Excavation Z2 classification - TOC content

Hello everyone,

-please feel free to move the topic to the appropriate section if this is not suitable here-

soon the earthworks are supposed to start here. The civil engineer commissioned an external soil analysis in advance, and last week I received an informal message that the excavated soil is classified as Z2 and that I must expect additional disposal costs of about €15-20/t - we are talking about approx. 200t.

According to the test report, 2.2% TOC is contained; a bore sample was taken from 0.0-0.9m, homogenized, and tested. However, the topsoil (15-20cm) is supposed to remain on the property, and only the excavated soil will be disposed of. Construction will only be with BP; the subsoil must be replaced by about 1m. Shouldn’t only the excavated "layer" have been tested? And more importantly: according to some conversations with acquaintances, the topsoil naturally contains significantly more TOC than the deeper excavated soil, is that correct? Then, actually, a significantly lower TOC concentration should be expected through a renewed sampling excluding the upper topsoil (this time with my presence), right?

Do you have any experience with this?

Best regards

Hi,
generally, one must differentiate between Z-classes and landfill classes.
I suspect, according to your statement, that a mixed sample from 0 - 0.9m was taken here. Which then includes the topsoil. If that is the case, it is no wonder that the TOC value is high. According to LAGA, the limit value for Z0 is 0.5%, for Z1.1 and Z1.2 1.5%. More important for you, however, is the classification into the respective landfill class if the material is to go to a landfill.
Here, the TOC limit value is 1.0% for DK0 and DK1. DK2 has a limit value of 3.0% TOC. The loss on ignition is also a criterion here, and each landfill must be contacted separately to see if they accept these values.

I would have a new analysis done without topsoil. It also doesn't make sense as it is.

Hello, here are a few values Dry matter: 78.3% Loss on ignition: 5.9% TOC: 2.2% In the Laga report, the whole mess is assigned a classification (Dep.V.) to DKII - we are building in Hesse, in case that is relevant. Your statement that there is more TOC in the topsoil than in the actual excavation material already gives me some confidence. Then I will definitely question the sampling and request a new analysis. Even if they charge me for it in the end, it still bears no relation to the thousands in additional disposal costs. Should I be present during the sampling to be sure? How did you handle that? Regards

A mixed sample is taken more often. I would, as you already described, have a new declaration made only for the excavated material to be removed. Costs about 600€. You can be present during the sampling. You can also have a picture taken of the sample bucket. What type of soil is beneath the topsoil? If the color is different, that is also an option.

According to the geological soil report, the probing rod was drilled 1.20m deep.

0.2m: Topsoil - silt, sandy, clayey, humic, soft consistency, dark brown, moist
0.7m: Slope loam - silt, clayey to strongly clayey, sandy, light brown, beige, soft, consistent, moist
1.2m: Weathered loam/-horizon - silt, clayey to strongly clayey, stony, sandy, strongly gravelly, grey-brown, stiff, semi-firm consistency, moist

According to the geological soil report, the driving probe was drilled 1.20m deep.

0.2m: Topsoil - silt, sandy, clayey, humic, soft consistency, dark brown, moist
0.7m: Hillslope loam - silt, clayey to highly clayey, sandy, light brown, beige, soft, consistency, moist
1.2m: Weathered loam/-horizon - silt, clayey to highly clayey, stony, sandy, highly gravelly, gray-brown, stiff, semi-solid consistency, moist

Ours looked roughly like that too. Water hardly drains away and on hot days everything is as hard as stone. Not the nicest subsoil. Definitely another new sample. The problem is that you first have to find a landfill that accepts such material. It may be that a few more tons would come up because landfill XY has to be driven to 50km further away...