Geoffrey John Hunter, watershed@bigpond.com
Engineering Coordinator: Stormwater, Penrith City Council, Penrith NSW Australia
Stormwater runoff is responsible for transporting many of the pollutants, which are degrading our waterways. The control of stormwater pollution is an integral part of the Stormwater Management
Plans that Councils in NSW have prepared in response to a Direction issued under Section 12 of the Protection of the Environment Administration Act, 1991 . Structural stormwater quality controls play an important role in meeting the pollution control objectives established in these plans. This presentation will examine many of the proprietary stormwater quality improvement devices
(SQIDS) available on the market and investigate the issues that should be considered when selecting a particular proprietary device to control stormwater pollution. Particular attention will be given to issues regarding the location of the devices within the catchment, their operation and maintenance. Three case studies in western Sydney and one from the Central Coast of NSW, will be used as examples of the real costs associated with stormwater pollution control.
“Urban runoff pollution results from numerous sources. It is the result of rainfall and snow melt that becomes contaminated as it travels through the atmosphere, along the land surface, and makes its way to a water body.
Urban runoff can enter a water body from an identifiable point source, such as a separate storm sewer outfall or a combined sewer overflow. It can also flow directly into a water body without an easily identifiable point of entry. Regardless of the point of entry, urban runoff has diffuse origins and, therefore, is difficult to manage and control.” (USEPA
1993)
Urban runoff management in its broadest and most comprehensive form involves controlling both the quantity and quality of the runoff.
Effects of Urbanisation on Stormwater
Quantity
As a catchment urbanises, components of its natural drainage system (depression storage, infiltration capacity, wetlands, floodplains, etc) may be removed or altered. Urban assets and infrastructure eliminate vegetation and compact the soil. The catchment becomes more impervious and rainfall does not infiltrate as readily, resulting in increased runoff, runoff velocities and peak flows. See
Figure 1 for the relationship between runoff percentage and imperviousness. Traditional drainage practices have focused on removing the water from the urban areas as quickly as possible to prevent flooding. This approach does not take into account:


off-site damage from accelerated flow;

increased downstream flooding;

water pollution;

deposition of sediments;

floodplain and channel erosion;

wildlife habitat and natural vegetation; and

loss of a freshwater resource.
Figure 1 Changes in Runoff Flows
Resulting from Paved Surfaces
(Source: Livingston and McCarron, 1992)
To combat the increased runoff, velocities and more frequent flood events, stormwater management now has to accommodate both water quantity and quality controls. Many of these incorporate permanent at source controls (on-site detention, grass swales, pocket wetlands, infiltration basins, bioretention, minimisation of impervious surfaces) and/or regional control facilities
(large retardation basins and wetlands). In combination these practices have the effect of slowing the runoff, creating more site storage, enhancing infiltration potential, reducing the flood peaks and mitigating the impacts of the smaller recurrence interval storms. The result is a runoff hydrograph from an urbanised catchment that more closely resembles the hydrograph from the undisturbed catchment.
Effects of Urbanisation on Stormwater
Quality
Land use directly affects water quality. In an undeveloped area, the natural physical, chemical, and biological processes interact to recycle most of the materials found in stormwater. As human land use intensifies, these natural processes are disrupted and our everyday activities add materials to the land surface. Leaves, animal wastes, oil, greases, heavy metals, fertilizers, pesticides and other materials are washed off by rainfall and are carried by stormwater to our wetlands, lakes, rivers and bays."
(FDEP 1993) The relationship between pollutant concentrations and Imperviousness are shown in Table 1.
No matter how appropriate the Best
Management Practice (BMP) they can only accomplish significant levels of non-point source pollutant load reductions if they are properly designed and maintained.
Practices to mitigate the impacts of stormwater pollutants aim to prevent their entrainment and/or to remove them from the runoff as soon as possible.
Anolyte
TSS
Phosphate
TKN
BOD
5
COD
F.coliform
Iron
Lead
Zinc
5% Imp 50% Imp 90% Imp
80
0.04
0.52
9
26
9
0.36
0.004
0.0008
212
0.20
1.10
14
65
28
0.48
0.03
0.09
123
0.20
1.40
19
69
31
0.58
0.06
0.17
Table 1 Pollutant Concentrations as a
Function of Imperviousness (mean

