Septic System Soil Test vs. Soil Borings 1

[jheidt2543]

Just a general question that came up on a residential project. In the situation where only a septic system soil test has been taken and classified using the USDA 12 texture divisions and the other standard visual paramenters is there any kind of correlation that can be made to the Unified Soil Classification System?

Soil borings are seldom done for a small 1-5 lot development for structural purposes, but a septic system soil report is always required for private sewage system.

Just wondering what others do.

 

[jdonville]

jheidt2543,

My understanding is that even the USDA classification system requires particle size distribution testing. You can plot the % passings based on the USDA grain sizes for a rough USCS classification. I used to work in IL and ILDOT does a modified USDA classification system. We still performed the ASTM particle size test, so maybe the raw lab data is available in this format?!

Hope this helps,

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

The views or opinions expressed by me are my own and do not necessarily reflect the views or opinions of my employer.

 

[TDAA]

Even if the "Raw Data" is not available, if the person doing the classification was good at it, you should be able to get a reasonable idea of what the percentages are based on the USDA classification chart, then correlate that to the USCS.

This obviously has some major probability of error since it is an estimate of an estimate of a judgment, but it could get you in the ballpark, without having the term "loam" included.

 

[DRC1]

Generally septic system design is governed by state and local health officals. If you talk to the town engineer or health officer, they can usually help you. Generaly soil profiles are checked with shallow testpits and the soil is classified visually. Often agriculteral discriptions of the soils are given. Accuracy of the description varries widely. In addition to test pits, Perc test are done. These tests measure the apsorptive abilites in a manner similar to a slug test for permiability.