A Passive Approach to Treating Turbidity on Construction Sites

摘要

Construction sites of more than one acre are required to install systems to retain sediment that is produced on that site. These include silt fences, sediment traps, storm drain inlet protection, checks dams and others. However, turbidity created by suspended clays and fine silts is usually still quite high in water discharged from these systems. Storing runoff long enough for the sediment to settle is not practical as it can take weeks for this to happen. Filtering the runoff to reduce the turbidity can be very expensive and requires a large amount of maintenance. We have found that the use of Polyacrylamides (PAM) is the most practical and least expensive method for most situations. We have tested many of these devices and systems in conjunction with PAM using a passive approach to achieve turbidity levels that would match new federal regulations for effluent discharge established by the EPA. Introducing PAM to runoff water can be tailored to individual sites, but it is best accomplished when heavy sediment is removed first. While working with the different BMPs, to control the sediment load and introduce PAM, we have documented reductions in turbidity and suspended solids of up to 95% on active construction sites in North Carolina. This presentation will cover the important aspects of these systems and how we are able to optimize the use of PAM with them. The key features are the use of known materials, ease of installation, and costs which are not substantially higher, and sometimes lower, than common practices.