Applying petrophysical technology to groundwater remediation projects

Background/Objectives. Effective groundwater remediation depends on accurate and geologically realistic characterization of the subsurface. High Resolution Site Characterization (HRSC) methods such as Electrical Conductivity (EC), Hydraulic Profiling Tool (HPT), and downhole Geophysical logs such as Natural Gamma Radiation paired with advanced stratigraphic analysis techniques such as Environmental Sequence Stratigraphy (ESS) allow for improved mapping of the distribution and geometry of aquifers and aquitards. Leveraging relationships between HRSC and primary lithology data (i.e., lithologic boring logs, geotechnical samples from borings) has qualitatively reduced uncertainty in our understanding of the subsurface. However, HRSC data is being underutilized quantitatively by the industry as a whole. Here we investigate the viability of quantifying formation clay volume from gamma ray data using established petrophysical approaches as a site screening tool that may prove useful in the optimization of remedial design.

Approach/Activities. We analyzed a growing database of EC/HPT, gamma logs and primary lithologic data from primarily unconsolidated to semi-consolidated aquifers. Boring descriptions were used to generate graphic grain size logs which were compared to down-hole HRSC logs as an initial calibration to site lithology. Additional analysis was performed in discrete intervals using gamma ray log data to calculate an estimated clay volume curve using the Larionov equation. Cross plots of gamma ray derived clay volume vs. laboratory and/or HPT derived hydraulic conductivity measurements illustrate the potential relationship between gamma ray signature and a formation’s hydraulic conductivity at the site.

Results. In addition to serving as useful tools aiding in stratigraphic correlation, common HRSC tools can be utilized in a petrophysical manner. In the example analyses presented we demonstrate the limits of tool application as well as the increased need for data sets of paired geotechnical and HRSC data to further develop and perfect petrophysical applications within the current groundwater remediation practice.