Hornsby Shire Council

Attachment to Report No. EN38/08 Page 0












The Catchments Remediation Rate Capital Works Program


Annual Performance Report










Prepared by the Water Catchments Team


September 2008




Cherrybrook Lakes, Cherrybrook (Water Quality sampling site)









The 2007/2008 Catchments Remediation Rate Capital Works Annual Performance Report was prepared by Elizabeth Bulley and David Beharrell of the Water Catchments Team, Environment Division, Hornsby Shire Council. The report was prepared under the supervision of Ross McPherson, Manager, Water Catchments, and under the direction of Robert Stephens, Executive Manager, Environment Division.


For further information contact:


Water Catchments Team

Hornsby Shire Council

PO Box 37

Hornsby  NSW   1630


Phone: (02) 9847 6860

Fax:     (02) 9847 6598

Email:  dbeharrell@hornsby.nsw.gov.au



This report aims to provide quantitative data and analysis of the relative performance of different water quality treatment measures, including gross pollutant devices, sediment basins, wetlands and bioremediation systems that have been constructed to improve stormwater quality in Hornsby Shire. The results of the report will be used by stormwater and catchment managers to provide a better insight into determining the type of structures that are suitable for specific sites. Furthermore, the data provides valuable information about the costs (both capital and maintenance), benefits and device optimisation which can aid in the formulation of strategies to improve catchment/landuse practices by both structural and non-structural means.


The principal objective of installing stormwater treatment measures is to improve the quality of stormwater by removing pollutants and in some instances retaining stormwater flows. In 2007/08, 16 catchments remediation capital works projects were completed at a total cost of $957,000. These works involved the construction and/or installation of 11 sediment basins, four end-of-pipe gross pollutant traps, eight stream remediation projects, one bioremediation basin and six stormwater gardens. 


While these structural interventions provide treatment of pollutants, the Catchments Remediation Program also promotes and funds non-structural initiatives in the pursuit of improving stormwater quality. These include: monitoring, maintenance, ensuring stormwater controls on new development sites, street sweeping, environmental education, business auditing, compliance programs and pollution clean-ups.


The collection of performance data over the 2007/2008 financial year has allowed Council to examine the indicative maintenance costs and gross pollutant (sediment, litter and organic matter) removal from Council’s 370 + water quality improvement devices. The results show that 1236 cubic metres of sediment, litter and organic matter was removed from the Shire’s drainage system and waterways over an average 13 separate cleaning events.


The total cost to Council to maintain its water quality assets and adjacent landscaped areas was $354,000. This cost included device inspections, cleaning and desilting, material processing for reuse, disposal of litter to landfill, asset maintenance and repair, landscape maintenance and weed control in and around assets and maintenance of leachate treatment and reuse facilities.  The annual maintenance cost was more than previous years which can be attributed to two large maintenance projects: 1) the remediation of the Mt Colah stockpiling site ($87,000), and 2) Dredging the Lakes of Cherrybrook ($45,000), and the increased cost incurred by having to send recovered material to landfill.  


The report also provides information on costs, sizing and performance of wetland ponds constructed under the Catchments Remediation Program. In addition, Council has embarked on a program to remediate degraded creeks and former landfill sites and trial new and innovative stormwater infiltration, reuse and bioremediation systems.  Of particular interest in the 2007/2008 period were the bioremediation basin and stormwater gardens constructed at Cheltenham and Berowra.


Overall, the findings of this report give stormwater managers a better insight into the cost-effectiveness and performance of water quality improvement structures and the management of life-cycle costs for individual stormwater quality assets. The performance of these devices allows Council to both refine and modify the design of future water quality control measures, and judge their appropriateness for proposed remediation sites based on catchment size and land use impact.

Hornsby Shire Council

Attachment to Report No. EN38/08 Page 3





1.0      INTRODUCTION. 5

1.1      Report Objective. 5

1.2      Background. 5

1.2.1 Catchments Remediation Program.. 5

1.2.2 Catchments Remediation Rate (CRR) and Panel 6

1.3      Statutory Considerations. 7

2.0      Selection and implementation of the CRR Capital Works. 9

2.1      Selecting a stormwater treatment measure. 9

2.2      Project Management and Construction. 9

2.3      Maintenance Considerations. 9

2.4      Maintenance Operations. 10

2.5      Occupational Health and Safety (OH&S) and Risk Management. 11

3.0      Stormwater Treatment Measures. 12

3.1      Gross Pollutant Devices (GPD’s) 12

3.1.1.     Trash Racks (21) 12

3.1.2.     Litter Baskets (10) 14

3.2      Gross Pollutant Devices - Proprietary (247) 14

3.2.1.     Net Techs/Pratten Nets/Channel Nets (44) 14

3.2.2.     Underground Vaults (20) 15

3.2.3.     Ski-Jump Litter Traps (4) 15

3.2.4.     Pit Inserts (170) 15

3.3      Constructed Wetlands. 16

3.4      Sediment Basins. 17

3.5      Stream Remediation. 17

3.6      Bioremediation Basin - Castle Howard Road, Cheltenham.. 20

3.7      Stormwater Gardens - Turner Road, Berowra. 21

3.8      Developer Constructed Devices. 22


4.1 Rainfall measurement. 23

4.2      Performance of Gross Pollutant Devices. 23

4.2.1              Pollutant Removal Trends. 23

4.2.2      Maintenance Costs. 26

4.2.3      Dredging Lakes of Cherrybrook. 26

4.3      Wetland Performance. 27

4.3.1 Pollutant Removal Trends and Costs. 27

4.4      Material Disposal and Reuse. 28


5.1      General Maintenance Considerations. 30

5.2      Maintenance of Landscapes surrounding Gross Pollutant Devices. 30

5.3      Maintenance of Wetlands. 30


6.1      Foxglove Oval, Mount Colah. 32

6.2      Arcadia Park, Arcadia. 33

7.0      STREET SWEEPING.. 34

8.0      CONCLUSIONS. 35

9.0      REFERENCES. 36

Appendix A:  Rainfall data for Hornsby LGA. 37




Hornsby is located 25 kilometres north-west of the Sydney CBD and is the Council base for a Shire covering approximately 50,990 hectares and serving the needs of more than 157,000 residents. The Shire extends from Epping in the south to Brooklyn and Wisemans Ferry in the north fronting a large expanse of the Lower Hawkesbury River. A majority of the northern and central Shire consists of Regional and National Park and Nature Reserve. This unique natural character combined with the many creeks and estuaries has led to Council being termed the ‘Bushland Shire’.


In an attempt to conserve the ecological value of the Shire’s many natural waterways and to improve the quality of urban stormwater Hornsby Shire Council has taken an integrated approach to stormwater quality management by developing a range of capital and non-capital (preventative) measures. This initiative includes all major catchments under the Stormwater Management Plan framework, together with more closely modelled sub-catchment plans. Council’s progressive strategy has recognised the need to tackle these challenges using a broad approach to understanding and managing the total water cycle.  This has led to the development of a Sustainable Total Water Cycle Management Strategy (2005).


This report focuses on the performance of different stormwater quality control structures e.g. gross pollutant devices, constructed wetlands, sediment basins, stream remediation and leachate treatment works that have been constructed under Council’s Catchments Remediation Rate (CRR) Capital Works Program.



1.1       Report Objective

To provide quantitative data and an analysis of the relative performance of different stormwater and leachate quality improvement devices that have been implemented under the CRR program. Specific reference will be made to those devices constructed and/or installed in the 2007/2008 financial year.


1.2       Background

1.2.1 Catchments Remediation Program

In response to general water quality degradation, including red algal blooms and fish kills in the Berowra Creek estuary in September 1993, Hornsby Council placed a moratorium on all development assessments within the catchments of the West Hornsby STP.  To resolve this, the Minister for Planning established a Technical Working Party (TWP), comprising representatives of Council, the Water Board (Sydney Water) and the Department of Urban Affairs and Planning (DUAP).  Representatives from the Environment Protection Authority (EPA) and the Hawkesbury-Nepean Catchment Management Trust joined the TWP in early 1994.  The TWP confirmed that the two Sewage Treatment Plants (STP’s) contributed to the poor water quality of the creek.  Moreover, it highlighted the significant role of polluted urban stormwater, particularly runoff from developing and newly developed residential areas.


