International No-Dig st International Conference and Exhibition. Sydney, Australia 1-4 September Paper 2.12

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1 International No-Dig st International Conference and Exhibition Sydney, Australia 1-4 September 2013 Paper 2.12 TIDAL AFFECTED SEWER REHABILITATION IN BALLINA SHIRE Kieran Woodall Project Manager (BE Environmental) Kembla Watertech Pty Ltd ABSTRACT: Kembla Watertech was contracted by the NSW Department of Public Works to rehabilitate a number of infiltration affected reticulation sewer mains for Ballina Shire Council and Richmond Valley Council. Thorough initial planning and assessment was conducted on all sewer assets to confirm the need for rehabilitation and select the most appropriate rehabilitation method to ensure that approval would be provided to proceed. Rehabilitation consisted of approximately 6km of lining at Ballina including over 300 spot repairs (to prevent infiltration and the ingress of sand) and 200 Tiger-T s (junction rehabilitation liners). In Richmond Valley, approximately 6.5km of relining was completed with over 60 spot repairs and 300 Tiger-Ts. Complex issues presented themselves during the contract, mainly being weather and tidal influences. During the initial investigation stages, rain was experienced for 90% of a two month period which lead to multiple sewer systems running at 100%. Careful planning was required to work around the rainfall moving between Ballina and Richmond Valley in the off periods. In addition to the rain, due to the low lying areas of East and West Ballina as well as Evans Head requiring rehabilitation, multiple spot repairs had to be completed prior to lining to prevent infiltration and sand entering the system. Kembla s Quick-Lock system was heavily utilised and proved to be a success in these areas. Kembla Watertech worked closely with Department of Public Works, as well as local community members to successfully complete this project. INTRODUCTION This paper presents a case study for undertaking sewer rehabilitation in areas affected by tidal influence and major infiltration. The discussion will outline the scope of the project, the process followed to ensure efficient planning, the recommendation of appropriate rehabilitation solutions, the challenges faced and the outcomes of this project. Paper

2 BACKGROUND The coastal areas around Ballina are well known for high ground water tables affected by tidal movements. Significant areas of this project were suffering from severe infiltration throughout the sewer system that was heavily impacting the local Sewage Treatment Plant as well as serviceability for hundreds of residents. Areas issued for investigation and rehabilitation included the lowest lying areas including; East and West Ballina and Evans Head to the south. Past attempts to rehabilitate the sewerage system in this region had resulted in failures in part caused by infiltration. The principal this time around has been careful to ensure correct rehabilitation methods were chosen and designed a contract that allowed the maximum flexibility and involvement throughout to ensure the solution implemented achieved the desired outcomes. PROJECT SCOPE The complete scope of works required for this project was unknown at the start of the contract. The style of contract selected by the Principal involved the use of a schedule of rates covering investigation, cleaning, spot repairs and relining. Milestones were used to define the two major areas of work as outlined below. Milestone 1 - Ballina Shire Rehabilitation works carried out under Milestone 1, within the area of Ballina Shire, were as follows; Area 1 Ballina Island; Area 2 West Ballina; Area 3 North Ballina; Area 4 East Ballina; Area 5 Lennox Head Milestone 2 - Richmond Valley Rehabilitation works carried out under Milestone 2, within the area of Richmond Valley, were as follows; Area 6 Coraki; Area 7 Casino; Area 8 Woodburn; Area 9 Evans Head The full extent of required sewer rehabilitation works within each milestone was unknown and approval from the principal was required throughout the project on the basis of the detailed investigations undertaken on each sewer line. The benefit of this approach to the Shires of Ballina and Richmond Valley were that the principal (NSW Department of Public Works) was able to manage the approved budget on behalf of the clients to ensure the maximum amount of rehabilitation was carried out within the provisions of the contract. Rehabilitation Process The rehabilitation process developed for this project can be broken up into three main phases. 1. Investigation Phase 2. Recommendation and Approval Phase 3. Rehabilitation Phase Paper

3 Figure 1 Site Locations 1. INVESTIGATION PHASE Upon being awarded the contract for Sewer Mains Lining and Spot Repairs at Ballina Shire and Richmond Valley, immediate planning was undertaken to ensure a program of works was developed so that rehabilitation could commence as soon as possible. A work program was developed to first inspect all sewer pipes by ways of cleaning and CCTV. As outlined above, the two milestones were broken up into areas, Ballina with Areas 1-5 and Richmond Valley with areas 6-9. The plans included all information obtained through CCTV which would include and confirm: - Length and diameter of lines - Number of junctions - Severity of infiltration - Rehabilitation recommendation Challenges Faced Initial site visits and maintenance hole inspections revealed that the areas issued for investigation and rehabilitation were in the lowest lying areas including; East and West Ballina and Evans Head to the south. Depths of the maintenance holes varied but in some spots were up to 6m deep. With the ocean and rivers not far away, an approximate depth of the water table was estimated to be around 1-2m, meaning any sewer asset being investigated deeper than this was bound to have infiltration. Similar work has recently been completed by Kembla Watertech under the SRP Tidal Ingress Contract for Sydney Water, however a main difference discovered here was that in Sydney you would have a potential difference in water table of up to 2.0m due to tide shift, in Ballina and Evans Head however the ground conditions were always saturated giving no real tide gap during low tide periods to install the liners. Paper

