Water Quality Performance of Dry Detention Ponds with Under-Drains

This research is a field evaluation of the water quality performance of dry water quality ponds with underdrains. The evaluation is performed in terms of pollutant retention by measuring concentrations in the inflow and outflow from the pond. Three dry detention ponds, MnDOT pond 4012-03, MnDOT pond 4012-04 and a pond operated by Carver County, were investigated for their ability to remove total phosphorus, dissolved phosphorus, total suspended solids and volatile suspended solids.

The measured influent concentrations of most parameters in storm water runoff at the Carver County dry detention pond with under-drains were substantially lower than concentrations typically mentioned in other studies throughout the nation and influenced the pollutant retention efficiency of the pond. This study confirmed that dry detention ponds with under-drains are an option for water quality control. The results of this study indicate that various storm water pollutants can be removed by dry detention ponds with under-drains.

A comprehensive comparison of pollutant retention efficiencies of various dry detention ponds throughout the nation is also carried out in this study. Comparison of these values with the retention efficiencies of this study indicated that the pollutant retention performance of the Carver County pond was below the average expected performance of dry detention ponds but well within the expected variation, even with the low influent concentrations at the Carver County pond. This is an indication that the under-drains do provide improved pollutant retention when used with a dry detention pond.