In 2004, the base installed a 660-foot-long barrier, composed of iron filings and sand, below ground near a neighborhood in Roy. And it's worked great, Roginske said.

The mass of TCE in the plume has been reduced in half after groundwater seeps through the barrier, Roginske says. The barrier has next to no maintenance costs, but nitrate in the groundwater has caused a precipitate to form on the iron, reducing its ability to strip TCE from the water.

But it's still working, he said, adding that he's studying how to remedy the nitrate content of the water in Roy.

In Sunset, however, the groundwater has hardly any nitrate content. Some of the iron comes from Utah's training range and some is expected to come from Luke Air Force Base, in Arizona. And unlike the Roy PRB, for which the base purchased 950 tons of iron for $638,400, the Air Force already owns the iron.

E-MAIL: jdougherty@desnews.com