GLOBALWATERISSUESVOL. III: STORMWATER

K N O W L E D G E . S O L U T I O N S . A D V A N C E M E N T .

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Where intense tropical rainmeets rapid urbandevelopment, the loser isfrequently the local watercourse, into which all thetrash, silts, hydrocarbons, andother pollutants aredischarged with thestormwater runoff. The sea isthe final recipient, and riverinesilts and sediments can be

detected and often still seenmany miles out from theestuaries of large tropicalrivers.

To help mitigate thispollution, recent trials ofHydro International’sDownstream Defender® bythe National HydraulicResearch Institute of Malaysia(NAHRIM) have shown

promise in an installationclose to the capital, KualaLumpur. This Gross PollutantTrap (GPT), which is based ona hydrodynamic vortexseparation process, reducesgross pollution from stormflows.

Infrastructure andhydrological engineers Weida(M) Bhd conducted the trials

Tests conducted for the National Hydraulic Research Institute in Malaysiaconcluded that Hydro International’s Downstream Defender provides “first-flush” treatment in intense storm conditions.

Malaysian market streets pose a challenge for stormwater control management.

Malaysia’sDepartment ofIrrigation andDrainage hasrecognized fordecades that therapid urbanizationthat accompaniesstrong economicgrowth canexacerbate waterpollution problems.

Pollutant trap improves runoff quality in Malaysia

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for NAHRIM in a new urbanarea near Kuala Lumpur. Thetrial report concluded that theDownstream Defender is aneffective gross pollutant trap,which captures and storesnearly all gross pollutantscarried in the storm drain overthe trial period. “These trialsare encouraging because theyare helping to test theDownstream Defender’sability to provide “first flush”treatment in intense stormconditions, even though thedevice was originallydeveloped for more temperateUS and UK climates,” HydroExport Manager GraemeFenton said.

Malaysia’s Department ofIrrigation and Drainage hasrecognized for decades thatthe rapid urbanization thataccompanies strong economicgrowth can exacerbate waterpollution problems. As aresult, a series of measureshave been put in place toguide stormwater volume andquality control measures,culminating in 2001 in theManual Sahran Mesra AlamMalaysia (MSMA) for StormWater Management. MSMAemphasizes the need for storm

water control, at or near thesource, as an effective andefficient method of improvingstormwater runoff quality andmitigating the effects of stormflows on rivers.

The onset of rapid urbandevelopment in parts ofMalaysia has increased areasof impervious surfaces, whichdeliver high flash flowconditions under intense rainstorms. Urbanization alsoincreases the amounts ofdiscarded waste such aspolystyrene food trays andother packaging, and organicpollutants such as food,cooking oil and hydrocarbonsfrom vehicle facilities.

Rainfall is a major factorin transporting this pollutioninto the storm drains. Forexample, Kuala Lumpur hasan annual rainfall of nearly2400 mm with peaks up to280 mm in April andNovember; short durationshowers can also total 100mm or more in an hour inKuala Lumpur. East Coastareas can double these figures.

Urban Malaysia’s typicalstorm drainage comprisesdeep roadside drains, whichdischarge into high volume

monsoon drains andeventually into the river.

Real condition trialsWeida (M) Bhd. oversaw atrial installation of theDownstream Defender underactual street conditions incollaboration with NAHRIMto examine its performanceunder tropical urbanconditions. Researchersexamined the ability of theprocess to separate and retainfloatables, oil, grease, andsediment from contaminatedstormwater.

The site for the trial was inthe old town of SeriKembangan, south of KualaLumpur, which has beenrecently engulfed by rapidindustrialization andurbanization. It is a mix ofsmall and medium industriesintermingled with residential,retail, and open shop lotswhere informal commercialactivity can take place.

Additionally, a morningmarket operates throughoutthe week and a night marketopens on Monday evenings;both combine food andcooking stalls with sales ofother goods. Activity is thus

Urban Malaysia’stypical stormdrainage comprisesdeep roadsidedrains, whichdischarge into high volumemonsoon drainsand eventually into the river.

