Focus

A 456

Environews Focus

A 457

Focus | Paving Paradise

Paved surfaces are quite possibly the mostubiquitous structures created by humans.In the United States alone, pavements andother impervious surfaces cover morethan 43,000 square miles—an area nearlythe size of Ohio—accord-ing to research publishedin the 15 June 2004 issueof Eos, the newsletter ofthe American GeophysicalUnion. Bruce Ferguson,director of the Universityof Georgia School ofEnvironmental Design andauthor of the 2005 bookPorous Pavements, says thata quarter of a million U.S.acres are either paved orrepaved every year. Imper-vious surfaces can be con-crete or asphalt, they canbe roofs or parking lots,but they all have at leastone thing in common—water runs off ofthem, not through them. And with thatrunoff comes a host of problems.

Globally, it is a little more difficult tojudge the square mileage of impervioussurfaces. “We can extrapolate from theUnited States to a degree,” says Fergu-son, “but there are too many variables tojudge accurately.” The United States hasa lot of automobiles, and compared tomany other countries, Americans tend tobuild more (and wider) roads, more (and

bigger) parking lots, more (and moreexpansive) shopping centers, and largerhouses (with accompanying larger roofs).He says, “The United States might be ona par with Europe, but we’d be very dif-

ferent from India, forexample, or any countrywhere large numbers of thepopulace live in smaller,scattered villages, mostlywithout paved roads, park-ing lots, and the like.”

According to the non-profit Center for Water-shed Protection, as muchas 65% of the total imper-vious cover over America’slandscape consis ts ofstreets, parking lots, anddriveways—what centerstaff refer to as “habitat forcars.” Says Roger Banner-man, a researcher with the

State of Wisconsin Department ofNatural Resources: “You see some trulyinsane things in this country. I’ve seensubdivisions with streets that are thirty toforty feet wide. That’s as wide as a two-lane highway. Most developers are goingback to a twenty-five- to twenty-eight-foot width, but you can still see thesehuge streets.”

Upon these automotive habitats fall avariety of substances, and thereby hangs the rest of the tale. Impervious surfaces

All

imag

es:B

rand

X

Paving ParadiseThe Peril of Impervious Surfaces

Paving ParadiseThe Peril of Impervious Surfaces

Back

grou

nd p

hoto

: Ph

otod

isc

Focus | Paving Paradise

collect particulate matter from the atmos-phere, nitrogen oxides from car exhaust,rubber particles from tires, debris frombrake systems, phosphates from residentialand agricultural fertilizers, and dozens ofother pollutants. “On a parking lot, forexample, we have demonstrated buildups ofhydrocarbons, bacterial contamination,metals from wearing brake linings, andspilled antifreeze,” says Ferguson.

On a road of open-graded aggregate(stone), much of that material would seepdown into the pavement and soil, and thecommunity of microorganisms living therewould begin a rapid breakdown process. Butpollutants can’t penetrate an impervious sur-face, and the rapid flow of rainwater off ofimpervious surfaces means these pollutantsend up in the water. “So then,” saysFerguson, “not only do you have too muchwater, all moving too fast, you have pollutedwater that kills fish and makes water unfitfor drinking or recreation.”

When Water Has Nowhere to GoAreas across the country are being impact-ed by the growth in coverage by impervioussurfaces. In Maryland, for example, when

watershed imperviousness exceeds 25%,only hardier reptiles and amphibians canthrive, while more pollution-sensitivespecies are eliminated, according to a 1999Maryland Department of Natural Resour-ces report titled From the Mountains to theSea. Watershed imperviousness exceeding15% results in streams that are impossibleto rate “good,” states the report, and even2% imperviousness can affect pollution-sensitive brook trout.

The 1.1-million-acre Chesapeake Baywatershed, one of the most diverse and deli-cate ecosystems in the world, is now beingimpacted by the 400,000 acres of impervioussurfaces in Maryland. The Great Lakes, thestreams and rivers of the Pacific Northwest,the Everglades of Florida—all are being im-pacted in one or more ways by runoff fromstreets, parking lots, and rooftops.

Bannerman has spent the last 30 yearsstudying stream flow and the effect of urban-ization on watersheds, including the deple-tion of groundwater reserves. “Not allowingthe rainfall to infiltrate back into the aquiferis a very serious issue,” he says. “If that hap-pens, you lose the base flow [the portion ofwater derived from underground sources]

for streams, and you lose the wetlands fed bysprings. It’s a complete disruption of thehydrologic cycle.”

Bannerman cites the example of LakeWingra, a 1.3-square-kilometer lake inMadison. “A hundred years ago,” he says,“this lake was fed by around thirty-five sep-arate springs. But today, because the lake isnow almost entirely surrounded by urbanareas, there are only four streams feeding thelake. Local organizations have gotten activein trying to restore the lake’s water quality,but it’s not the same lake it was a hundredyears ago.” Lake Wingra now suffers fromalgal blooms caused by overfertilization,beach closures due to bacterial contamina-tion, turbidity, and drying of surroundingwetlands.

