STORMWATER RUNOFF TREATMENT WITH VORTECHS® STRUCTURES

The contaminant removal effectiveness of a three-chamber Vortechs® system in Providence, RI was measured. Target pollutants were polycyclic aromatic hydrocarbons (PHA), metals (Cu, Zn, Fe, Pb), nutrients, sediments, and fecal coliform bacteria The results of this study indicate that total suspended solids (TSS) were removed efficiently (65% to 85%). However, possible re-suspension of sediments during high flow conditions was observed. The Vortechs® did not remove total dissolved solids (TDS).

A high resolution sampling campaign was carried out during one particular storm in early winter. During this storm, about 311 mg of PAH entered the Vortechs® of which 42 mg were removed. A total of 269 mg dissolved PAH left the system unabated. The total dissolved PAH removal efficiency peaked at 16.8% early during the storm, but then decreased to 8.4% at the storm’s end. Significant differences in removal effectiveness existed between dissolved light molecular weight (LMW) and high molecular weight (HMW) PAH. The LMW PAHs average removal effectiveness was 21.1%, while HMW PAHs were not removed or even redissolved from contaminated bottom sediment. Hence, the most problematic HMW PAH, such as chrysene or benzo(a)pyrene, were not abated by the Vortechnis® system. The overall removal effectiveness for PAH associated with settleable sediments was 19.9%. LMW PAH loaded sediment entering the Vortechs® settled predominantly in the first chamber (“Grit chamber”), whereas HMW PAHs were found in higher concentrations in sediments from Chamber 3 (“Flow control chamber”). Mass fluxes were calculated for PAH and metal compounds.

Nitrate concentration in the Vortechs® influent and effluent concentrations were similar. Phosphate was removed at near 36% efficiency and removal was most effective during the initial phase of the December storm, but decreased to zero at the end of the storm. Both, zinc and iron concentrations in the Vortechs® influent and effluent were similar, indicating insignificant removal of these two compounds. About 13% of the copper was removed. Lead concentrations were close to or below detection limit in both influent and effluent. Fecal coliform bacteria removal was comparably high, i.e. ranging from 50% to 88% during the three spring sampling events.