Table 1: Data from stormwater pollution sampling

5 day weekday collection

Oil / grease from net point mg/l

Trash and flotables from net point wet weight kg

Silt / sediments from drainage sump wet weight kg

Before DDF After DDF Before DDF After DDF Direct DDF Before DDF After DDF Direct DDF Av. amount 171.7 14.6 1.125 0 8.1 2.444 0 9.8 Range; variation min/max

59 / 487 9 / 22 0.379 / 3.154

0 0.946 / 42.0

1.083 / 4.983

0 NB. Only 1 collection after 6 weeks

Weekend Amount 271.9 18 0.873 0 1.992 2.127 0 Incl. in single Range variation; min/max

24 / 1530 5 / 37 0.249 / 1.632

0 1.233 / 2.598

0.879 / 7.154

0 collection as above

N.B. The samples were taken on Fridays to examine weekday pollution over five days, and on Mondays to examine weekend pollution. Due to various factors that affected the possible sampling times for different categories, the number of weeks used to calculate the averages ranged between five and ten.

distributed over the wholeweek and encompasses a widevariety of possible pollutantsources.

The drains in the areacomprise a mix of improvednatural and man-madestructures. In the trial, a 1.2-m-diameter DownstreamDefender was installed undera tarmac road and connectedoffline to a roadside draincarrying stormwater runoffand effluent from the housing,wet market, restaurant andshops from the north. Aftertreatment in the DownstreamDefender, the effluent isdischarged back into the samedrain downstream before thewater is emptied into the mainmonsoon drain. A weir wall isused to direct flow into theDownstream Defender.

Sampling and measuringSampling of pollution forseveral weeks between May 7,2010, and August 27, 2010,before and after theDownstream Defenderinstallation was carried out ata point five metersdownstream of the outletpoint from the DownstreamDefender.

Trash was collected in avertical net at this point, whilesilt/sediment samples werecollected in a drainage sump.Once the DownstreamDefender had been installed,both trash and silt were alsocollected directly from theDownstream Defender sumpby a standard vacuum suctionpump for comparison with theresults at the downstreamnetting point.

Oil and grease werecollected with a manual scoopat the netting point before andafter the installation, and thedensity of hydrocarbons perliter of water were analyzed tomeasure the effectiveness ofthe trap.

For measurementpurposes, pollutants wereseparated into floatables(including trash) andsediments, which were eachwet-weighed both on site andin the laboratory, and oils and

grease, which were analyzedand their density measured inthe laboratory.

Urban Malaysia’s typicalstorm drainage comprisesdeep roadside drains, whichdischarge into high volumemonsoon drains andeventually into the river.

Results of trial collectionThe before and afterinstallation figures clearlyshow that the device removessubstantial amounts of oil andgrease pollution fromstormwater in the drain withboth the average amountcollected at the net point andthe peaks of pollution greatlyreduced.

NAHRIM concluded thatthe Downstream Defender isan effective gross pollutanttrap that captured and storednearly all gross pollutantscarried in the storm drain overthe trial period. In addition,NAHRIM pointed out that itwas easy to maintain thedevice with a vacuum suctiontruck, and that this would berequired in the SeriKembangan installation atleast twice a year for theobserved pollutantaccumulation or manualcollection would be requiredtwice a month. Moreinstallations wouldsubstantially reduce themaintenance cost of deployinga truck per unit.

Calista Kim Kher San, theproject engineer for Weidawho installed and monitoredthe installation for NAHRIM,explained that the device “isalso very effective in trappingthe large amounts of bigfloatables, such as liter plasticbottles and polystyrene foamblocks, which are morecommonly found in the drainshere than in many Westerncountries.” He anticipatesfurther installations plannedto start protecting the riversaround Kuala Lumpur such asthe Gombak and the Klang.“We have also installed oneunit at the main bus station inPetaling Jaya, a large urbanarea contiguous with Kuala

Lumpur, where a substantialreduction in oil and greasepollution has been achieved.We are currently developingriver-cleaning stations and onsite detention centers using itin conjunction with additionalpollution handlingequipment,” he added.

Diagram of the DownstreamDefender, developed by HydroInternational.

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Oil and greasewere collected witha manual scoop atthe netting pointbefore and after theinstallation, and thedensity ofhydrocarbons perliter of water wereanalyzed tomeasure theeffectiveness of the trap.

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Trees are used frequently as a“green” infrastructurestormwater control in cities.But when it comes tominimizing urban runoff, alltrees are not equal. “[Largertrees] provide a lot moreecological services,” accordingto Peter MacDonagh, directorof design and science atKestrel Design Group(Minneapolis). For instance, atree that has a 762-mm (30-in.) diameter-breast-height(DBH), which is the diameterat approximately 1.4 m (4.5ft) off the ground, provides 70times the ecological services ofa tree with a 76-mm (3-in.)DBH, he said.

