D.C.'s $2.7 billion CSS overhaul shows promise for local rivers
DISTRICT OF COLUMBIA - For decades D.C. has had an undersized and outdated combined sewer system; about a third of the entire District still uses the combined sewer systems. The combined sewer overflow from this system has been causing pollution of D.C.’s rivers on a grand scale.
Like many urban waterways, D.C.’s Potomac, Anacostia and Rock Creek Rivers had been unsafe for recreation or fishing due to the excessive trash, bacteria and industrial pollutants caused by urban runoff and CSO.
Yet, over several years now, the urban D.C. rivers have been receiving their highest river report scores to date. In 2018, the Anacostia River had passed its first annual health-check in 10 years. That same year, the Potomac River received its highest-ever B grade; a high climb from its first passing score of D+ in 2007.
And, better yet, D.C.’s river water quality is expected to improve much more within the next decade. This is all thanks to the Clean Rivers Project, the product of a Long-Term Control Plan started in 2005.
In 1999 the Anacostia Watershed Society, a nonprofit environmental group, won a landmark lawsuit against the D.C. Water and Sewer Authority for combined sewer overflows into the Anacostia River. Then, in 2005, an LTCD was signed between D.C. Water, the District of Columbia, the EPA and DOJ. This plan legally mandated schedules for the implementation and operation of CSO-control BMPs in D.C. by 2025.
This LTCD prompted the ongoing Clean Rivers Project: a $2.7 billion project to reduce CSOs in D.C.’s rivers. It is one of the largest infrastructure overhauls in the city’s history.
Paid for by residents paying a monthly Clean Rivers fee, the project plans to use a hybrid of green and gray infrastructure to clean D.C.’s three main waterways. The project plans to reduce 96 percent CSO volume system-wide, reduce 1 million pounds of nitrogen pollution to Chesapeake Bay per year, and reduce the chance of flooding in select areas from 50 percent to seven percent.
The project’s structures include new sanitary sewers and separate storm water lines, manholes, sewer laterals, catch basins, and a ventilations system with granular carbon filters.
One of the project’s largest aims is a series of large-diameter concrete sewer tunnels, each 23 feet wide and about 100 feet below ground, cumulating to a total length of 18 miles. The tunnels will capture any sewage overflow during events of high runoff and bring the overflow to the Blue Plains Advanced Wastewater Treatment Plant.
Each of the tunnels are excavated by massive tunnel boring machines, capable of both excavating earth and constructing the tunnel’s concrete walls simultaneously.
At the beginning of tunnel excavation, the machine would be ceremoniously launched and given an affectionate name, such as “Lady Bird” or “Chris,” before excavating a tunnel running anywhere from half a mile to five miles.
Currently, four tunnels – the Blue Plains Tunnel, Anacostia River Tunnel, First Street Tunnel, and Northeast Boundary Tunnel – have been fully excavated.
Since the service of the Blue Plains and Anacostia River Tunnels began in March 2018, SCOs to the Anacostia River have seen a 90 percent reduction, according to D.C. Water.
The First Street Tunnel will act as a large underground storage tank until 2023. The Northeast boundary Tunnel - the project's longest tunnel, running five miles' length and costing $583 million - is expected to be completed by 2023.
One Potomac River Tunnel is still undergoing permitting, design and coordination, is hoped to begin construction by mid-2023 and is hoped to begin service by 2030.
In 2016, D.C. Water negotiated a modification to the 2005 LTCP to allow select green infrastructure to replace gray infrastructure in the required BMPs by 2030.
A similar tunnel anticipated for Rock Creek had instead been replaced with a hybrid of gray and green solutions, to be completed by early 2030.
D.C. Water's green infrastructure projects concern a variety of popular GI techniques including downspout disconnection, permeable alleys and parking lanes, and bioretention planters and curb extensions. For more on D.C.'s green infrastructure, see "Further green infrastructure planned for D.C. neighborhoods".