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Surface reservoirs.

Surface reservoirs can be constructed by damming the downstream side of a natural valley or by excavation of earth embankments. In either case, water loss by seepage can be a serious problem and intensive soil and geological study must be undertaken before construction.

Where a natural site is suitable and not subject to flooding, an earthen base can be used for a distribution system ground storage reservoir by utilizing an impermeable lining and cover. In any case, soil analyses and subsurface investigations are important. Firms supplying instruments and service for such investigative work include ELE Int'l./Soiltest Products Div.; Forney, Inc.; Gilson Company, Inc. Sensitive tilt-meters and angle-sensing devices that can be used to track the deformation of clams, storage tanks, embankments, and so forth are available from Applied Geomechanics Inc.

Natural Liners & Erosion Control

Natural liners are usually deep layers of undisturbed clay, sometimes over 100 ft deep. Although subsurface investigation is necessary, these make ideal seepage barriers. Where natural clay does not exist, clay can be transported to the site and compacted to a depth of several feet to form the seepage barrier. Bentonite is a form of clay available in both powder and granular types. American Colloid Co. supplies this material. Application rates vary with bentonite depending on the types of native soil it is to be used with. Normally, application rates range from 2 to 8 lb per sq ft. A 12-in. earth cover helps keep the clay moist. Bentomat-geosynthetic clay liners are produced by Colloid Environmental Technologies Co. and SLT North America, Inc. Bentonite is also useful for sealing wells and related subsurface structures.

Erosion of berms in large earthen structures from wave action and instability of soils can be avoided by installing gabions, metal cages, or baskets filled with rock. Also called revet mattresses, these construction materials are discussed in Section B of this manual under erosion control. Another method consists of pressure-injection of cement mortar or fine aggregate concrete into flexible forms placed along the bank or berm to be protected.

Rigid Liners

A hard rigid floor for the reservoir can be constructed of concrete, asphaltic, or fiberglass materials. While these are generally the most expensive, rigid liners permit cleaning with mechanical equipment (that might otherwise damage other types of lining materials). However, rigid materials are susceptible to cracking due to ground movement from settling and from freeze and thaw cycles.

Gunite has been used in many instances with some of success. It and similar pneumatically applied mortars can be placed by equipment furnished by various companies as discussed in Section B of this manual. Gunite-lined reservoirs can be very efficient and can also be built by the various firms listed in Section B. An economical reservoir lining is provided by soil-cement techniques, prepared by mixing cement with native soil, if suitable, or imported soil, compacted, and cured to form a hard surface. The cement requirement is determined by standard tests and averages about ten percent by volume. A 6-in. thickness is required to prevent seepage.

Granular bentonite attached to a woven fabric sheet comes from Fluid Systems; James Clem Corp.; and SLT North America, Inc. C.I.M. Industries Inc. manufactures the components used to form CIM Industrial Membrane Systems, a squeegeed, rolled, or sprayed seamless asphalt-extended polyurethane membrane on fabric reinforcement.

Prefabricated asphalt panels are available as lining materials, sometimes combined with fiberglass reinforcement, plasticizers, or plastic sheeting. Information on asphalt liners can be obtained from the Asphalt Institute. A carefully prepared surface is necessary to apply these materials. Reinforced asphalt (with fibers of polyester), used in some roadway construction, can form a strong waterproof layer.

Flexible Membrane Liners

The synthetic resins and polymers, used to manufacture thermoplastic materials, have been perfected to make possible a relatively inexpensive, quickly applied flexible liner, able to withstand conditions encountered in water storage. These include polyvinyl chloride (PVC), chlorinated polyethylene (CPE), chlorosulfonated polyethylene, polyisobutylene (butyl), ethylene propylene diene monomer (EPDM), polychloroprene polymer (neoprene), polyolefin, and others. In application of these materials their properties should be understood. All do not have the same weathering capabilities or ability to withstand exposure to ozone or ultraviolet radiation, extremes of hot and cold, chemicals, and ice formation.

Consideration needs to be given to structural qualities also. Most flexible membranes are available with or without fabric reinforcement. Reinforcement or backing materials include polyester yarn, nylon, fiberglass, and polypropylene. Manufacturers of the resins, polymers, and reinforcing materials; the basic sheeting material manufacturer or calenderer of materials; and the fabricator of the finished reinforced product are all interested in the end use of their products and can provide guidance as a result of years of experience. Also, several firms have had extensive experience in the installation of reservoir membranes, which is valuable. The consulting engineer and the user armed with adequate knowledge of local conditions can obtain information from such firms, prepare the site and foundation, and select an experienced installer. With the team effort involved, a durable reservoir can be easily constructed.

Other uses of the membranes are in connection with rigid liners such as asphalt or concrete, particularly when the latter have cracked or deteriorated. The membranes offer compatibility for such fabrication, and an installer can place the floor as well as the roof in a turnkey operation; or old concrete reservoirs incapable of structurally supporting concrete or other heavy material covers, can be easily covered with membranes.

