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.     

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

A prominent feature of Monitored Natural Attenuation (MNA) is the prediction of the fate of contaminants from field data. The validity of field data was evaluated by hydrogeological investigations at a BTEX-contaminated site. Results from the following investigations were taken into consideration: Pump test, bore hole data, and measurements of precipitation and groundwater level changes. Moreover, changes in contaminant concentrations and changes in hydraulic gradients were investigated. There was a statistically significant dependence of contaminants on a fluctuating groundwater level (±1.4m), which had different effects: at high groundwater levels, contaminant concentrations in the near-source area were lower and were associated with a plume extension downstream. Hydraulic gradient fluctuations between 1.5‰ and 15.1‰ were observed. Lower hydraulic gradients prevailed in the source area at high groundwater levels, whereas the downstream area had steeper gradients. The direction of hydraulic gradients varied between 12° and 67°. Accounting for these features will allow an evaluation of field data in support of MNA. Hydrogeologic investigations proved to be of importance for a subsequent assessment of NA processes in the aquifer.     

Natural Attenuation-Untersuchungen an einem mit LCKW kontaminierten Altdeponiestandort

The Natural Attenuation of chlorinated hydrocarbons leaking from an abandoned landfill was the focus of an investigation conducted within the framework of the Bavarian joint research project “Nachhaltige Altlastenbewältigung unter Einbeziehung des natürlichen Reinigungsvermögens”. The research focused on two contaminant plumes, one having a diffuse TCE/PCE source and the other a cis- DCE source. The TCE/PCE plume had a maximum concentration of 52 μg/l total chlorinated hydrocarbons near the source area. Cis-DCE concentrations near the source of the second plume were up to 7,000 μg/l. In addition, degradation products (VC and Ethylene) were detected in this region, which indicate reductive dechlorination of the cis-DCE, TCE or PCE pollutants. However, other investigations indicate that the natural attenuation potential of the site is low and that the reduction in concentration is dependant more on dilution and other unknown processes. Stemming from this research, a new approach was developed using Solid Phase Micro Extraction (SPME) and GC/FID analytical techniques for microcosm testing. Furthermore, an airtight column was developed that allows the detection of sorption of highly volatile substances in low concentrations within an aquifer material.     

Natural Attenuation: hohe Anforderungen an die Modellsimulation

The evaluation of contaminated sites with respect to their potential for natural attenuation to relevant orders of magnitude in concentration and reasonable time scales requires estimating future plume behaviour. In this regard, model simulations are a valuable tool, e.g. through studies of predictive scenarios, but they have to fulfil demanding criteria that common software codes often cannot meet. We first present an overview of work completed within the framework of the joint research project BayFoNA in the domain of modelling. The herein described universal software tool is capable of reflecting the relevant processes of contaminant propagation and transformation, including, for example carrier facilitation or general temperature dependent decay reactions. Due to site heterogeneity, highly localized reactions, as well as aspects including nonlinearity or varying time scales, the quality of the numerical methods can have a decisive influence on the assessment of the natural attenuation potential. Therefore non standard locally mass conservative finite element discretizations were applied, employing functions of higher order to reduce numerical dispersion (which, in some cases, may lead to an overestimation of microbial degradation), or a globally implicit solution algorithm to avoid splitting errors and convergence problems. The simulation tool also allows the identification of unknown parameters by well defined experiments. Applications in the joint research project demonstrate the implementation of the techniques in the case of BTEX contamination, and helped clarify issues related to the migration of arsenic.     

Nutzung von Natural Attenuation zur Reduktion der PAK-Belastung in heterogenen Porengrundwasserleitern

Grundwasser - Heterogene Porengrundwasserleiter erschweren die Prognose des Fahnenverhaltens PAK-belasteter Grundwässer. An einem Modellstandort in Bremen wurde ein in der Praxis gut...     

