ELLENBROOK SEWER PRESSURE MAIN - EPA WA€¦ · The Water Corporation is preparing a Public Environmental Review (PER) for the proposed Sewer Pressure Main along Gnangara Road between

ELLENBROOK SEWER PRESSURE MAIN

Environmental Risk Assessment

Prepared for

Gutteridge Haskins & Davey Pty Ltd

October, 97

.- ---------------- .........

628.21.3(941. II II II II II IOIH IllIIIL 'u1tanc Sers"ices 1)

DNV 970478/1 Copy A :Ltject Number 2763)

Department of Environmental Protection Library

Gutteridge Haskins and Davey Pty Ltd

DNV Consultancy Services Ellenbrook Sewer ERA

October, 1997 '

LIBRARY DEPARTMENT OF ENVIRONMENTAL PROTECTION

WEST RAL1A SQUARE 141 ST. GEORGES TERRACE, PERTH

ELLENBROOK SEWER PRESSURE MAIN

Environmental Risk Assessment

Preparedfor

Gutteridge Haskins & Davey Pty Ltd

Prepared bYJ.K[3 65~:

Zie'* T. J. Kristoffersen

Reviewed by M. Wylie

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....

Issue Date 21 October, 1997 Revision 1

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Gutteridge Haskins and Davey Pty Lid DNV Consultancy Services Ellenbrook Sewer ERA October, 1997

CONTENTS Page

INTRODUCTION................................................................................................................. 1.1 Background .................................................................................................................. 5 1.2 Scope of Work..............................................................................................................5 1.3 Objectives ..................................................................................................................... 6

DESCRIPTION OF DEVELOPMENT.................................................................................7 2.1 Existing Arrangements .................................................................................................. 7 2.2 Proposed Development ................................................................................................. 7 2.3 Proposed Pipeline.........................................................................................................9 2.4 Gnangara Water Reserve............................................................................................12

METHODOLOGY..............................................................................................................13 3.1 Qualitative Workshop to Identify and Rank Options.................................................14 3.2 Ellenbrook Interim Pressure Main ERA Workshop (previous study workshop).......14 3.3 Relative Risk Ranking................................................................................................15 3.4 Risk Mitigation Workshop.........................................................................................15 3.5 Consequence Assessment...........................................................................................15 3.6 Frequency Analysis....................................................................................................16

HAZARD IDENTIFICATION ............................................................................................ 17

CONSEQUENCE ASSESSMENT......................................................................................18

FREQUENCY ANALYSIS ................................................................................................19

RISK ASSESSMENT .........................................................................................................20 7.1 Risk Criteria...............................................................................................................20 7.2 Primary Risk Results .................................................................................................. 20 7.3 Secondary Risk Results..............................................................................................21 7.4 Tertiary & Quatemary Risk Results..........................................................................21

CONCLUSIONS.................................................................................................................23

RISK MITIGATION MEASURES.....................................................................................24 9.1 Pipeline Design...........................................................................................................24 9.2 Pipeline Construction ............................................................................................. . ... 24 9.3 Pipeline Operation...................................................................................................... 25 9.4 Detection Strategies.................................................................................................... 25 9.5 Spill Mitigation Measures ..........................................................................................25 9.6 Emergency Response.................................................................................................. 26

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Gutleridge Haskins and Davey Ply Ltd DNV Consuitancy Services Ellen brook Sewer ERA October, 1997

10. REFERENCES..................................................................................................................27

APPENDIX 1 RISK EVALUATION WORKSHOP I

APPENDIX 2 ERA OF ELLENBROOK INTERIM PRESSURE MAiN II

APPENDIX 3 RELATIVE RISK RANKING HI

APPENDIX 4 RISK MITIGATION WORKSHOP IV

APPENDIX 5 FREQUENCY ANALYSIS V

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1. INTRODUCTION

1.1 Background The Water Corporation is preparing a Public Environmental Review (PER) for the proposed Sewer Pressure Main along Gnangara Road between Ellenbrook and Wangara. Gutteridge Haskins & Davey Pty Ltd (GHD), the principal contractor, has retained Det Norske Veritas (DNV) to provide part of the Environmental Risk Assessment for the PER.

The planning study calls for an assessment of environmental risk related to the existing and proposed commissioning/operation of the sewer pressure main and subsequent development of risk reduction measures to minimise risk of groundwater contamination. An Interim Ellenbrook Pressure Main ERA has already been carried out by DNV (Ref. 1) and the discussions surrounding the present submission has indicated further evaluation of risk was required.

Contamination of groundwater in Western Australia is a serious environmental issue as has been described in the Department of Environmental Protection (DEP) bulletin 763 (Ref. 2). Wherein it is estimated that there are 1500 contaminated sites in Western Australia alone. The majority of contaminated sites have resulted from unsatisfactory industrial practices for storage of chemicals and for the containment and disposal of wastes.

The Gnangara Groundwater Reserve is arguably one of the most strategically important resources of the Perth Metropolitan area, providing in the region of 40% of drinking water consumed in this area. In recognition of this strategic importance the Gnangara Groundwater Reserve has been designated as a Priority One Protection Area by the Water & Rivers Commission (W&RC).

It is against this background that the transport of sewage across the Gnangara Priority One Protection Area has been reviewed. DNV's role was to provide a primary risk assessment for potential groundwater contamination resulting from acute sewer leakage events.

1.2 Scope of Work The scope of work includes review of proposed sewage transport routes and pipeline configurations to select, on a qualitative basis, "best options". A risk assessment of the best option(s) would then be conducted to show that the risk associated with the selected route and configuration is ALARP (as low as reasonably practicable).

This study does not include detailed consequence modelling in terms of dilution and migration through soil or in the Gnangara basin, or the subsequent dilution and treatment in a water treatment plant. For the purposes of this study this specialised input will come from a.separate study done by hydrologists Rockwater Pty Ltd (Ref. 4).

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1.3 Objectives

The objectives of the study is to provide input to the environmental management program of the PER in the form of an assessment of the lowest risk option, the overall acceptability of the proposed sewer main and effective strategies for reduction of environmental risk.

Specific objectives for this study were to:

Overview previous findings of risk assessment studies to ensure a common understanding and inclusion of unresolved issues in the current assessment;

Specifr all relevant sewage transportation alternatives i.e. pipe materials & configuration, route options, location above ground or below etc.;

Establish acceptable risk criteria against which to evaluate the selected alternatives;

Identify scenarios which could lead to pollution of the water reservoir or other land areas along the sewage transport route;

Do an initial coarse screening of the options to defme the best option or pair of options.

Review risk reduction options as well as tertiary and quaternary risk for the Ellenbrook Sewer Main Development

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2. DESCRIPTION OF DEVELOPMENT

2.1 Existing Arrangements Presently sewage is transported by truck along Gnangara Road for disposal. Approximately 17 trucks per day or 350 cubic metres of sewage is transported. This is considered an interim measure and not generally considered acceptable as a long term solution.

2.2 Proposed Development The North East Corridor Structure Plan (March 1994) identified the requirements for a number of key infrastructure facilities to be located in the corridor to service its long term development. One being a major wastewater pump-station to service the entire corridor and pump effluent via a pressure main along Gnangara Road in the North West Corridor.

Gnangara Road forms the boundary for two Underground Water Pollution Control Areas (UWPCAs) designated by the Water & Rivers Commission to protect groundwater recharge areas which are important for public water supply. Wanneroo UWPCA lies to the north of Gnangara Road; Mirrabooka UWPCA lies to the south of it. The UWPCAs extend westwards as far as Lake Gnangara and eastwards to Roberts Road. Much of the pressure main route lies within the highest category of UWPCA protection, with a Priority 1 classification.

The area under study is underlain by the Bassendean Sand, which forms part of the superficial formations aquifer that supplies the public water supply bores. The Bassendean Sand is fine to medium grained, moderately well sorted, with surrounded grains. It is permeable and consists essentially of quartz sand which has a limited capacity to adsorb or fix contaminants.

The superficial aquifer along the route is unconlined, and the water table is generally 2-5m below ground surface in the vicinity of the six existing bores; the intervening unsaturated zone consists entirely of sand, with some patchy iron cementation ("coffee rock"). The natural direction of groundwater flow is towards the south.

The proposed pressure main would directly overlie the capture zones (areas which contribute groundwater) for six existing public water supply wells and four proposed wells, and is upgradient of a number of other public water supply wells.

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2.3 Proposed Pipeline This study considers the potential impact of a sewer pressure main across the Priority 1 Area running parallel to the Gnangara Road.

The proposed pipeline is a 500mm diameter rising (pressurised) main sewer to be laid within the road reserve, and running from a pump station at the south-west corner of the intersection of Lord Street and Gnangara Road west along Gnangara Road for about 12 kilometres, then north up Hartman Drive to discharge into the Gnangara Branch sewer.

The pipeline is to be constructed from 12m mild steel pipe sections. The pipe sections are to be internally lined with cement and externally coated with polyethylene to minimise corrosion potential. Pipe sections are to be connected through the use of rubber ring joints. Approximately 1000 joints will be made on this pipeline.

In accordance with recommendations made previously in the Ellenbrook Interim Pressure Main ERA (Appendix 2), pipe sections internally coated with polyethylene will be used in the vicinity of air valves.

An 8km section of this pipeline traverses the Gnangara Priority I Area and is in a straight line with a dogleg around the Ampoi Service Station (situated about 250m east of bore M3 10). Welds will be required for the "dogleg" bends and these will be welded on site.

The pipeline will be graded to high and low points and is expected to run below the level of the water table in some places.

The following features are included in the design:

Route markers every 250m Air/Scour valve pits will be sealed Pits will be located at a maximum distance from well heads Scour valves to be secured with keyed locks Scour valve outlet to be extended to camlock fitting for easy tanker connection Block stock valves for isolation and testing installed at scour pits Signage for emergency contacts on marker posts Monitoring and control includes flowmetering, pressure detection and level detectors in pits. Valve branch on either side of stop valves to assist draining

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2.4 Gnangara Water Reserve Groundwater levels in the vicinity of the six existing production bores along the route of the proposed main are at about 42m AHD (September 1988). Near M390, water levels are at about 37m AHD. Ground elevations range from about 65m AHD on the western side to between 45m AHD and 50m AHD in the central and eastern parts of the pipeline route.

There are six existing public water supply bores along Gnangara Road, adjacent to the pressure main route, and a further four are proposed along the eastern part of the route, subject to final approvals. Bore locations are shown on Figure 2 and details of these bores are presented in Table 4.1 below. There are additional public water supply bores to the south of Gnangara Road, as shown in Figure 2.

TABLE 4.1: PUBLIC WATER SUPPLY BORE DETAILS

Bore No. Northing Easting Collar 1995 Screen Wellhead (m) (m) RL Pumpage Interval Protection

AHD Quota (mbgl)* Zone2 Radius (m3/d) (m)

PRODUCTION BORES

M300 6481469 393822 45.37 1123 31.53-48.29 500

M310 6481515 395424 46.09 1099 22.05-53.29 500

M320G 6481523 396322 46.75 1370 21.0348.46 500

M330G 6481534 397257 47.78 1879 21.76-52.55 500

M340G 6481540 397938 47.04 1105 20.7445.43 500

M350 6481507 398876 45.89 822 31.00-46.00 500

PLANNED PRODUCTION BORES

M360 6481569 399854 44.91 1644' 0.0048.00 500

M370 6481578 400717 44.25 1644' 48.00-60.00 500

M380 6481587 401716 41.89 1644' 0.0046.00 300

M390 6481560 402566 42.59 822' 0.00-20.00 300 26.0048.00

Metres below ground level

Planned rate

Protection Zones are surface and subsurface areas surrounding a water bore supplying a public water system through which contaminants are likely to move towards the bore.

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3. METHODOLOGY

Figure 3.1 below schematically outlines the methodology applied to this project. The approach taken is consistent with the classical risk assessment methodology with a bias towards qualitative evaluation. This consists of a systematic analysis of what can go wrong. The normal conditions of operation of the system are defined and then the following questions asked:

What accidental events can occur in the system?

How frequently would each event occur?

What are the consequences of each event?

What are the total risks (frequencies x consequences) of the system?

What is the significance of the calculated risk levels?

These questions correspond to the five basic components of risk. Once a system has been analysed, if the risks are assessed to be too high according to some criteria, the system can be modified in various ways to attempt to reduce the risks to an acceptable level, and the risk levels recalculated. The process may therefore be viewed as iterative, where the design of the system may be changed until it complies with the needs of society. By objectively assessing the risks from each part of the system (either qualitatively or quantitatively), the risk assessment enables the most effective measures to reduce risks to be identified in a systematic and consistent fashion.

A workshop was convened including personnel from DNV, GHD, Water Corporation, DEP, Water & Rivers Commission, Shire of Swan, City of Waneroo and Ministry for Planning as outhned in Appendix 1 to identify rank options.

The workshop prepared the grounds for the analysis of the statistical data on pipeline failures which is a major activity in this study. Best industry pipeline data available to DNV was used to quantify the risk.

The risk was calculated as the chance of occurrence and size of spills onto surrounding ground for input to the consequence/ dispersion modelling being conducted by GHD's consultants team.

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Figure 3.1 : Flow Diagram ERA

Qualitative Workshop to Identify & Rank Options

Hazard Analysis associated with Preferred Option(s)

Semi-Quantitative Qualitative/ Descriptive

Frequency Analysis Consequence Analysis

Risk Analysis

Definition of acceptance criteria. Risk Assessment

2nd Workshop to Identify Risk Reduction

Strategies

Prepare Report

On conclusion of the risk quantification exercises outlined above, the initial workshop team were invited to reconvene and review risk reduction options as well as tertiary and quaternary risk. Outcomes of this workshop are outlined in Appendix 4.

3.1 Qualitative Workshop to Identify and Rank Options The Risk Evaluation Workshop employed a What-If analysis technique. What-If Analysis is a structured brainstorming methodology utilising a multi-disciplined team to identify hazards and risks associated with a proposed or existing project, process or design.

The flexibility of the What-If analysis technique, allows the team of analysts to consider the consequences and safeguards relating to various plausible "what-if' scenarios, relevant to the subject under consideration. The team makes qualitative risk evaluations resulting in recommendation development aimed at treating the risk i.e. minimising, controlling or further evaluating the identified risk.

The What-If Analysis results are included in Appendix 1.

3.2 Ellenbrook Interim Pressure Main ERA Workshop (previous study workshop) In general the methodology of the Ellenbrook Interim Pressure Main ERA Workshop was that of a classical risk assessment; i.e. a systematic approach to the analysis of what can go wrong. The workshop team included persons from Water Corporation and GHD with in depth knowledge of design, manufacturing, installation and operation of the type of pipelines in question.

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The focus of the analysis was on assessing the most effective way of mitigating the risks by ranking the risks and then attempting to reduce the most critical aspects.

The Ellenbrook Interim Pressure Main Workshop results are included in Appendix 2.

3.3 Relative Risk Ranking The main purpose of using Relative' Ranking methods is to determine the process areas or operations that are the most significant with respect to the hazard of concern in a given study. The theory behind Relative Ranking methods has its roots in the three basic questions used in risk analysis:

What can go wrong? How likely is it? What would the effects be?

The philosophy behind Relative Ranking approaches is to address these risk analysis questions to determine the relative importance of processes and activities from a safety standpoint. Thus approximate relationships of process attributes are compared to determine which areas present the greater relative hazard or risk.

The relative ranking results for the Risk Evaluation Workshop (3.1) are included in Appendix 3.

