For decades, Tooele Army Depot dumped the solvents, acids, explosives and other chemicals resulting from its maintenance of vehicles and munitions. They contaminated the scarce groundwater in the desert area.

Now, the Army is beginning the first phase of a project that's expected to last 30 years to clean up that contamination.It has awarded a $7.58 million contract to the firm of Metcalf & Eddy to begin a project that will, essentially, pump contaminated water out of the ground, clean it and then pump it back into the ground.

"This is a positive development for Tooele and demonstrates the Army's commitment to cleaning up the environment," said Rep. Jim Hansen, R-Utah, a member of the House Armed Services Committee, who announced the contract.

That first-phase contract will run through February 1993 and fund engineering, installation and testing of a system to remove trace amounts of trichloroethene and other solvents around the base.

Hansen said the new system will extract groundwater and pump it to a treatment plant. Treatment will filter out contaminants through a process called "air stripping" and charcoal filtration. Treated water will be monitored to ensure it meets required standards, and then will be pumped back into the ground.

The Army estimates the entire cleanup process for the north area of the base will require 30 years of continuous treatment.

The Deseret News last year revealed some of the problems through the decades that contaminated base groundwater, which came to light from documents obtained through the Freedom of Information Act.

For example, solvents and other industrial wastewater were dumped into unlined ponds for years - meaning water could seep through the bottom. After a suit by the state, the Army built a $4.5 million plant in 1988 to filter contaminants out of wastewater.

Documents also pointed out other problems.

They said the Army found a landfill where paint thinners, pesticide containers, battery acid and other chemicals were dumped and may be leaching into groundwater. They identified another area where barrels were stored upside down to empty out residue, which might also threaten groundwater. They also located trenches where chemical munitions were buried and where groundwater percolating around them might be contaminated.

Tooele spokeswoman Susan Broadbent said while the new facility will help remove solvents, it is not designed to address another problem the base is facing with nitrates from buried explosives.

In tests beginning in 1981, the Army found that the soil beneath four ponds was contaminated with high concentrations of the explosives TNT, DNT and RDX to a depth of at least 60 feet.

In 1984, to help prevent migration of the contamination, the Army covered the ponds with soil and placed a synthetic cap to retard water from percolating. But the Army kept dumping 7,200 gallons of laundry and shower wastewater into other ponds nearby - which continued to worsen nitrate contamination by explosives.

The U.S. Army Toxic and Hazardous Materials Agency is also evaluating what action should be taken to clean up the south area of the base, which is located in Rush Valley.