Thread: Whats under your streets?
08-06-2004, 08:46 AM #1
- Join Date
- Dec 1998
Whats under your streets?
From Sioux Falls South Dakota.
Note that many of these type utilities are now installed by the use of boring machines rather than the trench method.
FrPotential disaster in storm sewers
Punctured lines reveal unreported problems
The Sioux Falls storm-sewer system was carelessly punctured to make way for gas lines that now protrude into the concrete sewer tubes in about 20 spots, making them rife with potential disaster, city officials say.
What's more, they say, some contractors knew about the hazards, never reported the incidents and even tried to cover them up.
When heavy storms strike, sewer pipes can quickly fill with water and debris, including rocks that could hit and break the gas lines that are penetrating the system. Should that happen, gas could seep into the sewers and become explosive if ignited.
Something as simple as a passerby flicking a cigarette into a storm inlet along the street could provide the spark, and the sewer pipe below might erupt and blast through ground-level pavement.
"It basically creates a gas pipe bomb," said Kevin Smith, the city's assistant director of public works.
Smith noted that the storm sewage line is not directly connected to houses, so people are not in danger in their homes.
The city came across the problem in the wake of a June 16 storm in which nearly 8 inches of rain fell in a few hours, causing flooding and sewage backup and raising concerns about the capacity of the city's storm-sewer system.
City crews visually inspected 15 of the storm sewer pipe's 250 miles and found 46 instances where utility lines were drilled through, rather than above or below. They took video and photos to document it and estimate that roughly half are gas lines. Smith said the city eventually might have to inspect the entire sewer system for similar problems.
Electric, phone, cable and city water lines were among the culprits, but the gas lines, because of the inherent danger, raised immediate alarm, said Lyle Johnson, public works director.
"It's clearly a dangerous situation," he said, "and we're acting now to take care of it."
Des Moines-based MidAmerican Energy Co. has agreed to work with the city to pinpoint trouble spots and repair damage.
"We were obviously surprised," said Mark Reinders, a spokesman for MidAmerican. "If we'd known about it before, we'd have fixed it before. ... You hire contractors and trust them to do good work."
The repair work, which will probably involve tearing up some streets or boulevards, could begin as soon as next week and is expected to be completed this summer.
Utilities to cover costs
The city on Thursday said it could not provide a map of the areas affected because it is in the midst of linking problem sites it found underground to specific blocks above ground and to the utilities involved. Specific addresses will be made public in coming days, officials said.
Most of the problems are thought to be in central Sioux Falls - neighborhoods inside the boundaries of Interstates 90, 29 and 229, Smith said.
"We're waiting for more specific information on locations. As soon as we get that narrowed down, we'll get the work done," Reinders said.
Ballpark repair costs won't be known until crews determine how much digging is needed. But the expense probably will be covered by the utility companies: "This is not the responsibility of Sioux Falls taxpayers," Smith said.
The storm-sewer pipes, most of which range from 24 inches to 48 inches in diameter, were punched open via so-called horizontal boring, in which contractors hired by utility companies drilled into the ground to create a tunnel to lay gas and other lines.
Johnson said that during such work, it is not uncommon for drillers to hit a rock or some other natural obstruction. But in the case of the storm sewer pipes, drillers would hit the first side of the concrete line, then go through, then hit the other side shortly after, a warning sign that they were plowing through a sewer line. In at least some cases, Johnson said, crews would have recognized this and should have stopped and reported the problem to the city and to the utility company.
That did not happen.
In fact, Smith provided pictures to show that in at least two cases, contractors attempted to patch the punctured holes with grout, evidence they knew what happened and had tried to disguise it.
Smith said the city has yet to determine which contractors were involved. He said city staff plan to match the locations of the damage to the building permits to determine who is responsible. Additionally, he said, the city attorney's office is looking into what fines could be assessed.
Striking by accident
Delvin DeBoer, a professor at South Dakota State University with expertise in environmental engineering, said the city has legitimate reason to be concerned about a gas explosion and is taking responsible action. But he said it's possible that in many cases, the contractors simply made honest mistakes when drilling into the storm-sewer system. He said it can be difficult to tell whether you are drilling through rock or a cement sewer pipe.
Moreover, DeBoer said, such mistakes are not rare in big cities with older neighborhoods. While today's engineers create detailed maps that show precisely where things are underground, records from several decades ago often are not as precise. That, he said, means that for contractors working in older neighborhoods, some guesswork is involved.
"These things are not desired by anyone, and I know that (contractors) are careful to avoid them," DeBoer said. "But when you are in a big, growing city, you will have these problems."
Smith acknowledged that. He said it's not a universal excuse, though, since at least some contractors clearly knew they drilled through the storm-sewer system and did not report it.
"Having this happen accidentally is one thing," Smith said. "Having it happen, knowing about it and not telling anyone, that's another."
Reinders said he didn't think MidAmerican, which covers every large city in Iowa, had similar problems with contractors in those cities. He said what may be unique about Sioux Falls is that, following the June flooding, it had reason to inspect miles of its storm-sewer system, whereas other cities may not recently have done so.
Like other similarly sized cities - including Sioux City, Iowa - Sioux Falls inspects sections of its storm-sewer system annually but doesn't have the staff to pore over the entire 250 miles. Nor does it typically need to, because deterioration of the system usually evolves over several years, making it necessary to cover the system during a multi-year period.
Utility companies involved in the mistakes found so far - cable, electric and others - are being notified of the problem, Smith said.
Higher permit fees
As for future work, he said the city is considering raising utility permit fees to pay for staff to inspect every horizontal boring job to make sure it's done right. Based on activity of recent years, that could involve 500 locations a year, Smith said.
"We'll probably have to go in and visually check out every one to make sure they didn't hit anything," Smith said.
City Council members reached Thursday said the idea of heightened enforcement deserves serious consideration, although some said the city should look into finding a way to handle the work with existing staff hours rather than raise permit fees.
"Whenever you raise fees, you risk having those new costs passed along to customers," said council member Darrin Smith.
Council member Andy Howes said new precautions to prevent the gas-line intrusions are paramount because "you could all of the sudden be talking about an entire area blowing up. It's quite frightening when you think about it. ... We need to take action because as it stands right now, the people putting these things in aren't taking the needed responsibility for it. At least some of them have proven untrustworthy."
Johnson, the public works director, said debris that clung to gas and other lines hanging into the sewer pipes also may have contributed to sewage backup during the June storm that caused flooding.
"It doesn't take much to restrict that flow," Johnson said.
"We're not blaming the utility companies directly, but they are hiring the contractors to do this work, and it obviously isn't getting done the way it is supposed to be done."
Reach Kevin Dobbs at 977-3924.
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