3.4 Risk Mitigation Workshop The workshop employed brainstorming with the aid of checklists to develop risk mitigation strategies aimed at improving pipeline integrity for each aspect of the development and operation.

Risk mitigation focused on:

prevention strategies for the pipeline design phase and pipeline construction phase. control strategies for pipeline operation and leak detection. treatment strategies for spill mitigation, emergency response and remediation.

The Risk Mitigation Workshop Results are included in Appendix 4.

3.5 Consequence Assessment Consequence assessment is one of the key steps in Risk Analysis. It provides the link between identifying potential loss of containment incidents and determining the impact of those incidents on the environment.

Both the Risk Evaluation Workshop and Ellenbrook Interim Pressure Main ERA qualitatively considered consequences relating to undesired events. Quantification of adverse consequences is outside the scope of this study.

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Outcomes from the above workshops are detailed in Appendix I & 2.

3.6 Frequency Analysis

The frequency analysis of main leakage was based on generic failure data. The generic failure data is derived from failure data for a wide variety of process and power industry plant, and as such is not specific to sewage pipelines. DNV proprietary software LEAK was used in conjunction with the VEREDA database to assist in the calculation of leak frequencies for the sewer main. These failure rates were then modified to reflect specific conditions relating to the proposed Ellenbrook Sewer Main.

The frequency analysis followed the historical approach with elements of data review covered during the Risk Mitigation Workshop i.e.

Define the context: Clear specification of incident for analysis. Review of source data : Historical accident data, company/national, adequate description. Determine failures and equipment exposures. Check data applicabifity : Check effect of technological change, pipeline environment, modified procedures. Reject non-applicable data, modifS' equipment exposure. Calculate likelihood: (failures/exposures) Validate likelihood : recheck against known data.

Detailed frequency analysis results are included in Appendix 5.

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4. HAZARD IDENTIFICATION

Pipelines for the transport of "hazardous" substances such as sewage may have significant environmental impact with respect to construction activities, physical hindrance, habitat fragmentation and leakage or spills.

From both the Ellenbrook Interim Pressure Main ERA Workshop and Risk Evaluation Workshop it was apparent that sewage leakage from the overland pipeline into the Priority 1 Groundwater reserve was the only hazard warranting further examination. Construction activities and the logistics involved in operating and maintaining a buried overland pipeline in this sensitive area where not considered a significant contamination threat by the workshop participants.

The Risk Evaluation Workshop team reviewed the findings of the Ellenbrook Interim Pressure Main ERA Workshop relating to potential pipeline failure and subsequent leakage. These findings were accepted as representative of potential causes for pipeline failure and no new causes were developed at this forum.

Causes for pipeline failure were identified during the Ellenbrook Interim Pressure Main ERA workshop as outlined in Appendix 2. These causes were as follows:

Corrosion in welds

Damage on backfilling

Damage to inner lining during transport (causes corrosion)

Excavation (damage to coating)

Excavation (damage to joints)

Excavation (damage to pipe)

Fatigue caused by incorrect transporting

Gas attack on concrete lining (causes corrosion)

Corrosion (for other causes)

Joints in bends slipping due to hydraulic forces

. Leaks from air valves or scour valves

Material defects from manufacturing

Overpressure of pipe

Pipe deformation on backfihling

Poor installation of joints

Seismic activity

Vandalism

These identified hazards were taken into account during the pipeline failure frequency analysis discussed in section 6 and detailed in Appendix 5.

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5. CONSEQUENCE ASSESSMENT

Consequence assessment is one of the key steps in Risk Analysis. It provides the link between identifying potential loss of containment incidents and determining the impact of those incidents on the environment. The evaluation of potential sewage leakage consequences on the environment and in particular the water table was dealt with by Rockwater Pty Ltd (Ref. 4).

For the purpose of presentation here the continuum of possible leak sizes are divided into two categories:

Small leak : leak which is too small to be detected by the flow metering instrumentation.

Large leak : leak which would be detected by the flow metering instrumentation.

These correspond to the categories used by Rockwater Pty Ltd (Ref. 4). The lower limit of what can be detected by a flow metering system has been set to 86 Id/day. All releases below this leak rate is therefore considered small. A nominal "worst case" scenario of 1400 Id/day has been used by Rockwater to represent the large leak category.

Large leaks can be expected to cause rapid shut down of pumps based on the detection of the leak. The amount actually leaked to the surrounding ground could therefore be quite small. Small leaks on the other hand could continue undetected over some time and therefore result in a larger amount released before detection and mitigation.

A buried pipeline would traverse the Gnangara Water Mound below the water table in some areas. Immediate groundwater contamination may result from any leak in these areas. In the areas where the pipe is above the water table the effects are more difficult to predict. Very small releases may never reach the water table due to capillary effects and uptake by plants. Please refer to the study by Rockwater Pty Ltd. for details (Ref. 4).

A finding of the Risk Evaluation Workshop was that sewage is not generally considered a significant environmental contaminant with permanent adverse effect, however potential accumulation of trace contaminants should not be discounted.

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6. FREQUENCY ANALYSIS

The failure frequency for small and large leaks was developed using generic DNV industry databases and software as outlined in section 3 and detailed in Appendix 5.

Failure cases considered were small and large leaks as previously defined. In the absence of an expected leak hole size this was calculated assuming a 6 bar operating pressure and leakage rate of 86 k/i and 1400 k/i for small and large leaks respectively.

Source data was reviewed extensively and although letters from product users were received indicating satisfactory service periods with no detectable leakage for one year, this was not a historical period with sufficient length to provide a statistically significant sample size.

Industrial pipeline failure causes have been previously defined by DNV and categorised and subcategorised. Each sub-category has been assessed and allocated a percentage contribution to the overall failure frequency. Through selection of the appropriate parameters pertinent to the pipeline under consideration, it is possible to develop an approximation of the failure frequency for pipelines with insufficient recorded history.

The rubber ring joints connecting pipelines were considered similar to flanges for failure frequency calculations. It was found that the joint failure frequency dominates the risk of leak due to the number of joints required for the pipeline.

No allowance was made for pressure testing on the premise that routine pressure testing. potentially increased the probability of joint failure through repeated high pressure cycles over an extended period of time.

Results of the frequency analysis are detailed in Appendix 5 and summarised in Primary Risk Results.

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7. RISK ASSESSMENT

7.1 Risk Criteria The EPA/DEP have developed a risk classification regime to assist in assessing potential adverse environmental impact. For purposes of this study this classification is outlined in Table 5.1 below:

Table 7.1: Environmental Risk Classification

RISK DESCRIPTION Primary The frequency and size of leakage. Secondary The frequency of the leak impacting on the groundwater. Tertiary The potential for groundwater quality degradation from sewage

infiltration into the groundwater system and the risk to public health from various contaminants.

Quatemary ___________

The potential of medium to long term degradation of water quality from contaminants arising from sewer main leakage.

While suggesting that the combined risk of groundwater contamination from the Gnangara Road upgrade and potential Ellenbrook Sewer Main Development should not exceed the anticipated risk posed by the current road, the DEP supports the concept of reducing the risk to as low as reasonably practicable (ALARP).

Risk reduction to ALARP criteria implies that risk reduction measures should be implementedas long as the cost of implementing these measures is not grossly disproportionate to the reduction in risk achieved. While there are many examples of this criteria being successfully applied to the loss of human life, the application of ALARP to environmental issues is still developing.

7.2 Primary Risk Results During both the Ellenbrook Interim Pressure Main ERA Workshop and Risk Evaluation Workshop it was apparent that sewage leakage from the overland pipeline was identified as the primary risk contributor to acute contamination of the Gnangara Water Mound.

For the purpose of presentation here the continuum of possible leak sizes are divided into two categories:

Small leak : leak which is too small to be detected by the flow metering instrumentation.

Large leak: leak which would be detected by the flow metering instrumentation.

The annual leak frequency and size of sewage leak anticipated is presented in Table 7.2. for the 8000m sewage pipeline crossing the Gnangara Priority 1 Area. The

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modified leak frequency accounts for the specific failure contributors related to the Ellenbrook Sewer Main, a detailed breakdown is provided in Appendix 5.

From Table 7.2 we that leaks from the pipeline can be expected with a return period of 135 years, with 20% of the leaks being less than 86 kllday and that leaks from the joints can be expected every 4 years with 78% of these having a leak rate of less than 86k1/day.

Table 7.2 : Frequency and Size of Sewage Leak

Pipeline Rubber Ring Joints

Total Modified

Less than 86 kllday 0.0015 0.2033 0.2049 0.1619 More than 86 kllday 0.0059 0.0636 0.0696 0.0550

TOTAL 1 0.0074 0.2600 0.2744 0.2 169

The assumption that the leak rate and frequency for rubber ring joints can be equated to those from flanged pipe connections therefore has two important implications on the results:

The total frequency is dominated leaks from the joints. This is as expected although the absolute frequency of the leaks is therefore highly sensitive to whether this assumption is correct.

The leak size distribution is very different for the pipeline and for the joints. The dominance of the leak frequency for the joints results in a dominance of the leak size distribution for the joints. The leak size distribution for joints is very biased towards smaller leaks.

7.3

Secondary Risk Results Large leaks were considered to be acute events with the potential to contaminating the groundwater in close proximity to the leak in a short space of time. All leaks above 86k1/day were considered to be large leaks. A "worst case" leak size of 1,400 id/day was selected as representative of large leaks. Smaller leaks would have the potential to contaminate the water resource through accumulated effects, since the leak would take some time to detect.

Both small and large leaks can therefore be considered to have the potential to impact on the groundwater. Therefore the results in Table 7.2 also outline the secondary risk. Please the report from Rockwater for details (Ref. 4).

7.4

Tertiary & Quaternary Risk Results Tertiary and Quatemaiy Risk estimation was outside the scope of this study. However risk mitigation strategies outlined in section 9 will also result in significant reduction in tertiary and quatemary risk.

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8. CONCLUSIONS

The construction and operation of a sewage pipeline across a sensitive groundwater area will require extensive commitment by the operator to risk management principles in order to ensure the ongoing integrity of the pipeline so as to minimise the risks associated with the transport of sewage across the Gnangara Priority I area.

Risk management focuses attention on ways to prevent accidents from occurring and to mitigate the consequences. Through the risk assessment process this has been evident. However, in case of failure of a this pipeline the cost relating lost capacity and repair could be extremely high, and it is likely to have significant environmental impact.

Mitigation decisions that have been evaluated include:

location of pipeline relative to sensitive areas location and spacing of isolation valves leak detection pipeline repair and contingency plans inspection and maintenance strategies

Throughout the review process design has been modified to include recommendations of risk studies and workshops. Specifically relating to pipe material selection, valve containment, corrosion inhibition and pipeline routing and these are defined further in section 9;

Location of a buried pipeline north of Onangara Road appears to be the best option following the relative risk ranking exercise outlined in Appendix 3.

To ensure the viability of the proposed development a number of risk mitigation measures need to be put in place as outlined in section 9.

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9. RISK MITIGATION MEASURES

Recommendations from the risk mitigation workshop are outlined below in 9.1 to 9.6.

9.1 Pipeline Design

Measures to ensure pipeline integrity and operational needs are included during design to minimise potential spill size.

Design to minimise use of valves, bends and fittings. Maxiniise distance between valves, bends and fittings from bores in critical welihead areas. Consider performance and compatibility of pipeline system. All valves, flange joints to be in pits to facilitate inspection! maintenance. Develop a construction QA Plan including manufacturers guidelines. Comprehensively review geotechnical environment to determine bedding requirements. Include provision for monitoring systems flow, pressure etc. Include requirements for back-up systems. Make provision for safe removal and storage of sewage at scour points. Ensure manufacturers & pipe construction QA systems are in place and adequate. Design for standard fittings and equipment. Materials of construction and coatings to be appropriate for application. Design to be subject to formal review cycle (HAZOP).

9.2 Pipeline Construction

Measures to ensure pipeline integrity during construction and commission to minimise the potential for spill.

Physical inspection and QA verification to be carried out by independent third party. Provide incentives for contractor, supplier ,etc. to maintain high standards throughout Make use of approved contractors with demonstrated performance (& accredited pipelayers) with specific focus on the rubber ring joints which are a major leak potential. Monitor bedding and backfill compaction. Integrity testing on completion of assembly (progressively between valves). Pipelayer to demonstrate competence prior to commencement of constniction. Safety Plan to address the introduction of new personnel (ref. 6 also). Pipeline route to be accurately recorded during construction process. Contractor to provide safety/ pollution control plan.

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9.3 Pipeline Operation Measures to ensure pipeline integrity during normal routine operation.

Establish a procedure for routine pipeline system inspection and testing, and follow best practice. Operating procedure/ maintenance schedule to be in accordance best practice. Defme areas of responsibility and verify compliance through audit. Incident management system to include maintenance breakdowns. Monitor sewage quality during operation to identify abnormal sources to facilitate control of undesirable contaminants. Operators to be trained and competent (demonstrable). System to be automated and fail safe (pump shutdown on pipe failure). Implement corrosion monitoring to measure wall thickness and pipeline coating effectiveness. Develop a pipeline corridor control program (i.e. permits to dig, liaison with other utilities, signage, etc).

9.4 Detection Strategies Measures to ensure early detection of potential leak conditions.

Flow monitoring equipment to be regularly calibrated and flow measurements routinely reconciled. Develop an operational plan for calibration of control/monitoring devices to ensure accuracy! reliability. Provide monitoring for leaks in interstitial spaces around critical components and pipes. Pipeline to be routinely pressure tested. Obtain resources to identify suspected leaks (people/ equipment' skills). Review potential for continuous acoustic leak detection. A corrosion monitoring program should be developed to ensure critical pipeline parameters are monitors on a regular basis i.e. wall thickness, coating integrity etc. Pipeline corridor control program (i.e. permits to dig, liaison between other utilities, signage).

9.5 Spifi Mitigation Measures Measures to ensure minimal environmental impact from potential spills (passive systems).

Sewage transport pumps to automatically shut down on loss of pressure. Provision of secondary containment in critical areas (valves and breathers etc.).

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9.6 Emergency Response Measures to ensure prompt and effective spill remediation (active systems).

The Emergency Response Plan should include provisions for mitigation, remediation and adequate response. Leaks are to be isolated as soon as possible to limit spill size. Ensure access for emergency response crews and equipment. Establish hierarchy of emergency response & priority also including 3rd party interests. Identify critical spares / skills necessary for emergency response effectiveness. Establish the requirement and availability of equipment. Place public signposts indicating emergency contact number at strategic locations along the route.

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10. REFERENCES

DNV (1996): "Environmental Risk Assessment of Ellenbrook Interim Pressure Main", Gutteridge Haskins & Davey Pty Ltd, October 1996

AS/NZS 4360: "Risk Management", Australian! New Zealand Standard, ISBN 07 337 01477.

DEP (1995): "Contaminated Sites - Assessment and management of contaminated land and groundwater in Western Australia", August 1995

Rockwater (1997): "Hydrological Conditions Along Gnangara Road and Possible Impact ofAccidental Leakage from the Proposed Ellenbrook Sewer Main ", October 1997

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APPENDIX I

RISK EVALUATION WORKSHOP (15 September 1997)

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TABLE OF CONTENTS

I.!. INTRODUCTION.........................................................................................................................3 1.1.1 Background..............................................................................................................................3 1.1.2 Purpose.....................................................................................................................................3 1.1.3 Objectives.................................................................................................................................4 1.1.4 Venue.......................................................................................................................................4 1.1.5 AflalySts .................................................................................................................................... 4

1.2. METHODOLOGY........................................................................................................................ 5

1.2.1 AS/NZS 4360........................................................................................................................... 5 1.2.2 What-If Analysis......................................................................................................................5

1.3. ASSUMPTIONS ............................................................................................................................

