• Introduction
• Water Supply and Treatment
• Water Storage and Distribution
• Wastewater Collection
• Wastewater Treatment
• Storm Water Collection

Introduction

The Blue Plains Wastewater Treatment Plant (take a virtual tour) is the largest advanced wastewater treatment plant in the world, with a capacity of 370 million gallons per day (mgd), a peak capacity of 1.076 billion gallons per day and covering 150 acres.

To distribute water and support the distribution system, the Authority operates over 1,200 miles of pipes, five pumping stations, five reservoirs, four elevated water storage tanks, 36,000 valves and 8,700 hydrants.

To collect wastewater, the Authority operates 1,800 miles of sanitary and combined sewers, 22 flow-metering stations, nine off-site wastewater pumping stations, and 16 stormwater pumping stations within the District.  Separate sanitary and storm sewers serve approximately two-thirds of the District of Columbia.  In older portions of the system, such as the District's downtown area, combined sanitary and storm sewer systems are prevalent.

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Water Supply and Treatment

Georgetown conduit and raw water reservoir

The supply and treatment system includes the raw water sources, large capacity pipelines carrying raw water to the water treatment plants, and the water treatment plants.

The Washington Aqueduct Division operates and maintains the raw water supply facilities and treatment plants that supply water to the distribution systems of DCWASA, parts of Northern Virginia, and a portion of the Federal Government.

DCWASA is responsible for the treated water distribution system serving the District and certain Department of Defense and other small customers outside the District.

Raw water supply, piping, and treatment facilities of the Washington Aqueduct's water system include the Great Falls Intake on the Potomac River; two raw water conduits from Great Falls to the Dalecarlia Reservoir; the Little Falls Intake and Pump Station on the Potomac River; the Dalecarlia and McMillan Reservoirs and Water Treatment Plants; the Georgetown conduit and raw water reservoir; the Washington City Tunnel; and the East Shaft Pump Station.

Raw Water System

The source of raw water for the Dalecarlia and McMillan Water Treatment Plants (WTP) is the Potomac River.  Water is withdrawn at the Great Falls Intake and flows by gravity through two pipelines to the Dalecarlia Reservoir forebay, where it is pumped to the Dalecarlia Reservoir via a booster pumping station.  Water may be withdrawn from the Little Falls Intake on the Potomac River and pumped up to the Dalecarlia Reservoir.  The Dalecarlia Reservoir acts as a presedimentation basin for water drawn into the Dalecarlia WTP and for water diverted to the Georgetown Reservoir for subsequent treatment.

Water Treatment Plants

McMillan Water Treatment Plant

Treated water is supplied to the District from the Dalecarlia and McMillan WTPs.  The original Dalecarlia WTP was completed in 1928.  The plant capacity was increased in the 1950's by the addition of two additional sedimentation basins, a 30 mg clearwell, a 577 mgd finished water pumping station and additional filters.  A new chemical building and an additional filter building were completed in 1964.  The plant has a capacity of 164 million gallons per day (mgd) based on filtration rates of two gallons per minute per square foot, and a maximum capacity of 264 mgd.  Its treatment scheme consists of screening, chemical additions for flocculation and sedimentation, rapid sand filtration, and chemical additions for chlorination, fluoridation and pH control.

The original McMillan WTP was constructed in 1905 as a slow sand filter plant.  It was replaced in 1985, with a new rapid sand filtration plant at the same site with an average design capacity of 120 mgd based on a filter design rate of 4 gpm/sf, and a maximum capacity of 180 mgd.

The design capacity of the Dalecarlia and McMillan WTPs was based on population growth and water use projections greater than have been realized.  Consequently, the treatment capacity of the plants exceeds the day-to-day demands and peak requirements of the customers.

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Water Storage and Distribution

Bryant Street Pumping Station

The water distribution system within the District is intended to provide an average water pressure of approximately 50 pounds per square inch to the customer's tap.  A difference in ground elevation of approximately 410 feet from the low point to the high point in the District requires that the water system be divided into seven service areas.

The Low Service Area includes the area around the federal buildings, along the Anacostia River, and located between ground elevations 0 to 70 feet.  The Low Service Area is supplied from the Washington Aqueduct's Dalecarlia Pumping Station and DCWASA's Bryant Street Pumping Station.  Treated water storage in the Low Service Area is provided by DCWASA's Brentwood Reservoir (25 mg at overflow elevation 172 feet).

The First High Service Area generally serves the area west of the Anacostia River with ground elevations between 70 and 140 feet.  The First High Service Area is supplied from the Washington Aqueduct's Dalecarlia Pumping Station and DCWASA's Bryant Street Pumping Station.  Treated water storage in the First High Service Area is provided by the Washington Aqueduct's Foxhall Reservoir (20 mg at overflow elevation 250 feet) and DCWASA's Soldiers Home Reservoir (15 mg at overflow elevation 250 feet).

