Monday, December 17, 2012

EPA approves DC Water’s Green Infrastructure Plan

Image from DC Water: GI= green infrastructure, CSO= combined sewer overflow

On Friday, December 14, 2012, the US Environmental Protection Agency officially announced its support for District of Columbia Water and Sewer Authority, DC Water's, proposal to extend the deadlines in the Consent Decree with the United States in order for them to test green infrastructure (GI) alternatives to its Clean River Project, its long term plan to control overflows for the District’s combined sewer system. Currently, the Clean Rivers Project is a $2.6 billion system of tunnels and diversion sewers for the capture of stormwater to prevent overflows to Rock Creek and the Anacostia and Potomac rivers and storage for later treatment at DC Water’s Blue Plains Advanced Wastewater Treatment Plant.

The EPA has announced its support of the modification of the consent decree so that DC Water may construct Green Infrastructure Demonstration projects. These projects will be used to evaluate (over the next 8 years) the effectiveness of green infrastructure to reduce 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, potentially reducing costs and/or improving control of stormwater overflows. As part of the agreement with EPA, DC Water will proceed with preparation of the Environmental Impact Statements required for the Potomac Storage Tunnel while the GI Demonstration Project and Alternatives Analysis are underway and as indicated above the Anacostia Tunnel projects will proceed on schedule.

District of Columbia's sewage system is one of the oldest in the United States and the combined storm water and waste water flows in the oldest section of the system have created a pollution problem whenever it rains. The combined volume of rainwater and sewage is too much for the Blue Plaines Advanced Wastewater Treatment Plant to process, so DC Water releases the excess rainwater mixed with untreated sewage to the Anacostia River, Potomac River and Rock Creek to prevent the sewage from backing up in homes and businesses and the Capitol. The sewage flow released in this way has violated the National Pollutant Discharge Elimination System, NPDES, permit which is how EPA regulates sewage treatment plants. The history of Washington DC’s NPDES permit and allowed outflows can be read here.

The BluePlains Advanced Wastewater Treatment Plant is located on the southernmost tip of Washington DC, across the river from Alexandria. Blue Plains sits on 150 acres of land and has a rated annual average day capacity if 370 million gallons per day (mgd) and a peak wet weather capacity of 1,076 mgd. The system needs a larger storm rated capacity to accommodate the old central city section which accounts for one third the area of the District and still has the old combined sewer system that overflows with predictable regularity during rain storms. DC Water is under a consent order from the EPA and the Department of Justice to meet new effluent limits for total nitrogen released and better control of the system during storms. To comply with the consent order DC Water developed the $2.6 billion Clean Rivers Project.

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 will 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 were 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.

In addition, seven years into the Clean Rivers Project, DC Water is facing the reality of the rate increases necessary to support the combined costs of the projects that will still not meet the TMDL. Building the 13-mile network of 23-foot-diameter tunnels to carry combined storm runoff and sanitary sewage to the Blue Plains Advanced Wastewater Treatment Plant for treatment rather than releasing untreated sewage and stormwater runoff to the rivers and creeks during heavy rainstorms is incredibly expensive and still may not be enough to solve the problem. So far the more than $600 million that has been spent for the Clean Rivers Project for in engineering preliminary work address mostly the Anacostia River Tunnel (which is really an interconnected series of three tunnels). According to Alan Hayman of DC Water, the Anacostia Tunnels will cost about $1.6 billion when completed and will have the greatest reduction in overflow releases. DC water is hopeful that the green infrastructure will allow downsizing of Potomac and Rock Creek tunnels (delay sewer rate increases) and ensure that DC Water ends up compliant with the NPDES permit, consent decree and the Chesapeake Bay TMDL. Green Infrastructure, if successful, can continue to grow and expand in effectiveness as these practices become commonplace and accepted.  
from DC Water 

No comments:

Post a Comment