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