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 News from the Field
Many water systems experience loss of chlorine residual. Sometimes this problem is bigger in systems that purchase water from a larger system. Even though the water quality from the supplier may be good, the length of time the water is in the second distribution system can result in loss of chlorine residual and other water quality issues. Montgomery County Rural Water District No. 11 serves nearly 500 customers in an area north of Coffeyville in southeast Kansas. Like many rural water districts, this system experiences problems maintaining chlorine residuals to all areas of the distribution network. The district purchases water from the City of Coffeyville. After boosting the pressure, Montgomery RWD 11 sends water through 50 miles of pipeline ranging in size from 2-inch to 6-inch. The district uses two standpipes that are side by side to maintain pressure during times of peak demand—a somewhat unusual situation (see photo at right). Most people served are in the southern boundary area, while the homes to the north are more spread out. The southern portion is closer to the water source and does not show regular signs of chlorine residual problems. In the northern portion, routine flushing is required to maintain chlorine residuals at minimum standards. This flushing has been time consuming and costly in terms of both water purchased and labor. Gaining control of the process The district needed to re-chlorinate the water purchased from the city. The source water contained combined chlorine residual, making the problem even trickier. To overcome this and not create additional issues with overfeeding chlorine or with regulatory requirements, the district installed flowmeters, a continuous amperometric chlorine analyzer and flow-paced metering pumps to inject a sodium hypochlorite solution. The flowmeters continuously monitor flow both into and out of the standpipes while the analyzer updates current chlorine residual levels. The flow-paced pumps ramp up when higher water demand is recognized and slow down for lower flows. The district can now control when and how much chlorine to feed to bring the levels back to what was present at treatment. Data loggers are used to track this information; the information is downloaded to a computer located at the site. Standpipe and dead-end line problems solved The district’s two standpipes are separated by only a few feet to accommodate peak flow conditions. They are constructed with a single riser pipe extending just a couple of feet from the bottom of the tank. The tanks cycled continuously but would still stratify, leaving a column of water in the tank for long periods of time— and time for the chlorine residual to dissipate. The district extended the riser pipes to 76 feet above the bottom of the tank, giving better water circulation throughout the height of the tank. Dead end lines in the northern section of the district also contributed to loss of residual. Using reserve funds in addition to funds borrowed locally, the district has installed almost 11,500 feet of new high-density polyethylene pipe to close the loops. These loops really helped the flow in the northern areas of the district, which has also helped with chlorine residuals. Flushing has been reduced considerably. A job well done Water systems must continue to work towards improving operations to stay ahead of ever-changing regulations. Tony Pauzauskie, manager/operator for Montgomery RWD 11, says, “The board of directors has been good to work with on this project. These things take time. There are a number of changes coming and we are doing what we can to be prepared.” Article and photos used with permission from The Kansas Lifeline, July 2007 issue. |
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