In terms of stormwaterrunoff, Minneapolis uses treesas a part of a greeninfrastructure strategy tohandle the frequent 25-mm-per-24-hr (1 in.-per-24-hr)storms, so gray infrastructurecan handle the larger storms,MacDonagh said. Duringthese smaller storms, a 560-mm (22-in.) DBH tree canintercept 80% of thestormwater in its canopy,while a 51-mm (2-in.) DBHtree only can intercept about15%, he added.

A tree’s size and ability tointercept stormwater often

correlate to its age. A 40-year-old tree can intercept 18,925L/yr (5000 gal/yr) ofstormwater, a 20-year-old treecan intercept 5110 L/yr (1350gal/yr), and a 10-year-old treecan intercept 1890 L/yr (500gal/yr), MacDonagh said.

However, the average lifespan of a “street tree” in the20 largest U.S. cities is onlyabout 13 years, MacDonaghexplained. Therefore, theservices that urban treesprovide often are limited. “Wefeel that a tree’s life [span]should be at least 50 years,”MacDonagh said.

Helping trees thriveTo live up to their stormwatermitigation potential, treeshave to reach a mature age.

Planting 100,000 trees so theycan grow large is morebeneficial than planting amillion small trees that willnot reach maturity, accordingto MacDonagh. For example,in Minneapolis, Dutch elmtrees larger than 762 mm (30

in.) in DBH constituted 10%of the total tree populationbut provided about 32% ofthe stormwater benefits fromthe city’s tree population, he said.

One of the keys to large,long-lived trees is adequate

Calculating the returns on your green infrastructure investment. Trees are usedfrequently as a “green” infrastructure stormwater control in cities. But when itcomes to minimizing urban runoff, all trees are not equal.

Bigger trees, better benefits?

A project in Minneapolis used a suspended pavement system tosupport loading on sidewalks while keeping soil loose for tree growth.Kestrel Design Group

Regardless ofconstraints,MacDonaghbelieves that allcities have thepotential toincrease their totaltree canopy.

Jennifer Fulcher, WE&T

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moisture. If planned properly,trees do not need to beirrigated, because they can relyon stormwater, MacDonaghsaid. Stormwater can bedirected toward trees throughpervious paving, catch basins,or trench drains, to providetrees both the moisture andnutrients they need to thrive.

Trees also need anadequate volume of loose,oxygen-rich soil, MacDonaghsaid. At 85% compaction insoil, tree roots stop growing.“If the soil conditions arebetter, there’s a much largerrange of species that can beput in there,” MacDonaghsaid. Planting a wide variety oftree species also helps avoid amassive number of tree deathsif a disease affecting a singlespecies spreads through a city,he said.

To avoid compacted soil,structural cells can be installedthat support surroundingpavement while maintainingloose soil. With this system, 17m3 (600 ft3) of shared soil isneeded to grow a large tree,while 68 m3 (2400 ft3) of soil

would be needed to grow thesame tree using structural soil,MacDonagh said.

Excavating even morearea, especially horizontally,and then backfilling will havea positive effect on long-termtree growth and is “the leastexpensive solution,” accordingto Greg McPherson, researchforester with the U.S. ForestService Pacific SouthwestResearch Station.

Quantifying benefitsIn addition to helping reducestormwater runoff andintercepting rainfall, treesreduce air pollutants andsequester carbon dioxide.Trees also help keep buildingswarm on cold days byblocking wind and cool on hotdays by providing shade.

Trees help to reduce theurban heat-island effectbecause, throughevapotranspiration, theydisperse heat more efficientlythan pavement or masonry,MacDonagh said. During a29°C (85°F) day, thetemperature in the interior of

the city would be about 33°C(92°F), but 152 mm (6 in.)above the tree leaves, thetemperature will be about29°C (85°F), he said.

In the long term, trees with50-year life spans prove morecost-effective than trees with13-year life spans, MacDonaghsaid. It costs $6000 to replace atree every 13 years for a returnon investment of $3000; every$1 invested produces $0.50 inbenefits, he said. However, acase study in Minneapolisshowed that a group of treesthat grew through 50 yearswithout being replaced cost$7500, for a return oninvestment of $20,000; every$1 invested produced $2.50 to$3 in benefits.