1.4. FINDINGS ....................................................................................................................................8

1.5. REFERENCES..............................................................................................................................9

1.6. WHAT-IF WORKSHEETS ........................................................................................................ 10

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- 1.1. INTRODUCTION

1.1.1 Background

The Water Corporation is preparing a Public Environmental Review for the proposed Sewer Pressure Main along Gnangara Road between Ellenbrook and Wangara. Gutteridge Haskins & Davey Pty Ltd (GHD), the principal contractor, has retained Det Norske Veritas (DNV) to provide part of the Environmental Risk Assessment for the PER.

DNV Consultancy Services were commissioned to facilitate a one day workshop to review proposed sewage transport routes and pipeline configurations to select, on a qualitative basis, "best options" for further analysis.

In accordance with AS/NZS 4360:1995 this workshop dealt with the context of the risk management process and identified risks. Risks were also broadly analysed, assessed and treatment strategies were proposed. The outcomes from this workshop as well as outcomes from the August 1996 study (Ref. 1) form the basis for further evaluation of the risk of groundwater contamination from the proposed Sewer Pressure Main along Gnangara Road between Ellenbrook and Wangara.

Contamination of groundwater in Western Australia is a serious environmental issue as has been described in the Department of Environmental Protection (DEP) bulletin 763 (Ref. 2). Here an estimate of 1500 contaminated sites have been identified for Western Australia alone. The majority of contaminated sites have resulted from unsatisfactory industrial practices for storage of chemicals and for the containment and disposal of wastes.

The Gnangara Groundwater Reserve is arguably one of the most strategically important resources of the Perth Metropolitan area, providing in the region of 40% of drinking water consumed in this area. In recognition of this strategic importance the Gnangara Groundwater Reserve has been designated as a Priority One Protection Area by the Water & Rivers Commission (W&RC).

It is against this background that the transport of sewage across the Gnangara Priority One Protection Area has been reviewed.

1.1.2 Purpose

The purpose of this workshop was to:

Overview previous findings of risk assessment studies to ensure a common understanding and inclusion of unresolved issues in the current assessment; Specify all relevant sewage transportation alternatives i.e. pipe materials & configuration, route options, location above ground or below etc.; Establish acceptable risk criteria against which to evaluate the selected alternatives; Identify scenarios which could lead to pollution of the water reservoir or other land areas along the sewage transport route; Do an initial coarse screening of the options to define the best option or pair of options.

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1.1.3 Objectives

The objectives of this study were to:

Identify hazards relating to the transport of sewage over a Priority One Groundwater Area, Analysis of risks in terms of likelihood and consequence in the context of existing and proposed controls. Propose measures aimed at the minimisation of risk in the form of recommendations,

1.1.4 Venue

GHD House 239 Adelaide Terrace Perth

1.1.5 Analysts

Graham Ledgerwood Rod Burton Clarke Hendry John Bond John Cox Marie Ward Tony Allen John Erceg Adrian Tomlinson Alex Marsden Wes Horwood Keith Collins Simon Leverton Tony Norrish Johan Potgieter Thrym Kristoffersen

- Water Corporation - Water Corporation - Water Corporation - Water Corporation - Water Corporation - Ministry for Planning - Rockwater - Shire of Swan - Waters & Rivers Commission - Waters & Rivers Commission - Department of Environmental Protection - Department of Environmental Protection - Gutteridge, Haskins & Davey - Gutteridge, Haskins & Davey - Det Norske Veritas (Facilitator) - Det Norske Veritas (Scribe)


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1.2. METHODOLOGY

1.2.1 ASINZS 4360

Management of risk is defined by AS/NZS 4360 as an iterative process consisting of well defined steps which, taken in sequence, support better decision making by contributing a greater insight into risks and their impacts. The risk management process can be applied to any situation where an undesired or unexpected outcome could be significant or where opportunities are identified.

1.2.2 What-If Analysis

What-If Analysis is a structured brainstorming methodology utilising a multidisciplined team to identify hazards and risks associated with a proposed or existing project, process or design. This technique has been recognised as an acceptable risk assessment technique through its inclusion in the list of acceptable risk evaluation techniques outlined in USA legislation i.e. OSHA 1910.119 regulating process safety management systems. The structured HAZOP methodology has evolved from the What-If methodology.

The flexible What-If analysis technique, allowed the team of analysts to consider the consequences and safeguards relating to various plausible "what-if' scenarios, relevant to the subject under consideration. The team made qualitative risk evaluations resulting in recommendation development aimed at treating the risk i.e. minimising, controlling or further evaluating the identified risk.

Risk mitigation strategies will be developed further once the risk quantification exercise has been concluded.

The team was well constituted and included the following expertise:

environmental engineering/ management hydrogeological expertise project management pipeline construction mechanical & civil engineering strategic planning environmental legislation safety & risk engineering! management

The workshop initially reviewed the findings of the previous studies (Ref. 1.). This was followed by an overview of the proposed design for a pipeline over Gnangara Water Mound. Prior to analysis the reservoir environment was described with charts outlining past and present water levels as well as current pollution contours from a previous liquid waste handling facility.

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The initial workshop approach was a coarse screening of sewage treatment options, firstly considering p(tential for avoiding transport across the Priority One Area and secondly for transport across the Priority One Area.

Thereafter various pipeline elevation and route options across the Priority One Area were analysed.

Finally, incident cases for pipelines were analysed primarily considering potential effects to the groundwater. A minor leak was defined as a leak which would not be detected by monitoring equipment and would not create any visible telltale on the ground surface. A major leak was defined as a leak which would be detected by monitoring equipment and would have clearly visible effects on the ground surface.

Risk ranking, while providing valuable insights into individual perceptions, was not progressed as it became apparent that issues relating to cost, logistics, scheduling and strategic planning where dominpting the risk proffle.

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1.3. ASSUMPTIONS

The Onangara Priority One Area is considered to be a sensitive groundwater resource to be conserved for public drinldng water purposes. As such, developments and activities in this area are strictly controlled.

The proponent has in this case been required by the DEP to demonstrate that the risk associated with a sewage pipeline through the Priority One Area is assessed to be as low as reasonably practicable (ALARP).

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1.4. FINDINGS -

Workshop findings are outlined in the What-If Worksheets in section 7.

General findings from the days proceedings include:

Deviation from the current proposal will entail review of current area strategic plans, increased cost, continuation of sewage transport by road (with its increasing risk profile), review of alternate solution sensitivities and negotiation with new interested third parties.

Worlds current best practice for sewage pipeline design, construction and commissioning is the minimum standard.

Sewage contamination of Water Corporation bores was found to be generally unacceptable, and adverse public reaction to such an event would be anticipated.

Sewage was not generally considered an environmental contaminant with permanent adverse effect, however potential accumulation of trace contaminants was not discounted.

Excavation along pipeline route to be subject to strict controls via an appropriate management plan which includes permitting, marker tapes (AS 2885), signage etc.

Any pipeline system across the Priority One Area to be subject to routine integrity testing.

Secondary containment may reduce the risk of groundwater contamination, and also make the project more acceptable to the public.

Secondary containment options would be discussed in more detail during the risk mitigation workshop.

The development of a sewer pipeline failure frequency data base from existing data for sewer pipeline systems would assist with the estimation of system reliability as well as risk quantification.

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1.5. REFERENCES

DNV (1996): "Environmental Risk Assessment of Ellenbrook Interim Pressure Main ", Gutteridge Haskins & Davey Pty Ltd, October 1996 DEP (1995): "Contaminated Sites - Assessment and management of contaminated land and grounthvater in Western Australia", August 1995 AS/NZS 4360 (1995): "Risk Management", Standards Australia, 1995

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1.6. WHAT-IF WORKSHEETS


1. ROUTING OF SEWAGE AWAY 'iM GNANGARA PRIORITY ON J'.OTECTION ZONE

WHAT IF... CONSEQUENCES SAFEGUARDS/MITIGATION RECOMMENDATIONS

11 Pipeline routed No potential for groundwater Existing technology with known 1. Determine comparative sewage toxicity and contamination potential.

around groundwater contamination in priority one zone.

reliability, Sewage is a common contaminant protection zone.

Increased retention times with and not generally considered to be

potential sewage deterioration highly hazardous.

in transit. Increased logistics including ground purchase, determination of area sensitivities, construction access, etc. Time and cost implications. Uncertain project sensitivities.

1.2 New sewage Limited potential for Existing technology with known 1. Review alternatives to establish suitable technologies as well as

treatment plant to serve constructed

groundwater contamination in priority one zone.

reliability, Sewage is a common contaminant comparative cost.

regional needs. Strategic development plan and not generally considered to be 2. Determine threats and opportunities for

revision, highly hazardous. alternate routes/processes.

Time and cost implications. Uncertain project sensitivities.

( p PRIORITY ONE PROTE\) AON ZONE

2. ROUTING OF SEWAGE OVER GF .GARA

WHAT IF... CONSEQUENCES SAFE GUARDS RECOMMENDATIONS

2.1 Transport by • Potential for groundwater Generally accepted practice. LThis is not considered an acceptable practice for any extended period of

truck. contamination. Increased sewage truck traffic time.

and batch handling operations. Spill size limited to truck capacity.

2.2 Transport by • Potential for groundwater None. 1. This is not considered apractical solution for the transport of sewage

conveyor. contamination, Conveyor system sealing

and would probably entail the

presents a challenge. construction of a drying plant.

Aboveground operation.

2.3 Transport by • Potential for groundwater Existing bores may be used to contamination from a remediate

1. Demonstrate that spill will not degrade water quality below specified water

pipeline, contamination. Potential to set precedent for sewage large spill (worst case). quality objectives.

development across priority 2. Develop an appropriate spill detection

one groundwater resource strategy and contingency plan to limit potential groundwater impacts.

areas. Potential public concern

Only domestic sewage to be

relating to development across transported in pipeline system. Pipeline system design to be in

a priority one groundwater accordance current best practice and reserve. demonstrate system integrity.

L 3. SEWAGE PRE-TREATMENT

WHAT IF... - CONSEQUENCES SAFEGUARDSIMITIGATION RECOMMENDATIONS

3.1 Production of dry Erection of new sewage drying Dry waste is not mobile in the Include report on previous feasibility

plant. environment, study in the Environmental Impact sewage.

Generation of large amounts of Gas pipeline access potential. Statement.

water for disposal. Energy intensive option.

3.2 Production of Erection of new sewage pre- Existing sewage treatment Include report on previous feasibility study in the Environmental Impact

sewage paste. treatment plant. Generation of large amounts of

technology, Statement.

water for disposal. Potential for increased production of H2S due to increased retention time.

4. PIPELINE ELEVATION )T.

CONSEQUENCES SAFEGUARDSIMITIGATION RECOMMENDATIONS WHAT IF...

Pipeline creates a visual Inspection and maintenance of relatively simple. pipeline

1. Review impediments to surface development (i.e. gradient, etc.). 4.1 Pipeline above

ground. intrusion, Potential effect on wildlife Emergency response for minor 2. Establish optimal design criteria fully

movement, leaks is uncomplicated, restrained vs. expansion loops.

Pipeline creates a physical No degradation of protective 3. Review requirements for clearance

barrier to further development, permeable layer of coffee rock, between pipeline and traffic to limit

Potential for third party Feasible design as terrain is potential for vehicle collision.

interference (i.e. collision), relatively flat. Materials of construction limited to materials suitable for above ground application (i.e. UV resistant etc.). Sewage exposed to heating while in transit from solar radiation.

Immediate groundwater Conventional technology. 1. Develop leak detection and isolation 4.2 Pipeline below ground. contamination from pipeline

leakage due to watertable Sewage maintained at constant low temperature in an isothermal

strategy. 2. Make provision for backfilling trench

proximity to pipeline. environment. with modified soils with high

Destruction of "coffee rock" contaminent retention characteristics.

integrity. 3. Review feasibility of secondary

Trenching below the watertable containment during risk mitigation

during pipeline construction. Potential pipeline excavation

workshop. Valve design, selection and location to

required for pipeline incidents. minimise potential for leaks. Revisit production bore monitoring program frequency and analysis in line with sewage "telltale" contaminants.

( I-,

5. LOCATION OF PIPELINE

WHAT IF... CONSEQUENCES SAFEGUARDS/MITIGATION RECOMMENDATIONS

5.1 Pipeline located Negotiations with private Potential contamination should be South away from the carried

1. Optimal location of pipeline to be determined by groundwater modelling

South of the water property holders for right of Water Corporation bores by the (up-gradient vs. down-gradient).

bores along Gnangara way. Potential Impact on Whiteman natural flow of groundwater. 2. Determine cost, time and logistical

Road. problems associated with alternate Park. pipeline routes.

5.2 Pipeline located at Potential for Gnangara Road Increased distance from water 1.As with 5.1.

the North side of the development to cover sewer bores along Gnangara Road.

Gnangara Road pipeline.

reserve. Negotiations with private property holders for right of way (land resumption).

5.3 Pipeline located in Pipeline failure could impact None. 1. As with 5.1.

the median of the use of Gnangara Road.

Gnangara Road reserve.

5.4 Pipeline located Pipeline failure in close Contamination may be contained 1. As with 5.1.

South of Gnangara proximity to a bore is likely to and removed through use of bore

Road reserve, result in rapid contamination of as remediation bore.

drinldng water and bore closure.

6. PIPELINE FAILURES

CONSEQUENCES SAFEGUARDS/MITIGATION RECOMMENDATIONS WHAT IF...

Contamination of groundwater Pipeline to be fabricated in accordance World's current best

1. Pipeline to be subject to periodic integrity testing (establish optimal 6.1 Single pipe -

minor leak. over time. Potential effect on local practice. testing frequency and install state of

vegetation. Pipeline to be operated in the art flow accounting system).

Potential effect on the water accordance World's current best Bore monitoring program to address

quality of private and practice. detection requirement. Review the requirement for monitoring

production bores with potential bores as well as monitoring public health consequence.

philosophy. Develop a shutdown philosophy in accordance environmental and health criteria.

Leak only anticipated at Second pipe should contain minor leak and groundwater prevent

1. Determine desirability of this or other secondary containment method where 6.2 Double pipe -

minor leak. (Pipe within a pipe)

fixtures and fittings. Identification of leak location contamination, pipeline runs through welihead critical

zones. and subsequent repair may be Second pipe provides an inert sleeve allowing detection of minor 2. A cost evaluation should be done to

problematic. leaks. compare the cost of increased quality

Continued operation of pipeline control and higher pipeline

system possible until suitable specification vs. double pipe

arrangements have been made for configuration.

repair. 3. The use of a double pipe configuration should be subject to a feasibility study.

Potential disruption of road Emergency response access along 1. Consider ease of repair when selecting material. pipeline 6.3 Single pipe -

major leak. traffic or undermining of road, if pipeline in close proximity to

Gnangara Road. 4.5 hour sewage production 2. Emergency response plan to be

Gnangara Road. retention capability at the pump updated to include pipeline

Potential affect on local activities (i.e. Whiteman Park,

station. Low pressure operation 4bar.

contingencies. 3. Pipeline system design to include

Market Gardens etc.). provision for emergency temporary

PIPELINE FAILURES (CONTINFi.")

