Water Efficiency June 2012 : Page 39
you’re done. Once you get above gallons in a 1-inch rain event— 100,000 or 150,000, fi berglass is and stores the harvested water in not as cost-eff ective, but, still, a 15,000-gallon fi berglass tank if you can’t get somebody to do from Containment Solutions. concrete for you, it’s a very viable Water is also stored in a 10,000 alternative. gallons aboveground galvanized “When you do something steel tank, which serves as an like this, you balance the site, advertisement for the project. the amount of water you need to Th e system includes pre-store, and the materials you’ve tank and post-storage fi ltration got available. For the water to preserve water quality. An district, we put in a 325,000-gal-automatic pump system pro-lon poured-in-place rectangular vides pressurized rainwater for concrete tank on a hillside on irrigation, drawing fi rst from the inside loop of a hairpin turn. the15,000-gallon underground We had limited space, and we tank. When the underground wouldn’t have been able to get tank is empty water fl ows into it the required number of fi berglass from the aboveground tank, and tanks in there. Th e rectangular when both tanks are dry, a level shape fi t right in.” sensor switches the system to municipal water. CONCRETE Portability and ease of Concrete has long been a mate-installation were part of what rial of choice for water stor-attracted Jack Dietrich to fi ber-Droughts—like the one in Texas—make age. Precast concrete vaults are glass tanks. Dietrich is District water storage crucial readily available for small capacity applications, Manager of the Crested Butte South Metropolitan to water resource management. and various types of prestressed poured-in-place Water District in Crested Butte, CO, and a prin-underground tanks are in common use for large-ciple in Water Operations, Inc., which designs and volume municipal storage. Prestressed concrete has builds water storage systems. When he couldn’t get had internal stresses induced to balance out stresses from the concrete he needed for a poured-in-place reservoir for a externally applied loads. One way of doing this is to wrap a Colorado subdivision, he specced fi ve 30,000-gallon Darco tank in high-strength wire, and then cover it with shotcrete. fi berglass tanks. Various configuration are available: 1) cast-in-place concrete “Th ere was so much building going on around here, we with vertical prestressed reinforcement, 2) prestressed cast-couldn’t even get a quote for concrete,” he says. “I really like in-place shotcrete with a steel diaphragm, and 3) shotcrete fi berglass for anything 150,000 gallons and under because or precast concrete panels with a diaphragm. Whatever the it’s easy. You order the tank, it shows up, you plumb it, and Standards As anyone working in the water industry knows, various industry-specific agencies have established standards associated with water storage. NSF (formerly known as the National Sanitation Foundation) 64 is commonly cited by fiberglass tank manufactur-ers to verify that their tanks are suitable for potable water storage. “The most important element of the equation is the quality of the storage tank,” says David Heiman, Director of Marketing at Containment Solutions. “Tank manufacturers utilize NSF ap-proved materials to construct a tank which meets its standards, and in the case of fi berglass tanks the material is resin. This NSF-approved resin forms the water contact surface, and when it cures with the rest of the glass-and-laminate mix, it hardens as one homogenous tank laminate.” This being said, Tom Tietjen at Xerxes points out that its fac-tories are NSF-inspected, and its NSF 64 certifi cation applies to the entire tank, materials, and construction, not just the interior surface. Wrapped concert water tank manufacturers will remind you that American Waterworks Association standard D110 sets the bar for prestressed wrapped concrete tank construction (D-115 applies to the kind of post-tensioned tanks in use at Denver Water) and that they are also regulated by the American Con-crete Institute. An engineer designing a concrete underground tank may tell you it meets H20 loading standards, H standing for highway and 20 meaning you could drive a 20-ton truck over the buried structure. Because compliance with all of these stan-dards is voluntary and the organizations that draft them have no enforcement authority, how a standard actually aff ects the productivity or serviceability of a proposed installation can be diffi cult to sort out, especially because the standards eff ectively pit one kind of technology against another. An industry profes-sional is the best source for helping mangers determine what a given standard may mean in terms of future maintenance or possible risks. CONTAINMENT SOLUTIONS, INC. JUNE 2012 WATER EFFICIENCY 39
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