scientific water quality management programs for entire river basins, and much more effective waste treatment processes than exist today. Such water quality management programs must be designed to conserve and protect all beneficial water uses by their ability to deliver the required quality of water at the times and places where it is needed. They must be designed to measure and evaluate all of the variables affecting water quality management decisions, both immediate and long range.

The development, design and operation of scientific water quality management programs for river basins will require the development and application of computer systems, hydraulic and mathematical models, automatic instruments, telemetering systems, and a wide variety of other data collection, evaluation, and storage procedures and equipment. Reliable methodology for detecting water pollutants, particularly those resulting from new technology, and for measuring their effects on water uses is required. Valid procedures for projecting economic and demographic growth are essential to the long-range applicability of water quality management programs, currently being planned to cover a period of 50 years.

URBAN WASTE PROBLEM

The concentration of population and industry in urban areas is already creating serious water pollution problems from the vast amounts of complex wastes being discharged into limited water resources, even where these wastes are treated. Chicago serves as a typical example. Although the city provides the best treatment as now practiced, the daily treated effluent is equivalent to the raw sewage from 1 million persons and contains solids amounting to 1,800 tons, causing serious pollution downstream in the Illinois Waterway.

NEW CHEMICAL WASTES

It is already apparent that industrial and municipal wastes and surface and ground waters are undergoing important changes in composition. Products of our chemical technology are finding their way into our waterways in ever-increasing amounts and in more and more locations as chemical plants increase in size and number, and as their products are increasingly used in the home, in industry, and in agriculture. Synthetic detergents, pesticides of all kinds, and various petrochemicals are examples of these contaminants which are resistant to modern waste treatment and to destruction by natural stream purification processes. Therefore, these substances may persist almost indefinitely in the receiving streams. Existing water purification processes are not reliable in removing these persistent materials. Our best methods for detecting and identifying these contaminants are only partly effective.

WATER REUSE

Studies of treated municipal wastes have emphasized the fact that modern treatment methods cannot remove all the soluble compounds present in the incoming sewage. Spot surveys at Toledo, Cleveland, Boston, and Detroit showed that a single municipal use of water

produces an average increase of about 250 parts per million of inorganic solids and 175 parts per million of volatile solids. The concentration of inorganic materials is not appreciably affected by sewage treatment, and even highly treated sewage plant effluents still contain 50 to 150 parts per million of organics based on the volatile solids test.

In the face of a naturally fixed water supply, the growing needs of expanding population and industry will require that water be used over and over. Reuse of water already is well established in some areas; it will appear in others also. Eventually reuse will become an accepted and necessary practice in most densely populated areas. Reuse of water will not be possible in densely populated and industrialized areas or in water-short areas unless much more effective treatment processes are developed. These new treatment processes will need to be based on chemical-physical separation principles, capable of achieving an actual conversion of waste waters to fresh water. This will require major research that is already underway and discussed in succeeding sections of this report. The design, construction, operation, and maintenance of these new separation systems will require extensive use of new procedures, equipment, materials, instruments, and chemicals.

THE DESIGN AND CONSTRUCTION OF WATER

DISTRIBUTION SYSTEMS

GENERAL

A waterworks distribution system includes pipes, valves, hydrants, and appurtenances for conveying water; reservoirs for storage, equalizing, and distribution purposes; booster pumping facilities; pressure control devices; instrumentation and control; service pipes to consumers; meters; and all parts of the conveying system after the water leaves the main pumping station or the main distribution reservoirs. Planning.-Planning of water systems calls for careful consideration of current and possible future trends in the use of urban land. The criteria of 15 or even 10 years ago may no longer apply. Historically there has been a continual increase in the standard of living in the country. With this trend has come the use of many new appliances to make life easier and more comfortable, such as automatic dishwashers, garbage disposals, water-cooled air conditioners, home washing machines, and swimming and wading pools. Also the trend in residential housing with more spacious living has created increased sprinkling demands.

Distribution problems.-Furthermore, the demands of the outlying districts are no longer governed strictly by residential requirements. Industries are moving out of congested traffic areas and the shopping public has become more adverse to frequent trips downtown. This affects the distribution of the firefighting demand. The peak rates of residential consumption are often several times the average daily rate, and the pattern of usage has been changing in recent years.

THE PROBLEMS INVOLVED

The above use and demand factors must be evaluated in the selection and sizing of pipe, in addition to the cost of purchasing the pipe and laying the mains. Related to the problems of sizing mains are those of selecting materials which will minimize the corrosiveness of the water conveyed and of the soil surrounding the pipe.

Design and construction must include a thorough evaluation of high pressure requirements, conditions of high beam and crushing loads, abnormal shocks and stresses, and bedding conditions in which the piping system is to be laid. These factors are related to initial cost, maintenance costs, and continuity and quality of service.

The principal problems involved in providing distribution storage are to determine the capacity required and to establish a location that will serve the system effectively as well as avoid offense to the neighborhood.

The big change in peak water consumption rates has brought about reconsideration of factors which govern pressures in the distribution system. It is not easy to provide pumping and processing capacity

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to keep pace with these factors, much less that of instantaneous demands. The balancing of availability with demand must come from storage, both on the ground and elevated.

