Eduard Hoehn

Behavior of Organic Compounds during Infiltration of River Water to Groundwater. Field Studies

The behavior of organic micropollutants during infiltration of river water to groundwater has been studied at two field sites in Switzerland. In agreement with predictions from model calculations, persistent organic chemicals exhibiting octanol/water partition coefficients smaller than about 5000 moved rapidly with the infiltrating river water to the groundwater. The biological processes responsible for the “elimination” of various micropollutants (e.g., alkylated and chlorinated benzenes) occurred predominantly within the first few meters of infiltration. Alkylated benzenes were “eliminated” at faster rates than 1,4-dichlorobenzene. Anaerobic conditions in the aquifer near the river hindered the biological transformation of 1,4dichlorobenzene. Among the compounds that were found to be persistent under any conditions were chloroform, l,l,l-trichloroethane, trichloroethylene, and tetrachloroethylene. With respect to such chemicals, bank filtration is ineffective as a first step in the treatment of river water for water supplies. Since in many European countries a significant fraction of the groundwater is recharged through infiltration of river water (1,2), the impact of river pollution on groundwater quality is of major concern. In addition, many waterworks use natural or artificial bank filtration as a first step in the treatment of river water for water supplies (3, 4). Therefore, the behavior of organic pollutants during infiltration is of great interest. The transport and fate of organic pollutants in a river water-groundwater infiltration system is determined by several interacting processes, including advection, dispersion, (ad)sorption/desorption, hydrolysis, redox reactions, and biological transformations. In laboratory experiments, individual processes may be studied under controlled conditions (5,6), and mathematical models may be developed to predict the effect of a particular process on the transport and fate of a compound in the environment (7,8). However, comprehensive field investigations are needed to evaluate the applicability of laboratory studies and model calculations to natural systems. To date, most of the field studies on natural river water-groundwater infiltration systems have been conducted with respect to the use of bank filtrate for public water supplies (e.g., ref 3). These studies have usually been confined to monitoring selected water constituents in the river and in groundwater wells near the region of infiltration. The temporal and spatial variations in concentration of organic compounds along the infiltration path have not been thoroughly investigated. Consequently, the results of such investigations provide only very limited insights into the behavior of individual compounds during infiltration. In this paper, we report the results of two field studies aimed at investigating the transport and fate of organic micropollutants, including chlorinated hydrocarbons, alkylated benzenes, and chlorinated phenols during natural infiltration of river water to groundwater. In the near

Patchiness of River–Groundwater Interactions within Two Floodplain Landscapes and Diversity of Aquatic Invertebrate Communities

Abstract In fluvial systems, the interactions between rivers and groundwater significantly affect various ecological structures (for example, riparian vegetation) and functions. To examine the effects of hydrological exchange between groundwater and surface water on the distribution of aquatic invertebrates within a riverine landscape, we investigated the main stem, tributaries, and various surface and subsurface waters of two floodplains of a southern Alpine river (Brenno, Switzerland) in terms of their physicochemical, hydraulic, substratum, and faunal characteristics. The origins of the water were investigated by analyzing geomorphic settings and physicochemical variables. The two floodplains had different hydrological regimes. The middle floodplain was dominated by lateral inputs and exfiltration of hillslope groundwater from two different subcatchments. Bank filtration of river water sustained subsurface water only close to the channel. The aquatic habitats of the middle floodplain formed a rather homogeneous group with high taxon richness and intrahabitat diversities. These aquatic habitats resembled mountain springbrooks in their physicochemical characteristics and faunal compositions. In the lower floodplain, the exchange between river water and groundwater was more extensive. The aquatic floodplain habitats of the lower floodplain were fed mainly by deep and shallow alluvial groundwater, hyporheic exfiltration, and partly by surface water. In contrast to aquatic habitats of the middle floodplain, habitats of the lower floodplain showed a low intrahabitat and a high interhabitat diversity in terms of both substrate characteristics and faunal compositions. For both floodplains, ordination analyses showed a high concordance between the structure of the invertebrate community and the characteristics of the environmental habitat, including chemical, geomorphic, and hydraulic variables. Ordinations grouped aquatic habitats according to the origins of the waters. Taxon richness was related to local structural diversity, but species turnover was related to differential vertical and lateral connectivity. Exfiltration of groundwaters provided aquatic floodplain habitats for several specialized species. The results of this study show the significance of the river–groundwater connectivity for the creation of the habitat mosaic that sustains biodiversity in floodplains and thus have important implications for managing the ecological integrity of floodplains.

