Flow of non‐aqueous phase liquids (NAPL) in the unsaturated zone is thought to be driven by gravity with a dominant vertical flow direction, and lateral spreading to be limited to the gradient of the relative permeabilities. The effect of soil profile build‐up, preferential flow, aging, and groundwater level fluctuations is mostly neglected. The objective of our study was to check the effects of such processes on the fate of NAPL in the unsaturated soil zone. At a hazardous waste site, we conducted a field survey of the unsaturated soil zone and monitored the groundwater for a two year period. We conducted spatially resolved and depth dependent soil sampling and analysis and the evaluation of former ram and core drilling protocols. The samples were analyzed for the 16 EPA PAH and alkanes with GC‐MS and GC‐FID. 13C‐NMR spectroscopy was used to assess structural changes of the NAPL phase. Flow of bulk NAPL along macropores and along preferential permeability structures, like sedimentation discontinuities, are the dominant transport pathways which cause large lateral spreading beyond those expected by the relative permeability gradient. Accumulation of NAPL was found at locations with abrupt textural changes and within the zone of capillary rise. Aging of NAPL results in the depletion in soluble and volatile compounds but also in oxidation and polymerization. It increases the chemical diversity and decreases the mobility of the NAPL. Thus, NAPL flow ceases much earlier than expected from the capillary forces. As chemical transformation is restricted to the NAPL water/air interface, a skin‐like thin film is formed which encapsulates and preserves the bulk NAPL from further hardening, limiting contaminant mass transfer from the NAPL to the aqueous phase.

Nitrous oxide emissions from urban wastewater were measured in a combined sewer in Bayreuth, Germany. The closed-chamber method was used to evaluate N 2 0 emissions. Nitrous oxide was analysed by gas chromatography with electron capture detector. Longitudinal and daily variations of N 2 0 fluxes were determined. N 2 0 emissions ranged from 0.1 1...3.8 mg mP2 h-I depending on the level of wastewater in the sewer. Data indicate that N 2 0 is mainly formed in the biofilm by nitrification and/or denitrification. In laboratory experiments, samples with wastewater and wastewater/biofilm mixture were incubated with and without NaCl. After two hours of incubation, N 2 0 release was in a range of 42 ... 429 ng N 2 0 per millilitre wastewater or wastewater/biofilm. Incubated samples without NaCl addition showed no significant difference between wastewater and wastewaterlbiofilm mixture. If salt (NaCI) was added before incubation, samples with wastewater/biofilm mixture emitted 4.8 times more N 2 0 than wastewater samples. It is assumed that high concentrations of NaCl inhibit further microbial reduction of N 2 0 to N2. Based on the field data, a first estimate for N 2 0 emission from sewers is 3.5 g N20 per year and person. Zusammenfassung: Lachgasemissionen aus stadtischem Abwasser wurden mit Hilfe der ,,closed-chamber"-Methode in einem Abwasserkanal (Mischkanalisation) in Bayreuth (Deutschland) ermittelt. Raumliche und zeitliche Variabilitat von Lachgasemissionen wurde bestimmt. Die Quantifizierung des Lachgases erfolgte an einem GC-ECD. Je nach Abwasserhohe im Kana1 konnten N20-Emissions-* Dip1.-Geookol.

Sewage containing volatile contaminants is a potential VOC-source in cities. Thus we tried to evaluate volatilization out of the sewerage system by measurements of contaminants in sewer gas and sewage. Our results from a medium sized town with little industry showed that sewer gas is mainly contaminated with alkanes, small aromatic compounds and chlorinated hydrocarbons. For three chlorinated hydrocarbons (chloroform, trichloroethene, tetrachloroethene) we determined mass transfer coefficients out of sewage and used these data to estimate mass fluxes from sewage and emissions out of the sewerage system for two sewer stretches. Considerable emission of chlorinated hydrocarbons from sewage, i.e. fluxes of some 10 to 100 g per m2·d, occurred only when the contaminant input via sewage was between some g and mg per litre for a single compound. For concentrations that were about 3 orders of magnitude less, emissions were negligible.

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A combined method of passive and active sampling of volatile organic compounds (VOCs) in a sewer system is presented. Passive sampling devices are used to locate and identify volatile organic compounds in the sewer atmosphere. Passive sampling is a time-integrating method and its results are only qualitative. To get quantitative information active sampling of wastewater is necessary. Concentrations of VOCs obtained from active sampling are used as input values for a simplified form of the two-film-model. This model allows to compute concentrations of VOCs at different points in a sewer stretch. We employed this method to describe the behaviour of volatile chlorinated hydrocarbons within a sewer stretch in Bayreuth, Germany.