Management of Urban Stormwater Pollution:

First 50 Years Stockholm, Sweden

Nov. 13, 2012

Jiri Marsalek Water Science & Technology Branch

Burlington, ON, Canada

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Presentation Outline

• Introduction – historical perspective

• Stormwater pollution characteristics

• Sources of pollutants in stormwater

• Stormwater pollution impacts • Solutions: Impact mitigation • Conclusions

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INTRODUCTION

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Urban Stormwater Pollution: Context

• Urban stormwater is defined here as surface runoff from urban areas

• It is conveyed by storm sewers (or open drains), or drains into combined sewers, where it contributes to combined sewer overflows (CSOs)(not addressed here)

• Increased surface runoff and the pollution conveyed by this runoff represent impacts of urbanization

• The issues of stormwater quality (the main topic of this talk) cannot be completely separated from those of stormwater quantity (flows contribute pollutants from the atmosphere, mobilize pollutants from the catchment surface and transport them)

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Urbanization: Water Balance Changes (after Schueler)

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Stormwater Pollution: Timelines

• First paper on stormwater pollution published in US by Weibel et al. (1964) – mostly conventional pollutants (also some pesticides and indicator bacteria)

• 1980s - reports on US EPA Priority pollutants in stormwater samples (US EPA, 1983), and in stormwater and sediment samples (a Canadian program)

• Makepeace et al. (1995) in a literature review identified 25 chemicals or groups with potential effects on human health and aquatic life

• By now, more than 600 substances identified, but not necessarily at environmentally significant levels

• Current challenges: control of some legacy pollutants and micropollutants (e.g., under EU Water Framework)

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SW POLLUTION CHARACTERISTICS

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Stormwater Pollutants of Environmental Interest • The list of pollutants of interest depends on local

receiving waters and the impacts caused by stormwater, and their selection and priorities vary accordingly

• In general, the main constituents (or groups of constituents) of concern include:

– suspended solids (transport attached contaminants, interfere with photosynthesis, blanket spawning beds, may damage fish tissues),

– trace metals (Cd, Cu, Pb, Zn – risk of toxicity), – trace organics from traffic by-products (polycyclic aromatic

hydrocarbons – risk of toxicity), – nutrients (P and N, in various forms - eutrophication),

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Stormwater Pollutants of Environmental Interest (cont.)

– chloride (in cold climates - toxicity), – indicator bacteria (upstream of drinking water intakes, or

swimming waters – risk of faecal contamination), – waste heat (succession of cold water fisheries) – micropollutants (toxicity)

• Some of these pollutants occur in the form of solids (either being solids or particulates, or being attached to suspended solids and sediment)

• More information on these pollutants follows

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Critical Constituents in Highway Runoff

• Solids (total and volatile) • Oxygen demanding substances (COD,

TOC) • Nutrients (NO2+3, TKN, PO4) • Heavy metals (Cu, Pb, Zn, Ni, Fe, Cd) • Hydrocarbons (including PAHs) • Phenols • Herbicides (weed control) • Deicing agents (chlorides, cyanides)

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SWP Descriptors – physical & Chemical

• Physical: – Pollutants can be dissolved or chemicals attached to solids, or

sediment – Solids represent a wide spectrum of materials (primary particles

– clay, silt, sand, or flocculated aggregates) – Temperature (runoff heats up on impervious surfaces, ∆ T up to

10 C – Density (dissolved solids laden runoff)

• Chemical: – Up to 600 chemicals identified in SW – More attention paid to POPs, new emerging chemicals – Reporting totals no longer sufficient, often interested in

speciation

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NURP SW Quality Data

Constituent EMC – median Site (NWRI)

EMC – 90th Percentile site

TSS [mg/L] 100 300 BOD [mg/L] 9 15 COD [mg/L] 65 140 T P [mg/L] 0.33 (0.28) 0.70 TKN [mg/L] 1.5 3.3 T Cu [µg/L] 34 (27) 93 T Zn [µg/L] 160 (490) 500

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Metals in Sediment (µg/g)