Ground water pollution by roof runoff infiltration evidenced with multi-tracer experiments

The infiltration of urban roof runoff into well permeable subsurface material may have adverse effects on the ground water quality and endanger drinking water resources. Precipitation water from three different roofs of an industrial complex was channelled to a pit and infiltrated into a perialpine glaciofluvial gravel-and-sand aquifer. A shaft was constructed at the bottom of the pit and equipped with an array of TDR probes, lysimeters and suction cups that allowed measuring and sampling soil water at different depths. A fast infiltration flow was observed during natural rainfall events and during artificial infiltration experiments. For a better understanding of the behaviour of contaminants, experiments were conducted with cocktails of compounds of different reactivity (ammonium, strontium, atratone) and of non-reactive tracers (uranine, bromide, naphthionate), which represent different classes of pollutants. The experiment identified cation exchange reactions influencing the composition of the infiltrating water. These processes occurred under preferential flow conditions in macropores of the material. Measuring concentration changes under the controlled inflow of tracer experiments, the pollution potential was found to be high. Non-reactive tracers exhibited fast breakthrough and little sorption.

Hydrogeological Issues of Riverbank Filtration — A Review

Engineers and scientists are faced with the problem of the behavior and fate of contaminants during the infiltration of river waters to groundwater. Sontheimer [1], e.g., found that induced bank filtration resulted in the elimination of some of the contaminants and could thus be considered as the first treatment step for the production of drinking water from river water. If rivers that naturally lose water to aquifers are contaminated, e.g., from outlets of sewage treatment plants, then the groundwater may become contaminated, too (e.g., Schwarzenbach et al. [2]). The quality of the water, which is freshly infiltrated from the river, revealed to be strongly dependent on the residence time and the mixing rate of river water and deeper groundwater. In a few infiltration systems, some contaminant compounds could partly be eliminated from the aquatic environment, and the quality of river water has somewhat improved (e.g., von Gunten and Lienert [3]). Today’s concerns are broader than looking at the water quality. The state of the groundwater/surface water ecosystem and its evolution in the future is of interest. In many floodplains, the state of riverbeds and banks is far from being natural (e.g., Brunke and Gonser [4]; Bencala [5]). Various forms of land use, such as hydropower generation, flood prevention, or the need of arable land, require a safe and defined bank line and a channeled riverbed. These requirements are in conflict with the needs of the vegetation and animals at the bank and in the bed of rivers (riparian zone).

The Behaviour of Organic Pollutants in a Natural River – Groundwater Infiltration System

Publisher Summary The fate of organic pollutants during groundwater infiltration is of great interest because many waterworks use bank filtration as the first step in the treatment of river water for public water supplies. To elucidate the processes responsible for the behavior of organic substances during infiltration, laboratory studies and field measurements are necessary. This chapter reviews some of the results of an ongoing field study on the behavior of volatile organic pollutants and dissolved organic carbon (DOC) fractionated with a new method in a natural river–groundwater infiltration system. The volatile organic compounds in river and groundwater samples are enriched by the closed-loop gaseous stripping/adsorption/elution procedure described by Grob and Zurcher. Gas chromatography and gas chromatography/mass spectrometry (GC/MS) are used for quantification and identification. The DOC fractionation is based on the different adsorption behavior of the organic compounds present in the water on a nonpolar surface. With this new method, the DOC is separated into three fractions: (1) hydrophilic at pH 2 (not adsorbed on RP-18), (2) hydrophobic at pH 2 (adsorbed on RP-18) and hydrophilic at pH 8 (eluted with buffer solution), and (3) hydrophobic at pH 2 and PH 8 (adsorbed on RP-18 eluted with organic solvents).

Datenerhebung bei Grundwasseruntersuchungen

Daten zur Erkundung des Grundwassers werden mit Methoden erhoben, die in den Untergrund nicht eindringen und mit solchen, die in den Untergrund eindringen. Bei den ersteren handelt es sich v.a. um geophysikalische Methoden. Diese werden gesondert behandelt, wahrend hier die letztere Methode erwahnt wird. Es handelt sich v.a. um das Abteufen von Bohrungen, Baggerschlitzen und Rammsondierungen. Im Zusammenhang mit der stofflichen Zusammensetzung von Grundwasser entscheidet der Zweck der Untersuchung uber die Methode: 1. Entnahme von moglichst sauberem und ungestort gelagertem Gesteinsmaterial; 2. Moglichst viele Einzelmessungen uber die raumliche Verteilung von Messgrossen der geologischen Formation, wie z.B. Durchlassigkeit, Porositat; 3. Billiger und rascher Aufschluss zwecks Einbau von Probenahme-Rohren mit moglichst kurzen Filterstrecken in moglichst vielen verschiedenen Tiefenlagen (Cherry,1983); 4. Direkter Einblick in die obersten paar Meter des Untergrunds, mit der Moglichkeit, viel gestortes Gesteinsmaterial zu entnehmen; 5. Billige Bestimmung der Lagerungsdichte des untiefen Untergrunds, mit der Moglichkeit, ein schmales Rohr zur Beobachtung des Grundwasserspiegels zu versetzen. Haufig muss mehr als einer dieser Zwecke erfullt werden. Deshalb gibt es nicht das bestmogliche Verfahren. Vor allem die im voralpinen Raum gelegenen glaziofluviatilen Schottern (Kies-Sand-Gemischen), welche die vorrangig fur Trinkwasser genutzten Vorrate an Grundwasser enthalten, bilden eine Herausforderung an die Bohrtechnik zur Erfullung obiger Zwecke (Hoehn et al., 1983).