The Second High Service Area generally includes the area west of the Anacostia River, between Rock Creek Park and Eastern Avenue, and having ground elevations between 140 and 210 feet.  The Second High Service Area is supplied from the Washington Aqueduct's Dalecarlia Pumping Station and DCWASA's Bryant Street Pumping Station.  Treated water storage in the Second High Service Area is provided by the Washington Aqueduct's Van Ness Reservoir (14.6 mg at overflow elevation 335 feet).

Inside the Bryant Street Pumping Station

The Third High Service Area generally includes the area west of the Anacostia River, separated by Rock Creek Park, bounded by Eastern and Western Avenues, and having ground elevations between 210 and 350 feet.  The Third High Service Area is supplied from the Washington Aqueduct's Dalecarlia Pumping Station and DCWASA's Bryant Street Pumping Station.  Treated water storage in the Third High Service Area consists of DCWASA's Fort Reno Reservoir No. 1 (5.4 mg at overflow elevation 424 feet) and the Washington Aqueduct's Fort Reno Reservoir No. 2 (20 mg at overflow elevation 424 feet).

The Fourth High Service Area generally includes the area west of the Anacostia River, separated by Rock Creek Park, bounded by Eastern and Western Avenues, and having ground elevations above 350 feet.  The Fourth High Service Area is supplied from DCWASA's Fort Reno Pumping Station (western portion) and the 16th & Alaska Pumping Station (eastern portion).  Treated water storage in the western portion of the Fourth High Service Area is provided by DCWASA's Fort Reno Elevated Tank No. 2 (0.16 mg at overflow elevation 485 feet).

The Anacostia First High Service Area generally includes the area located southeast of the Anacostia River, and located between ground elevations between 70 and 170 feet.  The Anacostia First High Service Area is supplied from DCWASA's Anacostia Pumping Station which draws water from the Low Service Area.  Treated water storage in the Anacostia First High Service Area is provided by DCWASA's Fort Stanton Reservoir No. 1 (3 mg at overflow elevation 258 feet) and Fort Stanton Reservoir No. 2 (10 mg at overflow elevation 258 feet).

The Anacostia Second High Service Area includes the area located southeast of the Anacostia River along Southern Avenue, and located at ground elevations above 170 feet.  The Anacostia Second High Service Area is supplied from DCWASA's Anacostia Pumping Station which draws water from the Low Service Area.  Treated water storage in the Anacostia Second High Service Area is provided by DCWASA's Good Hope Road Elevated Tank (0.5 mg at overflow elevation 382 feet) and the Boulevard Elevated Tank (2 mg at overflow elevation 382 feet).

Water Storage and Pumping

Fort Reno Pumping Station

The water storage and pumping responsibilities are shared by DCWASA and the Washington Aqueduct.  DCWASA operates four treated water pumping stations (Anacostia, Bryant Street, Fort Reno, and 16th & Alaska), and eight reservoirs and elevated tanks.  The Washington Aqueduct operates the Dalecarlia Pump Station and three reservoirs (Foxhall, Van Ness, and Fort Reno).

Water Distribution

The water distribution system, which is operated and maintained by DCWASA, includes almost 1,300 miles of pipes and mains ranging from 4 to 78 inches in diameter.  DCWASA's water transmission and distribution system includes about 87% cast iron pipe, 8% ductile iron pipe, 2.5% steel pipe, and 2.5% reinforced and prestressed concrete pipe.

The distribution system includes appurtenances necessary for proper system operation, inspection, and repair, such as main line valves at regular intervals to allow flow control, air release valves to prevent air entrapment, blow-off valves for draining the pipeline, check valves to permit flow in one direction only, and closed division valves to allow transfer of water during emergency conditions from service areas with higher ground elevations to service areas with lower ground elevation.  The system includes over 36,000 valves and hydrants.

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Wastewater Collection

O Street Pumping Facility

The wastewater collection system consists of approximately 1,800 miles of sanitary and combined sewers, 125,000 building sewers, 22 flowmetering stations, and 9 wastewater pumping stations.  The sewers range from 8-inch pipelines to 27 foot arches.  Historically, the sewers are generally constructed of vitrified clay, brick, and concrete.  Current sewer construction materials typically consist of PVC, ductile iron, and concrete.  Force mains are generally constructed of iron, steel or concrete.  The system is predominantly separate sanitary and storm sewers (2/3 of the geographic service area); however, combined sewers serving both sanitary flow and stormwater drainage are prevalent in the downtown area and in older portions of the service area.  Combined sewer overflows (CSOs) occur during certain storm events when the capacity of the combined sewer system is unable to convey the mixture of wastewater and stormwater to the treatment plant.  These are presently 60 CSO outfalls listed in the National Pollutant Discharge Elimination System (NPDES) Permit issued by EPA to DCWASA.

