76th Annual Victorian Water Industry Operations Conference & Exhibition Page No. 54 Bendigo Exhibition Centre, 3 to 5 September, 2013

CASE HISTORY – GEOMEMBRANE & FLOATING COVER SYSTEM, SA WATER, WATTLE PARK

RESERVOIR

Paper Presented by:

Bob Cahill

Authors:

Brian W. Fraser, Layfield Group Ltd, Vancouver, Canada

Paul Vince, SA Water Corporation, Adelaide, South Australia

Alex Gersch, Fabtech, Wingfield, South Australia

76th Annual WIOA Victorian Water Industry Operations Conference and Exhibition Bendigo Exhibition Centre 3 to 5 September, 2013

76th Annual Victorian Water Industry Operations Conference & Exhibition Page No. 55 Bendigo Exhibition Centre, 3 to 5 September, 2013

CASE HISTORY – GEOMEMBRANE & FLOATING COVER SYSTEM, SA WATER, WATTLE PARK RESERVOIR

Brian W. Fraser, Layfield Group Limited, Vancouver, British Columbia, Canada Paul Vince, SA Water Corporation, Adelaide, South Australia Alex Gersch, Fabtech, Wingfield, South Australia ABSTRACT As part of a water security review to address severe drought conditions, South Australia Water Corporation (Owner) identified the need for several essential infrastructure projects which included an upgrade to the Wattle Park potable water reservoir. The Wattle Park reservoir, with an 84 million litre (22 million gallon) capacity, required a new geomembrane liner and floating cover system. At prior storage and treatment reservoirs using normal levels of chlorination for a disinfectant, the Owner had experienced premature failures with certain liner and cover materials. Based on the operational importance of the Wattle Park project, a new performance specification for the geomembrane and floating cover material was developed. Meeting this specification required a specially stabilized and formulated geomembrane. This paper addresses the technical review criteria for selecting a new geomembrane as well as a number of project challenges and techniques used by the contractor related to the installation of a new liner and floating cover. 1.0 INTRODUCTION

Around 2003, South Australia began experiencing severe drought situations which impacted water supplies, and resulted in strict water restrictions being enforced in many regions of the State. As part of a 2010 strategic review of its water security, the South Australia Water Corporation (Owner) identified the need to proceed with several essential water management infrastructure projects. Among these, included was an important upgrade to the Wattle Park potable water storage reservoir that provides drinking water to the City of Adelaide, the capital of South Australia.

Figure 1: Wattle Park reservoir cover nearing installation completion stage

The Wattle Park water storage reservoir, with an 84 million litre (22 million gallon) capacity, required a new 14,500 m2 (156,000 ft2) geomembrane liner and 14,500 m2 (156,000 ft2) geomembrane floating cover system. The reservoir, originally constructed in 1929, was concrete lined. After leaks in the

76th Annual Victorian Water Industry Operations Conference & Exhibition Page No. 56 Bendigo Exhibition Centre, 3 to 5 September, 2013

reservoir resulted in local flooding, a Chlorosulphonated Polyethylene (CSPE) liner and floating cover was installed in 1986. In 2010, independent material testing conducted on behalf of the Owner determined that the CSPE geomembrane had only 10% remaining of its original retained tear strength. This created a number of safety and performance concerns, resulting in the Owner prohibiting any walking on the cover system required for maintenance purposes until a new floating cover system could be commissioned. In 2010 the Owner and its consultant undertook a technical review process of geomembranes that would be suitable for the Wattle Park reservoir liner and floating cover.

