipan, and caliche. Even with proper surface grading, as shown in the graphic below, water percolates down until it reaches the restrictive layer then move horizontally. These restrictive layers may not follow the same slope as the ground surface. The restrictive layer can slope towards the foundation, slope away from the foundation or even create a depression that holds water like a bowl. The restrictive layer can be a few inches to several feet thick. In the southern part of Missouri the restrictive layer is typically found 2 to 4 feet below the ground surface. The graphic depicts subsurface water running back towards the foundation. This restrictive layer can be responsible for seasonal high water tables, especially where a depression in the restrictive layer holds water.


In my area, it’s all about the hardpan. Two and a half feet down, bam. Hardpan. Parts of my yard it’s only a foot down.

Great post and illustration, Randy. Dam, you must have been reading my mind. Just about to create a blog and was thinking of material to use.

May I add to that; bedrock, frozen soils, dense soils, cemented soils, saturated soils, and a clay layer are examples of restrictive layers.

Thus the importance of properly sloped lots with the correct soil, soil loss and and the importance of properly backfilled lots that require restrictive soils.

Thanks again.
PS: Next time you read my mind, stay away from the dirty bits please.

I grew up in Lubbock, TX, where that layer was caliche. It ranged from a foot to 3’ below the surface. Digging through it with hand tools was like chipping concrete.

In my area of Oregon we have a lot of clay (so Claypan?) and that sketch is very on point. It’s common to have proper grading, gutters/downspouts functioning properly and still a wet crawl space which leaves everyone scratching their heads. Also, lots of foundation settlement for the same reasons.

Mark Anderson videos might shed a little light.

Does this explain why we have groundwater?

No, but it can create a perched (temporary) water table during wet weather. In southern Missouri we get our water from a aquifer 200 to 300 feet below the ground surface.

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