McPherson said the U.S.Forest Service has worked formany years to calculate boththe environmental andeconomic values provided bytrees.

“To convert [environmentalbenefits] into a dollar value iscomplicated, because no one ispaying the tree for doing thesethings,” McPherson said. The

Forest Service equates thesebenefits to cost savingsprovided, he noted. Forexample, it calculates the costof electricity needed to heatand cool a home during theyear without trees and thenmodels the placement of treesaround that home to calculatehow much the tree saves inenergy costs. The agency hasdeveloped an online urbantree-benefit calculation toolcalled i-Tree, available atwww.itreetools.org.

Planting the right treeEven though large treesprovide many benefits, notevery site in a city can supporta large tree. Constraints, suchas pipelines or otherunderground infrastructure, aswell as buildings and electricalwires aboveground, “affect thesize of the tree that you willplant, because you want a treethat will grow and thrive in thesite,” McPherson said. “Thegoal is to get a tree that willperform admirably for a longperiod of time with minimummaintenance,” he said.

The optimal size of a treevaries based on site conditionsand the goals for the treefunction. If a tree is plantedfor social and aestheticpurposes, it does not have togrow as large as a tree plantedto mitigate stormwater or tocapture air pollutants,McPherson said.

McPherson also points outthat approximately 75% ofthe land in U.S. cities isprivately owned. Therefore,planting the right type of treewith adequate soil andmoisture often depends not onprofessional foresters andarborists but on the public. Heencourages citizens to seek outresources and assistanceonline and through localenvironmental organizations.

Regardless of constraints,MacDonagh believes that allcities have the potential toincrease their total tree canopy.“There’s really no reason inmost cities in the United Statesthat [we] can’t obtain a 40%canopy,” he said.

Supporting sidewalks with structural cells avoids soil compaction and enables trees to thrive in less soil.Kestrel Design Group

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908,000 m3/d (240 milliongal/d) of sanitary and wetweather flow. The plantfeatures the largest biologicalaerated filter process in theUnited Sates and the firstlarge-scale ballastedflocculation process forphosphorus removal in theNortheast. The total cost ofthese improvements was about$175 million.

A monitoring programshowed significant decrease inlevels of ammonia andphosphorus in LakeOnondaga. The programcollects data and informationneeded to assess theeffectiveness of improvementsand includes field andlaboratory components toidentify the sources ofmaterials(nutrients, sediment,microorganisms, andchemicals) to the lake,evaluate lake water qualityconditions, and examine theinteractions betweenOnondaga Lake and theSeneca River.

CSO abatement programLike many northeastern cities,Syracuse has a combinedsewer system with bothsanitary water and stormwaterentering a single sewer line.Under heavy precipitation andsnowmelt, this combined flowtriggers SO events thatoverload sewer systemcapacity and release the flowinto local waterways. Forty-nine CSO discharge pointsthroughout the 3140-ha(7750-ac) combined sewerservice area account for morethan 1.9 million m3 (500million gal) of CSO dischargeannually. The Onondaga Lakewatershed extendsapproximately 460 km (285 mi).

The amended consentjudgment included a provisionfor comprehensive “gray”infrastructure for CSOmitigation. The countyplanned to construct regionaltreatment facilities (RTFs)throughout Syracuse. In 2008,a residential neighborhood inthe Midland sewer district

became home to the first RT.The 20,800-m3 (5.5-million-gal) subsurface facilitycaptures and treats flow fromfive CSO outfall areas. Whenit rains, the facility canprovide storage with eventualdiversion to the Metro plantfor comprehensive treatment.When the storage capacity isexceeded, the facility provideslimited primary treatmentwith direct discharge toOnondaga Creek. Thesereduced levels of treatment,coupled with communitydissatisfaction about the

building of a treatment facilityin a residential neighborhood,set the stage for a change indirection of the CSOabatement program.

While $250 million worthof RTF contracts werereadied, the newly electedOnondaga County executivepetitioned the federal courtsfor an extension to theamended consent judgment toallow for the development of arevised plan.

This porous concrete parking surface is one of many parking lots that were retrofitted with green infrastructure.

With the support of the U.S.Environmental Protection Agency (EPA),the U.S. Department of Justice, the NewYork attorney general’s office, the NewYork Department of EnvironmentalConservation, and numerous communitypartners, green infrastructure in Syracusebecame a reality.