6.

WHAT IF... CONSEQUINCES - SAFEGUARDSIMITIGATION RECOMMENDATIONS - 6.3 Single pipe - . Potential sewage accumulation Major leak should always be

4. bypass and isolation. Review the adequacy of sewage

major leak. and overflow of pumpstatiofl. detectable. retention capacity at the pumping

(continued) Disruption of sewage removal station as well as storage time

service, Potential public effect

5. constraints. Pipeline system to have automatic

including smell, unhygenic shutoff features to limit potential spill conditions, media interest etc. Potential for public water bore

6. size. Final pipeline system to be subject to

closures. HAZOP prior to approval for detail design as well as prior to approval for construction.

6.4 Double pipe - As with 6.2. As with 6.2. 1. Install state of the art monitoring and detection devices.

major leak. Include annulus clean-up in emergency contingency planning.

Excavation around pipeline to require an excavation pennit.

APPENDIX 2

ERA OF ELLENBROOK INTERIM PRESSURE MAIN

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TABLE OF CONTENTS

11.1. INTRODUCTION .......................................................................................................................4 11.1.1 Background............................................... 11.1.2 Objective................................................... 11.1.3 Scope and Methodology...........................

11.2. DESCRIPTION OF PHYSICAL SITUATION...........................................................................5 11.2.1 Overall Route.......................................................................................................................... 5 11.2.2 Public Water Supply Bores..................................................................................................... 5 11.2.3 Soil Conditions.......................................................................................................................6 11.2.4 Pipeline Description................................................................................................................6

11.3. HAZARD IDENTIFICATION ..................................................................................................... 8

11.4. CONSEQUENCE MODELING................................................................................................10 11.4.1 General..................................................................................................................................10 11.4.2 Assessment of Consequences for Each Scenario .................................................................. 11

11.5. FREQUENCY ANALYSIS.......................................................................................................12

11.6. RISK ANALYSIS......................................................................................................................13 11.6.1 Overall Results...................................................................................................................... 13 11.6.2 Options for Risk Mitigation.................................................................................................. 14

11.6.2.1 Sealed Valve Pits .......................................................................................................................................... 14 11.6.2.2 Pit Location................................................................................................................................................... 15 11.6.2.3 Welded Joints................................................................................................................................................15 11.6.2.4 Use of PE 1mm. ............................................................................................................................................ 15 11.6.2.5 Welded Bends...............................................................................................................................................15 11.6.2.6 Management of Excavation Activities..........................................................................................................15 11.6.2.7 Indicator Plates on the Suthce ..................................................................................................................... 15 11.6.2.8 Internal inspection (by camera on UVPC or in person on all other pipes) ................................................... 15 11.6.2.9 Flow Metering .............................................................................................................................................. 15 11.6.2.10 Resistivity Metering .................................................................................................................................... 16 11.6.2.11 Residential Sewer Only .............................................................................................................................. 16 11.6.2.12 Improved Rubber Ring Seal ....................................................................................................................... 16

11.7. CONCLUSIONS AND RECOMMENDATIONS ....................................................................17

11.8. DETAILED RESULTS FROM QUALITATWE RISK ASSESSMENT WORKSHOP.........18

11.9. GROUNDWATER CONTAMINATION CONSEQUENCE ASSESSMENT.........................19

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EXECUTIVE SUMMARY

The Water Authority of Western Australia (WAWA) have contracted Gutteridge Haskins & Davey (GHD) as design engineers for a sewerage pressure main, crossing the Wanneroo groundwater reservoir and along Gnangara. In conjunction with this work the Department of Environmental Protection (DEP) require that an assessment of the risk of contamination of the ground water be carried out.

To fulfill the requirements of the DEP, GHD have requested Det Norske Veritas to carry out a risk assessment of the pipeline. Dames & Moore were subcontracted for an assessment of the environmental impact.

The analysis focus was on assessing the most effective way of mitigating the risks by ranking the risks and then attempting to reduce the most critical aspects. Four different types of pipeline types were assessed:

Rubber ring jointed (RRJ) plastic Rubber ring jointed cement lined mild steel (MS CL RRJ) Welded cement lined mild steel (MS CL W) Rubber ring jointed Polyethylene lined mild steel (MS PE RRJ)

The potential causes and consequences were identified by brainstorming in a workshop involving personnel from WAWA and GHD with in depth knowledge from design, manufacturing, installation and operation of the type of pipelines in question. Controls in terms of prevention and mitigation of these hazards were also identified. Ranking of the causes with respect to importance and grouping of the consequences with respect to size of leak enabled a comparison between the different pipeline materials and joint types available.

The basic option (least expensive) of using plastic (RRJ) would seem inappropriate due to the sensitive nature of the area. The concrete lined mild steel (RRJ) shows an improved capability to withstand leaks and should be deemed fit for purpose. However, to further prevent and mitigate potential releases of sewer the following recommendations are made:

All valve pits should be sealed and located outside the well bore safety zones Welded joints should be considered in the sections of the pipeline running through well bore safety zones Polyethylene lining should be used on high points in the pipe in order to prevent gas attacks All bends should be welded Surface markings for the pipeline should be considered where practical in order to reduce the chance of damage due to excavation

These measures address the most important causal factors of the pipeline, in particular in the most sensitive areas. The study has also identified important management system controls which WAWA will need to consider when installing and operating the pipeline.

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II.!. INTRODUCTION

11.1.1 Background

The Water Authority of Western Australia (WAWA) have contracted Gutteridge Haskins & Davey (GilD) as design engineers for a sewerage pressure main, crossing the Wanneroo groundwater reservoir and along Gnangara. In conjunction with this work the Department of Environmental Protection (DEP) require that an assessment of the risk of contamination of the ground water be carried out.

To fulfill the requirements of the DEP, GFID have requested Det Norske Veritas to carry out a risk assessment of the pipeline

Dames & Moore were subcontracted for an assessment of the environmental impact.

This report describes this assessment.

11.1.2 Objective

The objectives of the reported study were to:

Assess the consequences of a release of sewer from the proposed Interim Sewerage Pressure Main along Gnangara Road; Evaluate the risk of groundwater contamination from the proposed pipeline; and Assess options for reduction of contamination risks, in particular those regarding to selection of pipe material and type of joints.

11.1.3 Scope and Methodology

In general the methodology is that of a classical risk assessment; i.e. a systematic approach to the analysis of what can go wrong. For this purpose a h'ard identification and risk assessment workshop was held, involving personnel from WAWA and GHI) with in depth knowledge from design, manufacturing, installation and operation of the type of pipelines in question.

The analysis focus was on assessing the most effective way of mitigating the risks by ranking the risks and then attempting to reduce the most critical aspects.

The scope of the facilities studied is defined in Section 2.

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11.2. DESCRIPTION OF PHYSICAL SITUATION

11.2.1 Overall Route Gnangara Road forms the boundary for two Underground Water Pollution Control Areas (UWPCAs) designated by the Water & Rivers Commission to protect groundwater recharge areas which are important for public water supply. Wanneroo UWPCA lies to the north of Gnangara Road; Mirrabooka UWPCA lies to the south of it. The UWPCAs extend westwards as far as Lake Gnangara and eastwards to Roberts Road. Much of the pressure main route lies within the highest category of UWPCA protection, with a Priority 1 classification.

11.2.2 Public Water Supply Bores There are six existing public water supply bores along Gnangara Road, adjacent to the pressure main route, and a further four are proposed along the eastern part of the route. Bore locations are shown on Figure 1 and details of these bores are presented in Table 4.1 below. There are many additional public water supply bores to the south of Gnangara Road.

TABLE 4.1: PUBLIC WATER SUPPLY BORE DETAILS

Bore No. Northing Eastmg Collar RL 1995 Screen Wellhead (m) (m) AND Pumpage Interval Protection Zone2

Quota (mbgl)* Radius (m3/d) (m)

PRODUCTION BORES

M300 6481469 393822 45.37 1123 31.53-48.29 500

M310 6481515 395424 46.09 1099 22.05-53.29 500

M3200 6481523 396322 46.75 1370 21.03-48.46 500

M330G 6481534 397257 47.78 1879 21.76-52.55 500

M3400 6481540 397938 47.04 1105 20.74-45.43 500

M350 6481507 398876 45.89 822 31.00-46.00 500


M360 6481569 399854 44.91 16441 0.00-48.00 500

M370 6481578 400717 44.25 1644' 48.00-60.00 500

M380 6481587 401716 41.89 1644' 0.00-46.00 300

M390 6481560 402566 42.59 822' 0.00-20.00 300 26.00-48.00

* Metres below ground level 'Planned rate 2 Welffiead Protection Zones are surface and subsurface areas surrounding a water bore

supplying a public water system through which contaminants are likely to move towards the bore.

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Gulteridge Haskins and Davey Pry Ltd App 2.6 DNV Consultancy Services Ellenbrook Sewer ERA October, 1997

11.2.3 Soil Conditions The area under study is underlain by the Bassendean Sand, which forms part of the superficial formations aquifer that supplies the public water supply bores. The Bassendean Sand is fine to medium grained, moderately well sorted, with surrounded grains. It is permeable and consists essentially of quartz sand which has a negligible capacity to absorb or fix contaminants.

The superficial aquifer along the route is unconfmed, and the water table is generally 2-5m below ground surface in the vicinity of the six existing bores; the intervening unsaturated zone consists entirely of sand, with some patchy iron cementation ("coffee rock"). The natural direction of groundwater flow is towards the south.

The proposed pressure main would directly overlie the capture zones (areas which contribute groundwater) for six existing public water supply wells and four proposed wells, and is upgradient of a large number of other public water supply wells.

Groundwater levels in the vicinity of the six existing production bores along the route of the proposed main are at about 42m AHD (September 1988). Near M390, water levels are at about 37m AHD. Ground elevations range from about 65m AHD on the western side to between 45m AHD and 50m AHD in the central and eastern parts of the pipeline route.

11.2.4 Pipeline Description The planned pipeline will be approximately 15 km long and is planned to be routed underground. Four different types of materials and joint types can be used (in order of increasing cost):

Rubber ring jointed (RR.D plastic Both UVPC and HOBAS are in frequent use for this type of services. The pipeline would be manufactured in 6m elements which would be connected during installation. The failure mechanisms are similar for the two and they are therefore for the purpose of this study treated together. In this case nominal diameter of 450mm would be chosen.

Rubber ring jointed cement lined mild steel (MS CL 111th The type of joints used for this type would be almost identical to that of the RRJ plastic, although the elements would be manufactured in 12m lengths. A nominal diameter of 500 mm would be used.

Welded cement lined mild steel (MS CL VT) This is identical to the previous with the exception of the joints being replaced by welds. The cement lining on the inside of the pipe would be complemented with an additional layer inside each weld to protect against corrosion.

Rubber ring jointed Polyethylene lined mild steel (MS PE RRJ) This pipeline is identical to the MS CL RRJ with the exception of the lining which would be of PE rather than cement. This increases the resistance against gas attacks (corrosion).

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Gunerldge Haskins and Davey Pz'y Ltd App 2.7 DNV Consultancy Services Ellen brook Sewer ERA October, 1997

All mild steel pipelines would be externally coated with polyethylene.

A combination of the different pipeline types is also possible.

The pipe will have a diameter of either 450 mm (UVPC) or 500 mm (all other materials).

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Gutteridge Haskins and Davey Ply Ltd App 2.8 DNV Consultancy Services Ellen brook Sewer ERA October, 1997

11.3. HAZARD IDENTIFICATION

The potential causes and consequences were identified by brainstorming in a workshop involving personnel from WAWA and GHD with in depth knowledge from design, manufacturing, installation and operation of the type of pipelines in question. Controls in terms of prevention and mitigation of these hazards were also identified.

The following causes were identified (for full details see section 8):

Corrosion in welds Damage on backfilling Damage to inner lining during transport (causes corrosion) Excavation (damage to coating) Excavation (damage to joints) Excavation (damage to pipe) Fatigue caused by incorrect transporting Gas attack on concrete lining (causes corrosion) Corrosion (for other causes) Joints in bends slipping due to hydraulic forces Leaks from air valves or scour valves Material defects from manufacturing Overpressure of pipe Pipe deformation on backfilling Poor installation ofjoints Seismic activity Vandalism

Specific preventative controls against each of these were then identified. These include (for full details see section 8):

Chamfering of pipe end Correct compacting Correct packaging for transport Dead flanges bolted onto scour valves

. Design Inspection programme Internal lining and external coating Pressure testing before use Quality system with manufacturer Safety Factor in design Sewer will be mostly located at 1200 mm depth while other services are at 600-900 mm Specified to Australian Standard Training Transport procedures Use of lubricant for joints Valves contained in pits Witness mark on pipe

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Gutteridge Haskins and Davey Pty Ltd App 2.9 DNV Consuitancy Services Ellenbrook Sewer ERA October, 1997

With respect to consequences only likely hole sizes and duration of leaks were discussed (see also further analysis in Section 4). Common mitigation measures identified were:

Medium size or greater leaks would cause soil erosion and be detected (mostly by the public). Pumps may be shut down so that pipe pressure is reduced and leak would almost stop. The soil conditions (sand) would naturally act as a filter, although probably only effective for small leaks. All water from nearby well bores will be subject to treatment. The chance of contaminated water actually being received by the public would therefore be very low. All water bores are tested regularly and the water quality at the water treatment plants are constantly monitored. any contamination, including heavy metals, should be discovered well in advance of contaminated water being delivered to the public.

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Guileridge Haskins and Davey Ply Lid App 2.10 DNV Consuliancy Services Ellen brook Sewer ERA October, 1997

11.4. CONSEQUENCE MQDELING

11.4.1 General It is understood that the sewerage station booster pump discharge into a single pressure main, and are designed to operate 12 hours per day.

The line taken to reach the water table can be estimated from the following version of Darcy's Law:

V= K, 0

where: V = seepage velocity (m/d);

K1 = hydraulic conductivity (mid) at a hydraulic gradient of 1; 0 = porosity

Darcy's Law is relevant to flow through porous media, and for this calculation, it is assumed that the soil is fully wetted (i.e. end of winter). A large leak, even in summer, would soon result in fully saturated conditions.

The calculation for vertical leakage from the sewerage main is based on a hydraulic gradient of 1 and a vertical hydraulic conductivity of 1 .5 mId. It is typical to assume vertical hydraulic conductivity to be 10% of the horizontal conductivity (15m/d) due to vertical anisotropy in the Bassendean Sand. A. porosity of 0.3 (30%) has been used, and is typical of the Bassendean Sand.

The estimated vertical leakage rate is therefore about 5m/d. The time for the leakage to reach the aquifer will range from about 10 hours where the water table is 2m below the pipe, to 4.4 days where the pipe is located 22m above the water table. On reaching the water table, the leakage will enter the unconfined aquifer and be drawn towards the public water supply bores.

The infiltration capacity of the Bassendean Sand is high. As long as the rate of leakage is small, it infiltrates as fast as supplied and the leak may not be detected, especially as the pumps come on every 12 hours. Under high pressures (i.e. during pumping), sewerage from holes in the pipeline injected into the Bassendean Sand may take a shorter time to reach the aquifer.

Leakage from the pipe will be vertical as long as the Bassendean Sand has the capacity to absorb the leakage. Excess leakage will move laterally and upwards, especially when the pumping head exceeds the effects of gravity. The upward leakage will become evident when the ground level is reached.

