Geophysics‐Based Contaminant Mass Discharge Quantification Downgradient of a Landfill and a Former Pharmaceutical Factory

Abstract

Contaminant mass discharge is a commonly applied tool to evaluate the environmental impact of contaminated sites on water resources. At large contaminated sites with heterogeneous sources, such as landfills, the number of wells available is often not sufficient, leading to a high uncertainty of mass discharge estimates. In this study, we tackle the uncertainty of the contaminant mass discharge due to low sampling densities by interpolating limited water‐sample data with the support of surface direct current resistivity and induced polarization geophysical data. The method relies on finding a conceptual link between the bulk conductivity imaged from geophysics and the contaminant concentrations. We investigate the link between (1) imaged bulk and electrical water conductivity, (2) water conductivity and conservative ionic species, (3) water conductivity and redox‐sensitive species, (4) water conductivity and semipersistent organic species, and (5) water conductivity and biodegradable organic compounds. The method successfully identify similarities between the distribution of the bulk conductivity and chloride and pharmaceutical compounds in a landfill leachate plume and between the bulk conductivity data and benzene and chlorinated ethenes for a contaminant plume from a former pharmaceutical factory. Contaminant concentrations were interpolated through regression kriging, using geophysical data as the dependent variable. The distribution of concentration determined with the novel method showed a lower mean relative estimation error than the traditional method of kriging only contaminant concentration data. At large sites, the method can improve contaminant mass discharge estimates, especially if surface geophysical measurements are integrated in the site investigation at an early stage.

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

“…Note that degradation will not be a limitation as long as the compounds remain, however, it may be difficult to apply the method if the composition of compounds in the plume changes due to, for example, sequential degradation. For instance, the method could not be applied for the chlorinated ethenes due to reductive dechlorination taking place in the aquifer somewhere between the source and the stream (Rønde et al ; Balbarini et al ).…”

“…Groundwater and hyporheic zone water samples collected below the streambed showed that groundwater contaminated by pharmaceutical compounds discharges along a 2‐km stretch of the stream (Rasmussen et al ; Sonne et al ). A discharge area (red rectangle in Figure ) with high groundwater concentrations of benzene, chlorinated ethenes, mainly cis DCE ( cis ‐1,2‐dichloroethene) and vinyl chloride (VC), and pharmaceutical compounds was found (Rønde et al ; Sonne et al ; Balbarini et al ). Outside this area, chlorinated ethenes were only found to enter the stream in low concentrations, in contrast to the pharmaceutical compounds, which entered the stream over a larger area (Sonne et al ).…”

“…Outside this area, chlorinated ethenes were only found to enter the stream in low concentrations, in contrast to the pharmaceutical compounds, which entered the stream over a larger area (Sonne et al ). Chlorinated ethenes are affected by reductive dechlorination in the strongly reduced parts of the plume (Rønde et al ; Balbarini et al ).…”

“…Postglacial freshwater sand and peat deposits overlie the meltwater sand deposits close to the stream. Below this, there is a Miocene Odderup sand layer (Heron et al ; Balbarini et al ; Maurya et al ). The top of the Miocene sand deposits can be found between 30‐ and 25‐m asl.…”

“…To date, pharmaceutical plumes originating from landfills have only been investigated in a few studies (Eckel et al ; Holm et al ; Barnes et al ; Buszka et al ). As an example, the plume at Grindsted landfill in Denmark discharges more than 1000 kg/year of sulfonamides and barbiturates into the surrounding groundwater (Balbarini et al ). The landfill studies reveal that the pharmaceutical compounds seem to pose a severe risk for groundwater and surface water compared to more degradable compounds usually studied at contaminated sites, although some degradation occurred.…”