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QUEENSLAND UNIVERSITY OF TECHNOLOGY

Influence of transport

systems on urban

stormwater quality.

Thesis 2013

Hamish Truda

5/14/2013

Abstract

Stormwater management is a fundamental step in securing the availability of potable water sources

for the future. This investigation was focused on compiling evidence to correlate the decline in urban

stormwater quality with transport systems. This investigation has determined that aspects of

transport systems, pollutant processes and catchment changes play a fundamental role in

controlling urban stormwater quality. From the investigation it’s clear the decline in urban

stormwater is heavily impacted by the characteristic of transport systems. Based on these findings,

appropriate measures will have to be initialised to manage the impacts of the changing traffic

systems on urban stormwater.

Acknowledgements

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I would like to thank first and foremost my parent, Heath Truda, for the immense support and

guidance I’ve been given, allowing me to complete this thesis. I would also like to thank my

supervisor, Dr Prasanna Egodawatta, for his patience and assistance in helping me along the way.

Finally, I would like to thank Lyn Morgain for the support she has provided in completing this paper.

Table of Contents

Abstract

1.4 Outline of the thesis ...................................................................................................................... 2

Chapter 2 URBAN STORMWATER QUALITY ............................................................................................ 3

2.1 Background ................................................................................................................................... 3

2.2 Primary urban stormwater pollutants .......................................................................................... 4

2.2.1 Litter ....................................................................................................................................... 4

2.2.2 Solids ...................................................................................................................................... 5

2.2.3 Water-borne pathogens......................................................................................................... 5

2.2.4 Nutrients ................................................................................................................................ 6

2.2.5 Toxicants ................................................................................................................................ 6

2.3 Pollutant processes ....................................................................................................................... 7

2.3.1 Build-up .................................................................................................................................. 7

2.3.2 Wash-off ................................................................................................................................. 8

2.4 Atmospheric deposition ................................................................................................................ 9

2.5 Atmospheric pollutant accumulation ........................................................................................... 9

2.5.1 Urban traffic ........................................................................................................................... 9

2.5.2 Rainfall and antecedent dry period ..................................................................................... 10

Chapter 3 URBAN TRANSPORT SYSTEMS .............................................................................................. 11

3.1 Introduction ................................................................................................................................ 11

3.2 Traffic related pollutants ............................................................................................................ 11

3.2.1 Solids and sediment ............................................................................................................. 11

3.2.2 Airborne particulate matter ................................................................................................. 12

3.2.3 Hydrocarbons ....................................................................................................................... 14

3.2.4 Heavy metals ........................................................................................................................ 15

3.3 Australia’s urban traffic ............................................................................................................... 16

3.4 Transport related catchment changes ........................................................................................ 17

3.5 Impacts of vehicle generated pollutants .................................................................................... 18

................................................................................................................................ ii

Chapter 1 INTRODUCTION ...................................................................................................................... 1

1.1 Background ................................................................................................................................... 1

1.2 Research problem ......................................................................................................................... 2

1.3 Aims and objectives ...................................................................................................................... 2

.................................................................................................................................................. ii

Acknowledgements

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3.5.1 Air ......................................................................................................................................... 18

3.5.2 Water ................................................................................................................................... 18

Chapter 4 CONCLUSION ........................................................................................................................ 20

Reference list ........................................................................................................................................ 21

List of Figures

Figure 1 - Impacts of urbanisation on hydrology (Adapted from Fletcher, Andrieu & Hamel 2013) ..... 3

Figure 2 - Pollutant build-up and wash-off characteristics of (a) source limited and (b) source

unlimited (adapted from Vaze and Chiew 2002) .................................................................................... 8

Figure 3 - Pollutants sources (filled circles = primary source, hollow circles = secondary source)

(Adapted from Marsalek 2011 - pending) ............................................................................................ 16

List of Tables

Table 1 - Vehicle emissions and sources ............................................................................................... 13

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Chapter 1 INTRODUCTION

1.1 Background

Water is one of the crucial substances that contribute to survival of society. Of the minute amount

that is available as fresh surface water-0.3%, increasing population numbers, transport types and

volume are affecting water availability and quality. Stormwater ends up in receiving waterways,

along with the pollutants it transports and absorbs. Traffic activities within the urban environment

are introducing large concentrations of pollutants and changing the characteristics of urban

catchments. Understanding stormwater pollutants and the impacts transport systems have is crucial

for water quality management.

Marsalek and Viklander (2010) have identified three main urban processes that effect stormwater:

atmospheric deposition, changes to catchment surfaces and land-use activities. The particulate

matter and dissolved chemicals in the atmosphere and on urban surfaces are categorised as

atmospheric deposition. These pollutants are the main sources of deposition on surfaces and air

pollution. For example, Marsalek and Viklander (2010) found that traffic activities contribute 30%

Copper, 20% Lead and Zinc in urban environment alongside atmospheric deposition. Catchment area

pollution sources come from the catchment surface materials. The catchment properties determine

the degree of soil erosion and water quality. The soil that’s eroded is a major source of total

suspended solids in urban stormwater. This process occurs naturally but urbanisation and poor land

management have produced an intensified speed of erosion. Urban land uses and activities produce

pollutant sources that can be attributed to the human activities on the land. More specifically,

activities related to residential land use, open spaces, traffic and road maintenance all contribute to

the overall poor quality of storm water.

