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November 2007
guest feature
Stormwater Runoff
Issues
By Jim Lindell, Marketing Manager
All Photos Courtesy GreenGrid and
©Weston
Residents
in the United States have long believed they have some of the safest
drinking water in the world. Thanks to effective water-treatment systems
and policies enacted decades ago, people living in America are rarely
concerned that the tap water they use for drinking, cooking, or bathing
will lead to illness.
However, despite this lack of concern, the reality is that waterborne
illnesses are prevalent in the United States and may actually increase
in the near future because of climate change, population growth, and
shifting land use¹. As cities and suburban areas grow, land that
once absorbed storm water runoff is now covered by impervious surfaces,
such as building roofs, streets, and parking lots. As snowmelts
and storm water travel over these surfaces, the runoff collects
pathogens, metals, sediment, and a variety of chemical pollutants, which
can be deposited directly into nearby streams and waterways. This is
becoming a major threat to water quality throughout the United States.
The impurities in storm water runoff have been linked to chronic and
acute illnesses as a result of direct exposure through drinking the
water, or more indirect exposure from such actions as eating seafood
that has been infected by the contaminated water. Additionally,
the impervious surfaces in our cities often become stagnant pools of
storm water, which breeds areas for mosquitoes and disease vectors for
West Nile virus, hemorrhagic fever, and other infectious illnesses.
As cities and municipalities recognize the dangers of increased storm
water runoff—especially as their local populations grow—they look for
new ways to manage storm water and treat drinking water, keeping it free
of impurities to protect public health. For example, the city of
Portland, Oregon, is often cited as a leader in developing
innovative—and less expensive—methods to treat and manage storm water
runoff through a variety of low impact development techniques including
the integration of landscape architecture and site design.
However, storm water–treatment systems are becoming increasingly costly
and usually require significant infrastructure investments costing
millions of dollars and often involving overcoming difficult
technological obstacles. For this reason, some localities are
considering entirely new strategies and technologies—such as the
installation of green roofing systems on more facilities—as a way to
help reduce storm water runoff and costs for local taxpayers.
Waterborne Disease
Although it has not been widely reported, it is interesting to note that
since 1948 studies have revealed the most serious outbreaks of
waterborne disease have followed extreme rainfall events. For
example, it was heavy spring rains and snowmelt that preceded the
Milwaukee cryptosporidium outbreak of 1993, which became the
largest single waterborne-disease outbreak ever recorded in American
history.
Cryptosporidium is a protozoan pathogen that causes a variety of
intestinal illnesses. In a span of just two weeks, more than 400,000
people of an estimated 1.6 million Milwaukee-area residents became ill
from drinking contaminated water, and more than 100 died². It was
later discovered that one of the city’s two water-treatment centers had
become contaminated, likely because it was overstressed from attempting
to treat storm water runoff, which allowed for sewage and polluted water
to pass untreated through the filtration system.
Other studies have found that the runoff from building roofs onto urban
and suburban streets, parking lots, and lawns after major rainfall
events generates large loads of bacteria in storm water. This
runoff is responsible for an estimated 47 percent of the pathogen
contamination in New York’s Long Island Sound³. The problems are
compounded because there, as in other parts of the United States,
drainage pipelines have accumulated large volumes of sediment and
contaminants.
Because there is no sunlight in these pipes, the natural die-off of
bacteria can be inhibited, which creates bacterial reservoirs within the
pipes. The contaminated runoff, combined with the bacteria-laden
pipes, is often discharged into waterways because local treatment
centers are overwhelmed and simply unable to treat the runoff.
The results of these discharges and untreated water are waterborne
illnesses. Approximately 99 million people in the United States
suffer from acute gastrointestinal illness each year, at a cost of
billions of dollars. It is estimated that as many as 40 percent of
these illnesses are caused by contaminated drinking water. And
exposure to cryptosporidium, which caused the outbreak in
Milwaukee mentioned earlier, is much more common in the United States
than most people realize. In fact, it is estimated that 17 percent
to more than one-third of all people tested in the United States have
evidence of cryptosporidium infection by the time they are young
adults.
Water-Treatment Issues
Even in an unusual situation where cost would not be an issue and all
storm water runoff could be treated adequately, contaminated water would
not necessarily be eliminated and could still be consumed by the public.
In fact, this “ideal” situation could actually result in new problems.
Cleaning community drinking water usually involves filtering the water
to remove sediment and then using chlorine to disinfect it.