concentrations in mg/L) (Adapted from
Chang et al, 1990)
Filtration practices (sand filters, bio-filtration, porous pavements) have proved efficient in the USA, especially when used high in the catchment eg. carparks, commercial and industrial sites. Infiltration systems have proved successful where soils are permeable and groundwater contamination and/or its proximity to the infiltration system is not an issue. Strict adherence to soil erosion and sediment control plans, during construction, has greatly reduced the amount of sediment entering the receiving waters. These practices have been well documented in the literature but their consistent enforcement throughout the catchment is necessary if they are to be effective.
Pollutants commonly found in urban stormwater are described in Table 2, which has been adapted from the Victorian
Stormwater Committee, 1999. Source control should be the central theme of stormwater management. BMPs refer to those practices that are used for a given set of conditions to achieve satisfactory water quantity and quality enhancement at a minimum cost (Livingston and McCarron,
1992). They can be physical, structural, or management practices that, when used singly or in combination, prevent or reduce pollution of water
For stormwater management to be effective,
BMPs must be applied throughout the watershed. Nonetheless, the increase in pollutant loads from urban areas is typically so large that, even with the use of BMPs, it is unlikely that pollutant loads will be reduced to pre-development conditions. "Results suggest, that appropriately designed and properly sited BMPs can provide some mitigation of stormwater impacts on stream communities. However, the resulting communities differ greatly from those in undeveloped watersheds and reflect a fundamental alteration in stream biotic diversity." (Jones et al, 1996).
Pollutant
Sediment
Urban Source
Soil erosion & car washing
Pavement and vehicle wear
Atmospheric deposition
Spillage/illegal discharges
Organic matter (leaves, grass)
Weathering of bldgs/structures
Nutrients
O
2
Demanding
Substances
Organic matter decay
Atmospheric deposition
Sewer overflows/septic tanks
Animal/bird faeces
Spillage/illegal discharges pH (acidity)
Organic matter (leaves, grass)
Fertilisers
Sewer overflows/septic tanks
Animal/bird faeces
Detergents (car washing)
Atmospheric deposition
Spillage/illegal discharges
Microorganisms
Atmospheric deposition
Spillage/illegal discharges
Organic matter decay
Erosion of roofing material
Animal/bird faeces
Sewer overflows/septic tanks
Organic matter decay
Toxic Organics Pesticides and herbicides
Spillage/illegal discharges
Sewer overflows/septic tanks
Heavy Metals
Gross
Pollutants
(litter & debris)
Atmospheric deposition
Vehicle wear
Sewer overflows/septic tanks
Weathering of bldgs/structures
Spillage/illegal discharges
Pedestrians and vehicles
Waste collection systems
Leaf-fall and lawn clippings
Spills and accidents
Oils and
Surfactants
Increased
Water Temp.
Asphalt pavements
Spillage/illegal discharges
Leaks from motor vehicles
Car washing & organic matter
Runoff from impervious areas
Removal of riparian vegetation
Table 2 Pollutants in Urban Stormwater

Before a particular BMP or series of BMPs can be determined, the land take, catchment area, objectives for the receiving waters, soil and groundwater requirements all have to be considered and investigated, and the preferred practice adopted that best fits with these constraints.
For the purposes of this paper, structural
SQIDs will be classified as:
At Source Control — located as close to the source of pollution as possible;
In-Line Control — constructed as a structural member and an integral part of the drainage system;
End of Line Control — situated as the last structural component of the formal drainage system.
Costs for each device can be derived from
DPWS, 2001 (supply only) or by contacting the supplier directly. Installation costs are site specific and dependent on the nature of the soil (rock, shale, clay, sand etc) as well as access to the site, and can result in the installation costs being 2 to 3 times the supply cost. Contact details for each manufacturer are contained in DPWS, 2001.
At Source Controls

Pit Inserts – are installed as an integral component of the gully pit (not within the pipeline) and screen the pollutants out of the runoff as it enters the pit. They are generally located directly beneath the grate and/or the lintel.
Contacts:
Dencal: (03) 9801 3057
Enviropod: (02) 9807 7477
Ecosol RSF100: (02) 9560 2802
Pit Bull: (02) 4975 3012
Pratten Insert: 0419 419 478
Prime Composites: (02) 9525 6515

Lintel and Grate Covers (Excerpts) – are external to the grate and/or lintel of the pit and filter the runoff before it enters the pit. They are intentionally placed across the pit opening and can be used to prevent the runoff entering the pit
(especially good for construction sites).
Durham: (02) 4587 7011
Pit Bull: (02) 4975 3012

