Stormwater ponds as a source of long-term surface and ground water salinisation

We investigated the spatial and temporal distribution of chloride and conductivity in a long hydroperiod retention pond and two short hydroperiod detention ponds. In both cases we observed greatly elevated conductivities in surface and ground waters with peak conductivities exceeding 45 mS cm−1 in the retention pond and 25 mS cm−1 in one detention pond. Pond ground water conductivity remained highly elevated into the summer months and never declined to local stream conductivity levels. Conductivity and chloride concentrations were also elevated in floodplains adjacent to all ponds throughout the year. First order streams draining the detention pond floodplain were consistently elevated in conductivity and were a year-round net source of ions to the second order stream into which they flowed. These results indicate that both short and long hydroperiod stormwater ponds have the potential to serve as long-term, year round sources of chloride to adjacent surface and ground waters.