Older tanks a silent danger
New systems help detect, prevent leaks, make cleanup easier
By Jeremy Pearce / The Detroit News
Out of sight and out of mind, leaking underground storage tanks pose unseen threats to drinking water that can surface miles from a faulty tank’s location.
Gasoline, oils and their chemical components tend to travel along with ground water, which is fluid by nature, making the limits of pollution often too slippery to assess.
Scientists calculate that a lone underground tank leaching 10 gallons of gas can release enough benzene, a known carcinogen, to taint 12 million gallons of water in the course of a single month.
“The typical leak seeps down to the water table and, if it’s fast enough, it pools on top of that ground water,” said Dr. Joseph N. Ryan, a University of Colorado engineer who studies leaking tanks.
“Gasoline is lighter than water and some of its chemicals are soluble. That’s a bad combination.”
Experts warn of a brew known as BTEX, consisting of benzene, toluene, ethylbenzene, xylene and MTBE, short for the gasoline additive methyl tert-butyl ether. Both are common, travel easily with water and represent distinct health hazards.
Recognition of chemical dangers pushed the U.S. Environmental Protection Agency to adopt tighter national guidelines for storage tanks and a 1998 deadline for removal of outdated, corroding tanks.
New federal guidelines demand systems for leak detection and fuel overflow. Few tanks now are made of raw steel, which is apt to rust. Instead, most are lined with fiberglass or attached to a weak electric current designed to halt deterioration. Some tanks are constructed with double walls for added strength.
The technology for cleaning up leaks has also improved. Environmental engineers wielding sniffing machines — actually, photoionization detection units — can check soil for even tiny traces of escaping chemicals.
“We nearly always find something,” said Jerome Meyer, a geologist with Innovative Environmental Solutions Inc., a private contractor based in Brighton.
“In our experience, maybe 5 percent or less of storage tank sites have no evidence of contamination,” he said. “Essentially, they’re all dirty.”
Meyer and other experts try to map the borders of pollution by testing soil and drilling points around a tank at varying depths. Water samples from the borings are analyzed for as many as 65 chemicals.
Results determine how much soil should be removed and if health officials will have to monitor a chemical plume.
In the very worst cases, where contamination may spread to wells, sewers, basements of buildings or surface waters, state officials may sink permanent test wells to try to chart pollution migration.
“You can’t just guess when you’re talking about people’s drinking water. You have to have good, solid information,” said Meyer. “You have to monitor those wells.”
You can reach Jeremy Pearce at (313) 222-4825 or jpearce@detnews.com.
