Where Does Washington Get Our Water?

We sadly had to strike the final chapter in the book The Potomac River because of size constraints, so I've posted it here on my blog instead. It’s a fascinating look at where the Washington, DC area gets its water – and how we deal with wastewater. 

Having fresh, safe tap water pumped into your home is one of the great achievements of modern life – something that we easily take for granted. We no longer have to rely on backyard pumps for drinking water, nor do we have to use an outhouse or a chamber pot when nature calls. You turn the dishwasher, shower or tap on, or flush the toilet, and the water magically appears.

But it really isn’t magic at all. Rather, our tap water is based on complex infrastructure that is largely buried underground and administered by municipal agents. Washington, D.C. is slightly unusual in that our primary municipal water supplier is a division of the U.S. Army Corps of Engineers known as Washington Aqueduct.

The Washington area gets an average of thirty-nine inches of rain per year. This may rise with global warming, as the mid-Atlantic is projected to become rainier. Though the river’s flow varies greatly by season, the average flow is seven billion gallons of water per day. About 400 million gallons are removed daily from the Potomac, providing 80 percent of the water for more than five million people in the Washington metropolitan area. This is largely surface water drawn from the river, rather than pumped from a well, and serves our bathing and car washes, dishwashers, fire hydrants, lawns, swimming pools, toilets and washing machines. Of this, about 370 million gallons are returned to the river after treatment at Blue Plains.

People who lived in early Washington got their water primarily from wells. There was no water distribution or sewage system. Congress recognized the problem after a fire broke out in the U.S. Capitol on Christmas Eve in 1851, causing heavy damage to the building. Firefighters had too little water to put the fire out.

On March 3, 1853, Congress assigned the U.S. Army Corps of Engineers to build a water distribution system for the District, a job the corps has had ever since. Montgomery Meigs was tasked with building the Washington Aqueduct and appropriated $100,000 for the project (it eventually ballooned to $2 million).

Montgomery Meigs built the Washington Aqueduct that provides 

drinking water for the Washington, D.C. area. Library of Congress. 

Meigs designed a system that runs by gravity. He built the Washington Aqueduct Dam, just above Great Falls, as the intake so water could run downhill without pumps. Water flows ten miles under MacArthur Boulevard and over the Cabin John Bridge – designed by Meigs for the aqueduct – to Dalecarlia Reservoir. Meigs built both Dalecarlia and Georgetown reservoirs to remove sediment from the water. 

The Washington Aqueduct Dam stretches all the way across the Potomac River just above Great Falls. Visitors can stand atop the intake, a large, flat concrete structure near the Great Falls Visitors Center. Garrett Peck

The Washington Aqueduct Dam from the Virginia side. Garrett Peck 

Washington Aqueduct built graceful Union Arch, better known as the Cabin John Bridge, to carry drinking water tens miles from Great Falls to Washington, D.C. Library of Congress. 

Washington Aqueduct serves as a water wholesaler, treating 170 million gallons of water per day, then selling the water to distributors in Arlington, Falls Church and Washington. In the 1950s it opened an auxiliary intake at Little Falls. It is a demand-based system, withdrawing less water in winter and more in summer.

The aqueduct brings water to the Dalecarlia reservoir, where there is a fork in the pipe: 40 percent of the water continues to the Georgetown Reservoir for sediment removal and then on to McMillan Reservoir, while 60 percent is chemically treated at Dalecarlia Water Treatment Plant for Virginia customers. “The two different water treatment facilities reflects the growth of the system over 150 years,” remarked Tom Jacobus, Washington Aqueduct’s general manager. Arlington and Falls Church are served by pipes along Chain and Key bridges.

For District residents, water from Georgetown Reservoir is piped via the underground City Tunnel to the McMillan Water Treatment Plant, just above Howard University, where it is chemically treated. McMillan installed the Slow Sand Filtration Plant in 1905 as the latest in water filtration, giant catacombs that used sand rather than chemicals to purify the water. Frederick Law Olmstead, Jr. designed the twenty-five acre grounds that are an architectural wonder. It operated until 1985 when an upgraded filtration plant was built adjacent.

Washington Aqueduct uses chloramine, a compound of chlorine and ammonia, to chemically treat water. This improves the taste of the water. However, every year for six weeks in spring, chlorine replaces the chloramine, giving our drinking water that familiar swimming pool odor. This is done to kill germs that have built up in the system.

Cities have built massive infrastructure to supply water and remove sewage from your home. Much of it is underground, so you rarely see it unless a water main breaks – an increasing occurrence, as most cities are not investing nearly enough to replace their aging infrastructure. Washington Aqueduct indicated that Washingtonians are actually using less water. This is in part because of more water-efficient appliances, but the major reason is that local water authorities are addressing leaks in the water distribution system by upgrading pipes and water mains.