Bruce Wilson, a research scientist withthe Minnesota Pollution Control Division,is midway through a satellite survey of im-pervious surface area in that state. WhatWilson has seen thus far is enough to causesignificant concern about the state’s growthand development, and the impact of imper-vious surfaces on the water system.

“Impervious surfaces are impacting thelakes and streams on a number of fronts,” he

says. “Velocity of runoff isa big one. Water runs off ofthese surfaces so rapidly, itcreates mini-tsunamis thatcan cause serious, even ir-reparable, harm to thestream ecosystem. . . . Andof course, the ability torecharge the groundwatersystem is being impacted. Ifyou get into a twenty- tothirty-percent drop in infil-tration [into the aquifer],which means a loss of baseflow, the impact on streamsbeing fed by surface watergets magnified still further.”

Another big problem forurban areas is the flashflooding that can occurwhen heavy rains fall over acity, according to hydrome-teorologist Matt Kelsch, anauthority on urban flashflooding with The Univer-sity Corporation for Atmos-pheric Research in Boulder.Since runoff from an acre ofpavement is about 10–20times greater than the runofffrom an acre of grass, Kelschsays impervious surfaces canquickly trigger devastatingfloods that can produce ahost of their own environ-mental health hazards.

A 458 VOLUME 113 | NUMBER 7 | July 2005 • Environmental Health Perspectives

Impervious Cover of Various Land Uses

Source: Ferguson B. 2005. Porous Pavements. Boca Raton, FL: Lewis Publishers; page 2.

Perc

en

tag

e o

f la

nd

co

vere

d

100

90

80

70

60

50

40

30

20

10

0

2-ac

re res

iden

tial

1-ac

re res

iden

tial

1/2-

acre

res

iden

tial

1/3-

acre

res

iden

tial

1/4-

acre

res

iden

tial

1/8-

acre

res

iden

tial

Indu

stri

al

Com

mer

cial

& b

usin

ess

Shop

ping

cen

ters

Roofs

Pavements

Environmental Health Perspectives • VOLUME 113 | NUMBER 7 | July 2005 A 459

“In urban areas, anywhere from thirty toforty percent of the rainfall runs right intowhatever stream is in the area, and in heavi-ly urbanized areas it can be more than fiftypercent,” he explains (by comparison, hesays, the amount of runoff in subsaturatedwoodlands is often less than 5%). “If thewater overflows the stream banks, it’s goingto seek the path of least resistance. In mostcases, that’s going to be the roadways.”

In many desert areas, Kelsch says, engi-neers take advantage of the natural topogra-phy, building houses at higher elevationsand installing roads that lead up to residen-tial areas. What this does is make the roadsfar more dangerous. More than 50% of thefatalities in flash floods occur on roads,according to Kelsch.

Floods are often given numerical designa-tions such as “hundredyear flood,” meaning sucha flood happens onceevery 100 years (or has a1% chance of occurringin any given year). TheFederal Emergency Man-agement Agency main-tains a national list offlood zones and maps ofimpacted areas. The prob-lem, says Kelsch, is thatwe’ve changed the playingfield. “A couple of factorscome into play,” he says.“First, this is still a prettynew country, so mostplaces haven’t been devel-oped long enough toknow about the historicalrisk of a devastating flood. Secondly, whenwe urbanize an area, we alter the historicalfrequency of these events. The more wedevelop an area, the more rainfall we put asrunoff directly into streams that have evolvedto handle only a fraction of that runoff, andthe more that happens, the greater the likeli-hood of a catastrophic flood.” Several suchfloods hit New Orleans in the 1980s, andthree hit St. Paul–Minneapolis between 1990and 2001.

Heat Islands and the StreamWilson is also studying the “heat island”impact on Minnesota’s trout streams, animpact he says evidence and experiencesuggest is significant. Impervious surfaces,particularly roads and parking lots, are gen-erally dark, and thus heat-absorbing, sothey heat the rainwater as it hits. A suddenthunderstorm striking a parking lot that hasbeen sitting in hot sunshine (where surfacetemperatures of 120°F are not unheard of )can easily yield a 10°F increase in rainfalltemperature. And that heated water isn’t

coming off just one parking lot or onestreet, but more likely several, all addingheated water to a stream or river.

Many aquatic organisms, at differentstages of their lives, are vulnerable to evensmall increases in water temperature. “I’veseen trout streams in Wisconsin and else-where in the Midwest lose whole populationsbecause of—at least in part—the rise in tem-perature caused by runoff from impervioussurfaces,” Wilson says. “Increased tempera-ture also decreases the water’s ability to holdoxygen, which has a further detrimentaleffect on the aquatic life.” Warm tempera-tures can cause a variety of problems for fish,including decreased egg survival, retardedgrowth of fry and smolt, increased suscepti-bility to disease, and decreased ability ofyoung fish to compete for food and to avoidpredation. Especially affected are species thatrequire cold water throughout most stages oftheir lives, such as trout and salmon.

