Twin Falls Water Supply and Purification
Plant Supplied from Snake River, in Idaho, Through Canal and 24-Inch Pipe—Problem of Polluted Water—Modern Mechanical Filtration—Meters Saved Much Water Waste
ABOUT ten years ago, upon the site where Twin Falls, Idaho, now stands, there was nothing more than a barren sage brush waste, therefore, water for irrigation and domestic needs has played an important part in the up-building of this modern city, which now has about 10,000 population.
In providing water for irrigating the farms, the city also has provided through the same canal water for its domestic needs and fire protection. The water supply is from the Snake River, taken from a canal which is located about two and one-half miles south of Twin Falls. From this canal the water for municipal use flows through a 24-in. pipe line, passing through a Venturi meter and also through a float valve which automatically regulates the elevation of the water in the receiving basins.
The water supply for Twin Falls, as in all other western cities, must he in adequate volume for garden irrigation, laws, and an unusually large amount for domestic requirements because of the very dry summer seasons. This necessitates procuring three to four times as much water per capita as the average municipality uses throughout the Eastern States. The total capacity of the plant is, therefore, planned for six million gallons per day and the water consumption during certain hours of the day has already reached this large volume.
Problem of Polluted Canal Water
Many cities through Idaho, Washington, Oregon, Utah, Montana and other western states procure their water supply from irrigating canals similar to Twin Falls and these cities using such source of supply have found the canal water, so contaminated as to be unsafe to drink without purification. This contamination usually arises because of drainage into the irrigating canals from farm houses and from discharging of raw sewage without treatment into the streams. The conditions in Twin Falls are, therefore, quite similar to those in many other of the western municipalities and the successful handling of this same problem at Twin Falls may be of interest and helpful to the municipalities of many other western states that must sooner or later solve this same question of providing an absolutely safe water for domestic and commercial needs.
At Twin Falls the canal supply is at sufficient elevation above the city to permit of a gravity plant, the water flows from the canal through a 24-in. pipe line, measured with a Venturi meter into a receiving basin. The leve’ of the water in the receiving basin is regulated by an automatic float valve which maintains a constant elevation over the filter. The canal at Twin Falls as is usual with canals must be emptied at certain seasons of the year for repairs, and at times the water in the canal is low, and to provide for this emergency low service pumps are utilized for lifting the water from the canal at these low stages into the settling basins. A large settling basin of approximately twenty – million – gallon capacity has been provided for storage of water during times of repair. The filtration system is no different than other purification plants that have been described quite fully in engineering periodicals, except that advantage has been taken in this plant of all of the modern improvements and methods utilized in handling of the water. Sulphate of alumina is used as a coagulate and this is fed through dry feed machines in a pulverized condition, feeding through a hopper and delivered to the water as a ribbon of chemicals over a small wheel. In order to insure a thorough mixing of the sulphate, baffle walls are so arranged as to give the water a travel of 1,600 feet, passing up and down through these baffle walls.
Master Controller Regulates Operation
After this thorough mixing the water passes to two concrete lined settling basins where approximately 85% of the sediment and impurities are removed from the water. After the settling basin treatment the water passes over a weir to a concrete flume, flowing on to the sand filters. Six of these sand filters are provided with a normal capacity of one million each, making a total of six million gallons per 24 hours. Each of these filters is provided with marble top operating tables with hydraulically operated valves and water from each filter passing through a Venturi meter with a recording equipment, so that the rate of each filter can be easily observed. On the operating table each filter also has a control stand so arranged as to indicate the time when the filter requires washing, which will be shown by the loss of head of each filter recorded on the operating table. The washing of the filters is accomplished with a wash water pump of large capacity. The plant is provided with a master controller which forces the plant to operate in proportion to the demand of the city, which is one of the latest improvements in purification equipment and is very desirable from a standpoint of an economical operation.
Nothing has been left undone to make the Twin Falls purification plant one of the most modern in the United States. The purification plant delivers the water to the city free from turbidity, odor, color, and tests made show an average of 98% of all bacteria removed. The design of the purification works, both interior and exterior, has been of a character that is pleasing to the eye and makes the entire plant one of the show places of the municipality. The water after purification flows to the city by gravity through a line two and one-half miles long and 24-in. in diameter. This gravity flow line is of California Redwood pipe, the line being built of continuous stave pipe assembled in the trench. The purification plant is on a hill 190 feet above the city and is delivered to the municipality at a pressure in the mains throughout the business district of 70 pounds per sq. inch.
For the building of the purification plant and improvements in the distributing system, Twin Falls voted a bond issue of $375,000. While this bond issue may seem high for a city of 10,000, yet it is less than one-half the amount of an estimated cost of a former gravity supply, which had been considered, but for which the voters failed to ratify a bond issue. The entire purification plant, settling basins, and pumping equipment is so arranged that additional units may be added as the growth of the city justifies an increase in capacity.
Meters Save Much Waste of Water
Before the plant was turned over to the city the consulting engineers, Burns & McDonnell, Kansas City, Mo., through their resident engineer, C. E. Painter, made an investigation of the meter situation, with a view of recommending the complete meterization of the entire city. The result of this investigation showed only 38 meters out of 1,800 taps and the city commissioners immediately ordered 500 meters, and a price contract was made for future orders, and within a short time Twin Falls will be 100% metered. This report of the engineers showed that the present purification plant would have to be extended and enlarged within five years unless prompt action was taken toward curtailing the unnecessary waste of water. Between 11:00 A. M. and 1:00 P. M. and from 5:00 to 7:00 P. M. water in Twin Falls was used at the rate of seven million gallons per day. It will, therefore, be seen that the plant had to run in excess of its normal six million capacity during these peak load hours, but with the restrictions on the waste of water the present capacity of the plant should be sufficient for 15 to 20 years. An investigation was made of 24 customers using water on a flat rate. Leaky plumbing was found responsible for the largest loss on these 24 hours and meters were installed on these 24 users. A later investigation was made to determine the result and it was discovered that $196 was the revenue produced under the flat rate, while under the yearly rate with meters a revenue of $303.88 was produced and of these 24 customers 50 per cent, were being overcharged and the other 50 per cent, were being presented water free of charge by the municipality. The city council and the mayor cooperated with the consulting engineers in carrying out the recommendations and at Twin Falls, as it should in other municipalities, it was felt unwise to operate a modern water purification system and then permit the water to be wasted through illegitimate use.
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The entire water system at Twin Falls was designed and supervised by Burns & McDonnell, consulting engineers, with C. E. Painter as their resident engineer. The general construction contract was awarded to Heuser-Packard Construction Co., and a local contractor, Mr. 1 laskins, laid the mains and distribution system. The filtration plant was erected by the Pittsburgh Filter and Eng. Co., of Oil City, Penn.
The accompanying cuts will illustrate some special features of the plant. It frequently happens that municipalities will procure a model purification plant and then leave the operation to an inexperienced person and poor results will often follow, however, at Twin Falls the city officials procured a trained filter operator in J..E. Byers, who has recently returned from the army service, and under his operation the purification plant receives constant attention, daily analysis of water and the consumers are assured of uniform results with a minimum amount of chemicals and safe water free from dangerous bacteria.