• Assessment – grossly polluted sediment

Metal QEW MOEE Guidelines

LEL SEL

Cu 314 16 110

Ni 162 16 75

Pb 402 31 250

Zn 997 120 820

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New Concerns - Micropollutants

• Micropollutants find their way into stormwater • Example – Perfluorinated chemicals (FFCs), used in a variety of

consumer products (adhesives, cleaning products, repellent coatings)

• Produced adverse health effects in laboratory animals (impact immune, liver and thyroid function)

• Transported with wet deposition (in-cloud and below cloud scavenging); their concentration may reflect local atmospheric contamination

• Annual fluxes of PFCs for four locations in Japan and USA were estimated at 11,000 – 22,800 ng/m2 , in urban areas, a large fraction of this burden will be transported by stormwater

• As new contaminants appear, we may be able to derive their stormwater fluxes from relevant environmental data

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SWP Descriptors - toxicological

• Difficulties with all-encompassing chemical protocols led to toxicity measurements

• Various types measured – acute, chronic or genotoxicity

• Toxicity testing often conducted in batteries of tests – to cover different toxicity types and bioassay properties

• Most common – Microtox®, Daphnia magna, fathead minnow (7-day), SOS chromotest

• Biomonitoring

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Frequencies of Toxicity Detection

00.10.20.30.40.50.60.7

No Potential Confirmed Severe

Toxicity

Frac

tion

MLDH RunoffUrban Runoff

MLDH runoff - severely toxic

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Descriptors – microbiological

• Interested in pathogens and parasites • Difficulties in measuring techniques led to studies of

indicator organisms (to detect fecal pollution) • Large progress in DNA probes identifying specific

organisms • Common indicators – fecal coliform, E. coli

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Indicator Bacteria in Stormwater

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

E. coli / 100 mL

R1 R2 R3 R4 R5 R6 R7 R8 CO IN HW BMP1 BMP2 BMP3

Stormwater source / land use

Residential SW Ponds

Commercial

Industrial

Highway

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SOURCES of POLLUTANTS

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Sources of Pollutants in Stormwater

• Atmospheric deposition – Wet and dry deposition, air transport from local and

remote sources

• Catchment surface – Materials released by erosion, attrition or elution of

catchment surface (e.g., soil erosion, attrition of pavements, elution or dissolution of building materials – mostly metals)

• Land use activities – Traffic and road maintenance (metals, oil & grease,

PAHs, spills, applications of road salts and abrasives), residential land activities (garden chemicals, grass clipping, litter, pets)

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U.S.A

250 500 750

1000 100

100

0 5 Km

N

PAH Deposition in Sault Ste. Marie (Canada)

Isoloading Contours

(ug/m ) 2

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Sediment Yield vs. Urbanizing Drainage Area

10

10

10

10

10

2

3

4

5

0.01 0.1 1 10 100 1000 10000

URBAN – FULLY DEVELOPED

Drainage Area (km2)

SED

IME

NT

YIE

LD

(t /

km2

/ yea

r)

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General Sources of Heavy Metals

Heavy Metals

Highest median C [ug/L]

Source

Cd 8 Vehicle service

Cr 100 Landscaped area Cu 160 Urban rec. water Pb 75 CSO Ni 40 Parking lot Zn 100 Roof runoff

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Sources of pollutants in traffic byproducts (major = , minor = )

Constituent Brakes Tires Fuel, liquids

Asphalt Deicing

Solids – organic

Solids, inorganic

Hydrocarbons

Cu

Pb

Zn

Chloride

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Sources of Heavy Metals in Urban Stormwater (Fuchs 2006)

0%

20%

40%

60%

80%

100%

Cu Pb Zn

OthersTrafficBuildings

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STORMWATER POLLUTION IMPACTS

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Impact Scales

• Impact can be summarized in a chart showing both temporal and spatial scales (after Lijklema et al. 1989)

Accumulation in sediments

Sedimentation (coarse material)

Resuspension

Mixing in rivers

Acute toxicity

Coagulation and

flocculation in lakes

BOD - O 2 Bacterial die-off

Mixing in lakes

Changes in benthic communities

Algal blooms

Bioaccumulation of toxicants in

fish

Year

Week

Decade

Month

Day

Hour

Minute

Local Whole system

Effects on Macro-

phytes

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Physical Impacts: Temperature Rise of Urban Runoff