Resins and Polymers. Manufacturers of resins and polymers include the E. I. DuPont De Nemours Co., Inc.; Occidental Chemicals Corp.; Union Carbide.

Sheets and Rolls. Manufacturers of sheeting or calender rolls of film include Crafco Inc.

Liners. Companies that furnish liners include Akzo Nobel Geosynthetics Co.; Covertech Fabricating Inc.; Environetics, Inc.; Exxon Chemical Co.; Fluid Systems; Gundle Lining Systems, Inc.; Hinspergers Poly Industries; JPS Elastomerics Corp., Environmental Products Div.; MPC Containment Systems Ltd.; National Seal Co.; Palco Linings, Inc.; Phillips Fibers Corp.; Plastic Fusion Fabricators, Inc.; Poly-Flex Inc.; Reef Ind., Inc.; Fred B. Rivas Co.; SLT North America, Inc.; Serrot Corp.; Thor Enterprises, Inc.; Union Carbide.

Underliners. Enkadrain[R] from Akzo Nobel Geosynthetics Co. can be used as a "underlining" to help cushion the impermeable geotextile, vent gases, and to help drain subsurface water. Geomembrane underliners are also produced by National Seal Co.; SLT North America, Inc.

Liner Sealing. Various types of welding machines are often used for heat-seaming thermoplastic liners. Extrusion welders are available from Kamweld Products Co., Inc.

Liner Leak Detection. From installation and other problems, leaks may develop in the liner. GeoSyntec Consultants' Materials Testing Laboratory has testing services for many types of flexible liners. Leaks can also be detected by sectioning off part of the liner and blowing smoke underneath. Superior Signal Co., Inc. makes smoke blowing equipment for this purpose.

Reservoir Evaporation Retardants & Covers

In some areas water loss through evaporation is an important factor. In these same areas long exposure of the water surface to sunlight promotes algae growth. The simplest solution, if the reservoir is not very extensive, is a cover. The flexible membranes discussed above in this chapter are suitable for this purpose and can be made to be air-supported.

Companies that can furnish floating type membrane covers include Gundle Lining Systems Inc.; JPS Elastomerics Corp., Environmental Products Div.; National Seal Co.; Palco Linings, Inc.; SLT North America, Inc.; Serrot Corp.

Fiberglass covers can be custom produced by Canbar Inc.; Composite Technology, A Unit of W.R. Grace & Co.; Fiberglass Structures & Tank Co.; MFG Water Treatment Products Co.; Pat Lindsay Associates, Inc.; and Topps Industries.

Temcor's "Polyframe" domes use aluminum in geodesic concepts to provide strength and corrosion resistance, without requiring heavy foundation support. Clear span aluminum fixed roof cover systems are made by Thermacon Enviro Systems.

Collapsible Tanks & Other Structures

Miscellaneous Systems. Amfuel markets a "Fabritank," which is in effect, a liner and integrated cover, usable as a reservoir supported by earth embankments. It also produces a free-standing, portable tank for use in the field for emergencies and temporary storage. Disposable tanks for temporary containment can be prefabricated by Gundle Lining Systems Inc.

Pillow-style tanks for storage of various fluids are furnished by Aero-Tec Laboratories, Inc. (ATL); Oil Mop, Inc.; and Fred B. Rivas Co.

Fiberglass-based structural systems are furnished by various manufacturers for covering open basins and reservoirs. Fiberglass covers in different styles and sizes are produced by SynTechnics, Inc., FRP Div.; and Topps Industries.

Fiberglass tanks with capacities from several hundred to over a thousand gallons are available from Topp Industries; and Xerxes Corp.

Aluminum sheeting has been used for reservoir covering.

Controlled Aeration. Another way to reduce water loss is to balance water temperatures by controlled aeration with a continual flow of air from bottom-laid tubing and diffusers. As bubbles slowly rise, they circulate the water throughout the reservoir. Surface temperatures and hence evaporation are lowered. Aeration and circulation also prevent water stratification and stagnation. Water thus tastes better - odors, pH, DO, iron, and manganese levels all are improved when brought to acceptable levels.

A further discussion of aeration systems and diffusers can be found in Chapter D-4 of this manual.

Temporary Water Diversion. There are numerous projects in which it is necessary to divert water to be able to perform excavation and foundation work for water works projects. Cofferdams, earthwork, sheet piling, and other means have been used to protect construction sites from water. One other means is with the use of an impermeable, flexible fabric liner mounted to steel support members. Such a system can be used in many ways and in numerous configurations, plus it can be dismantled and used elsewhere.
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Title Annotation:Water Supply and Treatment
Publication:Public Works
Date:Apr 15, 1995
Words:1595
Previous Article:Developing groundwater.
Next Article:Customer metering.
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