Studies in virus and bacteria transport (Bales et al, 1995) in a sandy aquifer under natural gradient conditions indicate that viruses may travel several metres downgradient from the source. Bacteria could persist for tens of metres downgradient, whilst other sewage constituents including boron, chloride, sodium, phosphorus, ammonia, nitrate, detergents and volatile organics may travel 1,000s of metres in contaminant plumes.

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Guiteridge Haskins and Davey Py Lid App 2.11 DNV Consuliancy Services Ellen brook Sewer ERA October, 1997

11.4.2 Assessment of Consequences for Each Scenario

The consequences were for each cause of failure allocated in one of four categories:

Small leaks (<25 mm hole). These would last for a long time without necessarily being detected and some could also escalate to the medium category before detection. Medium leaks (>25 mm hole). Leaks of this size would cause soil erosion and more than likely be discovered by the public within relatively short time. Pipe burst. These would be discovered soon after occurring due to the extensive soil erosion and large quantities of sewerage released. Burst/leaks while working near by. This relates to excavation activities which causes the leaks directly. Detection would be immediate and shut down of pumps can be effected very quickly.

The most critical leak locations would be within the well bore safety zone as the time taken for a release to contaminate the wells would then be the shortest.

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Guilerldge Haskins and Davey Pty Lid App 2.12 DNV Consuliancy Services

Ellenbrook Sewer ERA Ociober,1997

11.5. JREQUENCY ANALYSIS

Prediction of actual frequency of occurrence is difficult to assess. Instead, the relative importance of each failure cause was established. The most important (i.e. frequent) failure cause was assigned the value "10", while the most infrequent were assigned "1". This enables an internal ranking of all the other causes.

Table 1: Ranking of Likelihood of Occurrence for each failure Cause

CAUSE PLASTIC RRJ MS CL RRJ MS CL W MS CL RRJ

Excavation (damage to pipe) 10 - - - Poor installation ofjoints 9 7 - 7

Excavation (damage to coating) - 7 7 4

Leaks from air valves or scour valves

7 7 7 7

Excavation (damage to joints) 5 5 - 5

Gas attack on concrete lining - (causes corrosion)

5 5 1

Pipe deformation on backfihling 4 - - - Damage on backfilling 3 - - - Damage to inner lining during - transport (causes corrosion)

3 3 1

Corrosion in welds - - 3 - Vandalism 2 2 2 2

Fatigue caused by incorrect 2 transporting

1 1 1

Joints in bends slipping due to 2 hydraulic forces

1 - I

Overpressure of pipe 1 1 - I

Seismic activity 1 1 - 1

Material defects from 1 manufacturing

1 - 1

Corrosion (for other causes) - 1 1 1

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Gutteridge Haskins and Davey Py Ltd App 2.13 DNV Consultancy Services Ellenbrook Sewer ERA October, 1997

11.6. RISK ANALYSIS

11.6.1 Overall Results The main differences between the pipes can be summarised as follows:

Excavation is the main cause for leaks on most of the pipelines. However the plastic types and the RRJ types are much more prone to failures than the other. All RRJ pipe types have inherent problems with leaks in joints Corrosion problems are prominent for cement lined pipes

A common area of concern is the air valves and scour valves which have the potential to leak.

The most critical leak locations would be within the well bore safety zone as the time taken for a release to contaminate the wells would then be the shortest.

A summary of the risk assessment results is shown in Table 2. The Plastic RRJ pipe is recognised to have the highest potential for leaks, while the fully welded mild steel would have the least potential. The results are graphically shown in Figure 2.

Table 2: Likelihood of each Consequence Category for each Pipeline Type

PE MS RRJ CL MS W CL MS RRJ PLASTIC RRJ

Burst 7 6 7 22

Medium leak 12 12 18

Small leaks 14 20 23 7

Total 33 26 42 47


Gutteridge Hasklns and Davey Ply Lid App 2.14 DNV Consultancy Services Ellenbrook Sewer ERA October, 1997

25

20

15

10 PLAS11C RRJ

- MS RRJ

IS W

RRJ

bUSt Medium Small leak leaks

Figure 2 : Likelihood of each Consequence Category for each Pipeline Type

Whereas the fully welded steel pipe may seem attractive from a risk perspective, this is also the most expensive pipe type, and it can therefore not be concluded directly that this should be used. However, it would seem that plastic RRJ, as the worst ranking of the four, would be inappropriate for the purpose, given the sensitivity of the area. This is not the least due to the shorter sections used (6 m as opposed to 12 m for steel), and therefore twice as many joints, which would tend to mean an increase in locations with potential problems with joint leaks.

The concrete lined mild steel with welded joints would mitigate most of the causes identified with joints, while the polyethylene lining is particularly good against corrosion caused by gas attacks. While these may be too expensive too run along the whole route it may well be effective to use these in particular sections.

Each of the critical failure causes and leak points have been examined and addressed with respect to potential for risk reduction in order to conclude on the optimum choice.

11.6.2 Options for Risk Mitigation

11.6.2.1 Sealed Valve Pits All valves would normally be located in dedicated valve pits. As valves are a potential source for leaks it was suggested that the valve pits could be lined and sealed and therefore contain the leak.

Various options for detection of liquid in the pits were discussed. Although an on-line detection system using telemetry would be only a solution which effectively would alert WAWA of any accumulation of liquid, detection by public due to smell is likely following a

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Gulteridge Haskins and Davey Piy Ltd App 2.15 DNV Consultancy Services Ellen brook Sewer ERA October, 1997

Leak in a sealed pit (leak would most likely be small and take considerable time to fill the pits).

11.6.2.2 Pit Location Having identified the valves and therefore the pits as having a higher potential for leaks it is natural to suggest location of the pits away from the bore holes (say outside the defmed 500m safety zone).

11.6.2.3 Welded Joints It was suggested that the parts of the pipeline which passes through the 500m safety zone around each well bore may be welded instead of RRJ to avoid the possible leaks associated with joined pipes.

11.6.2.4 Use of PE lining Gas attacks are particularly frequent on high points of the pipe as gas would accumulate here. Use of PE lining on this high points instead of concrete lining would significantly reduce the risk of any gas attack on the pipeline.

11.6.2.5 Welded Bends Bends on the pipeline will cause stresses on the joints due to the hydraulic force acting on the pipe. By fully welding the bends it is possible to avoid the chance of a joint slipping in this situation.

11.6.2.6 Management of Excavation Activities Some hazardous services (e.g. gas pipelines) insist on their presence during excavation activities in the vicinity of their pipelines. WAWA could do the same for particularly sensitive pipelines. However, given the exchange of locational information already and the difficulties in managing such an inspection system, it may be a better option to use surface markers for the pipe (see below).

11.6.2.7 Indicator Plates on the Surface To reduce the potential of excavation activities damaging the pipeline it was suggested that indicator plates showing the pipeline route could be used.

11.6.2.8 Internal inspection (by camera on IJVPC or in person on all other pipes) Internal inspection of each joint as they are completed is a relatively simple task, except for the plastic RRJ which would be only 450 mm diameter and therefore would not allow for direct visual inspection (except with camera). Such inspection is encouraged in order to prevent the leaks caused by poor installation.

11.6.2.9 Flow Metering Adding some kind of flow metering (calibrated against the normal flow from the pump) could potentially identify leaks along the pipeline route. However, the work group felt that there were considerable problems associated with the required accuracy of such a flow meter and also with the calibration of it.

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11.6.2.10 Resistivity Metering The overall resistivity in steel pipes changes when the pipeline is damaged (i.e. leaking). By measuring the resistivity it is therefore possible to detect leaks. This method is used for locating small leaks on buried pipelines. However, the group felt that this method would be unsuitable for permanent installation.

11.6.2.11 Residential Sewer Only

The amount of harmful substances in sewer collected from residential users is veiy limited. Currently there are only residential users planned for this area. Restricting the use of the pipeline for this purpose only (i.e. not allowing collection of industrial sewer to go through, I the future) was discussed at length and it was concluded that such restrictions would be impracticable.

11.6.2.12 Improved Rubber Ring Seal

An improved rubber ring seal would mitigate many of the leak problems from joined pipes. There have been a large development in seal quality over the years and the current seal being used is of the highest quality. No further improvements are advertised.

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Gutterldge Haskins and Davey Py Ltd App 2.17 DNV Consuliancy Services

Ellenbrook Sewer ERA October, 1997

11.7. CONCLUSIONS AND RECOMMENDATIONS

The results of the hazard identification demonstrates the extent of risk management applied on the varies types of pipeline types.

The basic option (least expensive) of using plastic (RRJ) would seem inappropriate due to the sensitive nature of the area. The concrete lined mild steel (RRJ) shows an improved capability to withstand leaks and should be deemed fit for purpose. However, to further prevent and mitigate potential releases of sewer the following recommendations are made:

All valve pits should be sealed and located outside the well bore safety zones Welded joints should be considered in the sections of the pipeline running through well bore safety zones Polyethylene lining should be used on high points in the pipe in order to prevent gas attacks All bends should be welded Surface markings foi the pipeline should be considered where practical in order to reduce the chance of damage due to excavation

These measures address the most important causal factors of the pipeline, in particular in the most sensitive areas.

This study has also identified important management system controls, such as:

material specification training inspection (of materials and work carried out)

WAWA need to consider how to best manage these aspects with respect to

selection of manufacturer inspection of pipeline upon arrival selection for installation contractor ensuring adequate training of contractors specification of pipeline material and transport inspection and follow-up of installation etc.

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Gutteridge HaskLr,s and Davey Pty Ltd App 2.18 DNV Consultancy Services Ellen brook Sewer ERA October, 1997

11.8. DETAILED RESULTS FROM QUALITATIVE RISK ASSESSMENT WORKSHOP

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Gutteridge Haskim & P Ltd ' DNV Consultancy Sefl.

2 September, 1997 Environmental RA of Interim Pressure Main

Table 1: Plastic (UVPC or HOBAS) Rubber Ring Jointed (RRJ)

CAUSE

Excavation (damage to pipe)

PREVENTION

Normal to exchange information of pipe

location with other services

Sewer will be mostly located at 1200 mm depth

FREQUENCY

10

CONSEQUENCE

Burst (immediately discovered)

MiTIGATION

Medium size or greater leaks would cause soil erosion and be detected (mostly by the public)

while other services are at 600-900 mm

Pressure testing before use

Visual inspection (external)

9 Mediqm size leak (>25 mm

hole) Poor installation ofjoints

Witness mark on pipe

Chamfering of pipe end

Use of lubricant

Leaks from air valves or scour

Training Pumps may be shut down so that pipe pressure is reduced and Dead flanges bolted onto scour valves 7 Small leaks (<25 mm hole)

valves All valves located in pits leak would almost stop

Inspection programme



5 Medium size leak (>25 mm hole) detected straight away Excavation (damage to joints)

Sewer will be mostly located at 1200 mm depth while other services are at 600-900 mm

Correct compacting 4 Medium size leak (>25 mm hole) Pipe deformation on backfilling

Training

Pressure testing before use 3 Burst Damage on backfilling

Sand specified for backfilling

- Training

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DNV Consultancy Ser Gutteridge Haskins & Dave)' Py Ltd September, 1997 Environmental RA ofinterim Pressure Main 3

Table 1 : Plastic (UVPC or HOBAS) Rubber Ring Jointed (RRJ)

PREVENTION FREQUENCY CONSEQUENCE MITIGATION CAUSE

Fatigue caused by incorrect Correct packaging for transport 2 Burst The soil conditions (sand) would naturally acts as a filter,

transporting Visual inspection on arrival although probably only effective

Training for small leaks

Joints in bends slipping due to Thrust blovk 2 Burst

hydraulic forces (use of welded steel in bends)

Pipe is buried 2 Burst All water from nearby well Vandalism bores will be subject to

Valves contained in pits treatment

Overpressure of pipe Safety Factor in design > 2 1 Burst

Seismic activity Possible that location on sand plain may help 1 Burst

Material defects from Quality system with manufacturer 1 Burst

manufacturing Specified to Australian Standard

Certificate

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Gutteridge Haskins & P Ltd September, 1997 Environmental RA of Interim Pressure Main 4

Table 2 : Concrete Lined Mild Steel, Rubber Ring Jointed (RRJ)

PREVENTION FREQUENCY CONSEQUENCE MITIGATION CAUSE

Excavation (damage to coating Normal to exchange information of pipe 7 Small leaks (<25 which gradually

mm hole) to grow

Medium size or greater leaks would cause soil erosion and be

which then causes corrosion) location with other services medium size detected (mostly by the public)


Poor installation ofjoints Pressure testing before use 7 Medium size leak (>25 mm hole)




Use of lubricant

Training ___________

Leaks from air valves or scour Dead flanges bolted onto scour valves 7 Small leaks (<25 mm hole) Pumps may be shut down so that pipe pressure is reduced and

valves All valves located i leak would almost stop

Inspection programme -

Excavation (damage to joints) Normal to exchange information of pipe 5 Medium size leak (>25 mm hole) detected straight away location with other services


Gas attack on concrete lining Design 5 Small leaks (<25 which gradually

mm hole) grow to

(causes corrosion) Use of PE lining at high points medium size

Damage to inner lining during Transport procedures 3 Small leaks (<25 which gradually

mm hole) grow to

All water from nearby well

bores will be subject to transport (causes corrosion) Inspection on arrival medium size treatment

Training

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Gutteridge Haskins & Davey Ply Ltd DNV Consultancy Serb I

Environmental RA of Interim Pressure Main 5 September, 1997

Table 2 : Concrete Lined Mild Steel, Rubber Ring Jointed (RRJ)

CAUSE PREVENTION FREQUENCY CONSEQUENCE MITIGATION

Pipe is buried

Valves contained in pits

2 Burst

The soil conditions (sand) would naturally acts as a filter, although probably only effective for small leaks

medium size

Vandalism

Fatigue caused by incorrect transporting

Joints in bends slipping due to

Overpressure of pipe

Correct packaging for transport

Visual inspection on arrival

Traming

I Burst

hydraulic forces

would always use welded steel in bends 1 Burst

Safety Factor in design > 4 1 Burst

Seismic activity

Material defects from manufacturing

Corrosion (for other causes)

Possible that location on sand plain may help 1 Burst

Quality system with manufacturer

Specified to Australian Standard

Certificate

1 Burst

Internal lining and external coating 1 Small leaks (<25 mm hole) which gradually grow to

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Gutteridge Haskins & Davey Ply Ltd DNV Consultancy Serv.

