Heavy metals remediation?

[mmenarry]

Folks,
I have a site with heavy metals contamination, primarily Lead (600ppm), Zinc (1000ppm) & Tin (8000ppm).

The site was a "brownfield" site approximately 30 years ago, the contamination is not related to current activities on site. The levels above are from a soil survey conducted approximately 10 years ago, we are intending to re-survey to monitor for changes.

What sort of remedial/treatment processes would be available for soils contaminated with these sort of levels? We are currently intending to redevelop part of the site, and it may prove more sensible to initiate remedial action now, rather than later.

Michael

 

[soiledup]

Michael,

Wait for the results from the new survey. From this you should be able to determine if the site is completely contaminated or whether you can delineate the site into 'hotspots'. The end use of the site is very important. If it has a sensitive end use (say school, or housing) then the guideline values may vary from say an industrial complex.
Any areas that will be covered with hardstanding / concrete / paving there will be no pathway for the contamination to pose a threat to human health. Areas of soft landscaping or allotments should be identified, probably excavated and infilled with clean cover from a certified source.
Sorry, I'm waffling a bit. It isn't that complicated really but a good geo-environmental engineering firm should be able to take care of this for you.

 

[JasonG]

Capping, as soiledup mentions, is a great remededy for commercial sites that will be redeveloped. You could also look into encapsulation. Both are appropriate if direct contact is your concern

Soil stabilization is an alternative if you need to prevent leachate from contaminating the groundwater.

A good stating point for your research is this EPA website:

http://www.epareachit.org/.

If leachability is a concern use the SPLP method instead of the TCLP method. I find that many consultants mistakingly use TCLP to test leachability in in-situ soils.

 

[mmenarry]

Thanks for the replies folks, but I don't think capping would be allowable in our case (welcome to the EU!).

In the interim, leachate is more of a concern (sandy-clay soil) into the water table below. I'm having the previous survey repeated - if the metals content is approximately the same, then I presume that the metals are fairly stable (for the time being, i.e. not leaching to any appreciable degree).

If I see a reduction in the metals content, am I right in assuming that leachate would be the main reason for this? Or are there other vectors that could reduce the metals content? There is no organic cover on the site in question (industrial site)

Thanks in advance,
M.
p.s. - there is a small BTEX plume on the site as well (old boiler house - USTs) but I have plenty of options in relation to dealing with that, not sure if that might affect options on the above.

 

[JasonG]

Leaching is the primary reason I can think of for a true reduction in metals concentrations. Unless it's surface soil that could have eroded. I've heard that some plants can take up metals as well.

However, a "true reduction" in concentrations is important to define (as opposed to an apparent reduction). You'd have to consider the accuracy of the analytical method (typically +/- 25%). Also, is the lab using the same method now that they used 10 years ago?

 

[soiledup]

Basing the investigation around the proposed end use of the site is the most important part. For instance if the site is being converted into an allotment for people to grow vegetables then there will be exposure to humans through the handling of the soil and possibly through ingesting vegetable that have 'taken up' the metals. If however the site is going to be used as, say, a tarmac car park then there is very little risk involved with the end users of the site. (A risk assessment for the construction workers building it would still be required).

soiledup

 

[mmenarry]

JasonG - Metal conc.s were taken at approximately 1.0-1.5m deep, soil erosion hopefully won't be a factor, but I was thinking along the same lines as you.
I'll be using the same firem that conducted the previous survey, basically repeating the survey (with a few extra points for the BTEX plume), so it should be as close as I can get to the original.

soiledup - Ordinarily, that would be fine, but remediation would be the option more than likely forced on us at decommissioning, regardless of end use (or potential end use). As I said, welcome to the EU!

Thanks folks!

M.

 

[soiledup]

I am in the EU (UK). We, more often than not, are required to remediate ground conditions, but the remediation strategy must be tempered by a good understanding / sound risk assessment of how the contaminants could affect potential end users. It may not be necessary to excavate the whole site and replace with clean cover.

This basically comes down to using a good geo-environmental site investigation company who should be able to mitigate any planning conditions imposed.

 

[mmenarry]

Soiledup - close enough, the site itself is in Northern Ireland. The River's Authority is responsible for Env Protection there.

Remediation would be the company's preferred route anyway, it's just a matter of cost - hence my query on current technologies for HM removal.

Thanks!

M.

 

[JasonG]

Good luck mmenarry. Let us know what you end up using.