Eventually, given no additionalchanges, the temperatures would drop, butin the interim the impact on wildlife could

be serious. Oregon is one state that is exam-ining the science of water temperature effectson stream life. Oregon standards for optimalsalmon and trout rearing and migration callfor water temperatures of 64.4°F. Accordingto a 2004 report by the Oregon IndependentMultidisciplinary Science Team, whichadvises the state government on scientificmatters related to the Oregon salmon andwatershed management, studies have shownthat adult salmon begin to die off at temper-atures of 69.8–71.6°F, and some species oftrout at slightly higher temperatures.Although young salmon can survive slightlyhigher temperatures, the impact on theirgrowth and survival rate is well documented.

Impact of Building MaterialsNot yet as well documented is the impact ofpollutants released into stormwater runoff bybuilding and paving materials themselves.Asphalt is one concern, as it contains coal tarpitch, a recognized human carcinogen, aswell as polycyclic aromatic hydrocarbons(PAHs) including benzo[a]pyrene, anothercarcinogen. Another potential source of pol-lution is wood used for utility poles, playstructures, and other structures that has beentreated with chromated copper arsenate(CCA; a substance now being phased outdue to health concerns), pentachlorophenol,or creosote. According to a paper present-ed at the 2004 Annual Water ResourcesConference by Melinda Lalor, a professor ofenvironmental engineering at the UniversityA

ll im

ages

:Frie

nds

of L

ake

Win

gra

Focus | Paving Paradise

Impervious to change? Despite communityefforts, Wisconsin’s Lake Wingra still suffers theeffects of its urban surroundings including algalblooms, bacterial contamination, and turbidity.

of Alabama at Birmingham, in 1987 theUnited States alone produced some 11.9 mil-lion cubic meters of CCA-treated wood,1.4 million cubic meters of pentachlorophe-nol-treated wood, and 2.8 million cubicmeters of creosote-treated wood. And struc-tures, once built from such materials, areintended to last a long time. The health risksof arsenic and chromium are well known,and while copper is not generally a humanhealth risk, low concentrations of certainionic forms of this metal are toxic to marineflora and fauna.

“In general,“ says Lalor, “pollutant leveltends to vary depending upon the age of thematerial, and the harshness of the environ-ment to which it is exposed. As materialages and is exposed to high levels of sun-light, temperature extremes, chemicals inthe environment such as salt from roads,and so on, leaching out will increase.”

If the pollutant source is a coating, thenpollution levels decrease with age, but canstill have a significant impact, she says. “Ifyou look at the asphalt used in a parkinglot, the top coat is quite toxic. So if youhave a heavy rain [soon] after the parkinglot goes in, it’s not unusual to see fish killsdownstream.”

Lalor cites research published in volume35, issue 9 (1997) of Water Science andTechnology showing that stormwater fromroofs and streets contributed 50–80% ofthe cadmium, copper, lead, and zinc meas-ured in Swiss combined sewer system flows.

Polyester roofing materials shed the highestconcentrations of metals, followed by tileroofs, then flat gravel roofs. The Swissresearchers also found PAHs and organichalogens in the roof runoff.

The chemicals released can have a sig-nificant impact on environmental andpotentially human health. “Some materials,such as metals, are especially toxic to faunaat various stages of their life cycle,” saysLalor, “while some organics, particularlypetroleum-based organics, can function aspseudoestrogens. So while they may notcause death, they can trigger a significantdisruption in the physiology of the organ-isms exposed to these pollutants.”

According to Lalor, although there aremandated tests for urban stormwater dis-charge, there are currently no tests mandat-ed for building materials to determine theirpotential for toxics release. “If a communitywants to develop around their drinkingwater source, they should know aboutrelease potential from building materials sothey can carefully select those with whichthey build,” she says. “We don’t yet have thescience to support it, but it would be a pos-itive step to be able to go to a builder andsay, ‘Look, here’s a list of twelve buildingmaterial alternatives that would be mostenvironmentally benign for this site andthese conditions.’”

Lalor says New Zealand has been theleader in this sort of study, and that nationis preparing to put regulations in place

regarding building materials and environ-mental impact. But such studies haven’tbeen elevated to a high enough priority inthe United States to build the science weneed for setting new policies. She adds, “Weneed to address the entire life cycle of build-ing materials, from what goes into their cre-ation, to the impact of construction on theenvironment, to the impact of whatevermight leach out during their lifetime, to theend-of-life disposal issues.”

The Promise of Porous PavementsDespite the overwhelming body of evidencesupporting the negative relationshipbetween impervious surfaces and the envi-ronment, no one would seriously suggestthat we stop paving streets or building park-ing lots. What, then, are the options?

