WILLMAR -- The First Street South and 28th Avenue intersection won't be dug up when a portion of the interceptor sewer pipeline leading to the new wastewater treatment plant is constructed through there.
Instead, a tunnel-boring machine will install the pipe underground. One access point will be excavated on the east side of First Street. Another will be excavated on the street's west side.
As the machine bores through the soil, it will pull sewer piping along behind it. The soil will be conveyed out the back, lifted out, placed into waiting trucks and hauled away.
"It's just not practical to close First Street to traffic,'' said Craig Holmes, program manager for treatment plant consultant Donohue and Associates. "We do not want to disrupt traffic.''
The 225-foot tunneling job will take about a week and will most likely be subcontracted by the underground utility contractor.
"Some have their own boring equipment, but that's a specialty. Most of those companies subcontract that,'' Holmes said.
He and Kenneth Sedmak, Donohue senior program manager, discussed the tunneling work and other aspects of the $88.1 million project during an update session Wednesday morning at the Willmar Fire Station training room for Public Works Department employees, wastewater treatment operators, city officials, Willmar Township board members and others.
The Willmar City Council will receive the presentation Monday night.
"It's ready to go for bids once the City Council approves it for bidding,'' Holmes said. The project will be referred to the Public Works/Safety Committee for recommendation, with the anticipation that the council will vote May 5 to advertise for construction bids.
Contractors will have six weeks to prepare their prices. Contracts would be awarded July 21.
Holmes said the project is mostly on schedule. The city would have liked to have had contracts awarded by now, but litigation over acquiring land for the conveyance corridor delayed it a few months.
The city and landowners are waiting for Judge David Mennis to decide whether the city has the right to acquire land along the conveyance corridor or whether the landowners have the right to require the city to obtain permanent utility easements.
But Holmes said there's still good reason to believe that the plant will be operating by the November 2010 deadline set by the Minnesota Pollution Control Agency. The agency says the existing plant uses failed technology and does not comply with effluent standards.
The conveyance system consists of a force main and an interceptor.
The gravity-operated interceptor will carry municipal waste 5½ miles from the existing plant south to 28th Avenue and then west to the new treatment plant site, located a mile south of state Highway 40 and just west of County Road 116.
The pressure-operated force main will carry industrial waste from the Jennie-O Turkey Store plants on Benson Avenue and Willmar Avenue. Jennie-O will continue to pre-treat its waste, according to Holmes.
The routes of the pipelines will converge at a point between 30th Street Southwest and County Road 5.
The pipelines will separately carry the municipal waste and the industrial waste to the new plant where the wastes will be treated separately. The separate treatments are needed because the two waste streams don't complement one another particularly well for a number of reasons, said Holmes.
Both treatments will use a biological process in which billions of bacteria will eat the dissolved waste material. As the biomass grows, it produces excess that is thickened and applied on land. Some bacteria are returned to eat some more.
The plant is expected to discharge an average of 5.2 million gallons of treated effluent into Hawk Creek every day. The Joint Ditch Authority has approved the discharge and the discharge permit has been approved by the Minnesota Pollution Control Agency.
Before the effluent is discharged, the water will be aerated and the dissolved oxygen content increased to make the water "friendly'' to fish and aquatic organisms.
The water will be disinfected with ultraviolet light. Ultraviolet light avoids the use of chemicals, said Holmes. He said more communities are using ultraviolet light or ozone to disinfect effluent.
"When you release this amount of wastewater into a receiving stream like Hawk Creek, it is best that it doesn't have any chemical residuals in it. This way, we can hit it with light and there's no chemicals employed.''
The existing plant will be decommissioned after the new plant begins operation but will serve as a collection point for the interceptor.