Article date: March 29, 2001

Basin closure similar to process for closing landfills

By Dan M. Telvock

A major project that engineers are working on now at the Avtex Superfund Site is the closure of basins on the property that contain both hazardous and non hazardous material.

FMC on-site manager Douglas Bement said the plant generated three waste materials that engineers are dealing with now— sulfate sludge, flyash, and waste viscose.

The sulfate sludge has 20 percent of its weight as zinc, which drives environmental concerns because zinc in high amounts becomes toxic to wildlife.

Bement said there are three viscose basins— No. 9, No. 10, and No. 11— that have been pinpointed as the cause of the groundwater contamination at the site, and a study is underway on how to best alleviate the problem.

Basins, 9, 10, and 11 have wells inside them and each of them discharges hazardous green and red water, which is viscose waste— the culprit of contamination in the groundwater.

Bement said these basins are constructed on fractured bedrock, and the liquid is sent downstream, under the Shenandoah River , and eventually loses concentration as it filters through the bedrock.

If the basins were enclosed in clay like the other basins, it is very possible that there would be no groundwater contamination.

"We’re still investigating the best remedy for those," said Bement.

The eight other viscose basins on the property were covered during the plant’s daily operations and Bement said those basins continue to be regulated to assure state and federal standards are met.

"We’re still making sure they meet regulations," said Bement.

Bement said the remaining basins fall under phase one of what he called a "multi-year project."

Sulfate basin No.5, the southern most basin, will be constructed into a wetlands area, after all sludge is removed from it. The sludge from this basin and basin no. 2 will be consolidated into sulfate basin No. 4, which will be capped— covered with two feet of soil at minimum — and revegetated.

Bement said the consolidated basin will "rest for two seasons" to allow vegetation to grow.

To fully close the sulfate basins, Bement said a geomembrane made of high density polyethylene will be used and will prohibit any infiltration of particles or the exiting of particles.

FMC consultant Rick Goss said the geomembrane is primarily used to keep rainwater out and to keep the sludge inside from being released. The entire closure process is very similar to the closing of a landfill, he said.

Bement said the geomembrane will also provide a structural component to the final covering.

The basins will have a soil cap, then the geomembrane, with natural and added clay covering all three remaining sides.

Four flyash basins on the property will also be closed. Bement expects to have five basins (four flyash and one sulfate basin) closed by next spring and the entire basin closure project to be completed by 2003.

Goss said the Lord Fairfax Soil and Water Conservation District and the Valley Conservation Council will oversee the land use after the basin closure project is completed, and the basins will go through indefinite monitoring.