A new liner, a floating cover, and a wildfire.
By Andrew Mills
There are times when an unusual project turns into one that is absolutely unique, literally “one of a kind.”
That’s exactly what happened on a water reservoir project off the west coast of California on Catalina Island. This project was interesting enough, what with tour buses and bison nearby during construction, but when the reservoir came through a wildfire unscathed it became truly memorable (Photo 1).
Manufacturing and fabrication
The Wrigley Reservoir is the main treated-water reservoir on Santa Catalina Island, Calif. (Catalina Island). Located on the mountain above the town of Avalon, the reservoir provides potable water to the town and other parts of the island.
In 2006, the job was to replace an existing liner and cover on the Wrigley Reservoir. The project included 120,000ft2 of 45-mil potable water grade Hypalon® for the liner and a similar amount for a floating cover. The liner and cover system were designed according to the Reservoir Floating Cover Guidelines published by the California/Nevada Section of the American Waterworks Association (AWWA, 1999).
Early in 2006, fabrication of the liner and cover for the reservoir commenced. As part of the ISO 9001 quality program, an inspection of the manufacturer’s facilities in San Jose, Calif. was conducted, and it fully met all requirements.
From there the material went to the fabrication shop, which at the time was in Hollister, Calif. Panels were welded to the custom sizes needed to fit the panel layout of Wrigley Reservoir.
Two interesting aspects about the fabrication process stoo dout. The first was that 3-in.-wide welds were used for all welding on these panels. The 3-in.-wide weld extended to the edge of the top panel, effectively welding down the edge and eliminating a flap on the surface.
The second was that these panels were rolled up, without folds, on rolls that were 34ft wide. The fabrication shop used a 36-ft-wide winder that allows the creation of fabricated cover panels without folds. These rolled panels were then wrapped and shipped to the project site (Photo 2).
Logistics and installation
Of all the unusual situations to deal with on this project, the biggest problem was logistics.
The roads through the town and up the steep mountain required a truck trailer no longer than 40ft. Most truck trailerstoday are 45ft or longer and it took a while to find shortertrailers to rent. Even special insurance had to be purchased totake them onto the barge (ferry) to the island.
Installation of the liner and cover started in March 2006. Because of the location, a number of special considerations were required. Since 1975, most of the island’s interior and 48 miles of coastline have been managed by the Catalina Island Conservancy. This organization is tasked with protecting of the island’s biological communities and managing the recreational use of the island.
The Wrigley Reservoir is in the middle of the Conservancy and is surrounded by natural areas, making this a construction project in the middle of a large nature park. So in addition to the typical issues on a construction site, there had to be an awareness of—of all things—nearby tourists and local bison.
One of the local attractions on Catalinais a herd of bison that had been left on the island after a film shoot in the1920s. Periodically, they wandered ove rto the reservoir. The gate in the fence surrounding the reservoir had to be kept closed to keep the curious bison out of the construction site.
There was also some concern that the bison would damage the fabricated cover panels stored outside the fenced-in reservoir. These new panels were covered using strips of material taken out of the old floating cover and the bison did not bother them.
Another unusual requirement was that the job site be kept clean at all times because a very popular stop for local tour buses was just across the road from the reservoir. The job site could not detract from the panoramic views of the island.
Before the new liner and cover could be installed, the old cover material had to be removed and disposed. While meeting with the operators of the island’s local landfill to discuss how to dispose of the cover material, they asked us to cut it into 4ft x 5ft pieces and to stack up and strap them into bundles. Garbage on Catalina Island is compacted before it is placed in the landfill as a landfill space-conservation measure. By stacking and strapping the cover pieces into 4 x 5s, they matched the size of the compressed bricks of garbage that go into the landfill (Photo 3).
Once the old cover was removed,a geocomposite drainage material was placed over the base, tying it into the existing leak-detection system. The old liner was left in place (Photo 4) and holes were made in the bottom to connect to the leak-detection sumps. On top of the geocomposite, the 45-mil liner was installed (Photos 5a, 5b). The liner was welded in the field with 3-in.-wide welds. A detailed quality plan included periodic destructive test of seams and 100% nondestructive testing of all seams with a probe, an air lance, and vacuum box tests on the T-seams (Photos 6a, 6b). On this job, a full-time technician was dedicated to quality assurance.
Cover placement and return to service
Once the liner was installed and tested, the cover placement began.
