Integrierter Einsatz von Scherwellenseismik und Direct-Push-Verfahren zur Erkundung eines urbanen Grundwasserleiters

In a highly permeable urban aquifer with a lower cretaceous mudstone aquiclude in the district “Südstadt” of Hannover/Lower Saxony, a stationary plume of chlorinated hydrocarbons was investigated within a research framework on the use of monitored natural attenuation. In the vicinity of the isolated contaminant source a glacial channel was detected as a possible secondary source supplying the plume. Due to dense housing the channel morphology and possible pathways could not be mapped accurately by classical geological methods. Therefore, the structure of the aquifer was mapped with shear wave seismics on seven profiles covering a range of more than 3.5?km, utilizing a newly developed mobile land streamer unit. The seismic profiles were adjusted with 16 electric conductivity (EC) and penetration logs measured with direct push, delivering a high resolution image of the near surface bedrock. Due to its mobility and the characteristics of shear wave seismics this combination of methods is ideally suitable for work on sealed surfaces.     

Tiefenorientierte Pumpversuche zur Bestimmung der hydraulischen Anisotropie in einem geschichteten Grundwasserleiter

Grundwasser - Die horizontale Schichtung von Sedimentkörpern bewirkt, dass die effektive hydraulische Durchlässigkeit eines sedimentären Grundwasserleiters in horizontaler Richtung...     

Geophysikalische Verfahren zur Erkundung und Charakterisierung von Grundwasserleitern in quartären Rinnen

Geophysical methods for the investigation and characterization of groundwater resources in porous media are shown using the subglacial Ellerbeker Rinne as an example. Five seismic sections illustrate the shape, internal structure and surrounding hydrostratigraphy of 25?km of this buried valley that, in some places, is more than 2?km wide. Data from the transient electromagnetic airborne survey reveal the distribution of electrical resistivity down to a depth of 300?m. The groundwater-saturated channel in the valley is clearly distinguishable from the Tertiary clays. A good and fast overview on the character of the confining beds down to 100?m depth was provided by the frequency-domain helicopter-borne electromagnetic method. A reliable interpretation was obtained by combining the different methods with borehole information and expert geological knowledge.     

Identifikation NSO-heterocyclischer Prioritärsubstanzen zur Erkundung und Überwachung Teeröl-kontaminierter Standorte

The German Federal Soil Protection and Contaminated Sites Ordinance (BBodSchV) requires the monitoring of NSO-heterocyclic hydrocarbons without specifying the extent of such analysis. An assessment procedure for the identification of NSO-heterocyclic priority substances was thus created within the “KORA” project (“Natural Attenuation: Retention and Degradation Processes Reducing Contaminations in Groundwater and Soil”) funded by the German Federal Ministry of Education and Research (BMBF). This assessment includes physicochemical properties, biodegradability, toxicity, and groundwater propagation of these substances at creosote-contaminated sites. In addition to unsubstituted compounds, the derived list of 20 priority NSO-heterocycles also contains substituted derivatives as well as relevant transformation products.     

Prognose zur Entwicklung der Nitrat- und Sulfatkonzentration in einem tiefen Grundwasserleiter durch hydrogeochemische Untersuchungen

The areas within the ‘Niederrheinische Tiefebene’ are intensively used for agricultural production. The underlying hydrogeologic structure of the area is composed of multiple layers of productive unconsolidated aquifers. The high input of nitrate in the near-surface aquifers restricts the pumping of groundwater only from the deep aquifers which increases the vertical hydraulic gradient. This leads to enhanced flow from the upper aquifers into the deeper systems. Simultaneously, the concentrations of several hydrochemical indicator parameters (chloride, sulphate, iron, calcium, total carbon dioxide) have increased. Nitrate is removed by the reaction with sulphide minerals within the deeper aquifers. In this paper, the relevant processes in the anaerobic system are described, with special emphasis on lithotrophic dentrification at the Rasseln water works. The aim is to predict the prospective trend of the water quality in the deep aquifer with a focus on nitrate. Therefore, the behaviour of a conservative component (chloride) was also analysed relative to the behaviour of more reactive components (sulphate, iron, nitrate). As a result of this analysis, a long-term reduction of nitrate in the deep aquifer (Neurather Sand, Horizont 6D) at the Rasseln water works, which leads to a low concentration of nitrate in the raw water, was predicted. Furthermore, the results have shown that the sulphate concentration will likely not reach the legal limit for drinking water (240?mg/l, TVO 2001).     