6 September, 1997 Envonmental RA of Interim Pressure Main fr

Table 3: Concrete Lined Mild Steel, Welded Joints


Normal to exchange information of pipe location with other services


7 Small leaks (<25 mm hole) which gradually grow to medium size


Excavation (damage to coating which then causes corrosion)


Leaks from air valves or scour valves

Pwnps may be shut down so that pipe pressure is reduced and leak would almost stop

Dead flanges bolted onto scour valves

All valves located in

7 Small)eaks (<25 mm hole)


Gas attack on concrete lining (causes corrosion)

Design

Use of PE lining at high points


All water from nearby well bores will be subject to treatment

Damage to inner lining during transport (causes corrosion)

Transport procedures

inspection on arrival


Traming

Corrosion in welds Internal lining complemented to cover each weld


Vandalism Pipe is buried 2 Burst


Fatigue caused by incorrect The soil conditions (sand) would naturally acts as a filter, Correct packaging for transport I Burst

transporting Visual inspection on arrival .

although probably only effective


Overpressure of pipe Burst Safety Factor in design >4 1

Possible that location on sand plain may help 1 Burst Seismic activity

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Corrosion (for other causes) I Internal lining and external coating

Weld failures Inspection of each weld

Records of inspection kept

Small leaks (<25 mm hole) which gradually grow to mediujn size

Small leaks (<25 mm hole) which gradually grow to medium size

Gutteridge Haskins & Davey Ply Lid DNV Consuliancy Serb


Table 3 : Concrete Lined Mild Steel, Welded Joints

CAUSE I PREVENTION

Material defects from Quality system with manufacturer

manufacturing

I

Specified to Australian Standard

Certificate

FREQUENCY 1CONSEQUENCE

1 I Burst

MITIGATION

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Gutteridge Haskins & Davey Pty Ltd ' DNV Consuliancy Se


Table 4 : Polyethylene Lined Mild Steel, Rubber Ring Jointed (RRJ)

CAUSE PREVENTION

Pressure testing before use


FREQUENCY CONSEQUENCE MITIGATION

7 Medium size leak (>25 mm hole) Poor installation ofjoints



Use of lubricant

Training Pumps may be shut down so that pipe pressure is reduced and Dead flanges bolted onto scour valves 7 Small leaks (<25 mm hole)

Leaks from air valves or scour valves All valves located in pits leak would almost stop


Excavation (damage to joints) Normal to exchange information of pipe


5 Medium size leak (>25 mm hole) detected straight away


Excavation (damage to coating which then causes corrosion)







Pipe is buried 2 Burst Vandalism


medium size

Design

Use of PE lining at high points

1 Small leaks (<25 mm hole) which gradually grow to Gas attack on concrete lining

(causes corrosion)

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Gutteridge Haskins & Dave)' Ply Ltd .. DNV Consultancy Serb .


Table 4 : Polyethylene Lined Mild Steel, Rubber Ring Jointed (RRJ)


Damage to inner lining during Transport procedures 1 Small leaks (<25 mm hole) All water from nearby well

transport (causes colTosioll) Inspection on arrival which gradually grow to bores will be subject to

medium size treatment Training

The soil conditions (sand) would naturally acts as a filter, Fatigue caused by incorrect Correct packaging for transport 1 Burst

transporting Visual inspection on arrival although probably only effective


Joints in bends slipping due to Would always use welded steel in bends 1 Burst

hydraulic forces

Overpressure of pipe Safety Factor in design > 4 1 Burst

Seismic activity Possible that location on sand plain may help I Burst

Material defects from Quality system with manufacturer 1 Burst

manufacturing Specified to Australian Standard

Certificate

Corrosion (for other causes) Internal lining and external coating 1 Small leaks (<25 mm hole) which gradually grow to medium size

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REPORT GROUNDWATER CONTAMINATION RISK ASSESSMENT

ELLENBROOK SEWERAGE MAIN GNANGARA ROAD

for DNV Technica

DAMEs& MOORE Level 5, 85 The Esplanade Ref: GD:amc/29384-004-3731DK:282-B322/PER South Perth WA 6151 20 June 1996 Tel: 09 367 8055

Fax: 09 367 6780 A.C.N. 003 293 696

I

I

DNV Consuliancy Services A2641 Page 19 Oclober, 97 Gutteridge Haskins and Davey Ply Ltd Ellenbrook Sewer ERA

11.9. GROUNDWATER CONTAMINATION CONSEQUENCE ASSESSMENT


Letter

Revision 0 20 June. /996

for DNV Technica Page 2

97-9-25

DNV Technica 1st Floor 360 Burwood Road HAWTHORN VIC 3122

Attention: Mr David Willis

Dear Sir,



Dames & Moore is pleased to present a draft copy of the above report.

We trust this report meets with your approval and shall be pleased to discuss any points that may arise.

Yours faithfully DAMES & MOORE

G. Domahidy Consultant-in-Charge Geoscience & Environmental Engineering

Ref: GD:emcP29384-004-3731DK:282-B322/PER

Report for discussion purposes only Revision 0 Groundwater Contamination Risk Assessment, Eltenbrook Sewerage Main, Gnangara Road 20 June 1996 for DNV Technica

TABLE OF CONTENTS

Page NO

1. INTRODUCTION

2 PUBLIC WSTER SUPPLY BOREFIELD

HYDROGEOLOGICAL SEllING

ASSESSMENT OF LEAKAGE

SUMMARY AND CONCLUSIONS

REFERENCES

LIST OF TABLES

TABLE 1. PUBLIC WATER SUPPLY BORE DETAILS

LIST OF FIGURES

FIGURE 1 LOCALITY PLAN

LIST OF APPENDICES (cont'I)



for

DNV Technica

1.0 INTRODUCTION

It is proposed to install an underground sewerage main along Gnangara Road in Western

Australia. It is understood that the 15km pipeline will follow the general undulations of the

surface, and will be graded at a minimum of 1:300.

DNV Technica commissioned Dames & Moore to conduct a risk assessment on groundwater

contamination resulting from a potential sewer pipe failure. Any pressure main failure, whether

small and persistent or a sudden large burst would threaten a number of existing public water

supply bores. This report presents a compilation of relevant hydrogeological and infrastructural

information and an assessment of the effect of failure using general hydrogeological and

hydraulic parameters.

2..0 PUBLIC WATER SUPPLY BOREFIELD

Gnangara Road forms the boundary for two Underground Water Pollution Control Areas

(UWPCAs) designated by the Water & Rivers Commission to protect groundwater recharge

areas which are important for public water supply. Wanneroo UWPCA lies to the north of

Gnangara Road; Mirrabooka UWPCA lies to the south of it. The UWPCAs extend westwards as

far as Lake Gnangara and eastwards to Roberts Road. Much of the pressure main route lies

within the highest category of UWPCA protection, with a Priority 1 classification.

There are six existing public water supply bores along Gnangara Road, adjacent to the pressure

main route, and a further four are proposed along the eastern part of the route. Bore locations are

shown on Figure 1 and details of these bores are presented in Table 1 below. There are many

additional public water supply bores to the south of Gnangara Road.

Report - for discussion purposes only Revision 0 Groundwater Contamination Risk Assessment, Ellenbrook Sewerage Main, Gnangara Road 20 June 1996

for DNV Technica Page 2

TABLE 1

PUBLIC WATER SUPPLY BORE DETAILS

Bore No. Northing Easting Collar RL 1995 Pumpage Screen Interval Welihead Protection Zone2 (m) (m) AHD Quota (mbgl) Radius

(m3/d) (m) PRODUCTION BORES

M300 6481469 393822 45.37 1123 31.53-48.29 500

M310 6481515 395424 46.09 1099 22.05-53.29 500

M3200 6481523 396322 46.75 1370 21.03-48.46 500

M330G 6481534 397257 47.78 1879 21.76-52.55 500

M340G 6481540 397938 47.04 1105 20.74-45.43 500

M350 6481507 398876 45.89 822 31.00-46.00 500


M360 6481569 399854 44.91 16441 0.00-48.00 500

M370 6481578 400717 44.25 16441 48.00-60.00 500

M380 6481587 401716 41.89 16441 0.00-46.00 300

M390 6481560 402566 42.59 8221 0.00-20.00 300 26.00-48.00

$ = meues below ground level 1 = plannedrate 2 = Wellhead Protection Zones are surface and subsurface areas surrounding a water bore supplying a public

water system through which contaminants are likely to move towards the bore.

3..0 HYDROGEOLOGICAL SETTING

The area is underlain by the Bassendean Sand, which forms part of the superficial formations

aquifer that supplies the public water supply bores. The Bassendean Sand is fine to medium

grained, moderately well sorted, with subrounded grains. it is permeable and consists essentially

of quartz sand which has a negligible capacity to adsorb or fix contaminants.

The superficial aquifer along the route is unconfined, and the water table is generally 2-5m

below ground surface in the vicinity of the six existing bores; the intervening unsaturated zone

consists entirely of sand, with some patchy iron cementation ("coffee rock"). The natural

direction of groundwater flow is towards the south.

The proposed pressure main would directly overly the capture zones (areas which contribute

groundwater) for six existing public water supply wells and four proposed wells, and is

upgradient of a large number of other public water supply wells.

GD:inic12938004313iDK282B3221l'ER DAMES & MOORE

Report - for discussion purposes only Revision 0 Groundwater Contamination Risk Assessment, Ellenbrook Sewerage Main, Gnangara Road 20 June 1996 for DNV Technica Page 3

Groundwater levels in the vicinity of the six existing production bores along the route of the

proposed main are at about 42m AHD (September 1988). Near M390, water levels are at about

37m AHD. Ground elevations range from about 65m AHD on the western side to between 45m

AHD and 50m AHD in the central and eastern parts of the pipeline route.

4..0 ASSESSMENT OF LEAKAGE

It is understood that the sewerage station booster pumps discharge into a single pressure main,

and are designed to operate 12 hours per day.

Leakage from any holes in the pipeline will infiltrate the soil and move vertically downwards.

The line taken to reach the water table can be estimated from the following version of Darcy's

Law:

V= K1 0

where: V. = seepage velocity (mid);

K1 = hydraulic conductivity (mid) at a hydraulic gradient of 1;

0 = porosity

Darcy's Law is relevant to flow through porous media, and for this calculation, it is assumed that

the soil is fully wetted (i.e. end of winter). A large leak, even in summer, would soon result in

fully saturated conditions.

The calculation for vertical leakage from the sewerage main is based on a hydraulic gradient of 1

and a vertical hydraulic conductivity of 1 .5mld. It is typical to assume vertical hydraulic

conductivity to be 10% of the horizontal conductivity (15m/d) due to vertical anisotropy in the

Bassendean Sand. A porosity of 0.3 (30%) has been used, and is typical of the Bassendean Sand.

The estimated vertical leakage rate is therefore about Smld. The time for the leakage to reach the

aquifer will range from about 10 hours where the water table is 2m below the pipe, to 4.4 days

where the pipe is located 22m above the water table. On reaching the water table, the leakage

will enter the unconfined aquifer and be drawn towards the public water supply bores.

The volume of leakage will depend on the size of the hole and whether the pump is operating.

The volume of possible leakage ranges from 60m3/d to 605,829m3/d under a pressure of 50m,

and from 86m3/d to 856,770m3/d if the pressure is lOOm.

Ref: GD:m29384004373282B322I' DAMES & MOORE


The infiltration capacity of the Bassendean Sand is high. As long as the rate of leakage is small,

it infiltrates as fast as supplied and the leak may not be detected, especially as the pumps come

on every 12 hours. Under high pressures (i.e. during pumping), sewerage from holes in the

pipeline injected into the Bassendean Sand may take a shorter time to reach the aquifer.

Leakage from the pipe will be vertical as long as the Bassendean Sand has the capacity to absorb

the leakage. Excess leakage will move laterally and upwards, especially when the pumping head

exceeds the effects of gravity. The upward leakage will become evident when the ground level is

reached.

Studies in virus and bacteria transport (Bales et al, 1995) in a sandy aquifer under natural

gradient conditions indicated that viruses may travel several metres downgradient from the

source. Bacteria could persist for tens of metres downgradient, whilst other the sewage

constituents including boron, chloride, sodium, phosphorus, ammonia, nitrate, detergents and

volatile organics may travel 1 ,000s of metres in contaminant plumes.

5..0 SUMMARY AND CONCLUSIONS

The proposed sewerage main along Gnangara Road will pass adjacent to six existing public

water supply bores and four future production bores. These bores are developed in the

Bassendean Sand, a fine to medium grained, well sorted quality sand that forms an unconfined

aquifer. The pipeline route is on the boundary of two Underground Water Pollution Control

Areas, designed to protect public water supplies.

Any leakage from the pipe will be vertical. The rate of vertical movement in the Bassendean

Sand is calculated to be about 5mJd. The time to reach the aquifer will depend on the elevation

of the pipe relative to the water table. It is estimated that this will range from 10 hours on the

eastern side of the route and 4.4 days on the western side. However, if injected from holes under

pressure, the sewerage may take a shorter time to reach the aquifer.

On reaching the water table, the sewerage will be diluted and will then be drawn towards the

water supply bores. Depending on the location of the leak, bacteria can travel tens of metres,

while major ions, detergents or volatile organics can travel 1 ,000s of metres.

* * *

Ref GD:anc1293844)04-3731DK;282-B322IPEP. DAMES & MOORE


6..0 REFERENCES

Bales, R.C., Li, S., Maguire, K.H., Yahya, M.T., Gerba, C.P., and Harvey, R.W., 1995. Virus

and Bacteria Transport in a Sandy Aquifer. Cape Cod. MA. Groundwater Vol. 33, No.

4, pp 653-661.

cf; GDan,c/29384.004-373/DK:282-B322/PER DAMES & MOORE

APPENDIX 3

RELATIVE RISK RANKING


Gutteridge Haskins and Davey Pty Ltd DNV Consullancy Services Ellenbrook Sewer ERA October, 1997

TABLE OF CONTENTS

III.!. INTRODUCTION......................................................................................................................3

111.2. ROUTING OF SEWAGE AWAY FROM GNANGARA PRIORITY 1 AREA.......................4

111.3. ALTERNATE MODES OF SEWAGE TRANSPORT..............................................................6

111.4. PIPELINE ELEVATION ...........................................................................................................8

111.5. LOCATION OF PIPELINE .......................................................................................................9

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Gutteridge Ha.skins and Davey Pty Ltd App 3.3 DNJ' Consultancy Services Ellenbrook Sewer ERA October, 1997

111.1. INTRODUCTION

Relative Ranking is actually an analysis strategy rather than a single, analysis method. This strategy allows hazard analysts to compare the attributes of several processes or activities to determine whether they possess hazardous characteristics that are significant enough to warrant further study or control. Relative Ranking can also be used to compare several process siting, generic design, or equipment layout options, and provide information concerning which alternative appears to be the "best", or least hazardous, option. These comparisons are based on numerical values that represent the relative level of significance that the analyst gives to each hazard. Relative Ranking is normally performed early in the life of a process, before the detailed design is completed, or early in the development of an existing facility's hazard analysis program.

The main purpose of using Relative Ranking methods is to determine the process areas or operations that are the most significant with respect to the hazard of concern in given study.

The theory behind Relative Ranking methods has its roots in the three basic questions used in risk analysis:

What can go wrong? How likely is it? What would the effects be?

The philosophy behind the Relative Ranking approach is to address these risk analysis questions to determine the relative importance of processes and activities from a safety standpoint before performing additional and more costly hazard evaluation or risk analysis studies. Thus approximate relationships of process attributes are compared to determine which areas present the greater relative hazard or risk. Subsequently, additional hazard evaluation studies may first be performed on the more significant areas of concern.

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111.2. ROUTING OF SEWAGE AWAY FROM GNANGARA PRIORITY 1 AREA

Three basic options were explored during the workshop outlined in Appendix I for the disposal of sewage namely:

Develop an alternate sewage disposal strategy (i.e. treatment plant, sewage inerting, etc.). Route pipeline around Gnangara groundwater priority 1 area. Route pipeline across Gnangara groundwater priority 1 area.

These basic options are rated according to relative spill potential (A), relative cost to implement (B) and relative spill remediation cost (C). A rating of 1-3 is applied, 1 being the lowest and 3 being the highest. This is a discrete rating not indicating order of magnitude but rather to allow for differentiation of options.

The relative rank (R) is considered to be a function F(A,B,C) and for our purposes a simple product of the three parameters. A higher R infers a greater relative risk, a lower R relative risk.

