sewer

Asset Management Plan -Sewer

Sewer

Wagga Wagga City Council // Asset Management Plan // Sewer //

This Supporting Section should be read in conjunction with Council’s Asset Management Plan, the Asset Management Policy (which sets out Council's philosophy of asset management) and Council’s Asset Management Strategy (which provides Council with a clear direction and goal for managing the community's $1.185 billion (as at June 2010) worth of assets).

The condition of Council’s assets has been audited as part of the asset inspection regime, rated against the asset condition reference sheet and captured in Council’s electronic mapping system. The condition of all Council’s assets is rated from excellent to very poor.

As at 2010, the condition of entire sewer pipe network has not been rated. In 2010 CCTV investigations were conducted on approximately 5km of the network. The condition rating for the network which has not been CCTV rated has been extrapolated from the age and material of each section of the sewer infrastructure.

As more of the network is CCTV rated the appropriate actual condition ratings will be applied and the subsequent change in value to the network will be calculated and recorded. Council’s electronic mapping system for sewer, PipePAK differentiates between the sections which have been audited and those which have not.

The colours on the following maps indicate the condition of the asset, as detailed in the below table.

1 Excellent Dark Green

2 Good Green

3 Average Yellow

4 Poor Orange

5 Very Poor Red

The first map indicates the condition of sewer pipes from excellent to very poor in the Wagga Wagga Local Government Area (LGA). This condition rating is based on extrapolated condition rating and the CCTV condition rating. The following table highlights the proportion of sewer pipes in each condition ranging from excellent to very poor.

1 Current Asset Base

Sewer


Excellent 47% 288km

Good 39% 239km

Average 11% 69km

Poor 2% 15km

Very Poor 1% 1km

Sewer


The second map indicates where pump stations and sewerage treatment plants are located in the Wagga Wagga LGA.

NB there is also a Treatment Works in the outlying area to the south east of Forest Hill, which is not included in this map.

Sewer


Size of the NetworkCouncil owns and maintains approximately 612km of sewer pipe, 37 pump stations and 5 treatment plants conducting secondary and tertiary sewerage treatment. In the Wagga Wagga LGA 23,610 properties in the Wagga Wagga urban area, Ladysmith and Uranquinty are connected to the system which collects 5,380 ML of sewage each year (Sewer Business Plan).

Challenges of the NetworkThe challenges facing the sewer network include:

the need to ensure the effluent reuse schemes fully comply with the requirements of the Australian Guidelines for Water Recycling 2006

reviewing greenhouse gas emissions and implementing processes to minimise emissions

maximising effluent reuse and development alternative schemes

the size of the sewage treatment plant in Forrest Hill may not meet the demand when new areas are developed

the need to provide safe, reliable and cost effective services to unserviced rural villages

high number of sewer main chokes and collapse, service complaints and frequent customer interruptions compared to other NSW sewer utilities of similar size

the management of increasing energy costs

the management of the non-sequential development on the fringe of the Wagga Wagga urban area and

the management of the high biological and chemical load from liquid trade waste

There are also a number of challenges facing the business of sewer management, including:

potential impacts of on-going drought and climate change on revenue and assets

ageing infrastructure

proposed and potential changes to the businesses as a result of the review of water utilities in NSW

non-compliances with OEH (Office of Environment and Heritage)Licenses for effluent discharges

failures of onsite wastewater treatment systems in the rural villagesand

the retention and attraction of skilled employees

Sewer


Condition Ratings Reference SheetsThe condition of the sewer pipe infrastructure network is audited against a rating scale which ranges from excellent to very poor. This scale is used as the basis of all assessments of the sewer pipe infrastructure network by Council’s Surveillance Team. The rating scale forms the Condition Rating Reference Sheet below.

NB Condition Rating Reference Sheets will be developed for pump stations and treatment works in future revisions of this Asset Management Plan.

2 Condition Assessment

Sewer


Risk and Condition Rating IndicatorsCouncil also uses Risk and Condition Rating Indicators to determine a prioritised works schedule for the maintenance, renewal and replacement of large asset categories. These indicators are used in addition to the Condition Ratings Reference Sheet to enable further analysis of the worst sections of the asset class.

