Assessing the Transport of Pharmaceutical Compounds in a Layered Aquifer Discharging to a Stream

Abstract

A groundwater plume containing high concentrations of pharmaceutical compounds, mainly sulfonamides, barbiturates, and ethyl urethane, in addition to chlorinated ethenes and benzene was investigated. The contamination originating from a former pharmaceutical industry discharges into a multilayered aquifer system and a downgradient stream. In this study, geological and hydrogeological data were integrated into a numerical flow model to examine identified trends using statistical approaches, including principal component analysis and hierarchal cluster analysis. A joint interpretation of the groundwater flow paths and contaminant concentrations in the different compartments (i.e., groundwater and hyporheic zone) provided insight on the transport processes of the different contaminant plumes to the stream. The analysis of historical groundwater concentrations of pharmaceutical compounds at the site suggested these compounds are slowly degrading. The pharmaceutical compounds migrate in both a deep semiconfined aquifer, as well as in the shallow unconfined aquifer, and enter the stream along a 2‐km stretch. This contrasted with the chlorinated ethenes, which mainly discharge to the stream as a focused plume from the unconfined aquifer. The integrated approach developed here, combining groundwater flow modeling and statistical analyses of the contaminant concentration data collected in groundwater and the hyporheic zone, lead to an improved understanding of the observed distribution of contaminants in the unconfined and semiconfined aquifers, and thus to their discharge to the stream. This approach is particularly relevant for large and long‐lasting contaminant sources and plumes, such as abandoned landfills and industrial production sites, where field investigations may be very expensive.

Groundwater–surface water interaction in Denmark

“…The dynamics of groundwater–surface water interaction also affect the transport of contaminant substances (Sonne et al, 2017) including pharmaceutical compounds (Balbarini et al, 2020). The discharge of contaminants driven by groundwater and its effect on the ecological status have also been investigated (Sonne et al, 2018), as has the natural attenuation occurring before groundwater is discharged to a stream reach (Ottosen et al, 2020), which was undertaken by monitoring a real case study in the area of Grindsted.…”

Natural attenuation of a chlorinated ethene plume discharging to a stream: Integrated assessment of hydrogeological, chemical and microbial interactions

“…The aquifer consists of a ~10 m thick Quaternary meltwater sand layer underlain by a ~70 m thick Miocene sand layer interbedded with clay and lignite. Near the stream, postglacial freshwater sand and peat deposits are present closest to the surface, and a clay and lignite layer separates the two sand layers into a shallow unconfined and a deep semi-confined aquifer (Maurya et al, 2018;Balbarini et al, 2020). On a local scale, the flow field goes from nearly horizontal at transect CP1 to nearly vertical at the streambed at transect 2 (Figure 1, Rønde et al, 2017).…”

“…A plume containing chlorinated ethenes, BTEX (benzene, toluene, ethylbenzene and o,m,p-xylenes) and pharmaceuticals discharges to Grindsted stream from an old factory site located 1.5 km north of the stream (Balbarini et al, 2020). A plume core approximately 50 m in width and 4 m in thickness, which consists mainly of cis-DCE and VC, was delineated along the north bank at transect CP1 (Rønde et al, 2017).…”

“…The pharmaceutical compounds were found to contribute to less than 1/3 of the DOC (Balbarini et al, 2020) (Table S3 and S10). Balbarini et al (2020) suggested that some degradation of the pharmaceuticals may occur in the plume core from the Grindsted factory site, despite that persistence of these compounds has been reported in the literature. The argument for this is the shortage of competing sources of nitrogen, sulphur and carbon, due to the prevalent redox conditions and low DOC content.…”