Oct. 9--Trustees of the Metropolitan St. Louis Sewer District on Thursday tentatively agreed to cover a $2.8 million cost overrun in an expansion of the Lemay sewage treatment plant.

This summer when a contractor working on expanding the plant, workers installed a temporary plug in waste water line that was next to a concrete clarifier tank that is 150 feet in diameter.

The plug failed resulting in a flood that caused the cement bottom of the tank to rise and damage sludge collection equipment in the tank. Tarlton Corp., the contractor for the expansion, is replacing the tank bottom. The equipment is 24 years old; the staff decided that replacing it is a better approach than repairing it now and replacing it five to 10 years from now, Brian Hoelscher, director of engineering, said.

The cost of the new bottom and equipment is $1.8 million. The staff also wants to spend $1 million to replace a deteriorated inflow main 96 inches in diameter. Tarlton workers discovered the deterioration when excavating for the project.

The district is expanding the plant so it can handle 220 million gallons a day of sewage in dry weather instead of 160 million gallons a day and 340 million gallons a day in wet weather instead of 240 million gallons a day. The difference is storm water that the plant shunts around secondary treatment in storms, Hoelscher said.

The total cost of the Lemay plant expansion is $94.5 million. To finance the $2.8 million, the district would use money saved by bids being lower than estimates on other projects, Hoelscher said. The expansion should be complete by March.

Also the trustees tentatively agreed to add $113,000 to a contract with TGB Inc. of St. Louis to pay for a change in plans for the installation of a standby generator at Lemay Pump Station 3. A newly installed generator could provide electricity for two pumps in case of a power outage instead of serving one pump.

At the last minute, the manufacturer of a new generator for the station stopped taking orders because of changes in federal regulations, Hoelscher said. Instead, the district will modify a slightly larger pump, change the pump location and provide a new pad and natural gas meter for it.

Trustees tentatively agreed to spend $3,339,000 for the installation of wetlands to offset those lost by an expansion of the Missouri River treatment plant. Mitco LLC of Salisbury, Mo., will develop the wetlands near the Cuiver and Missouri rivers and near the confluence of the Missouri and Mississippi rivers, Lance LeComb, a district spokesman, said. Mitco and the Army Corps of Engineers would decide where the wetlands would go, he said.