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Assessing redox conditions in soil and groundwater is challenging because redox reactions are oxygen sensitive, hence, destructive sampling methods may provide contact with air and influence the redox state. Furthermore, commonly used redox potential sensors provide only point measurements and are prone to error. This paper assesses whether combining electrical resistivity (ER) and self-potential (SP) measurements can allow the mapping of zones affected by anaerobic degradation. We use ER imaging because anaerobic degradation can release iron and manganese ions, which decreases pore water resistivity, and produces gas, which increases resistivity. Also, electrochemical differences between anaerobic and aerobic zones may create an electron flow, forming a self-potential anomaly. In this laboratory study, with four sand tanks with constant water table heights, time-lapse ER and SP mapped changes in electrical/electron flow properties due to organic contaminant (propylene glycol) degradation. Sampled pore water mapped degradation and water chemistry. When iron and manganese oxides were available, degradation reduced resistivity, because of cation release in pore water. When iron and manganese oxides were unavailable, resistivity increased, plausibly from methane production, which reduced water saturation. To bypass the reactions producing methane and release of metallic cations, a metal pipe was installed in the sand tanks between anaerobic and aerobic zones. The degradation creates an electron surplus at the anaerobic degradation site. The metal pipe allowed electron flow from the anaerobic degradation site to the oxygen-rich near surface. The electrical current sent through the metal pipe formed an SP anomaly observable on the surface of the sand tank. Time-lapse ER demonstrates potential for mapping degradation zones under anaerobic conditions. When an electrical conductor bridges the anaerobic zone with the near surface, the electron flow causes an SP anomaly on the surface. However, electrochemical differences between anaerobic and aerobic zones alone produced no SP signal. Despite their limitations, ER and SP are promising tools for monitoring redox sensitive conditions in unsaturated sandy soils but should not be used in isolation.

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Degradation of organic chemicals in natural soils depends on oxidation-reduction conditions. To protect our groundwater resources we need to understand the degradation processes under anaerobic conditions. Available iron and manganese oxides are used as electron acceptors for anaerobic degradation and are reduced to the dissolved form of metallic cations in pore water. To monitor this process is a challenge, because anaerobic conditions are difficult to sample directly without introducing oxygen. A few studies have shown an impact of iron reduction on spectral induced polarisation (SIP) signature, often associated with bacterial growth. Our objective is to study the impact of iron and manganese oxide dissolution, caused by degradation of an organic compound, with spectral induced polarisation signatures. Twenty-six vertical columns (30 cm high, inner diameter 4.6 cm) were filled with a sand rich in oxides (manganese and iron) with a static water table in the middle. In half of the columns, a 2 cm high contaminated layer was installed just above the water table. As the contaminant degrades, the initial oxygen is consumed and anaerobic conditions form Every three days over a period of one month, spectral induced polarisation (twenty frequencies between 5mHz and 10 kHz) data were collected on six columns: three contaminated replicates and three control replicates. Chemical analysis was done on twenty columns assigned for destructive water sampling, ten contaminated columns and ten control. The results show an increase of the real conductivity associated with the degradation processes, independent of frequency. Compared with the pore water electrical conductivity in the saturated zone, the real conductivity measurement revealed the formation of surface conductivity before iron was released in the pore water. In parallel, we also observed an evolution of the imaginary conductivity in both saturated and unsaturated zones at frequencies below 1 Hz. Overall, the anaerobic reduction of iron and manganese oxide during the organic degradation increased both the conductive and polarisation component of the complex conductivity.

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SUMMARY: Tracers should be used to monitor emissions of leachate from landfills, in order to evaluate environmental pollution. We investigated a selection of parameters commonly found in leachate, in addition to isotopic and radioactive tracers, and their efficiency in tracing leachate in the environment, with emphasis on groundwater. A study at 6 landfills focused on the occurrence of the isotopes 13C and 3H in leachate, surface and groundwater, in relation to the water balance at the sites. The content of heavy carbon (δ13C) in leachate varied between 5.5 to 25.5, in groundwater it reached 4.7 when polluted, and varied between -11.8 to -24.2 when unpolluted, and in surface water from -13.1 to -19.7. Measurements of tritium did not show any systematic trend in the leachate and groundwater samples. Also the elements Fe, B and Cr, and to a minor degree Mn and Zn, showed higher contrasts in leachate/groundwater concentrations. A comparison of the concentrations of tracer compounds with detailed estimation of the water balance at 3 landfills showed that 13C seems to be the most reliable tracer and the factor correlating best with estimates of diffuse losses of leachate to groundwater.

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For subsurface solute transport, flux concentrations are key, while usually resident concentrations are measured. Flux concentrations are frequently estimated from resident concentrations by temporal moment analysis. We tested this approach by simulating transport of an injected tracer during steady flow in an aquifer with a heterogeneous saturated hydraulic conductivity. We constructed grid-cell scale breakthrough curves (BTCs) from flux concentrations and approximate BTCs from resident concentrations and estimated flux concentrations. We assembled these BTCs into spatio-temporal leaching surfaces at various aquifer cross-sections for subsequent analysis. Resident concentrations were unsuitable to assess solute movement in the aquifer. Temporal moment analysis worked well when the entire aquifer cross-section was considered, but performed poorer at the grid-cell scale because it approximates the local velocity by the trajectory average. The leaching surfaces served as valuable tools to demonstrate and quantify the limitations of temporal moment analysis.

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I et stort datamateriale er det påvist at kulturlag i Nedre Langgate 43 i Tønsberg er bra bevart fra ca 1 meter dybde fra overflaten og ned til 4 meter. Dårlige bevaringsforhold er spesielt avdekket i den sørøstlige og nord-vestlige delen av tomten. Kulturlagene i 1,5 m dybde eller lavere ligger godt beskyttet mot nedbrytning, og sterkt reduserende miljøforhold tyder på at oksygen ikke når disse lagene. De beste bevaringsforhold ble funnet i kulturlag under den tidligere kjelleren. Undersøkelsen har vist at jordkjemisk data fra flere borehull vil kunne gi overveiende forståelse over ei tomts innhold av organisk materiale og redokssensitive parametre som påvirker beskyttelse av kulturlag. Geofysisk kartlegging viste nye fordeler ved at målinger utføres uten fysisk inngrep i grunnen og uten å påvirke kulturlagene. Metoden ga opplysninger om tette lag med høyt vanninnhold i kulturlag øst og nord-øst for den tidligere kjelleren og et større område med tørrere, porøse masser i den sør-østlige delen av tomten. Kartleggingen bekrefter resultatene fra jordkjemisk analyse og modellering.