About the research

Unmanaged construction stormwater runoff can pose a risk for the quality of downstream water bodies. Temporary sediment control practices are designed to capture sediment particles and reduce the turbidity of discharge; however, commonly used practices have limited performance in capturing fine-sized sediment particles. Flocculants can be introduced to construction stormwater runoff to enhance the performance of sediment control practices by increasing the settling velocity of suspended materials. This research study explored practical methods to enhance guidance for proper selection, use, and application of flocculants in construction stormwater management through (1) a state of the practice survey, (2) soil assessments, (3) bench-scale experiments, (4) flume experiments, and (5) intermediate-scale flume and large-scale evaluations. In total, 14 different products were used for bench-scale experiments. Best performing products for unique soils were identified with a match test study, which ranked products based on their performance. Results indicated that polyacrylamide (PAM) and chitosan-based products work most effectively across tested soil samples compared to other tested products. Testing results also showed the potential of flocculants to perform well in underdose conditions. Results revealed that pH, temperature, and flocculant concentration all significantly affect soil settling velocity which greatly influenced the accuracy of residual flocculant concentration predictions. Optimum dosage delivery mechanisms were evaluated through flume experiments by using block, sock, granular, and stock solution flocculant forms. A 40 ft (12 m) long flume was designed and constructed at the Auburn University - Stormwater Research Facility. Testing results indicated that the use of ditch checks for flocculant applications in channelized flow significantly improves the agitation and mixing by providing up to 96% turbidity reduction. Large-scale evaluations were accomplished using an in-channel sediment basin application using semi hydrated PAM-based flocculants in block form. Testing results indicated that flocculant usage provided a 90% turbidity reduction and showed residual concentration values from 5 to 8 mg/L exist in the discharge point. Flocculant application was evaluated on wattle ditch checks using granular PAM-based flocculant and silt fence ditch checks using block form PAM-based flocculant. Application and reapplication quantities and intervals were developed based on findings.