The Indicators are used to develop an overall Works Schedule Priority Rating for each individual asset or section of an asset. The first stage considers the risk that the condition of the asset poses to the community. The following table details the Risk Rating Indicators for the sewer network.

Sewer Risk Rating Indicators

Weighting Number of chokes reported

1.2 > 6 chokes per annum

1.1 4-6 chokes per annum

1.0 1-3 chokes per annum

Weighting Number of connections

1.3 >30

1.2 21-30

1.1 11-20

1.0 1-10

The second stage of the process considers the Condition Rating Indicators. The age of the pipe is considered for the sewer network.

The older the sewer pipe (or the closer the pipe is to the end of its design life), the high the risk of failure due to internal and external pressure, cracking, root penetration and/or chemical corrosion. Each section of sewer pipe is rated against the Condition Rating Indicators detailed in the below table.

Sewer Condition Rating Indicator

Score Within percentage of its design life

1 30% of design life ending





Sewer


The results of the Risk and Condition Rating Indicators analysis are combined to give an individual asset or section of the asset a Works Schedule Priority Rating. For example a section of sewer could be rated as follows:

Sewer Section XYZ

Number of chokes (CH) 1.1

Number of Connections (C) 1

Age (A) 3

Works Schedule Priority Rating Formula

(C+A)CH

Works Schedule Priority Rating (1 + 3 )1.1 = 4.1

The Work Schedule Priority Ratings for sections of sewer infrastructure are then ranked from highest to lowest to produce prioritised schedule of works for maintenance, replacement and renewal of the network.

Intervention LevelsTo guide Council’s response to customer requests a set of reactive triggers has been developed for each asset category. These triggers are called intervention levels and include target response times. The following table details the intervention levels and response times for maintenance of the sewer network.

Sewer Intervention Levels

Mains Blockages and collapsed pipes

Corrective action taken within 60 minutesduring work hours or 120 minutes after hours

Overflows Corrective action taken within 60minutesduring work hours or 120 minutes after hours

Pump or other breakdown including power failure

60 minutes during work hours or 120 minutes after hours

Spur line blockages and collapsed pipe

60 minutes during work hours or 120 minutes after hours

Odour Corrective action taken within 4 working days.

Sewer


Condition Inspection RegimeThe condition and risk of the sewer pipe network will be assessed simultaneously as part of the Condition Inspection Regime. This inspection will audit the condition of each section of the sewer pipe network against the Condition Rating Reference Sheet and also assess the risk based on location and usage.

The entire sewer network will be audited via CCTV over the next 3 years. Until Council has completed a network wide surveillance of the sewer networkit is difficult to accurately state a realistic interval for the frequency of these inspections. Subsequent revisions of this Asset Management Plan will identify the inspection frequency and regime once determined from the completed first surveillance.

It is proposed the inspection regime should address the pipe material most at risk of failure, for example clay, then by the age of the pipe. Obviously the older the pipe, the closer it is to the end of its design life.

Pipes closer to the end of their design life need to be inspected more frequently. A new pipe or one less than 10-15 years old may only need to be inspected once during that time.

Ad hoc inspections will be conducted in response to customer requests, on a needs basis and where the asset degrades due to un-foreseen or unusual circumstances, like a storm event. These inspections are done onsite by trained Surveillance Officers and the results are captured in Council’s electronic mapping system (ArcGIS).

Sewer


3 Life Cycle ManagementLife cycle management details how Council plans to manage and operate the asset category at the agreed level of service while minimising life cycle coststhroughout the useful life of the asset.

For most local government assets there are four key phases to the life cycle, namely: acquisition, operation and maintenance, renewal, and disposal.

Costs occur in each phase of the asset life cycle. It is important to attribute these life cycle costs to each phase to allow for effective decision making about how the asset will be managed.

The life cycle costs of assets include:

initial capital investment

operation and maintenance

refurbishment and renewal

administration, overheads and taxes

depreciation

capital use rate charges or rate of return and

disposal of the asset at the end of its useful life

The initial capital or investment cost of a new asset is a significant cost and often dominates the decision as to whether to acquire the asset or expand the infrastructure network. However, it is important to include all the costs associated with each phase of the asset life cycle, including ongoing operation and maintenance, future renewal and disposal.

