Storm sewer treatment system
From 1910 until 1962, the 3M Company’s world headquarters was located on a 46-acre parcel of land on the East Side of St. Paul, Minn. This area has recently been redeveloped by the Saint Paul Port Authority and renamed Beacon Bluff. A major issue with the redevelopment of this area was stormwater runoff, which previously was untreated and ran directly into the Mississippi River. Loucks Associates designed an underground detention system to treat this runoff.
A major component of the water treatment system was the 680 linear feet of perforated 10-foot-diameter corrugated steel pipe made from aluminized type 2 steel whose service life is expected to exceed 100 years in this type of application. Constructed access points were placed above each section of pipe for ease of maintenance. Permanent metal ladders were welded to the pipes for access. The outside circumference of the pipes was wrapped in geotextile fabric that prohibited fine particles from migrating into the pipe. The entire system can retain up to 1 million gallons of runoff, which greatly reduces the risk of downstream flooding. The runoff for this project combined the old 3M site with the surrounding neighborhood. The existing neighborhood had a network of storm sewers whose effluent was untreated. Once this existing system was linked with the detention system, all of the runoff was effectively treated.
The underground detention system was installed by Rachel Contracting and manufactured by TrueNorth Steel. It utilized the SAFL Baffle, a specialized baffle or metal grate named for and engineered by the University of Minnesota’s St. Anthony Falls Laboratory. This patent-pending innovation traps approximately
90 percent of sediment from stormwater runoff and stores it in a sump, where it can be periodically removed through access ports in the top of the detention system. By removing the sediment from the stormwater runoff, the contaminants – which often attach themselves to the sediment particles – are removed as well.
The constructed section for the detention system consisted of compacted engineered fill to the top of the pipe. To make use of an otherwise waste product that would occupy space in the local landfill, several feet of shredded rubber tires were placed as backfill. The shredded tires created additional void space for the stormwater runoff to infiltrate, capturing more sediment and contaminates as the runoff percolates through the various fill types on top of the retention pipe. The final lift of fill on top of the shredded rubber tires is 2 feet of granular sand.
Several collection areas are constructed with the project to test the effluent. Through use of plastic pipe risers, these samples can be obtained without physically entering the underground system. By capturing samples from above, the effluent runoff from the detention system will be tested and tracked to ensure the system’s effectiveness. This state-of-the-art stormwater treatment system allows for a cost-effective, ecologically friendly solution to meet updated watershed requirements.
Information provided by the National Corrugated Steel Pipe Association
Deep tunnel shafts
Wastewater tunnels are getting larger and deeper across the country, and use of large-diameter centrifugally cast fiberglass-reinforced polymer mortar (CCFRPM) pipes for these applications is increasing. On two recent large-diameter tunnels in the Minneapolis-St. Paul area – Woodbury L73 and Victoria Intercept Sewer Tunnel – CCFRPM was selected for both the tunnel and the manhole risers. Both installations are for the same owner, the Metropolitan Council of Environmental Services (MCES). The risers were about 75 feet deep for Woodbury and 100 feet on the Victoria project. “Since the two-pass tunnel used fiberglass pipes as the liner, it only made sense to continue the corrosion resistance in the shafts to the surface,” said Vince Paparozzi, area sales manager for Hobas Pipe USA.
On the Woodbury project, the contractor opted to install the tunnel liner rather than cut out the riser access and laminate the fiberglass risers to the mainline tunnel, 72-inch-diameter fiberglass carrier pipe. For the Victoria project, the installer opted to have Hobas manufacture the T-Base systems at their manufacturing plant in Houston and the contractor installed the T-Base and risers using gasketed joints.
Traditionally, risers for large-diameter tunnels have been manufactured of concrete, but CCFRPM risers offer lighter weight, corrosion resistance, and compressive strengths greater than most concrete products. Another key issue is corrosion resistance. Instead of using PVC liner or some type of coating, owners can use CCFRPM pipe and not worry about corrosion. The contractor receives the benefits of time and cost and the owner gets 100-year corrosion-resistant design, according to Hobas.
