Assessment of Polyacrylamide Concentration in Construction Stormwater Runoff Using an ASTM D6459 Rainfall Simulator

Abstract

Polyacrylamide (PAM) is a polymer used in construction stormwater management as both an erosion and sediment control measure. PAM is considered one of the environmentally safest polymers on the market, however overapplication concerns dictate that large quantities in runoff be avoided. For slope erosion applications, ensuring proper concentration requires methods for testing residual concentrations. This research investigated residual concentrations of PAM when dry-applied at a rate of 25 lb/acre (28 kg/ha) for slope stabilization and subjected to 1-h of simulated rainfall following ASTM D6459-19 protocols at three 20-min successive 2-, 4-, and 6-in./h (5-, 10-, and 15-cm/h) intensities. Residual concentrations were determined by centrifuging runoff samples to remove soil and reading absorbance from an ultraviolet-visible spectrometer, comparing values to those at known concentrations. Concentrations in collected runoff samples were found to surpass values found in previous research and in other PAM applications, especially during first flush, and were high enough to affect water viscosity. An alternative application method is presented that may mitigate PAM runoff concentration. The spectrometry method was also used to highlight the possibility that polymers used in hydromulches may also deposit excess concentrations in stormwater runoff, and that formal residual testing of such products is warranted. The processes used for this study demonstrated how discharge may be monitored and regulated to minimize undesirable runoff conditions from construction sites and underscore the importance of appropriate design and implementation when using additives for erosion control.