(8c) Detailed Water Quality and Temperature Comparison of Two Identical Drinking Water Storage Tanks: One with Passive Mixing and One with No Mixing Device

The degradation of finished water in storage tanks is of great concern to water utilities. It is widely assumed that tank mixing enhances water quality, and slows the creation of disinfectant byproducts (DBP's). In an attempt to enhance water quality and react to future, tighter regulations on DBPs, the Birmingham Water Works Board (BWWB) is conducting a study to examine storage tank mixing effectiveness. This will be achieved by comparing a tank with a turbulent jet-mixing device to an identical tank with no passive or active mixing.

Part 1

Two identical 2.5 million gallon reservoir tanks, located less than sixty feet apart, are supplied finished water from the same source at essentially the same pressure. Both tanks will maintain roughly identical volumes through daily fluctuations. Each tank is fitted with five (5) temperature sensors spaced at equidistant elevations inside the tanks. Each tank's temperature is measured, at each elevation, in ten (10) minute intervals to ensure detailed time versus temperature data. The data collected will document amount of temperature stratification, which is an indicator of mixing effectiveness.

Part 2

Sampling ports are installed in both tanks, described in part 1, at elevations nearly identical to the elevations of the temperature sensors. Both tanks will be sampled for free chlorine, total haloacetic acid (HAA's), and total trihalomethanes (TTHM's) at varying heights. These parameters will be measured over a twelve (12) month period to account for seasonal variation. A properly mixed tank should show little variation top to bottom of the sampled parameters.

The combined information from this project should give a detailed comparison between the tanks and determine effectiveness of the turbulent jet mixers. The data collected will provide useful information on effectiveness of passive mixing systems.