have been cleaning up an old fuel depot for about 10 years.

As James Williams reports, cleanup workers have abandoned machine power

and turned to Mother Nature to get the job done.

This abandoned fuel depot used to supply the entire installation.

Six underground storage tanks held 72,000 gallons of fuel.

Fort Jackson eventually switched to aboveground tanks,

but that didn't stop fuel from leaking into the soil and groundwater.

Lahiri Estaba is the environmental cleanup manager at Fort Jackson.

He says they have used machines to help clean the groundwater

but now they're turning to Mother Nature to do the rest.

We planted these trees--175.

It's a combination of poplars and willows,

almost an even number of each.

The process is a fairly young science called phytoremediation.

The trees basically just draw the water,

and they don't metabolize the constituents--they give them off.

Just checking the irrigation.

Researchers at the U.S. Department of Agriculture

have spent about two decades studying the ability of certain plants to clean up,

or remediate, soils contaminated by heavy metals.

I first learned about it at a Princeton groundwater course in '95.

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These poplars and willows are particularly suited for volatile organics

and they use them a lot for chlorinated solvents and petroleum.

It's a low cost method with benefits to humans.

Better air from them giving off oxygen as well.

Fort Jackson does not get drinking water from this location,

but by law, the installation must restore the area to drinking water standards.

Estaba says it's difficult to predict exactly when,

but at a capacity of moving up to 800 gallons a day,

he believes the trees can remediate more than 90% of the area within 3 years.

James Williams, Fort Jackson, South Carolina.