Case History on Defined Sump Floating Cover System, MWD Southern California, Skinner Water Treatment Plant

As part of a potable water reservoir project for the Metropolitan Water District of Southern California, Layfield Environmental Systems fabricated and installed a flexible geomembrane defined sump floating cover system. On this project Layfield operated as the general contractor with a scope of work that included removing and replacing the existing floating cover and installing a new 65,000 m² (700,000 ft²) floating cover system. The project also included an additional 28,000 m² (300,000 ft²) of a chafer reinforcement material around the perimeter of the floating cover, rain water removal pumps, upgrading of the existing electrical systems, installation of drain pipes, mechanical work and the design and operation of a temporary water treatment facility. This project encountered some serious installation challenges including a tight 180 day installation schedule as this was a critical reservoir with an operational capacity of 130.4 hectares (326 acre feet) providing treated water to Riverside and San Diego Counties. A special consideration on this project was the requirement to capture all water that was collected from the construction site. This included the design and operation of a temporary water treatment facility as the Regional Water Quality Board had set strict discharge limits on the water released from the site. The water treatment plant was designed to capture nuisance chemicals or contaminants in rainwater as a result of construction. There was also major water leakage of up to 1,135 litres (300 gallons) per minute at the influent and effluent gates requiring continuous pumping and dewatering strategies throughout the duration of the project. The project was further challenged by excessive poor weather as part of an El Nino year in California. This paper discusses the various technical challenges and the innovative design and project management solutions incorporated to help finish the project on schedule.