Hinkle Reservoir is the largest potable water reservoir for the San Juan Water District (SJWD) located at the base of Folsom Dam in Granite Bay, CA (See Figure 1). SJWD provides water to 150,000 residents located in their retail and wholesale areas. The reservoir serves as a Clearwell for the SJWD’s Sidney N. Peterson Water Treatment Plant. A Clearwell is the final storage stage in a municipal drinking water purification system that allows sufficient time for the disinfectant to eliminate any remaining pathogens after the filtration and disinfection stages.
The reservoir was originally constructed in 1916 and has undergone multiple modifications over the years. In 1979the reservoir was modified and enlarged which included the installation of a Hypalon® (CSPE) geomembrane floating cover, bottom liner system, and baffle curtain.
Hinkle Reservoir is an earthen embankment reservoir with 2:1, 2.5:1 and 3:1(horizontal to vertical) side slopes, 22-foot-high earthen embankments, and a20-foot normal maximum water operating depth. The reservoir has a maximum capacity of 62 million gallons and a horizontal surface area of 13 acres. The reservoir interior was originally constructed as earthen floor and slopes. Hydraulic structures inside the reservoir include inlet and outlet structures, drain vault, and an overflow weir structure.
After 43years of service SJWD decided to replace the existing geomembrane floating cover, bottom liner, and baffle curtain. In 2022 bids were requested for the reservoir rehabilitation project, which included replacement of water inlet and outlet valves, a new site drainage pipe, electrical power, other site improvements, and a design-build component for the replacement geomembrane floating cover, bottom liner, and baffle curtain. The project was awarded to the general contractor, Steve P. Rados Inc., in June 2022. Colorado Lining International (CLI)was retained as the geomembrane fabrication and installation subcontractor and Hilts Consulting Group (HCG) was engaged to perform engineering design and construction support for the geomembrane aspects of the project. The project schedule was extremely aggressive with a scheduled outage of only 3.5 months starting in December 2022 with a return to service date of April 2023.
While the prior floating cover system performed well for over 40 years, the new design incorporated advancements in the industry over the past four decades. Prefabricated geomembrane panels were delivered and stored on site prior to reservoir decommissioning to ensure material supply chain issues would not impact the construction schedule (See Figure 2). Once dewatered, geomembrane materials were installed by over 30 onsite personnel working extended hours 7days a week. In spite of numerous severe winter storms, the project was completed early allowing SJWD to return the reservoir to service ahead of schedule.