An Active Case for Passive Treatment
While site selection, grading setbacks, scheduling and vegetative buffers are ideal tools for managing sediment and turbidity from a source control standpoint, projects are frequently sited in areas where these factors are infeasible, leading to the need for robust systems of erosion and sediment control BMPs that require intense maintenance and attention – and which sometimes, despite our best efforts, do not meet the requirement of keeping sediment onsite. This technical presentation begins with a brief review and summary of recent research on passive application of polyacrylamide or other flocculants/coagulants, particularly with respect to the relative outcomes and benefits of using passive treatment vs. limiting the toolbox to traditional BMPs.
The literature review is followed by a case study, based on a 15-acre mass graded site on a steep slope, draining directly to a jurisdictional water. Sediment management and CGP compliance at this site was a challenge that required close and frequent coordination between the project owner, QSD, QSP, engineer, and contractor. Traditional approaches for managing sediment on this site were faithfully deployed, and included sediment basins/traps, gravel bags, reinforced silt fence, soil binder, and visqueen.
However, due to the soil types on the site, the basin design standards resulted in unreasonably large basins, and could not be installed within the site constraints. The large basin sizes also required a full stop to all construction activities the day prior to a rain event, thus extending the project schedule and resulting in increased cost and increased time of exposed soils. An alternative approach that incorporated passive application of polyacrylamide in the basins and along the concentrated flow paths would have been the ideal solution for this site, providing multiple benefits including: reduced potential for discharge of sediment to the jurisdictional water, smaller basin sizes, cost savings, and improved compliance with the CGP.
Passive treatment is a powerful tool in the BMP toolbox, which has not yet received the regulatory green light. This talk will provide a scientific case for adding passive treatment as an allowable BMP to the next iteration of the Construction General Permit. Passive treatment represents the next step forward in construction site sediment management, advancing the practice and improving water quality through practical application of a proven technology.
Audience participation will be encouraged through questions and polling of construction site experiences.