TRADITIONAL DESIGN AND CONSTRUCTION PRACTICE

The materials most commonly chosen in the past for distribution system pipes include cast iron, steel, concrete, and asbestos-cement. Cast iron pipe.-Cast iron pipe has been the most generally used material in distribution practice in sizes up to 24-inch. It is generally made by centrifugal casting in either metal or sand-lined molds. The use of seal-coated spun cement linings has effectively controlled loss in carrying capacity due to corrosion and tuberculation. Although there are about six general classes of field joints for cast iron pipe, bell-and-spigot joints have been standard for years. They are generally made in accordance with the specifications of the American Standards Association and the American Water Works Association. Bell-and-spigot joints are poured with melted lead and caulked after pouring, poured with a sulfur base compound, or caulked with lead wool or portland cement.

Reinforced concrete pipe.-Reinforced concrete, as used for pressure conduits, especially those of larger diameter, offers the advantages of continuously high capacity, and with the currently used rubber ring joint, a low rate of leakage. The pipe is usually made at or near where it is to be laid, using local labor and local materials insofar as they are available. It is made in sizes from 16-inch up to 13-foot diameter, and for pressures up to 250 pounds per square inch. The joints of these pipes are made with a more or less modified bell and spigot. The usual designs include steel bell-and-spigot rings, with a sealing element made of either lead or rubber. There are several AWWA standards for concrete pipe, including reinforced concrete steel cylinder pipe, prestressed and nonprestressed and reinforced concrete pipe, nonsteel cylinder and nonprestressed. In steel cylinder pipe, the steel cylinder is continuous and is welded to the joint rings, thus forming a continuous steel water seal throughout the length of the pipe. Concrete pipefittings are available.

Asbestos-cement pipe.-Asbestos-cement pipe is made of a mixture of asbestos fiber, portland cement, and silica, formed under high pressure into a dense, homogeneous structure. The pipe is available in diameters of 3 inches to 36 inches and for working pressures up to 200 pounds per square inch. The pipe is said to be free from both internal and external corrosion, tuberculation, electrolysis, and has good hydraulic characteristics. Joints consist of an asbestos-cement sleeve with two roll-on or slip-on rubber rings. Compatible fittings are available in cast iron and in copper for small sizes.

Steel pipe.-Steel pipe is made from the smallest size to several feet in diameter, and in lengths up to 50 feet or more. Normally it has not been used in water distribution system practice in sizes 12 inches in diameter and under. Fittings are generally fabricated by welding. Joints may be welded or of the bolted rubber-ring, sleeve type such as dresser couplings. Steel pipe generally is lined with cement mortar or coal tar enamel in order to minimize corrosion and tuberculation. Exterior coatings generally are coal tar enamel, although cement mortar coatings have been used.

Other materials used for distribution piping include wrought iron and plastics.

Valves.-Valves are a necessary part of a water distribution system since they serve to isolate a section of the system in the event of a main break, thereby minimizing the damage which would be caused by an unrestricted flow of water. Valves are also used to facilitate repairs and to permit cut-ins for new mains and services.

Aside from completely stopping flow, valves are used for throttling or controlling quantities of water flowing in a pipe. Other uses include pressure and level control and proportioning flow. They may function automatically, actuated by pneumatic, hydraulic, or electrical control systems.

The types of valves in common use in water distribution systems include gate, globe, rotary, butterfly, pressure reducing, and check valves, as well as several other kinds.

Storage tanks.-Storage capacity is determined by consideration of: (1) The reserve required to meet standby operations, often sized by fire insurance regulations (2) growth and development of the area served and present and future rates of water use, (3) the feasibility of maintaining the reserve volume of water desired at the contemplated elevation for pressure maintenance, and (4) the adequacy of the supply.

Elevated and ground storage tanks and standpipes are utilized to aid in supplying water demand and maintaining pressure in the system. They are constructed of steel or concrete and their design involves primarily structural considerations after capacity and location factors are determined. Ease of maintenance is highly important, as is protection against deterioration. In residential locations, the designer should never overlook esthetic considerations, involving to a great extent the appearance of the structure.

Meters. One other important part of the water distribution system is the meters which are installed. There are two principal objectives in metering: (1) Providing an impartial record of the water consumed, and (2) equitably dividing the cost of rendering service. The water meters used in a municipal water system to measure the flow to customers are known as service meters; those measuring the flow to or in the distribution system as main line meters.

The characteristics which are of special importance in service meters are accuracy and sensitivity, both when new and after use; durability; low pressure loss; cost of purchase and installation; ease and low cost. of maintenance. There are three basic types of service meters normally used. These are the disk meter, the oscillating piston meter, and the turbine meter. Where extreme rates of flow are experienced by large customers, a compound meter is used combining the disk or piston meter with the turbine type. Main line meters may be propeller or venturi type.

NEW MATERIALS, EQUIPMENT, AND DESIGNS AND THE NEW APPLICATION OF OLDER MATERIALS, EQUIPMENT AND DESIGNS

One of the major advances in the waterworks field in recent years has been the use of computers by engineers for analyzing existing distribution systems and designing new ones. What used to be a time-consuming and complicated process, particularly with existing