WSDOT is considering the use of Polyacrylamide (PAM) flocculent to reduce stormwater runoff turbidity at highway construction sites. This research project conducted a testing program to determine the dissolution rates of PAM introduced to simulated stormwater flow by using an experimental geotextile "tea-bag" dosing system.
The testing program simulated "tea-bags" placed in 2 configurations: 1) suspended in a pipe culvert, and 2) placed in a standard catch-basin insert. The flume in the Saint Martin’s College School of Engineering Hydraulics Laboratory was used to conduct a full-scale simulation of flow regimes for these 2 configurations.
Five types of geotextile fabric, five types of PAM flocculent, and ten configurations of tea-bag placement were tested. Empirical relationships between the dissolution rate and flow were found by regressing the test results.
PAM dissolution rate was found to vary as an inverse power function with flow rate, and directly with the amount of PAM introduced into the flow stream. The type of geotextile fabric and the type of PAM flocculent had only a minor effect on dissolution rate.