On 27 April 1994, the participating organisations of the TWP signed a Statement of Joint Intent (SoJI - also known as the Community Contract for Berowra Creek) agreeing to work together to achieve the ecologically sustainable development (ESD) of the Berowra Creek catchment and the recovery of the environmental health of the creek.  The Community Contract, included agreements to upgrade the STP’s and it bound the parties to the preparation and implementation of a Water Quality Management Strategy.  It also required Council to prepare and implement a strategy to reduce stormwater nutrient ingress to Berowra Creek and to utilise water sensitive design in its consideration of future developments.


However, the level of pollutants and the urgent need for action was not confined to Berowra Creek. Water quality in the other major catchments within the Shire had also deteriorated because of urbanisation. Remedial works to reduce pollution and improve water quality were required throughout the entire Shire including relevant areas draining the Cowan Creek, Lane Cove River and the Hawkesbury River catchments.


In 1995, the Water Catchments Team initiated the first phase of the ongoing strategic planning for catchment management within the Shire. The result was the production of a Catchments Remediation Program Five-Year Plan which detailed the proposed expenditure of the Catchments Remediation Rate towards meeting the objectives of the Statement of Joint Intent and in turn improving water quality in the Shire’s waterways. The Plan included financial forecasts of rate income over a five year period together with capital investment and non-capital expenditure including asset management.


It was hoped that Hornsby Shire Council’s Catchments Remediation Program would give stormwater managers a better insight into the cost-efficiency and performance of individual devices, but more importantly, monitoring of devices will reflect the individual characteristics of sub-catchments and the associated point sources of pollution, which can be targeted through pollutant minimisation strategies. It was also seen that community and industry awareness projects are important to complement the Catchments Remediation Program, whilst Local Government can also review work practices and strategies in relation to sediment and erosion controls on building sites (and there enforcement), street sweeping, street tree planting, rubbish collections and kerbside recycling collections.


Additional objectives of the Catchments Remediation Program, which still apply today, aim to address:

·  Innovation – products and services – generate and use ideas to add value to the community as stakeholders, provide productivity improvements, continue leadership and management capabilities in local government

·  Health and safety – provide a safe and healthy aquatic environment for the community, council staff and contractors

·  Performance – better understand community needs and expectations, ensure/deliver reliability, durability, quality and maximise the cost/benefit of installed capital projects

·  Justify expenditure through regular reports to the community, protect and service assets and continually improve operations.


1.2.2 Catchments Remediation Rate (CRR) and Panel

Council’s catchments remediation work up to 1997 was only partly funded by the CRR, with the majority of funding being at the expense of other traditional Council services e.g. Parks. However, the cost of Council’s ‘Statement of Joint Intent (SoJI) for Berowra Creek’ obligations and remediation works in the other catchments was highlighted to be much more than was covered by the rate. The proposal to increase the CRR from 2% to a 5% levy on ordinary rates in 1997 was presented with the idea to accelerate remediation capital works and return resources to traditional services that had suffered funding cuts. The increased funding was intended for planning, design, construction, maintenance and management of remediation devices. The proposal to increase the CRR to 5% was adopted by Council on the 13th April 1997 and still applies today.


Approximately 50% of the CRR is directed to non-capital costs including project management and a series of studies, associated with meeting the SoJI objectives. These studies are designed to identify more precisely the cause and effect mechanisms of pollution generation in the Shire, develop effective longer term remedies for the problems, and establish appropriate technological and monitoring techniques to determine and report progress.  The remaining 50% of CRR funding is allocated to on-ground capital remediation works and subsequent routine maintenance of all constructed devices. Current remedial environmental protection works include the design and construction of wetlands, gross pollutant devices or stormwater quality interception devices, leachate control from old landfill sites, sediment basins and creek stabilisation/rehabilitation.


The Catchments Remediation Rate Expenditure Review Panel (the Panel) was established in July 1997 following community consultation on increasing the CRR from 2% to 5%. The Panel meets twice annually to review expenditure following the second and fourth quarters of each financial year and currently comprises six community members, relevant council staff and two nominated Councillor/s. The purpose of the Panel is to ensure accountability and transparency of expenditure of CRR funds.



1.3       Statutory Considerations

It should be noted that the Hornsby Shire Local Environment Plan (LEP), 1994, permits Council to undertake the construction or maintenance of stormwater drainage and water quality treatment devices, bush regeneration and landscaping without obtaining development consent. The proposals for construction are assessed under Part V of the Environmental Planning and Assessment Act, 1979, which requires Council to prepare a Review of Environmental Factors (REF).  This identifies and evaluates the impacts of an activity to determine whether the impacts are likely to significantly affect the environment. The REF must also consider impacts of the activity on critical habitat or threatened species, populations or ecological communities or their habitat, under section 5A of the EP&A Act.


The Threatened Species Conservation Act (TSC Act) 1995 specifies a set of seven factors which must be considered by decision makers in assessing the effect of a proposed activity on threatened species, populations or ecological communities, or their habitats. These factors are collectively referred to as the seven part test of significance.


The outcome of any threatened species assessment should be that activities are undertaken in an environmentally sensitive manner, and that appropriate measures are undertaken to minimise adverse effects on threatened species, populations or ecological communities, or their habitats. If the application of the seven part test finds that a significant effect is likely then:

·  A Species Impact Statement must be prepared and the concurrence of the Director General of the Department of Environment and Climate Change (DECC).

·  The activity may be modified such that a significant effect on threatened species, populations or ecological communities, or their habitats is unlikely be sought.


Council is also required to notify and exhibit work proposals as per Notification Protocol contained in Council’s Exempt and Complying Development DCP (1999). This entire procedure has been quality assured under the NATA certified ISO 9002 – Quality Management System and the ISO 14001 – Environmental Management System, which the Water Catchments Team of Council received in July 2000. These international standards will ensure that document control, corrective and preventative actions and environmental procedures are appropriately applied to all related projects.



1.4       Asset/ Lifecycle Management


Lifecycle management enables Council to plan interventions, whether its maintenance or renewal, at the optimum stage of an asset’s deterioration to enable cost effective extensions of its useful life. There are a number of activities considered in lifecycle management:   

·  Operations are those activities that have no effect on asset condition but are necessary to keep the asset appropriately utilised. 

·  Maintenance is the day to day work required to keep assets operating at agreed service levels, and falls into two broad categories: planned (proactive) maintenance is maintenance activities planned to prevent asset deterioration; and unplanned (reactive) maintenance is maintenance activities to correct asset malfunctions and failures on an as required basis (e.g. emergency repairs).  Maintenance work is required to maintain the asset’s ability to provide the agreed service level but does not extend the life of the asset.  Operations and Maintenance expenditure are considered an “Expense” for Council’s financial accounting purposes. A key element of asset management planning is determining the most cost-effective mix of planned maintenance in order to reduce unplanned maintenance to a minimum.

·  Renewal work is the substantial replacement of the asset, or a significant asset component, to its original size and capacity.  This work generally aims to return the asset to a condition or state similar to the original asset. 

·  Replacements (or reconstruction) are those projects that are created for the extension or upgrading of assets required to cater for growth or to maintain or improve on the levels of service.


The Stormwater Drainage Asset Management Plan (SDAMP) 2006 provides a financial forecast for water quality assets in the Shire over a 20 year period. Cumulative operating expenditure identified in the Plan, includes the cumulative operation/maintenance expenditure and asset renewals and upgrades associated with assets reaching their optimum life or age.  To ensure responsible financial management the assumptions made in the modelling were very conservative. Hence, both renewal and projected maintenance cost were set at a high level to allow for unforeseen circumstances or unpredictable rises in costs.