Extensive studies have shown that traffic and related activities contribute significant amounts of

harmful pollution into the atmosphere and urban areas, acting to pollute the urban storm water

quality (Viklander 1998). Of most concern are the heavy metals, hydrocarbons, some bacteria and

the activities that are introducing them. Studies of urban stormwater pollution continue to attract

the attention of environmental organisations within the community, demanding better

understanding and the development of strategies to reduce pollution of urban stormwater.

Understanding transport systems and the pollutant impacts on urban stormwater quality is a crucial

step for developing these strategies.

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1.2 Research problem

Increasing vehicle usage and urban stormwater pollution is a growing concern for urban areas. For

example, according to Australian Bureau of Statistic (2012) the average annual traffic growth from

2007 to 2012 has been 2.2%. Alongside traffic growth, urbanisation turns the once heavily vegetated

and open land into residential, industrial and commercial hubs. This process is a fundamental step

for society but involves large scale clearing of land and introduction of new factors that can upset

the dynamic equilibrium that exists between the land and the urban water cycle. With the growth of

vehicle use and related enhancements to transport system infrastructure, the potential for

environmental harm increases. Traffic systems are one of the most significant sources of stormwater

pollutants and therefore exert substantial harm on urban aquatic environments. Stormwater

pollutant management is dependant on developing an understanding of the impacts of transport

activities in the urban environment.

The research problem is centred on the relationship between stormwater and traffic activity

emissions. This relationship is established through a number of processes such as direct and indirect

pollutant wash-off, build-up, atmospheric deposition on road surfaces and atmospheric pollutant

build-up. Additionally, the study is based on understanding the different pollutant types and the

potential harm they pose on human health. Urban storm water quality is reliant on finding a median

where human demand can be satisfied but with an underlying environmental goal.

1.3 Aims and objectives

The aim of this thesis is to identify and explore the underlying factors that correlate stormwater

quality with traffic systems in an urban environment. Investigating the contributors to urban storm

water quality decline and the form of traffic systems to provide an analysis of where the pollutants

are originating and how they’re impacting water bodies.

1.4 Outline of the thesis

This literature review is divided into four chapters, each chapter represents the relevant information

for each sub topic. Chapter 1 is an introduction to the thesis with the rational, aims and objectives.

The remaining chapters of this report establish a review of the literature for each topic. Chapter 2

introduces the complexities of urban stormwater, discussing the pollutant types and the processes

for entering urban stormwater. Chapter 3 presents a review of the traffic systems and it’s impact

within urban settings. Specifically focusing on transport pollutants, urban catchment changes and

the characteristics of Australia’s transport system. The impacts of transport pollutants on water and

air quality have also been discussed in chapter 3. Finally, chapter 4 concludes the investigation of

literature correlating urban stormwater declination with transport systems.

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Chapter 2 URBAN STORMWATER QUALITY

2.1 Background

The impact of transport systems on the environment and urban stormwater quality has drawn much

attention from researchers in recent years. The constant demand for new urbanised areas alongside

growing private and industrial vehicle use has caused the degradation of stormwater and

consequential environmental impacts. Transformation of natural and rural land into urban,

residential and industrial hubs leads to the dominance of impervious surfaces where once heavily

vegetated land existed. The impacts are evident in receiving waterways and aquatic habitats, with a

range of vehicle related pollutants transported in stormwater causing significant quality impacts

(Barry et al. 2004). The urban area characteristics modify the quantitative aspects of rainfall events,

which inturn further decreases the quality. These quantitative changes are primarily associated with

the introduction of impervious surfaces such as roads and paved paths. The increasing dominance of

impervious surfaces severely alters the hydrological cycle, illustrated below in figure 1.

Figure 1 - Impacts of urbanisation on hydrology (Adapted from Fletcher, Andrieu & Hamel 2013)

Fletcher, Andrieu & Hamel (2013) identified the primary post-development changes to the

hydrological cycle as follows:

Increased runoff volume;

Increased peak runoff;

Increased runoff velocity

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Decreased in infiltration;

Decreased time to peak flow;

Decreased base flow; and

Reduced time of concentration.

This research indicates that the quantitative alterations are causing changes to urban catchment

characteristics, primarily through the reduction of infiltration (Fletcher 2013). In doing so, the

frequency of runoff and pollutant wash-off is increased, thereby further impacting the quality of

stormwater (Karr 1991). Clearly, there are significant changes occurring in the quantitative and

qualitative features of urban catchments. Additionally, the increased pollutant sources related to

traffic and other anthropogenic activities are fundamentally influencing urban stormwater pollution

(Wei et al. 2009).

Stormwater pollutant sources have been classified as either point or non-point sources (USEPA

1997). Stormwater runoff is a non-point source pollutant, as the contaminants can only be traced to

the general area. As the urban water environment is a crucial component of urban areas,

stormwater quality is a significant environmental concern (Ahyerre et al. 1998). Therefore, an

understanding of the full range of pollutant types, sources and processes are crucial for

implementing effective management techniques.

2.2 Primary urban stormwater pollutants

Pollutants originate from a number of different sources, and can include visible solids and

microorganisms (EPA 2009). Regardless of where they originate they can all have different and

compounding effects on urban stormwater. The United States Environmental Protection Agency

(2007) has identified five categories of stormwater pollutants: litter, solids, pathogens, nutrients and

toxicants.

2.2.1 Litter

Sartor& Boyd (1972) identified that litter originates from three major sources; printed materials,

packaging materials and disposed materials, but the exact type of litter found in an area is related to

the user and their disposal method. When incorrectly disposed of, litter can enter waterways during

rain events and can be deposited in local drains and onto pavement. Sartor & Boyd (1972) further

noted that litter is not a major category of stormwater pollutants and that it could be effectively

removed with appropriate waste management practices. Although, the presence litter in waterways

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can significantly increase the turbidity and suspended solid content, over time degrading and further

increasing waters oxygen demand (Sartor & Boyd et al. 1972).