According to Ferguson, there are ninedifferent families of porous pavement mate-rials. Some of these materials are already wellknown in the United States; they includeopen-jointed pavers that can be filled withturf or aggregate, “soft” paving materialssuch as wood mulch and crushed shell, andtraditional decking.

Other families include porous concretesand asphalts being developed by engineersand landscape architects. Ferguson says thesematerials use the same components andmanufacturing processes as conventionalimpervious materials, “and as a general rule,carry the same health and environmentalissues. . . . Same chemicals, same energy costs

to manufacture, but far dif-ferent benefits in its use.”These new formulations stillprovide solid, safe surfacesfor foot and vehicle traffic,but also allow rainwater topercolate down into subsur-face soils.

The porosity of porousasphalt is achieved simplyby using a lower concentra-tion of fine aggregate thanin traditional asphalt; it canbe mixed at a conventional

A 460 VOLUME 113 | NUMBER 7 | July 2005 • Environmental Health Perspectives

Phot

odis

c; in

set:

Pho

toA

lto

Focus | Paving Paradise

Awash in toxicants. Chemicals used in paved surfaces can be toxic to fish, wildlife, andpossibly humans.

Environmental Health Perspectives • VOLUME 113 | NUMBER 7 | July 2005 A 461

asphalt plant. Under the porous asphalt coat-ing is a bed of clean aggregate. Importantly,this aggregate is all of the same size, whichmaximizes the void spaces between the rocks,allowing water to filter through. A layer ofgeotextile fabric beneath this bed lets waterdrain into the soil and keeps soil particlesfrom moving up into the stone.

Porous asphalt was actually developedmore than 30 years ago, according toFerguson, but it didn’t pan out at that time.Part of the problem, he believes, was—andcontinues to be—the low level of federallyfunded research. “Back in the early eighties,when porous pavement was new, theEnvironmental Protection Agency [EPA]was really interested, especially in porousasphalt,” he says. “But one of the problemswith porous asphalt back then was that on ahot day, the binder softened and migrateddown to a cooler layer. That released the sur-face aggregate and clogged the lower layer.”According to Ferguson, the EPA became dis-couraged and discontinued studies.

Since then, however, porous asphalt tech-nology has been improved by French,Belgian, and Irish researchers, Ferguson says.During the late 1980s and early 1990s, theydiscovered that adding polymer fibers andliquid polymers to the asphalt prevented thebinder from draining down through theaggregate. “Today, even though [porousasphalt] started out here, what we’re using hasbeen imported back from Europe,” he says.

Ferguson says porous pavement consti-tutes only a minute fraction of all the pavingdone each year in the United States.“However,” he continues, “the rate ofgrowth of porous paving, on a percentagebasis, is very high, primarily because of pub-lic concern about and legal requirements forurban stormwater management. Thisgrowth is happening both in the big asphaltand concrete industries, and in the smallerindustries that supply competing materialssuch as concrete blocks and plastic geocells.”

One argument against pervious surfacesin high-traffic areas is that they’re not as

durable as their impervious ancestors. That,says Ferguson, is simply not true. “I’ve seenpervious pavement in good shape in placeslike Minnesota and Alaska, where you havetremendous climatic extremes,” he says. “InGeorgia and Oregon, it’s now routine toresurface highways by putting a layer of per-vious asphalt over the impervious surfacebelow. That way, water drains laterally belowthe surface, giving you better traction andvisibility.” Although the major advantage tothis practice is highway safety, rather than re-infiltration of the water into the groundwa-ter, it still allows for more water to return tothe groundwater table than would be the casewith an impervious surface, where it merelyevaporates back into the atmosphere.

Some pervious surfaces have the addi-tional benefit of allowing pollutants tocome into contact with microbes beneaththe surface. According to Ferguson, thesenaturally occurring microbial communitiesthrive on the large surface area of the pervi-ous pavements’ internal pores and breakA

ll im

ages

:Bru

ce K

. Fe

rgus

onFocus | Paving Paradise

Breaking through barriers. Porous pavements come in manyforms. Parking spaces in Columbus, Ohio (top left) are made ofrecycled clay aggregate. Shoppers at the Mall of Georgia, thelargest mall in the U.S. Southeast, can park in a turf overflow lot(bottom left). The spaces between open-jointed pavers at Ontario’sSunset Beach Park lakefront access lot (above) admit water and pre-vent pollution of Lake Wilcox.

down contaminants (particularly petroleumby-products) before they can leach downinto the water supply.

“Coventry University scientists did astudy recently, where they applied oil to alab mockup of a porous road surface,” hesays. “They dumped far more used oil onthe surface than you’d ever find accumulat-ing on a parking lot, and none of it reachedthe soil layer below”—instead, microbesdigested it all. The Coventry team, led byChristopher J. Pratt, published an overviewof their work in the November 2004 issue ofthe Quarterly Journal of Engineering Geologyand Hydrogeology.