The key feature of these financial projections is that it is envisaged that in approximately ten years the opportunity for new capital works across the Shire will steadily decline, resulting in a simultaneous increase in operational and renewal costs. The life cycle analysis modelling of catchment remediation program, as with Council’s Asset Management Plans, will be reviewed at regular intervals to allow for the input of monitoring and knowledge gained over time. 








Hornsby Shire Council

Attachment to Report No. EN38/08 Page 8




2.0       Selection and implementation of the CRR Capital Works


2.1       Selecting a stormwater treatment measure

The selection and implementation of structural treatment measures involves six steps (Victoria Stormwater Committee, 1999). These are:

1. Determine treatment objectives

2. Develop treatment train

3. Site identification

4. Short-list potential treatments

5. Compare potential treatments

6. Detailed design



2.2       Project Management and Construction

Due to the varying degrees of expertise in different fields the Environment and Works Division have forged a partnership approach to deliver CRR capital works projects. Over the past 10 years, the Works Division’s Design and Construction Branch has been able to incorporate the additional design, construction and project management responsibilities associated with CRR capital works into their annual civil works improvement program.


It is believed that there are a number of benefits both to the Works and Environment Division and to the Council as a whole as a result of this partnership.  Some of these are:


·  Projects are developed ensuring compatibility with local engineering and environment standards, and making sure that all issues are addressed

·  What is learnt from involvement in these projects is utilised in all Council works so that we are setting the standards for developers/builders to follow

·  Opportunities for Works Division staff to be involved in environmentally "cutting edge" technologies

·  Involvement of staff in the Works Division in an area of environmental management, with a flow-on effect resulting in better understanding of sustainability issues

·  Opportunities for Environment Division staff to become more aware of engineering issues in the development of projects

·  Potential expansion of the core business of the Works Division.


The combination of the push towards competitive tendering and the need to seek specialised engineering and contractor services has also given management the impetus to consider contracting out or tendering some of the design and construction activities. At present a small proportion of the works is contracted out (usually low-risk remediation projects such as stream remediation works and minor GPD’s) together with specialised design and consulting services. As a result of this strategy, the Environment Division has being satisfied at the quality of work achieved and the cost-benefit involved.



2.3       Maintenance Considerations

Included within the CRR capital works budget is provision for monitoring and maintenance of all structures on a regular, recorded basis. Due to the current strain on Council’s resources, the increasing number of structures being built and the resulting demand for timely and efficient maintenance, Council has continued to utilise contractors (on a 3 year contract) to undertake maintenance works under Council supervision.


Maintenance typically involves regular cleaning of Gross Pollutant Devices (GPD’s) and periodic maintenance of sediment traps and wetlands in terms of sediment removal, bank repair, weed control/spraying and some general landscaping work. Fundamental design principles allow ease of draining/flow bypass and access for maintenance of all water quality control devices which results in efficient and cost-effective maintenance techniques in the long term.


The existing contracts stipulate the contractor’s responsibilities. These are outlined as follows:


·   To maintain existing water quality remediation structures to ensure optimal functioning and a weed-free surrounding landscape

·  To ensure quality control/assurance throughout the maintenance process incorporating:

o minimal pollution of the site during cleaning and transport of materials

o efficient, accurately documented records of contents removed and/or actions taken

o compliance with Council’s environmental checklist

·  The Contractor/s will be required to provide both a status and cleanout report sheet for each structure after maintenance. Council requires this to evaluate GPD performance, device accountability and landscaping/bush regeneration costs per unit area

·  The Contractor/s will be required to dispose of waste material to a nominated landfill, or preferably a privately operated screening recycling operation that offers a competitive rate per tonne (or compost onsite in the case of vegetation). The only exception being the liquid/solid mix waste removed by vacuum from wet sump devices such as the CDSâ, Humeceptor and Ecosol units. This waste shall be disposed of to an approved location at Council’s expense

·  That the Contractor/s has a proven record of Occupational Health and Safety (OH&S) commitment, training and record keeping.



2.4       Maintenance Operations

The frequency of maintenance varies between treatment measures. A majority of litter/gross pollutant devices need regular inspection and maintenance after each significant rainfall event. In 2007/2008 Hornsby Shire recorded approximately 50 large events (>10mm of rainfall in the previous 48hrs) which resulted in higher than average yields (refer to Section 4.1).


Larger wet vault gross pollutant devices are inspected and maintained on a quarterly basis, whilst constructed wetland and leachate treatment systems are maintained on a more regular monthly schedule. Sediment basins are inspected and maintained as required bi-annually. These basins need periodic maintenance in terms of sediment removal, bank repair or minor structural repairs. The scope of these works is based on additional quotations for specific works, upon joint inspection by Council’s Superintendent and the Contractor (see Table 2.0).


In 2004, Council engaged WBM Oceanics and Ecological Engineering to prepare ‘Maintenance Guidelines for Stormwater Treatment Measures’ under NSW Stormwater Trust funding. The resulting document provides a detailed breakdown of maintenance procedures from planning and inspection through to cleaning, disposal, monitoring and reporting.






  Table 2.0 Maintenance Operations for Stormwater Treatment Measures

Stormwater Treatment Measure


Inspection Frequency

Maintenance Frequency

Waste Destination


GPD (end of pipe)


Storm event (>10mm in 48hrs)

Selective based on inspection (within 5 working days)

Council material handling site. Stockpiled for screening and reuse

Within 2 working days from completion


(wet vault)


Quarterly (minimum)

Selective based on inspection (within 5 working days)

Solids to Council material handling site. Stockpiled for screening and reuse. Liquid fraction decanted to passive open space.

Within 2 working days from completion


(pit insert)



Selective based on inspection (within 5 working days)

Council material handling site. Stockpiled for screening and reuse

Within 2 working days from completion

Constructed wetland system or Leachate treatment system



Scheduled monthly

Weed material composted onsite. Sediment tested for contaminants prior to disposal to landfill or reuse


Sediment basin and Creek remediation


Bi-annually or storm event (depending on  magnitude)

Selective based on inspection (within 10 working days)

Weed material composted onsite. Sediment tested for contaminants prior to disposal to landfill or reuse

Within 2 working days from completion





2.5       Occupational Health and Safety (OH&S) and Risk Management

All contractors are required by Council to have an OH&S Policy in accordance with the NSW OHS Act 2000 and OHS Regulation 2001 which aim to secure and promote the health, safety and welfare of people at work. Employers and supervisors of staff and contractors have a duty of care under the Act to protect employees and demonstrate due diligence in their OHS Management Systems. Council and contractor policies must address:

·  certificates of currency for public liability and professional indemnity insurance, third party

·  motor vehicle insurance and workers compensation

·  safe work practices and procedures (hazard identification and risk analysis per site/device)

·  induction and safety training (Green or White card)

·  corrective action and documentation

·  incident / accident recording and investigation

·  personal protective equipment (PPE)


By ensuring these requirements are met by both Council staff and contractors the risks identified during the cleaning and maintenance process can be analysed, evaluated and risk treatment plans implemented in accordance with AS/NZS 4360 Risk Management.


Hornsby Shire Council

Attachment to Report No. EN38/08 Page 11





The principal objective of stormwater treatment measures is to improve the quality of stormwater by removing pollutants, including litter, sediment, nutrients and associated bacterial contamination. Stormwater structural treatment measures can be grouped into three categories: primary, secondary and tertiary (Victoria Stormwater Committee, 1999)


Table 3.0 Pollutant sizes and treatment measure (Adapted from Engineers Australia, 2006)


Treatment Category

Treatment process

Typical retained contaminants

Treatment measure


Physical screening or rapid sedimentation techniques

Gross pollutants and coarse sediment

GPT, sediment basins


Finer particle sedimentation and filtration techniques

Fine particles and attached pollutants

Sediment basins, Biofilters


Enhanced sedimentation and filtration, biological uptake, adsorption onto sediment

Nutrients and heavy metals

Wetlands, Biofilters, Stormwater gardens


In 2007/2008, 16 catchment remediation rate capital works projects were completed at a total cost of $957,000. These works involved the construction of 11 sediment basins, four end-of-pipe gross pollutant traps, eight stream remediation projects, one bioremediation basin and six stormwater gardens.  These projects are detailed in combination with previously constructed devices across Hornsby Shire (Locations mapped in Figure 1) and are in bold for easy differentiation.