Nachweis von Strukturdefekten in Elementwänden mittels zerstörungsfreier Prüfverfahren

Der Beitrag befasst sich mit der Nachweisbarkeit von Strukturdefekten in Elementwänden mittels zerstörungsfreier Prüfverfahren. Innerhalb einer Versuchsreihe wurden in Elementwänden vordefinierte Fehlstellen eingebaut, die während der Betonage auf der Baustelle auftreten können. Die Messungen wurden durch verschiedene Messteams mit Ultraschall‐Echo‐, Impact‐Echo‐ und Impuls‐Radar‐Verfahren an einem vorgegebenen Messraster ausgeführt. Dabei konnten die Strukturdefekte vielfach zerstörungsfrei nachgewiesen werden. Die wesentlichen Untersuchungsergebnisse werden nachfolgend dargestellt. Verification of Failure in Prefabricated Walls Using Non‐Destructive Testing Methods This essay deals with the verification of failure in prefabricated walls using non‐destructive testing methods. Series of tests were carried out considering several imperfections which might occur on site during construction. Three measuring methods were used by different parties to carry out the tests. These methods were the Ultrasonic Echo Method, the Impact‐Echo Method and Impulse Radar Technique, where in many cases failure could have been detected in using these methods. The main research results are presented here.     

Einflüsse von Oberflächenversiegelungen auf die Schadstofffahnenentwicklung im Grundwasserabstrom einer ehemaligen Kokerei

Changes in the electron acceptor supply must be considered in order to simulate reliable future plume spreading in groundwater. For example, decreasing amounts of electron acceptor mass fluxes from the unsaturated zone caused by less groundwater recharge due to surface sealing could lead to further plume spreading during the forecast horizon. However, to accept monitored natural attenuation (MNA) as an alternative remediation strategy, steady state plumes have to be proved. This article deals with the quantitative impacts of different amounts of surface sealing on future plume spreading by using a reactive transport model. Due to these interventions, the results show significant changes in plume length (increases up to 50 %) and in some cases the plumes no longer attain steady-state conditions. This underlines the necessity of considering surface sealing scenarios for MNA concepts at such sites.     

Probleme bei der Berechnung von Stahlbetonkonstruktionen mittels dreidimensionalen Gesamtmodellen

Design of three‐dimensional Finite Element Models In practice, complex three‐dimensional finite element models of an entire structure are used more and more often to design a reinforced concrete building. As daily experience shows, results from computer analysis are often trusted with blind faith. For reasons of time, the required checking of the model as well as a clear documentation of the main results remain undone. This development raises questions regarding the safety of structures in the future. The various problems of a complex 3‐d finite element analysis will be demonstrated by a simple structure, an arch bridge. It will be shown, that no software is able to design this bridge, at least in parts. An independent checking of the computer results is always required.     

土壤中LNAPL的自然衰减实验研究

目前,石油污染及其治理问题受到环境工作者的广泛关注。本文选用柴油作为LNAPL的代表,通过实验分析了LNAPL的自然衰减规律(挥发作用、生物降解作用和吸附作用等),估算了低浓度时各种作用对土壤中柴油去除的贡献率。结果表明,土壤中的LNAPL在自然条件下能发生一定的衰减作用,而且当浓度较低时,自然衰减作用对柴油去除率较高,达到了62.86%。因此,在适当的条件下,利用LNAPL的自然衰减作用可以有效地分解LNAPL化合物,达到降低污染物浓度的目的,为进一步研究LNAPL的治理和防护奠定了基础。     

Überwachung der Auswirkungen von Flussaufweitungen auf das Grundwasser mittels Radon

The restoration of the perialpine river Töss in a floodplain of northern Switzerland (Linsental) included the removal of bank reinforcements and tracer studies in the river and in oberservation wells of the adjacent alluvial groundwater. The river water is continuously recharging the aquifer system and the groundwater is used extensively as drinking water. Radon activity concentrations of freshly infiltrated groundwater are interpreted as radon groundwater age between the river and a well. A first flood after the restoration operations resulted in a widening of the river bed and in a reduction of the flow distance to the wells. Sixteen days after a second flood, the results of radon measurements were compared with those from before the restoration. The radon age of the groundwater between the river and the wells decreased, probably as a result of the reduction of the flow distances. Concentrations of autochthonous and coliform bacteria increased after the restoration operation and even more one day after the first flood. Thus the findings on the bacteria corroborate the interpretation of the radon concentrations. The restoration has not yet reduced the quality of the groundwater, which is pumped for drinking water. The study is contributing to the solution of land-use conflicts between river restoration and the supply of drinking water from the alluvial groundwater.