Other Ways of Controlling RunoffApproaches to dealing with the spread ofimpervious surfaces go beyond changing thebuilding material itself. Kelsch says a return tomore reasonable street width is one measure,and many communities are increasing theirnumber of green areas as a means of allowingrainfall to infiltrate back into the ground.

For urban areas with nearby lakes,Bannerman says construction of “rain gar-dens” is becoming a popular method thathomeowners and businesses can use to helpcontrol stormwater runoff. Such gardens aredesigned with dips in the center to capturewater, which then can slowly filter into theground rather than run off into the stormsewer. Ideally these gardens are situated nextto a hard surface such as a sidewalk or drive-way, and are planted with hardy nativespecies that can thrive without chemical fer-tilizers or pesticides.

Ponding basins like those used inFresno are another option. This city of justover half a million in Southern California’sSan Joaquin Valley gets less than 12 inchesof rain annually and draws most of its waterfrom underground aquifers and the nearbyKings and San Joaquin rivers. Beginning inthe late 1960s, the city started constructingseveral ponding basins—large basins wherestormwater can settle, then drain downthrough the soil. Water systems managerLon Martin says the city had two goals inestablishing these ponding basins: “First wasto keep stormwater runoff from flooding thecity and from going into the rivers, poten-tially causing water quality problems.Secondly, the city has begun a program ofintentional aquifer recharging.”

To date, he says, the city has connectednearly 80 of the possible 150 ponding basinsto its groundwater recharge system. Rechargefrom stormwater is one part of the equation,but the city also takes its May–October waterallotment from the two rivers, diverts thewater to these basins, and then allows gravityto pull the water down through the sandyloam soil into the aquifer.

Green roofs, another method of control-ling rainwater runoff, are just what the nameimplies: roofs planted with all types of vege-tation. Also known as “eco-roofs,” these sur-faces can be either extensive (lighter inweight, relying on a few inches of soil andusing plants like herbs, grasses, and wild-flowers) or intensive (much heavier, with a12-inch soil depth that can accommodatetrees and shrubs). According to the nonprof-it Earth Pledge Foundation, green roofs canabsorb nearly 75% of the rainfall that landson them, and they can also reduce the urbanheat island effect.

Green roofs perform several roles, oneof which is water harvesting, or basicallycatching rainwater for use elsewhere. “Thiswater is cleaner than that off the pave-ment,” Ferguson says. “[Water harvesting]is now being practiced in areas where wateris less available, such as the Southwest orthe Pacific Northwest, with their dry sum-mers. . . . [It] can be a valuable tool in areaswhere water is scarce.”

In Germany, approximately 10% of thebuildings have green roofs, and the city ofTokyo recently mandated that usablerooftop space of greater than 1,000 squaremeters atop new buildings must be 20%green. Green roofs are also found in NorthAmerican cities including Chicago, Toronto,and Portland, Oregon.

Beyond ImperviousnessRecognizing the environmental health threatof impervious surfaces as well as other pointsources of pollution, the EPA established astormwater permitting program under the

National Pollutant Discharge EliminationSystem. Phase I of the stormwater program,promulgated in 1990, required permits forseparate stormwater systems serving com-munities of 100,000 or more people, and forstormwater discharges associated with indus-trial and construction activity involving atleast five acres. Phase II, promulgated in1999, addressed remaining issues and urbanareas of fewer than 100,000 people, as wellas smaller construction sites and retail, com-mercial, and residential activities.

But further change will require a shift inhow we think about runoff. Bannermansays, “What we’ve begun to do, and mustcontinue to do, is to get away from the ideathat rain is wastewater—something to getrid of, to pass along to our neighbors down-stream. We need to keep it where it falls,and the way to keep it is to get it back intothe ground.”

For flash floods, Kelsch says, “there is nosolution. Flooding is going to happen, inspite of everything we can do. What we needto do is what we can to lessen the impact ofthe inevitable. That means building out offlood plains, and increasing the amount ofrainwater we send back into the aquiferswhile decreasing the amount we dischargeinto streams.” Building design and use ofpermeable paving materials will help, hesays, but we need to realize these aren’t totalsolutions. Further, he adds, “If we get stuckin the mindset that we have to have a solu-tion, we may not do anything. And that willmake the problem still worse.”

Lance Frazer

A 462 VOLUME 113 | NUMBER 7 | July 2005 • Environmental Health Perspectives

Focus | Paving Paradise

On top of the problem. The green roof atop Chicago City Hall contains more than 100 plantspecies that absorb stormwater and reduce the ambient air temperature by as much as 7–8ºFcompared to a nearby tar roof.

Con

serv

atio

n D

esig

n Fo

rm

Linking

Lessons

Learning

Tomorrow’s Scientists

EHP can help you give your students the tools to succeed.

For more information on the EHP Student Edition and Lesson Program log on today at www.ehponline.org/science-ed.

ehp

e h p o n l i n e . o r g / s c i e n c e - e d

L E S S O N :ehp Rescuing Water from the Roof Summary: Students read the EHP Student Edition article “Paving Paradise: The Peril of

Impervious Surfaces,” identify problems with paved surfaces, and then calculate the volume of water that could be collected from the school roof.

