Underground storage tanks were developed to store dangerous and flammable materials in relative safety. But tank corrosion, poor fittings and overfills can cause toxic chemicals to seep into the surrounding soil and groundwater.

Registered tanks are most common at gas stations, automotive repair shops, oil companies, industrial plants, or sites previously used for these purposes. Unregistered tanks are located underground at homes that use oil heating and frequently are left in place when a gas or electric furnace replaces the oil burner.

Leaking underground tanks are common on commercial property, but residential sites also are at risk. And a leaky tank can prove to be a costly problem for homeowners, because the property owner is responsible for cleanup under Washington's Model Toxins Control Act.

If there is an unused tank on the property, an owner has two options under the Uniform Fire Code: removal or "abandonment" in place.

If the property previously had a tank, verify that it was properly closed or removed by a certified contractor under DOE guidelines. Have the surrounding soil checked for contamination.

All nonresidential tanks must be licensed and certified in compliance with DOE guidelines. In 1990, new state laws were enacted to prevent contamination of soil and groundwater from tank leakage, faulty piping and overfills.

Washington State established a program under the Heating Oil Pollution Liability Protection Act to provide insurance coverage for active, in-use heating-oil tanks. Coverage does not apply to unused heating-oil tanks.