dry cleaning solvent (PCE) remediation 2

[groundwork]

What's the latest and greatest destroyer of perchloroethylene (PCE)in the groundwater? I've got a groundwater headache (apx 45 ppm) and I'd like to pump and treat as aggressively as nature will allow. Any thoughts will be appreciated.

 

[aspearin1]

You may want to check out some work by Dr. Robert Bowman. He's done lots of work with surfactant modified zeolite for trapment of PCE.

http://www.stcloudmining.com

would also have some information. Generally they use this as a reactive barrier, but it could also work as a filter media that could later be incinerated. The less you have to deal with Pump and Treat, the better. It's expensive, labor intensive, and in 10 years, all the PCE will likely be back (hidden in the bedrock). I hope you have a good Hydrogeologist on your team. Good Luck.

 

[groundwork]

Thank you aspearin1. I am a pretty good hydrogeologist; so I got that going for me, which is nice. Additionally, as luck would have it, my subsurface conditions lend themselves quite nicely to pump and treat and later distruction. There's a handy clay layer at nine feet bgl onsite and a coarse sand lying right on top of it. I feel that, after soil excavation and QP backfill, I'll be able to install a recovery well and go to town. The hydrology of the site is a bit less of a concern as is a fallback position, in the form of a material or solvent that recks the PCE I cannot remove. Again, we'e only talking about 45 parts per million here. But New Jersey doesn't want to see any more than ONE part per billion! Yikes!

 

[aspearin1]

Is not 1 pmm below the level of detection of PCE? I thought 2ppm was the limit.

 

[groundwork]

dear aspearin1: For EPA method 624 for volatiles in an aqueaous medium (water), my lab's detection limit is 0.58 parts per billion (ppb). Not that I've ever seen one!

 

[aspearin1]

It must have been 2 ppb I was thinking of.

 

[Donovoid]

groundwork,

IMHO in-situ bioremediation of PCE with sodium lactate has proven over the last 4 years to be a very economical approach to remediating dry cleaning sites contaminated with PCE. The sodium lactate is diluted to 5-20% of the delivered concentration and then injected into the saturated zone in the highest concentration area through a direct push injection or via a well. The lactate is fermented to form organic acids that then provide bioavailable hydrogen for the sequencial dechlorination of the PCE to TCE to DCE to VC to ethene and ultimately to carbon dioxide, water and chloride.

Dr. Kent Soreneson at INEEL has published quite a bit on full scale remediations. You can find info on this project at both

http://tech.inel.gov/tech-detail.asp?id=149

and at

http://www.jrwtechnologies.com/Literature.htm

. The second site gives several case studies including a drycleaner site.

 

[1ddt]

Groundwork (environmental)

I've had alot of luck with the molasses injection in the source area, or some other carbon sourcr. If the regulatory agencies will allow it, potassium permanganate does quite nicely as there are no daughter products spawned. The offshoot is that groundwater will take on amn orange color for a small time and there's also the possibility of releasing free iron. It's much more efficient than pump-and-treat.ddt

 

[ripsnub]

The use of electron donors (hydrogen releasing compounds-polylactate ester)and development of an anaerobic environment are quite effective at remediating chlorinated solvents insitu. The use of air stripping as part of a simple pump and treat system is also very good. I have used both technologies for PCE and its degradation products (i.e. TCE, DCE, VC)with great success. Lower chlorinated constituents (VC) tend to degrade better under aerobic conditions. Of course understand the site conditions, hydrogeology and water chemistry before selecting any remediation alternative. Check out Regenesis at [www.regenesis.com] for insitu release compounds. Carbonair has a nice site and free modeling software for air stripping at [www.carbonair.com]

Good Luck.

 

[jeffraines]

At your concentrations, you probably have DNAPL. I don't think in-situ bio will do anything for free product. Normally, I would then recommend some form of chemical oxidation. But if you have a confining layer at 9 feet, why don't you just dig it up?

 

[1ddt]

If there's a confining layer at 9 ft bgs, you might also consider a funnel and gate system (ala Waterloo). It's a great system which, unfortunately, in my area, we can't use due to the depth of confining layers.

 

[separate]

The PCE specific gravity will probably be in the 1.47 - 1.6 range. The product, if in a free state will need to be separated to remove the high load of DNAPL prior to other processes so those processes aren't overloaded. Depending on what else is in the water you will probably need to use an all stainless oil water separator for coarse removal. This should get you down to 5- 10 mg/L, then further processes as are being mentioned in this thread can be considered. Definitely look at air stripping, modified clay filtration to see if these will help. You can contact Pan America Environmental

http://www.panamenv.com

for separators and clay filters and other equipment.

