water and waste committee 15 august 2018 · 15.08.2018 · 9 7-9 feb 2015 7 247.2 332.6 390.8 10...

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WATER AND WASTE COMMITTEE

15 AUGUST 20182

REPORT ON SEWERAGE SYSTEMS DURING HEAVY RAIN

B. Millar | 24/10/1 | #5790770

RECOMMENDATION:

It is recommended that Council notes the report on sewerage system performance during periods of heavy rain.

EXECUTIVE SUMMARY:

Cairns Regional Council owns and operates a 1,132-km network of gravity sewers and 182 pumping stations to provide sewerage services to 67,520 connected properties. During periods of rainfall, stormwater and/or groundwater can enter the sewerage system through a range of potential pathways. Particularly heavy rainfall can cause the sewerage system to become overloaded and result in the release or spilling of sewage from the system.

An analysis of data shows that 324 sewage surcharges on private property have been reported to Council in association with thirteen storm events since 2009. The reported instances have both reduced in number and narrowed in spread for the events since March 2012. This is supported by a reduction in customer service complaints received over the same period for sewerage services. Cairns’ sewerage services also perform favourably when compared with other providers with a similar tropical climate.

The improvement in sewerage services has been enabled by the significant investment in sewerage infrastructure augmentations and renewals made progressively by Council through its annual capital works program. The program is informed by comprehensive master planning exercises, and regular inspections and condition assessments, to resolve the competing challenges of growth, ageing infrastructure, and rainfall-derived inflow and groundwater infiltration.

The area of Westcourt – Bungalow has reported the most number of singular and repeat instances of sewage surcharges on private property. This area, together with Manunda and Manoora, is recognised as experiencing ongoing problems. Council’s capital works program includes the following specific projects to improve the sewerage system performance in these areas, which are planned for completion in 2019/20 at a total value of $22.8m:

Upgrades to the major pump station at Lennon Street, Manunda;Earlville Sewerage Upgrade, involving the upgrade of gravity sewers and a new major pump station in McCoombe Street, Bungalow;Upgrade of an existing major pump station at Marshall Street, Bungalow; and,Upgrade of an existing major pump station at Brown Street, Bungalow.

Agenda Water and Waste Committee – 15 August 2018 #5833388

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The above program of works seeks to achieve an affordable level of service provision to resolve the competing challenges affecting sewerage performance. Any sewerage system, though, has a design capacity that may be exceeded by specific events, such as periods of particularly heavy rainfall endemic to tropical far north Queensland.

It is recommended that Council notes this report on sewerage system performance during periods of heavy rain.

BACKGROUND:

The following motion was carried unanimously during General Business of the Water and Waste Committee Meeting on 20 June 2018:

“General Manager Water and Waste to prepare a report detailing problems with the sewerage system during periods of heavy rain in terms of back flushing and any other faults that we are aware of and that the report be specific in nature as to numbers and locations, what measures need to be taken to rectify the problems and anticipated costs.”

Cairns Regional Council owns and operates sewerage systems with the primary objective of collecting and conveying sewage for treatment to an appropriate standard. Premises are serviced by private sanitary drains and connected to Council’s sewerage system at a property connection branch (PCB). The PCB denotes the point of ownership and responsibility between Council and the property owner.

During periods of rain of any intensity, stormwater and/or groundwater can enter the sewerage system through a range of potential pathways:

through defects (e.g. cracks, gaps, tree roots etc.) in Council’s underground sewerage network, including along sewer pipes and at access chambers (e.g. manholes); or,at the tops of manholes, where they may be under ponded water, for example; or,through defects in the sanitary drainage system on private property connections to sewerage; or,non-compliant or illegal connections, such as roofwater or other stormwater systems, directly to sewer.

During heavy and high-intensity rainfall, the volume of stormwater and/or groundwater entering the above potential pathways can overload the sewerage system, resulting in spills or surcharges of sewage. Sewerage systems typically include emergency relief systems to control the release of sewage during these events:

Emergency Relief Structure (ERS) on Council’s sewerage system:o An ERS permits controlled overflows of sewage at predetermined

locations in order to prevent overloaded or blocked sewers from discharging at sensitive locations, on private property and inside buildings1.

