The water main that ruptured and left hundreds of thousands of Montgomery County residents boiling water for most of three days last week is expected to be fully repaired and back in service on Thursday.
Washington Suburban Sanitary Commission spokeswoman Lyn Riggins said Ross Contracting of Mount Airy hopes to secure a new 54-foot length of state-of-the-art ductile iron pipe by then to replace the precast concrete section believed to have blown sometime June 15 in Bernard Frank Park near Meadowside Lane in Derwood.
The gush of roughly 100 million gallons of water from a 48-inch main temporarily turned a secluded section of woodland into a small cataract.
Water pressure was restored to all WSSC customers by 9 p.m. June 16, but it took until the evening of June 18 to get back a series of laboratory tests that confirmed the water was safe to drink and use for common household tasks without boiling.
A restaurant closure shuttered Monday night about 1,200 county eateries for two days from the Potomac River eastward to Burtonsville and from Shady Grove Road north to Damascus. City of Rockville restaurants were not affected by the order.
No incidents of illness related to possible water contamination were reported, said Mary Anderson, a spokeswoman for the county health department.
Since the break, a 36-inch main that runs parallel to the broken pipe has supplied all, rather than part, of the water that the utility distributes in a section of its system that runs between Shady Grove Road and Georgia Avenue, Riggins said.
Although the water mains should be back to normal by Thursday, it will take longer to backfill the trench and restore eroded parkland, she said.
Early estimates of the costs are $50,000 for water main repairs and another $50,000 for environmental restoration, Riggins said.
Maintenance backlogs have long been a problem at the utility, and WSSC commissioners failed this year, over the protest and warnings of then-general manager Andrew D. Brunhart to agree to charge customers large fees aimed at catching up.
A proposal for the budget year that begins July 1 would have increased the average residential customer’s bill by $300 a year, largely through a fee meant to repair and replace failing pipes and valves.
Instead, the WSSC’s governing board approved an increase that will increase the average residential ratepayer’s about $45 in the coming year, with little of that increase going to rehabilitating the water delivery system.
The WSSC’s water main assessment program was trimmed in the past decade under pressure not to increase rates and the threat of turning the public utility over to a private operator.
The WSSC’s current budget allocated $1 million for water main assessment.
The section of pipe that burst was 38 years old and had not been inspected, although a section of the line about one mile away was checked with experimental hydrophone probes about five years ago. No problem was found then.
The utility has turned away from the hydrophone probes, typically located 100 feet apart, and has begun installing fiber optic cable to provide continuous monitoring of mains larger than 42 inches. But few miles of the larger pipes that are on the priority list have those monitoring cables and the section that burst was not yet on any installation schedule, WSSC spokesman Jim Neustadt said.
Last year, the utility’s workers laid 12 miles of fiber-optic cable along large mains in Potomac and Adelphi to give round-the-clock notice of an impending break. They plan to install six more miles of such cable by next month and at least six more miles each year.
By the end of next July, the utility expects to have continuous monitoring in about 18 miles, or 18 percent, of large precast concrete water mains.
The water distribution system includes 143 miles of large, high-pressure mains similar to the one that burst and many of those mains are made of materials — such as cast iron or pre-cast concrete, like the one that broke — that are at or near the end of their lifespan.
While some of those are at risk of ‘‘catastrophic failure,” according to the utility’s studies, the pipe that broke was not considered old and was made of a type of pre-cast concrete that was not considered likely to fail soon.
Until last week, the utility has had no problems with pipes of this type, Neustadt said.
Engineers are still trying to figure out why the pipe broke, and parts of it have washed away, so ‘‘I don’t know if we will ever be able to say,” Riggins said.
Utility officials found some evidence that pinpoint infiltration may have weakened internal metal reinforcements, but said they could not say whether the break suggests that parts of water delivery system composed of such pipe are more vulnerable than they supposed.
