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The Main Pumping Station Diversions Project is an essential part of the Clean Rivers Project. Whenever it rains, combined sewer overflows (CSOs) discharge into the Anacostia River from Washington, DC’s antiquated sewerage system. Two diversion chambers are installed near Tingey Street to divert CSOs into the Blue Plains Tunnel by way of the Main Pumping Station Drop Shaft.
The Blue Plains Tunnel stores and conveys the CSOs to the Blue Plains Advanced Wastewater Treatment Plant (Blue Plains) for treatment prior to discharging to the Potomac River. Ventilation control facilities were constructed within the Main Pumping Station Drop Shaft to regulate air flow in the tunnel system.
The project is in front of DC Water’s historic Main Pumping Station, originally built in the early 1900s. The above-ground portions of the Main Pumping Station diversions were constructed within the Main Pumping Station compound. Final design of the structures was coordinated with the District Historic Preservation Review Board (HPRB), the Commission of Fine Arts (CFA) and the National Capital Planning Commission (NCPC) for compatibility with the historic Main Pumping Station building.
Work on the Main Pumping Station Diversions, Division 1 project included constructing a 100-ft long, below-grade surge tank, two sewage diversion structures, flow channels, vent and odor control facilities, and internal flow elements within a 100-ft deep shaft. NUCA member Corman Kokosing Construction Co. designed most of the excavation support, including 48-in. diameter secant piles and a combination king pile/sheet pile system with three levels of internal bracing. A 72-in. fiberglass reinforced plastic (FRP) sewer pipe was excavated under an active arch sewer inside a liner plate tunnel.
Two reinforced concrete diversion structures were constructed atop active 100-year-old arch sewers (16- and 12-ft wide) with excavation 25- to 30-ft deep. The diversion chambers take rising storm water overflows over a series of weirs and into cast-in-place concrete channels leading into a 100-ft deep shaft and tunnel for eventual treatment at Blue Plains. Utilities were relocated and protected during construction.
There were strict dewatering standards which required water to be quantified and tested for pH and turbidity before discharging. Temporary excavation support designs were subject to restrictive load and ground movement criteria, and geotechnical instrumentation devices continually monitored ground movement.
The tunnel passing beneath Tiber Creek Sewer, although only 70-ft long, was designed and constructed to accommodate wet, soft ground while measures were put in place to protect the existing sewer above. Hand mining the 96-in. diameter liner plate tunnel was also employed. This two-pass method enabled maintaining close tolerance to line and grade.
A maze of utilities was relocated and/or protected around and within the construction zone, including relocating a private duct bank, coordinating with Pepco to relocate their electrical lines, self-performing relocating a water line and sewer lines, and coordinating utility relocations with Verizon, Comcast, and Washington Gas. Several relocations were staged in phases to keep systems operational.
Deep excavation supports were accomplished via support of excavation methods, including:
- Owner- and contractor-designed 48-in. secant pile walls up to 100-ft deep.
- Sheet pile walls up to 75-ft deep to include a king pile wall system.
- Soldier and lag construction, including steel ladder beams with flat liner plate lagging.
- Liner plate shafts that allowed working around existing facilities with minimal disturbance.
- A perimeter wall around the support of excavation perimeter for flood protection.
- Extensive geotechnical instrumentation and monitoring based on limiting support of excavation movement per Owner-provided parameters.
- Excavation condition assessments preparation ahead of excavation using finite element analysis methods to prevent damage to adjacent facilities.
Benefit to the Community
The project was located in a congested urban site. Corman eliminated parking on one side of Tingey Street, placed barriers between the construction staging area and traffic, widened the radius of an adjacent intersection, placed temporary curb and restriped the roadway to keep traffic moving. This was especially important due to the proximity to the Washington Nationals’ baseball stadium. The company’s Maintenance of Traffic Plan anticipated an increase in pedestrian and vehicular traffic during the baseball season. Working with DC Water and the DC Department of Transportation, Corman modified the original plan as the parameters of the influx became known.
Following completion of the project Moussa Wone, Design Manager for the DC Clean Rivers Project, wrote: “Corman’s ability to work with stakeholders on the final design, its capacity to design a majority of the intricate support of excavation, along with its willingness to work day and night shifts six days a week to meet the aggressive project schedule are testaments to the Corman team’s effort to complete the project to our satisfaction, and demonstrates the partnering spirit Corman brought to this collaboration.”
Other parties involved in the project included: Whitman, Requardt & Associates (WRA) (Lead Designer); Brayman Construction (Secant Piles, Auger Cast Piles); Quinn Consulting Services (QA/QC Engineering); Mohawk Bridge & Iron (Rebar); and Haywood Baker (Ground Improvement).
Project Name: Main Pumping Station Diversions, Division 1
Category: Sanitary Sewer Collection
Contractor: Corman Kokosing Construction Company
Lead Designer: WRA
Project Owner: DC Water | Clean Rivers Project
Location: Washington, DC