Turbidity Control in Construction Sites Using Defense Matrix and Polyacrylamide.

Sediment loss from construction sites is one of contributors to surface water pollution in North Carolina. Installing fabric fence in storm water conveyance systems is the one of ways to retain large sediments, but it may not be effective in removing suspended sediments. Flocculating agents such as polyacrylamide (PAM) have been demonstrated to reduce turbidity in runoff when the right method is deployed for dosing the runoff.  With recently mandated EPA regulation on the turbidity of construction sites (<280 Nephelometric Turbidity Units, NTU), there is increasing attention to the application of PAM for turbidity control. We conducted a field  test to evaluate a double-walled barrier system based on Typar^TM (DM) for its use for sediment retention and its efficacy for reducing turbidity in conjunction with PAM. Two DM check dams were installed in a series in an experimental ditch, first DM filled with rocks and second DM filled with mulch typical of a tub grinding output on construction sites. The DM check dams without PAM treatment were effective in retaining large sediments but the turbidity level at the ditch outlet was still beyond the regulatory threshold (280 NTU). With granular PAM treatment on either rock-DM or on additional wattle installed prior to the first DM, turbidity level dropped down to <60 NTU. Our results suggested that the use of DM fabric combined with PAM treatment could be another option for stormwater runoff management in construction sites.