Vice President speaks of DC Water Clean Rivers project 30 Apr 2020

With recent approval of the Potomac River CSO Tunnel, DC Water, the public utility water management company for Washington DC and its service area, begins the final major element of its 25-year Clean Rivers program to reduce combined sewer overflows into the Potomac and Anacostia Rivers and Rock Creek.

Fig 1. Full scope of the DC Water CSO Clean Rivers project

The proposed 5-5-mile long x 18ft diameter (9km x 5.5m) Potomac Tunnel will run along the east shore of the Potomac River, passing beneath parks and gardens of the Washington DC riverside and alongside famous landmarks, including the Lincoln Memorial and the Kennedy Center Concert Hall. Ahead of a fully defined scope, the contract has a budget estimate of between US$450 million and $550 million and will be completed in two drives from a new shaft to be constructed in West Potomac Park, located between the iconic Tidal Basin and Lincoln Memorial.

“The two parts of the Potomac Tunnel are in quite different geology,” said Carlton Ray, Vice President for DC Water in an interview with TunnnelTalk. “The south drive is in the soft sedimentary deposits of previous program drives, and the drive north is the first of the program in rock. It will be either two TBMs needed, one of soft ground and the other of hard rock design, or a single dual mode TBM may also be appropriate for both drives. The decision will be for the engaged contractor to make. We have used both new and refurbished machines on program contracts and so both can be proposed for evaluation.”

To progress the Potomac design-build contract, a call for qualified construction groups is anticipated for late 2021, with an invitation for shortlisted groups to present proposals in mid-2022 and an award of contract in Summer 2023. “Rather than a prequalification process, we invite experienced groups to present expressions of interest and from the best qualified we select a shortlist of typically three,” said Ray. “The successful group is selected based on a best value selection process, with technical proposals reviewed and scored before opening the cost proposals. In recognising the expense and effort of preparing design-build proposals, we also pay a stipend to the unsuccessful proposers, which has been about $450,000 for previous procurement processes of this size.”

Advance of the Kennedy Centre CSO-021 shaft which will be connected to the Potomac River Tunnel

The design-build procurement method was adopted for the Clean Rivers project from the start, explained Ray. McMillen Jacobs Associates is the tunneling and geotechnical engineer in the client Program Consultant Organization, with Greeley and Hansen managing hydrology and scheduling. Construction management is awarded on a contract by contract basis.

“We selected the design-build procurement method as it allows for additional ingenuity,” said Ray. “There are mandatory requirements in each of the contracts and sometimes there is a need to push back on alternatives presented by the design-build teams, but we would recommend the design-build procurement process.”

Progressing the 25-year project

Development of the Clean Rivers program to control combined sewer overflowed into the rivers started in the late 1998. “It is the older parts of the network that are combined systems,” said Ray. “These systems serve the historic part of the city including the White House and the Capitol Building, and the communities that grew up on the banks of the Anacostia and Potomac Rivers and Rock Creek. Our service area extends also across the Potomac to the Dulles Airport and other communities in Virginia, and north into Maryland. The networks all flow to the Blue Plains wastewater treatment plant.”

Carlton Ray, Vice President, Clean Rivers, DC Water

The plan to meet National Environmental Protection Agency requirements to control CSOs into national waterways was agreed with regulators in 2003 and a Consent Decree was signed with the Federal Government in 2005 to progress the Clean Rivers project.

The tunnels serving the Anacostia and Potomac Rivers, to meet theConsent Decree program, comprise a network of 18 miles (29km) of deep level tunnels with 26 shafts to intercept overflow outlets and have the flow run by gravity to a pumping station shaft to the south where it is lifted into the expanded wastewater treatment plant at Blue Plains (Fig 1). The objective is to reduce combined sewer overflows into the waterways by 96% over a period of 25 years and meeting specific milestones along the way.

“We are now 15 years into the 25-year program, we are on budget and have met every construction milestone in the Consent Decree. The budget from now to 2030 and adjusted for inflation, is $2.7 billion,” said Ray.

The tunnels serving the Anacostia River comprise 12.8 miles (20.7km) of tunnels that were divided into four contracts and started in 2011 with a $330 million design-build Blue Plains contract awarded to the Traylor/Skanska/Jay Dee JV with design engineer CH2M (Table 1). This was followed by the $254 million Anacostia tunnel awarded in 2013 to the Impregilo/Healy/Parsons JV.

Fig 2. Route of the new Potomac CSO Tunnel

In December 2015, the $157 million First Street Tunnel was broken out of the Northeast Boundary Tunnel and awarded to Skanska/Jay Dee JV to address local flooding caused by undersized sewers in the District.