2.2.2 Solids

The USEPA (2012) defines totals solids (TS) as a combination of dissolved solids, suspended solids

and sediments in water. Solids are classified depending on their particle size and how they act in a

water body. Total dissolved solids (TDS) is the measurement of organic and inorganic substances

passing through a filter (0.45 µm OR 2 µm) in solution in water. The presence of TDS affects the

water balance of aquatic organisms. In low concentration (<300mg/litre) an organism will swell and

water will absorb into its cells. Higher concentrations (>500mg/litre) will affect an organism’s ability

to maintain cell density, increasing the difficulty to maintain its position in a water column. Total

suspended solids (TSS) refers to the portion of solids in a water sample that fail to pass through a

filter (0.45 µm OR 2 µm) and remain suspended in the water body. Suspended solids can act as

carriers of toxins, that attach to the suspended particles. These particles are transported and

deposited when the velocity of the carrying body decreases, but can remain in suspension for long

periods of time. Sediment is any particulate material that is transported by water or wind and

eventually deposited. The presence of sediment can affect the clarity of water and aesthetic

appearance. In high concentration it decreases the penetration of light through the surface of water,

thus slowing photosynthesis process and altering the temperature profile.

2.2.3 Water-borne pathogens

Pathogens are microorganisms that can cause disease. Some pathogens are naturally occurring but

others are transported into water bodies from a carrier, commonly in faecal waste and shedding

from humans or animals (OzCoast 2012). Once a pathogen leaves its host it has a limited survival

period before decaying. The Australian Drinking Water Guidelines (1996) identifies pathogens of

particular concern to be bacterial pathogens, protozoa, viruses and cyanobacteria.

Bacterial pathogens can occur naturally or are excreted. Naturally occurring bacteria may cause

disease growth in humans with compromised immunity. Excreted bacteria enters the environment

through faeces and can be spread through interaction with contaminated water.

Protozoa mostly occur naturally as aquatic organisms that have no significant effect on health. The

two forms of protozoa and can cause adverse health effects are enteric protozoa and select free-

living organisms. Enteric protozoa are introduced to the environment through faeces and from

dormant cysts, as part of the faecal-oral cycle (ADWG 1996). Free-living protozoa are a common

cause of infections in Australia. Spread through recreational and domestic activities, their presence

can cause naegleriafowleri and acanthamoeba.

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Viruses are the smallest of all pathogens, microscopically varying in shape and size. Essentially,

viruses are molecules that enter cells and replicate in them (ADWG 1996). Viruses of concern are

those, which replicate in human intestines and are excreted in large numbers. Cyanobacteria, also

known as blue-green algae, occur as single cells that migrate towards the surface of water in

response to light. They can damage liver and nerve cells in the form of hepatoxins and neurotoxins.

2.2.4 Nutrients

Nutrients are essential components for plant growth and development. Nutrients are naturally

occurring in the environment acquired through the contact of water with rocks and soils (WHO

2012). Contamination of urban water occurs through the chemicals introduced by industries,

agricultural activities, urbanisation and water treatment/distribution methods. Accumulation of

excessive nutrients can degrade stormwater quality and impact receiving waterways. The

overabundance of nutrients can pollute a water body with surplus algae, reducing dissolved oxygen

and suffocating aquatic life and increasing eutrophication (OzCoasts 2012).

2.2.5 Toxicants

Toxicants are chemical pollutants that can cause harm or impact living organisms at certain

concentrations (EPHC - 2011). In the context of urban stormwater, heavy metals and hydrocarbons

are of specific interest.

A) Heavy metals

Heavy metals are widespread within urban areas and find their way into polluting the stormwater

(Fairfax 2013). Heavy metals are a group of elements that exhibit metallic properties and have a high

atomic weight in concentrations that exceed Australian Guidelines (EPA SA 2012). Metals are

naturally occurring in the Earth's crust, they're released into hydrologic cycle and soils when

chemical and physical weathering of metamorphic and igneous rocks occurs. Furthermore, the

introduction of heavy metals through anthropogenic activities is common and can have significant

toxic effects on flora and fauna. The Department of Social, Environmental, Water, Population and

Communities (2012) attributed motor vehicles and domestic solid fuel burning as a significant

contributor to heavy metal pollution of urban stormwater. These compounds can be present in

dissolved or particulate form but their concentration in water can kill marine life and cause changes

to the abundance and diversity of habitats (EPA 2013).

B) Hydrocarbons

Hydrocarbons are organic compounds consisting entirely of hydrogen and carbon. The majority of

hydrocarbons found on earth occur naturally in crude oil, where decomposed organic matter

provides an abundance of carbon and hydrogen. However, anthropogenic activities have significant

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influence on the presence of hydrocarbons in the environment. Hydrocarbons are the principal

constituents of petroleum and natural gasses, as well as primary raw materials for the production of

plastics, fibres, industrial chemicals and so forth. By definition, hydrocarbons can be separated into

four groups, being alkane, alkene, alkynes and aromatic hydrocarbons (Shukla et al. 2012).

Hydrocarbon contamination can cause severe degradation to the environment and human life,

depending on their toxicity and physical nature (Abha & Singh 2012).

2.3 Pollutant processes

Pollutants accumulate and build-up on urban surfaces, they are then transported during rain events

into the waterways. Such pollutants then contaminate urban stormwater, especially when

concentrated in large quantities.

