Poorly made 1970s-era concrete water pipes like the one that failed in Prince George's County last week are common to the D.C. area and represent an ongoing infrastructure problem if not an immediate threat, officials said.
Beneath Prince George's and Montgomery counties lie 350 miles of concrete cylinder pipes, the second-largest concentration in the nation behind Detroit. The system stretches throughout the region, with some sections tucked into forests while others run under main roads.
The pipes, made of prestressed concrete that encases steel bands, do not meet current industry standards, although they originally were said to have a 100-year life expectancy. They range in size from 16 inches in diameter to 96 inches, with the largest pipes that carry massive amounts of water potentially impacting hundreds of thousands of people if they fail or burst.
"When the big pipes break, they break catastrophically," said Jerry Irvine, a spokesman for the Washington Suburban Sanitary Commission, which provides water to most of the two Maryland counties. Pipes of 54 inches and more generally qualify as "big." The 54-inch pipe that failed in Prince George's County last week was projected to affect up to 200,000 people.
Mr. Irvine explained that when concrete corrodes, water gets to the metal bands, which also corrode, and they snap. Bursting pipes spew shrapnel-like debris, gush water and leave gaping craters.
"Concrete and water are a bad mix," he said.
Concrete might have been a bad choice of material for water mains, but more factors are involved in determining their life span. Tom Curtis, the deputy executive director of the American Water Works Association, said pipes' positioning, surrounding terrain, the amount of water pressure and external vibrations like those from subways also strain pipelines.
"Some of WSSC's concrete pipes may be fine for many more years while other sections need to be replaced sooner," Mr. Curtis said. "I don't know how long that particular system will last."
But where the potential ruptures will occur is anyone's guess.
Routine inspections have shown that 2 percent of the pipes needed some sort of fixing, with a smaller percentage of those actually threatening to rupture. In 2011 and last year combined, the percentage translated to more than 3,000 water mains that needed repair in Montgomery and Prince George's counties, WSSC spokesman I.J. Hudson said.
Among them, a major water main that exploded in Chevy Chase in March caused water restrictions for 1.8 million people in Montgomery and Prince George's counties and a loss of 60 million gallons of water.
Utility officials have long realized the shortcomings of the concrete pipes and have attached fiber optic cables to detect structural weaknesses before they burst, beginning with the largest pipes. The cables detect the sounds of snapping bands. In the Prince George's instance, an increasingly rapid series of pings from the cables alerted workers to the breaking steel.
The cables have detected around a dozen cases of snapping bands but are not "100 percent guaranteed" to warn of all breakage, Mr. Hudson said. WSSC will rely on their inspection and detection methods to find failing and broken mains, replacing the concrete pipes as needed with a new steel model.
Officials cited valves as the biggest issue in Prince George's County's recent pipe repairs.
"If we had good, sound operating valves, no one would have ever heard of this system," WSSC General Manager Jerry N. Johnson said.
The valves control the flow of water in the pipes. If a valve hadn't frozen, the county would not have faced a water outage. The main would have been fixed and "no one would have said anything," Mr. Hudson said.
The system's some 78,000 valves need frequent repairs. WSSC is also creating more pipeline that adds redundancy to its service so that more than one line can funnel water to residents. The $36 million in funding for that project is expected to last through next year.
Note: An earlier version of this report incorrectly stated the number of miles of concrete pipe beneath Montgomery and Prince George’s counties. The report also misstated the extent of the Washington Suburban Sanitary Commission’s service area. The mistakes have been corrected.