• Urban areas contain many sources of heat which increase the temperatures of surface runoff

• In summer months, rainwater is heated on hot impervious surfaces (pavements, roofs) or in stormwater ponds and wetlands

• Stormwater runoff temperatures may exceed those in the receiving waters by up to 10° C

• Thermal impacts of heated runoff are particularly noticeable during low flows in receiving streams

• Uncontrolled thermal enhancement may cause the original cold-water fishery to be succeeded by warm-water fishery (the same for invertebrates)

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Measured and Modelled SW Pond Water Temperatures (after Van Buren et al.)

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Densimetric Stratification

• Densimetric stratification can be caused by physical (thermal) or chemical (salt) phenomena

• Impacts on transport, mixing and water quality (inhibits vertical mixing)

• Where salt is used in winter road/street maintenance, chemostratification (high TDS, chloride) dominates

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Densimetric Stratification in a Frozen Stormwater Pond

Ice

Outlet Inlet

Temp.= 1.6 C, TDS = 860 mg/L

Temp.= 2.3 C, TDS = 1080 mg/L

Temp.= 2.5 C, TDS = 1300 mg/L

Temp.= 0.5 C, TDS = 664 mg/L 0.4 m

0.8 m

1.1 m

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Chemical Impacts

• Reduced DO - not a major concern for stormwater • Nutrient enrichment and eutrophication - a significant

concern for impoundments • Eutrophication degrades ecosystems by reducing

food to herbivores, water clarity, algal decomposition (oxygen demand)

• Stormwater may cause both acute and chronic toxicity

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Toxicity

• When assessing chemical effects, concentrations of individual constituents are compared to the levels known to cause biological effects (effective concentrations, EC)

• In SW, WW and CSOs, biological effects may be caused by ammonia, chloride, chlorine, trace metals, and trace organics (last two, higher in SW)

• Difficulties with interpretation of chemical data (establishing ECs for all chemicals, chemical bioavailability, influences of ambient conditions - e.g., hardness, pH, and combined effects of chemical cocktails) led to the use of biomonitoring

• The most common form – toxicity testing

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Applications of Road Salts

• Chloride concentrations in urban winter runoff and snowmelt frequently occur above the toxic levels (chronic 150-389, acute 600-860 mg/L)

• Management tools are studied/applied in a number of countries

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Dissolved Oxygen

• DO is important for: – aquatic life and plants (need some minimum DO

levels) – stream capacity to assimilate waste, and – the processes at the bottom sediment/water

column interface • The precise definition of harmful (low) DO levels is

under discussion, but minimum levels for cold-water biota are usually specified as 9.5 mg DO/L in the early stages of life and 6 mg/L for warm-water biota

• Hypoxia may occur in stormwater ponds in summer, or under the ice cover

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Nutrients: TN and TP

• Nitrogen and phosphorus are two most important constituents affecting the productivity of aquatic systems

• Originate from both natural or anthropogenic sources

• Fully or partly treated wastewater and CSOs carry higher concentrations in both soluble and particulate fractions than stormwater

• N and P occur in various species, which have different implications with respect to toxicity or eutrophication

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Microbiological Pollution Impacts

• High levels of indicator bacteria in stormwater (104-

5/100 mL) have to be reduced to 102, or even 0, for specific water uses

• Control of microbiological pollution on beaches is complicated by wildlife – birds represent a major source

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Combined Impacts

Biological Community

Performance

Chemical Variables

Flow Regime

Habitat structure

Biotic Interactions

Energy Sources

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Terraview Pond

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Benthic Community Structure

• Only 2 species present at all sites • No evidence of severe contamination

02468

101214161820

0 20 150 400 450 475 500 600

Distance from An Upstream Reference Point (m)

Tax

a R

ich

nes

s

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2000

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6000

8000

10000

12000

14000

0 20 150 400 450 475 500 600

Distance from An Upstream Reference Point (m)

Tot

al B

enth

os C

oun

ted Storm

PondStorm Pond

n/a

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Solutions: Impact Mitigation