The greater Washington metropolitan area is serviced by three main water authorities: the Fairfax County Water Authority; the Washington Suburban Sanitary Commission (Montgomery and Prince George’s Counties in Maryland); and DC Water, formally known as the District of Columbia Water and Sewer Authority (covering the District, Arlington, Alexandria, and parts of Fairfax, Montgomery, and Prince George’s Counties). All three use Potomac River water.

What Happens After I Flush?  

 

DC Water operates the Blue Plains Advanced Wastewater Treatment Plant, the sewage treatment plant for much of the Washington metropolitan area established in 1938. It is also the largest advanced wastewater treatment plan in the world. Blue Plains resides in far Southwest, directly across the Potomac from Old Town Alexandria and within a stone’s throw of the Woodrow Wilson Bridge. It provides treatment for the District, Dulles International Airport, part of Montgomery and Prince George’s counties in Maryland, and part of Fairfax and Loudon counties in Virginia. (Alexandria and Arlington process their own sewage.) The 150-acre plant can process 370 million gallons of wastewater a day – and up to a billion gallons in the event of an emergency.

All the solids we eat and nutrients we intake end up in our sewers. My tour guide at Blue Plains, Mark Ramirez, called the facility a “nutrient recovery plant.” Yes, Blue Plains offers weekly guided tours. And yes, primary sewage treatment doesn’t smell very good, though it does improve as you travel through the complex to visit secondary treatment and the follow-on treatment phases that remove biosolids from the water.

A primary treatment tank at Blue Plains helps solids settle from wastewater.  Garrett Peck

Secondary treatment at Blue Plains uses bacteria to consume biologic matter in wastewater. 

Garrett Peck.

Blue Plains is the largest electricity consumer in the District: it takes considerable energy to pump water and aerate the sewage. Some 10,000 tons of trash and 8,000 tons of grit (coffee grounds, egg shells, potholes and sand) are removed annually from the water and sent to landfill.

Human waste contains high levels of nitrogen and other chemicals. If these chemicals are dumped into a river, algae will grow voraciously, consuming all the oxygen and suffocating all other aquatic animal and plant life. When winter arrives, the algae dies, and the river is effectively dead. Thus nitrogen removal is a key component of advanced sewage treatment, and a key goal in helping clean up the Chesapeake Bay watershed.

Biosolids, also known as sludge, is the remaining nutrient-rich organic material after wastewater has been treated. Blue Plains produces more than 1,200 tons of biosolids daily, sending this to be spread on farmland and forests as fertilizer and returning the nutrients to the environment.

After the wastewater has been sufficiently treated, a process that takes about a day, the clean water is returned to the Potomac. Blue Plains has several pipes that extend 150 yards into the river where water is discharged. It is apparently a good fishing spot on the Potomac, as the water is warm and high in oxygen. Bald eagles are often seen circling overhead to catch fish.

About seventy-five times each year, rainstorms overwhelm the sewage system in older Washington neighborhoods, causing combined sewer overflows (CSO). Billions of gallons of untreated sewage overflows into the Anacostia, Potomac and Rock Creek, creating an environmental threat to these streams. The Anacostia River bears the brunt of the overflow. DC Water broke ground in 2011 on its multibillion dollar Clean Rivers Project to build two enormous underground holding tunnels that will store runoff during heavy rains until it can be processed at Blue Plains.

Reservoirs

In the 1950s, the U.S. Army Corps of Engineers built reservoirs along the Potomac watershed to prepare for drought. There are a number of dams and reservoirs on the river: the Little Falls Dam, just above the District border; the Washington Aqueduct Dam above Great Falls; and the Bloomington Dam in Garrett County, Maryland. There are also surviving dams from the C&O Canal.

The Bloomington Dam was built starting in 1971 on the North Branch and completed ten years later at a cost of $175 million. It created the seven-mile long Jennings Randolph Reservoir. Its function is not only to store water, but also to control the high acidic runoff from abandoned coalmines in the Allegheny Plateau. Since the acid separates from clean water, the dam has the ability to release water at different depths, ensuring that the proper mix is released downstream. The completion of the Bloomington Dam was a major factor in the cleanup of the Potomac River. The Jennings Randolph Reservoir holds 13.4 billion gallons of water, though the reservoir is gradually filling with sediment because of the dam.

The Jennings Randolph Reservoir on the Allegheny Plateau is the largest reservoir 

on the Potomac and helps reduce acidity from coalmine runoff in the river. 

Garrett Peck.

Little Seneca Dam, built about the same time as Bloomington Dam, created the largest immediate reservoir for the Washington area, the Little Seneca Reservoir. It is not on the Potomac, but rather twenty miles up Seneca Creek near Germantown, Maryland. It holds 3.8 billion gallons of water.

The Little Seneca Reservoir and the Jennings Randolph Reservoir are the main water reserves for the Washington metropolitan area. Together they store more than seventeen billion gallons of water. Few cities have such substantial reserves, which explains why Washington, D.C. has water even during droughts. The Interstate Commission on the Potomac River Basin administers both reservoirs.

Drink up! 

Garrett Peck

www.garrettpeck.com