§ A182-8. Disinfection of mains.
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All new work shall be disinfected by the contractor. Disinfection shall be performed in an approved manner in accordance with the American Water Works Association's Standard for Disinfecting Water Mains, Designation C-651, except that the tablet method described in Section 5.1 of C-651 shall not be used.
A.Preventive measures during construction.
(1)Keeping pipe clean and dry. Precautions shall be taken to protect pipe interiors, fittings and valves against contamination. Pipe delivered for construction shall be strung so as to minimize entrance of foreign material. When pipe laying is not in progress, as, for example, at the close of the day's work, all openings in the pipeline shall be closed by watertight plugs. Joints of all pipe in the trench shall be completed before work is stopped. If water accumulates in the trench, the plugs shall remain in place until the trench is dry.
(2)If dirt that, in the opinion of the Engineer or job superintendent, will not be removed by the flushing operation enters the pipe, the interior of the pipe shall be cleaned and swabbed as necessary, with a 5% hypochlorite disinfecting solution.
B.Preliminary flushing. The main shall be flushed prior to disinfection. The flushing velocity shall not be less than 2 1/2 feet per second. The rate of flow required to produce this velocity in various diameters is shown in Table I. No site for flushing should be chosen unless it has been determined that drainage is adequate.
TABLE I Required Openings to Flush Pipelines* (40 pounds per square inch residual pressure) Pipe Size (inches) Flow Required to Produce 2.5 Feet per Second Velocity (gallons per minute) Orifice Size (inches) Hydrant Outlet Number Nozzles Size (inches) 4 100 15/16 1 2 1/2 6 220 1 3/8 1 2 1/2 8 390 1 7/8 1 2 1/2 10 610 2 5/16 1 2 1/2 12 880 2 13/16 1 2 1/2 14 1,200 3 1/4 2 2 1/2 16 1,565 3 5/8 2 2 1/2 18 1,980 4 3/16 2 2 1/2 NOTES: * With 40 pounds per square inch residual pressure, a two-and-one-half-inch hydrant outlet nozzle will discharge approximately 1,000 gallons per minute and a four-and-one-half-inch hydrant nozzle will discharge approximately 2,500 gallons per minute. C.Form of chlorine for disinfection. The most common form of chlorine used in the disinfecting solutions is liquid chlorine (gas at atmospheric pressure), calcium hypochlorite granules and sodium hypochlorite solutions.
(1)Liquid chlorine.
(a)Liquid chlorine shall be used only when suitable equipment is available and only under the direct supervision of a person familiar with the physiological, chemical and physical properties of this element and who is properly trained and equipped to handle any emergency that may arise. Introduction of chlorine gas directly from the supply cylinder is unsafe and shall not be permitted.
(b)The preferred equipment consists of a solution feed chlorinator in combination with a booster pump for injecting the chlorine gas — water mixture into the main to be disinfected. Direct feed chlorinators are not recommended because their use is limited to situations where the water pressure is lower than the chlorine cylinder pressure.
(2)Calcium hypochlorite. Calcium hypochlorite contains 70% available chlorine by weight. It is either granular or tabular in form. The tablets, 6-9 to the ounce, are designed to dissolve slowly in water. A chlorine — water solution is prepared by dissolving the granules in water in the proportion requisite for the desired concentration.
(3)Sodium hypochlorite. Sodium hypochlorite is supplied in strengths from 5.25% to 16% available chlorine. It is packaged in liquid form in glass, rubber or plastic containers ranging in size from one-quart bottles to five-gallon carboys. It may also be purchased in bulk for delivery by tank truck. The chlorine — water solution is prepared by adding hypochlorite to water. Product deterioration must be reckoned with in computing the quantity of sodium hypochlorite required for the desired concentration.
D.Application of solutions.
(1)The hypochlorite solutions shall be applied to the water main with a gasoline- or electrically powered chemical feed pump designed for feeding the chlorine solutions. For small applications, the solutions may be fed with a hand pump, for example, a hydraulic test pump.
(2)Feed lines shall be of such material and strength as to withstand safely the maximum pressures that may be created by the pumps. All connections shall be checked for tightness before the hypochlorite solution is applied to the main.
E.Methods of chlorine application.
(1)Continuous feed method.
(a)This method is suitable for general application. Water from the existing distribution system or other approved sources of supply shall be made to flow at a constant, measured rate into the newly laid pipeline. At a point not more than 10 feet downstream from the beginning of the new main, the water entering the new main shall receive a dose of chlorine, also fed at a constant, measured rate. The two rates shall be proportioned so that the chlorine concentration in the water in the pipe is maintained at a minimum of 25 milligrams per liter available chlorine. To assure that this concentration is maintained, the chlorine residual should be measured at regular intervals in accordance with the procedures described in the current edition of Standard Methods of AWWA M12 — Simplified for Water Examination.
(b)Table II gives the amount of chlorine residual required for each 100 feet of pipe in various diameters. Solutions of 1% chlorine may be prepared with sodium hypochlorite or calcium hypochlorite. The latter solution required approximately one pound of calcium hypochlorite in 8.5 gallons of water. If liquid laundry bleach with 5.25% chlorine is used, then 4.25 gallons of water is to be mixed with one gallon of bleach to obtain 1% solution.
