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MONITORING OF A BEST MANAGEMENT PRACTICE POND
Citation:
O'CONNOR, T. MONITORING OF A BEST MANAGEMENT PRACTICE POND. Presented at 2005 Pennsylvania Stormwater Management Symposium, Villanova, PA, October 12 - 13, 2005.
Impact/Purpose:
To inform the public
Description:
The USEPA's Urban Stormwater Management Branch has monitored stormwater drainage and best management practices (BMP) as part of its research program. One BMP being monitored, a wetland/retention pond, is in the Richmond Creek (RC) watershed in the New York City Department of Environmental Protection's Bluebelt program, which incorporates BMPs on a watershed basis. The BMP, designated RC-5, removed suspended solids (SS), but not chemical oxygen demand (COD). Calculated SS loads demonstrated a 61% removal in excess of anticipated removals of 55-57%. Of three events monitored for COD, one had no removal, the second negative 146%, and the third 37%. This increase in COD during the second event may be due to biological activity in RC-5, and seasonal considerations, i.e., decaying leaves and wetland vegetation going into dormancy. The largest SS and COD discharges occurred on 12/11/03, which was the largest rain (>1 in.) and flow event monitored. As part of this monitoring effort, continuous monitoring equipment indicated concentrations of ammonium (NH4+) exceeded 2 mg/l, with a maximum concentration of 8 mg/l recorded. These observations happened between 12/5/03 and 12/11/03 after a snow event on 12/5/03 and 12/6/03. Increased conductivity was measured at the influent to RC-5 contrary to typically low conductivity readings after precipitation. Deicers (sodium chloride) spread on the roadway most likely caused increased NH4+ readings, as sodium ions are a known interference. A controlled laboratory experiment was performed to determine whether decaying leaves may have contributed to these elevated NH4+ readings. Decaying leaves did increase NH4+ concentrations, but not at rates measured in the field. However, the high COD effluent loading discharged on 12/11/03 was initially attributed to leaf decay; the NH4+ data from the controlled experiment appears to support this explanation.