Leaking underground storage tanks remain a leading cause of groundwater pollution even after more than a half-million sites have been cleaned up. Even modern tanks will eventually leak.

FILE - Workers remove a 10,000-gallon underground gasoline storage tank to be replaced with a new tank at a gas station in Sacramento, Calif., May 23, 2003.

The 75-year-old tank in Washington state is leaking some 3.5 gallons of waste each day into an area where an estimated 200,000 gallons have already leaked from other tanks at the site.

While leaking underground storage tanks are located in nearly every town in the U.S., those who live closest to these sites tend to be in communities that are lower income with a higher proportion ...

While leaking underground storage tanks are located in nearly every town in the U.S., those who live closest to these sites tend to be in communities that are lower income with a higher proportion ...