R=AxBxC

OPTION A B C R 1. Alternate strategy 1 3 1 3 2. Route around P1 area 3 2 2 12 3. Route across P1 area 2 1 3 6

Rational for ranking allocation:

1. An alternate strategy is assumed to reduce the spill potential lower than a pipeline option and also away from the P1 area. 2. A pipeline route around the P1 area will be longer than the proposed route across the P1 area. Spill potential is a function pipeline length and will therefore be higher than a route across P1.

1. The development of an alternate strategy will be resource intensive, timeous and more complex than the other two options. It is anticipated that the cost for adopting this option will therefore exceed the cost of both other options. 2. A pipeline route around the P1 area will be longer as well as entailing the purchase of additional land. Studies into alternate route sensitivities will also need to be done therefore this option is considered to be more expensive than a route across P1.

1. It is assumed that an alternate strategy will remove the requirement for remediation/ clean-up and will therefore have the lowest possible remediation/ clean-up cost. 2. As a route around the P1 area will remove the risk of contamination of this area and should be over a less sensitive area remediation requirements should not be as stringent therefore the cost of remediation/ clean-up should be lower than a route across P1.

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Using this approach it is apparent that the alternate sewage disposal strategies should be explored as a first option. General fmdings of the workshop in Appendix I indicate that deviations of this nature from the current proposal will entail review of current area strategic plans, increased cost, continuation of sewage transport by road, review of alternate solution sensitivities and negotiation with new interested third parties. Further review of this option is outside the scope of this study and will not be explored fuither here.

On the assumption that alternate sewage disposal strategies have been screened out only option 2 and 3 remain for further evaluation.

A simple ranking of option 2 and option 3 is made in the table below:

OPTION A B C R 2. Route around P1 area 2 2 1 4 3. Route across P1 area 1 1 2 2

It is apparent that of the two pipeline options routing across the Gnangara Priority 1 Area is the preferred option (i.e. the shortest distance between two points). This is the option taken forward for further evaluation.

Further review of routes around the Gnangara Priority 1 Area is outside the scope of this study and will not be explored further here.

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Ellen brook Sewer ERA October, 1997

111.3. ALTERNATE MODES OF SEWAGE TRANSPORT

Alternate modes of sewage transport considered during the workshop included:

Transport by truck. Transport by conveyor. Transport by pipeline.

Pre-treatment of sewage as well as vacuum systems were discussed but are screened out here as they form part of option 1 "Alternate sewage disposal strategy" discussed in 111.2. Vacuum systems were considered non-feasible due to the density of sewage and distance to be covered and were screened out during the workshop.

These basic modes of sewage transport are rated according to relative spill potential (A), relative cost to implement (B) and relative spill remediation cost (C). A rating of 1-3 is applied, 1 being the lowest and 3 being the highest. This is a discrete rating not indicating order of magnitude but rather to allow for differentiation of options.


R=AxBxC

OPTION A B C R

1. Transport by truck 1 1 1 1

2. Transport by conveyor 3 3 2 18

3. Transport by pipe 2 2 2 8


A: 1. Transport by truck ensures that potential spill size is limited to truck capacity with spill frequency dominated by vehicle collision risk.(although with increased shipments as required in a future case, the risk will increase significantly).

It is widely recognised that pipes isolate substances from their surrounding environment more effectively than conveyor systems and will therefore have less potential to spill sewage.

While pipeline leak frequencies for major leaks are expected to be lower than transport risks of option 1, the potential consequences of a major leak from a pipeline are expected to be more severe.

B: 1. Transport by truck should entail no capital expenditure, only incurring operating cost which while remaining the most economical in the short term will continue to increase with increasing sewage load. In addition to the cost issue the public perception of such a convoy of sewage trucks would need to be taken into account. 2. The capital cost of a conveyor system as well as ongoing operational expense is expected to exceed the cost of a pipeline system.

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C: 1. As spill size is limited for transport by truck the potential cost of remediation/ clean-up is considered to be lower than the other two options. 2. & 3. Both options 2 and 3 may incur considerable clean-up remediation costs no differentiation is apparent they have therefore received an equal weighting.

Using this approach it is apparent that trucking sewage would be initially the preferred sewage transport option. Trucking sewage however is only considered an option in the short term and for a finite number of haulage trips. Road safety hazards as well as local health hazards may well dominate a risk profile for this option due to frequent batch handling operations. This was not considered an acceptable practice for any extended period of time by the participants in the workshop covered in Appendix I.

Option 2. was also found to be unacceptable at this forum. Also considering its relative ranking option 2 is screened out and will not be taken forward.

It is then apparent that transport by pipeline is the preferred mode of transport for transport of bulk sewage over large distances. This option is taken forward for further evaluation.

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111.4. PIPELINE ELEVATION

Two pipeline elevations were considered during the workshop:

I. Pipeline above ground 2. Pipeline below ground

These basic pipeline elevations are rated according to relative spill potential (A), relative cost to implement (B) and relative spill remediation cost (C). A rating of 1-2 is applied, 1 being the lowest and 2 being the highest. This is a discrete rating not indicating order of magnitude but rather to allow for differentiation of options.


R=AxBxC

OPTION A B C R 1. Pipeline above ground. 2 2 1 4 2. Pipeline below ground. 1 1 2 2


1. Above ground pipelines are subject to failure mechanisms resulting in leaks such as pipe support failure, external impact and daily temperature fluctuations not affecting underground pipelines. Therefore the relative spill potential is considered higher for option 1 than option 2.

1. From discussion during the workshop covered in Appendix 1 it is apparent that above ground pipelines are more costly and require more supports than below ground pipelines.

1. The cost of remediation for an above ground pipeline should be lower than for a below ground pipeline due to early leak detection, direct access for easy repair, sand buffer between the pipeline and water table and allowance for undamaged coffee rock which may contain some of the contaminants and retard migration to the water table.

From the above it is apparent that option 2 a below ground pipeline is the preferred option. habove ground pipeline (option 1) also creates a significant physical barrier to any future developments and may have adverse public perception implications.

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Gutterldge Haskins and Davey Py Lid App 3.9 DNV Consuliancy Services

Ellen brook Sewer ERA -October, 1997

111.5. LOCATION OF PIPELINE

Four potential pipeline locations were considered during the workshop:

Pipeline located South of the water bores along Gnangara Road. Pipeline located at the North side of the Gnangara Road reserve. Pipeline located in the median of the Gnangara Road reserve. Pipeline located South of the Gnangara Road reserve.

These basic pipeline location are rated according to relative bore water contamination (A), relative cost to implement (B) and relative spill remediation cost (C). A rating of 1-4 is applied, 1 being the lowest and 4 being the highest. This is a discrete rating not indicating order of magnitude but rather to allow for differentiation of options.


R=AxBxC

OPTION A B C R

1. Pipeline South of bores 1 4 1 4

2. Pipeline North of Gnangara Road 2 1 2 4

3. Pipeline Gnangara Road median. 3 2 2 12

4. Pipeline South of Gnangara Road. 4 3 2 24


1. A large leak in any of these locations is expected to reach the groundwater, therefore a more discernible effect would be to consider the effect on water bores along the Gnangara Road. Water flow gradients are such that a spill in this area is not expected to adversely affect bore water quality. 2. Options 2 to 4 move progressively nearer to the line of water bores along Gnangara Road and are therefore expected to have a greater change of adversely affecting bore water quality due to closer proximity.

1. Purchase of ground and review of local sensitivities dominates this cost picture. This route is currently privately owned and purchase is anticipated to be protracted and costly.

Ground is available and largely held by CALM. Pipeline development at this stage would not negatively impact in the current deforestation program.

This option would entail re-design of the Gnangara route as well as re-routing a power line and Telstra telephone cable.

Locating the pipeline South of the Gnangara road would entail the relocation/closure of 3 existing water bores.

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Gutteridge Haskins and Davey Pty Ltd App 3.10 DNV Consultancy Services Ellen brook Sewer ERA October, 1997

C: 1. The urgency of remediation and clean-up is reduced by the natural flow of the groundwater moving the contamination away from the Priority 1 protection area. 2. The cost of remediation and clean-up is likely to be very similar for option 2,3 & 4 given their relative proximity to wellheads and the natural gradient in the groundwater.

From the exercise above options 3 and 4 are screened out with option 1 the preferred option, followed by option 2.

It is apparent that the routing of the pipeline South of the Gnangara Road bores (option 1) is the pipeline location with the lowest environmental impact. Due to potential significant problems anticipated for Option 1, relating to land purchase and yet unidentified sensitivities it rapidly comes apparent that option 2 is the preferred route.

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APPENDIX 4

RISK MITIGATION WORKSHOP (3 October 1997)

K:\CS_WA\PROJECTS\GHD\2763RPT_VO\2763.Ap4

Gutieridge Haskins and Davey Pty Ltd

DNV Consultancy Services Ellenbrook Sewer ERA, October, 1997

TABLE OF CONTENTS

IV.l. INTRODUCTION ..................................................................................................................... . IV.l.l Purpose..................................................................................................................................3 IV.1.2 Objectives..............................................................................................................................3 IV.1.3 Venue....................................................................................................................................3 IV.1.4 Analysts.................................................................................................................................3

METHODOLOGY.....................................................................................................................4

FINDINGS ................................................................................................................................. 5

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Gutteridge Haskins and Davey Py Ltd App 4.3 DNV Consullancy Services

Elienbrook Sewer ERA October, 1997

IV.!. INTRODUCTION

IV.!.! Purpose

The purpose of this workshop was to review risk reduction options as well as tertiary and quaternary risk for the Ellenbrook Sewer Main Development.

IV.1.2 Objectives

The objective of this workshop was to identify possible strategies of risk management and risk reduction with due regard for estimates of the likely extent of contamination (if any) and monitoring procedures to detect leaks.

Specific areas for consideration were:

Pipeline Design : Measures to ensure pipeline integrity and operational needs analysis during design to minimise potential spill size. Pipeline Construction : Measures to ensure pipeline integrity during construction and commission to minimise the potential for spill. Pipeline Operation : Measures to ensure pipeline integrity during normal routine operation. Leak Detection Strategies : Measures to ensure early detection of potential leak conditions. Spifi Mitigation Measures : Measures to ensure minimal environmental impact from potential spills (j)assive systems). Emergency Response : Measures to ensure prompt and effective spill remediation (active systems).

IV.1.3 Venue

GHD House 239 Adelaide Terrace Perth

IV.1.4 Analysts

Clarke Hendry John Bond John Cox Mick Cudmore Adrian Tomlinson Alex Marsden Simon Leverton Tony Norrish Peter Winfield Reg Williamson Ray Pillage Johan Potgieter

- Water Corporation - Water Corporation - Water Corporation - Water Corporation - Water & Rivers Commission - Water & Rivers Commission - Gutteridge, Haskins & Davey - Gutteridge, Haskins & Davey - Gutteridge, Haskins & Davey - Tubemakers - Tubemakers - Det Norske Veritas (Leader)

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IV.2. METHODOLOGY

The workshop employed brainstorming with the aid of checklists to develop risk mitigation strategies aimed at improving pipeline integrity for each aspect of the development and operation.

Risk mitigation focused on:

prevention strategies for the pipeline design phase and pipeline construction phase. control strategies for pipeline operation and leak detection. treatment strategies for spill mitigation, emergency response and remediation.

Upon completion of this exercise the team proceeded with the development of weighting factors to be applied to generic data for pipeline leak frequencies as outlined in Appendix 5: Frequency Analysis.

All issues discussed were considered to be of similar importance and no ranking of priority actions was done.

The team was well constituted and included the following expertise:

environmental engineering! management hydrogeological expertise project management pipeline construction pipeline fabrication mechanical & civil engineering environmental legislation safety & risk engineering! management

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IV.3. FINDINGS

Recommended risk mitigation measures are outhne in the Table 3.1 below.


Gutteridge Haskins and Davey Piy Ltd App 4.6 1 DNV Consultancy Servk

October, 1997 Ellen brook Sewer ERA

TABLE 3.1 : PRO1OSED RISK MANAGEMENT AND REDUCTION STRATEGIES

A: PREVENI1UI 1. Design to minimise use of valves, bends and fittings. 2. Maximise distance from bores in critical wellhead areas. 1. Pipeline Design

3. Consider performance and compatibility of pipeline system. 4. All valves, flange joints to be in pits to facilitate inspection! maintenance. 5. Develop a construction QA Plan including manufacturers guidelines. 6. ComprehensivelY review geotechnical environment to determine bedding requirements. 7. Include provision for monitoring systems flow, pressure etc. 8. Include requirements for back-up systems. 9. Make provision for safe removal and storage of sewage at scour points. 10. Ensure manufacturers & pipe construction QA systems are in place and adequate. 11. Design for standard fittings and equipment. 12. Materials of construction and coatings to be appropriate for application. 13. Design to be subject to formal review cycle (HAZOP).

Physical inspection and QA verification to be carried out by third party. Provide incentives for contractor, supplier ,etc. to maintain high standards throughout.

Pipeline Construction

Make use of approved contractors with demonstrated performance (& accredited pipelayers). Monitor bedding and backfill compaction. Integrity testing on completion of assembly (progressively between valves). Pipelayer to demonstrate competence prior to commencement of construction. Safety Plan to address the introduction of new personnel (ref 6 also). Pipeline route to be accurately recorded during construction process. Contractor to provide safety! pollution control plan.

B: CONTROL 1. Pipeline Operation

1. Routine pipeline system inspection and testing to current best practice i.e.:

Visual Integrity testing Frequency of testing to address system reliability criteria Full function test (of component & control systems) QA reporting & evaluation of data Audio - start points of main to be identified Routine sampling & analysis of groundwater (including current bore monitoring data)

Operating procedure/ maintenance schedule to be in accordance best practice (1.). Define areas of responsibility and verify compliance through audit.

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Gutteridge Haskins and Davey Py Ltd App 4.7 DNV Consultancy Servk'


Incident management system to include maintenance breakdowns. Monitor sewage quality during operation to identif' abnormal sources to facilitate control of

undesirable contaminants. Operators to be trained and competent (demonstrable). System to be automated and fail safe (pump shutdown on pipe failure).

2. Leak Detection Flow monitoring equipment to be regularly calibrated and flow measurements routinely reconciled.

Develop an operational plan for calibration of control/monitoring devices to ensure accuracy! reliability.

Provide monitoring for leaks in interstitial spaces around critical components and pipes. Pipeline to be routinely pressure tested. Obtain resources to identif' suspected leaks (people/ equipment! skills). Review potential for continuous acoustic leak detection.

C: TREATMENT 1. Spill Mitigation Sewage transport pumps to automatically shut down on loss of pressure.

Provision of secondary containment in critical areas.

2. Emergency Response The Emergency Response Plan should include provisions for mitigation, remediation and adequate

response. Leaks are to be isolated as soon as possible to limit spill size.

Ensure access for emergency response. Establish hierarchy of emergency response & priority also including 3rd party interests.

Identif' critical spares / skills necessary for emergency response effectiveness. Establish the requirement and availability of equipment. Place public signposts indicating emergency contact nwnber at strategic locations along the route.

The priority of call-out to address potential groundwater contamination to be high (top priority).

3. Remediation Provide facilities with adequate capacity to accommodate contained material/ recovered effluent.

Identif' the level of local contamination to determine an action plan. Develop spill remediation contingency plans. Emergency management and operating procedure to be closely related. Sufficient insurance's should be held to ensure adequate funding for any spill remediation measures

which may be required.

