The usefulness of outcrop analogue air permeameter measurements for analysing aquifer heterogeneity: testing outcrop hydrogeological parameters with independent borehole data

Abstract

Outcropping sediments can be used as easily accessible analogues for studying subsurface sediments, especially to determine the small-scale spatial variability of hydrogeological parameters. The use of cost-effective in situ measurement techniques potentially makes the study of outcrop sediments even more attractive. We investigate to what degree air permeameter measurements on outcrops of unconsolidated sediments can be a proxy for aquifer saturated hydraulic conductivity (<i>K</i>) heterogeneity. The Neogene aquifer in northern Belgium, known as a major groundwater resource, is used as case study. <i>K</i> and grain size data obtained from different outcropping sediments are compared with <i>K</i> and grain size data from aquifer sediments obtained either via laboratory analyses on undisturbed borehole cores (<i>K</i> and grain size) or via large-scale pumping tests (<i>K</i> only). This comparison shows a pronounced and systematic difference between outcrop and aquifer sediments. Part of this difference is attributed to grain size variations and earth surface processes specific to outcrop environments, including root growth, bioturbation, and weathering. Moreover, palaeoenvironmental conditions such as freezing-drying cycles and differential compaction histories will further alter the initial hydrogeological properties of the outcrop sediments. A linear correction is developed for rescaling the outcrop data to the subsurface data. The spatial structure pertaining to outcrops complements that obtained from the borehole cores in several cases. The higher spatial resolution of the outcrop measurements identifies small-scale spatial structures that remain undetected in the lower resolution borehole data. Insights in stratigraphic and <i>K</i> heterogeneity obtained from outcrop sediments improve developing conceptual models of groundwater flow and transport

The usefulness of outcrop analogue air permeameter measurements for analyzing aquifer heterogeneity: quantifying outcrop hydraulic conductivity and its spatial variability

“…The transferability of the obtained K statistics to the corresponding subsurface sediments should be scrutinized before considering them representative of the in situ aquifer or aquitard properties. A first attempt to gain some insights into this transferability is presented by Rogiers et al (2013b).…”

The impact of sedimentary anisotropy on solute mixing in stacked scour‐pool structures

“…The present study is motivated by the numerous aquifer‐analog studies that have been undertaken to gain a better understanding of heterogeneity in aquifer systems formed in glacial outwash deposits [e.g., Heinz et al ., ; Kostic et al ., ; Bayer et al ., ; Rogiers et al ., ; Höyng et al ., ; Weissmann et al ., ]. These deposits are associated with large ice masses and occur in the proglacial environment, beyond the terminal point of a glacier.…”

Bestimmung der hydraulischen Durchlässigkeiten eines Sandsteins mithilfe eines Luftpermeameters

“…Rogiers et al (2014a, b) konnten mithilfe des Luftpermeameters räumlich hochauflösende Aquiferheterogenitäten der hydraulischen Durchlässigkeiten an unkonsolidierten Sanden bestimmen. Des Weiteren verglichen Rogiers et al (2013) kf-Werte aus Aufschlüssen und Bohrlöchern. Hier zeigte sich, dass die kf-Werte aus den Aufschlüssen, die mit dem Luftpermeameter bestimmt wurden, aufgrund ihrer höheren lokalen Auflösung tendenziell höher waren als die kf-Werte, die mittels hydraulischer Pumpversuche in Bohrlöchern bestimmt wurden.…”

“…Mallants et al 1997;Bagarello und Provenzano 1996;Schulze-Makuch et al 1999;Whitaker und Smart 2000). Filomena et al (2014) untersuchten die Bestimmung der hydraulischen Durchlässigkeit mit verschiedenen kommerziellen Permeametern, u. a. auch dem tragbaren Tiny-Perm II, der auch in den vorher genannten Arbeiten von Rogiers et al (2013Rogiers et al ( , 2014a zum Einsatz kam, sowie mit zwei Luftpermeametern nach dem Prinzip der Hassler Zelle an verschiedenen Sandsteinen. Für die Messung mit der Hassler Zelle muss die Gesteinsprobe jedoch exakt in Abhängigkeit der Maße des Probenhalters präpariert werden, um Umläufigkeiten während des Versuchs zu vermeiden.…”