EHP Article: “Paving Paradise: The Peril of Impervious Surfaces” EHP Student Edition, October 2005, p. A456–A462 http://ehp.niehs.nih.gov/members/2005/113-7/focus.html

Objectives: By the end of this lesson, students should be able to: 1. identify environmental health concerns related to paved surfaces; 2. calculate the area of a roof surface; 3. perform unit conversions between inches, centimeters, and meters, and between cubic

meters and gallons; and 4. calculate a volume of water.

Class Time: Part 1 only: 45–50 minutes; Parts 1 and 2: 2 hours

Grade Level: 9–12

Subjects Addressed: General Science, Environmental Science, Mathematics, Geometry, Health

Prepping the Lesson (20–25 minutes)

INSTRUCTIONS: 1. Obtain a class set of EHP Student Edition, October 2005, or download the article “Paving Paradise: The Peril of

Impervious Surfaces” at http://ehp.niehs.nih.gov/members/2005/113-7/focus.html. 2. Make copies of the Student Instructions. 3. Review the article, lesson, and Student Instructions. 4. Decide if you want students to do both parts of the lesson. 5. If students do Part 2, gather the necessary materials. 6. Depending on the layout of your school and the level of your students, be prepared to review geometry concepts as

needed to assist them with calculating the area of the roof and the volume of rain captured by the roof.

MATERIALS (per student): • 1 copy of EHP Student Edition, October 2005, or 1 copy of the article “Paving Paradise: The Peril of Impervious Surfaces” • 1 copy of the Student Instructions and the Water Rescue Data sheet if the student will be doing Part 2 • Calculator

MATERIALS (per group): • Large tape measure with meter units for each student group

VOCABULARY: • aquifer • area • asphalt • green roof • heat island • impervious • perimeter • porous • volume

EHP Lesson | Rescuing Water from the Roof Page 2 of 8

BACKGROUND INFORMATION: The article provides sufficient information to complete Part 1 of the lesson. The health effects information that students provide in their answers can be general (i.e., a chemical is a carcinogen or toxic) or inferred (i.e., heat can cause heat stroke or flooding can cause drowning or automobile accidents), since the article provides only a few specific examples of health effects.

Part 2 of the lesson requires students to measure the perimeter of the particular school building to be studied, calculate the area of the roof, and then calculate the volume of water that comes off the roof.

If the shape of the school building is square or rectangular, then most students should be able to do all of the calculations needed to estimate the volume of water. If the building has a complex or unusual shape, you may want to have less-advanced students treat the building as a square or rectangle and more-advanced students, or those who have taken geometry, attempt to calculate the actual area using their perimeter measurements.

The formulas for calculating the area of shapes are:

Square or rectangle: length x width = l x w

Triangle: 1/2 base x height = 1/2bxh

Circle: p x radius squared = πr2

Trapezoid: 1/2(short side + long side)height = 1/2(a+b)h

Ellipse: π (short radius x long radius) = πab

Sector: 1/2 r2(angle in radians) = 1/2 r2θ

Students will also be asked to perform unit conversions. A website for unit conversions is included in the Resources section to assist you with grading. When students perform their calculations they should show all of their work or steps clearly, including the cancellation of their units. They should also have the correct units displayed at the end of their calculations. Students at all levels should do this because it demonstrates to you that they understand the calculations, and more importantly, it prepares them for the more advanced and complex calculations and unit conversions used in physics and chemistry.

RESOURCES: Environmental Health Perspectives, Environews by Topic page. Choose Water Pollution, Built Environment, http://ehp.niehs.nih.gov/topic

Math is Fun, Area of Plane Shapes, http://www.mathsisfun.com/area.html

Online Conversions, http://www.onlineconversion.com/

Texas Water Development Board, http://www.twdb.state.tx.us/assistance/conservation/Alternative_Technologies/Rainwater_Harvesting/rain.asp

Water Resources Research Center, http://ag.arizona.edu/AZWATER/publications/sustainability/report_html/index.html

Implementing the Lesson

INSTRUCTIONS: 1. Hand out the Student Instructions and a copy of the article “Paving Paradise: The Peril of Impervious Surfaces.” 2. Instruct the students to read the article and answer the questions in Part 1 of the Student Instructions. 3. If the students will be doing Part 2 of the lesson, inform them that they are going to measure the outside (perimeter)

of the building and then will use those measurements to calculate the area of the roof and the volume of water that comes off the roof during a rainstorm.

4. Review basic geometry concepts as needed and instruct the students about how and where they will measure the school (i.e., just the main building, the entire complex, just square and rectangular parts, etc.). If the school has several buildings you may want to assign buildings to groups.

