Geophysical Monitoring of a Field‐Scale Biostimulation Pilot Project

Abstract

The USGS conducted a geophysical investigation in support of a U.S. Naval Facilities Engineering Command, Southern Division field-scale biostimulation pilot project at Anoka County Riverfront Park (ACP), down-gradient of the Naval Industrial Reserve Ordnance Plant, Fridley, Minnesota. The goal of the pilot project is to evaluate subsurface injection of vegetable oil emulsion (VOE) to stimulate microbial degradation of chlorinated hydrocarbons. To monitor the emplacement and movement of the VOE and changes in water chemistry resulting from VOE dissolution and/or enhanced biological activity, the USGS acquired cross-hole radar zero-offset profiles, travel-time tomograms, and borehole geophysical logs during five site visits over 1.5 years. Analysis of pre- and postinjection data sets using petrophysical models developed to estimate VOE saturation and changes in total dissolved solids provides insights into the spatial and temporal distribution of VOE and ground water with altered chemistry. Radar slowness-difference tomograms and zero-offset slowness profiles indicate that the VOE remained close to the injection wells, whereas radar attenuation profiles and electromagnetic induction logs indicate that bulk electrical conductivity increased down-gradient of the injection zone, diagnostic of changing water chemistry. Geophysical logs indicate that some screened intervals were located above or below zones of elevated dissolved solids; hence, the geophysical data provide a broader context for interpretation of water samples and evaluation of the biostimulation effort. Our results include (1) demonstration of field and data analysis methods for geophysical monitoring of VOE biostimulation and (2) site-specific insights into the spatial and temporal distributions of VOE at the ACP.

4D active time constrained resistivity inversion

“…ERT imaging in a time-lapse mode, often involving permanent electrode installations, has proven to provide in many cases images of larger volumetric scale, in comparison to standard geochemical, hydrogeological sampling which may involve large volume (pumping test or tracer test). Several applications of time-lapse ERT have been reported involving among others groundwater exploration (Ramirez et al, 1993;Park, 1998), the study of hydro-geological properties (Day-Lewis et al, 2002;Dahlin, 1996;Looms et al, 2008;Daily et al, 1992Daily et al, , 2000Daily et al, , 2004, the mapping and monitoring of salt-water intrusion in aquifers and transport processes of contaminants (Lane et al, 2006;Vargemezis et al, 2007;Nimmer et al, 2007;Kuras et al, 2009;Ngugen et al, 2009;Ogilvy et al, 2009;Wilkinson et al, 2010).…”

Application of time-lapse ERT imaging to watershed characterization

“…Timelapse geophysical measurements have been shown to be successful in monitoring and understanding physical processes in the subsurface, e.g. ͑Ramirez et al, 1993͑Ramirez et al, , 1995Lumley, 2001;Tsourlos et al, 2003;Singha and Gorelick, 2005;Lane et al, 2006;MacBeth et al, 2006;Anno and Routh, 2007͒. In a general sense, time-lapse methodologies can be utilized to determine the rate at which a process is occurring, define the volume of subsurface region affected by a particular process, and understand the complex interactions between various subsurface processes. Time-lapse is especially important for near-surface studies since the medium is much more dynamic due to the proximity of the air-earth interface.…”

Time-lapse borehole radar monitoring of an infiltration experiment in the vadose zone

“…Water content estimates are needed to model and predict pollutant transport through the vadose zone, and to subsequently design an efficient and reliable remediation plan. Time-lapse GPR has been used successfully to image mass transport such as vegetable oil emulation (Lane et al, 2006) and saline water (Chang et al, 2006). The timelapse imaging at field sites can be divided into three main modes of operation: surface-based or single-borehole reflection surveying (Truss et al, 2007), surface-to-borehole surveying (Cassiani et al, 2004), and cross-borehole surveying (Binley et al, 2001(Binley et al, , 2002Kowalsky et al, 2005).…”

“…In crosshole GPR, two acquisition geometries are usually employed: multi-offset gathering (MOG, tomography geometry) and zero-offset profiling (ZOP, level-run geometry) (Binley et al, 2001;Lane et al, 2006). MOG offers multi-dimensional imaging through high-resolution tomography, but is relatively slow due to the large number of measurements (Alumbaugh et al, 2002).…”