Most Economical Water Storage Technology Available
Properly designed reservoir floating cover systems prevent fluid loss due to evaporation, reduce chemical demand and improve water quality by preventing contamination from bird droppings, airborne particulates, dead animals pollen and other pollutants. Floating covers block off sunlight preventing algae bloom. They also reduce the production of trialomethane (THM) type compounds such as chloroform from forming that result from the combining of organic substances with chlorine due to reductions in chlorine demand.
Floating cover systems were introduced over 30 years ago. Many have provided a service life beyond 20 years. When first introduced, materials and designs were not developed and in some cases had limited success. Today, with advancements in design and materials, floating covers offer the low cost quality solution of choice where water quality standards require potable water reservoirs be covered.
Floating cover applications range from anaerobic digestion covers for wastewater systems, to potable water reservoir covers for municipal drinking water applications. In farming applications they have been successfully used with enzymes to capture methane gas that is used to fuel electricity producing generators that can satisfy 150% of a typical swine farm's electrical power requirements. This alternative generates renewable "green energy" from an otherwise polluting system that provides zero return on investment.
Floating cover systems offer the best performance when they are constructed with a polyester fabric reinforced geomembrane such as Hypalon or polypropylene. Reinforced cover membranes with United States National Sanitation Foundation Standard No. 61 (NSF-61) approval for contact with drinking water are often encountered in thicknesses of .91mm to 1.14mm and are engineered and manufactured to survive the effects of weathering for 20-30 years.
Floating cover systems require site specific planning and design to be successful. Floating covers must be designed to rise and fall with varying reservoir water levels and have drainage systems for the removal of storm water. Depending upon site, storm water can be conducted through a reservoir and drained to the outside by way of gravity flow or removed from the cover via electrical pumps and discharge hoses. Reservoir access is maintained by the installation of hatches. There are essentially two types of water-tight floating cover systems commonly specified for drinking water storage applications: the weight tensioned defined sump style (Burke style) and the mechanically tensioned (REVOC style). Weight tensioned defined sump covers use a combination of floats and weights to affect tension and surface geometry. The geometry is controlled in such a manner that strategically located drainage channels or sumps are formed for the collection of storm water. Storm water is conducted through the sump channels to either gravity drains or sump pumps for removal. Mechanically tensioned (or REVOC ) type systems use spring or weight loaded cable tension to achieve definition and stability in the cover. A REVOC style floating cover system consists of tension producing elements attached to the cover's interior at specific intervals all around the reservoir's perimeter. The mechanically tensioned portion of the cover is thus held into place and becomes a defined plate that is protected from wind uplift and drifting. The outer cover perimeter is relaxed and forms a sump where storm water can be diverted off of the cover through a drainage system. The cover geomembrane material makes direct contact on top of the water without additional floats for buoyancy. The REVOC cover system requires less maintenance and lower cover membrane replacement costs and is generally considered a superior system in cold weather applications. The key design elements making both types of floating covers hugely successful is that they are water-tight and designed to function at all water levels without undue stress. Floating covers are a very economical method of protecting precious water. The cost can be 20% of that for other cover options. Industry recognized guidelines exist for the design, installation and maintenance of floating cover systems. An example is the American Waterworks Association (AWWA) standard D130-87 which contains the most current standard practices observed for system compliance to US national health and safety regulations. The California-Nevada Section American Water Works Reservoir Floating Cover Guidelines dated March 1999 offers an excellent source of design, operations and maintenance guidelines. Most agencies have found the best way to procure a state of the art operational floating cover system is to engage in a negotiated contract method with an experienced and reputable supplier. The second best alternative is to work through a qualified engineering firm to develop proper plans and specifications for the solicitation of competitive bids.
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