5. Break the students into groups and give them a tape measure and data sheet. Remind them to collect the data in meters. 6. After the students have collected the measurements, instruct them to individually do the calculations. Each student

will turn in his or her own work. Remind the students to show their work and the units. 7. After the students have calculated the number of gallons of water that come off the roof, discuss some of the

possible uses or applications of that water (e.g., use it to water lawns or gardens). You may also want to discuss some of the limitations of using rain barrels, especially if you live in a wet climate. Have students generate ideas about how more water could be stored and used throughout the year (e.g., use large underground cisterns).

e h p o n l i n e . o r g / s c i e n c e - e d

EHP Lesson | Rescuing Water from the Roof Page 3 of 8

NOTES & HELPFUL HINTS: • In this activity we are assuming that all of the water that falls onto the roof could be collected. In reality some of the

water may evaporate, exit from multiple areas, or pool on the roof. • If the roof of the school is sloped and without eaves, then the amount of water collected would be similar to that of

a flat roof. However if the roof has large overhangs then the amount of water collected could be significantly more. • Students could design a water collection, storage, and distribution system for the school. They should consider

possibilities like using pumps or gravity feeds to distribute the water. • Students could also calculate the potential cost savings in water bills for the school if stored rainwater were used to

water landscaping. • If the school purchases some rain barrels be sure there is netting or covers to prevent mosquitoes from reproducing

in standing water. You may want to have students investigate or discuss the potential concerns with mosquitoes as vectors for diseases.

• If you have access to water quality testing kits, you may want to have students collect and test water from the roof and parking lots. Be sure to have students wear protective gear when collecting and testing the water.

Aligning with Standards

SKILLS USED OR DEVELOPED: • communication (notetaking, oral, and written) • comprehension (listening, and reading) • computation • critical thinking and response • graph reading • observation • technological design • unit conversions

SPECIFIC CONTENT ADDRESSED: • paved surfaces • water contamination • water collection • unit conversions • area • volume • environmental health

NATIONAL SCIENCE EDUCATION STANDARDS MET:

Unifying Concepts and Processes Standard • Change, constancy, and measurement

Science As Inquiry • Abilities necessary to do scientific inquiry

Life Science Standards • Interdependence of organisms

Science and Technology Standards • Abilities of technical design • Understanding about science and technology

Science in Personal and Social Perspectives Standards • Personal and community health • Population growth • Natural resources • Environmental quality • Natural and human-induced hazards • Science and technology in local, national, and global challenges

e h p o n l i n e . o r g / s c i e n c e - e d

EHP Lesson | Rescuing Water from the Roof Page 4 of 8

Assessing the Lesson

Part 1 Step 2: Answer the following questions:

a) Look at the graph titled “Impervious Cover of Various Land Uses” on page A458. What percentage of land is covered by the impervious roof surface for a common industrial complex?

Approximately 24%

b) List three examples of problems caused by impervious surfaces. Students may have any three of the following examples. If a student lists an example that is not here, check for accuracy.

• They collect particulate matter, nitrogen oxides from car exhaust, rubber particles, metals from brakes and building materials, phosphates from fertilizers, bacterial contamination, antifreeze, petroleum products, chromated copper arsenate, creosote, and pentachlorophenol from wood products; asphalt itself contains polycyclic aromatic hydrocarbons.

• Water moves too quickly, causes erosion, and cannot be absorbed into the ground. • Causes turbidity and overfertilization in lakes and streams, which may cause algal blooms. • Flash flooding on roads, overfilling sewage systems. • Acts as a “heat island.”

c) Give three examples of how a large amount of impervious surfaces may adversely affect human health. Students may have any three of the following examples. If a student lists an example that is not here, check for accuracy.

• Toxic and carcinogenic chemicals can run off into the drinking water supply and lakes and streams where people may eat the fish or swim.

• Lack of infiltration into the groundwater can significantly reduce the drinking water supply in some areas.

• Bacteria from animal fecal matter or overflowing sewage systems can cause illness. • Increased heat can cause heat exhaustion or heat stroke in people, especially the elderly. • Flooding can cause drowning or automobile crashes.

d) Provide examples of how porous pavements and green roofs help solve identified problems. A complete answer would list all of the examples below. Assign points based on the completeness of the

answer.

• Porous pavements can increase traction and visibility on a wet road. • Some pollutants can be broken down into less-harmful substances by microbes just below the surface

of porous pavements or in the soil layer on the green roofing material. • Porous pavements and green roofs slow the speed of the water. • Green roofs can decrease the roof temperature.

Part 2 Step 3: Each student should have completed the Water Data Sheet and have a calculated area for the building they

measured. Look for details in their notes/descriptions (i.e., can you tell exactly which wall they measured?). Also check for accuracy in their area calculations and use of units, and that they showed all of their work.

