The harvesting tank at Apex Oval receives flows from east Dubbo catchment which is approximately 61 hectares in area. The catchment consists primarily of residential, commercial and light industrial buildings. The stormwater line that runs past Apex Oval
is 1500 mm in diameter which drains in a northerly direction.
A 900mm off take pipe has been installed which diverts water to the GPT and ultimately
to the water storage tank. In flows greater than the capacity of the 900mm pipe the water
will continue down the 1500mm stormwater main.
There are three devices to filter the quality of water before it enters the storage tank. First in line is the GPT. The considerations for selection of an appropriate GPT device were:
All diverted flows needed to be treated. There was to be no bypass flows of the treatment device.
The treatment device was to filter stormwater prior to the water entering into the
Hydrocarbon treatment both in volume and outcome quality were significant concerns whilst a number of GPT suppliers are able to remove gross pollutants, a higher level of sediment treatment was necessary to reduce a long term build up of sediment in the main storage.
A single unit device for ease of management was preferable.
For these reasons a SPEL off-line Stormceptor Class 1 4600 Series GPT was selected. This product can remove 99.9% of hydrocarbons and 85% of Total Suspended Solids. In order to connect to the stormwater off take pipe an excavation of around 8 metres was necessary.
The second stage of filtration is the inlet outlet chamber constructed downstream of the GPT. This structure allows for further sediment control by having water drop into a pit, losing velocity and therefore dropping out sediment. The intake pipe is set above the level where sediment shall deposit. This is in place as a contingency should the GPT fail.
The third structure to protect the water quality of stormwater entering the underground tank is a chamber within the tank itself. This area was surrounded by a geotextile fabric from the main storage area and provides the final layer of protection to prevent silt and larger pollutants into the reservoir.
The 900mm pipe takes water from the GPT to the tank. The tank has a below ground external pump system that extracts the water and distributes through the irrigation network. There is capacity to send the water through a filtration unit.
The need for further water treatment such as chlorine or UV has not been established. Preliminary testing results show there is currently no requirement for further treatment in order for the Apex Oval Stormwater Harvesting Scheme to irrigate in accordance with Australian Guidelines for the reuse of captured stormwater.
As a risk management measure only the surface of Apex Oval is to be irrigated during the testing phase as it is able to be locked preventing public access. The outer fields during this proofing period shall remain on town water irrigation. This shall enable ongoing testing throughout December 2012 prior to the facility being opened for the 2013 winter season.
The figure overleaf provides a schematic layout of the system. Note that the thin green line identifies the location of Dubbo City Council’s existing stormwater pipe network.
The original 12ML tank design was modified to become a 10ML tank. This was to account for the need to reduce the cost of the tank to a cost that was closer to the forecast cost in the project budget. It should be noted that the feasibility study of the tank showed that a tank of between 10ML and 12ML was the most cost effective size. Approval was given by the Commonwealth for the new 10 ML design on 16 August 2011.
The layout of the original tank design was to be across the full extent of the playing surface. This was no longer viable due to the lack of support provided by the saturated garbage and gravel layers which became apparent after detailed geotechnical analysis. The design team then worked on a layout that moved the tank to cover only a third of the playing surface and have a deeper profile so it was able to sit on a clean rock base. This was the ultimate design adopted by Council and approved by the Commonwealth.
The tank was of a recycled plastic modular construction. In simplistic terms the modular units are covered in a waterproof layer that is plastic welded closed and waterproof. Around the tank are placed drainage cells that protect the tank from groundwater building up under the tank thus preventing issues regarding tank buoyancy arising.
Figure6: Note themodular natureofthe tankstructure. Thewaterprooflayeris what the units aresitting on. As the tankreacheditsfull size thewaterprooflayerwas wrappedaroundthe modular unitsandweldedtogether.
The pump system has the capacity to deliver water at 25l/s at the sprinkler head as this is the requirement of the installed irrigation system. To control the irrigation system Council has installed its web based centralised irrigation management system.
This control system can be accessed by tablet or smart phone. The software is able to manage water input and output. The control system has inputs from moisture sensors at differing levels in the soil profile of the playing surface. Dry and wet bulbs in the tank provide data to the system as well. This means precise amounts of water can be delivered to the grass surface and the tank when required.
For example in the event of a lack of rainfall the control system shall know when additional water is required for a specific irrigation cycle. The system shall start the bore and supply the exact amount of water required for the programmed irrigation cycle thus maximising the tank capacity available for the collection of stormwater.
The irrigation system utilises harvested stormwater over other sources of water.
The playing surface constructed above the tank and over the remainder of the damaged playing area consists of:
The structure of the playing surface is the same as is found on major sporting facilities on the eastern seaboard such as AAMI stadium in Melbourne and ANZ Stadium in Homebush, Sydney. The economic advantage to Dubbo in having such a playing surface centres on the ability to attract regional level tournaments and possibly national level games such as NRL premiership rounds.
Legend Couch has been shown in trials to be a hard wearing turf suited to high profile sporting grounds. Furthermore it is regarded as a water efficient cultivar (Cynodon sp).
For the duration of the construction project the membership of the steering committee was as follows:
Mr Murray Wood, Director Parks & Landcare Services Division, Dubbo City Council
Mr Wes Giddings, Manager Sporting Facilities, Parks & Landcare Services Division, Dubbo City Council
Mr Ian Bailey, Manager Works Services, Technical Services Division, Dubbo City
Mr James McKechnie, Manager Recreation Services, Community Services Division, Dubbo City Council
Representative Environmental Services Division – as required
The Parks & Landcare Division is the asset owner of Apex Oval and is the end user of the
stormwater harvesting and irrigation system. The Parks & Landcare Division was the grant applicant within Council and the recipient of the funding. The Manager Sporting Facilities project managed the component of the project that dealt with irrigation system and playing surface tender.
