Performance evaluation of stormwater treatment controls at an industrial site

Abstract

Discharges from industrial activities may contain various hazardous pollutants including metals, oils and grease, organic toxicants, chemical oxygen demand, nutrients and suspended sediment. Limited information is available on the characteristics of the pollutant constituents that affect treatment and treatment technologies that can effectively treat the runoff from industrial activities. Understanding the association of contaminants with different particle sizes is important for determining suitable treatment controls. The primary objective of this research was to evaluate the performance of treatment controls (a pre-treatment hydrodynamic separator device followed by a dry infiltration pond) at a heavy industrial site and describe the pollutant characteristics that affect stormwater treatability for different flow conditions. Water quality monitoring through a seven month monitoring period showed that suspended sediment concentrations (SSC), COD, nutrients, and heavy metals were commonly found in the industrial runoff. Multivariate analyses were performed to identify the correlations between site hydrological and water quality parameters. The calculations showed strong correlations between hydrological parameters. Strong correlations were also observed between suspended sediment and metal concentrations. Treatment performance was evaluated based on the particle size distributions using several data exploratory methods. These showed that the hydrodynamic separator device had low to moderate reductions for SSC and low reductions for metals. The Hydrodynamic separator device also showed moderate reductions for particle sizes greater than 12 µm. The dry infiltration pond showed very high removals for particulate solids concentrations and mass, medium to high removals for heavy metal concentrations and high removals for masses of the metals. Significant moderate to high reductions in concentration and mass were observed for particle sizes greater than 3µm. The dry pond also showed high runoff reductions (75 to 100%) for storm events smaller than 1.5 inches and associated high removals of pollutant masses for all constituents and moderate runoff reductions (about 50%) for events greater than 1.5 inches. As part of this research, groundwater contamination potential was evaluated based on measured metal concentrations in the soil profile under the dry infiltration pond and by using a water chemistry vadose zone fate model. The results indicated high retention capacity of both particulate-bound and filtered metals in the surface soils in the pond. Vadose zone chemical fate modeling showed retention of metals to the soils at depths well above the water table. However, the increased runoff entering the pond greatly accelerates the pollutant migration in the subsurface, with metals potential reaching about a meter below the ground surface during a 50 year operational period. Other pollutants having greater mobility (such as nitrates) could reach the several meter deep water table quickly and, if present in problematic concentrations, result in potential groundwater contamination.