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Safe enough to drink

May 14th, 2014 / By: / Case Study

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

By Jack Sine

Introduction

Last November, Newport Beach, Calif., completed a major water reservoir renovation project that it expects will solve the city’s decades-long water quality issues. The 22-acre Big Canyon Reservoir was originally constructed in 1958, with the plan that it would hold up to 195 million gallons of potable water—enough to serve 70% of the city’s population—and cost less than purchasing water from the local water district. Unfortunately … the reservoir attracted pests.

Triple threat

The problem was actually three problems: algae, animals, and insects. The reservoir was simply built to store drinking water, not 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 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. That 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.

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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 new state law requiring covers for man-made reservoirs.

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

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Cover degrades, lawsuit

Five years later, city employees working at the reservoir reported signs of premature wear on the cover, including cracking and small holes. When the workers discovered a “black particulate matter” that appeared to be flaking off from 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 (the lawsuit involved Newport Beach vs. both the manufacturer and the contractor) … and now Newport Beach officials were back at square one.

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New material, 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 under way, city officials searched for a company to execute and install a new cover. MPC Containment, a company with offices in Chicago, Houston, and San Diego, 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.

A cover made of 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 selected for the job. 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.

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The project begins

Johann Konrad, general manager of MPC’s Environmental Division, oversaw the project to its completion. “After the city drained the reservoir, we used a cable and pulley system along with forklifts to remove the old cover,” said Konrad. “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.”

The project included had one major task to complete before installing the chafer strips and cover: Construction of a 500ft-long concrete pad to hold a 500ft × 33ft water diversion baffle.

“The first cover had no baffles inside the reservoir and that kind of short-circuited the reservoir,” said Konrad. “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,” he said. “It could travel directly from inlet to outlet with inadequate exposure.

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

“We also installed air baffles because air accompanies the incoming water and has to be removed,” said Konrad. He said that the two 250ft × 2ft baffles were permanently welded to the underside of the floating cover, designed to 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 was 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.

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Final assembly

Before the floating cover was installed, chafing strips were 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-ft panels of 45-mil CSPE into 30ft-wide panels in lengths up to 150ft. 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 5 million square feet of asphalt.

“The job actually began away from the reservoir,” Konrad said. “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.”

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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 5-ft panels of 45-mil CSPE, welded off-site into 30ft-wide strips in customized lengths up to 250ft. 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 securely, it also sealed off the reservoir from animals and insects.

“When we finished the installation, we still had work to do,” Konrad said. “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 had completed the 6-month project with no accidents or injuries. Big Canyon Reservoir resumed operation ahead of schedule. And the new cover is warrantied for 30 years, with expectations that it could be in service longer than that.

Jack Sine is a New York City-based freelance writer specializing in green building, environmental, and technical issues.

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