In all, an estimated 6.5 million gallons spilled from the 1970s-era line.
Tredyffrin is not the only community grappling with busted pipes, or the threat of them. The Valley Forge spill is just the most recent example of the deterioration of the region's - indeed, the country's - aged mains.
The nation's water infrastructure, carrying sewage and drinking water, is reaching the end of its useful life, according to a 2012 report by the American Water Works Association. The industry group estimated that expanding and restoring it will cost $1 trillion in the next 25 years "if we are to maintain current levels of water service."
The Northeast's pipes are older than most; some date to the late 1800s. Several experts said the pipe that broke in Tredyffrin - which shares operation of the lines with other Chester County municipalities - was "relatively young."
John Brosious, deputy director of the Pennsylvania Municipal Authorities Association, calls the state's pipes "a hidden quandary. You just pray that what's under the ground is working. You don't ever really know until it breaks."
Emergency repairs cost 300 percent more than routine pipe replacements, according to the industry-accepted norm.
In Southeastern Pennsylvania, at least a quarter of the systems have "existing or potential capacity issues," said Cosmo Servidio, regional director of the state Department of Environmental Protection.
As for New Jersey, "we're an old, urbanized state," said DEP spokesman Larry Hajna. "A lot of those lines in the ground, they need to be addressed."
Unlike potholes, which people notice and complain about, a problem sewer is out of sight and, all too often, out of mind. Meters to detect leaks might signal trouble, but even a camera run through the line won't see where a pipe is weakened from the outside .
Because many sewer lines are gravity-fed and have to run downhill, they're generally deeper than pressurized drinking-water pipes. So it costs more to dig one up.
The public often balks at not just the expense of fixing pipes, but also the disruption of dug-up streets and detours. So if the choice is between spending money to repair a line that isn't broken - yet - vs. building a park, guess which wins.
Plus, the expense is staggering. The Philadelphia Water Department has a "replacement rate" of 10 percent of its lines over 12 years - meaning the oldest pipes would be 120 years old by the cycle's end - at a current estimated cost of $500 million.
Half a decade ago, the Delaware County Regional Water Quality Control Authority (Delcora) faced a $30 million bill to replace a 42-inch main not even three miles long.
Delcora got lucky. It put the job out for bids during the recession and wound up paying $17 million. According to Delcora executive director Joe Salvucci, because much of the engineering work was done in advance, the water authority also got a state grant and a low-interest loan through the Pennsylvania Infrastructure Investment Authority (PennVEST), a state agency with partial federal funding.
That's what systems need, officials say: state and federal money. No other pockets are deep enough to fund such extensive work.
New Jersey's Environmental Infrastructure Trust, a revolving fund similar to PennVEST, has provided $6 billion in low-interest loans since 1986. "But at the end of the day, it's still a loan . . . that's the issue" for municipalities, said executive director David Zimmer.
Meanwhile, new technologies are being developed to help pipe owners assess their systems, an annual requirement in Pennsylvania. The Upper Montgomery Joint Authority, which has 32 miles of pipe serving Pennsburg, East Greenville, and Red Hill, recently tested an Electro Scan device that can find subtle problems early-on, even small cracks - at $4 to $6 per foot of pipe. With it, the authority could better target rehab money for its lines, many of them terra cotta pipes of mid-1960s vintage.
"We're not a real old system," said superintendent Glenn Quinn. "But it's old enough. Old enough that you have to constantly be willing to do repairs."