2.3.1 Build-up

This process involves the accumulation of pollutants over a period of time, both on pervious and

impervious surfaces. The introduction of large impervious areas acts as a base for pollutants to

concentrate. Additionally, anthropogenic activities in an area can affect pollutant build-up, such as

the density of population, land uses and daily traffic (Sartor & Boyd 1972). Natural weather

processes also contribute to accumulation of pollutants on surfaces, such as wind erosion,

deposition and accumulation on surfaces that build up over dry periods (Egodawatta 2009).

Vaze's (2001) investigation of physical processes of pollution build up indicated that pollutant

accumulation occurred relatively quickly after rain events and then reached a stage of redistribution

(Egodawatta 2007). Studies have shown that traffics systems and related activities contribute

significantly to the abundance of heavy metals in urban storm water (Vaze 2001). Furthermore,

Krieder (2010) found traffic systems pollutant contribution is also dependent on the volume of traffic,

traffic speeds, pavement texture and the vehicle spillages.

The build-up and wash-off processes are dependent on the urban and natural environment but they

work simultaneously under modelling conditions. Problems arise when considering whether there

are no pollutants present after a rainfall event of if pollutants remain on the surfaces. The complete

removal of pollutants from a rainfall event is considered source limited. Alternatively, where

pollutants accumulate and aren’t completely removed it’s termed unlimited or transport limited. As

a result, the wash-off behaviour is impacted by the availability of pollutants as well as the

characteristics of the area, represented in figure 2.

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2.3.2 Wash-off

Pollutant wash-off is the process that allows pollutants to runoff surfaces during rainfall events. The

wash-off process has two defined steps, the initial rainfall dissolution and detachment of pollutants

and the transportation of pollutants (Vaze, J 2001). Firstly, the raindrops land on surfaces and the

kinetic energy of the rain dislodges pollutants, which are then in suspension. There are two types of

pollutant wash-off characteristics, being pollutants that are lodged in the surface and those which

are soluble. Initial rainfall flows horizontally across surfaces, dissolving the soluble particles and

suspending them. As the kinetic energy of the rainfall increases, pollutants are dislodged

(Egodawatta & Gonnetilleke 2008). The pollutants can be both suspended in the water or roll across

the surfaces, depending on velocity of the water. The characteristics of the wash-off process can be

severely impacted by large areas of pollutant build-up, abundance of soluble and settle-able

pollutants and the functionality of traffic systems (Vaze et al. 2002). Vaze and Chiew (2002)

illustrated the hypothetical pollutant build-up process under two conditions (a) source limited and (b)

source unlimited, figure 2.

Figure 2 - Pollutant build-up and wash-off characteristics of (a) source limited and (b) source unlimited (adapted from Vaze and Chiew 2002)

In a source limited environment (figure 2a) the pollutant load starts at zero after the antecedent dry

period and a majority of pollutant load is washed off. The build-up of source unlimited pollutants

(figure 2b) allow some pollutants to remain after the rain event. This is occurs when pervious areas

are continuously supplying pollutant loads and they accumulate on the impervious surfaces. After a

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rain event not all pollutants are removed from the surface and the build-up of pollutants returns

over a short period of time. However, unlike the build-up process antecedent dry periods of time

have minimal effect on the availability of sediment on surfaces. Accordingly, Ming-Han & Barrett

(2008) found that the mean pollutant concentrations were decreasing the longer the antecedent dry

period lasted.

2.4 Atmospheric deposition Atmospheric deposition is the process where pollutants that are suspended in the atmosphere are

transferred back onto solid surfaces. Atmospheric deposition can be divided into two processes

referred to as dry deposition and wet deposition. Wet deposition is a process associated with rainfall,

while dry deposition occurs during antecedent dry periods. Research relating to atmospheric

deposition has been focused primarily on wet deposition and few investigations have identified the

importance of dry deposition and it’s relationship with stormwater quality (Sabin et al. 2005).

However, more recently studies have shown that dry deposition can have substantial impacts on

pollutants presence in urban stormwater, especially the concentration of heavy metals in

comparison to wet deposition (Morselli et al. 2003).

Sabin et al. (2005) noted that pollutant concentration in the atmosphere is directly proportional to

dry deposition and that densely urbanised areas had higher concentrations of atmospheric

pollutants. Therefore, the relationship between deposition fluxes and higher loading from

atmospheric deposition is relative to urban activities such as vehicular travel (Sabin et al. 2005). A

study in Los Angeles found that upwards of 60% of trace metal pollutant loads in stormwater was a

result of atmospheric deposition. Luo (2001) found that dry deposition depends on antecedent dry

periods, atmospheric pollutant load, temperature and relative humidity. Wet deposition depends on

two characteristics, rainfall duration and intensity (Xiatong et al. 2012). Huston et al. (2009) noted

that solids mass is a predominant feature of wet deposition when compared to dry deposition.

2.5 Atmospheric pollutant accumulation The accumulation of atmospheric pollutants due to transport activities is an area of major concern,

not only for the impacts on urban stormwater but also air pollution (Sabin et al 2005). Atmospheric

pollutant build-up was discussed earlier in Chapter 2 but there are two factors that influence the

pollutant build-up characteristics. Sabin et al. (2005) noted that rainfall and antecedent dry periods

and urban traffic conditions are the primary factors that influence pollutant build-up.