Abbau aromatischer Kohlenwasserstoffe und Metabolitenbildung im Grundwasserleiter eines ehemaligen Gaswerkstandorts

Hydrochemical investigations were performed at a contaminated site in the area of a former gasplant at Düsseldorf, Germany, between October, 1995 and November, 1996. The changes of the biodegradation processes in the aquifer during the remediation of groundwater and soil were monitored. The organic contaminants present in the groundwater were mainly BTEX (benzene, toluene, ethylbenzene, xylenes) and low moleuclar weight PAH (plycyclic aromatic hydrocarbons). At the beginning of the remediation activities, natural degradation of the contaminants occurred with sulfate reduction as the prevailing terminal electron accepting process. Due to oxygen input into the aquifer during soil removal the biodegradation process was disturbed and the concentrations of aromatic hydroarbons and sulfate rose significantly. The aromatic acids occuring as metabolites of the aromatic hydrocarbons reacted specifically to the changes in the degradation processes.     

Identifizierung und Quantifizierung natürlicher Abbauprozesse in einem mit Chlorethenen kontaminierten Grundwasserleiter

This article discusses the results of an investigation into natural attenuation processes at a former landfill which is leaching aliphatic hydrocarbons and chlorinated ethenes. The high degree of metabolisation of the chlorinated ethenes downstream of the landfill indicates the occurrence of reductive dechlorination, which was quantified by geochemical investigations and reactive transport modelling. In the vicinity of the deposit, the contaminated Buntsandsteinaquifer is divided into at least two subaquifers, the upper one of which is the most highly contaminated. Directly downstream of the landfill, the redox-environment is highly reduced, allowing reductive degradation processes to continue. The high transformation rates in this area lead to a conversion of more than 90% of the Perchloroethene (PCE) and Trichloroethene (TCE) leached from the landfill and leaves Cis-Dichloroethene (Cis-DCE) as the main contaminant found in the subsurface. Further downstream, the redox-environment becomes increasingly oxidised where (cometabolic) aerobic degradation processes will probably dominate, which will especially degrade the less chlorinated ethenes. Over the short term, however, the continuous delivery of PCE and TCE from the landfill will prevent the retreat of the contamination in the subsurface by natural attenuation alone. Nevertheless, in combination with source control measures, natural attenuation could be an alternative strategy for plume management.     

Hydrogeologie des Kabul-Beckens (Afghanistan), Teil I: Grundwasserleiter und Hydrologie

Shallow groundwater currently represents the main source for water supply in Kabul. Detailed information on the hydrogeology of the Kabul basin is therefore needed to improve the supply situation and to develop sustainable concepts of groundwater use. The basin is situated at the intersection of three major fault systems and comprises three major aquifers, all consisting of coarse sandy to gravely material originating from the surrounding mountains. The aquifers were deposited by several rivers draining the basin. Marl is the basal layer of the aquifers. Usually the aquifers are covered by loess loams which are an important feature in groundwater protection. The coarse aquifer material has high permeability. Deeper parts are affected by cementation of pore spaces, resulting in formation of semi-diagenetic conglomerates which decrease well yields. The main groundwater recharge occurs after the snowmelt from direct exfiltration from the rivers and from foothill infiltration. The high withdrawals of the last few years and a steadily rising population have led to a strong overexploitation of the groundwater resource as indicated by falling groundwater levels and deteriorating groundwater quality.     

Hydrogeologische Erkundung von Grundwasser in der ariden und vulkanisch aufgebauten Westkordillere Boliviens

Grundwasser - In der ariden Westkordillere von Bolivien wurde ein 2000 km2 großes Gebiet geologisch und hydrogeologisch untersucht mit dem Ziel, Bohransatzpunkte zur Grundwassererkundung...     

Sanierung eines PCE-Schadens in einem makroskopisch oxischen Grundwasserleiter durch Stimulation anaerober dehalogenierender Bakterien

Grundwasser - Eine erfolgreiche biologische In-situ-Sanierung von PCE-kontaminierten Grundwasserleitern erfordert hinreichend reduzierende Bedingungen sowie die Anwesenheit von molekularem...     