On deep tunnel projects, corrosion resistance is a major concern as many systems are designed to provide storage of combined storm and sanitary sewage in the tunnel after a big rain event. As the rain event subsides, the sewage is gradually released for treatment. Storage events can lead to increased hydrogen sulfide, which is then released at manholes due to turbulence. Corrosion resistance of the shafts is as important as the sewer line. With the corrosion-resistant risers as well, MCES has a complete corrosion resistant system.
Information provided by Hobas Pipe USA
Powerhouse discharge pipe
PacifiCorp used 3,000 feet of precast concrete pipe, elbow, transition pieces, and manholes, supplied by Oldcastle Precast, for the out-flow pipe and the in-flow pipe of its Lemolo No. 2 tailrace re-routing project in Douglas County, Ore. PacifiCorp was required to reroute the Lemolo No. 2 powerhouse discharge to Toketee Reservoir in accordance with the North Umpqua Settlement Agreement Section 5.4. After a seven-year design process, construction of PacifiCorp’s Lemolo No. 2 tailrace re-routing project is almost complete.
Oldcastle Precast provided a 108-inch-diameter concrete pipeline that transitioned into 96-inch-diameter concrete pipe and then back into 108-inch concrete pipe. The pipe is t-lok lined pipe in portions to meet hydraulic design criteria. The precast concrete pipe was manufactured in 12-foot lay lengths with numerous custom castings. The pipeline makes multiple turns and grade changes. Inlet and outlet pieces were poured with steel rings cast into the pipe to allow connection to a cast-in-place headwall. In addition, Oldcastle Precast supplied three T-Top manhole pipe sections, each having a 48-inch manhole cast into the pipe section for access to the pipeline.
The Lemolo No. 2 tailrace re-routing project consists of in-water construction of the cofferdam for the inlet and an outlet structure. To stay on schedule, they built from both ends. The 3,000 feet of pipe was buried along the Toketee-Rigdon road and across the Toketee recreation area. The pipe will carry 700 cubic feet per second from the Lemolo 2 plant tailrace and eliminate ramping in the Lemolo 2 full flow reach of the North Umpqua River.
Weekly Brothers Inc. is the general contractor overseeing construction and McMillen LLC is the project engineer. The project was scheduled for completion at the end of October 2011.
Information provided by Oldcastle Precast
Irrigation canal headgate
The Yakima-Tieton Irrigation District (YTID) needed a headgate replacement for the main canal on the Tieton River. Additionally, the project needed to convert 100 feet of canal to underground pipe to solve a recurring falling rock problem that was a maintenance and safety concern.
YTID worked with RH2 Engineering Inc. on the project. They decided to tie the new headgate into the existing concrete headgate structure with a cast-in-place pipe inlet structure. In order to connect the old structure with the new structure, they chose 100 feet of 96-inch-diameter DuroMaxx steel reinforced polyethylene (SRPE) pipe from CONTECH Construction Products Inc. DuroMaxx was chosen because the pressure-rated polyethylene resin provided an unmatched durability and the 80-ksi steel reinforcing ribs provided structural integrity. Combined with its high-performance ElectroFusion joint and cost effectiveness, DuroMaxx was the perfect solution.
A new concrete structure serving as a pipe outlet and housing the new 10-foot-wide by 12-foot-tall, steel radial gate was also constructed. The gate structure was cast-in-place concrete designed to accept a prefabricated radial gate from several alternative gate suppliers.
The work was completed on time and on budget with only minor revisions to the existing YTID canal control system. RH2 provided design, permit assistance, coordination with the Bureau of Reclamation, contract administration, and periodic construction inspection to help YTID obtain a superior finished product.
“DuroMaxx provided a cost-effective, easy-to-assemble solution for a project with limited access, limited budget, and limited options for 96-inch-diameter pipe,” said Mason Mendel, P.E., with RH2.
Information provided by CONTECH Construction Products Inc.