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The effects of adding oxygen to anaerobic aquifer materials on biodegradation of phenoxy acid herbicides are studied by laboratory experiments with aquifer material from contaminated sites. The results suggest that stimulated biodegradation by addition of oxygen might be a feasible remediation technology at herbicide-contaminated sites, although oxygen consumption by the sediment could limit the applicability.

Research indicates that the exposure of a Danish subsurface aquifer to phenoxy acid herbicides at less than 40 microgram per litre alters the composition of microbial population. In herbicide-exposed sediments microbial phenoxy acid degraders are abundant as determined by the detection of herbicide degrading genes in the microbial population from contaminated areas of the aquifer.

Introduction In the past, landfills typically were constructed without liners or other measures to prevent release of leachate into the subsurface. Leachate from these old landfills can be highly variable [...]

H2 concentrations in the Grindsted Landfill in Denmark ranged from 0.004 to 0.88 nM. An alternative partial equilibrium approach of combining the measured H2 and the terminal electron-accepting processes (TEAPs) into an actual potential in situ energy yield proves useful in explaining the occurrence of concomitant TEAPs. Fe reduction was found to be the most dominant TEAP, but concomitant methanogenesis and sulfate reduction were observed as well.

Nitroaromatic compounds (NACs) proved useful in the characterization of predominant reductants such as Fe(II) in an anaerobic leachate-contaminated aquifer. The NACs were transformed into aromatic amines within 2-70 days in the leachate plume as well as in microbially active and microbially deactivated experiments. Results revealed that Fe(II) associated with ferric iron minerals can be used as a highly reactive reductant in anaerobic aquifers.

The first-order degradation rate constants of benzene, toluene, o-xylene, nitrobenzene, naphthalene, biphenyl, o- and p-dichlorobenzene, 1,1,1-trichloroethane, tetrachloromethane, trichloroethene, tetrachloroethene, phenol, o-cresol, 2,4- and 2,6-dichlorophenol, 4,6-o-dichlorocresol and o- and p-nitrophenol in an aerobic aquifer were determined using in situ and laboratory batch microcosms. First-order degradation rate constants for aromatic and phenolic hydrocarbons were within the 0.01 and 0.9 day range. No systematic differences were noted between rate constants determined in situ and in the laboratory.

The vertical transport of contaminants from source areas is employed in many risk assessment models and screening tools in order to estimate the contaminant mass discharge (CMD) into underlying aquifers. The key parameters for estimating CMD are the contaminant source area and concentration, and the vertical water flux, the latter of which depends on the vertical hydraulic conductivity and the vertical hydraulic gradient in the subsurface. This study focuses on advancing the use of the combined membrane interface probe hydraulic profiling tool (MiHPT) to investigate the vertical hydraulic gradient across a clay till overlying a sandy aquifer at a contaminated site in Denmark. Only the HPT is necessary for the estimate of vertical hydraulic gradient. The hydraulic head, clay till thickness, and resulting vertical hydraulic gradients found using the MiHPT compared well with observations from nearby nested wells. The parameter with the largest discrepancy was the thickness of the clay till. The advantage of the MiHPT is its relatively quick depth discrete access to information regarding subsurface permeability, vertical hydraulic gradients and contaminant distribution across a site. In this case study, performance of additional dissipationtests during the HPT log to acquire determination of the vertical hydraulic gradient increased the cost by 3% compared to standard HPT logs. Article Impact Statement: Using a MiHPT it is possible to determine the vertical hydraulic gradient from a clay till aquitard to the underlying groundwater aquifer. [ABSTRACT FROM AUTHOR]

The leachate plume stretching 30m along the Grindsted Landfill in Denmark contains high concentration of pharmaceutical compounds from the landfill's groundwater downgradient. The kinds of pharmaceutical compounds have expanded from sulfonamides in the 1930s to barbiturates in the 1970s. However, a survey of the landfill revealed natural reduction in the concentration of pharmaceutical compounds despite the increased use of drugs because of rapid aerobic degradation, dilution and sorption. The attenuation prevents concentrations of pharmaceutical wastes from rising from 50m of the landfill.

A study was conducted to identify the parameters which influence redox-sensitive groundwater flow in a landfill leachate plume in Grindsted, Denmark. Analysis of trace metals present in the water indicated high methane production and reduction in iron, sulfate, manganese and nitrate in the plume. The landfill contained rich methanogenic and sulfate-reducing zones, while high aerobic activity was observed in areas far from the landfill. In between the two were areas called transition zones.

The leachate plume stretching 300m along the Grindsted Landfill in Denmark exhibited a natural reduction of organic compounds because of increased degradation. The groundwater was rich in organic compounds including benzene, toluene, ethylbenzene and xylenes. High aerobic activity in the surrounding areas of the plume significantly reduced amount of organic compounds from 60m of the plume. Pesticides were also absent within the immediate vicinity of the landfill because of active degradation.

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. Article impact statement: Semipersistent pharmaceutical compounds resulted in long‐term groundwater and stream water risks. [ABSTRACT FROM AUTHOR]