3.1       Gross Pollutant Devices (GPD’s)

Gross pollutants are typically those materials greater than 0.05mm, both degradable and non-degradable, which detrimentally impact physically, visually and bio-chemically on aquatic ecosystems. For the purposes of this report, a gross pollutant device (GPD) can take many forms including traditional gross pollutant traps with trash racks (refer to photo below), litter baskets, nets, pit inserts and underground sumps.  Some GPD’s are fabricated to fit specific locations, whereas others are bought off the shelf (proprietary devices).  At present over 370 GPD’s have been installed and constructed throughout the Shire.



         Trash Rack, Water St, Hornsby

Trash Racks (21)

Norwood Avenue, Beecroft

Clarinda Street, Hornsby

Berkley Close, Berowra

Malsbury Road, Hornsby

The Gully Road, Berowra

Old Berowra Road, Hornsby

Warrina Street, Berowra Heights

Hamley Road, Mt Kuring-gai

Belltree Place, Castle Hill

Denman Parade, Normanhurst

Woodgrove Road, Cherrybrook

Bellamy Street, Pennant Hills

Odney Close, Cherrybrook

The Comennara Parkway, Thornleigh

Beecroft Road, Epping

Larool Cresent, Thornleigh

Tekopo Road, Glenorie

New Farm Road, West Pennant Hills

Northcote Road, Hornsby

Wilga Street, West Pennant Hills

Water Street, Hornsby



3.1.2.     Litter Baskets (10)

Mittabah Road, Asquith

Shepherds and Macquarie Drives, Cherrybrook

Wattle Street, Asquith

Clovelly Road, Hornsby

Sutherland Road, Beecroft

Burdett and Sherbrook Roads, Hornsby

Bambil Road, Berowra

The Comenarra Parkway, Thornleigh

Berowra Waters Road, Berowra Heights

Janet Avenue, Thornleigh



3.2       Gross Pollutant Devices - Proprietary (247)

3.2.1.     Net Techs/Pratten Nets/Channel Nets (44)

Stratford Place, Asquith

Gleneagles Crescent, Hornsby

Baldwin Avenue, Asquith

Clarinda Road, Hornsby

Joalah Crescent, Berowra

Sherbrook Road, Hornsby

Ti-tree Close, Berowra

Binya Close, Hornsby

Childrey Place, Castle Hill

Raphael Drive, Hornsby Heights

Kenburn Avenue, Cherrybrook

Pacific Highway, Hornsby Park

Flametree Close (West), Cherrybrook

Parklands Road, Mount Colah

Flametree Close (East) , Cherrybrook

Jessica Place, Mount Colah

Pecan Close, Cherrybrook

Pacific Highway, Mount Kuringai

Glenoak Way, Cherrybrook

Pacific Highway, Mount Kuringai

Alberta Avenue, Cowan

Hinemoa Avenue, Normanhurst

New Line Road, Dural

Brittania Street, Pennant Hills

Ridge Street, Epping

Brittania Street, Pennant Hills

Pembroke & Stanley Road, Epping

Blantyre Place, Thornleigh

Galston Road, Galston Gorge

Blantyre Place, Thornleigh

Burdett Street, Hornsby

Duneba Drive, Westleigh

Rosemead Road, Hornsby

Duneba Drive, Westleigh


         Channel Nets, Burdett St, Hornsby                                        Nettech, Pacific Hwy, Hornsby














3.2.2.     Underground Vaults (20)

Dudley Street, Asquith

Millbrook Place, Cherrybrook

Gardenia Street, Asquith

Monterey Place, Cherrybrook

Jacinta Avenue, Beecroft

Rosemary Place, Cherrybrook

The Gully Road, Berowra

End Lockyer Place, Dural

Woodcourt Road, Berowra Heights

Pike Road, Hornsby Heights

Dusthole Bay, Berowra Waters

Hunter Street, Hornsby Mall

George Street, Brooklyn

Sefton Road (Council Depot), Thornleigh

Dangar Road, Brooklyn

Dartford Road (Road Reserve), Thornleigh

Foley Place, Castle Hill

Unwin Road, Waitara

Castle Howard Road, Cheltenham

Boyd Avenue, West Pennant Hills






3.2.3.     Ski-Jump Litter Traps (4)

Anthony Street , Carlingford

George Street, Pennant Hills

Off Heights Place, Hornsby Heights

Old Northern Road, Wisemans Ferry



3.2.4.     Pit Inserts (170)

Beecroft/Carlingford/Epping  (35)

Pennant Hills Commercial area, Pennant Hills (4)

Mills Park Tennis Carpark, Asquith

Thornleigh Industrial/Commercial (11)

Wattle Street, Asquith (3)

Thomas and Orara Streets, Waitara (6)

Berowra Waters Road & Pacific Hwy, Berowra (4)

Eucalyptus Drive, Westleigh

Dusthole Bay, Berowra Waters


Brooklyn Road, Brooklyn (5)


Cairnes Road, Glenorie


Hornsby Industrial area, Hornsby (20)


Dural Street, Hornsby (3)


Hornsby CBD (70)


Pacific Highway, Mount Colah


Sue Place, Mount Colah (2)


Denman Road, Normanhurst (2)


Pit Insert, Dural St, Hornsby




3.3       Constructed Wetlands

Natural wetlands are transitional environments between terrestrial and aquatic habitats. They are characteristically shallow environments that are cyclically, intermittently or permanently inundated by fresh, brackish or saline water. Wetlands provide habitat for biota such as emergent macrophytes, macroinvertebrates, amphibians, reptiles and birds which are dependant on the inundation of the wetland.


In managing urban stormwater pollution of natural waterways, constructed wetlands are often built to mimic nature and to achieve improvements in stormwater quality through natural physical and chemical processes. Furthermore, they provide additional benefits through the provision of habitat for aquatic and terrestrial fauna, maximising biodiversity and enhancing aesthetics.


To date, Council has constructed wetlands funded through the Catchments Remediation Rate (CRR) at the following locations:


Lamorna Avenue, Beecroft

Clarinda Street, Hornsby

Midson Road, Beecroft

Clovelly Road, Hornsby

Plympton Road, Beecroft

Laurence Street, Pennant Hills

Brooklyn Road, Brooklyn

Dartford Road, Thornleigh

Hastings Park, Castle Hill

John Savage Crescent, West Pennant Hills

Ridge Street, Epping

Boundary Road, West Pennant Hills (Wallameda)

Sallaway Road, Galston





Midson Rd Wetland, Beecroft







3.4       Sediment Basins

Hornsby Shire Council maintains fifty-nine (59) sediment basins throughout the Shire which have either been constructed under the Catchments Remediation Program.

Council scheduled the cleaning of a number of established basins in 2007/2008. It is important that sediment basins are cleaned at least bi-annually (or at 30% capacity) so as to prevent colonisation of weeds and the release of potentially bio-available contaminants caused by disturbance events (eg. scour and re-suspension).


During 2007/2008, 11 new basins* were constructed at:

Boundary Street, Berowra

Stewart Avenue , Hornsby

Castle Howard Road, Cheltenham (x2)

Murralong Road, Mount Colah

Kirkham Street, Cheltenham (x2)

Nicholas Crescent, Normanhurst

Alberta Avenue, Cowan

Duneba Drive Westleigh

James Henty Park, Dural


*The ten new basins were included in the 59 sediment basins that council currently maintains.