 

[Donovoid]

I have to respectfully disagree with one point that jeffraines makes when he says, "I don't think in-situ bio will do anything for free product." Resent field studies and full scale remediations have shown that in-situ bio is probably the most cost effective method of cleaning up chlorinated solvent NAPLs. It turns out that the dechlorinators can best outcompete other bacteria in the high concentration areas near NAPL because those areas are more toxic to the other bacteria. In December there was an outstanding online conference sponsored by EPA on remediation of NAPL. The following presentation shows full scale evidence of the in-situ bioremediation of DNAPL. This presentation also can be viewed with the speakers audio describing the slides. It is well worth checking out.

http://www.clu-in.org/studio/napl_121002/ppframe2.cfm?s=59&p=32&res=800x600&simul=1

Also, you can check out the JRW Technologies web site (

http://www.jrwtechnologies.com)

for specific information on bioremediation products and case studies.

 

[jeffraines]

Donovoid is right of course that in-situ bio will work on the dilute plume down gradient of the source. Sorenson's work at INEEL was for a waste injection well where they had thousands of gallons (if not more) of DNAPL. But that was at some large depth (greater than 80 meters as I recall) in fractured bedrock. As long as that source is there, you will be injecting lactate for hundreds of years. That will put your kids through college as long as you can find someone to pay you to monitor the situation.

Funnel and gate will also work to control migration, but won't address the source. In the long run, it might still be cheaper to use a funnel and gate because the present value of the hazardous waste you'll create through excavation will be high compared to the present value of monitoring your gate. I like funnel and gate over in-situ bio knowing nothing about site hydrogeology, but either might be the right answer. In-situ chemical oxidation to remove the source followed by one or the other might also be worth looking at.

So, it all depends on what the client wants. Most clients (in this case, I assume it's either a government agency or an insurance company) would pay a little extra (not twice) to get the liability off their books.

Jeff

 

[IsaacA]

Based on the high levels of VOCs you mentioned (45 ppm), you probably have a very large amount of VOC mass bound to the soil within the saturated zone and you probably even have DNAPL somewhere. Pump and treat will only be effective on the dissolved mass and you will be relying solely on partioning of the adsorbed mass into dissolved phase if you rely solely on pump and treat. Therefore, I recommend using in-situ oxidation to drastically reduce the VOC mass loading within the saturated zone. Check out

http://www.mecx.net

and their expertise with all types of in-situ oxidation technologies.
Donovoids response might only partially solve your problem because lactate is a hydrogen donor which will helps dechlorinate compounds requiring anaerobic degradation (i.e., PCE to TCE then to DCE). Therefore, lactate would potentially stall out when you get to DCE. The reductive dechlorination of DCE to VC and VC to ethene to carbon dioxide requires aerobic conditions and so you would need a source of oxygen to complete the reductive dechlorination.
1ddt's response is interesting. Investigate possible fouling considerations when using molasis.

 

[Donovoid]

IsaacA is expressing the commonly held belief that in situ bio will stall out at cis-DCE. In most cases that stall out it is because of inadequate reducing conditions. To get past cis-DCE it is necessary to drive the ORP down to sulfate reducing conditions. The most popular slow release hydrogen donors out there many times don't reach sulfate reducing conditions. On the other hand, the sodium lactate injected at several hundred mg/L will result in strongly reducing conditions in the range of methanogenesis. That will drive the DCE all the way to ethene. The only exception is a site that does not have the correct dechlorinating bacteria present. Less than 3% of all of our sites fall into that category. In that case they bioaugment and then drive everything to ethene.

The other advantage of sodium lactate is that it lowers the interfacial tension between the DNAPL and aqueous phase and increases the mass transport gradient by between 10 to 50 times the natural dissolution rate. At INEEL that 100+ year project has been cut down to a 10 year project. For most drycleaning sites it takes 12 to 18 months to get complete remediation.

The cost advantages of treating the source areas at drycleaner sites with this BET technology are significant.

 

[1ddt]

The one problem I have, which hopefully is endemic only to our sole source Central Valley Aquifer, is the fact that it's quite cost prohibitive to search for DNAPLs due to our alluvium containing discontinuous clay lenses. Usually, if were are talking about a mom-and pop dry cleaning facility, we can tell that DNAPLs are present; however, the largest insurance policy I've seen from them is approximately $100,000, which can be eaten up in litigation quickly. Therefore, we work with the regulators and apply the money toward wellhead treatment. I concede that this is no cure; however, with so many supply wells, it's difficult to determine the location of the DNAPL pool, even though we are sure of the presence. I have great hopes that direct-push technologies using the SCAPs or UVIF system will eventually find success in detection of DNAPL as it has with LNAPLs. The cost is approximately $5000/day, which buys approximately 12 borings, using a saphire window, all to total depth of up to 60 feet. I'm using on on one of my sites now, and can hardly wait for the efficiecy of DNAPL detection to improve. Sorry for the lengthy diatribe, however,in my area, one of the hardest tasks is location of the source. A

http://www if

only I just had Ottowa Sand Aquifers.

 

[KOVA]

If you have decided on the PAT, you might want to consider Hydraulic/pneumatic fracturing and enhancing the performance(greatly). Thats the easiest and most efficient way of getting around the clay layer.But thats before you make sure there is no DNAPL present at the site. You can then try permanganate or a surfactant to glean the site of any residuals.