Application of Polyacrylamide-based Floc Logs for Turbidity Control at Highway Construction Sites.

摘要

Runoff waters generated on highway construction sites can have turbidities in excess of the proposed EPA regulatory standard of 280 NTU due to large areas of exposed soil. The objective of this research was to develop best management practices (BMPs) for the use of anionic polyacrylamide (PAM) based Floc Logs, for turbidity control. Five commercially available types of PAM-based Floc Logs were evaluated in jar tests, using soil excavated from Cato Springs Research Center (CSRC, Fayetteville AR) and six types of clay from the Clay Minerals Society (Chantilly, VA). These results show that no single Floc Log type was suitable for all six types of clay, and that jar tests should be conducted using field soils to select the appropriate Floc Log type for turbidity control. Results from the jar tests were also interpreted alongside particle size distributions (PSDs) of each type of clay, which were measured by Coulter Counter. These results suggested that particle surface charge, and not PSD, was the dominant flocculation mechanism for the clays used in the jar tests. Subsequent inline channel tests at the CSRC and at the Bella Vista Bypass showed little to no turbidity reduction, which was attributed to insufficient PAM dosing, mixing, and/or settling time. However, results from basin-scale sedimentation tests at the CSRC showed that a single Floc Log was capable to treating more than 2,000 L of turbid water (i.e., 95-99% turbidity reduction in ~5 minutes) provided that the Floc Log was presoaked in tap water for 15 minutes. The Floc Log was capable to being reused without compromising turbidity reduction, provided a turbulent mixing period of at least 15 minutes. On balance, PAM-based Floc Logs were shown to be an effective tool to treat turbid water in sedimentation basins provided a period of rapid mixing.