Investigation of a chalk aquifer: Advantages and limits of diffusion samplers and low-flow sampling techniques

Abstract

In order to estimate the vertical contaminant distributions in a chalk aquifer, two sampling techniques are used in the piezometers. The first is passive multi-level sampling, using dialysis membrane diffusion samplers. The second is the low-flow purging technique. Geochemical groundwater zones are also established by profiles of temperature, conductivity, dissolved oxygen, pH and redox potential. These sampling techniques enhance three-dimensional visualization of the chemical and physical parameters in the chalk aquifer. Except for the cases where there are large variations in the concentrations, these two methods provide approximately the same results. But these techniques should not be applied with the same aim. Dialysis membrane diffusion samplers preserve the weak chemical variations of an aquifer, but lead to mistakes in determining iron concentrations. Conversely, the low-flow rate technique preserves the iron concentration, but the depth resolution is weaker (on a scale much greater than 1 m) because pumping produces a mix of flow horizons. Copyright © 2007 IAHS Press.