     Newly constructed sediment basin, Kirkham Street, Cheltenham





3.5       Stream Remediation

Many creeks become physically degraded when the natural hydrology of the catchment is altered. This most often results in creek bank scour and erosion which is accelerated through processes such as the clearing of riparian vegetation and increased stormwater runoff from impervious surfaces. This degradation can have a detrimental impact on water quality often resulting in an increase in sediment transport and associated sediment bound contaminates.


Aquatic flora and fauna are impacted through a loss of habitat, increased competition with weeds, poor light penetration into the water column due to increased turbidity levels and smothering of benthic organisms with increased sedimentation.


In the remediation of a degraded section of stream the following techniques are used:


·  Creek bank stabilisation - Typically using locally sourced sandstone boulders that prevent the creek bank from eroding any further, and provide habitat for fauna and flora on the rock surface and in cracks between rocks. A variety of softer creek bank armouring strategies are also incorporated, including the pinning or staking of jute mesh/matting, woven blankets, fallen logs and chain-wire mesh. These approaches are often combined with native plant cells or tubestock.

·  Meanders - To aid in the reduction of flow velocities during storms.

·  Riffle zones and natural rock fall structures - Are used to provide in-stream habitat, stabilise the creek bed, aerate the water and allow maximum UV light treatment from sunlight to destroy faecal bacteria.

·  Pool zones - Are incorporated to create habitat for fauna and macrophytes and to dissipate flow velocities which allows sediments to drop out for later removal.

·  Revegetation of riparian zone - This zone is planted with indigenous native tubestock to improve habitat, enhance faunal corridors and vegetation links, provide a food source for both terrestrial and aquatic organisms and to stabilise the banks.

·  Stabilising stormwater outlets - Rock armouring around stormwater outlets reduces erosion and scour caused by high flows.

Sites that have undergone stream remediation since implementation of the Catchments Remediation Program have been summarised in Table 3.1. In 2007/2008, eight (8) new sites underwent creek remediation works in the suburbs of Cheltenham, Berowra, Normanhurst, Westleigh, Hornsby and Mount Colah and are highlighted in bold.

           Creek remediation works, Duneba Drive, Westleigh








Table 3.1 Stream Remediation Projects in the Hornsby Shire


Berowra Creek Catchment


Lane Cove River Catchment



Berowra – Boundary Street

Beecroft – Fearnley Park

Castle Hill – Hastings Park

Beecroft – Lamorna Avenue

Cherrybrook – Woodgrove Road

Beecroft – Midson Road

Hornsby – Clarinda Street

Beecroft – Norwood Avenue

Hornsby – Reddy Park

Beecroft – Plympton Road

Hornsby – Stewart Avenue

Beecroft – Ray Park

Hornsby HeightsHeights Place

Carlingford –  Anthony Street

Mount Colah – Murralong Road

CheltenhamCastle Howard Road

Mount Colah – Parklands Road

CheltenhamKirkham Street

Pennant Hills – Laurence Street

Epping – Kent Street

West Pennant Hills – John  Savage Crescent

Epping – Ridge Street (west)

West Pennant Hills – Wilga Street

Normanhurst – Hinemoa Avenue

Westleigh – Duneba Drive

Normanhurst – Nicholas Crescent

Westleigh – Eloura Road

Pennant Hills – Orchard Street


Thornleigh – The Comenarra Parkway

Cowan Catchment

Epping – Ridge Street (east)

Hornsby Ck –  Sherbrook Road

Epping – Pembroke Road


Epping – Stanley Street

Hawkesbury River Catchment

Cherrybrook – Flametree Crescent

BrooklynBrooklyn Road




In addition, the majority of gross pollutant devices discussed in this report also incorporate some stream remediation to stabilise banks around the devices and improve habitat immediately up and downstream.


Although the environmental benefit of stream remediation works is difficult to quantify, the works provide a significant benefit in terms of a reduction in erosion and associated sediment loads moving to the lower reaches of the creeklines and receiving waters, improved native riparian and aquatic habitat and enhanced visual aesthetics.










3.6       Bioremediation Basin - Castle Howard Road, Cheltenham

In March 2008, Council began work on a bioremediation system in Cheltenham to treat urban stormwater to a tertiary level. The system encapsulates the “treatment train” approach by combining the use of a GPD, porous piping and bioremediation basin.


Gross pollutant device: To ensure optimal performance and prevent clogging of the system a CDSâ Unit has been installed. This unit uses vortex forces to remove larger refuse and sediment, which is stored in an offline sump, before delivering stormwater to the bioretention basin.


Text Box: A representation of a Rocla CDSâ unit (Rocla, CDSâ Technologies, 2007).

Porous piping: After leaving the CDS unit, stormwater (free of gross pollutants) is directed into specially designed porous concrete pipes. Stormwater exfiltrates (leaks) through the permeable walls of the pipe into the surrounding substrate filter media. During this process mechanical filtration takes place. Furthermore, biofilms develop within the porous pipes system which assists by digesting pollutants, such as organics and nutrients.


Text Box: Porous piping (HydroConâ ) formed part of the treatment train


Bioremediation basin: When the exfiltration capacity of the pipes is reached (that is, water is coming in faster than it leaks out) then the stormwater will surcharge (back–up) into the basin itself and percolate vertically down through the vegetation and filter media.  Text Box: Bioremediation basin at various stages of construction Both the vegetation type and filter media (loamy sand) have been specified to comply with the latest findings from current research to maximise the treatment performance of the bioremediation basin.  While the concept is simple thousand of hours of research, both nationally and internationally, have gone into determining the most favourable specifications.

High flow by-pass: The system also has a high flow diversion channel installed to redirect high stormwater flows that may damage or erode the filter media and vegetation from the system. 


As this is the first system of this specific design configuration to be constructed in Hornsby Shire Council it is planned to undertake sampling up and downstream of the basin to determine its effectiveness at reducing pollutant concentrations. This will be done using automated samplers that provide the ability to sample stormwater from rain events before and after stormwater has passed through. Results from this sampling program will be used to determine whether similar systems will be installed elsewhere throughout the Shire.  They will also add to a growing database of work being done nationally on the development of best practise stormwater quality management. Furthermore, the site will be used as a demonstration site to educate other local governments and the general community in the benefits of bioremediation in treating stormwater.



3.7       Stormwater Gardens - Turner Road, Berowra

In June 2008, Council completed the installation of six stormwater gardens on Turner Road, Berowra.  These systems (also known as biofilters or bioremediation systems) have been demonstrated to be effective at-source structural stormwater pollution control measures (Fletcher et al 2005).


Stormwater flows over the vegetated area and slowly percolates through the filter media. Pollutant removal is achieved though the interface of the vegetation and filter media as a result of enhanced sedimentation in the vegetation zone, mechanical filtration, sorption and other chemical processes in the filter media and plant and biofilm uptake of pollutants (Hatt et al 2006). An underdrain collects the treated water and delivers it to existing stormwater infrastructure.






One of the six stormwater gardens installed on Turner Road, Berowra (Illustration reproduced courtesy of Brisbane City Council)






















3.8       Developer Constructed Devices

Hornsby Shire Council currently requires developments greater than 2500 square metres in area to provide permanent stormwater quality treatment devices on or adjoining their subject sites. Developers are conditioned by Council to also provide maintenance during the construction phase in accordance with an approved Asset Maintenance Plan. Following completion of the development, two scenarios can result:

1.            Developer Constructed, Council Maintained

These devices were installed by Developers as a condition of development consent (usually Torrens Title) and have been taken over by Council to maintain after which 80% of the lots have had dwellings erected and occupied. Council will usually seek a financial contribution from the developer towards operating and life cycle costs.

2.            Developer Constructed, Community Association Maintained

These devices have also been installed by Developers as a condition of development consent and either, continue to be maintained by developers in the short term or are the responsibility of the body corporate to maintain under Community or Strata Title.


Council currently keeps a record of these stormwater quality assets in order to ensure all maintenance complies with the consent conditions post-occupation. Council usually reaches a mutual agreement with developers to take over the basins as Council assets, in return for a sum of money which has been estimated to sustain the maintenance of basins over a 20 year life cycle.


