American Water Works Association Research Foundation Study.
One concern with the blended supply of surface water ground water and desalinated seawater was how the new water chemistry would affect the member government distribution systems, which had operated with only groundwater for decades. Initial research indicated there should be no impacts to regularly maintained systems, however, Tampa Bay Water and its members sought test the various supply mixes to ensure this high-quality blended maintained its integrity when it reached customers’ taps.
Two factors must be considered when determining the best way to adjust the chemistry of the blended water:
The percentage of each type of water in the blend may vary depending on the season. For instance, during wet periods when Tampa Bay Water is permitted to withdraw the maximum amount of surface water, there will be a higher percentage of surface water and desalinated water in the blend than during dry times.
All of Tampa Bay Water’s member governments have their own distribution systems with pipes of differing materials, conditions, sizes and ages. Without proper chemical adjustments along the way, the blended water may interact differently with the inside of the member government’s retail distribution pipes. This could result in water discoloration and otherwise affect the aesthetic quality of the water.
Tampa Bay Water adjusts pH and alkalinity at various points prior to delivering the drinking water to its member government. These adjustments minimize color changes that could result from the varying conditions and materials found in the individual member government’s local pipe systems. The member governments themselves also have an opportunity to perform other elective treatments, such as softening the water, pH adjustment and adding fluoride, prior to delivering the water to their customers.
Since Summer 2001, Tampa Bay Water and its member governments, in collaboration with the University of Central Florida, have been conducting pilot studies in orrder to understand how the various blends of water impact the various types pipe in the distribution systems. These studies will help Tampa Bay Water and its member governments mitigate any factors affecting the aesthetic value and overall quality of the water after it has traveled through the retail distribution systems. These pilot studies are part of a three-year, $2.6 million treatment and distribution-blending project and are managed through the American Water Works Association Research Foundation. The results of this pioneering study are expected to be used by other water utilities across the country.
To simulate how the blended water will react within the different distribution systems, sections of pipe from some of Tampa Bay Water’s member governments have been collected. These pipes, which range from two to six inches in diameter and are several hundred feet long, are representative of the types of pipes that exist in the actual retail distribution systems.
The study involves creating samples of different water blends in ratios representative of what will occur within the actual system. These various blends are then fed through the pipes using hydraulic retention lines that mimic what Tampa Bay Water’s member governments have. It is critical to ensure that the speed of the water traveling through the pipes and the time that the water remains in contact with the pipes is representative of actual conditions.
Water quality data from actual and pilot distribution systems is being correlated and modeled for prediction of water quality change based on blend, treatment and time. Physical and aesthetic parameters being measured include temperature, turbidity or clarity, taste and odor, particle count and color. Chemical and biological characteristics are also being evaluated.