In July 2017, the Salini Impregilo/Lane JV was awarded the Northeast Boundary Tunnel for a design-build contract value of $580 million. The refurbished Herrenknecht EPBM, used previously on the Anacostia Tunnel by the JV, is progressing northward from the shaft at CSO-019 near the Robert F Kennedy (RKS) Stadium and broke through on 9 April into the intermediate W Street shaft. The contract is currently about 48% complete and on target to meet tunneling the completion date in 2021 with overall place in operation scheduled for 2023.

The Potomac Tunnel when it is built will connect to the Blue Plains Tunnel at the JBAB shaft (Fig 1) with all diverted CSO flows then directed to the Blue Plains treatment plant and treated effluent returned to the Potomac. “We started with the Anacostia River contracts because, as a tributary of the larger Potomac, it is slower moving and had become silted up over the years, which made the CSO situation more problematic,” said Ray.

Green solutions

In 2016, the Federal Environmental Protection Agency (NEPA) encouraged cities to consider green infrastructure (GI) options to limit flow of stormwater into combined sewers and eventually via overflows into the waterways. “DC Water evaluated opportunities to include GI as part of the CSO controls because of the economic, social and environmental benefits it provides to the community. As a result of that evaluation, the Consent Decree was revised and we advanced a programme of GI,” explained Ray. These projects include the construction of bioretention and porous pavement facilities that allow stormwater to soak away into the ground, as well as the greening of otherwise concreted surface areas and increasing park lands where rain is absorbed by the ground rather than flowing into the sewers “We have created several GI areas in our CSO service area, including one at the west end of the Potomac CSO tunnel. If studies confirm that the green infrastructure is practicable and cost effective, the Potomac tunnel will terminate at the combined sewer outfall CSO-024. If not, the tunnel will carry on for an extra 5,000ft to CSO-029. That gives us the range of between $450 million and $550 million for the Potomac Tunnel estimate.”

When asked about the green infrastructure initiative, Ray said that an assessment report is currently in development for submitting to the EPA to finalise the practicability of stormwater being absorbed by nature, and minimise rain water flowing into the combined sewers. “Because GI was not contemplated in the program originally, more of the budget was spent on upgrading the Blue Plains treatment plant to treat the full anticipated design volume of the interceptor program.”

Blue Plains Tunnel Dewatering Pumping Station and TBM working shafts at start of construction in 2011

Budget control

Keeping the project on track both timewise and budget-wise has been the mission of Director Ray since he joined DC Water in 2009. He moved to Washington DC from Indianapolis where he was managing the start of the city’s DigIndy CSO programme which is also progressing currently. “Managing the budget goes hand in hand with staying on schedule,” explained Ray, “and we have managed to meet all the milestones in our program.”

One of the most important targets was to place in operation the Blue Plains and Anacostia River Tunnels by the Consent Decree date of 23 March 2018. “We met the target on 20 March, with three days to spare. Since then, the 7 mile Blue Plains and Anacostia River CSO tunnels have diverted more than 7 billion gallons of CSO flow to the Blue Plains treatment plant.”

The Northeast Boundary Tunnel is the last remaining tunnel to be placed in operation along the Anacostia River. It is scheduled to be placed in operation in 2023, ahead of the Consent Decree deadline of 2025. The Potomac Tunnel is scheduled to be online by the program completion date of 2030.

Director Ray site visit to Northeast Boundary job site

Controlling the budget, said Ray, is a combination of several factors. “We have worked hard on overall management of the design-build construction contracts and to empower the inspectors and QCs to make decisions at site level where possible. We have also adopted the partnering concept with the design-build contractors. We all meet regularly, me included, to discuss progress and any issues that may arise. This ensures that the parties to the contract are not talking past each other. This is not discounting that issues occur – they do. Tunneling and shaft sinking is difficult and risky work, and that work is best managed by establishing a partnering relationship between the parties from the start.”

DC Water has also engaged a Dispute Review Board on all its construction contracts. “We are big advocates of the DRB process,” said Ray. The DC Water experience with the concept is also acknowledged by the DRB Foundation. “The DRB visits are programmed two or three days after the partnering sessions and while the DRB findings are non-binding, the process has resolved several situations through the years.”

In closing the interview, Ray spoke about the current situation with regards to the Covid-19 pandemic. “Clean Rivers CSO program. On the current Northeast Boundary construction contract, we have continued working. There is no slowdown of the TBM and the Salini Impregilo Project Manager has established working procedures where all on site observe physical distancing. Site workers use gloves as part of their PPE and are wearing face masks, and there are no physical team meetings. These are conducted online. For site deliveries, the drivers are required to stay in the trucks and vehicles. There have been some scares among colleagues, and it is a concern for us all. We are working to keep everyone as safe as possible. Safety is our first priority.”