Listed below are sites where developer built wetlands and sedimentation basins required have been constructed as a condition of development consent. It should be noted that only the Shepherds Drive, Cherrybrook and Sydney Road, Hornsby Heights constructed wetlands are currently under the care, control and management of Council. The remaining wetlands are managed by Community Associations or developers under approved Plans of Maintenance.


Summer Hill Way, Berowra

The Outlook, Hornsby Heights

Foley Place, Castle Hill

Kalang Road, Mount Colah

Shepherds Drive, Cherrybrook (The Lakes)

Huntingdale Way, Thornleigh

Millstream Grove, Dural

Wild Ash Avenue, Thornleigh

Sydney Road, Hornsby Heights

The Sanctuary, Westleigh



Hornsby Shire Council

Attachment to Report No. EN38/08 Page 22





4.1 Rainfall measurement

Daily rainfall data is obtained from the Bureau of Meteorology at nine sites across the Shire. This data is used to examine the relationships between total yields of gross pollutants and rainfall. In 2007/2008 the Hornsby Council area recorded above average annual rainfall and was subject to a high proportion of large rainfall events (Refer to Appendix A for statistical data). This explains the comparative increase in yields referred to in following section.



4.2       Performance of Gross Pollutant Devices

4.2.1              Pollutant Removal Trends

The collection of performance data over the 2007/2008 financial year has allowed Council to examine the indicative maintenance costs and gross pollutant removal trends for the 370+ water quality improvement devices in the LGA. The results indicate that in 2007/2008 the gross pollutant devices have served to remove approximately 1236 cubic metres of sediment, litter and organic matter from the Shire’s waterways.  These volumes were large and can be best explained by two anomalies:

1.            The above average rainfall that resulted in greater volumes of pollutants being mobilised and captured (refer to figure 4.3); and

2.            The higher than normal sediment and organic yield resulting from the cleaning out of a number of sediment basins and the dredging of the Lakes of Cherrybrook (150m3). As a result, sediment volumes accounted for approximately 48% of the total pollutant load captured, litter 5% and organic matter 47%.


The following series of figures examine the performance of GPD’s in 2007/2008 and against previous years. 


Figure 4.1: The relationship between average monthly volume of gross pollutants and average monthly rainfall.



When pollutant volume is analysed against average annual rainfall all three categories of gross pollutants are mobilised and captured after only 10 mm of rainfall, evident on the graph by the steep rise in the curve. This phenomenon is referred to as the “first flush” effect, after which the volume captured continues to rise at a much slower rate in relation to rainfall volumes.


It can be seen that the load of litter recovered from all devices over the period is fairly consistent for all size rainfall events (indicated by the flat dotted line). This is most likely due to the fact that litter is readily mobile and floatable in the formal drainage system (curb, gutter and pipes) and most of it will be flushed and collected in downstream GPD’s, even in small rain events. However, the fact that the curve for sediment is steadily climbing, proportional to rainfall, illustrates that after the initial flush the transport of sediment is directly proportional to stormwater volumes and associated energy.


Figure 4.2: Volumes of pollutants removed from GPD’s (2007-2008)

The actual volume of pollutants removed from month to month varied greatly in the 2007-2008 period. A clear correlation between monthly removal rates and rainfall cannot be made due to: 1) variable lag times between rainfall events and cleaning events, and 2) the disproportionally high volumes removed from sediment basins and wetlands which are in addition to regular cleaning events.


However, a strong correlation is found between rainfall and pollutant yield from Council’s GPD’s when viewed annually, as shown in Figure 4.3.  With increased rainfall there is increased stormwater run-off into Council’s drainage system that results in pollutants being mobilised, transported and trapped by GPD’s.


Figure 4.3: Pollutant volume removed from GPD's against average annual rainfall over the last three years

Figure 4.4 Prediction of annual gross pollutant rates using landuse area.



Hornsby Shire Council is now at a stage where the data gathered from the various gross pollutant devices can be used to predict the annual gross pollutant (export) rates on the basis of landuse. Figure 4.4 shows how the annual export rate of pollutants exponentially increases with the amount of catchment that is urbanised (excludes bushland/open space). This information can be used when planning for future devices, in terms of expected export rates and known device capabilities. Stormwater managers can then compare actual pollutant export rates with the predicted values in order to gauge the efficiencies of devices through time.


The high frequency of Hornsby Council’s inspection and cleaning of the devices combined with the unique trap designs for ease of maintenance, ensures that the pollutant trapping efficiency is optimum for each storm event and that materials do not decompose or stagnate causing additional problems with the release of pollutants into the water column.



4.2.2   Maintenance Costs

The total cost to Council to maintain its water quality assets and adjacent landscaped areas was approximately $347,000 in the 2007/2008 financial year ($257,000 for cleaning/maintenance, $90,000 for landscaping/vegetation maintenance). This cost included device inspections, cleaning and desilting, material processing for reuse, disposal of litter to landfill, asset maintenance and repair, landscape maintenance and weed control in and around assets and maintenance of leachate treatment and reuse facilities. However, the higher than expected costs were as a result of two one-off maintenance projects:

·  Remediation of Mt Colah stockpiling site: $87,000 (Refer to section 4.4 for further detail);

·  Dredging of Lakes of Cherrybrook:  $45,000


Table 4.0 presents the averages in terms of capital investment and operational cost for individual basket, trash rack and proprietary devices from the period June 2001-June 2008. The average annual installation and maintenance cost per hectare of catchment for proprietary traps is still quite high in comparison to the traditional trash racks and baskets. However, the proprietary devices average annual capture per hectare offsets these higher costs by being superior to the traditional devices, mainly as a result of their closer proximity to the pollutant source.


Table 4.0 GPD Comparative Costs from July 2001 - June 2008


Average Clean Cost $

Average Annual Maintenance Costs $/yr *

Trash Rack (n=21)



Large Trash Basket (n=10)



Proprietary Device (n=58)



Pit inserts  (n=170)




4.2.3   Dredging Lakes of Cherrybrook 

In March 2008, as part of the CRR maintenance program, Council initiated dredging works at the Lakes of Cherrybrook. This activity involved the removal of depositional material (organic matter and sediment) from the upper and lower ponds. Contractors dredged the lower pond using a walking excavator and trucks.  Sediment plumes on both the tributaries to the upper pond were removed in a less invasive manner through the use of eduction trucks.


The dredging works form part of an overall water quality and ecological improvement initiative for the lakes embarked upon under the CRR program in 2008. Other components of the initiative proposed in 2008/2009 include:

·  Installation of aerators in both ponds to increase dissolved oxygen levels, enhance water quality and hopefully reduce the prevalence and severity of Botulism outbreaks.

·  Deployment of rafted reedbeds in the lower pond, which act as floating wetlands and provide high levels of water quality treatment.

·  Planting of native aquatic plants at the interface between water and land to enhance water treatment, stabilise banks and provide habitat.

   Contractors removing dredge spoil, Lakes of Cherrybrook                        Lower pond after dredging, Lakes of Cherrybrook



4.3       Wetland Performance

4.3.1 Pollutant Removal Trends and Costs

A summary of wetland related annual costs and monitoring data is contained in Table 4.2. The average maintenance cost for Council’s major wetlands is calculated at $3,035 per site per year (or 1.6% of the average capital cost).


The size of catchments draining to these constructed wetlands ranges from 15-400 hectares. The average pond surface area to catchment area ratio calculates at 0.23% which is below the minimum design size recommended by DLWC (1998) of 2% of the catchment area. It should be noted that this recommendation does not account for the variability associated with different catchment land uses, pollutant loads, peak flows, topography and soils. It is best used to determine preliminary wetland feasibility. Because the nature of Hornsby Shire is so topographically constrained (ridge top development that does not afford large areas for wetland construction) and contains significant remnant bushland, the wetland feasibility threshold is much lower than average.


