ULTRA-TRACE LEVELS OF EMERGING CONTAMINANTS IN A HEAVILY-USED, URBAN GROUNDWATER SYSTEM (Invited Presentation)

Groundwater resources in urban areas are susceptible to contamination from aging sewer systems, and subsurface exfiltration of raw sewage is of particular concern where groundwater is used for water supply. Emerging wastewater tracers, such as pharmaceutical and personal care compounds, artificial sweeteners, and human-specific pathogens and hormones hold significant promise for identifying impacts from leaky sanitary sewers.

We evaluated the presence of emerging contaminants, common to wastewater, in groundwater within a densely-sewered urban area in Wisconsin, USA. The groundwater system is heavily pumped, consisting of a regionally extensive, sedimentary sequence of aquifers and aquitards. Monitoring wells ranging from 9.5 to 80.2 m depth were sampled for a wide variety of organic and inorganic constituents and human enteric viruses. Laboratory techniques included use of high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), which provided detection limits for some organic compounds as low as 10^-9 g/L. All wells tested were positive for at least one organic compound. Carbamazepine, sulfamethoxazole, and artificial sweeteners acesulfame and cyclamate, were the most frequently detected. Seventy percent of the wells tested for pathogens were virus-positive on at least one occasion. None of the wells were positive for steroidal hormones.

The data reveal the widespread presence of wastewater constituents at significant depths within the groundwater system, suggesting that sewer exfiltration affects groundwater in this hydrogeologic setting. Sampling for a subset of these constituents over time may assist in monitoring sewer system infrastructure and help prioritize repair and replacement efforts. While pathogens, even at extremely low concentrations, can cause water-borne disease, implications for public health from the organic wastewater contaminants are not clear. The concentrations detected were orders of magnitude lower than those in medication and processed foods, but their presence in groundwater could erode public confidence in the safety of municipal water supplies.