2.5.1 Urban traffic

Australia’s current urban traffic conditions and estimations for future growth have been discussed in

further detail in chapter 3. However, it’s noted that Australia has experienced sizeable growth in

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urban vehicle usage and predictions from the Bureau of Infrastructure, Transport, and Regional

Economics (BITRE) estimate this growth will continue until a state of saturation is reached. This

increase contributes significantly to the presence of pollutants in urban atmosphere and in turn

receiving waterways (Colvile et al. 2001). Vehicle emissions are linked with traffic congestion, traffic

flow, vehicle type, vehicle age, grade of the road and the fuel consumption (EPASGV 1999). A study

complete by the Australian Academy of Technological Sciences and Engineering (1997) determined

that traffic volume capacity is a crucial factor that impacts the presence of volatile organic

compounds. Furthermore, it was noted that deterioration of a vehicle through its usage life can

increase an individual vehicles emission by up to ten times more than that of a typical new vehicle

(AATSE 1997).

Pohjola et al (2002) noted that climatic conditions influence the vehicle induced atmospheric

particulate matter. The findings indicated that the concentration of atmospheric particulate matter

were higher during the spring months. Also, Karer et al. (2006) concluded that traffic sources are

responsible for the majority of pollutants in atmospheric deposition. Additionally, Motallebi et al.

(2003) noted that suspended particulate matter in the atmosphere can be traced to heavy duty

traffic concentrations. Therefore, traffic related pollutant sources for build-up characteristics are

fundamentally based on traffic volumes and heavy traffic.

2.5.2 Rainfall and antecedent dry period

Rainfall and antecedent dry periods influence airborne particulate mass. Raindrops absorb

particulates that are then removed during rainfall events, thereby reducing the atmospheric

particulate matter concentration (Ravindra et al. 2003). Sabin et al. (2005) noted that atmospheric

pollutant concentration is directly proportional to dry depositions and that higher populated urban

areas would be expected to have high deposition. Therefore, it can be concluded that after rainfall

events, the concentration of atmospheric particulate matter is low and that dry deposition depends

on the time between rainfall events.

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Chapter 3 URBAN TRANSPORT SYSTEMS

3.1 Introduction

Chapter 2 outlined the variety of pollutants that are impacting stormwater quality such as litter,

solids, pathogens and toxicants. Chapter 2 also discusses the pollutant processes, being build-up and

wash-off and the variables that impact these processes. Further developing the discussion, chapter 3

focuses on urban transport systems and the transport related activities that introduce pollutants.

Elaborating on the impacts of transport pollutants on waterways, the methods by which they enter

the waterways and what vehicle related activities are generating them. Also discussed are the

current traffic conditions for urban areas within Australia, predictions for future traffic growth and

the transport related catchment changes. Motorised methods of transport are fundamental in a

modern functioning society, allowing access and mobility for every day living. Urban Transport

systems face major challenges in the near future due to the continuous growth of urban population,

private vehicle ownership, congestion and the fragility of public transportation systems. Inadequate

or poorly functioning transport systems may become a binding constraint on both economic growth

and social development, along with the increased negative impacts on health and the environment

3.2 Traffic related pollutants

As urban areas expand they become engines of economic growth, managing the relationship

between transport system use and the environmental issues is a major concern facing society (WCTR

2004). Sartor and Boyd (1972) identified solids and sediment, hydrocarbons, heavy metals and

airborne particulate matter as the major pollutants produced as a result of traffic related activities.

Additionally, transport pollutants are influenced by the age of the vehicle, traffic congestion, age of

the road and the road geometry (North 2006). These are all matters influenced by public policy and

demand created by the community and industries.

3.2.1 Solids and sediment

Road deposited sediment (RDS) refers to the accretion of particulate matter on street surfaces.

Sartor et al. (1974) concluded that driving style, topography, road usage and vehicle condition

heavily impact sediments presence in urban environments. For example, Dunne & Reid (1984) found

that a commonly used road segment contributed one hundred and thirty times as much sediment as

that of abandoned road segment. Higher levels of traffic on road segments detrimentally increase

the sediment load because loose material is deposited and carried away in rain events, which is then

replenished after the event by continuous traffic presence. Additionally, numerous studies have

shown that street sediment is composed of a wide range of particle sizes (Robinson & Taylor 2003;

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Brinkmann & Shaften 1985). Vehicles re-suspends particles within close proximity to the road, due

to induced turbulence and vehicle function (Sartor et al. 1974).

Barry et al. (2004) and Brodie and Young (2006) noted that the major contributor to suspended

particles in urban catchments is road runoff. Robin et al. (2008) conducted a study measuring source

contribution to the emission of airborne PM2.5 in Canada, finding that road sediment contributed

eighteen percent, while vehicle emissions only contributed one percent. Egodawatta (2007) noted

that higher fraction of fine particles, which are less than 100 μm, remain in suspension for longer

time. Therefore, there is higher likelihood that these particles will reach receiving waterways. Ellis

and Revitt (1982) determined that fine sediment contained higher concentrations of metals

pollutants such as zinc, copper and lead with particle fractions smaller than 250 μm. Vehicular

activity sources of sediment include vehicle exhaust emissions, vehicle tyre and body wear, road

salts, road paint and brake-lining material (Kevin & Philip 2009). Kennedy (2002) found that tires

and brake pads from New Zealand vehicles emitted zinc and copper concentrations equal to and

exceeding seventy and five times the concentration of uncontaminated surface soil, respectively

(Roberts et al. 1996).