Technical Services Division
The Works Services Branch of the Technical Services Division was the coordinator of the engineering component of the project as well as providing service delivery for the bulk
earthworks. Elements under the auspices of the Works Services Branch included:
Detailed design of tank and stormwater system Environmental approvals regarding waste and construction Tank Tender and subsequent contract
Excavation of tank site
Installation of stormwater piping, GPT and associated infrastructure
Community Services Division
The Manager Recreation Services was responsible for liaising with sporting groups and
supply of equipment for Irrinet centralised control system.
Nicholson Projects Pty Ltd
Subcontractor for earthworks to Evergreen and contractor
to Council to install concrete edging to playing field.
Turfthelot Pty Ltd
Subcontractor to Evergreen for playing surface.
Contractor to Council to supply and lay turf on the surrounds.
Service providers involved in the delivery of the project are listed below: TABLE 4: Private Sector businesses engaged
Dubbo City Council has formal policies in regard to purchasing. Any purchase over $150,000 is required to be publicly advertised for a period of 28 days. After subsequent analysis by the Tender assessment panel a report is required to be submitted to Council’s Works & Services Committee for review and approval. The Works & Services Committee then makes a recommendation to the Ordinary Meeting of Council in regards to the recommendations of the tender report. After the Ordinary Meeting of Council a contract can be signed between Dubbo City Council and the Council approved tenderer.
Council sought two tenders for the Apex Oval Stormwater Harvesting Project. They were:
1. Supply and installation of a 12ML underground tank.
2. Installation of an International Standard Sand Base Playing Field and Irrigation
System for Apex Oval.
The Works Services Branch of Dubbo City Council’s Technical Services Division was engaged by the Parks & Landcare Division to undertake detailed design, contract development and management of the tank installation and the associated stormwater infrastructure. This is because engineering related disciplines were outside the expertise of the Parks & Landcare Division staff.
Works Services undertook the following activities:
Concrete work for stilling chamber adjacent to the tank
Stormwater pipe installation
Sewer main relocation
Stormwater pit installations
The expenditure and contributions for the scheme at completion are tabulated in table 5. No project-generated income was earned on project monies.
TABLE 5: ProjectFunding
Dubbo City CouncilContribution
Note that this includes $9,800,000 in in-kind tipping fees.
* Includes final payment received as a result of the final report being approved.
Council's Internal Auditor carried out a probity review of the tender process followed in awarding Contract SF4.7.7 to Dubbo Terrazzo and Concrete Industries Pty Ltd (Yoff Pty Ltd) in August 2011. The Internal Auditor reported to Council's Audit and Risk Management committee that no sufficient and competent audit evidence came to the attention of the Internal Auditor in regard to awarding the contract in a manner that contravenes Council or Department of Local Government policies or procedures. The Audit Committee recommended that the report be noted and Council, at its meeting held on 25 May 2012 adopted such recommendation.
Council engaged SMEC Australia Pty Ltd to undertake a technical review of Rainsmart's modular tank system for stormwater retention/detention. The conclusion of their report is that "It is not expected the creep displacement would compromise the operation of the cells." In short the product is fit for purpose.
In regards to the playing surface construction above the tank the following standards were applied by an independent company to ensure the playing surface was built to specification:
AS 1141 Methods of sampling and testing aggregates
AS 1289 Methods of testing soils for engineering purposes
In addition Council required evidence that the supplier of the sports turf was supplying “Legend” couch - the genuine cultivar as specified in contract documentation. The assessment was undertaken by Independent Turfgrass Consulting.
Council held four public viewing sessions of the Apex Oval project (Table 6 below). These information sessions allowed people to walk in a controlled manner onto parts of the site and ask questions of the project management team.
TABLE 6: Dates ofPublicViewingSessions
WHAT COULD BE VIEWED
15 November 2011
The excavation, water management, beginning of tank assembly
17 January 2012
Extent of tank installation and damage from storm flooding
28 March 2012
Installed and sealed tank, backfilling over tank
10 July 2012
Installation of sand profile for playing surface
Stakeholder Meetings were held with the sporting groups that use Apex Oval and/or play the same code as clubs based at Apex Oval. These stakeholder meetings took place 11 August
2011, 27 September 2011, 11 and 17 December 2011. In early December 2011 the decision was made by Council that Apex Oval would be unavailable for the entire 2012 winter season. This decision was made due to the long range forecast predicting above average rainfall during construction. The early decision was made to allow contingency plans for clubs and sporting organisations to plan for the upcoming 2012 winter season as well as negotiate on assistance they required.
This decision did receive some high profile publicity but it should be noted that the 2012 season progressed well at the alternative venue of Victoria Number 1 Oval.
The media was invited for opportunities to look over the site and then inform members of the community that didn’t attend public viewing sessions. These media opportunities took place on the following dates:
14 November 2011
17 January 2012
26 March 2012
12 September 2012
As can be seen from the aerial photograph provided in this document (Figures 1 & 9) there are a number of private residences neighbouring the Apex Oval site. Council held a briefing session on the 12 September 2011for those residents prior to construction commencing to discuss the proposed works programme.
The Apex Oval project also had a presence on Council’s website under the Major Projects banner found on the home page. This articulated the funding arrangements for the project and the key outcomes.