Filtration Media – can be used as an effective treatment for fine particulates and dissolved pollutants. Bio-retention and sand filters can be incorporated into the landscaping on small impervious sites such as carparks. The StormFilter™ utilises cartridges containing media within a gully pit to filter the runoff.
Beresford Concrete Products:(02) 4392 3300
Ingal Civil Products: (02) 9710 5555
In Line Controls

Ecosol RSF 4000 & RSF 6000 GPTs – are underground wet vault traps that rely on a hydraulic weir to divert the runoff into a deep separation chamber where it is filtered through a 3 mm mesh screen before flowing into a parallel by-pass flume. Water diverted into the separation chamber is forced into the bypass flume through a vertical riser, which creates a slight backwater situation and forms the hydraulic weir. Intended to trap gross pollutants and coarse sediment.
Contact: (02) 9560 2802

Rocla Downstream Defender – oil and grit separator consisting of three concentric cylinders with a separation chamber beneath. Stormwater enters the system through the outer cylinder, which has a sloping base opening into the separation chamber. The heavier particles separate out and are retained as the stormwater and remaining suspended solids are diverted into the central cylinder where they slowly rise and overflow into the second cylinder, which is connected to the outlet pipe. Cleaning

is by eduction and must be carried out before the captured material packs down hard. Generally supplied as a pre-cast unit
Contact: 131 004 (Toll Free)
 Rocla CleansAll® - an underground gross pollutant and sediment trap that utilises a screened basket to separate the gross pollutants followed by a deeper sump for silt retention. Baskets must be cleaned at 50% full to prevent an unacceptable increase in energy levels upstream of the device. Generally supplied as a pre-cast unit. Cleaned by lifting the baskets out and emptying them into a waiting truck. Stored water and fine sediments need to be pumped or sucked into an appropriate containment vessel for disposal.
Contact: 131 004 (Toll Free)

Stormwater Rubbish Trap – a gross pollutant and coarse sediment trap, which can be modified to incorporate an Atlantis
Drainage Cell to provide fine particulate separation. This device incorporates a series of cages across an underground rectangular chamber to capture positively buoyant pollutants and drop out coarse sediment. Once through the cages the runoff is detained by, and filtered through the Atlantis Drainage Cell before discharging to the outlet pipe. Access into the underground chambers is required for cleaning, which entails removal of the cages and evacuation of the sediment.
Contact: (02) 9389 0580

Continuous Deflective Separation – better known b y its acronym CDS™
Technologies. Gross pollutants and sediments are separated from stormwater by centrifugal forces, which also prevents the screen from becoming blocked by debris and other items such as plastic bags. The mesh screen is made of expanded metal and can be supplied in stainless steel if required. The circular motion of the water cleans the screen and helps maintain the design treatable flow rate throughout the storm. Pollutants are stored wet, in a sediment sump that may be up to 7 m deep depending on the size of the catchment being treated.
Baskets can be fitted to smaller units to facilitate cleaning. Smaller units can be supplied as fibreglass pre-cast units whereas the larger devices are generally cast in-situ. Captured material should not be allowed to build up to the level of the screen. Cleaning is best carried out with a HIAB “grab bucket”, but this does not provide for decanting of the stored water, which requires additional equipment to educt or pump it into an appropriately sealed storage unit for disposal.
Contact: (02) 9807 7477

Humegard ™ - a gross pollutant and coarse sediment trap designed to be installed within stormwater drainage systems constrained by flat grades and low head. They remove gross pollutants from the flow by means of a boom and a holding chamber. The boom creates only a marginal increase in the head loss across the structure (k

0.2). Trapped debris is stored wet in a separation chamber and sump that are located offline from the pipeline. High velocities
(>1.5 m/s) can cause a reduction in the efficiency of the device. Restricted access into the holding chamber can be an issue during cleaning and maintenance but this can be overcome with the installation of additional access lids. Can be cast in situ or supplied in modular pre-cast units to be assembled on site.
Contact: (02) 9832 5555
 Humeceptor™ – developed in Canada where it is known as a Stormceptor, it is a pre-cast device designed to specifically remove oil and fine sediment out of stormwater runoff from small industrial catchments and carparks. It is divided into two components, a fibreglass bypass chamber, and a concrete treatment chamber. Stormwater flows into a circular by-pass chamber where the low flows are diverted down and into a treatment chamber by a low weir and

