Reducing Turbidity of Construction Site Runoff: Factors Affecting Particle Destabilization with Polyacrylamide

Abstract

The U.S. Environmental Protection Agency is in the process of developing a nationwide standard for turbidity in construction site runoff. It is widely expected that this standard cannot be met with conventional erosion and sediment control measures; consequently, innovative practices for managing sediment on construction sites must be developed. One emerging practice is the use of polyacrylamide (PAM) to improve sediment control by promoting flocculation of particles in runoff. For this practice to be used efficiently, it is essential to understand how soil and PAM properties affect flocculation. A protocol for creating modified synthetic stormwater runoff from soil samples was developed and used on soils from six Texas construction sites. Flocculation tests were performed on these synthetic stormwaters with PAM doses from 0.03 to 10 mg/L. The polymers used ranged from anionic PAMs of 0% to 50% charge density and 0.2 to 14 Mg/mol molecular weight as well as one co-polymer. A neutral PAM and the co-polymer were found to be most effective in reducing the turbidity of all the modified synthetic stormwater below 200 NTU at doses of 10 mg/L. Hardness and electrophoretic mobility tests indicated interparticle bridging to be the bonding mechanism. The high molecular weight (HMW) anionic PAMs were effective on only two of the six modified synthetic runoffs. As the charge density of these HMW PAMs increased, their effectiveness decreased.