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Underground solution saves US$500 million 17 Jul 2013
DC Water News Release
An innovative tunnel dewatering pump station is selected by DC Water as the solution to its Federally-imposed nitrogen removal targets. The US$215 million design-build contract, awarded to PC Construction/CDM Smith, is one of the largest ever awarded by DC Water as it works to deliver its multi billion dollar Clean Rivers Project.
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Clean Rivers Project tunnels

The underground solution, which saves US$500 million on conventional methods, is aimed at reducing nitrogen discharge into the Potomac River and Chesapeake Bay as well as bringing relief from combined sewer overflows (CSOs) to the District's waterways.
The proposal received the highest technical score and was the lowest cost.
When DC Water's new permit limits for 2015 were first announced, DC Water analyzed possible solutions for lowering nitrogen to the required levels. The first proposal called for adding more nitrogen removal facilities at the Blue Plains treatment plant and would have meant stacking treatment tanks on top of the existing ones. Instead, this innovative solution stores flow inside the CSO tunnels so that even during peak flow during wet weather the flows can receive treatment. This design saved roughly $500 million.
The tunnel dewatering pump station is a complex pumping facility that will be built into the shaft that currently serves as an entrance to the tunneling process. It will be the equivalent of a 10-storey building, built downwards underground, for the purpose of lifting the tons of combined sewage that will be conveyed in the tunnels after rainstorms up to surface level for treatment.
The contract also includes an enhanced clarification facility to treat up to 225 million gallons per day of excess flow during rainstorm events. The flow then can either be sent for secondary treatment or discharged into the Potomac.
DC Water Board of Directors Chairman Allen Y. Lew said: "Right now there are several billion dollars in construction projects under way at the Blue Plains Advanced Wastewater Treatment Plant, and the most costly are federally mandated. These costs are borne mostly by our ratepayers; therefore, we continue to seek measures to lessen the rate increases. Supporting creative solutions and negotiating competitive contracts go a long way towards achieving that mission."
"We are pleased to work with PC/CDM Joint Venture on this important component of our wet weather plan," said DC Water General Manager George S. Hawkins. "And we are proud of the innovative solutions we continue to put in place. The projects that make up the wet weather plan achieve both nitrogen reduction and CSO abatement to improve the health of our waterways. By combining separate goals into related projects, we will save hundreds of millions of dollars."
"Our joint venture is excited to work with DC Water on this unique project in our nation's capital," said Kevin McCarthy, president of PC Construction . "We look forward to being part of this massive project to protect the environment."

Blue Plains treatment plant

For decades, DC Water has been a pacesetter in restoring the Potomac River and Chesapeake Bay by improving performance and treatment capabilities at the Blue Plains Advanced Wastewater Treatment Plant. Blue Plains has successfully achieved nitrogen removal since 1999 and was the first to achieve the Chesapeake Bay Agreement goal of 40 percent nitrogen reduction. The current projects further reduce nitrogen levels to the limits of technology.
The latest contract award is part of the so-called Clean Rivers Project, a multi-billion dollar project designed to enable DC Water to reduce untreated CSO discharges to within agreed limits as part of a Federal Clean Water Act-imposed Long Term Control Plan.
Other elements of the project include excavation of a series of deep CSO storage tunnels, the first of which (Blue Plains Tunnel, 4.5 miles x 23ft) is due for imminent TBM launch by the Traylor/Skanska/Jay Dee JV. Later this year a JV of Impregilo/SA Healy will launch on the 2.4-mile long Anacostia River Tunnel, and two further tunnel projects are currently planned for 2018-2021.
References
Green surge threatens CSO storage solution - TunnelTalk, June 2013
DC advancing clean river mega-project - TunnelTalk, May 2013
Blue Plains tunnel teams selected in DC - TunnelTalk, March 2011
Miles of new tunnels to clean up DC waterways - TunnelTalk, August 2009

           

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