LNAPL (Diesel Fuel) Recovery Methods 1

[ripsnub]

Looking for some general concensus and feedback on approach for LNAPL recovery. Have a fairly thick product layer on watertable with +/- 5 ft seasonal groundwater flux. Propose oileophilic top loading skimmer pump (Xitech) with vacuum enhancement (up to 10" H20). Area is in sandy-silts with some gravels (est. K = 45ft/d).

Thanks.

 

[waterexpert]

Or you could pump it out, and recover with oil/water separators. I've got a couple of plants doing this. It's a nice cheap option, works fine.

 

[gunga]

I used to work on a similar site with fluctuating GW, diesel fuel, and a conducitive layer of sand. We intially started with some GW depression pumps to keep the NAPL contained, then added skimmer pumps and vacuum enhancement. We found two things really assisted in the vacuum enhancement: large diameter recovery wells (12&quot and relatively large vacuums (~40-60"H2O). Xitech pumps work well, depending the amount of silt they can need pretty frequent maintenance.

 

[Focht3]

With a properly designed screen and filter media combination, silting should not be an issue -



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[gunga]

I agree, unfortunately the previous three consultants were less concerned with proper well design than they should have been. The client wasn't interested in new wells, but didn't seem to mind the O&M or well rehab once a year. A case of picking my battles.

 

[ripsnub]

I have been playing with some different technologies as site conditions are quite heterogeneous -- we have been conducting an extended RI and finding all sorts of interesting subsurface conditions affecting product and groundwater recovery. I am currently running pilot tests using the Xitech skimmer pumps under normal and vacuum enhanced conditions. I have also installed QED/CEE Hammerhead total fluids pumps to deal with the areas with less LNAPL. Many of our wells have from 3 to 15 feet of diesel with sustainable recovery rates with little to no drawdown in product thickness around 15 gal per hour. Thanks for you comments - all suggestions are welcomed.

-- ripper

 

[gunga]

any estimate of the quantity of diesel down there (from product thickness, soils samples, tank losses, etc.)? Otherwise, I would say kick up your pumping rate until you see the production decrease or generate some decent drawdown.

 

[Focht3]

A pump rate of 1 quart (about a liter) per minute is pretty small; I wouldn't expect that you would get any measurable drawdown! And you aren't making that much headway against the contaminant pool - with the risk that the plume is continuing to spread. I'd recommend significantly increasing the pump rate, too - with one big caveat. You are likely to get a lot more silting, and perhaps appreciable loss of ground around the wells, after you increase the pump rate.

I'll bet your client will become a lot more interested in putting in new wells as his O&M costs go up...




Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.

 

[jvvenkat]

Have anyone used any software that is used to calculate the LNAPL revovery and LNAPL volume in aquifer based on LNAPL thickness in monitoring well?

Your input is greatly appreciated.
Thx.

 

[ripsnub]

Yes, API has excellent references, guidance, and modeling tools for estimates of product recovery based on monitoring well thickness as well as pumping and applied vacuum scenarios. Be aware that a very sound understanding of the vadose zone properties and liquids involved is an absolute in getting reasonable model results. See link below:

http://api-ep.api.org/environment/index.cfm?bitmask=002008008000000000

Good Luck.

 

[ripsnub]

I should clarify the vadose smear zone, oil/water interface and oil saturated zone.