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‘Save the Rain’In November 2009, the federalcourts approved a new planusing “gray” storage facilitiesto address wet weather flow inthe combined system andinnovative “green”infrastructure to prevent wetweather from entering thesewer system. With thesupport of the U.S.Environmental ProtectionAgency (EPA), the U.S.Department of Justice, theNew York attorney general’soffice, the New YorkDepartment of EnvironmentalConservation, and numerouscommunity partners, greeninfrastructure in Syracusebecame a reality. At the time,Onondaga County was theonly regional authority in thecountry to include the use ofgreen infrastructure in aconsent judgment.

The Save the Rainprogram, planned anddesigned in 2010, uses twounderground storage facilitiesto collect CSO flow duringwet weather events andtransfer stormwater to theMetro plant after peak levelssubside. A comprehensivegreen infrastructure programwill capture the city’sstormwater and reduceimpacts of runoff to the sewersystem. The combinedapproach will treat 95% ofthe annual CSO volumes andachieve water qualitystandards in Onondaga Lakeand its tributaries byDecember 2018. The capturerate reflects 89.5% of flowthough gray infrastructure and6.5% (946,000 m3/yr, or 250million gal/yr) through greeninfrastructure.

While planning the greeninfrastructure program, thecounty continued work onseveral gray projects, includingsewer separation andrestoration efforts andconstruction of an interceptorreplacement sewer. It alsoconstructed several pilot greeninfrastructure projectsthroughout the city, includingrenovation of several surfaceparking lots downtown.

In 2011, the countyexecutive announced theProject 50 campaign, initiating50 distinct greeninfrastructure projects withinthe calendar year. Thisaggressive plan featuresseveral signature projects. The county has installed a6130-m2 (66,000-ft2) greenroof on the Nicholas J. PirroConvention Center, one of thelargest in the Northeast. Acapture-and-reuse system atthe Onondaga County WarMemorial Arena will store upto 56,775 L (15,000 gal) ofrainwater and snowmeltrunoff from the roof. Thesystem filters, disinfects, andreuses the capturedstormwater to provide ice atthe rink for the SyracuseCrunch minor league hockeyteam, the first team in theUnited Sates to skate on“green ice.” The county also isbuilding an innovativewetland system to treat CSOdischarge before it entersHarbor Brook, one of twomain tributaries within thecombined sewer service area.These projects followsuccessful demonstrationprojects completed in 2010,including work at city-,county-, and state-ownedparking lots, as well as theRosamond Gifford Zoo atBurnet Park.

To engage the localbusiness community, thecounty’s Save the Rainprogram created a GreenImprovement Fund, offeringgrants to private propertyowners in the combined sewerdistricts. The program is themost successful public–privatepartnership for greeninfrastructure in the country.More than 70 applicationshave been received. More thana dozen green infrastructureprojects have been installed onprivate property to date, andOnondaga expects more thantwice as many projects in2012.

The Project 50 campaignexceeded campaign goals, with60 projects either complete orunder construction. This effort

is expected to reduce CSOdischarges by more than189,000 m3 (50 million gal)annually. The 2011construction season also sawsignificant progress made onthe gray infrastructure side ofthe program, and the start ofconstruction on both storagefacilities is expected to becompleted by the end of 2013.

Since Onondaga decidednot to build three more RTFsand to better balance gray andgreen infrastructure, thecommunity will realizeadditional benefits, such asfewer construction impacts;reduced operation andmaintenance costs; andimproved neighborhoodaesthetics, habitat, and airquality. Local residents andcommunity organizations haveworked closely withOnondaga County toimplement projects that servethe dual purpose of CSOreduction and neighborhood

improvement. Syracuseneighborhoods alsoparticipated in workshops andcommunity forums tocontribute ideas forimplementation of variousprojects. The comprehensivenature of the program hasprovided the opportunity forsignificant community input.

The program garnerednational recognition in April,when EPA identified Syracuseas one of 10 communitiesthroughout the nation beingrecognized as a GreenInfrastructure Partner.

Bj Adigun is a programcoordinator, and Matthew J.Marko is a vice president inthe water business group andmanages the Syracuse, N.Y.,office of CH2M Hill(Englewood, Colo.).

This porous basketball court minimizes stormwater runoff.