Assessment of Stormwater Pond Performance through Water Quality Analysis and Hydrodynamic Modeling

Abstract

Traffic-related pollutants in stormwater runoff pose growing risks to aquatic ecosystems and human health. While stormwater ponds are commonly used to retain sediments, their efficiency in capturing emerging pollutants, such as tire wear particles (TWP), is less understood. This thesis combines field sampling and 3D hydrodynamic modeling to investigate pollutant retention and particle transport in a stormwater pond. For a field sampling campaign at a pond in Sweden, ISCO samplers were used to col lect water samples at inlet and outlet. Flow meters which monitored inflow and out flow during rain events were used and connected to the ISCO samplers to trigger sam pling at specific water flows. Laboratory analysis included pH, conductivity, suspended solids, nutrients, metals, and organic carbon. Results show that most pollutant loads are reduced through the pond, with outlet concentrations generally below guidelines. However, exceedances of total organic carbon and total nitrogen after long dry periods suggest pollutant build up between events. To further explore transport mechanisms, a 3D model of the pond was developed in MIKE 3 FM, simulating six scenarios: three with constant flow and three based on ob served rain events. Velocity patterns throughout the entire pond were analyzed based on hydrodynamic behavior. Particle tracking of particles with sizes and density of TWP was conducted for three scenarios to assess the behavior of size-defined particle classes under different hydrodynamic conditions. These results however were deemed unreli able as great mass losses were discovered when performing mass balance calculations. Whilst unreliable, the result from the particle tracking does indicated a strong size dependent settling pattern with larger TWP (100 µm) settling rapidly near the inlet, while finer TWP (10 µm) showed higher mobility, particularly under sustained or high inflow conditions. The results also indicates that rain intensity and wind affects the settling near the inlet. Overall, the study highlights the ponds’ capacity to retain coarse traffic-related parti cles, but also points to the need for more detailed modeling of finer particles. Recom mendations regarding management of pond and further investigation into pond perfor mance include careful vegetation management, and performing modeling that includes antecedent conditions and current vegetation near inlet, and also sensitivity analyses of particle properties to have an even better understanding of transport and sedimentation of emerging pollutants like TWP and microplastics.