A Tale of Two Site Conditions

A surprisingly number of times I will hear something to the effect that “All our soil is Type C because it’s all been previously disturbed.”

That line of thinking betrays a lack of understanding of what it means for soil to be Type C, as well as the effect of having been disturbed has on soil classification.

For a brief look at what Type C is according to Appendix A, I recommend the reader to look my previous article on the subject. For now, I’d like to look at just a few reasons why the site condition of being previously excavated does NOT make a soil classification automatically become Type C.

The strongest argument comes from the federal register where we quote from page 45939 where Type B soil is being explained:

“This definition is very similar to proposed paragraph (b)(13), except that the Agency has added specific examples to this definition to assist the user, as discussed, and has clarified that most disturbed soils are Type B.”

The authors of appendix A felt they have clarified that previously disturbed soils can be classified as Type B. Apparently the clarification isn’t obvious enough to some.

The second-best argument in my opinion is that the words “previously disturbed” appear only in the definition of Type A and Type B soil classification. If the authors of Appendix A meant the “previously disturbed” site condition to cause a soil to be defined as Type C, then those words would most definitely be found in the definition of Type C. They are not. That is because “previously disturbed” simply keeps soil from being classified as Type A. Perhaps that is one of the ways that the authors of Appendix A believed they have clarified the issue.

A third argument is that the effect of soil being underwater or having soil that is freely seeping water, is clearly a reason to classify that soil as Type C. The standard is very clear on that matter, and being previously disturbed does not have the same effect on soil that water has on soil. To equate the two site conditions of “water” and “previously disturbed” is a failure to appreciate the differences between the full effect that water has on soil, and the effect that being previously excavated has on soil. There is simply no comparison.

A final comment. In the above discussion, one could easily and correctly substitute the words “fissured” or “vibrations” for “previously disturbed”. The same argument stands for those site conditions as well. Those two site conditions simply keep soil from being classified as Type A.

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