The 45-mil cover was placed on top of the completed liner and anchored with the liner to a concrete curb at the top of the pond slope. The existing anchorage curb and steel batten bars were re-used.
After the cover was in place and tested, the floats and weights required for a defined sump cover system were laid out and attached. Float covers and straps for prefabricated sand tubes were made from the same material as the cover.
A large overflow structure at one end of the pond required refurbishing. Its metal frame roof was sandblasted and repainted. Replacing the rainwater removal pumps and installing level markings onto the final cover were also completed. The level marking letters and numbers were cut out from white Hypalon using stencils and were then adhered to the cover (Photo 7).
The final step in the construction of a potable water reservoir is to inflate the cover with air for cleaning and disinfection. The standard hatches that were built on the cover accommodate blower fans for inflation. Once the fans are placed, the cover is inflated so workers can get underneath. A final cleanup of the space between the liner and the cover was completed and visual inspection of the cover revealed whether any small defects existed.
Once final inspection was completed, the cover remained inflated for 3 days to air out the space and to allow any remaining solvent vapors to escape. After the cover space was aerated, the reservoir was partially filled with super-chlorinated water. This disinfection step is outlined in the standard C652 AWWA Standard for Disinfection of Water-Storage Facilities. After the chlorinated water had time to disinfect the reservoir, the water level was brought up to operating level. The reservoir was officially returned to service in July 2006.
At this point a nice upgrade to a water reservoir in the middle of a natural area on Catalina Island had been completed without incident.
The liner and cover were installed within a tight time frame, working 10-12 hours per day 7 days a week. The bison had been kept out of the construction site, although they did sniff around the fence occasionally. The cover was working well and the client was happy with the work.
Then, on May 10, 2007, a fire broke out on Catalina Island and burned 4,750 acres during a 5-day period. The most severe drought in 100 years, combined with high winds, sustained the fire and swept it across the island. Tragically, the fire appeared to have been caused by human hands. The Catalina Conservancy is still assessing the impact of the fire on the island’s ecology.
Since the Wrigley Reservoir is the primary source of water on the south end of the island, it was an important part of the firefighting. During the fire, the reservoir was staffed by 2 people from the water utility who filled fire trucks directly from the reservoir.
At one point, the fire cut off the main road from the reservoir to the town of Avalon and the 2 workers were stranded. The fire moved up the mountain and burned around and past the reservoir. (The area around the reservoir is mostly cleared with some grasslands and one stand of trees along one side.) The 2 utility workers took refuge in their vehicle on the downwind side of the reservoir and were unharmed. The fire’s closest approach ended about 10 ft from ther eservoir (Photo 8).
In the end, the fire burned around 3 sides of the reservoir without apparent damage to the facility or the floating cover, other than a collection of ash on the cover. In the weeks after the fire, the reservoir remained in use without any measurable decrease in water quality. The floating cover prevented ash and debris from getting into the pond so the reservoir could remain in service.
Inspections after the fire showed that a few small embers had fallen on the cover but were extinguished as soon as they burned a pinhole in the cover. The utility had the reservoir inspected by divers and did a complete inspection of the upper surface but found only a few defects. There was a layer of ash on the cover but otherwise there was no significant damage.
Layfield was contacted to clean and repair the cover in the summer of 2007.
Operational issues required that the water not be drained completely so the repairs were done while the cover was floating. The work crew repaired 1 holea bout the size of a dime and then cleaned the cover. The entire area was swept and pressure-washed. Water containing the ash and collected debris was pumped from the cover into a small holding pond. There was no other damage to the linerand cover system. The system remained in service throughout the cleaning.
Once the cover was cleaned, the entire upper surface was inspected again. Surprisingly, there was no significant damage as a result of the fire. The largest damage was the 1 dime-sized hole. There was no melting or scorching anywhere on the cover.
Overall, this was an interesting example of a floating cover project with unique site conditions and a tough schedule.
The cover and liner system used on the Wrigley Reservoir is similar to many other systems throughout California. These covered reservoirs are a well-established method of storing large volumes of treated potable water for immediate use.
There have been some concerns in the past about how a floating cover would hold up in an extreme situation such as a fire. This event demonstrates that a carefully constructed facility, with open space around the pond, will survive a fire without significant difficulty.
This is good news for California, where floating covers and fires are both relatively common.