New Methodology for Efficient Management of Chloramine Concentrations in Stormwater Systems

Abstract

Polluted urban stormwater effluents pose risks to receiving watercourses. Many municipalities have concerns about point-source releases of chloramine-treated drinking water that reach the drainage system through outdoor and industrial water uses. Since chloramine decay coefficients vary temporally and spatially, no available stormwater model can simulate them accurately. Therefore, a novel stormwater quality model (VDCS) is introduced to simulate chloramine decay. The model considers the variability of chloramine decay using three decay settings, as defined by the user: constant, land-use specific, and temporally and spatially-varying decay coefficients. The model was validated using the results of field sampling and MIKE URBAN simulations. Variable chloramine decay coefficients generated 67% and 100% higher concentrations than the constant decay coefficient. A new approach to develop water quality maps was introduced that shows the levels of chloramine at the system outlet as a result of point-source releases occurring anywhere in the stormwater system. The VDCS model along with MIKE URBAN and Arc-GIS were used to develop chloramine concentration maps for a case study stormwater basin in Edmonton. A practical fire hydrant discharge of 1.0 m3/s was used as a reference case under different dry and wet weather conditions. The Bayesian Kriging Method was used to generate the water quality maps using outputs of the stormwater hydraulic and quality models. For dry weather flows, results showed that chloramine concentrations were above limits over the entire basin, and only a design storm of a 10-year return period produced chloramine concentrations below regulation discharge limits. Overall, concentration maps provide a stand-alone tool that can help system operators to manage stormwater pollution without performing time- and labour-intensive simulations.