AWWA ACE94192

The Ed Heck reservoir is a cylindrical reservoir with an inside diameter of 154 feet, a depth of 30 feet and a normal operating range of 15 to 27 feet. The capacity is about 4 million gallons; the reservoir is fed by a 24 inch pipe and water exits through a 30 inch outlet pipe. The inlet pipe enters in at the bottom of the reservoir, and has a right angle elbow on it. The outlet is next to it at the bottom. The energy of the incoming water causes the water in the reservoir to rotate in a counter-clockwise direction. The normal daily operation is to pump about 8 million gallons to the tank, thus leading to an average detention time of 4/8*24, or 12 hours. During experiments in April of 1994, tracer studies with fluorides indicated that the T10 time of the reservoir is about 25 minutes. This short time is not sufficient to meet the required CT values under the Surface Water Treatment Rule. The required T10 times are estimated between 1 and 1 1/2 hours, depending on temperature, chlorine dosage, credits, tank levels, and other parameters. The question is: What can be done to increase the T10 time? To analyze this problem, two small scale models of the tank were built, and the flow patterns and detention times were analyzed with the help of a dye tracer. The flow patterns were recorded with a video camera and still photography.