4 In addition to the tidal issues, Kembla s Cleaning/CCTV crews couldn t have had any worse luck and arrived during a period of rainfall that lasted approximately two months and lead to nearly all sewers running at 100% in conjunction with ocean and river infiltration. Figure 2 Ballina Maintenance Hole with severe infiltration from sewer system Kembla s normal process was implemented by the Contract-Supervisor assigned to Ballina, beginning with initial site appraisals followed by letter drops and notification of residents to provide access for the work crews and eliminate any potential complaints. From here our Cleaning/CCTV crews were deployed to start the process of surveying 248 lines issued in the Ballina region and 272 in Richmond Valley. As mentioned earlier, a period of rainfall lasting approximately two months was experienced during the initial stages of investigation. Due to the unusual topography between the Ballina and Richmond Valley areas meant that Ballina could be hit with torrential downpours and yet at the same time, Richmond Valley was shining without a cloud in the sky. This predicament meant that careful planning and monitoring of the weather had to be done so that crews could jump between the two regions so that delivery of the rehabilitation plans on time was achieved. After the two month period, all nine rehabilitation plans had been submitted. 2. RECOMMENDATION AND APPROVAL PHASE The Principal reviewed the nine rehabilitation plans and recommendations and then approved the rehabilitation work program. Ballina had approved relining 135 of the sewer lines issued and the installation of spot repairs in a further 63 sewer lines. Of the sewer lines issued for relining, 74 of those required pre-patching to eliminate any infiltration and sand ingress prior to installation of a fold and form liner (Kembla s EX liner). Richmond Valley whose region was spread from Casino and Lismore in the west to Woodburn and Evans Head in the south, approved 107 sewer lines for relining and installation of spot repairs in a further 4 sewer lines. Of the work issued for relining, 7 of those located in Evans Head required spot repairs. 3. REHABILITATION PHASE By the third month into the contract, the rain had cleared but the tide was still up. A program had been developed to start with the spot repairs to deal with the running sand issue which would ultimately maximise final lining diameter. Paper

5 Kembla had recommended multiple rehabilitation systems under the contract based on the condition of the pipes. These included: - EX Method (Fold and Form lining) - SWP Diafit (Spiral Wound Lining) - Flexi-Liner (Small Diameter CIPP liner) - Tiger-T s (CIPP Junction Rehabilitation Liner) - Tiger Patch (CIPP GRP Spot Repair) - Quick-Locks (Mechanical Spot Repair Sleeve) Figure 3 Kembla EX Crew Site Setup Agreement was achieved between the client and Kembla of the suitability of each product as well as keeping costs down based on the condition of the pipe. Another key consideration in method selection was the ability to eliminate infiltration and sand ingress to ensure effective cleaning and maximising hydraulic capacity. Kembla s Quick-Lock system was utilised for all spot repairs due to ease of installation and effectiveness in stopping infiltrating sand. A number of lines were identified as having for example, three infiltrating joints. However after installing the Quick-Locks, the trench effect was observed where the head pressure of the water table was great enough to find the path of least resistance to the next joint. This meant on multiple occasions, several more Quick-Locks were required to be installed in each line to stop the infiltrating sand. Paper

6 Figure 4 Quick-Lock System These pipes, which were running at almost 100% flow due to infiltration previously, were now servicing normal dry weather flows which immediately had a positive impact on the sewage treatment plant downstream. Evans Head to the south of Ballina, seemed to be experiencing some of the worst serviceability due to the shallow depth of the water table as well as the sandy conditions of the ground. Lines required a combination of cleaning and installation of Quick-Locks at the same time to stop a significant amount of sand entering the pipes. Attempts had been made in the past to complete civil repairs on the lines however the results achieved after rehabilitation was complete were unrivalled. Figure 5 Pre rehabilitation (Sand with infiltration visible) Additional spot repairs saw Kembla utilise the Tiger Patch system which provided a seal for infiltration and damaged pipes whilst maintaining structural integrity. It was decided on using this system in lines that still had good serviceability but had infiltration at minimal points. Paper

7 Figures 6 Post Rehabilitation Whilst the EX method, a fold and form PVC based lining system was used for the majority of lines due to ease of installation, minimal impact on local residents and enhanced hydraulic liner performance, SWP Diafit, a spiral liner using PVC profile was installed in longer runs where access was an issue at intermediate maintenance holes and were generally used in larger diameter lines to avoid any hydraulic issues in reticulation pipe. Overall, the program saw a variety of rehabilitation methods used based on the effectiveness, site conditions and cost. CONCLUSIONS Upon completion of all works, all parties including NSW Department of Public Works, Ballina Shire and Richmond Valley were satisfied that a positive result was achieved and the program was a success. Kembla has completed the rehabilitation of sewer lines totalling more than 6,500m in Richmond Valley and 6,000m in Ballina Shire. Data is still being collected by treatment plant operators, however initial indications have revealed the following outcomes; A reduction in overall flows to treatment works A reduction in flash flow infiltration immediately following rain events A reduction in pump run times and overtime for operators during rain events. The successful outcomes achieved by this project highlight that infiltration alone does not dictate the most appropriate rehabilitation method as the associated ingress of sand is extremely difficult to control if infiltration pre rehabilitation is not controlled. Effective cleaning will ensure maximum hydraulic capacity will be achieved by maximising the internal diameter. A schedule of rates contract for projects such as this one, where investigation is necessary prior to rehabilitation is effective. This approach ensures the principal has flexibility in method selection and approval of rehabilitation recommendations. Paper