Wastewater-Treatment-Plant Effluent, Combined Sewer Overflows, and Urban Storm Runoff as Sources of Organic Compounds In the Lake Champlain Basin, Vermont

Some sources of organic wastewater compounds (OWCs) to streams, lakes and estuaries, including wastewater-treatment-plant effluent, have been well documented, but other sources, particularly wet-weather discharges from combined-sewer-overflow (CSO) and urban runoff may also be major sources of OWCs. Samples of wastewater-treatment- plant (WWTP) effluent, CSO effluent, urban streams, large rivers, an undeveloped (control) stream, and samples in Lake Champlain in New York and were collected from April through August 2006.

The highest concentrations of many OWCs associated with wastewater were in WWTP-effluent samples, but high concentrations of some OWCs in samples of CSO effluent and storm runoff from urban sites subject to leaky sewer pipes or CSOs were also detected. Total concentrations and numbers of compounds detected differed substantially among sampling sites. The highest total OWC concentrations (10 to 100 µg/L) were in samples of WWTP and CSO effluent. Total OWC concentrations in samples from urban streams ranged from 0.1 to 10 µg/L, and urban stormflow samples had higher concentrations than baseflow samples because of contributions of OWCs from CSO and leaking sewer pipes.

The relations between OWC concentrations in WWTP-effluent and those in CSO effluent and urban streams varied with the degree to which the compound is removed through normal wastewater treatment. Concentrations of compounds that are highly removed during normal wastewater treatment (including caffeine, Tris (2-butoxyethyl) phosphate, and cholesterol) were generally similar to or higher in CSO effluent than in WWTP effluent (and ranged from around 1 to over 10 µg/L) because CSO effluent is untreated, and were higher in urban-stream stormflow samples than in baseflow samples as a result of CSO discharge and leakage from near-surface sources during storms. Concentrations of compounds that are poorly removed treatment, by contrast, are higher in WWTP effluent than in CSO, due to dilution.