Water quality monitoring of five separate systems managed by council over the past 10 years has shown that levels of total nitrogen, phosphorus, suspended solids and faecal coliforms are significantly reduced under base flow and small storm flow events. Monitoring results are based on both grab and load-based samples (and multi-probe analytes) obtained by Council over multiple rainfall events and inter-events.

Two wetland sites were monitored during 2007-2008 period (Refer to the Water Quality Annual Report 2007/2008 fro statistical analysis). Sampling was not undertaken during large stormflow events. Clarinda Wetland was removing on average approximately 40% of Total Nitrogen and Oxidised Nitrogen, 50% Ammonium Nitrogen, 60% Faecal Bacteria and 30% Suspended Solids. Cherrybrook Lakes was found to be removing approximately 60% Total Nitrogen, Ammonium Nitrogen and Oxidised Nitrogen, 40% Phosphorus and 70% Faecal Coliforms. However, there was an average increase of Suspended Solids from 5 to 6.8 mg/L., probably resulting from an increase of algae and organic debris in the open water bodies and a nett decrease in dissolved oxygen in water flowing out of both wetlands, indicating oxygen was taken up by microbial and vegetative materials in the deeper still waters.

Table 4.2 Constructed Wetland annual costs and monitoring records to date.


Capital Cost $ (Year)


Pond Surface Area  (m2)

Pond Surface Area to Catchment Area (%)

Cost per m2 of pond


Average Annual Maint. Cost2


Monitoring Data


Laurence St, Pennant Hills

135,000 (1996)





June 1995 – June 2002

Boundary Rd, West Pennant Hills

288,000 (1996)





August 1998 –

June 2002

Plympton Rd, Beecroft

305,000 (2000)





November 99 – June 2002

Brooklyn Rd, Brooklyn

46,000 (1997)






Clovelly Rd, Hornsby

117,000 (1999)






Sallaway Rd, Galston

36,000 (2000)






Clarinda St, Hornsby

241,000 (2001)





July 2002 – current

Hastings Park, Castle Hill

445,000 (2002)





July 2001 –

August 2003

grab & load

Midson Rd, Beecroft

252,000 (2003)






John Savage Cres, West Pennant Hills

203,000 (2004)






Lamorna Ave, Beecroft








Dartford Rd, Thornleigh















1 Includes monthly grab sampling (wet/dry) and probe (total of 13 parameters). Analysis by NATA lab

2 Includes weeding/spraying, sediment/rubbish/debris removal, planting/mulching and replacement and reporting (excludes volunteer Bushcare labour)

3 Volunteer Bushcare present onsite

4 Capital costs incorporates up to 100m of stream remediation 

*Cost/m2 of pond is calculated using capital cost and average annual cost/year


4.4       Material Disposal and Reuse

The CRR maintenance program aims to reduce the quantity and cost of disposing of recovered material to landfill by reuse and recycling within the LGA. This activity has been undertaken by Council for a number of years and is seen as being ecologically and financially sustainable.


However, due to the increasing volumes that were being removed from GPD’s in 2007/2008, due to above rainfalls the amount of material that needed to be stored and mechanically sorted was becoming too large to be accommodated at the designated site in Mt Colah. Therefore, the decision was made in early 2008 to cease this activity until a more suitable site could be sourced and established. The Mt Colah site was cleared of all residual material and remediated at a cost of $87,000.


Until a future site is found, Council will incur ongoing disposal costs for GPD material in excess of $120,000 per annum based on extraction and disposal volumes from the previous two years. This cost is up to 80% more than is required when we are able to sort and reuse the material within the LGA. Furthermore, the material is now being exported to landfill sites outside of the Shire. This position is neither ecologically or financially sustainable, therefore Council staff will be pursuing all avenues to source a suitable site for material sorting and stockpiling.


Hornsby Shire Council

Attachment to Report No. EN38/08 Page 29





Due to the increasing number of devices being built and the resulting demand for timely and efficient maintenance, Council has continued to engage bush regeneration contractors on a 3 year basis. The contracts are annually renewed based on a performance evaluation of the previous year’s work and compliance with the conditions of the contract.



5.1       General Maintenance Considerations

The key objectives of the contract are:


i) to maintain planted native vegetation around water quality structures and nominated wetlands, using methods that have minimal environmental impact on aquatic organisms and water quality;


ii) treatment and eradication of any riparian and aquatic weeds giving priority to the treatment of categorised noxious weeds, applying herbicide according to manufacturers specifications and in a responsible and recorded manner (in terms of both environmental and personal safety); and


iii) to provide a maintenance report for each site after treatment, including a more detailed maintenance report for the wetland sites which is required to assess the extent of plant growth and site recovery from weed infestation.


5.2       Maintenance of Landscapes surrounding Gross Pollutant Devices

In 2007/2008, contractors were responsible for landscape maintenance around eighty plus sites at a cost of $57,690 (1825 hours). This involved weeding and spot spraying of the immediate area surrounding each water quality control asset including landscaped areas that have been mulched and planted with local native species. Some replacement planting and staking of existing tubestock is also required. Newly constructed devices will also require planting of terrestrial tubestock and in some cases, aquatic (macrophyte) plantings, with all plant stock being supplied by Council’s nursery. Maintenance reports and invoices are submitted to Council on a fortnightly basis. Targeted terrestrial weed species include - Privet, Camphor Laurel, Lantana, Blackberry, Turkey Rhubarb, Castor Oil plant, Balloon Vine, Madeira Vine, Honeysuckle, Morning Glory, Asparagus Fern, Mist Flower, Crofton Weed, Ochna, Ginger, Wandering Jew and other herbaceous weeds and grasses such as Kikuyu and Paspalum.



5.3       Maintenance of Wetlands

This involves the maintenance weeding/spraying of riparian areas and removal of weeds and nuisance plants within the shallow wetland ponds. In 2007/2008, contractors were responsible for maintaining 14 wetland sites at a cost of $33,000 (this includes four wetlands not built using funding from the CRR budget). Of this $33,000, 80% was dedicated to Councils four largest wetlands (Wallumeda, Laurence Street, Hastings Road and Clarinda Street). Time is also allocated to the removal of stormwater litter/rubbish strewn throughout the pond and edge areas. Replacement planting with macrophytes is also carried out, including occasional wetland establishment at new sites. A wetland maintenance sheet is required to be completed when conducting works within wetlands, as Council requires this information for wetland condition monitoring.


Target aquatic weed species include Typha (Bullrush), Barnyard Grass, Milfoil, Watercress, Cyperus eragrostis and other undesirable or noxious water plants (e.g. Ludwidgia (peruviana), Alligator Weed and Salvinia). If a W1 Noxious Weed category plant is found onsite, the Contractor is to immediately notify Council as required under the Noxious Weeds Act 1993.


       John Savage Wetland, West Pennant Hills: Contractors planting aquatic plants




Hornsby Shire Council

Attachment to Report No. EN38/08 Page 31





The Catchments Remediation Program has also been responsible for funding the treatment of polluted leachate from two of the Shire’s largest former municipal tip sites at Arcadia Park, Arcadia and Foxglove Oval, Mt Colah.  Instead of using the traditional technologies available for the treatment of leachate, Council has looked to more sustainable and innovative methods that can achieve pollution reductions and serve as a model for leachate treatment at a local government, state and national level.


This work is significant by way of the methodology which mimics natural processes of nitrification and denitrification. Council staff have worked together in a trans-disciplinary manner, together with specialised scientific consultants to design, construct and monitor both treatment systems. Council is committed to the long-term maintenance, monitoring and management of the two facilities in order to justify and apply the technological benefits to other landfills within the Shire. Monitoring to date has revealed a dramatic reduction in ammonia which has maximised the opportunities for reuse on adjoining open space and landscapes.



6.1       Foxglove Oval, Mount Colah

Foxglove waste disposal site was in operation from 1963 to 1980. This site produces approximately 10,000L/d of leachate due to the location of the tip on an existing drainage line, and the lack of a sound impervious capping layer over the oval. The main environmental concern within the leachate is the elevated ammonia concentrations ranging between 40 and 200 mg/L.