2.0 MATERIAL SELECTION

The material selection for the geomembrane and floating cover was a critical component of the Wattle Park project. SA Water has vast experience with floating covers as a result of operating eighteen (18) cover systems from the period of 1986 to 2010. The two main materials previously used for these floating covers included Reinforced Polypropylene (RPP) and CSPE. At a number of sites using normal levels of chlorination, the Owner had experienced premature failure and lower than expected service life of the covers specific to the use of RPP. It was determined by the Owner that these failures were likely linked to chemical degradation of the material when exposed to chlorinated water. The Owner co-authored and published a 2011 technical paper on the deterioration of flexible polypropylene liners and covers (Moore et al. 2011). Based on these past material problems, SA Water performed a detailed technical review of available industry lining materials. Their intent was to source a more fortified geomembrane technology that could be used for both liners and floating covers. A fortified geomembrane is defined as a product heavily treated with stabilizers providing enhanced heat, UV stability and chemical resistance (Schiers, J 2009). The Owner specifically targeted material endurance properties including high pressure oxidative induction time (HP OIT) normally tested in accordance with ASTM 5885. The GRI GM 17 (Geosynthetic Research Industry) industry standard specifies 400 minutes of HP OIT. The Owner also required long term weathering capabilities and paid particular attention to the ultra violet (UV) protection and long term weathering capabilities of the material. The objective was to specify a geomembrane and floating cover material with a 25 year weathering warranty and proven resistance to chlorinated potable water. The Owner required proven testing and certification on the geomembranes chemical resistance for chlorine and UV resistance. The geomembrane and floating cover materials also needed to be fit for purpose in terms of suitable mechanical properties including sufficient tensile, elongation, puncture, and flexibility properties. Another important requirement was for the material to be potable water compliant and meet both the National Sanitation Foundation NSF/ANSI Standard 61 Drinking Water System Components (NSF/ANSI Standard 61) and the Australian and New Zealand standards for testing of products for use in contact with drinking water (AS/NZS 4020:2005).

Layfield (Manufacturer) submitted performance specifications on its Enviro Liner® 6040HD (Polyolefin Alloy) geomembrane as well as material samples required for independent third party testing and verification. This specific geomembrane is a polyolefin alloy product and is categorized as a fortified material as a result of being produced from a highly stabilized formulation with an advanced UV antioxidant (AO) package. The materials endurance properties include a 2,000 minutes HP OIT and 90% tensile strength retention after 30,000 hours of accelerated UV testing in accordance to ASTM D4329. Table 1 below illustrates a number of the polyolefin alloy properties in comparison with GRI GM 17. Table 1: Geomembrane material properties comparison

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HD Performance Properties

ASTM Polyolefin Geomembrane

GRI GM 17

Thickness (min. ave) D 5199 40 mils (1.00 mm) 40 mils (1.00 mm) Tensile Strength at Break

D638 / D6693 191 ppi (33.5 N/mm) 152 ppi (27 (N/mm)

Elongation at Break D638/ /D6693

1200% 800%

Puncture Resistance D 4833 70 lbs (311 N) 56 lbs (250 N) Critical Cone Height D 5514 1.97 inches (50 mm) N/A Flexibility – Cycles without Cracking

D 6182 > 8000 N/A

Axi-Symmetric Break Resistance -% (min.)

D 5617 50% 30%

High Pressure OIT (min .ave)

D 5885 > 2000 mins 400

UV Resistance - Strength Retained

D 4329 30,000 hrs

90% N/A

Certifications (Potable Water) NSF 61 AS/NZ 4020

Pass Pass

N/A N/A

Ozone Resistance 100 pphm @ 40oC

D 1149 No Cracks Observed N/A

In addition to material specifications and samples, the Manufacturer submitted additional accelerated stress crack testing performed previously on its Polyolefin Alloy geomembrane with chlorine following ASTM D1693 for Environmental Stress Cracking of Ethylene Plastics. This testing protocol included immersing the geomembrane to a 1% (by volume) solution of sodium hypochlorite or the equivalent to 10,000 parts per million (ppm) at a constant fluid temperature of 50oC (1220F). The conclusion of this testing indicated that the polyolefin alloy geomembrane retained over 800 minutes of HP OIT after 1,000 hours of immersion with no noticeable surface cracking. This helped provide the Owner with additional assurance of the geomembranes strong chemical resistance to chlorine as a disinfectant in a longer term geomembrane and floating cover application. The Manufacturer also submitted testing and a published technical paper (Mills, 2009) on its geomembrane which completed 30,000 hours of accelerated UV testing. This testing demonstrated the polyolefin alloy geomembrane retained over 90% of the materials tensile strength after 30,000 hours of accelerated UV weathering testing in accordance to ASTM D 4329. Based on the Polyolefin Geomembranes performance specifications and the Owners testing verification, the Manufacturer’s material was specified for the Wattle Park project.

