SPLP leachate testing soil vs sediment

[MartyL]

This is on a topic that I don't have experience in, unfortunately.
On a site with an environmental cleanup of VOC/SVOC contaminated soil & sediment going on, I've got an engineering consultant that is testing a stabilization reagent on soil & sediment. The consultant has Synthetic Precipitation Leaching Process (SPLP) results on sediment that are beneath cleanup goals, which is good. Because the consultant thinks these sediment results are representative of soil results too, they want to forgo SPLP testing of the soil in a similar manner because they say it's unnecessary. The easy answer is to just deny their request, but I would like to have a better understanding.

It seems their assumptions include 1) that sediment's finer grains allow for more contact surface area than soil, so using sediment as an indicator is conservative 2) the concentration of contaminants in the sediment sample is just as high or higher than in the nearby soil, so the use of sediment is representative, if not conservative 3) the sediment has all the same contaminants as the soil 4) other factors that influence SPLP are similar between both the soil and sediment

The problem is number 4) above, which I wrote as a sort of catch-all, because I don't really know all the factors that influence SPLP.

I found one May 2008 document from Florida "Guidance for Determining Leachability by Analysis of SPLP Results" that explicitly states its guidance is to be applied to soil, but not sediment. Telling...but it doesn't say why.
The best reference I've found is from 2003, "An Assessment of Laboratory Leaching Tests", which suggests influencing factors for leaching are

[ul]
[li]particle size, shape, and surface area[/li]
[li]permeability of the matrix[/li]
[li]heterogeneity of the soil or fill material[/li]
[li]complexation with inorganic or organic compounds[/li]
[li]presence of NAPL[/li]
[li]some other things that should be consistent between soil & sediment, like temperature during leaching, physical properties of the leaching fluid, biological factors such as biodegredation that can change redox and pH conditions of inorganic contaminants (which we don't have), etc.[/li]
[/ul]

That same reference suggests that one should try to match lab and field conditions on things like liquid-to-solid ratio.

Any thoughts?

 

[GeoEnvGuy]

So the consultant is telling you they tested the sediment. which in my experience finer grained sediment is harder to clean than soil and usually worse in contamination concentration.

The other factors are permeability and related to the environmental conditions. Sediment has a lower permeability aka slower than soil so it requires more effort. If one is next to the other they are in similar environments.

If they are going to implement a splp system the soil will get cleaned up a lot quicker than the sediment. Confirmation samples will show that later.

 

[MartyL]

Thanks. Your reply has influenced the way I look at the issue, though I'm still checking references and I'll eventually post a follow up with more.

 

[MartyL]

The Project Manager set up a meeting with the engineering consultant. At the meeting they explained that they had done a poor job of communicating to us that their initial push forward without stopping to resample became unnecessary after they decided to demobilize from the site for a few weeks for weather reasons, giving them more time for sampling and lab analysis. With the extra time, they went ahead and resampled the soil for SPLP and got favorable results for that too. So that makes my original topic question moot.

If I'd had to make a decision, though, I'd have recommended they sample again, though I wouldn't have required them to wait for the results to move forward. It's not an expensive test. Also, I made sure that SPLP confirmation testing after the cleanup was part of the work plan.

 

[oldestguy]

With all this double checking, you may likely find that if any problem comes up later, your liability will be significant, possibly relieving the consultant of any liability. I'd leave well enough alone. Edit: Matter of fact your post here could well be used against you. There is a simple fix. You can delete all your postings.

 

[MartyL]

oldestguy,

Can you elaborate on what "all this double checking" is? What exactly, is the "well enough alone" you're referring to?
To be clear, the consultant ended up following the work plan without deviation (they withdrew their request to make a change, as explained above), and all my posts here suggest my position was that they do exactly that...save for not having to wait for lab results to move forward, which is not the same as a giving them carte blanche to ignore (or not collect) SPLP results all the way to project completion. I can't imagine how that relieves the consultant of "any liability"?

Actually, there's some details that I won't get into that are part of the reason I'm not worried about liability issues in this specific case, but I'm still interested in your perspective for how it may apply to future projects.