TABLE II Chlorine Required to Produce 25 Milligrams per Liter Concentration in 100 Feet of Pipe Pipe Size (inches) Volume of 100-Foot Length (gallons) 100-Percent Chlorine (pound) 1-Percent Chlorine Solutions (gallon) 4 65.3 0.013 0.16 6 146.5 0.030 0.36 8 261.0 0.054 0.65 10 408.0 0.085 1.02 12 588.7 0.120 1.44 (c)During the application of the chlorine, valves shall be manipulated to prevent the treatment dosage from flowing back into the line supplying the water. Chlorine application shall not cease until the entire main is filled with the chlorine solution. The chlorinated water shall be retained in the main for at least 24 hours, during which time all valves and hydrants in the section shall be operated in order to disinfect the appurtenances. At the end of this twenty-four-hour period, the treated water shall contain no less than 10 milligrams per liter of chlorine throughout the length of the main.
(2)Slug method. This method is suitable for use with mains of large diameter for which, because of the volumes of water involved, the continuous feed method is not practical.
(a)Water from the existing distribution system or other approved source of supply shall be made to flow at a constant, measured rate into the newly laid pipeline. The water shall receive a dose of chlorine, also fed at a constant, measured rate. The two rates shall be proportioned so that the concentration in the water entering the pipeline is maintained at no less than 100 milligrams per liter. The chlorine shall be applied continuously and for a sufficient period to develop a solid column of slug of chlorinated water that will, as it passes along the line, expose all interior surfaces to a concentration of at least 100 milligrams per liter for at least three hours. The application shall be checked at a tap near the upstream end of the line by chlorine residual measurements made according to the procedures described above.
(b)As the chlorinated water flows past tees and crosses, related valves and hydrants shall be operated so as to disinfect appurtenances.
(3)Tablet method. The tablet method, as contained in American Water Works Association Standard C-651, is not acceptable to the New York State Department of Health and shall not be used.
F.Final flushing. After the applicable retention period, the heavily chlorinated water shall be flushed from the main until the chlorine concentration in the water leaving the main is no higher than the generally prevailing in the system, or less than one milligrams per liter. Chlorine residual determination shall be made to ascertain that the heavily chlorinated water has been removed from the pipeline.
G.Bacteriologic tests.
(1)After final flushing and before the water main is placed in service, a sample or samples shall be collected from the end of the line and tested for bacteriologic quality and shall show the absence of coliform organisms. If the number and frequency of samples is not prescribed by the public health authority having jurisdiction, at least one sample shall be collected from chlorinated supplies where a chlorine residual is maintained throughout the new main. From unchlorinated supplies, at least two samples shall be collected at least 24 hours apart. In the case of extremely long mains, it is desirable that samples be collected the length of the line as well as at its end.
(2)Samples for bacteriologic analysis shall be collected in sterile bottles treated with sodium thiosulphate. No hose or fire hydrant shall be used in collection of samples. A suggested samples tap consists of a standard corporation cock installed in the main with a copper tube gooseneck assembly. After samples have been collected, the gooseneck assembly may be removed and retained for future use.
H.Repetition of procedure. If the initial disinfection fails to produce satisfactory samples, disinfection shall be repeated until satisfactory samples have been obtained. When the samples are satisfactory, the main may be placed in service.
I.Procedure after cutting into or repairing existing mains. The procedures outlined in this section apply primarily when mains are wholly or partially dewatered. Leaks or breaks that are repaired with clamping devices while the mains remain full of water under pressure require no disinfection.
(1)Trench treatment. When an old line is opened, either by accident or by design, the excavation will likely be wet and badly contaminated from nearby sewers. Liberal quantities of hypochlorite applied to open trench areas will lessen the danger from such pollution. Tablets have the advantage in such a situation because they dissolve slowly and continue to release hypochlorite as water is pumped from the excavation.
(2)Main disinfection.
(a)Swabbing and flushing. The following procedure is considered as a minimum that may be used.
[1]Swabbing with hypochlorite solution. The interior of all pipe and fittings used in making the repair (particularly couplings and tapping sleeves) shall be swabbed with a 1% hypochlorite solution before they are installed.
[2]Flushing. Thorough flushing is the most practical means of removing contamination introduced during repairs. If valving and hydrant locations permit, flushing from both directions is recommended. Flushing shall be started as soon as the repairs are completed and continued until discolored water is eliminated.
(b)Slug method. Where practicable, in addition to the procedures of swabbing and flushing, a section of main in which the break is located shall be isolated, all service connections shut off and the section flushed and chlorinated as described, except that the dose may be increased to as much as 300 milligrams per liter and the contact time reduced to as little as 1/4 hour. After chlorination, flushing shall be resumed and continued until discolored water is eliminated.
(3)Sampling. Bacteriologic samples shall be taken after repairs to provide a record by which the effectiveness of the procedures used can be determined. If the direction of flow is unknown, samples shall be taken on each side of the main break.