A tracer study is a mechanism for determining the movement of water within a water supply system. In such a study, a conservative substance is injected into the water and the resulting concentration of the substance is measured over time as it moves through the system. Historically, tracer studies have been used to study the movement of water through water treatment plants and distribution systems. Though conceptually quite straightforward, a successful field tracer study requires careful planning and implementation in order to achieve useful results.
Tracer studies have been most commonly used as a means of determining the travel time through various components in a water treatment plant (Teefy and Singer, 1990; Teefy, 1996). Its most frequent usage is to ascertain that there is an adequate chlorine contact time in clearwells as required by U.S. EPA regulations. Generally a conservative chemical such as fluoride, rhodamine WT, or calcium, sodium or lithium chloride is injected into the influent of the clearwell as either a pulse or a step function. Subsequently, the concentration is monitored in the effluent and statistics such as the T10 value (time until 10 percent of the injected chemical reaches the outflow) are calculated.
Tracer studies have also been conducted in distribution system storage facilities to understand the mixing processes within the facility. Fluoride was injected into the influent of a reservoir in California and sampled in both the effluent and at an interior point to assess mixing (Grayman et...
TABLE OF CONTENTS 