Einfluss oberflächennaher Wärmegewinnung auf geochemische Prozesse im Grundwasserleiter

The geothermal use of nearsurface aquifers for heat extraction and storage leads to temperature changes affecting the geochemical equilibrium of minerals. The modeling and experiments presented in this paper have shown that precipitation and solution of minerals can be generated. This study shows that, in quaternary sediments of Northwestern Germany, changes in temperature mainly effect the solubility of silicates (Amorphous Silica, Illite, K-feldspar, Albite). Besides the Silicates Alunite plays a crucial role. Furthermore a probable precipitation of Calcite was detected at temperature increase in groundwater. An estimate of the changes in pore space due to mineral precipitation showed no significant reduction. On the contrary, at most depths the pore space would slightly widen with temperature change. This is caused by feldspar solution. Thus, at the prosecution of nearsurface geothermal installations no unfavourable changes in the hydraulic properties of the studied quaternary aquifers are to be expected.     

Versuche zur Ermittlung der Eigenschaften von gebrochenem Verbundsicherheitsglas (VSG) und Berechnung der Resttragfähigkeit eines Glasbogens

Tests to determine the characteristics of broken laminated safety glass and a calculation of the remaining structural capacity of a glass arch. The aim of this work is to show, in an exemplary way, using a glass arch with tension rod possibilities to calculate the remaining structural capacity of broken laminated glass. To achieve this aim tensile and bending tests on PVB‐foil and broken laminated safety glass were carried out at 10 °C. Furthermore experiments to determine the friction between broken laminated glass and steel and neoprene were performed.     

Hydrogeologische Untersuchungen bei der Anwendung von Monitored Natural Attenuation (MNA) an einem BTEX-kontaminierten Grundwasserleiter

Bei “Monitored Natural Attenuation” (MNA)-Ma?nahmen werden anhand von Felddaten Prognosen zur Schadensentwicklung erstellt. Zur überprüfung der Aussagef?higkeit von Felddaten hinsichtlich MNA wurden an einer Grundwasserkontamination durch BTEX hydrogeologische Untersuchungen durchgeführt. Hierzu wurden Pumpversuchsdaten, geologische Bohrdaten und Niederschlagsdaten berücksichtigt, daneben die zeitliche Entwicklung der Grundwasserst?nde, der Schadstoffgehalte sowie der hydraulischen Gradienten des Grundwassers. Es zeigte sich eine signifikante Abh?ngigkeit der Schadstoffgehalte für BTEX maximal |r|=0,89 von einem bis zu ±1,4m schwankenden Grundwasserstand, der sich unterschiedlich auswirkt: bei hohem Grundwasserstand sind die Schadstoffgehalte in Herdn?he verringert, gleichzeitig erfolgt eine Ausdehnung der Fahne in Abstromrichtung. Die hydraulischen Gradienten schwanken zwischen 1,5‰ und 15,1‰. Im herdnahen Bereich ist bei hohem Grundwasserstand eine Gradientenverflachung, im Abstrom eine Gradientenversteilung festzustellen. Die Richtungen der horizontalen hydraulischen Gradienten variieren von 12° bis 67°. Unter Berücksichtigung dieser Abh?ngigkeiten ist eine differenzierte Betrachtung der Felddaten für eine nachfolgende Auswertung hinsichtlich MNA erforderlich. Die hydrogeologische und die hydraulische Erkundung ist eine wichtige Voraussetzung zum Verst?ndnis der hydrochemischen Prozesse bei NA in kontaminierten Grundwasserleitern. Die Ergebnisse zeigen, dass hydraulische und hydrogeologische Aspekte bei den in den USA gebr?uchlichen Protokollen zur Anwendung von NA eine zu geringe Beachtung finden.     

Ist Monitored Natural Attenuation (MNA) eine Option für LCKW-kontaminierte Grundwasserleiter?

An investigation of the chlorinated volatile organic compound (CVOC) biodegradation processes at a reference site with a contaminant plume of 4?km length in a terrace gravel aquifer has revealed that simultaneously spilled non-chlorinated contaminants (which serve as electron donors for reductive dechlorination) caused a transformation of the parent contaminants to cis-1,2-dichloroethene (cDCE) and vinylchloride (VC). Secondary spills in the area of the plume have lead to a complex pattern of different redox zones. In deeper areas of the aquifer, a lack of electron donors due to their migration properties could be observed. The complete mineralization at the plume tip seems to occur under anaerobic conditions via oxidative biodegradation pathways, or under aerobic conditions. High waters of the nearby Rhine river cause a staggering of the plume tip which is likely accompanied by growth of the aerobic fringe area. Pump and treat measures to capture the source area and dissolved plume have substantially altered the biodegradation conditions. On the basis of the investigation results, a simple model was developed to evaluate whether MNA may be an option at CVOC contaminated sites.