Another important aspect impacting the wash-off of solids is first flush behaviour. The South

Australian Environmental Protection Agency (2009) defines first flush as initial runoff containing high

concentration of pollutants. Wong et al. (2000) confirmed that first flush characteristics occur in over

60% of runoff events. Furthermore, suspended solids are capable of absorbing heavy metals and

hydrocarbons in stormwater (Hamilton et al. 1984). This is due to the electrostatic attraction

between suspended solids and other pollutants.

3.2.2 Airborne particulate matter

Airborne particulate matter is a complex mixture of solid and liquid particles. Consisting of organic

and inorganic components, particulate matter can be emitted from natural and anthropogenic

activities and are defined according to size of the particles, which make up a particular fraction.

Particles PM10 (diameter <10m) and PM2.5 (diameter <2.5m) are particularly concerning due to

their impacts on human health when inhaled.

Motor vehicle emissions are rated among the major contributors to fine particle concentrations in

the urban atmosphere, from their indirect and direct contributions to ambient particulate matter

levels (Schauer et al. 1996; Kleeman et al. 2000). The direct contributions are emitted from vehicles

sources such as exhaust, mechanical wear of tyres and brakes, the ejection of particles from

pavement, unpaved road shoulders and the re-suspension of particles (Mulawa et al. 1997; Rogge et

al. 1993; Sternbeck et al.2002). Whilst the indirect contribution originates from the emission of both

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organic and inorganic reactive gases, through the process of atmospheric transformation they form

secondary particulate matter (Puxbaum et al. 2000).

Puxbaum (2000) reported that particles emitted from motor vehicles consist of mineral oxides, soot,

water, variety of metals and organic compounds. The composition of the emissions is dependant on

the contribution of individual emission sources generated from combustion and non-tailpipe

emissions. During fuel combustion emissions are generated and released through the vehicles

tailpipe into the atmosphere (Rogge et al. 1993). These emissions are predominantly composed of

elemental carbon and organic carbon. Non-tailpipe emissions are the portion of particulate matter

that enters the atmosphere through transport related activities other than combustion, such as the

wearing of tyres, re-suspension of road dust and the abrasion of pavement (Cadle et al. 1999; Rogge

et al. 1993; Sternbeck et al.2002). Sternbeck et al. (2002) described brake and tyres wear as a

significant contributor to trace metals found in emissions in the urban atmosphere from motor

vehicles. Further emissions generated from transport systems and related activities and their

emission sources can be found in table 1.

Table 1 - Vehicle emissions and sources

Emission Emission source

Particulate matter (PM) Indirect and direct activities

Organic carbon (OC) Unburned hydrocarbons; road dust; diesel fuel (Rogge et al. (1993))

Elemental carbon (EC) Incomplete combustion of fuels (Sagebiel et al. (1997))

SO42- Fuels containing sulphur.

Cl- & Na+ Salts used as de-icing agents (Lough et al (2005))

K+ Re-suspension of road dust (Lough et al. (2005))

Si & Al Re-suspension of road dust; street abrasion; pavement wear (Kupiainen et al (2005))

Fe & Ca & Mg Tyre and break wear; motor oil and additives; re-suspension of road dust particles (Garg et al (2000))

Mn Brake wear; re-suspension of road dust (Allen et al (2001))

Zn Brake wear; tyre wear; motor oil (Garg et al. (2000))

Ba Brake wear; tyre wear (Garg et al. (2000))

Ti Brake wear; pavement wear; re-suspension of road dust (Garg et al. (2000))

Pb Brake and tire wear; fuel and motor oil additives; re-suspension of road dust (Westerlund et al. (2002))

Cu Break wear; tyre wear; wheel bearing; fuel and motor oil additives.

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Sb Brake wear; tyre wear; motor oil additives (Garg et al. (2000))

Garg (2000) determined, through elemental analysis, that the main proportion of PM mass was

accounted for by phosphorus, sulphur, silicon, chlorine along with the metallic species and only a

fraction being carbonaceous material. Furthermore, particles from pavement wear were determined

to be predominantly (90%) minerals with a small fraction of carbonaceous elements originating from

tyres and bitumen (Garg et al. 2000). Another important emission is the dust particles suspended in

the air, which consist of complex tailpipe emissions and particles generated through non-

combustion related activities. These particles can settle onto road surfaces and be re-suspended into

the atmosphere by vehicles or winds (Moosmiiller et al. 1998) but their composition is highly

variable.

3.2.3 Hydrocarbons

As discussed in chapter 2, hydrocarbons are a broad family of chemical compounds consisting of

hydrogen and carbon. They are the unavoidable by-products of combustion, specifically incomplete

combustion processes. From the four different forms of hydrocarbons, polycyclic aromatic

hydrocarbons (PAHs) are of most interest when considering transport pollution. Bjorseth (1985)

concluded that motor vehicles and related activities attribute approximately one-third of PAH

emissions in the United States.

Polycyclic aromatic hydrocarbons are potent atmospheric pollutants formed from organic

compounds that are generated by traffic activities (Yigitcanla 2012). They are of particular interest

because of their semi-volatile toxicity and consistent presence in urban stormwater (Stein et al.

2006). The United States Environmental Protection Agency (1999) identified sixteen PAHs, out of

the several hundreds generated from traffic activities, as of concern due to their toxic impacts on

aquatic flora and fauna. The sixteen PAHs include low molecular weight compounds such as

Acenaphthene (3 rings) and higher molecular weight compounds such as Benzopyrene (5 rings). Low

molecular weight hydrocarbons indicate that crude and refined oils are the primary sources (Fraser

et al. 2003), whilst the presence of higher molecular weight hydrocarbons implies that combustion

processes are the primary source (Brown and Maher 1992).

