SPATIAL AND TEMPORAL EVALUATION OF STORMWATER POND PERFORMANCE IN DISTRIBUTION OF CONDUCTIVITY AND CHLORIDE CONCENTRATIONS

Reliable performance of stormwater detention ponds is crucial in controlling excess stormwater runoff by absorbing precipitation and slowing down surges that can lead to flooding. Stormwater detention ponds also serve to improve water quality to nearby waterways by removing pollutants. Overtime the performance of stormwater ponds can degrade for a variety of reasons. Additionally, in regions with cold climates the performance of stormwater ponds can differ between winter and summer due to large volumes of water from snowmelt with a relatively high pollutant load. Cold winters may also cause the inlet and outlet areas to freeze. With these things in mind, we sought to evaluate the performance of a stormwater detention pond system on the GVSU campus in Allendale, MI twelve years post construction and during a winter season. Beginning in November 2022, samples were collected from 4 connected flow-through detention ponds on campus. Samples were collected roughly weekly from each pond over the winter months with collection still ongoing. Water temperature, specific conductivity, total dissolved solids, and oxidation-reduction potential were analysed using a Myron L Ultrameter II. Samples were also analysed for chloride concentration by titration. Results show spatial and temporal differences in distribution of conductivity and chloride. Conductivity and chloride are elevated and generally observed to be highest in pond 1 at the stormwater inlet (average conductivity 1116 uS/cm; average chloride 214 ppm) and lowest in pond 4 at the system outlet (average conductivity 488 uS/cm; average chloride 67 ppm). Other measured parameters show the similar trends and indicate the stormwater system is still performing reliably. Data also indicate that during cold weather there is an apparent lowered removal efficiency in the system due to a combination of ice cover, cold water and de-icing salts and likely a change in pond hydraulics with the change in seasons.