vertical pipe. The downstream section of the by-pass chamber is connected to the outlet stormwater pipe, ensuring that once the material is captured it is not rereleased. Must be cleaned at 15% full to ensure trapped oil is not re-mobilised and fine particulates are not re-suspended by turbulence. Access into the device is restricted and it must be cleaned by eduction.
Contact: (02) 9832 5555
 SPEL Stormceptor™ – developed in the
U.K. for oil and fine sediment control, it is designed as an easily transportable onepiece fibreglass unit. It is specifically designed to separate oil and other light liquids out of stormwater runoff from supermarkets, carparks and industrial areas. The unit is divided into two (2) chambers with interconnecting vertical ducts. The first chamber (Primary Zone) provides grit separation while the second chamber (Quiescent Zone) provides fine particulate separation and traps oil behind a weir, which does not have direct access to the overflow by-pass pipe. Gross pollutant separation is required before the runoff enters the device. There is provision within the device to mount monitoring equipment and sensors, as well as a coalescing plate separator. To increase the structural integrity of the fibreglass units it may be necessary to encase the unit in concrete. Access into the device is limited and cleaning is by eduction, there are specially designed inspection openings to determine the amount of material captured.
Contact: (02) 9683 5555
 Stormfilter® – a product developed by
Stormwater Management of Oregon
U.S.A. It is an underground concrete vault designed as a series of interconnected cells to firstly separate the gross pollutants and sediment, and secondly the free floating oil and fine particulates. The final chamber incorporates a series of cartridges that filter the water through various media
(activated carbon, perlite, zeolite, compost, geotextile fabric), selected on the basis of the pollutants of concern in the catchment. Pipe full by-pass can be accommodated through the device or with the use of a Storm Gate diversion weir.
However the cartridges have a very low
(1 L/s) treatable flow rate each. Ingal
Civil Products have converted the cartridges to fit within the Buffa Tank onsite detention system and can supply the system in modular fibreglass units. A specialised attachment for a HIAB is available to remove the cartridges for cleaning and oils and fine sediment can be removed by hand or eduction. The drainage system within the base slab allows the device to drain dry through the cartridges.
Contact: (02) 9710 5555

CI&D
– designed as an oil and fine sediment separator. This device utilises a Diversion Chamber to divert flows into a Storage Chamber where the sediments are separated from the runoff by centrifugal action and low water velocities. The use of internal baffles within the Storage Chamber retain the oil in the top of the Stormwater Silt & Oil
Arrestor. It can be supplied as a precast unit but must be cleaned by eduction.
Contact: (02) 9602 9022
End of Line Controls

Net Tech – gross pollutant traps consisting of a fabricated stainless steel pipe extension and a heavy duty UV stabilised polyethylene net. The extension is fitted to the end of the pipe at its point of discharge. It incorporates a release mechanism that allows the net to detach and choke off, trapping the rubbish inside, while still being attached to the end of the pipe. This ensures a pipe full bypass, but any additional material mobilised later in the storm will by-pass. The device is visible and the stainless steel fittings appear to be highly prized, and as a consequence vandalism can be a problem. Care must be taken to ensure the release mechanism is properly set and does not stick in the locked

position. Cleaning involves undoing the clamp on the net and emptying it into the back of a small truck.
Contact: 0414 574 300

Pratten Trap – utilise a galvanised steel cylinder attached to the end of the pipe or headwall with a net attached to the outlet end of the cylinder. The net is not automatically released and is held in place by a bolted clamp, and by-pass occurs as a result of increased head, which trips a trap door upstream of the material stored in the net. When incorporated into a concrete hob downstream of the headwall, with an integral trash rack this device can effectively trap gross pollutants and coarse sediment. A variation with a vertical drop is available for sites such as sea walls and retaining walls. Captured material is stored in a drained condition but the device is highly visible, which can be a concern for vandalism.
Contact: 0419 419 478

Ecosol RSF 1000 – can be provided as a complete mesh cage at the end of the pipe or can be incorporated as an integral component of an existing headwall. The object is to provide an enclosed chamber, within which a basket filters out gross pollutants, without compromising the hydraulic characteristics of the upstream pipe system. A drop is required to allow installation of the baskets below the pipe outlet. Surcharge is by overtopping the basket, which can re-suspend positively buoyant material.
Contact: (02) 9560 2802