The main transport related activities that are generating PAHs are the release of petroleum into the

atmosphere, motor vehicles exhausts, lubricating oil and the combustion of fossil fuels (Soclo et al.

2002). The primary source of PAHs being deposited on roads in urban areas is the incomplete

combustion of diesel fuel. An investigation undertaken by Tancell & William (1989; 1995) concluded

that pyrosynthesis of two and three ringed PAHs and lubricating oils can affect the emission of five-

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ring PAHs and the combustion process. The use of petroleum-based products is detrimental for the

functionality of transport systems, which results in the widespread presence of hydrocarbons in

urban areas. Furthermore, the presence of PAHs can be considerably impacted by the occurrence of

antecedent dry periods (Stein et al. 2006). During the dry periods PAHs are deposited onto surfaces

as atmospheric deposition and when a rain event occurs they’re transported into urban waterways.

Therefore, the impacts of PAHs are heavily related to pollution availability and transport capacity of

runoff, which in turn is controlled by the rainfall characteristics.

3.2.4 Heavy metals

Heavy metals have been identified as a significant environmental threat due to their toxicity in water.

The toxicity of heavy metals is primarily determined from the pH level of the metal, as toxicity

increases with pH whilst lower pH values represent higher solubility of the metals (EPA 2013).

Further extensive studies indicate that transport and related activities produce significant quantities

of heavy metals in urban areas (Viklander 1998). Fuchs et al. (2006) estimated that one-third of

heavy metals in urban stormwater are produced from traffic systems and their components. From

the dynamic traffic systems, the heavy metals of significance and their sources from traffic activities

is shown in Figure 3. The primary sources of metals and other constituents were identified to be

cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), zinc (Zn), nickel (Ni) and lead (Pb) (Marsalek &

Viklander 2010). It was further noted that in colder climates road maintenance is undertaken using

salt. This would be done to melt snow and ice for clearing purposes, further contributing to the toxic

levels of pollutants in urban stormwater associated with traffic activities.

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Figure 3 - Pollutants sources (filled circles = primary source, hollow circles = secondary source) (Adapted from Marsalek

2011 - pending)

Ndiokwere (1984) further illustrated the presence of heavy metals due to traffic activities, through

measuring their quantities on vegetation at varying distances from highways. Ndiokwere’s study

determined that the proximity to the highway directly impacts the concentration of heavy metals

and consequently the their concentrations in stormwater. The presence of heavy metals in urban

stormwater can be in particulate or dissolved form. The finer particles (<43 m) on urban roads only

account for a small portion of sediment mass (5.9%), whereas they contain half of the heavy metal

concentration (Sartor & Boyd 1972).

3.3 Australia’s urban traffic Australia’s traffic growth has been a dominant feature of the ever-developing continent. As traffic

growth continues, understanding Australia’s urban traffic characteristics and the related hazards is

paramount. The quality of urban stormwater is a key element of these impacts. The Bureau of

Infrastructure, Transport, and Regional Economics (BITRE) of Australia has produced a

comprehensive report analysing the different patterns of traffic growth in Australia’s states and

capital cities (BITRE 2012).

According to BITRE (2012) rapid traffic growth per capita occurred throughout the seventies and

since has consistently slowed, with many states approaching saturation. The term saturation refers

Page | 17

to the vehicles per capita, it represents the exponential growth in population and vehicle usage. A

more accurate depiction of Australia’s traffic patterns comes from vehicle kilometres travelled (VKT)

annually, which is recognised as the influential factor for states and territories traffic understanding.

The vehicle kilometres travelled per person annually has shown exponential increase up to 1978,

peaking at 8,000 vkt, and since the constant slowing towards saturation in 2009 at the 10,000 VKT

mark per person. Forecasts estimate that Australia’s vehicle kilometres travelled will increase by

15%, from 55 billion vkt per quarter in 2011 to 65 billion vkt per quarter in 2020, if the current

conditions remain the same (BITRE 2012).

Furthermore, the Bureau of Infrastructure Transport and Regional Economics (BTRE) have outlined

exact measurements for urban traffic growth within Australia. In Australia’s urban areas the total

travel has increased ten fold over the last sixty years (BTRE 2006). The majority of this growth,

approximately 90%, is attributed to privately owned light commercial vehicles. Reporting that there

were approximately 13.9 million motor vehicles in Australia for the year 2005 which travelled a total

of 206 billion kilometres. However, estimations show that commercial vehicle traffic is forecast to

increase more than private car traffic, at 3.5% and 1.7% per annum respectively.

Australia’s traffic systems have undergone exponential growth post World War Two and the pattern

of growth in traffic per person will continue on the trend towards saturation. The automobile and

commercial vehicles have multiplied, as mobility has increasingly become a feature of contemporary

living. Based on current and predicted traffic increases, it’s evident that Australia’s urban areas will

continue to experience further growth in VKT, creating internal congestion on road with increasing

numbers of vehicles. The impact on urban stormwater of current traffic conditions underlines the

essential requirement for Australia to implement measures reducing traffics systems pollutant

output.

3.4 Transport related catchment changes Transport systems influence on urban stormwater quality is not fully explained by direct transport

pollution, there are also changes made to the characteristics of urban catchments. Urban catchment

changes can be categorised by land uses, typically divided into residential, commercial and industrial

areas. In this case, the introduction of impervious surfaces required for vehicular travel is the

fundamental factor affecting stormwater quality (Brabec et al. 2002).