However, we know now that several microorganisms found in storm water
runoff are resistant to both filtration and chlorine. A 1995 study found
that 13 percent of sample drinking water that had been filtered and
treated with chlorine at a water-treatment facility still contained
cryptosporidium]4.
Some water-treatment facilities are now using ozone to disinfect water,
instead of or in combination with chlorine. However, although high
doses of ozone can inactivate cryptosporidium and other contaminants
that chlorine cannot, neutralizing the ozone after treatment presents
several technological difficulties. Plus, adding ozone to water
that contains bromide can form bromate, a potential human carcinogen.
The Role of Infrastructure and Green Roofs
Conventional urban storm water management requires a huge investment in
infrastructure. For example, since the Milwaukee cryptosporidium
outbreak of 1993, the city has invested nearly a billion dollars to
construct a tunnel and related systems for storing excess storm water
during and after heavy rainfall events.
Another instance of significant infrastructure investment has occurred
in New York City. In an attempt to minimize the amount of storm
water runoff that can contaminate its water supply in the Catskill
Mountains and in Delaware, the New York City Water Department has chosen
to spend 1.4 billion dollars to purchase land around these areas to act
as a buffer against development that can cause storm water runoff.
The city believes purchasing this land will prevent them from spending
more than 6 billion dollars to construct new water-treatment and
filtration facilities.
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The University of
Wisconsin-Milwaukee Great Lakes Water Institute greenroof,
2003; Photo ©Weston. See the
profile in The Greenroof Projects
Database. |
A study conducted by the University of
Wisconsin, which installed an extensive, modular green roof system in
2003 as shown above, found that the system helped reduce storm water
runoff by as much as 75 percent. Studies conducted by Weston
Solutions®, Inc., a leading environmental and redevelopment firm and
owner of GreenGrid, a green roofing system, showed that cumulative water
retention of a green roof during a simulated two-hour rainstorm produced
the following results:
• One inch of rainfall: 72.2 percent of the water retained
• Two inches: 57.3 percent retained
• Three inches: 43.2 percent retained
• Four inches: 33.7 percent retained
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Cumulative
Rainfall Retention on a Greenroof Over a Simulated Two-Hour
Rainstorm Event;
Photo ©Weston. |
A 2005–2006 study conducted by Green
Roofs for Healthy Cities indicates the green roof industry is growing
dramatically. The study sites a growth rate of more than 25 percent
above a similar study conducted in 2004–2005, representing more than
three million square feet of green roofs installed in 2006. The
green roof industry, according to the study, is growing rapidly in
response to the pressing need for cleaner air, improved energy
efficiency, more usable green space in communities, and better storm
water management. In fact, it concluded that the storm
water–management benefits of green roofs make them ideal for ultra-urban
areas; they don’t consume additional land, and they reduce the need for
costly drainage/filtering systems. One manufacturer of modular
green roofing systems reports that they have installed as many green
roofs in one month of 2007 as they did in all of 2006.
Simply put, green roofs are proving to be
ideal for growing urban communities. Not only do they help to
reduce storm water runoff, but green roofs play a significant role in
protecting human health as well.
Jim Lindell is the GreenGrid Green
Roofs National Marketing Manager. He has seven years of experience
in the green roof and environmental consulting industries.
GreenGrid is a business of Weston Solutions, Inc.
Jim
Lindell can be reached at Phone:
847.918-4011 or Email:
j.lindell@westonsolutions.com.
Learn more about GreenGrid Green Roof
Systems in The Greenroof Directory
here or at:
www.GreenGridRoofs.com.
References:
1. Stephen Gaffield, Robert L. Goo, Lynn Richards, and Richard Jackson,
“Public Health Effects of Inadequately Managed Stormwater Runoff,”
American Journal of Pubic Health, Sept. 2003.
2. Corso PS, Kramer MH, Blair KA, Addiss DG, Davis JP, Haddix AC. Cost
of illness in the 1993 Waterborne Cryptosporidium outbreak,
Milwaukee, Wisconsin. Emerg Infect Dis [serial online] 2003 Apr [September
12, 2007]. Available from: URL:
http://www.cdc.gov/ncidod/EID/vol9no4/02-0417.htm.
3. U.S. Environmental Protection Agency,
Long Island Sound Study: Summary of the Comprehensive Conservation and
Management Plan, 1994.
4. Ms. Annie Lechevallier “Giardia and Cryptosporidium in Raw and
Finished Water,” Journal of American Water Works Association, 1995.
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