Direct-push geochemical profiling for assessment of inorganic chemical heterogeneity in aquifers

Hyperfiltration of potassium nitrate through clay membranes under relatively low-head conditions

“…Two field studies found nitrate concentrations increased with depth in perched or shallow aquifers (Schulmeister et al, 2003b;Schulmeister et al, 2004;Smith et al, 1991) and three studies found an increase in chloride concentrations with depth towards bounding clay layers (Smith et al, 1991;Johnson and Chou, 1998;Ronen et al, 1987). Although several explanations, such as different water sources and differing levels of microbiological activity, can be offered for such solute concentration increases, hyperfiltration by clay-rich aquitards (relatively impermeable geologic strata) should also be considered as a possible mechanism for such solute concentration profiles.…”

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“…Concentrations of volatile organic compounds (VOCs) that vary by three or four orders of magnitude over vertical distances of tens of centimeters are not uncommon. Note that while the above discussion pertains to VOC plumes, several high‐resolution field studies also show strong spatial variability in concentrations of inorganic contaminants, especially in the vertical dimension (Bjerg et al 1992; Schulmeister et al 2004).…”

Direct-push multilevel sampling system for unconsolidated aquifers

“…Dissolved contaminant plumes downgradient of nonaqueousphase liquid (NAPL) source zones commonly show strong concentration gradients especially in the vertical direction (Anneser et al 2008;Cunningham and Fadel 2007;Einarson et al 2010;Guilbeault et al 2005;Schulmeister et al 2004). This is due to a number of factors, including geological heterogeneity, spatial and temporal variability in contaminant mass input, activity of bacteria responsible for biodegradation and aquifer recharge; therefore, the measured concentrations strongly depend on the sampling installations and sampling methods (Parker 1994).…”