The Stormwater Boom – consists of a floating boom, with an attached skirt that can be anchored to the invert of the creek or estuary or weighted to stay vertical in mid-water. It is not essential that the boom be installed in a constantly flowing creek or be continually buoyant, however it is preferable that it be installed in areas of permanent water. The skirted boom is designed to bow out in the direction of the flow entrapping the rubbish within it. As the water level rises the boom commences to float and the rubbish is retained upstream of the boom. The skirt is manufactured from a permeable fabric that allows filtered water to pass through, yet retains positively and neutrally buoyant solids. The height of the boom can be set to allow overtopping in extreme floods. If desired a sacrificial section (shackle) can be incorporated that breaks under extreme pressure.
Specialist equipment (water lift dredge or hand collection) is required for maintenance as these devices work best in areas of permanent inundation.
Contact: 0419 419 478

Bandalong Boom and Litter Trap – the boom is designed to collect or deflect floating debris into the litter trap. It is manufactured from polyethylene pipe in segment lengths of 3 or 6 metres. An aluminium mesh skirt is fixed to the underside of the boom to prevent material, floating mid-water, bypassing the boom. The litter trap is connected to the mid-sections of the polyethylene pipe and acts as the permanent collection chamber. The stainless steel fittings are highly prized by the boating community and vandalism is common. If the unit becomes grounded during low water situations the rigid aluminium skirt and rigid floats can be damaged. A recent modification provides vandal proof connections between the polyethylene floats.
Contact: (03) 9437 0021

Gross Pollutant Trap (Baffled Box) -
This is one of the most common and probably the oldest technology currently in use. It consists of a coarse sediment trap/sump, with a trash rack on the downstream end to remove litter and debris. They are generally poured in situ and require regular maintenance based on the storage capacity of the sediment sump. Captured material is generally stored wet. The trash rack should be cleaned after every major storm and/or when the open area of the rack is reduced by about 20%. Vehicular access

is a major consideration and the device needs to be drained before entry. In the
Baffled Box modification internal weirs provide energy dissipation and need to be removed to allow front-end loader access.
Contact: requires detailed designs by a civil and hydraulic engineer. Sedimentation calculations are generally based on Stoke’s
Law or physical models.
 Baramy® Gross Pollutant Trap – supplied as a pre-cast concrete treatment system by Beresford Concrete Products.
It utilises horizontal and vertical screens to filter the gross pollutants out of the runoff. They require a drop at the outlet of the piped drainage system and the entrained litter and debris is separated as the stormwater passes through the screens. The separated material is stored dry, which reduces the opportunity for the organic material to decompose and release nutrients. The grade of the access ramp is a major consideration when designing the unit and should be suitable for a wheelbarrow or have sufficient turning circle to accommodate a bobcat. A sediment sump can be incorporated downstream for coarse sediment control. Care must be taken to ensure adequate surcharge capacity without scouring out of the backfilled material surrounding the device.
Contact: (02) 4392 3300

Nicholas Ski-Jump - This device uses expanded metal mesh to screen out rubbish from stormwater flows at the outlet headwall of stormwater drainage systems. Sediment is captured in a chamber located beneath the litter and debris separation screens. All material is retained in a dry state to reduce the opportunity for nutrients to be released into the water column as the organic material decays. The stored material is removed by accessing the rear separation chamber and raking the material into a wheelie bin, which requires the access to the unit to be suitable for dragging a full wheelie bin by hand. Bypass occurs when the head level upstream forces the side trap doors
(wings) to open and the stormwater is surcharged around the stored material.
The coarse sediment separation chamber is provided below the gross pollutant screens and the device can be modified to fit within open channels.
Contact: (02) 9427 4910
Pollutant Removal Mechanisms
Horner et al (1994) listed “all the principal mechanisms that can capture, hold, and transform various classes of contaminants in urban runoff and the factors that promote the operation of each mechanism to improve water quality.” The effectiveness of the mechanism to remove pollutants is a function of time. Consequently Hydraulic
Residence Time is the most basic variable to consider when applying effective treatment practices.
Features that help achieve any objective:

Increasing hydraulic residence time;

Low turbulence;

Fine, dense herbaceous plants;

Medium-fine textured soils.
Features that help achieve specific objectives:

Phosphorus control – high soil exchangeable aluminium and/or iron content; addition of precipitating agents;

Nitrogen control – alternating aerobic and anaerobic conditions; low toxicants; circumneutral pH;
Metal control:

High soil organic content;


High soil cation exchange capacity;

Circumneutral pH.
Organic matter control:

Aerobic conditions;

High light;

High soil organic content;

Low toxicants;

