Résultat de la recherche
Biocolloid and solute tracer transport in gravel aquifers - a groundwater protection perspective
Migration conditions in a gravel aquifer of the upper Rhone River valley were studied using particle and solutes as contaminant surrogates. Transport rates were 130 to 480 m/d over distances to 22 in, up to 40 times faster than predicted using conventional flow/effective porosity parameters. In one well, a 1-m vertical pathway heterogeneity dominated the 12-m aquifer saturated thickness. Biocolloids were consistently detected earlier than solutes due in part to their significantly lower detection limits and possibly to preferential particle advection. Biocolloid detection occurred 3- to 7-times earlier than time to solute breakthrough peaks, those values commonly relied on when calculating reference velocity parameters. Relative colloid recovery was typically 1.5 to 4 percent and in one case was 72 % of the solute illustrating relatively low biocolloid attenuation in river gravel macropores. Transport direction was up to 90 degrees off those determined from head-derived measurements. Results suggest that reliable groundwater protection strategy in heterogeneous gravel aquifers may improve when field-verified with migration characterization using multiple tracer types.
Bacteriophages as surface and ground water tracers
Bacteriophages are increasingly used as tracers for quantitative analysis in both hydrology and hydrogeology. The biological particles are neither toxic nor pathogenic for other living organisms as they penetrate only a specific bacterial host. They have many advantages over classical fluorescent tracers and offer the additional possibility of multi-point injection for tracer tests. Several years of research make them suitable for quantitative transport analysis and flow boundary delineation in both surface and ground waters, including karst, fractured and porous media aquifers.
This article presents the effective application of bacteriophages based on their use in differing Swiss hydrological environments and compares their behaviour to conventional coloured dye or salt-type tracers. In surface water and karst aquifers, bacteriophages travel at about the same speed as the typically referenced fluorescent tracers (uranine, sulphurhodamine G extra). In aquifers of interstitial porosity, however, they appear to migrate more rapidly than fluorescent tracers, albeit with a significant reduction in their numbers within the porous media. This faster travel time implies that a modified rationale is needed for defining some gro und water protection area boundaries. Further developments of other bacteriophages and their documentation as tracer methods should result in an accurate and efficient tracer tool that will be a proven alternative to conventional fluorescent dyes.