Overflow Relief Gully (ORG) on private sanitary drains:o An ORG is a grated outlet located just above ground level outside the

premises but below the lowest fixture.

1 Gravity Sewerage Code of Australia (WSA 02-2014)


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o It is designed to operate as a release mechanism by directing the overflow outside. The height above the ORG of fixtures in the kitchen, bathroom, laundry, and floor waste gullies is relevant to directing the overflow outside.

The above issues are common to any reticulated sewerage system and not unique to Cairns.

COMMENT:

Record of sewage surcharge events on private property

Records of sewage surcharges on private property reported to Council are available since 2009. An analysis of daily rainfall suggests these reported incidents may be grouped into thirteen (13) distinct groups. Event information is provided in Table 1 and graphed against daily rainfall in Figure 1.

Table 1: Event information for property sewage surcharges report to CouncilEvent

No.Date period No. of property

surcharges reportedMax. daily

rainfall1Max. 3-day

total rainfall1Max. 5-day

total rainfall1

1 12 Jan 2009 38 278.4 325.4 393.62 8-9 Feb 2009 28 121.6 174.8 223.23 22 Jan 2010 1 27.8 34.2 39.44 26 Mar 2010 4 115.8 121.2 146.45 4-14 Feb 2011 54 268.6 296.8 3106 25 Feb - 7 Mar 2011 46 183 266.8 376.47 18-26 Mar 2012 82 158.6 245.6 393.68 12-13 Apr 2014 5 175.2 175.2 181.29 7-9 Feb 2015 7 247.2 332.6 390.8

10 17 Jan 2018 1 142.4 252 25211 6 Feb 2018 1 71.6 112.6 112.612 2-12 Mar 2018 43 130.8 246.4 272.813 21-26 Mar 2018 14 217.6 270.8 279

TOTAL 324 - - -Note: 1. Cairns Aero (BoM station number 31011)


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Figure 1: Daily rainfall and number of property surcharges (count by day)

Further information on the number of reported property surcharges by ABS Statistical Area 2 (SA2) level is provided in Table 2. Locations of reported property surcharges are mapped in Figure 2. Table 2: Event information by ABS Statistical Area 2 (SA2) level

SA2 Area

No. of reported property surcharges by Event Number

Total1 2 3 4 5 6 7 8 9 10 11 12 13Jan ‘09

Feb ‘09

Jan ‘10

Mar ‘10

Feb ‘11

Mar ‘11

Mar ‘12

Apr ‘14

Feb ‘15

Jan ‘18

Feb ‘18

Mar‘18

Mar ‘18

01. Clifton Beach -Kewarra Beach 4 5 1 4 1 15

02. Trinity Beach -Smithfield 6 2 1 6 2 1 1 19

03. Yorkeys Knob -Machans Beach 1 8 3 12

04. Redlynch 1 2 305. Freshwater -Stratford 4 5 1 10

06. Brinsmead 4 5 2 1 1207. Whitfield -Edge Hill 6 2 1 6 6 13 1 1 1 1 38

08. Cairns City 4 3 3 10 8 1 2 3109. Manunda 6 3 1 5 4 3 1 1 2 1 2710. Manoora 1 3 1 4 2 2 1 1411. Kanimbla -Mooroobool 6 2 1 5 1 1 16

12. Westcourt -Bungalow 3 4 1 15 13 1 1 17 9 64


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SA2 Area

No. of reported property surcharges by Event Number

Total1 2 3 4 5 6 7 8 9 10 11 12 13Jan ‘09

Feb ‘09

Jan ‘10

Mar ‘10

Feb ‘11

Mar ‘11

Mar ‘12

Apr ‘14

Feb ‘15

Jan ‘18

Feb ‘18

Mar‘18

Mar ‘18

13. Earlville -Bayview Heights 1 2 1 1 4 1 10

14. Woree 1 1 215. White Rock 2 8 1 1116. Mount Sheridan 3 2 5

17. Edmonton 1 2 4 718. Bentley Park 1 1 3 519. Gordonvale -Trinity 1 4 4 7 3 1 20

20. Babinda 1 2 3Total 38 28 1 4 54 46 82 5 7 1 1 43 14 324

Table 3 reports the number of properties with single or multiple instances of reported sewage surcharges based on the event data available since 2009. Table 3: Number of properties with single or multiple instances of reported sewage surcharges

