WILMINGTON, DE, Dec. 1, 2004 -- The 62 million gallon capacity Hinkle Reservoir in Granite Bay, Calif., provides quality water to more than 265,000 people annually in the Sacramento region. With a surface area of some 12.5 acres, Hinkle was a pioneer in floating reservoir covers since its reconstruction in 1980, and attracted interest from many international civil engineers, municipal administrators and legislators.
Remarkably, the original cover membrane based on DuPont Dow Elastomers Hypalon® chlorosulfonated polyethylene and still in place 25 years later, is expected to last another 20 years, according to recent forensic tests on the material. General manager Jim English, describes the reservoir with its floating cover as "an amazing success and a practical and economical solution" for the San Juan Water District (SJWD).
The cost effective solution
Alternatives such as steel and concrete tanks with rigid covers were considered in planning the reconstruction, but were judged to be too costly by SJWD, since, being a municipal facility, both cost and performance were equally important in the decision making process.
The cost effective solution was a patented floating cover design from Burke Industries, in San Jose, Calif., based on Hypalon, that proved to be up to 80 percent less costly than the other alternatives considered.
When fully extended the floating cover membrane is almost 5.7 hectares (14 acres) in size. Its performance is critical, particularly in view of the 265,000 population it serves, and the high water demand which turns over as much as two times per day during peak periods.
With the initial 25-year warranty on the floating cover nearing expiry, and to assess how well the cover was still performing, the SJWD recently hired an independent contractor to carry out destructive testing on a number of small panels cut from the floating cover membrane based on Hypalon.
Another 20 years service
The results were impressive. "We had all the appropriate forensic tests performed, and we were really pleased with the results," commented English. "Basically, the tests show that we can potentially get another 20 years of service out of the cover."
Mike O'Bleness, water quality manager at Hinkle Reservoir, concurs. "The report came back "excellent". With respect to the average quality of water protected by the membrane, turbidity has been exactly the same over the life of the installation, at 0.03 NTUs," or nephelometric turbidity units.
"Additionally, it holds chlorine residuals very well. We lose 1/10th of a part of chlorine, which we consider to be excellent." Prior to the installation of the cover, the Hinkle Reservoir had been losing hundreds of tons of chlorine to evaporation.
"The overall integrity of the floating cover has been great," continued O'Bleness. The crew that works at the Hinkle Reservoir has made a number of improvements to the engineering design of the installation, such as adding valves to the surface drains. And the membrane itself has not had any major rip failures. "Primarily the damage we have seen to the membrane has come from kids throwing rocks, or birds pecking," O'Bleness explained. And due to the ease of maintenance of Hypalon, the repairs have been relatively easy to handle.
Standing the test of time
In O'Bleness' opinion, the reservoir, with its initial pioneering design from Burke Industries, and floating cover based on Hypalon, "has had a track record that is very hard to argue with." The water quality has remained essentially constant over more than 2 decades. The cover has been relatively easy to maintain, and has successfully stood up to decades of time. And finally, recent forensic tests have shown that the cover potentially still has a long service ahead. "It has been pretty well bulletproof," O'Bleness remarked. It has performed so well that "I don't need to lose sleep over it." Nor do the hundreds of thousands of people that the reservoir serves.
About DuPont Dow Elastomers
DuPont Dow Elastomers (www.dupont-dow.com), a global supplier of specialty elastomers with headquarters in Wilmington, Delaware, USA, is a joint venture between the DuPont Company and The Dow Chemical Company, with more than $1 billion in sales. The company is the industry leader in chloroelastomers, ethylene elastomers and fluorinated elastomers, serving the automotive, chemical, construction, general rubber, plastics and wire and cable industries.
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