3.0 RESERVOIR LINER AND COVER

Fabtech (Contractor) an experienced liner contractor based out of Adelaide, South Australia was awarded the design, supply and installation contract for the Wattle Park containment project. The Contractor had previous fabrication and installation experience working with the manufacturer’s polyolefin geomembrane including floating cover applications which

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proved to be a valuable asset on the project. The scope of work for the Contractor included removing the existing CSPE liner and cover, repairing the concrete reservoir surface, fabrication and the installation of a new 14,500 m2 (156,000 ft2) polyolefin geomembrane liner and design, fabrication, and installation of a 14,500 m2 (156,000 ft2) floating cover. A leak detection system was also designed and installed by the Contractor utilizing the existing concrete lined reservoir as the secondary liner. This required the concrete expansion joints to be sealed using a flexible epoxy to ensure any leaks were contained and did not seep into the subgrade. A penetration through the concrete floor was made to access the redundant sub grade drainage system below the concrete lined storage. A 316 stainless steel grate and collection sump was installed to transfer any leakage to a monitoring and inspection sump outside the main reservoir. Overtop of this stainless steel grate a 10mm HDPE (0.4”) plate was installed to prevent the liner from penetrating into the grate and becoming damaged. The slopes of the concrete reservoir were lined with a 550 grams/ m2 (16 oz/ yd2) non woven geotextile to act as both a protective cushion and as a leakage flow path on the slope walls. The floor of the reservoir was lined with a geocomposite drainage layer and an additional layer of 550 grams/m2 (16 oz/yd2) geotextiles cushion to provide sufficient flow rate and protection to the liner so it would handle the 9.5 meter (31.2 ft) of fluid head pressure. The Contractor also supplied and installed electric mixers and an upgraded electrical perimeter security fence.

The project faced a number of challenges including very tight site access impacting the removal of the old liner and cover system, as well as installation of the new containment system. To help address the tight space constraints, the Contractor incorporated in-depth project management controls ensuring the sequencing of all suppliers and subtrades were properly planned and stayed on schedule. The contractor also prefabricated as much of the system components as possible including the slope sections of the liner and floating cover. The reservoir was situated in a major urban neighborhood resulting in required noise control, enhanced safety systems and traffic management. The crest of the dam varied between 1.5 m (4.9 ft) wide and 3.6 m (11.8 ft) with an electrical security fence on a concrete parapet wall at the top of the reservoir, and a chainmesh security fence on the outside of the crest. To facilitate removal of the old CSPE liner and cover and to prepare for the installation of the new geomembrane the electrical security fence was removed. The condition of the concrete surface could not be properly assessed until sections of the liner and cover were cut out and moved manually to inspect the surface. At this point in the project it was determined that mechanical equipment with a contact surface pressure of less than 100 kPa (14.7 psi) could be safely used without damaging the concrete surface. Two Bobcats were winched down the 1:2 side slopes and used to bundle the old geomembrane into 500 kg (1,102 lbs) bundles. To achieve the reach required to remove the old material a 130 Ton (286,600 lbs) crane was employed positioned on the edge of the storage to lift 6 Ton (13,440 lb) loads from the basin floor into waiting dump trucks which transported the used CSPE to an approved landfill site. In total 120 Tones (264,554 lbs) of material were removed. The new floating cover system incorporated a central plate cover design which was required to address the size of cover, depth of the reservoir, batter gradient, and awkward configuration of the storage reservoir. The design required a primary and secondary ballast system. The primary ballast consisted of 200 mm (7.9”) diameter sand tubes around the 5 sides of the central plate system which provided the necessary tension in the cover system. The