• Best Management Practices, including: – Source controls – Low Impact Development (LID) – Structural measures

• Applied at three scales: – On site – In the neighbourhood – On the catchment scale

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Source controls – success stories

• Phasing lead out of gasoline (preventing Pb releases) • Brake pads – reducing Cu (from 15% to 0.1%) • Banning lead weights for wheel balancing • Reducing salt application in winter road maintenance

(smart salting, alt. deicers)(5 x 106 t used in Canada) • Public awareness / education / participation (banning

cosmetic pesticides, recycling, cleaning up after pets) • Protecting coatings of metal roofs (prevents Zn elution) • Self-cleaning concrete (TiO2 nanoparticles,

photocatalysis) • Near source – street sweeping

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Phasing Pb out of gasoline

• Phasing Pb out of gasoline was higly effective

• Highway runoff data indicate reduction of Pb in runoff about 30 times (equivalent to preventing 97% of releases)

• This is actual prevention, not just a diversion

US Highway Data (1970s)

CDN Highway Data (1990s)

10

1

.01

.001

Pb (mg/L)

Z score-2 -1 0 1 2

Reduction 97%

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LID - Definition

• A comprehensive, landscape-based approach to sustainable urban development encompassing strategies to maintain existing natural systems, and their

hydrology and ecology • Typical LID literature focuses on site hydrology

and water balance and its preservation • LID measures: rainwater use, green roofs,

enhanced soil water storage, disconnection of impervious areas, maintaining vegetative canopy, infiltration, on-site storage (bioretention)

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Green Roofs (GR)

• GR either extensive or intensive • Hydrological benefits: reduced runoff (Q & V) • Ecological benefits: reduced runoff pollution (caution:

nutrients in roof runoff)

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Minimize DCIA

• Minimize directly connected impervious areas/surfaces: reduce areas, drain impervious onto pervious, pervious pavement

• Hydrological benefits: reduced runoff (Q and V), improved

groundwater recharge • Ecology benefits: reduce pollution,

improved aquatic habitats

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Vegetative canopy

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Drainage by swales (photos Kerr Wood Leidal)

• Traditional drainage by curb & gutter generates too much of fast runoff

• Replaced by swales

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Infiltration Facilities

• Trenches, wells, and basins

• Suitable for clean stormwater (e.g., roof runoff), watch out for chloride

• Pretreatment and regular maintenance is required

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On-site Runoff storage

• Storage without volume control reduces only peak flows; in conjunction with infiltration, it also reduces runoff volume

• Various types exist: rooftop storage, vault storage under parking lots, bioretention areas, swales

• Ecological benefits: storage facilities serve as aquatic habitats, and support flora and terrestrial habitats

Credit: M. Dietz

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LID Maintenance

• To sustain benefits, attention must be paid to maintenance and monitoring

• Some tasks are simple (sediment removal), others more involved (mulch replacement)

• Schedules of maintenance should be specified for individual types of structures/ facilities

• Maintenance on private property – requires homeowners education/cooperation, means of enforcement

• Some communities may require permanent sureties or bonds to be used when homeowners fail to maintain LID on their property

• Assign maintenance responsibilities

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Conventional BMPs: Stormwater Ponds

• Provide flow control, quality control, and recreational amenities

• Chemostratification reported for the Kingston (stormwater management) Pond (1997)

• In the following years, several other stormwater ponds were surveyed in winter and found stratified

Cataraqui Stormwater Pond

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Constructed wetlands

Purpose - detention and treatment in shallow pools with vegetation removing pollutants through a number of processes

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Riparian buffer zones

• Buffers are important for both urban and rural creeks • Main functions: overland flow treatment, flow storage,

habitat and ecological functions • Narrow buffers do not fulfill all of these functions

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Conclusions

• Stormwater runoff and pollution are significant factors to be considered in environmental protection

• Characteristics and impacts need to be assessed for devising effective controls

• Best estimates of SW pollution are obtained by field data collection, or modelling in the case of planning

• Impact mitigation can be achieved by BMPs comprising source controls, LID, and conventional measures

• Large achievement of the past 50 years – development of BMP and LID practices