Stage 1 of the rehabilitation process has been completed, which involved capturing the leachate using a leachate cut off drain, collection well, pump and soakage pit at the base of the landfill. The collected leachate is then pumped to a two-cell (vertical and horizontal flow), soil-based reed bed (shallow wetland) which significantly improves the quality of leachate leaving the fill. This treated leachate is then pumped to and irrigated (below ground drip) over the adjoining native woodlots and park. Costing around $300,000 to install, the system is able to treat around 10,000 L/day of ammonia rich leachate and has minimal ongoing costs. It has been calculated that the system saves Council about $40,000 p.a. (in lieu of waste water disposal costs).


The final stage of the leachate remediation was completed in Febuary 2008 and has involved the installation of a bio-reactor to treat 4,500-6,000L of leachate a day to a level compatible with standards for irrigation reuse. Developed and patented by Biospot P/L, the bio-reactor technology uses a process whereby Nitrosomonas and Nitrobacter are immobilised on a carrier (that is, bacteria able to process nitrogen compounds are placed in a tank “reactor” where they attach to plastic beads). The reactor design offers “Simultaneous Nitrification (that is conversion of ammonia to nitrite and nitrate) and Denitrification” (that is conversion of nitrate and nitrite to nitrogen). The design of the reactor optimises the production of nitrate and removal of ammonia from over 50mg/L to below 2mg/L.  The treated water from the reactor then passes through the reed beds where it is “polished” to a quality suitable for irrigation on the adjoining sportfield.


Monitoring results illustrating the high level of treatment achieved by the system can be viewed in the “Annual Water Quality Report 2007/2008”.



    Leachate bioreactor and control panel, Foxglove Oval, Mt Colah.






6.2       Arcadia Park, Arcadia

In 1997/98 the Arcadia landfill was remediated by capping the fill with clay and separating the stormwater and leachate collection systems. Stage 1 works involved the relocating of waste from adjacent properties, regrading the landfill to reduce batter slopes, separation of leachate and stormwater into separate collection systems, clay capping of the landfill surface and stabilisation/revegetation of these surfaces.


At present two concrete tanks at the base of the site collect around 60,000 litres of ammonium rich leachate every quarter. Council uses the same technology deployed at Mt Colah to treat approximately1000 L/day of leachate at the site. Costing less than $40,000, the payback period for the treatment system was calculated at 3 years based on savings associated with previous waste water disposal costs.


Hornsby Shire Council

Attachment to Report No. EN38/08 Page 33





Since 1997, the Catchments Remediation Rate (CRR) has funded a proportion Council’s Street Sweeping Program at a total cost of $226,000 per year. Street sweeping is an effective method by which gross pollutants (sediment, leaves and litter) can be collected at source by targeting problem leaf drop areas and high pollutant load land use areas, e.g. commercial and industrial.


In 2007/08, 2184 tonnes of material was collected from scheduled cleaning of roadside curb and guttering, with on average 110 km of road being swept per week. The majority of the material is leaf and bark (organic matter) resulting from high leaf drop during dry weather.


Figure 7.1 compares volumes extracted by GPD’s against street sweeping. Interestingly, in the case of street sweeping, rainfall can be observed to have an inversely proportional relationship, that is, street sweeping volumes increase the lower the rainfall. In simplistic terms this can be attributed to a combination of the high leaf drop during dry weather and material being available to be removed by street sweeping due to less frequent run-off events. 

Figure 7.1: Comparison of volume of pollutants extracted by GPD's and street sweeping against average annual rainfall

* Average Annual Rainfall calculated from rain gauges with complete annual records only.

The two Schartz A5600XL vacuum sweepers which were purchased in 2002 have had their sides labelled with environmental messages and acknowledgement of the CRR funding.


This activity remains a viable way to collect larger gross pollutants at source and hence prevent material and associated contaminants from entering the drainage system and waterways under stormwater flow.


Hornsby Shire Council

Attachment to Report No. EN38/08 Page 34






This report has aimed to provide quantitative data and analysis of the relative performance of different water quality control measures, including gross pollutant devices, sediment basins, wetlands and bioremediation systems that have been constructed to improve stormwater quality in Hornsby Shire. The results of the report can be used by stormwater and catchment managers to provide a better insight into determining the type of structure and suitability for specific sites. Furthermore, the data provides valuable information about the costs (both capital and maintenance), benefits and device optimisation which can aid in the formulation of strategies to improve catchment/landuse practices by both structural and non-structural means.


Overall, the findings of this report should give stormwater managers a better insight into the cost-effectiveness and performance of water quality improvement structures and the management of life-cycle costs for individual stormwater quality assets. The performance of these devices has allowed Council to both refine and modify future designs, and judge their appropriateness to proposed remediation sites based on catchment size and land use impacts.




9.0       REFERENCES



Brisbane City Council (2006).  Water Sensitive Urban Design – Technical Design Guidelines for South East Queensland.  Version 1 released June 2006. 


Collins, A. (2005). Stormwater Reuse Issues and Experiences – Hornsby Shire Council. Stormwater Industry Association 2005 Regional Conference, Port Macquarie, NSW, 20-22 April (12pp).


Cooperative Research Centre for Catchment Hydrology (2003). Model for Urban Stormwater Improvement Conceptualisation (MUSIC). Version 2 released December 2003.


DLWC (1998). The Constructed Wetlands Manual – Volumes 1&2.


EPA (1999). Environmental Guidelines: Assessment, Classification and Management of Liquid and Non-Liquid Wastes.


Engineers Australia (2006) Australian Runoff Quality Engineers Media


Hatt, B et al (2006) Filter media for stormwater treatment and recycling: the influence of hydraulic properties of flow on pollutant removal Water, Science and Technology IWA Publishing


Hornsby Shire Council (1997). Catchments Remediation Program Five Year Plan (Revised Edition). Report prepared by The Water Catchments Team.


Hornsby Shire Council (2002). Catchments Remediation Capital Works Annual Performance Report 2001/2002. Prepared by The Water Catchments Team, October 2002.


Hornsby Shire Council (2005).  Annual Water Quality Monitoring Report 2006/2007. Prepared by The Water Catchments Branch, October  2007.


Hornsby Shire Council (2006).  Draft Stormwater Drainage Asset Management Plan.  Prepared by the Water Catchments and Assets Branches, May 2006.


Microclimate (2006) Annual Progress Report for major CRR Wetlands. July 2006.


Rocla CDSâ Technologies Pty Ltd, Gross Pollutant Traps Product Brochure, November 2007.


University of Technology, Sydney (2004). Environmental Assessment of HydroCon Stormwater Infiltration Systems at Hornsby. Faculty of Engineering.


Victoria Stormwater Committee (1999). Urban Stormwater: Best practise environmental management. CSIRO


WBM Oceanics (2005). Maintenance Guidelines for Stormwater Treatment Measures. Final Report January 2005. Prepared for Hornsby Shire Council under NSW Stormwater Trust funding.





Location and Sources of Rainfall Data (BOM 2008)

Monthly/Annual Rainfall For Hornsby Shire (mm)


Location and

BOM Station No.s

W. Pennant Hills






Mt Kuring-gai










Pennant Hill


Wisemans Ferry


Monthly Average






























































































































































# Missing data (average does not take missing data into account)

Average rainfall and average number of days exceeding 10mm and 50mm of rain for 6 sites across the Shire 2007/2008. (Note: Figures in brackets are for 2006/2007)


Average Monthly Rainfall (mm)

Average No. of Days >10mm rain

Average No. of Days >50mm rain



2 (0)

0 (0)



2 (4)

2 (0)



1 (1)

1 (1)



1 (5)

0 (0)



7 (0)

1 (0)



7 (1)

2 (0)



4 (1)

0 (0)



8 (4)

1 (0)



2 (5)

1 (1)



5 (4)

1 (0)



4 (1)

0 (0)



6 (9)

3 (2)



50 (35)

13 (4)

# Missing data (average does not take missing data into account).