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.
With the short outage of only 3.5 months and the wet winter months that had not been experienced in many years in Northern California, it was critical to have a cohesive team to meet the deadline and ensure SJWD would be able to get the reservoir back online with no disruptions in service. With fast design changes by HCG and HDR, fast approvals by SJWD, an extremely competent General Contractor, and an excellent team of installers from CLI, the project was able to be finished ahead of schedule even with the loss of 49 weather days.
CSPE geomembranes were chosen for the replacement floating cover, bottom liner, and baffle curtain based on the 40-year life of the existing Hypalon® (CSPE) geomembrane. CSPE geomembrane roll stock is currently manufactured in narrow 5-foot widths so to reduce field seaming and testing (See Figure 3), large prefabricated geomembrane panels for the floating cover, bottom liner, and baffle curtain were fabricated in Viaflex’s climate-controlled fabrication plant. The prefabricated panels were delivered to the site prior to the decommissioning of the reservoir to ensure no procurement delays. The large panels also allowed for precise layout to control the location of the field seams in the reservoir which was crucial with the location of the floating cover rainwater collection troughs. The precise layout of the field seams also facilitated installation of the baffle curtain, which had to be attached to both the bottom liner and floating cover (See Figure 4).