MICROTUNNELED SEWERS SAVE CITY STREET REPAIRS AND DOLLARS

When workers build new sewer lines, they usually have to dig up the most of the street and then rebuild it when they are done. The residents on the street often can't get to their driveways and businesses often lose customers who can't park nearby.

But when Robinson Construction Co. of Perryville won the contract to build nearly 3 miles of sewers just west and south of downtown, it told the Cape Girardeau city government it could do it without digging up the street and save the city money at the same time.

You can see the result on Bloomfield Street near Henderson Avenue today. Workers stay in vertical shafts no wider than eight feet in diameter that are 120 feet apart. Although there is some disruption and the street is muddier than normal, everyone has access to their driveways and no one's yard is dug up.

Those workers are the first in the United States to use this method --

microtunneling -- for installing this kind of pipe.

Although the technology is costly, the city has a net savings of 10 percent by not having to reconstruct the whole street after installing the pipe, said Cape Girardeau city manager Michael G. Miller.

The project, the College/Henderson South Combined Sewer Overflow, is part of the $25 million in improvements funded by a bond issue Cape Girardeau voters approved in 1994. Contractors have built other sewers using conventional methods.

Currently, sewage from homes in the oldest parts of Cape Girardeau flow into the same sewage pipes as the stormwater from the streets. When it rains, the volume of sewage overwhelms the city's sewage treatment plant and flows untreated into local streams and the Mississippi River.

Workers will hook up the new sewer lines with every house. The older sewers will be the storm sewers.

The newer areas of Cape Girardeau already have separate stormwater and sanitary sewers.

To dig a 4-inch pilot line, workers in the shafts use a computerized boring tool that is hooked up by radio to satelites and the global positioning system. The system can tell where the drill bit is within one-tenth of a foot, said John Bennett, an engineer based in Cape Girardeau for Sverdrup Civil Inc., a St. Louis-based engineering firm. Cape Girardeau hired Sverdrup to oversee the engineering and design of the sewer project.

After the 4-inch shaft is complete, they install a circular device that with a configuration of lights on one end and bore a larger hole from the other end using a drill bit with a television camera on it.

By monitoring the lights on a televison screen at the bottom of the shaft, a worker can manuever the drill so it stays on target.

After installing the pipe in the shaft, the workers fill the shafts with a material that hardens within a day and is ready for a layer of pavement and traffic, Bennett said.

Because the drilling doesn't disturb the existing street much, and the material used to fill it hardens so well, the street is in better shape than it would be if the sewer were installed using conventional methods, Bennett said.

The filler used under streets after digging them up for sewer construction sometimes settles, causing the pavement to collapse five or six years later, he said.

Standing on Bloomfield Street Wednesday, Frank Robinson, owner of Robinson Construction, watched as his employees installed the pipe. "If you would have dug this sewer with a trench, you would have lost most of this street," he said.

Instead there were three shafts sticking up from the road next the curb on one side of the street, with most of the suface undisturbed.