Circumneutral pH.
NOTE: Other considerations include the pollutant load running off the catchment and the ability of the device to store that load between rainfall events without by-passing.
Many devices, in particular In-Line devices are intended to be charged by a low-flow weir. Where this is the case, care should be taken when calculating the pollutant load, as most of the heavier pollutants are contained within the lower portion of the pipeline. Bypass weirs and flumes should have sufficient capacity to by-pass the pipe full flow without surcharge, and without compromising the upstream hydraulic grade line .
Wet Vaults as Gross Pollutant Traps
Abood and Riley (1997) found that in the
Lane Cove Valley, gross pollutants had a deleterious effect on water quality, and the decomposition of the gross pollutants increased with time while ever the gross pollutants were kept within a wet anaerobic environment. They concluded that the pool of water “would be a major source of low water quality which would be flushed downstream in the early stages of a flood event. Programs of gross pollutant removal should be on a one month cycle, and possibly more frequent.”
Strynchuk, Royal and England (1999) reached a similar conclusion in their analysis of the effect of grass clippings and leaves on water quality when stored in a wet anaerobic condition. “The results of this study show that the majority of organic-based pollutants, which leach from grass clippings and leaves into water, will be released within 1 to 22 days, depending on the pollutant.” They concluded “that in order to avoid significant leaching of most ‘pollutants’, it is desirable to quickly remove organic debris from collection devices that retain water.”
Strynchuk, Royal and England (1999) also found that for leaves and grass clippings,
BOD
5
concentrations peaked at 9 days; colour was continuously released between 1 and 22 days; and phosphorus was released within the first day of immersion. Abood and
Riley (1997) found significant increases in
Phosphorus, Nitrogen, COD and Suspended
Solids, in non-aerated pools during the first
100 days after collection. Cigarette butts were found to increase phosphorus, suspended sediment, conductivity and COD loads within the samples within about 10 days of being immersed.
Wet vaults provide an environment conducive to the conversion of solid gross pollution into soluble pollutants. Anaerobic decomposition, low pH and low light conditions are all features of underground wet vaults. In combination they make it possible for pollutants bound to small particulates or stored in a solid form to be broken down and released back into the water column. The presence of anaerobic bacteria, within the vault, has the potential for significant gas production (hydrogen sulfide, methane) and this may occur within 7 days of collection.
Separation of the waste stream into individual pollutants, combined with regular cleaning and removal can alleviate problems associated with pollutant re-mobilisation in wet vaults. From the research quoted above, it would appear that wet vaults should be cleaned out as soon after a rainfall event as possible and at intervals not exceeding 30 days. Inspection of the device, to determine the need for cleaning, should occur after 10 mm of rainfall or every 2 weeks, whichever comes first.
This paper is meant to provide some guidance on the proprietary devices available and the location within the catchment that

best suits their individual design characteristics eg at-source, in-line, end of line etc. The in-line wet vault type of GPTs have proved very popular in western Sydney and some characteristics common to each device are emerging, especially with regard to installation costs. These characteristics can provide guidance to Local Government staff to allow them to plan and budget for gross pollution control throughout their developed catchments.
In general a GPT should not be installed on catchments in excess of 20 ha (TFR <
1.5 m³/s), and an underground, in-line wet vault suitable for this size catchment in western Sydney generally costs between
$80,000 and $150,000. Cleaning and maintenance costs vary depending on the number and proximity of devices and the tipping fees, but generally each device requires cleaning every month at a cost of between $500 and $1,500. If soluble pollutants are an issue and need to be removed then the capital works costs should be doubled i.e. approximately $20,000 per hectare of development. However Holroyd
City Council found that the incorporation of a flood attenuation system with a high level of water quality control, significantly increased the capital costs per catchment hectare.
Sydney Smith Park has a 26 ha residential catchment, and the stormwater management strategy for the catchment cost approximately $40,000 per hectare including attenuation of the 1:100 yr peak flows to 1:2 yr, design flows with gross pollutant control, sand filters and water re-use. (Peterson and
Ritchie, 2000)
A similar system at Blue Haven on the
Central Coast of NSW cost approximately
$15,000 per hectare of a 20 ha residential catchment, and the stormwater pollution controls in Plumpton Park, Blacktown cost approximately $12,500 per hectare for a 100 ha residential catchment. At Scope Creek in
Penrith, treatment of the dry weather flows from a 200 ha rural/residential catchment has cost $3,000 per hectare of its contributing catchment.
No one product provides the solution to all the pollution problems associated with stormwater runoff. However, source and at source controls can provide the opportunity to reduce costs by keeping structural controls small, unobtrusive and maintainable.
Pointless Personal Pollution is responsible for much of the pollution in stormwater. The most cost effective source control is preventing pollution from occurring in the first place. This can be achieved by making the polluters aware of the impact of their actions and effecting a behaviour change. Structural controls should endeavour to separate the waste stream and store the pollutants in a dry condition prior to collection.
Comprehensive stormwater management incorporates:

