Floating Cover and Liner for Water Reservoir
LOCATION: City of Astoria, Oregon TIMEFRAME: July - October 2009 PRODUCT: Geomembrane, Floating Cover, and Lining SystemPROJECT PARTNERS: Owner: City of Astoria Engineer: MWH Materials Supplier: Layfield Installation: Layfield
The City of Astoria has two uncovered potable water reservoirs that they had to cover in order to maintain EPA and AWWA standards. They have experienced multiple problems with birds bathing, frogs hatching, and dirt and debris landing in the reservoirs. The City of Astoria reviewed multiple options before deciding on a Hypalon (CSPE) floating cover. The first reservoir to be covered, Reservoir #3, consisted of a 163,355 square foot cover, a 165,000 square foot liner, and a baffle curtain that was 25’ tall x 650’ long for a total of 16,250 square feet.
The biggest challenge on this project was the weather and time constraints. Due to a particularly wet season that last for about 8 or 9 months along the Oregon Coast, the liners and covers could only be installed during the summer months. The first reservoir was taken out of service in July of 2009 and once it was fully drained, Layfield had 90 days in which to have the new cover installed and fully functional. The installation of the first liner and cover was made more difficult by all the sub-grade work that was required. The reservoir had not been drained in about 20 years and it was expected that the concrete floor would need some repairs. Once Layfield was able to get in the reservoir and determine the extent of the work required, it had to work with the engineers on the job to quickly determine what areas needed to be repaired and how. Layfield made the reservoir floor repairs in approximately two weeks and was able to continue on the installation schedule. Even though this work was expected, it made a tight construction timeline even tighter.
Layfield recommended using a potable grade 45 mil Hypalon (CSPE) geomembrane for this project. It is one of the best available flexible materials that can be used for floating covers that meets the NSF61 potable water specifications. MWH was selected by the City as the project engineer and the construction work was publicly tendered.
Layfield was selected as the General Contractor for the project. Layfield also fabricated and installed the liner, floating cover, baffle curtains, and appurtenances on the project.
The City had been experiencing problems with stagnant water and feared that a cover would only increase that issue. There are four inlets in the reservoir and one outlet in the center. Due to the original design parameters of the reservoir, it must be operated close to maximum capacity at all times, which greatly reduces water and chlorine mixture time. A unique solution to a challenge on this project was the use of a baffle curtain attached to the underside of the floating cover and stretched to the floor of the reservoir. The baffle curtain forced the water inside the reservoir to follow a serpentine path in a counter clockwise direction and greatly increased the amount of time that chlorine mixed with the water, thus, significantly reducing the amount of stagnant water in the reservoir. Layfield came up with a preliminary panel layout that facilitated fabrication and installation. Layfield’s experienced field crew was able to quickly and easily install the baffle under the floating cover.
Layfield completed the installation of the liner, floating cover and baffle curtains in October, 2009, taking approximately 55 days to complete the installation. Even with additional concrete repairs they were able to complete the job well under the 90 allotted days. A 24 hour leak detection test was performed on the reservoir with no leaks found. Four water samples were taken from the reservoir and sent to a third party to test for any bacteria contaminants. All four samples passed. The cover is operating as was designed and no defects have been discovered to date. At this point the client is very satisfied with the installation of the first cover and is glad that Layfield will be the contractor installing the liner and cover on the second reservoir, which is scheduled to begin installation in June of 2010.