Arnold and Gibbons (1996) noted that there was a relationship between decreased water quality in

receiving waterways and increased impervious surfaces. Furthermore, Mallin et al. (2008) noted a

correlation between high phosphorus concentration and increased impervious surface percentage.

Impervious surfaces have reduced surface roughness, compared with pervious surfaces, this allows

Page | 18

pollutants to wash-off in a rainfall event and be transported into receiving waters. Dietz and Clausen

(2008) noted that increases in impervious surface percentage can significantly amplify the

concentrations of total nitrogen and total phosphorus in stormwater runoff. The research findings

conclusively agree that impervious surface area is a significant component that needs to be given

consideration in quality management for urban stormwater.

3.5 Impacts of vehicle generated pollutants

Vehicle generated pollutants can be primarily classified as either water or air pollutions and can be

categorised, for most instances, as either gases or particulate matter (Chu et al. 2008). The

environmental impacts caused by these pollutants are heavily dependant on the traffic

characteristics, but primarily traffic volume is the controlling factor (Lim et al. 2005). Air and water

pollution caused by traffic activities is an important issue, especially in the urban context (Chu et al.

2008; Lim et al. 2005; Mallim et al. 2008). The particulate fraction of traffic-generated pollutants are

deposited directly onto roads and nearby surfaces, whilst the gaseous fraction of pollutants

accumulate in the atmosphere during antecedent dry periods (Lim et al. 2005).

3.5.1 Air

A number of recent studies have focused on investigating major air pollutants generated from

vehicle emissions (Lim et al. 2005; Chu et al. 2008). Delfino (2002) identified heavy metals,

hydrocarbons, ozone, nitrogen oxide, carbon monoxide, sulfur dioxide and total suspended

particulate matter as the primary pollutants. It’s been concluded that a number of these pollutants

pose potential health risks for those within the locality (Ghose et al. 2005). For example, Ghose et al.

(2005) noted that the main sources of ultra fine particles in the urban environment, which are

associated with causing lung disease, are diesel-powered vehicles. Furthermore, Kunzili et al (2000)

linked birth defects, child asthma, allergic reaction and cardiovascular disease with elevated levels of

air pollution and that exposure to poor quality air can aggravate existing health problems. The

degradation of air quality and the presence of fine particles could result in inhalation and deposition

in the respiratory system. As a result, the traffic generated pollutants that are suspended in the

atmosphere present serious environmental and health concerns for urban areas.

3.5.2 Water

As discussed earlier in chapter 3, transport related pollutants accumulate on road surface and are

generally a result of fuel leakage, wearing of tyres, exhaust emissions, vehicle degradation and

atmospheric deposition (Sartor and Boyd 1972). The quality of receiving waterways is heavily

dependant on urban stormwater acting as a carrier of pollutants (USEPA 1997). The high

concentrations of pollutants from transport activities are degrading urban stormwater quality and

Page | 19

as a result impacting the quality of receiving waterways (Lim et al. 2005). Additionally, some

pollutants float on top of water, creating an unhealthy film and during refuelling gas vapour is

emitted into the atmosphere where it mixes with rain (Sartor and Boyd 1972).

Alongside the degradation of water quality, pollutants in water bodies pose threats to human and

aquatic health. Toxicants such as heavy metals and hydrocarbons can impact aquatic animals life

cycle and ability to defend them self (USEPA 2007). Some aquatic plants have been recognised to

absorb portions of heavy metal content in waterways, these plants are then consumed by predators

and potentially end up as a human food source (Pertovic et al. 1999). Davis et al. (2001) noted that

heavy metals cannot be chemically transformed or destroyed. The main risk for human health is due

to consumption of pollutants, which are associated with cancerous diseases and weakened immune

systems.

Page | 20

Chapter 4 CONCLUSION This dissertation has been focused on summarising the important findings correlating the decline in

urban stormwater quality with transport systems and related activities. This review has primarily

focused on stormwater pollution as an aspect of the urban transport environment, with a thorough

investigation of transport generated pollutants in urban stormwater and their transport methods.

It’s evident that urban traffic is one of the primary sources of pollutants to urban stormwater. With

the attribution of vehicle-generated pollutants such as sediment, airborne particulate matter, heavy

metals and hydrocarbons, and changes to urban catchment characteristics, transport systems are

heavily influencing the quality of urban stormwater. Traffic generated pollutants are either directly

deposited onto the ground surfaces or suspended in the atmosphere until they’re deposited as wet

or dry deposition. As a result, stormwater transports these pollutants into receiving waterways,

creating significant quality problems. The quality impacts are enhanced as a result of larger and

faster flowing stormwater runoff, through the introduction of impervious surfaces.

Vehicles have been shown to generate significant amount of pollutants that are entering the urban

environment, both on surfaces and in the atmosphere. Polycyclic aromatic hydrocarbons and heavy

metals are of most concern due to their toxicity and impacts on receiving waterways. Additionally,

solids have been found to facilitate the transport of heavy metal and hydrocarbons, as they link to

particulates in air and build-up pollution. The accumulation processes of pollutants also play an

important role in stormwater quality, but the dynamic relationship between atmosphere and

changing urban surfaces highlights the lack of knowledge on this complex topic.

From the review of literature, it’s evident that there are a number of transport components that

attribute to the decline in urban stormwater. Understanding the influence transport systems have

on urban stormwater quality is a fundamental step towards developing appropriate mitigation

measures and quality management. With an understanding of pollutant generation, accumulation

and transportation, appropriate steps will need to be taken to reduce the impact transport systems

have on urban stormwater quality decline.

.

Page | 21

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