In heterogeneous porous aquifers, simulations and predictions of groundwater flow and solute (contaminant) transport require detailed knowledge of aquifer parameters and their spatial distribution. ...In most cases this information cannot easily be obtained at acceptable expenses. In general, subsurface investigation techniques are applied only at borehole locations, and the parameter values measured have to be regionalized in order to obtain continuous parameter fields. Geophysical measurements very often yield unsatisfactory results due to resolution, detection range and parameterisation problems. In such situations tracer tests offer the possibility to efficiently investigate the aquifer between the wells and to characterize the relevant aquifer properties based on effective parameter values. Tracer tests can be performed at laboratory and field-scales with depth integrated (two-dimensional) or multilevel (three-dimensional) set-ups, and under natural or forced hydraulic gradient conditions. Both non-reactive and reactive tracer compounds can be used. This contribution covers and gives examples on the following topics: depth integrated and three-dimensional natural and forced gradient tracer test methods together with their fields of application at different transport scales, novel tracer compounds and applications, high resolution multilevel–multitracer methods and high resolution multilevel–multitracer equipment, as well as approaches to evaluate tracer experiments and to quantify tracer transport. In this way the paper shows some recent trends in tracer based subsurface investigation and emphasizes the advantages and importance of modern tracer testing.
Zusammenfassung
Die mächtigen fluvialen Sand- und Kiesablagerungen im Raum Babenhausen (südöstlich von Frankfurt am Main) bilden ein bedeutendes Rohstoffvorkommen und werden sowohl für die Gewinnung ...von Sand und Kies als auch für die Förderung von Trinkwasser genutzt. Aufgrund der räumlichen Nähe beider Rohstoffnutzungen zueinander ist eine Gefährdung der Trinkwasserressource durch den Sand- und Kiesabbau nicht auszuschließen. Um das Gefährdungspotenzial abschätzen zu können, ist zunächst die Kenntnis über die räumliche Verteilung der hydraulischen Leitfähigkeiten in den Sedimenten entscheidend.
Auf einem Testfeld (50 × 40 m) im unmittelbaren Uferbereich eines Baggersees wurden deshalb konventionelle Pumpversuche, Multilevel-Pumpversuche sowie Siebanalysen durchgeführt. Die Untersuchungen ermöglichten eine Lokalisierung der hochdurchlässigen Tiefenbereiche. Die mittels Siebanalysen und Multilevel-Pumpversuchen ermittelten Durchlässigkeitsbeiwerte zeichnen über die Tiefe zwar einen ähnlichen Trendverlauf, weichen jedoch oft um eine Größenordnung voneinander ab.
Fluvial sediments in the Babenhausen area (southeast of Frankfurt am Main) form an important reservoir of sand and gravel, which is currently being mined in dredged lakes. As the fluvial sediments ...also contain a productive aquifer which is intensely used, possible contamination of the groundwater by sand and gravel mining must be prevented. In order to estimate risk potential, the spatial distribution of hydraulic conductivity in these sediments must be determined.On a test site (50 × 40 m) directly within the riparian zone of a dredged lake, standard pumping tests, multilevel pumping tests, sieve and sedimentation analyses were carried out. Investigations enabled locating zones with high hydraulic conductivities at specific depths. The hydraulic conductivities determined from each of these methods show a similar trend with increasing depth, but often differ by one order of magnitude.
Aquifers at industrial sites are commonly characterized by a multitude of contaminant source zones. Conceivably, dissolved contaminants originating from an up-gradient residual nonaqueous phase ...liquid (NAPL) source zone may be transported along the groundwater flow path into another residual NAPL source zone down-gradient. However, if and how contaminants from different zones may affect one another with regard to dissolution and transport has thus far been unknown. To identify and understand such potential interactions, the numerical model BIONAPL3D was applied to simulate the behavior of six dissolved polycyclic aromatic hydrocarbons (PAHs), stemming simultaneously from an up-gradient NAPL source zone, when they encounter a down-gradient NAPL source zone. The down-gradient NAPL source zone was assumed to be a residual benzene phase with a saturation of 10%. When the dissolved PAHs entered the benzene source zone, the aqueous PAH concentrations declined significantly due to their partitioning into the residual benzene phase. As benzene rapidly dissolved into the aqueous phase, the PAHs were resolubilized with negligible impact due to benzene co-solvency. The degree of resolubilization was much smaller than the initial loss due to partitioning into the benzene phase. Thus, the PAHs formed a new residual NAPL phase that, over time, replaced the original benzene source zone. The new NAPL phase continued to grow even after all of the benzene was dissolved. Our modeling approach is the first theoretical demonstration of a significant interaction of contaminants emanating from multiple source zones. It should be regarded as a starting point to consider source zone interactions at polluted field sites.
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