76th Annual Victorian Water Industry Operations Conference & Exhibition Page No. 59 Bendigo Exhibition Centre, 3 to 5 September, 2013

primary ballast line was designed to be 1.0 m (3.28 ft) deep at top water level with 1.9 m (6.2’) between the paired floats. The secondary ballast made of 150 mm (5.9’’) diameter sand tubes were installed in the corners and at the structures to take up excess material and enhance drainage. Another project challenge was the existing inlet configuration to the reservoir. There were 2 inlet points consisting of a single pipe at the northern end, and 3 pipes at the southern end of the reservoir. The pipes were surface mounted and encased in concrete. As a result, the cushion layer, liner, and cover all had to be installed up and over the structures. The cover design required a secondary ballast to help tension and control the excess material. To help reduce installation time and construction cost the Contractor prefabricated the slope panels for the geomembrane liner and floating cover. Site field welding was required for the floor section and the central plate cover system due to depth of the reservoir and access constraints. To ensure weld seam integrity, all factory and field seams were completed in accordance with the Manufacturer’s recommended seem strength values of 12.2 N/mm (70 ppi) in accordance with ASTM D6392.

The storm water removal system was designed to handle record levels of daily rainfall as recorded by the Australian Bureau of Meteorology in a twenty four hour period with a redundancy factor of 33%. This was achieved by using three individual submersible stainless steel pumps that were fixed in pump wells located on floating platforms in different sections of the primary ballast lines which divided the cover roughly into thirds. The pumps have integral level switches for automatic operation and are permanently connected with isolators at the ring beam. The level switches are set to operate when the ballast lines have 300 mm (11.8”) of water, and are set to stop operation with 150 mm (5.9’) of water in the ballast line. The pumps are connected via flexible PVC hoses and non-return valves, to HDPE pipes laid beside the walkways to additional connection points at the ring beam. The storm water is discharged to the natural local water course adjacent the main reservoir.

Figure 2: Schematic of Wattle Park floating cover The design, manufacture and testing of the containment system was required to conform to (AS/NZS 1170) (AS NZS 1657). The central plate cover system incorporated a design

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closely following the AWWA California-Nevada Section Reservoir Floating Cover Guidelines.

During installation of the liner, the geomembrane was progressively electrically leak tested and was verified to be leak free by the contractor. The floating cover at completion was then hydrostatic tested and also confirmed to be leak free. The liner and cover system then went through a final disinfectant treatment which was a requirement for potable water containment and was done in compliance with ANSI/AWWA C652. American Water Works Association, “AWWA Standard for Disinfection of Water Storage Facilities, ANSI/AWWA C652,” Denver CO.

4.0 CONCLUSION

The installation of the new geomembranes and floating cover system commenced on December 14, 2011, with the liner installation completed including electrical leak detection testing on January 2012. The new floating cover installation commenced on January 13, 2012 with completion of the cover system including all surface ancillaries on February 2, 2012. The hydrostatic testing of the cover was concluded in late February 2012. The project was completed on time and on budget. This project highlights advancements being made with today’s geomembrane technology through the use of improved film extrusion, high performance prime grade resins and advanced UV/AO additive packages. It also demonstrates the design, fabrication and installation capabilities available today in the Australia geomembrane market. In conclusion, the project’s success can also be accredited to excellent communication, cooperation and experience from all parties involved to design, manufacture, and construct an important potable water storage containment project.

5.0 ACKNOWLEDGEMENTS

The authors would like to thank and acknowledge Greg Moore of Moore Consulting Technology who was an active contributor in this project as part of the sourcing and qualification of materials, and with the development of the geomembrane and floating cover material specification.

6.0 REFERENCES

Moore, G., Shiers, J. and Vince, P., (2011). Deterioration Of Flexible Polypropylene Reservoir Liners and Covers In Contact With Potable Water

Schiers, J. (2009)., A Guide to Polymeric Geomembranes: A Practical Approach (Wiley Series in Polymer Science), 2009 Edition.

Mills, A, (2001)., “The Effects of Chlorine on Very Low Density Thermoplastic Olefins”, Geo-Frontier © and ASCE, Conference 2011

Mills, A., Martin, M. and Sati, R (2009). Long-Term Weathering Stability and Warranty Implications for Thin FilmGeomembranes, Proceedings of Geosynthetics 2009, Salt Lake City, Utah, USA.