"If it's not dangerous, then why are they spending so much money?" asks Brent Poll, a South Weber resident whose family discovered the pollution and brought it to officials' attention.

Loucks said Hill and EPA officials are still concerned about long-term exposure. "There is the potential for someone to be exposed at an unhealthy level," he said.

Poll said he would like to see more testing more often, because some contamination has continued to seep outside of the maps the Air Force uses.

Base workers check contaminant levels in 1,494 monitoring wells on and off base. But Elliott said that doesn't mean Hill officials know where all contamination is. Sometimes, contamination has been underground for decades, and workers discover it when excavating around base.

The Air Force groups contaminated areas into 12 Operable Units. Plumes are found on the base and in the seven surrounding cities.

Although contamination in the groundwater plumes varies, TCE is common to each Operable Unit.

Beneath the cities

Contaminated groundwater in South Weber came from three chemical disposal pits, three landfills and two fire-training areas. Between 1958 and 1973, fire training meant dumping gallons of jet fuel on the ground around an airplane and igniting it. Some of that fuel soaked into the ground.

Loucks said one groundwater plume in South Weber from an unlined chemical dump "used to be the most contaminated site in the whole Air Force."

About 50,000 gallons of contaminants were disposed of in one of the unlined chemical dumps away from most base operations, he said. The contaminants pooled underground and were kept from spreading by the geologic makeup of the soil beneath. About 45,000 gallons have been removed so far, but it still could be 50 years before the area is clean.

Contaminated groundwater is pumped from the ground and treated until water can be sent through the sewer district, Loucks said.

On South Weber's west side, part of a contaminated plume reaches into Riverdale, but another plume is Riverdale's largest contaminated area — beneath the Craigdale subdivision.

Besides TCE, there are also remnants of other solvents, and six extraction wells on the base pull water out of the ground and treat it. It's the only base site where clean water is reinjected into the ground to increase the flow of groundwater, flushing out contaminants. Wells in the subdivision extract water and send it through the sewer district.