Tarlton Corp., a St. Louis-based general contracting and construction management firm, has successfully installed a temporary diversion around a portion of the Metropolitan St. Louis Sewer District’s Lemay Wastewater Treatment Plant’s 96-inch influent pipe. The achievement, believed to be only the second 96-inch diversion completed in the United States, is part of a multiyear project to increase the MSD district’s peak wet-weather treatment capacity.
The Metropolitan St. Louis Sewer District serves the city of St. Louis and about 80 percent of St. Louis County, and operates seven wastewater treatment facilities. The Lemay plant is the second largest. Through these plants, the district treats an average daily flow of more than 330 million gallons.
Preparation for the diversion lasted several months and included installing temporary piping and a diversion structure. The last step in activating the diversion, which occurred November 13, required MSD to shut down flow to the plant for approximately 90 minutes so workers could remove a cap from an existing riser pipe. Wit the cap removed, the influent could flow through the diversion structure.
After draining the system of standing water, workers had less than 45 minutes to remove the massive cap and install a butterfly-shaped STOPPLE plug through a 60-inch opening cut in the existing 96-inch pipe at the tie-in point to force the flow through the diversion piping. They also erected six temporary steel gates in the grit structure to stop water from flowing between tanks.
Tarlton and Haberberger Mechanical Contractors Inc. will spend the month of December removing approximately 80 feet of existing pipe and installing new pieces to connect a new structure to the existing influent path, allowing MSD to more accurately measure flow into the plant and control flow into the wet weather expansion under construction. Once the new pipe is laid, another shutdown will be required to remove the plug, reattach the cap on the riser and remove the temporary gates.
“MSD could not shut down the pumps in the pump stations feeding the plant until flow into the plant was low,” explained Steve Cronin, vice president of the Tarlton Concrete Group. “The long-awaited event took place at 4:30 a.m. on November 13. We’re proud to say the operation went extremely well.”
Cronin credited all participating firms for “working through the challenges with great cooperation and teamwork.” In addition to MSD and Haberberger, Tarlton’s partners on the project are Black & Veatch Corp., KAI Design & Build and T.D. Williamson Inc., which installed the STOPPLE plug.
MSD tapped Tarlton in 2007 as general contractor for the $87 million, 30-month Lemay project, which will increase the peak wet-weather treatment capacity of the plant. Tarlton’s work includes tunneling, 12-foot-diameter sewer piping, construction of four primary clarifiers, two grit basins, a primary sludge pump station, grit handling building and numerous cast-in-place vaults, the deepest being 74 feet underground. Completion is scheduled for early 2010.