Application Snapshot:
Installation: Thunderbird Reservoir Renovation
Location: Glendale, Arizona
Purpose: Potable Water Storage Reservoir
Solution: 9146 XR-PW Geomembrane by Seaman Corporation
Owner: City of Glendale Water Services Department (GWSD)
Engineer: Wilson Engineers LLC
General Contractor: MGC Contractors Inc.
Fabricator and Installer: Field Lining Systems Inc. (FLSI)
Date Installed: 2024
The Thunderbird reservoir was constructed by the City of Glendale, Arizona in the mid 1980’s. Even then, increased population was putting demands on potable water supply, prompting the construction of additional online storage for finished water. The reservoir is located within the Thunderbird Conservation Park, a 1,185-acre (480-ha) protected environment, a part of, and at higher elevation than much of, the City of Glendale.
Facility Layout
The reservoir is triangular shaped with plan dimensions of 361 ft x 361 ft x 495 ft (110 m x 110 m x 150 m). Original site construction was cut and fill, resulting in 600 ft (180 m) of the perimeter being an earthen dam, and accordingly is regulated by the Arizona Department of Water Resources as a water supply impoundment. The height of the dam is 44 ft (13 m), the working depth of the tank is approximately 30 ft (9 m), and the overall maximum storage capacity is approximately 12 million gallons (45,000 cu m). Finished potable water is pumped from the Pyramid Peak water treatment plant into the facility and distributed to system users.
The facility is constructed with reinforced concrete walls and floors over an earthen base. A metal roof supported by 94 aluminum columns, anchored on the tank floor, preserves the quality and quantity of the stored potable water. A plan of the column layout for the tank is shown below. Two inlets are located along the long wall (western side) and the outlet is mid center along the same wall. The high velocity of the inlet water minimizes dead spaces in the storage.
Roof support column plan, Thunderbird Reservoir
Reservoir Renovation
In 2023, the City of Glendale Water Services Department (GWSD) initiated a planned roof replacement/upgrade project. During the project, the need for a replacement potable water geomembrane was discovered as the existing geomembrane was fully exposed for inspection. In 2015, the material had been installed to cover the inside of the concrete tank, and unfortunately, after only a few years, the membrane began showing signs of deterioration, attributed to lack of resistance to low levels of Chlorine in the finished water. While access to the interior of the tank would have been best while the roof was removed for replacement, that project was ongoing and needed to be completed. The geomembrane replacement was therefore a separate project, following the new roof.
Thunderbird Reservoir during roof removal. Existing geomembrane on floor.
Geomembrane Selection
GWSD and Wilson Engineering, their Consulting Engineers on the project, elected to line the tank with an XR-PW geomembrane, a thermoplastic Ethylene Copolymer. The barrier is a fabric reinforced, NSF 61 approved product that has extremely good resistance to Chlorine, Chlorine compounds, and all other common disinfectants. In fact, it has been tested against high levels of currently used disinfection chemicals and has documented test resistance. The actual version of the XR-PW geomembrane which was used was 50-mil thick with almost twice the reinforcing used with other products. The heavy fabric core of the 9146 XR-PW gives high puncture strength to the product as shown in the chart below which compares it to other Potable Water geomembranes. The existing liner and underlying geotextile were removed and some concrete structural repair was completed along with limited hand repairs. This proved sufficient to create a workable surface for a robust geomembrane with puncture, and seam strength 5X that of other geomembranes of similar thickness. A white color was chosen to enhance visibility in the enclosed tank environment.
Potable Water geomembrane puncture resistance
XR-PW properties - Manufacturer Data, minimums
HDPE properties- GSI GM 13 Min avg and Typical (higher) manufacturer Data
fPP-R properties-GSI GM 18 Min avg and Typical manufacturer Data
CSPE properties-GSI GM 28 Min avg and Typical (higher) manufacturer Data
Geomembrane Installation
Over 130,000 sq ft (12,000 sq m) of geomembrane was used to line the tank. A second manufacturing step produced large panels, eliminating much of the field seaming which would have been required with rigid geomembranes. All 94 posts supporting the roof required mechanical battens at the base to give a continuous seal adjacent to, and around, protrusions. FLSI, the fabricator/installer, custom manufactured fitted column collars with ½ in (1.3 cm) polyester rope and hem which allowed for easier and more secure sealing around the columns. Because these seals will be continuously below water, SS batten strips over compressible neoprene on both sides of the XR-PW geomembrane were used for each column. Similarly, tank perimeter sealing was done with mechanical battens above the maximum wetted perimeter level. In the case of new concrete construction, embedment strips of the XR polymer are normally supplied by the manufacturer for a more efficient sealing technique.
XR-PW Panel installation
As can be noted in the installation photos, the geomembrane was completed after the new roof was installed. This provided a cleaner environment and the floor access was needed for roof installation. With the flexible material, folded and rolled panels could be brought into the tank, through restricted openings, and spread easily, with minimal field seaming. Those same heat welding techniques are used for any repairs or modifications to the XR-PW during its service life. Some legacy potable water geomembranes boast long sunlight resistance but are not thermoplastic and require glues and solvents for repairs and modifications, in the presence of potable water. These products are not appropriate for modern potable water containment systems.
Finished Geomembrane Installation
Project Completion
Upon completion, the entire tank was cleaned with a bleach flush per the project specifications. A hydrostatic test was conducted on the finished geomembrane system with no measurable leaks detected.
The geomembrane installation began in late April 2024 and was completed in early June 2024. The Thunderbird reservoir is currently in service.
For information on other XR-PW projects, visit our website here.
All illustrations and photographs are supplied by FLSI.
Renovated Thunderbird Reservoir, 2024
