El Toro Water District R6 Reservoir — HypaFlex CSPE Liner and Floating Cover

Floating Covers


In September 2023, Layfield Geosynthetics completed the supply and installation of a 275 million gallon (1.04 billion liter) HypaFlex™ CSPE geomembrane liner, and HypaFlex™ CSPE weight tensioned floating cover for the El Toro Water District R6 potable water reservoir, located in Southern California. Spanning approximately 25 acres, the El Toro R6 reservoir ranks among the world’s largest potable water storage reservoirs, boasting a capacity of 275,000 million gallons. This project took 11 months to complete and included the prefabrication of the geomembrane liner and floating cover system at Layfield’s Lakeside, California production plant, and the subsequent on-site installation. Layfield Geosynthetics served as the general contractor for the project, managing various facets of construction, including earthworks, electrical upgrades, mechanical improvements, and liner and floating cover installation.

Originally constructed as a 233 million reservoir in 1967, the El Toro Water R6 reservoir underwent expansion in 2002 to reach its current capacity of 275 million gallons. This expansion significantly enhanced the ability of El Toro Water District to support the water needs of El Toro Water District, Santa Margarita Water District, and Moulton Niguel Water District. Today, the reservoir services over 300,000 customers in Orange County, California, for daily and emergency water supply.


Project Scope and Challenges

The project faced several notable challenges, including its sheer size and scale and the reservoir’s irregular shape. During construction, the project was also impacted by a number of record winter rain events requiring extensive pumping and dewatering efforts. The project scope included decommissioning of the old reinforced polypropylene cover. The prefabrication phase of the liner and cover included the supply and coordination of 195 liner panels and 193 floating cover panels, varying in length from 345′ to 358′ and various widths. Plant fabrication of the panels started in October 2022 and took 203 days to complete. The prefabrication of the geomembrane panels significantly reduced the amount of required field welding on-site, further reducing the installation time. This proved very important based on the unseasonable wet winter weather conditions that occurred during the winter months of the installation. The total material supplied was just under 1,200,000 ft2 of 60 mil HypaFlex™ CSPE for the geomembrane liner and 1,200,000 ft2 for the 45 mil HypaFlex™ CSPE floating cover.   The installation of the new liner started in February 2023 and was completed in early May 2023, with the floating cover system installation taking place from May 2023 to September 2023. Both the liner and cover system were mechanically anchored to a concrete berm around the perimeter of the reservoir.

The concrete reservoir was up to 65′ deep with both 3/1 and 5 1 slopes and constructed in an irregular configuration. This required a robust weighted trough system to be designed to provide the covers tensioning and buoyancy to support the fluctuating operating levels. Additionally, the liner and cover system needed to be designed and attached to various concrete inlet and outlet structures and incorporate a comprehensive rainwater collection and pump removal system.

As a result of the initially installed 45 mil reinforced polypropylene (RPP) cover demonstrating signs of degradation, a comprehensive review process on the replacement material selection was conducted by El Toro Water District, working closely with their selected design firm. HypaFlex™ Chlorosulfonated Polyethylene (CSPE), formerly known as Hypalon, was selected as the replacement material for both the floating cover and liner. The decision was based on HypaFlex™ CSPE’s 50-year performance history in hundreds of similar potable water applications and its ability to achieve a 30-year service life (10-years longer than the current Reinforced Polyethylene (RPP) cover and liner are able to provide). The HypaFlex™  CSPE material can also be repaired and serviced throughout its 30-year design life.



In August 2023, the floating cover underwent inflation and aeration as part of its final quality control testing and commissioning. In September 2023, the reservoir was filled, and the liner and cover system were commissioned successfully. The project was not only completed on time but also within budget, and Layfield Geosynthetics would like to acknowledge the dedication and professionalism demonstrated by all stakeholders involved.


Project Stakeholders

The Projects key stakeholders included the El Toro Water District as the owner and operator, Hilts Consulting Group, Inc. as the design Engineer of Record providing technical services during construction, Go2CQA performing third-party quality assurance for the geosynthetics installation, and Burke Industries as the CSPE liner and floating cover material manufacturer. The Santa Margarita Water District and Moulton Niguel Water District are also project stakeholders, sharing in the project’. Layfield would also like to acknowledge the dedication and professionalism of its employees and the project team involved.



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