Inside the O Street Pumping Facility

As part of the current Combined Sewer Overflow (CSO) Abatement Program implemented in the last decade, there has been an effort to maximize in-line storage and minimize combined sewer overflows to receiving waters.  The CSO Abatement Program consists of collection system optimization using inflatable dams, dynamically controlled weirs, outfall gates and other flow regulating devices, sewer separations, and a swirl treatment facility.  DCWASA is currently in the process of designing the replacement of the first generation of inflatable dams with a more durable version of this technology.

The Northeast Boundary Swirl Facility provides preliminary treatment including disinfection and some solids removal for combined sewage overflows prior to discharge.  The facility only functions during wet weather periods.  DCWASA is in the process of conducting a Performance Evaluation to assess the overall treatment efficiency of this facility.

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Wastewater Treatment

Aerial shot of Blue Plains Plant with the planned egg-shaped digesters

Wastewater is collected by the District of Columbia sewer system and from the Maryland and Virginia suburbs and is delivered to the Blue Plains Advanced Wastewater Treatment Plant (AWTP).

The Blue Plains AWTP is the largest advanced wastewater treatment facility of its type in the United States with a rated annual average day capacity if 370 million gallons per day and a peak wet weather capacity of 1.076 billion gallons per day. While other metropolitan areas have facilities with larger capacities, none of these provide the high level of treatment that Blue Plains does with its nitrification/denitrification and filtration process. Consistent with the high level of treatment provided, the plant's NPDES permit contains the most stringent effluent discharge requirements of any plant of its size. These limitations are as follows:

The existing wastewater treatment processes at the Blue Plains AWTP consists of preliminary treatment, secondary treatment, nitrification/denitrification, effluent filtration, chlorination/dechlorination and post aeration.

The solids treatment processes at Blue Plains are comprised of thickening and dewatering processes for primary sludge, secondary waste activated sludge (WAS), and nitrification/denitrification waste activated sludge. These facilities including screen and degritting processes, gravity thickeners, dissolved air flotation thickeners, sludge blending and centrifuge dewatering.

Until December 2000, a portion of the primary sludge and all the nitrification/denitrification waste activated sludge was anaerobically digested. The existing digesters have been taken and will be demolished. They will be replaced with egg shaped digesters, which will be sized to accommodate all of the plant's sludge. Presently, all sludge is lime stabilized.

Take a virtual tour of Blue Plains Advanced Wastewater Treatment Plant.

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Storm Water Collection

Entrance to the First and Canal Streets, SW Pumping Station

The Water and Sewer Authority Establishment and Department of Public Works Reorganization Act of 1996 (D.C. Law 11-111) that established DCWASA assigned certain responsibilities for storm water collection to DCWASA.  This role presently is primarily directed toward cleaning of surface drains and inlets, and operation and maintenance of a number of stormwater pump stations.  Stormwater issues are of necessity a shared responsibility with other public agencies.  For instance, the Department of Public Works collaborates with DCWASA in the design and construction of surface drainage infrastructure and has primary responsibility for protection of ground and surface waters which necessitates management of the appropriateness of connections to the public stormwater system to control non-point source pollution.  Historically, general tax revenues, as opposed to water and sewer enterprise fund monies, have been used to pay for certain drainage costs as part of the District's general government responsibilities.

It is anticipated that discussion between DCWASA and the groups identified above will result in a more appropriate and well understood relationship between these organizations relative to future responsibilities for planning, operation, and funding of stormwater system elements.

Overpass and driveway of the pumping station in Deane Ave., NE

On April 19, 2000, U.S. EPA Region III issued a Municipal Separate Storm Sewer System (MS4) Permit to the Government of the District of Columbia for management of the separate storm sewer system.  For the initial permit period, DCWASA has been designated the lead agency within the DC Government to coordinate activities of the Departments of Public Works and Health in achieving compliance with the permit.  This role has required City Council action related to DCWASA's chartering legislation and the issuance of a Memorandum of Understanding (MOU) between DCWASA and the District agencies designed to establish clearly defined lines of authority and communication.  DCWASA will lead the effort to develop a Storm Water Management Plan for the District as required by the MS4 Permit.

The MS4 permit requires that the District of Columbia develop a plan to bring stormwater management, including facilities, into compliance with federal law.  The plan is required to be submitted to the United States Environmental Protection Agency (USEPA) for approval by April 19, 2002.

The storm sewer system in the District of Columbia consists of approximately 8200 catch basins, 600 hundred miles of storm sewers and over 400 separate storm sewer discharges into the District's waterways.  There are fifteen storm water pumping stations located throughout the system.

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