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Safe enough to drink

June 1st, 2014 / By: / Geosynthetics

A new cover for an old water reservoir
provides a long-term solution.

Last November, Newport Beach, Calif., completed a major water reservoir renovation project that it expects to solve the city’s decades-long water quality issues. The 22-acre Big Canyon Reservoir, constructed in 1958, would hold nearly 200 million gallons of potable water—enough to serve 70 percent of the population—and be less costly than purchasing water from its water district. Unfortunately, the reservoir attracted pests.

Triple threat

The problem was actually three problems: algae, animals and insects. The reservoir was not built to accommodate other life; it was simply a storage facility with a concrete base and sloping asphalt sides. Initially, birds were the biggest problem. The city council tried to frighten them off with an air cannon, but so many complaints were received about the noise that the city had to find another solution.

The next attempt at controlling the birds involved stringing piano wire over the reservoir. The theory was that the wind would cause the wires to vibrate and make sounds that would irritate the birds and drive them off, and it worked, but the city still had to deal with algae, insects and other creatures such as frogs. All of these often affected water quality and posed ongoing problems.

Stricter environmental laws

When the environmental movement began to get a stronger foothold in California in the 1990s, new and more stringent laws were enacted regarding water quality. The culmination came in 2003 with a state law requiring that manmade reservoirs be covered.

Faced with the option of covering Big Canyon Reservoir or abandoning it, the council decided it made economic sense to keep it operating. City engineers worked with the design engineer and they chose a floating cover design using a 60mil-thick polypropylene composite with a special coating that would resist damage from UV rays. Armed with a 20-year guarantee from the manufacturer, the project began in 2003 and was completed in 2004.

The cover degrades

Five years later, city employees working at the reservoir reported signs of premature wear, including cracking and even small holes in the cover. When the workers discovered a “black particulate matter” that appeared to be flaking off the cover floating on the water in an outlet pipe, city engineers suspected the UV-resistant material.

Subsequent tests done by the city and the contractor revealed that the cover had virtually no UV-resistance. Eventually, the case went to court and Newport Beach officials were back at square one.

Better flow management

This time the city hired a specialty engineering firm to design the cover, stressing that it must be UV-resistant. MWH Global Inc., a firm specializing in wet infrastructure and with experience in managing water purity and availability, was chosen.

With the design phase underway, city officials searched for a company to execute and install the project. MPC Containment, a company with offices in San Diego, Houston and Chicago, was awarded the contract. The company had nearly 40 years of experience working with geomembranes in applications including floating covers, containment liners and collapsible tanks. Chlorosulfinated polyethylene (CSPE) synthetic rubber manufactured by Burke Industries Inc. in San Jose, Calif., a material known for its chemical, temperature and UV resistance, was chosen.

Typically used to make inflatable boats, folding kayaks and roofing materials, CSPE had a proven record of durability in the industry.

MWH engineers worked with the engineers from MPC Containment to evaluate the design’s compatibility with the CSPE material. After some changes were made in the design of water baffles, the project began.

The project begins

Johann Konrad, general manager of MPC’s Environmental Division, oversaw the project to its completion. “After the city had drained the reservoir,” he says, “we used a cable and pulley system along with forklifts to remove the old cover. Next, we repaired any damage to concrete and asphalt in the basin and washed it down in preparation for the install. We also upgraded the existing fencing so it would be more effective in keeping vermin out.”

They had one major task to complete before installing the chafer strips and cover. They had to construct a 500-foot-long concrete pad to hold a 500-foot by 33-foot water diversion baffle. “The first cover had no baffles inside the reservoir and that kind of short-circuited the reservoir. The flow of the inlet water under the old cover traveled directly to the outlet. The corners of the reservoir where chlorine and other antibacterial additives were being introduced to the water were holding high levels of antibacterials that were not being distributed to the incoming water in the proper amounts,” says Konrad. “It could travel directly from inlet to outlet with inadequate exposure.

“During on-site reviews, the engineers and designers discovered that the originally designed diversion baffle could be improved to ensure that the water received the expected exposure to antibacterial additives. MPC Containment and MWH, with input from the Newport Beach officials, redesigned the baffle. As a team they created a more efficient and stable curtain that met the needs of the city.

“We also installed air baffles because air accompanies the incoming water and has to be removed. The two 250-foot-by-two-foot baffles are permanently welded to the underside of the floating cover. They contain inlet air in a specific section of the cover where it is easily vented with no damage to the cover.”

Another feature of the MPC Containment installation is its rainwater containment trough (RCT) system. Ballasted by sand-filled tubes, more than a mile of troughs collect rainwater and pump it into canals that take it away from the reservoir.

Final assembly

Before the floating cover could be installed, chafing strips had to be placed over the sloping asphalt sides of the reservoir. The purpose of these strips is to prevent the cover from abrading on the asphalt sides as the reservoir levels rise and fall. Off-site, MPC Containment welded 5-foot panels of 45-mil CSPE into 30-foot-wide panels in lengths up to 150 feet. These were then transported to the Big Canyon Reservoir where they were welded to their neighbors and permanently installed over the asphalt. The chafing panels cover approximately five million square feet of asphalt.

“The job actually began away from the reservoir,” Konrad says. “While the city was emptying the reservoir, we were working off-site to assemble the chafer panels, floating cover panels, sand tube ballasts, float covers, hatch covers and vent covers. That all began in March 2013. In May we started removing the old cover and repaired and cleaned the empty reservoir and installed the baffle pad. Then came the installation of the chafer panels.”

After the chafer panels were installed, the crew began work on the floating cover, starting on the west side of the reservoir to a ramp on the east side. The panels consisted of five-foot panels of 45-mil CSPE, welded off-site into 30-foot wide strips in customized lengths of up to 250 feet. These were unrolled and welded together at the reservoir. They were held in place on the perimeter by a batten system that consisted of a batten bar and stainless steel bolts set in concrete. Not only did this system ensure that the floating cover was held secure, it also sealed off the reservoir from animals and insects.

“When we finished the installation, we still had work to do,” he says. “We used large fans to inflate the cover and went inside to look for pinholes. The few we found were marked and sealed.”

The reservoir was ready for filling on Nov. 11, 2013. The 30-man crew completed the six-month project with no accidents or injuries, and Big Canyon Reservoir resumed operation ahead of schedule. The new cover is warrantied for 30 years; the expectation is that it will exceed that figure.

Jack Sine is a freelance writer specializing in green building, environmental, HVAC and IAQ issues.
He can be reached at jack.sine@verizon.net or at
+1 845 831 6578.

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