SA2 AreaNo. of properties with ‘x’ reported surcharges Total

no.x=5 x=4 x=3 x=2 x=101. Clifton Beach - Kewarra Beach 2 11 1502. Trinity Beach - Smithfield 2 15 1903. Yorkeys Knob - Machans Beach 1 10 1204. Redlynch 3 305. Freshwater - Stratford 1 8 1006. Brinsmead 1 10 1207. Whitfield - Edge Hill 2 7 18 3808. Cairns City 2 2 21 3109. Manunda 1 1 22 2710. Manoora 2 10 1411. Kanimbla - Mooroobool 2 10 1612. Westcourt - Bungalow 1 1 1 14 24 6413. Earlville - Bayview Heights 1 6 1014. Woree 2 215. White Rock 3 8 1116. Mount Sheridan 5 517. Edmonton 2 5 718. Bentley Park 5 519. Gordonvale - Trinity 3 14 2020. Babinda 3 3Total 1 2 11 38 24 324


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Figure 2: Location of reported property sewage surcharge events (2009 – 2018)


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Customer Service Standards

Table 4 states the level of service and performance target adopted in Council’s Customer Service Standards. Annual performance since 2009/10 is illustrated inFigure 3.

Table 4: Customer Service Standard for sewerage service complaintsKey Performance Area

Level of Service Performance Target

Quality Effective transport of sewage – overflows and odour

10 complaints per 1000 connections per year

Figure 3: CRC sewerage service complaints (no. per 1000 properties) (National Performance Report Indicator Code C11)

Benchmarking with Other Similar Service Providers

Each year Service Providers (SPs) must collate and supply significant volumes of data on water and sewerage services to numerous State and Commonwealth agencies.

Figure 4 illustrates the number of sewerage service complaints (per 1000 properties) reported by SPs with a similar tropical climate to Cairns, in terms of wet season dominant rainfall. A South East Queensland SP of most-similar size to Cairns Regional Council, Redland City Council (connected pop. 136,000), is included as an additional comparator.


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Figure 4: Comparison of sewerage service complaints (no. per 1000 properties) for high wet season rainfall SPs and Redland City Council (NPR Indicator Code C11, ranked by FY 2016/17 performance)

Rectification of Issues

The record of sewage surcharge events on private property suggests an overall improvement in performance since 2009 (see Table 1 and 2). This is, to an extent, also reflected in the sewerage service complaints received over the same period (see Figure 3), noting that there was a change to complaint-reporting definitions and criteria around 2013/14. The general improvement in performance has been enabled by the investment in sewerage infrastructure augmentations and renewals made progressively by Council through its annual capital works program. Council’s annual sewerage capital expenditure since 2010/11 is graphed in Figure 5.

Council’s capital works program is informed by comprehensive master planning exercises, and regular inspections and condition assessments, to resolve the competing challenges of:

Population growth and increasing demand for services; Ageing infrastructure and deteriorating condition; and,Rainfall-derived inflow and groundwater infiltration.


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Figure 5: Annual capital investment in sewerage infrastructure (NPR Indicator Code F11)

It is acknowledged (as indicated in Table 2) that current sewerage system performance issues are predominant in the Westcourt, Bungalow and Earlville suburbs. Council’s capital works program includes specific projects to improve the sewerage system performance in these areas, including the following:

Upgrades to the major pump station at Lennon Street, Manunda including:o Capacity-augmentation of the pressure main (planned for completion in

2018/19 with a total investment of $9.7m)o Upgrade of the sewage pumps and electrical assets (planned for

completion in 2019/20 with a total project budget of $1.9m)Earlville Sewerage Upgrade, involving the upgrade of gravity sewers and a new major pump station in McCoombe Street, Bungalow (planned for completion in 2018/19 with a total project budget of $7.6m)Upgrade of an existing major pump station at Marshall Street, Bungalow (planned for completion in 2019/20 with a total project budget of $1.6m) Upgrade of an existing major pump station at Brown Street, Bungalow (planned for completion in 2019/20 with a total project budget of $2.0m)

It is noted that the above program of works seek to improve capacity and mitigate the competing challenges that affect sewerage performance. Any sewerage system, though, has a design capacity that may be exceeded by specific events, such as periods of particularly heavy rainfall endemic to tropical far north Queensland.

