Passive Chemical Dosing Apparatus for Construction Site Stormwater Turbidity Reduction

Abstract

A project with the objective to design, construct, and test an automated, passive flocculant dosing system for implementation on a construction site was conducted. Simulated performance of alternative systems was compared through a modeling study to select and design a prototype. A prototype sized for a one acre construction site was tested in a flume with a solution of water and suspended sediment. The initial and resulting turbidities were measured at five locations in the flume with and without flocculant dosing for three different flow rates. The designed system included a forebay, a passive, flow-based dosing system, a turbulent mixing system to facilitate floc development, and a settling basin. Modeling simulations showed it was capable of maintaining flocculant dosing concentrations in predetermined ranges and had a unique relationship between stage in a flow control structure and flocculant dosing concentration. Field scale tests demonstrated the prototype dosing system operated as intended and the flocculant dosed by the system was able to reduce inflow turbidity from a cumulative average of 2760 NTU to 400 NTU (85% reduction) for all tests in the channel.