An Approach to Evaluate Groundwater Flow Direction at Low Hydraulic Gradient Sites

The evaluation of groundwater flow direction can be challenging at sites where the magnitude of the hydraulic gradient is small and slight local changes in water levels can lead to significant variations on flow direction.  The evaluation of groundwater flow direction in these low gradient sites can become more complex if barometric effects are present. In some cases, failure to remove barometric effects can lead to an erroneous interpretation of groundwater flow magnitude and direction if the barometric noise is significant with respect to the observed temporal changes in water level measurements.

The current availability of data loggers that provide high-resolution and long-term monitoring requires the subsequent use of tools that can aid in the analysis of the collected data towards a comprehensive understanding of flow conditions.

An example is presented below where the understanding of groundwater flow direction was critical to associate plume development with potential sources and to appropriately craft a remedial strategy suitable for the flow conditions. To meet these objectives, an intensive hydraulic monitoring program was designed to collect a high resolution data set to further understand transient groundwater conditions. The data was analyzed in a two-step approach: (1) barometric effects were corrected and (2) a best-fit hydraulic gradient tool was used to evaluate flow gradient magnitude and direction over time. This two-step approach allowed for a comprehensive evaluation of the collected data set that resulted in a better understanding of flow and transport of contaminants at the site.