Surface drainage and flood protection;

Protection of aquatic habitat and biota;

Reduction of stormwater pollutants;

Erosion and sediment control;

Aesthetic & recreational opportunities;

Reuse of stormwater;

Values assigned to ecosystems;

A community education program.
When used in a series or “treatment train” a combination of BMPs can provide cost effective solutions. Structural BMPs are necessary to remove gross pollutants from runoff that would, if left untreated, reduce the effectiveness of natural treatment systems such as wetlands and bio-retention facilities.
To be successful any Stormwater
Management Program requires a comprehensive, continuous team approach incorporating federal, state and local governments and must be based on communication, cooperation, creativity and, most importantly, commitment.
The author acknowledges the assistance of the following companies and organisations in the preparation of this paper:

All Pumps Sales and Services, Bandalong
Engineering, Baramy, Boyden and Partners,
CDS Technologies, CSR-Humes, Ecosol,
Ingal Civil Products, Net Tech, Nicholas Civil,
Rocla Pipeline Products, Sinclair Knight
Merz, Stormwater Management, Stormwater
Systems, Brisbane City Council, Blacktown
City Council, Hornsby Shire Council, Holroyd
City Council, Penrith City Council, Wyong
Shire Council, Melbourne Water, CRC for
Catchment Hydrology, University of South
Australia, Swinbourne University, NSW EPA and various Government agencies throughout the U.S.A.
Abood M. and Riley S.J. (1997) “Impact on
Water Quality of Gross Pollutants”.
Research Report No. 121 Urban Water
Research Association of Australia, June
1997. (72 pages)
Allison R., Chiew F. and McMahon T. (1997)
“Stormwater Gross Pollutants”. Industry
Report 97/11 by the Cooperative Research
Centre for Catchment Hydrology, Department of Civil Engineering, Monash University,
December 1997. (17 pages)
Brown S., Shrestha S. and Riley S.J. (1999)
“The allocation of Resources to Stormwater
Pollution Control”. In Impacts of Urban
Growth on Surface water and Groundwater
Quality, proceedings of International Union of
Geodesy and Geophysics, at Birmingham,
UK, 18-30 July 1999. IAHS Publication no.
259 ISBN 1-901502-06-6. (pp.381-389)
Chang G., Parrish J. and Souer C. (1990)
“The First Flush of Runoff and its effect on
Control Structure Design”. Environmental
Resource Management Division, Department of Environmental and Conservation Services,
City of Austin, Texas. Summary in
Watershed Protection Techniques Center for
Watershed Protection, Vol.1, No.2, Summer
1994, Technical Note 28. (pp.88-90)
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McMahon T.A. (1997) “Urban Stormwater
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For the purposes of this paper, the following terms (taken from the Draft Stormwater Quality
Control Policy for Penrith City Council) have been defined as:
“Approval”/ “Approved” a consent, licence or permission or any form of authorisation issued by Council.
“Debris” accumulated material that is not necessarily of anthropogenic origin e.g leaf litter, branches, garden refuse, etc.
“Development” means: a) the use of land, and
“Free Oil”
“First Flush” b) c) d) e) the subdivision of land, and the erection of a building, and the carrying out of works, and the demolition of a building or work, and f) any other act, matter or thing referred to in section 26
(Environmental Planning and Assessment Act, 1979) that is controlled by an environmental planning instrument. free floating viscous liquids that do not emulsify in aqueous solution e.g. cooking oil, motor oil etc. treatment strategy shall meet the following criteria where: a) Cat chments ≤ 5 ha i) Gross Pollutants – a Treatable Flow Rate = 60 L/s/ha, with sufficient storage volume to retain the pollutants generated by the 1 st 30 mm of runoff; ii) Fine Particulates – a Treatable Flow Rate = 10 L/s/ha, with sufficient storage volume to retain the pollutants generated by the 1 st 13 mm of runoff; b) Catchments > 5 ha
Compliance with the modelling techniques in Appendix F Managing
Urban Stormwater: Council Handbook (Draft) NSW EPA (1997);
Minimum Treatable Flow Rate equivalent to the 6-month ARI critical storm for the catchment (maximum duration of 15 minutes for urbanised catchments
≤20 ha.);

