Trap Efficiency of a Small Constructed Wetland

When Wal*Mart Stores, Inc. proposed building a store in West Lafayette, Indiana, on commercially-zoned land, the company encountered opposition from area residents, primarily because the site bordered a wetland the community wanted to see developed into a habitat for indigenous species. Concerns over impacts of additional impervious areas on the quantity and quality of runoff prompted Wal*Mart to build an on-site biofiltration pond, a constructed wetland to treat nonpoint source (NPS) pollution in the first 1.27 cm (0.5 in) of runoff from the store's parking lot. To assess the chemical and sediment trap efficiency of this stormwater detention biofiltration pond, samplers were installed at the inlet and outlet. The purpose of sampling is to ascertain whether the constructed wetland is performing to specifications and to determine how performance varies seasonally as well as over a series of years as the wetland vegetation matures. Instruments at the inlet and outlet automatically measure water level, flow, pH, temperature, conductivity, and dissolved oxygen, and take water samples when a storm occurs. Samples are analyzed for common road contaminants such as salts and heavy metals. This approach provides more accurate data than standard "grab" analyses, as well as new insight into seasonal and long-term performance of constructed wetlands.