Styrene spill into organic soils oveylying bedrock

[rnancarrow]

I am involved as a reviewer for the remediaton of a spill of styrene monomer UN 2055, into organic soils overlying somewhat fractured granitic bedrock. The contractor has chosen dig and dump and replacement with medium sand, followed by topsoil and planting for restoration. I am concerned about recontamination of the sand by styrene styrene pockets in the bedrock that may not have been detected. The odor threshhld is very low, and is difficult to relate to soil and groundwater clean up criteria. Any one have any experience on a similar situation with styrene or another VOC?

 

[Dubliner]

Dear rnancarrow

First of all I don't have experience specific to your problem but I may be able to offer some direction.

If the bedrock is fractured granite then it may well contain groundwater. As liquid styrene has a density of around 0.9 relative to water (1.0) then it will float on, and will slowly dissolve into, the groundwater.

The depth to groundwater may be a key factor in determining where the downward migration of the styrene will be impeded. If it is 20m below ground level then I doubt that capillary action in the sand would be sufficient to draw styrene upwards against the combined chemical and physical effects of infiltrating rainwater (what are the chances of rainfall?).

If the fracturing is not continuous at depth then you may well have small reservoirs of liquid styrene in the bedrock, as you stated. In this case I suggest that you look into installing a layer of inert and environmentally-safe, absorbent, granular material which can be poured into place prior to addition of the sand, thus holding the styrene in place for longer so that chemical and biological breakdown processes can deal with the pollution.

I am not certain but there may be inert, environmentally-safe odour absorbers also, which could be mixed in with the sand to impede the upward migration of volatiles.

Finally, if groundwater is flowing through the fractured granite then you should point out that covering over the contaminaton at this one point will not stop the styrene from polluting the groundwater, which will almost certainly interact with other aqueous systems in the local environment. Styrene is a marine pollutant, is highly toxic and its vapours are explosive in air in concentrations between 0.9-6.8%

I hope this information helps in some way.

Regards,

Adam Beresford-Browne
URS Corporation Ltd

 

[rnancarrow]

Dubliner:

Thanks for the response on the styrene question. One of the complications we have is the soil above the bedrock, which is a mixed bag of silts, sands gravelly sands, some clay. The styrene has migated into some of these soils and contaminated them to the top of the bedrock. Some free styrene could have entered the fractured granite and migated down to the groundwater (20 m, and also could form sinks/sources for future migration into the sand. As odour is one of the concerns to the local community, this problem may persist, as the odour threshold is low (0.1 ug/m3. We are in the process of comparing this to the clean up criteria in soil, but this becomes more complex, given the nature of the surficial soils, of varying hydraulic conductivity. There are some models for VOC movement through unsaturated soils that I am familiar with,and they should provide a range of flux of gas.

Thanks for your help

rnancarrow

 

[DWD]

I checked

http://www.cleanuplevel.com

and it has styrenen cleanup levels ranging from 0.02 ppm up to 14,000 ppm. It appears that the higher levels are being used at locations where they used direct exposure to humans and that the lowere levels are where they were worried about leachability to groundwater.