An Assessment of Aquifer/Well Flow Dynamics: Identification of Parameters Key to Passive Sampling and Application of Downhole Sensor Technologies

Abstract : Contaminant redistributive effects in wells are nearly always present. Complete mixing appears to be very common; however, it is not universal. There is a continual balance between inflowing contaminant stratification (where present) and factors driving in-well mixing. Findings here imply common and very small drivers are responsible for slow but vigorous mixing relative to the residence time of water flowing through a typical well screen. Therefore, a tendency toward homogenization is anticipated to be common in field conditions. Most wells should experience strong redistribution effects, but some wells may maintain stratification or perhaps re-stratify differently from the surrounding formation. Ongoing technical transfer of these findings will promote better understanding in the environmental community that wells often represent a mixed flow-weighted average of the adjacent formation chemistry. This better understanding will yield cost savings in both short-term and long-term timeframes by accelerating the approval process for non-purge alternative sampling strategies, including passive sampling and in situ sensor technologies.