Monday, April 9, 2018

Anacostia Sewage Storage Tunnel Completed

from DC Water
Just in time for the spring rains, DC Water formerly the District of Columbia Water and Sewer Authority put its 7-mile-long sewer tunnel into operation. The newly completed tunnel segment is 7 miles long and 23-feet in diameter. Nannie, the tunnel boring machine named after the famous District educator, The Anacostia River Tunnel is now connected to the Blue Plains Tunnel at Poplar Point, adjacent to the Frederick Douglass Bridge. The newly completed tunnel system will capture and hold up to 100 million gallons of combined sewage in heavy rainfalls and deliver it to the Blue Plains Advanced Wastewater Treatment Plant for treatment.

Combined with the new 225 million-gallon-per-day Wet Weather Treatment Facility at Blue Plains, this tunnel portion will reduce combined sewer overflows by more than 80%. Mining for the next tunnel segment, the Northeast Boundary Tunnel, will begin this spring and is scheduled for completion in 2023.

Due to the age of the Washington DC sewer system, parts of those systems are what is called combined systems where sewer and stormwater are carried through the same pipes. Practically every time it rains, untreated sewage and rainwater (combined sewage) is discharged into Washington DC’s rivers and creeks. The storage tunnel system are $2.7 billion part of a $7.8 billion 20 year improvement program called the Clean Rivers Project that will install "diversion facilities" at strategic locations to capture this untreated sewage and divert it at completion a total of 157 million gallon tunnel system where it can be stored and conveyed to the Blue Plains Advanced Wastewater Treatment Plant for treatment when the capacity is available.

The Clean Rivers Project was conceived and agreed to under a consent order from the Environmental Protection Agency, EPA, to meet new effluent limits for total nitrogen released and better control of the system during rain storms. The Clean Rivers Project is comprised of a system of deep tunnels, sewers and diversion facilities to capture combined sewer overflows and deliver them to DC Water’s Blue Plains Advanced Wastewater Treatment Plant when the capacity is available to treat them.

The Clean Rivers project was amended in 2007 to include the construction of Enhanced nitrogen removal, ENR, facilities for additional $950 million. The new ENR facilities have the capacity to provide complete treatment for flow rates up 555 million gallons per day for the first 4 hours, 511 million gallons per day for the next 24 hours and at a rate of 450 mgd. When all the Clean River Project and ENR facilities components are completed, the Blue Plains Advanced Waste Water Treatment Plant is projected to be able to meet the nitrogen release standard under the NPDES operating permit, reduce the number of uncontrolled storm related releases of waste, but still not meet the Chesapeake Bay TMDL. Buried in Appendix B of the Watershed Implementation Plan II, WIP II, for Washington DC is the fact that they cannot meet the EPA mandated TMDL for the Chesapeake Bay for the combined sewer system and Blue Plains Waste Water Treatment plant with the existing programs. More needs to be done.

As part of the Clean Rivers Project, DC Water is also included installing Green Infrastructure to assist with the reduction of combined sewer overflows to the Potomac River and Rock Creek. These projects, begun in 2012with EPA approval will be evaluated for effectiveness in reducing stormwater runoff using techniques that mimic natural control measures to meet water quality goals under the National Pollutant Discharge Elimination System, NPDES, permit. If successful, these techniques could be used to help address the combined sewer overflow problems in the District (and Alexandria), potentially reducing costs and/or improving control of stormwater overflows to meet the Chesapeake Bay TMDL. The Anacostia River and Potomac River tunnel systems include more than 18 miles of tunnels and are constructed more than 100 feet below the ground.

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