Step 4: Fill in the Water Conversiopn Table below to calculate the volume of water in cubic meters and gallons that could be collected from the roof during two different rainstorms. Unless your teacher instructs otherwise, assume the roof of your school is flat. Show your work on a separate sheet of paper and clearly show unit cancellations. Unit conversions are listed below.

e h p o n l i n e . o r g / s c i e n c e - e d

EHP Lesson | Rescuing Water from the Roof Page 5 of 8

• Volume = the number of cubic units to fill a three-dimensional space • 1 cubic meter = 264.2 gallons [US, liquid] • 1 centimeter = 0.01 meter = 0.39 inch

Volume answers will be unique to the school, but sample calculations are provided below. When students do unit conversions they should always show their calculations, unit cancellations, and ending units. This will develop good habits for more involved series unit conversions often encountered in physics and chemistry and will help them understand the mathematical process.

Water Conversion Table

Rained 1” Rained 2.7”

Convert inches to centimeters (cm) 1 in x 1 cm/0.39 in = 2.6 cm 2.7 in x 1 cm/0.39 in = 2.6 cm x 2.7 = 7.0 cm

Convert cm to meters (m) 2.6 cm x 0.01 m/1 cm = 0.026 m 7.0 cm x 0.01 m/1 cm = 0.07 m

Volume of rain off the roof (m3)

Area (assuming a rectangular school building) = 30 m x 45 m = 1,350 m2

Volume = area x height = 1,350 m2 x 0.026 m = 35.1 m3

Using the same area. Volume = 1,350 m2 x 0.07 m = 94.5 m3

Volume of rain gallons 35.1 m3 x 264.2 gallons/1 m3

= 9,273 gallons 94.5 m3 x 264.2 gallons/1 m3 = 24,967 gallons

Step 5: If the average rain barrel holds 55 gallons, how many rain barrels would you need to collect all of the water from a storm that produces 1” of rain? Show your calculation below or on a separate piece of paper.

9,273 gallons —————————— = 168.6 barrels ≈ 169 barrels 55 gallons/barrel

Authors and Reviewers

Authors: Stefani Hines, University of New Mexico

Reviewers: Susan Booker, Liam O’Fallon, Dean Hines, Lisa Pitman, Wendy Stephan, Kimberly Thigpen Tart

e h p o n l i n e . o r g / s c i e n c e - e d

S T U D E N T I N S T R U C T I O N S :ehp Rescuing Water from the Roof

Part 1 Step 1:

Step 2:

Read the article “Paving Paradise: The Peril of Impervious Surfaces,” EHP Student Edition, October 2005, p. A456–462, http://ehp.niehs.nih.gov/members/2005/113-7/focus.html.

Answer the following questions:

a) Look at the graph titled “Impervious Cover of Various Land Uses” on page A458. What percentage of land is covered by the impervious roof surface for a common industrial complex?

b) List three examples of problems caused by impervious surfaces.

c) Give three examples of how a large amount of impervious surfaces may adversely affect human health.

d) Provide examples of how porous pavements and green roofs help solve identified problems.

e h p o n l i n e . o r g / s c i e n c e - e d

EHP Lesson | Rescuing Water from the Roof Page 7 of 8

Part 2 Step 3: Per your teacher’s instructions, assemble into groups. Each group should have at least one tape measure with meter

units. Each group member should have a pencil, calculator, and the Water Data Sheet, below. Your group will measure the perimeter of your assigned building. Below are some tips to help you.

• Remember to measure in the unit of meters. It is much easier to calculate the area and volume using meters compared to feet and inches.

• Perimeter = the sum of the lengths of all sides. • Area = the number of square units needed to cover a surface (two dimensional). • If your school building is not square or has angled walls, you may find it helpful to draw the building

layout on paper, then partition the building into squares, rectangles, triangles, circles, or other shapes. This will help you calculate the area.

Water Data Sheet

Side of Building Notes/Description

(e.g., east, front, cafeteria wall) Length in Meters

1

2

3

4

5

6

7

8

9

Area Show your work and write the units (attach additional pages as needed to show your calculations).

e h p o n l i n e . o r g / s c i e n c e - e d

EHP Lesson | Rescuing Water from the Roof Page 8 of 8

Step 4: Fill in the Water Converstion Table below to calculate the volume of water in cubic meters and gallons that could be collected from the roof during two different rainstorms. Unless your teacher instructs otherwise, assume the roof of your school building is flat. Show your work on a separate sheet of paper and clearly show unit cancellations. Unit conversions are listed below.

• Volume = the number of cubic units to fill a three-dimensional space • 1 cubic meter = 264.2 gallons [US, liquid] • 1 centimeter = 0.01 meter = 0.39 inch

Water Conversion Table

Rained 1” Rained 2.7”

Convert inches to centimeters (cm)

Convert cm to meters (m)

Volume of rain off the roof (m3)

Volume of rain gallons

Step 5: If the average rain barrel holds 55 gallons, how many rain barrels would you need to collect all of the water from a storm that produces 1” of rain? Show your calculation below or on a separate piece of paper.

e h p o n l i n e . o r g / s c i e n c e - e d