Sewer


Estimated Useful LifeThe lifespan of sewer pipe depends on the material used. The following table details the useful life of the various sewer pipes.

Pipe Material Design Life

Galvanised iron 20 years

Asbestos cement 45 years

Cast Iron, or uPVC, or HDPE 70 years

Cement lined ductile iron, or concrete, or reinforced concrete 90 years

Earthenware or vitreous clay 100ars

* uPVC – Unplasticised Polyvinyl Chloride* HDPE – High Density Polyethylene

Target Maintenance EventsThe Sewer network, operates on a cost recovery basis. The maintenance of the network is not financed by Council’s General Purpose Reserve, but from the income of the network, the Sewer Reserve. For this reason, maintenance events of the network are not included in this Asset Management Plan. However, this information will be considered in future revisions of the Plan as Council moves towards strategic asset management.

RenewalA detailed work plan for the renewal of the sewer infrastructure is developed annually to support this Asset Management Plan. This renewal program is prioritised based on condition and risk.

Disposal Currently, Council includes the cost to dispose of an asset in the unit rate of that asset type. As Council moves towards strategic asset management this cost will be captured separately. The Asset Management Plan will be updated to reflect this change as it occurs across the asset types.

Sewer


4 Level of ServiceThe Asset Management Plan for 2011 has been developed based on data collation, research outcomes and the results of Council’s internal stakeholder engagement process.

The next stage of the process is to ask the community to identify which asset condition is satisfactory to them. This will begin with an extensive community consultation process. The consultation will be in the form of a community survey which will be conducted online, at community gatherings, through focus groups and stakeholder meetings. The survey will use new technology, be based on images and a simple selection process. The outcomes of the consultation will form the foundation for true community engagement to occur in relation to the management of infrastructure across the Wagga Wagga LGA, in particular the development of agreed levels of service, supported by Council and the community.

As Council gathers data from the community about the level of service for each asset category the outcomes will be integrated into the Asset Management Plan.

Until the outcomes of the community engagement are known Council will provide costings to achieve an average condition for each asset category and use this as the satisfactory level of service.

Sewer


5 Financial ConsiderationsThe following graph details the proportion of the sewer pipe network in each condition.

Current Liability of the Sewer NetworkCouncil’s current liability in relation to the infrastructure network is the sum of all asset units which have a condition rating of poor and very poor. The current liability of the sewer network is estimated to be $51,812,452 (in 2010 dollars).

The Forest Hill Treatment Plant has an estimated current liability of approximately $451,634 (in 2010 dollars).

Sewer


The following tables detail the current estimated liability of the gravity mains and rising mains of the sewer network, based on extrapolated condition data.

Gravity Main Diameter Current Liability

100 $63,524

150 $31,094,535

225 $7,677,427

300 $2,096,122

375 $708,859

450 $2,359,800

500 -

600 -

750 -

Rising Main Diameter Current Liability

100 $640,454

150 $425,541

225 $1,203,463

300 $2,499,670

375 -

450 $472,415

500 $2,119,008

600 -

750 -

Projected Annual Maintenance CostsThe sewer network is not financed by Council’s General Purpose Reserve, but from the income of the network, the Sewer Reserve. For this reason, projected maintenance costs of the network are not included in this Asset Management Plan. However, this information will be developed and included in future revisions of this Plan.

Sewer


6 AssumptionsThere are some generic assumptions made in the management of assets in Wagga Wagga City Council, these are found in the Asset Management Plan. In addition, the following assumptions have been made in relation to the sewer network:

The extrapolated costings for the sewer network in this AssetManagement Plan are based on the following:

o NSW Reference Rates for a STW 200 EP

o Victoria Local Government Adjustment Rates and

o Sewer 2010 contract

The extrapolated costings also consider the age, type and diameter of the sewer pipe.

The estimated useful life of the sewer pipes included in this Plan are based on the NSW Reference Rates for STW 200 EP.

sewer

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