Optimized flux estimation of a sulfonamide contaminant plume discharging to a stream using fluorescence screening

Sulfonamides are widely used antiobiotics and a threat to water resources and related ecosystems. While the direct discharge from untreated sewer or wastewater to surface water is a well-known pathway to the aquatic environment, only a limited number of studies have looked at the discharge and fate of sulfonamides from a contaminant plume to surface water so far.

In this study, we investigated a sulfonamide contaminant plume discharging to a stream in Denmark. The sulfonamides (originating from a former production facility), are transported through a multilayered sandy aquifer and discharge to a groundwater-fed stream located down gradient. Our objectives were to evaluate if a screening using fluorescence properties could be used to delineate the sulfonamide contaminant plume and support the contaminant mass discharge estimation (both by transect method and in-stream measurements).

Direct push technics in combination with a fluorescence screening allowed a relatively unexpensive coarse delineation of high concentrations areas (as opposed to laboratory analysis) down to 15 m.b.g.s. and ergo optimization of monitoring wells / screen locations in the transect. Chemical analyses were combined with slug test and hydraulic gradient estimates via continuous monitoring to quantify the sulfonamide flux and its temporal variations in a 2 km-long transect along the stream (24 monitoring wells with 3 - 6 screens).

The estimated sulfonamide mass discharge (transect based) is in good agreement with the mass discharge calculated from in-stream measurements, highlighting the relevance of the screening approach to select appropriate measurement point locations. Furthermore, the comparison between the flux in both stream and groundwater compartments shows that the degradation of sulfonamides seems relatively limited in the near-stream and hyporheic zone, with the exception of the sulfanilic acid. The results of this study will be used for the prioritization of remedial actions along the main discharge zones.