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APPENDIX 5

FREQUENCY ANALYSIS

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Gutteridge Haskins and Davey Ply Ltd DNV Consultancy Services Ellen brook Sewer ERA October, 1997

TABLE OF CONTENTS

V.I. INTRODUCTION.......................................................................................................................3

V.2. PIPELINE FAILURE FREQUENCY.........................................................................................4

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V.!. INTRODUCTION

This appendix provides details of the generic failure rates used in this study, together with their sources and derivations. Most of the failure data is taken from DNV Technica's Onshore Failure Frequency Database.

The generic failure data is derived from failure data for a wide variety of process and power industry plant, and as such is not specific to sewage pipelines. DNV proprietary software LEAK was used in conjunction with the VEREDA database to assist in the calculation of leak frequencies for the sewer main. These failure rates were then modified to reflect specific conditions relating to the proposed Ellenbrook Sewer Main.

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V.2. PIPELINE FAILURE FREQUENCY

For welded piping, a confidential DNV Technica source (unpublished data from a major chemical company, L056 1980) gives general pipe leak frequency data as a ratio of pipe length (L) to diameter (D), as shown in Table V.2.4.1. This is considered by DNV Technica to be the best data on pipe failures which has been identified and hence is the basis for the data used in this study.

TABLE V.2.1: HISTORICAL PIPE LEAK FREQUENCIES

TYPE PERCENTAGE OF CROSS SECTIONAL

AREA

FREQUENCY (per year)

Smailleaks <1 2.8x10 7 L/D

Big leaks 5 1.2 x 10 L/D

Catastrophic leaks 20 5.0 x 108 L/D

Rupture 100 2.2 x 108 L/D

Total 4.7x iø L/D

The modifications to the generic pipeline frequencies for various failure categories are presented in Table V.2.2.

Attendees at the Risk Mitigation Workshop Appendix 4, were tasked with reviewing subcategories of pipeline failure causes with the view to developing mitigation factors for the Ellenbrook Sewer Main. Attendees scored and assessed potential areas for reduction in risk. DNV screened the outputs from the workshop and developed mitigation factors for pipeline failure frequencies, also based on industry experience.

Reasons for modifications are provided in Table V.2.2. Modifications have been Conservative and no modification of unknown parameters was made.

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TABLE V.2.2 PIPELINE FAILURE FREQUENCY MODIFICATIONS

CAUSAL FACTOR CATEGORY

CAUSAL FACTOR SUB-CATEGORY ORIGINAL PERCENTAGE

OF TOTAL

PERCENTAGE REDUCTION TO ACCOUNT FOR

SITE CONDITIONS

MODIFIED PERCENTAGE OF ORIGINAL

TOTAL

REASON FOR MODIFICATION

CORROSION Pipework or equipment from wrong materials 1.68 80 0.34 Materials of construction proven (jroviding QA of material supplied is adequate)

Corrosive contaminants in pipe contents 0.38 0 0.38 Potential corrosion due to dissolved CO2, H2S and uncontrolled chemicals disposed

Conditions cause accelerated corrosion 1.01 0 1.01 in sewage.

Corrosive external environment 1.03 0 1.03

Inadequate protection 0.74 80 0.15

Galvanic action 0.33 0 0.33

Unknown 4.11 0 4.11

EROSION Unfavorable flow pattern 0.22 100 0.0 Straight pipeline

High velocity of contents 0.14 100 0.0 Flow velocities low

Erosive external environment 0.05 100 0.0 Pipeline buried

Unknown 0.27 0 0.27

Erosive contents 0.11 100 0.0 Contents not erosive

K:\CS_WA\PROJECTS\GHD\2763\RPT_VI\2763.AP5

Guiiridge Haskins and Davey Ply Lid Ellen brook Sewer ERA

App 5.6 DNV Consultancy Servk.... October, 1997

CAUSAL FACTOR CAUSAL FACTOR SUB-CATEGORY ORIGINAL PERCENTAGE MODIFIED REASON FOR

CATEGORY PERCENTAGE REDUCTION TO PERCENTAGE MODIFICATION OF TOTAL ACCOUNT FOR OF ORIGINAL

SITE CONDITIONS TOTAL

EXTERNAL Removal of pipework supports 0.27 100 0.00 Pipeline buried

LOADING Failure of pipework/equipment supports 0.98 100 0.00 Pipeline buried

Inadequate supports for loading conditions 1.14 90 0.11 Potential buoyancy effects on pipelme

Excessive loading by human action 0.49 0 0.49

Unknown 0.11 0 0.11 Pipeline buried

TEMPERATURE Pipe/equipment inadequate for thermal 0.87 100 0.00 Ambient operation

conditions

Equipment failure leads to thermal stress 0.38 100 0.00 No high temperature operation

Change in conditions of pipe contents causes 0.60 100 0.00 Operational experience

stress No high temperature operation

Thermal shock 0.38 100 0.00

Domino effect 0.54 100 0.00

Unknown 1.01 0 1.01

WRONG IN-LINE Incorrect siting of correct equipment 0.16 0 0.16

EQUIPMENT OR LOCATION Incorrect installation at correct site 2.64 -200 5.28 Potential for incorrect installation of each

rubber ring joint

Insufficient equipment 1.09 100 0.00 Equipment to be adequate

Unknown 0.11 0 0.11

K:\CS_WA\PROJECTS\GHD\2763\RPT_Vl\2763.1W5

Gutr1dge Haskins and Davey fly Lid App 5. 7 DNV Consuliancy Servk.




OF TOTAL


SITE CONDITIONS


TOTAL


PROCEDURAL Pipe not cleared of contents before worked on 4.38 0 4.38

FAILURE Wrong pipe or wrong equipment worked on 0.87 0 0.87

Incorrect equipment status 3.62 0 3.62

Wrong sequence of operations or procedure 2.90 0 2.90

Pipe/equipment connected/disconnected 0.76 0 0.76

unknowingly

Insufficient isolation of pipework 1.56 50 0.78 Low pressure operation

Equipment not returned to normal operating 0.36 0 0.36

status

Unknown 3.78 0 3.78

12.54 0 12.54 Although pipe subject to extensive QC no DEFECTIVE PIPE Pipework reduction is allowed as a conservative

approach due o the sensitivity of the area.

5.92 100 0.00 All valves to be located in sealed pits. Valve (in line)

Joint (welded) 5.48 0 5.48 Site Welding

Rupture/Bursting disk 0.38 100 0.00 No rupture/bursting disk

Unknown 6.54 0 6.54

K:\CS_WA\PROJECTS\GHD\2763\RPT_V1\2763.AP5

Gu:adge Haskins and Davey Py Lid App 5.8 DNVConsultancy ServL




OF TOTAL


SITE CONDITIONS


TOTAL


OTHER Valve opens due to power failure 0.11 100 0.00 Fail safe

Process upset 0.33 0 0.33

Clogged pipe leads to back flow or other 0.65 100 0.00 Clogged pipes are rare in process service

problems

Foreign body contaminant prevents valve 0.05 100 0.00 Large bore piping

closing

Computer software causes incorrect valve 0.22 100 0.00

status

Bending moment caused by material going 0.05 0 0.05

around elbow

Pipe cut by weed trimmer 0.11 100 0.00 N/A

IMPACT Impact of other plant equipment or contents 1.68 100 0.00 No additional plant

Human impact 0.85 -1000 8.50 Identified as major hazard to buried pipeline due to potential digging in area

Pipeline buried Natural causes result in falling object 0.22 100 0.00

Vehicle impact 1.57 100 0.00 Buried pipeline

Unknown 0.43 0 0.43 Plant layout and procedures


Gutteridge Haskins and Davey Ply Ltd App 5.9 DNV Consultancy Servk.




OF TOTAL


SITE CONDITIONS


TOTAL


OVERPRESSURE Source pressure exceeds pipe or equipment 1.81 0 1.81 spec

Shutdown system to prevent overpressure fails 0.22 0 0.22

High pressure source connected to low 0.11 100 0.00 No high pressure source to low press

pressure

Unexpected reaction 4.34 100 0.00 Common sewage

Freezing of pipe contents exceeds pipe spec 1.18 100 0.00 Pipeline buried in WA

Water pressure surge from steam lines (slug) 0.76 100 0.00 N/A

Water pressure surge from fast open/close 0.11 0 0.11 Water Hammer possible

valve

Water pressure surge from pump shutdown 0.05 0 0.05 Surge effects possible

Unknown 2.91 0 2.91

Heating causes overpressure of contents 0.65 100 0.00 No extreme heating effects

K:\CS_WA\PROJECTS\GHD\2763RPT_V1\2763A15

Gufteiidge Haskins and Davey Pty Ltd App 5. 10 DNVConsultancy Servk.


CAUSAL FACTOR CAUSAL FACTOR SUB-CATEGORY ORIGINAL PERCENTAGE MODIFIED REASON FOR

CATEGORY PERCENTAGE REDUCTION TO PERCENTAGE MODIFICATION OF TOTAL ACCOUNT FOR OF ORIGINAL

SITE CONDITIONS TOTAL

VIBRATION Vibration of attached equipment 0.71 0 0.71

Vibration in pipework caused by equipment 0.33 100 0.00 Pipeline buried/vibration damper

defect

Failure to maintain sufficient stable conditions 0.22 100 0.00 stable operation anticipated

Designhinstallation error leads to pipe 0.05 100 0.00 Design/installation proven

vibration

Unknown 0.22 0 0.22

UNKNOWN 9.12 0 9.12

TOTAL 100.00 81.36

K:\CS_WA\PROJECTS\GHD\2763RPT_V1\2763.5

Gutteridge Haskins and Davey fly Ltd App 5.11 DNV Consullancy Services Ellen brook Sewer ERA October, 1997

Based on the rationale presented in Table V.2.2, pipework failure frequencies for the Ellenbrook Sewer Main are predicted to be about 81% of the generic frequencies for each size of pipe. This results in a total frequency of 3.8 x 10 LID.

Leak frequencies for proposed diameter of 500 mm section of the pipe can be calculated, using frequencies given in Table V.2.1. For the purpose of this report, a section of pipe is considered to be 1 m in length. The resulting generic and modified leak frequencies calculated are presented in Table V.2.3. Leak frequencies for larger diameter pipes are also included.

TABLE V.2.3 FAILURE RATES FOR PROCESS PIPING

PIPE DIAMETER MEAN FAILURE RATE (per metre/per year)

(inches) (mm) GENERIC MODIFIED

16 400 1.2x10 9.7x10 7

18 450 1.0x10 8.1x10 7

20 500 9.3 x 10 7.5 x 10

24 610 7.7x10 7 6.4x10 7

36 900 5.2 x I0 4.2 x 10

48 1 1200 1 3.9x10 7 3.2x10-7


Gutteridge Haskins and Davey Ply Lid App 5.12 DNV Consultancy Services Ellen brook Sewer ERA October, 1997

For pipes above 10" diameter, the hole size distribution for pressure vessels has been used. The pressure vessel distribution is considered more appropriate where the line sizes are large, as these large pipes are more easily seen and suffer failures which are similar to those experienced by pressure vessels rather than those experienced by small pipes.

The distribution given in Figure V.2.1 is used to obtain the percentage of failures that occur over a hole size range. The fractions are then multiplied by the total failure frequency as given in Table V.2.3 for the pipe size. The resulting generic frequencies for pipe sizes and hole sizes applicable to the proposed Ellenbrook Pressure Main are set out in Table V.2.5.

Smaller and larger pipes have been included to illustrate variance in failure frequency for pipe diameter.

TABLE V.2.5 PIPE FAILURE FREQUENCIES BY HOLE SIZE

PIPE DIAMETER HOLE SIZE CATEGORY FREQUENCY (per 1 m section /year) (mm)

(inches) (mm) GENERIC MODIFIED

8 200 10 (0.01 to 20) 1.4 x 10 1.1 x 10 50 (20 to 80) 7.4 x 10-7 5.9 x 10

200 (80+) 2.0 x 10 7 1.6 x 10 Total 2.3x10 1.8x10

20 500 10(0.01 to 20) 4.1 x 10 3.3 x 10 50 (20 to 80) 4.6 x 10 3.7 x 10

200 (80+) 5.5 x 108 4.4 x 10 Total 9.3 x 10-7 7.5 x 10

36 900 10 (0.01 to 20) 2.3 x 10-7 1.9 x 10 50 (20 to 80) 2.6 x 10-7 2.1 x 10

200 (80+) 3.1 x 10 2.5 x 10.8

Total 5.2 x 10-7 4.2 x 10

The proposed sewer main is constructed from pipeline sections connected by rubber ring -

joints. In the absence of generic failure frequencies for rubber ring joints an approximation that rubber ring joints have similar failure frequencies to flanges has been made.

For flanges, industrial sources (L056 Technica 1980) give figures covering the range of 4 x 10-4 (e.g. in LPG service) to 7 x 10 (e.g. in high temperature, high pressure service) failures per year. Since the quality of pipe flanges varies enormously with application, it seems sensible to regard this range as a reflection of flange and gasket quality.


60- 0

0 I

40--

a, 30-- 0)

CD

0.1 0.2 0.3 0.4 0.5 0.6 0,7 0.8 0.9 Hole Diameter, d/D ratio

Gutteridge Haskins and Davey Pay Ltd App 5.13 DNV Consultancy Services Ellenbrook Sewer ERA October, 1997

FIGURE V.2.1: HOLE SIZE DISTRIBUTION FOR PROCESS PIPING

DNV's LEAK program incorporating DNV's VEREDA database was used to calculate failure frequencies for the 8km pipeline crossing the Gnangara Priority 1 area. Each 12m pipe section was assumed to be connected by a rubber ring joint (667 joints in total).

LEAK is a program for the calculation of leak frequencies relating to processing piants and installations.

The VEREDA database contains leak and failure frequencies for various types of components. The VEREDA database contains recommended values for most common risk and reliability data applicable to risk and reliability analyses.

Table V2.7 outlines the calculated leak frequency for comparative process pipeline crossing the Gnangara Priority 1 Area.

K:\CS_WA\PROJECTS\GD\2763RPT_V1\2763.AP5

Gutteridge Haskins and Davey fly Ltd App 5.14 DNV Consullancy Services Elienbrook Sewer ERA October, 1997

TABLE V.2.7 ArNUAL FAILURE FREQUENCIES (8km)

Pipeline Rubber Ring Joints

Total

Less than 86 kI/day 0.0015 0.2033 0.2049 More than 86 kI/day 0.0059 0.0636 0.0696

TOTAL 0.0074 0.2600 0.2744 MODIFIED 0.0058 0.2054 0.2169

Comparison of generic failure rates for buried overland gas pipelines and modified failure rates for the Ellenbrook Sewer Main are presented in Table V.2.8 below. The modified failure rate for sewage pipelines is indicated to be 5 times higher than for a buried gas line. This is considered to be a fare comparison by DNV. (Please note rubber ring joint failure rates are not included in table V.2.8).

TABLE V.2.8 COMPARISON OF FAILURE RATES

PIPE DIAMETER MEAN FAILURE RATE (per metre/per year)

(inches) (mm) GAS SEWAGE

20 500 1.53 x 10 7.4 x 10

LIBRARY DEPARTMENT OF ENVIRONMENTAL PROTECTION

WESTRALIA SQUARE 141 ST. GEORGES TERRACE, PERTH


Documents

ELLENBROOK SEWER PRESSURE MAIN - EPA WA€¦ · The Water Corporation is preparing a Public Environmental Review (PER) for the proposed Sewer Pressure Main along Gnangara Road between