Formatted Title

Application of Environmental Sequence Stratigraphy (ESS) Informed with Nuclear Magnetic Resonance (NMR)

Background/Objectives

Environmental sequence stratigraphy (ESS) is a workflow that is used to develop robust three-dimensional geologic models as part of a processed-based approach for development of conceptual site models (CSMs). ESS informs how geological processes affect heterogeneity and anisotropy, which control groundwater flow and contaminant distribution. Traditionally, generating a sufficient data set to apply ESS has required collecting large amounts of physical data, including continuous coring and field base grain-size analysis, which can be costly. However, high‑resolution site characterization (HRSC) tools can be employed to quickly and efficiently collect the geologic data required to apply ESS. One HRSC tool that is gaining traction within the environmental consulting industry for ESS application is nuclear magnetic resonance (NMR). NMR is a geophysical logging tool that can be deployed in existing PVC well infrastructure, which avoids additional intrusive site investigation activities. NMR tools can also be deployed in newly drilled open bedrock boreholes and with direct push tool methods. NMR logging provides information about aquifer properties including porosity, pore size distribution, and hydraulic conductivity. NMR logging data combined with data collected with other HRSC tools allow for an improved understanding of hydrogeologic properties associated with geologic heterogeneity. This talk will discuss how NMR data collected at several sites overlying various geological environments was used to inform application of ESS.

Approach/Activities

We have found that inclusion of NMR logging as part of the downhole geophysical logging suite of HRSC tools enhances ESS interpretations and enables strategic placement of monitoring locations to evaluate four-dimensional groundwater flow and contaminant transport. ESS informed with NMR logging was completed at several sites within the United States: Triassic clastic sedimentary bedrock in the Newark Basin, Silurian carbonate sedimentary bedrock in the Midwest, Mississippian carbonate bedrock containing shoal sequences in the Midwest, Ordovician carbonate sedimentary bedrock in the Midwest, and Proterozoic crystalline metamorphic bedrock overlain by saprolite in the Southeast. We successfully deployed the NMR tool within existing PVC well infrastructure or newly drilled boreholes at these sites and evaluated the resultant data in conjunction with other HRSC datasets to develop robust geologic models.

Results/Lessons Learned

We will provide ESS interpretations and geologic models developed from data collected using NMR logging in conjunction with other HRSC tools at these sites. We will discuss how those interpretations improved our understanding of hydrostratigraphic control on contaminant fate and transport. We will discuss how hydraulic parameter estimates with NMR, calibrated with quantitative aquifer parameter data, were used to quantify groundwater flow and contaminant transport to provide insights on mass flux. We will also discuss the limitations of NMR in interpreting mobile water percentage in different bedrock lithologies and differentiating between primary and secondary porosity contributions to groundwater flow. At all sites where NMR logging was completed, the data resulted in a more complete understanding of aquifer characteristics controlling contaminant fate and transport.