San Juan Water District’s Hinkle Reservoir Floating Cover and Liner

San Juan Water District's goal was to replace the world's oldest floating cover and liner in continuous operation for one of the nation's largest earthen drinking water storage reservoirs. Hinkle Reservoir occupies an area of approximately 12.5 acres and is considered one of largest earthen drinking water storage reservoirs in the United States. The reservoir provides operational and emergency storage for the District and serves as the main storage for all District wholesale agencies, which include Citrus Heights Water District, Fair Oaks Water District, Orange Vale Water Company, a section of the City of Folsom north of the American River, and the District's own retail service area. Because the Reservoir is essential to the District's operations, and provides drinking water to more than 265,000 customers in the greater Sacramento region, the project had to be completed during a short wintertime window.

Originally built in 1916, Hinkle Reservoir was located in what is now Folsom Lake before being moved to its current site in the 1950s. To meet new environmental regulations and protect water supplies from contamination, the District installed a Hypalon geomembrane liner and floating cover in 1980. Although the cover and liner were originally guaranteed for 25 years, the District significantly extended the system's lifespan through regular maintenance and testing to ensure its integrity. In 2022, with the system now more than 40 years old, the District determined a replacement was necessary.

Hinkle Reservoir was taken offline from November 2022 to April 2023, and storage was switched to two temporary one-million-gallon storage tanks located on the District's water treatment plant site. A continuous, high-quality water supply was provided to customers during this time, without any interruptions, which attested to the excellent design and team collaboration to ensure that no issues occurred during construction. In addition, there were no recordable lost-time injuries for the 26,000 man hours worked on this project. This excellent safety record can be attributed to the contractor's implementation of the injury prevention and safety programs followed by all employees and subcontractors.

Throughout the construction process, the District kept the public and its customers clearly informed about the status of the project. The District updated customers through its website, social media, and mailed newsletters. Additionally, the District's monthly Board meetings provided an opportunity for the community to ask questions about the project.

The project team, which included the District, design engineer, construction manager, and contractor, met before construction started to develop a plan to ensure on-time project completion, which included discussing any potential risks to the project during construction and how to mitigate those. Existing structures were reused to the greatest extent possible, which included the batten bars, anchors, anchor bolts, curb, and horizontal beam. An underwater condition assessment enabled the team to evaluate the conditions of these structures and determine what could be reused. The vertical guide was also refurbished, which provided additional cost savings. Because of the successful application of construction management techniques, the liner and cover replacement were completed one week ahead of schedule.

Hinkle Reservoir is very unique, due to its massive size and irregular shape. There is no other reservoir like it in the nation. As a result, very few people are qualified to manage the operational challenges involved in this replacement project. The design engineer team for the project included Dennis Gerber, who is one of the few floating cover and liner specialists in the nation. He also happens to be the person who designed the original reservoir liner and cover in 1980. At nearly 90 years old, Dennis was instrumental in guiding the team through the potentially significant operational challenges that needed to be resolved to take the Hinkle Reservoir offline for the cover and liner replacement.

Despite the project complexity and fast-tracked schedule, the cover and liner replacement project was completed on time, under budget, and without service interruptions. Hinkle Reservoir was placed back into service in April of 2023.