Council could consider additional works for further improving the performance of its sewerage system and reduce sewage surcharges to address:

Adverse influences from stormwater drainage systems, including high tides effecting low-lying areas; and, Non-compliant or defective private property sanitary drains.


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Stormwater system influences

A particularly challenging issue to resolve is the adverse influence of stormwater drainage systems on the sewerage systems in low-lying areas of Cairns. In this situation, drainage and flooding issues can cause the sewerage system to back up and overflow into private properties at some locations. An approach to managing this issue is to install a reflux valve on the private sanitary drain, which has been carried out by Council previously.

The reflux valve will close when the sewerage system outside the property is full or surcharged and prevent sewage from the Council reticulation system backing up into the property drain. However in certain circumstances, the property drain may not have enough ‘force’ to be self-draining in heavy rainfall events. Therefore during such times of heavy rainfall, it would be advised that occupants of the property minimise the use of fixtures and water using appliances, such as dishwashers and washing machines to prevent the private drain from overflowing within the property.

The reflux valve could be installed by Council at its cost (approx. $3,000 to $5,000 per installation) with the property owner being responsible for ongoing maintenance.

Defective or non-compliant property drains

Council regularly tests for defects or non-compliant works on private property drains. Where a defect or non-compliance is detected, a notice is issued to the property owner with the intent it will be rectified. An analysis of Council’s inspection records availablesince 2012 indicates of the 167 defects detected, only 44 (26%) had been rectified when re-inspected.

Council could consider a policy and funding of greater enforcement, or other means, to improve the rectification-rate of non-compliant or defective works detected through Council’s regular inspection processes.

OPTIONS:

Option 1 (Recommended)

That Council notes the report.

Option 2

That Council notes the report and requests further information regarding additional works to further improve the sewerage system performance, potentially considering:

more detailed investigation of specific problem areas or issues, and corresponding costs to rectify; or,a policy to support the enforcement of corrective action to rectify defective or non-compliant property drains.


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CONSIDERATIONS:

Risk Management:

Cairns Regional Council Water and Waste has an Environmental Management System based on the AS/NZS ISO14001:2015 standard and uses a risk-based approach to identify and manage potential environmental risks associated with the provision of sewerage services.

Council Finance and the Local Economy:

Cairns Regional Council’s $165.7 million capital works program for 2018/19 consists of an investment in sewerage infrastructure of $19.3 million, including:

Earlville sewer main upgrade - $6.5mTreatment plant upgrades - $5.7mSewer relining program - $3.4mSewer pump station upgrades - $2.8m

Community and Cultural Heritage:

Council’s committed investment in sewerage infrastructure works will improve wastewater management that will result in a reduced risk to public health.

Natural Environment:

Council’s committed investment in sewerage infrastructure works will improve wastewater management that will result in a reduced risk to the natural environment.

Corporate and Operational Plans:

The provision of sewerage services supports the following Strategic Goals of the 2017-2022 Corporate Plan:

Natural Assetso Value and protect Cairns’ pristine natural environmento Maintain clean air, water and waste

Serving the Communityo Deliver best-value customer service to the community

Statutory:

Cairns Regional Council’s Water and Waste department is a commercialised business unit of Cairns Regional Council under the Local Government Act 2009 with a charter including the:

Collection and treatment of sewagePlanning for and delivering wastewater infrastructureMaintenance of the community’s wastewater infrastructure

Council also has obligations under the Environmental Protection (Water) Policy 2009and Environmental Protection Regulation 2008.


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Policy:

Cairns Regional Council Water and Waste has adopted an Environmental Policy to demonstrate Council's commitment to providing wastewater management services in an environmentally responsible manner, and to a standard that meets government and community expectations.

Ben MillarPrincipal Engineer – Strategy, Planning and Assets

Mark WuthActing General Manager Water and Waste


water and waste committee 15 august 2018 · 15.08.2018 · 9 7-9 feb 2015 7 247.2 332.6 390.8 10...

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