The uncertainty of biodegradation rate constants of emerging organic compounds in soil and groundwater - A compilation of literature values for 82 substances.

The present study reports on biodegradation rate constants of emerging organic compounds (EOCs) in soil and groundwater available in the literature. The major aim of this compilation was to provide an assessment of the uncertainty of hydrological models with respect to the fate of EOCs. The literature search identified a total number of 82 EOCs for which 1st-order rate constants could be derived. It was found that for the majority of compounds degradation rate constants vary over more than three orders of magnitude. Correlation to factors that are well known to affect the degradation rate, such as temperature or redox condition was weak. No correlation at all was found with results from available quantitative structure-activity relationship models. This suggests that many unknown site specific or experimentally specific factors influence the degradation behavior of EOCs in the environment. Thus, local and catchment scale predictive models to estimate EOC concentration at receptors, e.g., receiving waters or drinking water wells, need to consider the large uncertainty in 1st-order rate constants. As a consequence, applying rate constants that were derived from one experiment or field site investigation to other experiments or field sites should be done with extreme caution.

The fate of organic micropollutants during long-term/long-distance river bank filtration.

The fate of organic micropollutants during long-term/long-distance river bank filtration (RBF) at a temporal scale of several years was investigated along a row of monitoring wells perpendicular to the Lek River (the Netherlands). Out of 247 compounds, which were irregularly analyzed in the period 1999-2013, only 15 were detected in both the river and river bank observation wells. Out of these, 10 compounds (1,4-dioxan, 1,5-naphthalene disulfonate (1,5-NDS), 2-amino-1,5-NDS, 3-amino-1,5-NDS, AOX, carbamazepine, EDTA, MTBE, toluene and triphenylphosphine oxide) showed fully persistent behavior (showing no concentration decrease at all), even after 3.6 years transit time. The remaining 5 compounds (1,3,5-naphthalene trisulfonate (1,3,5-NTS), 1,3,6-NTS, diglyme, iopamidol, triglyme) were partially removed. Their reactive transport parameters (removal rate constants/half-lives, retardation coefficients) were inferred from numerical modeling. In addition, maximum half-lives for 14 of the fully removed compounds, for which the data availability was sufficient to deduce 100% removal during sub-surface passage, were approximated based on travel times to the nearest well. The study is one of very few reporting on the long-term field-scale behavior of organic micropollutants. It highlights the efficiency of RBF for water quality improvement as a pre-treatment step for drinking water production. However, it also shows the very persistent behavior of various compounds in groundwater.

An integrated laboratory method to measure and verify directional hydraulic conductivity in fine-to-medium sandy sediments.

The constant-head permeameter test (CHPT) is widely used in sandy samples as a standard method in the laboratory to investigate hydraulic conductivity (K). However, it neither can be used to consistently determine directional hydraulic conductivity (DHC) nor guarantee the comparability of measured K values of samples with different sizes. Therefore, this paper proposes an integrated laboratory method, called modified CHPT (MCHPT), for the efficient determination and verification of consistent DHC values in fine-to-medium sandy sediments, based on a new methodological framework. A precise and standardized procedure for preparing the experimental setup of MCHPT was conducted, based on the integrated experimental setup of CHPT and tracer tests. Moreover, a formula was yielded for the time-optimized sample saturation control. In comparison with grain size-based methods, the validity of consistent Kh and Kv values determined by MCHPT was convincing.

Fate of para-toluenesulfonamide (p-TSA) in groundwater under anoxic conditions: modelling results from a field site in Berlin (Germany).

This article reports on a field modelling study to investigate the processes controlling the plume evolution of para-toluenesulfonamide (p-TSA) in anoxic groundwater in Berlin, Germany. The organic contaminant p-TSA originates from the industrial production process of plasticisers, pesticides, antiseptics and drugs and is of general environmental concern for urban water management. Previous laboratory studies revealed that p-TSA is degradable under oxic conditions, whereas it appears to behave conservatively in the absence of oxygen (O2). p-TSA is ubiquitous in the aquatic environment of Berlin and present in high concentrations (up to 38 µg L(-1)) in an anoxic aquifer downgradient of a former sewage farm, where groundwater is partly used for drinking water production. To obtain refined knowledge of p-TSA transport and degradation in an aquifer at field scale, measurements of p-TSA were carried out at 11 locations (at different depths) between 2005 and 2010. Comparison of chloride (Cl(-)) and p-TSA field data showed that p-TSA has been retarded in the same manner as Cl(-). To verify the transport behaviour under field conditions, a two-dimensional transport model was setup, applying the dual-domain mass transfer approach in the model sector corresponding to an area of high aquifer heterogeneity. The distribution of Cl(-) and p-TSA concentrations from the site was reproduced well, confirming that both compounds behave conservatively and are subjected to retardation due to back diffusion from water stagnant zones. Predictive simulations showed that without any remediation measures, the groundwater quality near the drinking water well galleries will be affected by high p-TSA loads for about a hundred years.