“Gross Pollutants”
“Litter” term used to collectively describe litter and debris transported by urban runoff, of a size that may be retained by a 5 mm mesh screen. all material of human (anthropogenic) origin that is capable of being mobilised by stormwater runoff.
“Nutrients” a substance that provides nourishment to another organism. For the purposes of stormwater runoff it may be defined as Total
Nitrogen(TN) consisting of nitrate nitrogen (NO
3
-N), nitrite nitrogen
(NO
2
-N), ammonium nitrogen (NH
4
+ -N) and organic nitrogen, and
Total Phosphorus (TP) consisting of; filterable phosphorus
(orthophosphate PO
4
-3 -P, condensed phosphates, organic phosphorus and colloidal phosphorus); and particulate phosphorus
(organic particles and inorganic particles that may or may not be adsorbed to fine particulates).
“Pollutant”
“Sediment” a contaminant that adversely alters the physical, chemical, or biological properties of the environment. solid material of varying size, both mineral and organic, that is in suspension, is being transported, or has been moved from its site of origin by air, wind, water or gravity, and comes to rest on the earth’s surface either above or below sea level. Coarse Sediment is defined as soil partic les ≥0.5 mm in diameter. Fine Particulates are defined as all material ≥0.02 mm but <0.5 mm in diameter.
Fine
Sediment is the fraction of soil consisting of silt (0.002 mm to 0.02 mm in diameter) and clay (<0.002 mm in diameter).
“Soil” 1.(Agronomy) the unconsolidated mineral and organic matter on the immediate surface of the earth that serves as a natural medium for the growth of land plants.
2.(Engineering) earth and rock particles resulting from the physical and chemical disintegration of rocks, which may or may not contain organic matter. It includes fine materials (silts and clays), sand and gravel.
“Total Suspended Solids”
include a range of inorganic and organic particles suspended in the water column, which can be defined as the filterable residue retained on a 2.0 μm pore size filter dried at 105˚C.
“Treatable Flow Rate” the minimum flow that a pollution control device must be capable of treating, without bypass, to achieve the desired gross pollution retention criteria for the particular Development Style and Catchment
Area. For the Cities of Blacktown and Penrith in western Sydney, the Treatable Flow Rate (TFR), for sites equal to or less than 5 ha in area, shall be 60 L/s for every hectare of catchment for gross pollutants and 10 L/s for every hectare of catchment for fine particulates. The goal of establishing a TFR is to capture and retain gross pollutants generated by the first 30 mm of runoff, and to capture and retain fine particulates generated by the first 13 mm of runoff.

Simplistic Format for Selecting a Particular Device
Before comparing individual devices it is necessary to first identify all the site constraints e.g. pollutant type, hydraulics, flooding, access, available infrastructure etc. and ensure that each of the devices can meet the specific needs of those constraints.

Geoff Hunter is the Engineering Coordinator: Stormwater at Penrith
City Council and has 30 years experience in Stormwater
Management, 17 years in Local Government and 13 years with private Consultants and Contractors. Penrith is located 60 kms west of Sydney on the Hawkesbury-Nepean River, at the foot of the Blue
Mountains
Geoff holds qualifications in Surveying, Soil and Water Management,
Stormwater Wetland Management and Environmental Management.
He was awarded a Churchill Fellowship to investigate “ The Use of
Wetlands for Soil and Water Management ” in the USA (1996) and a
Bursary from the IMEA to research “Comprehensive Stormwater
Manag ement” in NZ and the USA (1998). His areas of interest include Constructed Wetlands, Bio-filtration, sand filters, stormwater pollution control, natural resource management and stream rehabilitation. In the last 5 years, Geoff has presented numerous papers on Environmentally Sensitive Stormwater Management, structural stormwater controls and the impacts of urbanisation on aquatic ecosystems.
He is the Local Government representative to the Stormwater
Industry Association (NSW), provides technical assistance to the
State Stormwater Advisory Committee and is a member of the
Environment Panel of the Institute of Public Works Engineering
Australia (NSW)
Postal Address : Geoffrey Hunter, PO Box 63, Penrith NSW
Australia 2751
E-mail : watershed@bigpond.com