Integrated Surface Geophysical Methods for Characterization of the Naval Air Warfare Center, New Jersey

Overview

[Photo: USGS scientist wearing GPS backpack walks along cable.]

Two-dimensional (2D) electrical resistivity field set up at Naval Air Warfare Center research site, New Jersey. Eric White (USGS OGW BG) walks the 2D-resistivity line, collecting GPS data.

As part of its applied research initiatives, the USGS Office of Ground Water, Branch of Geophysics (OGW BG) assists in the planning and collection of surface geophysical data at the USGS Toxic Substances Hydrology Program's Naval Air Warfare Center (NAWC) research site in New Jersey, where volatile organic compounds have contaminated bedrock. This is an ongoing applied research project conducted in collaboration with other USGS Toxic Substances Hydrology Program scientists.

Purpose & Scope

OGW BG applied research at NAWC includes the collection of multi-method surface geophysical data to evaluate and demonstrate the benefit of surface geophysical methods for site characterization. Surface-geophysical methods are rapid, minimally invasive ways to characterize the geologic framework at contaminated fractured-rock sites. At NAWC surface-geophysical surveys have been conducted in undeveloped fields adjacent to the research site due to dense industrial infrastructure typical of many contamination sites.

Methods & Activities

OGW BG has conducted multiple surface geophysical surveys at the NAWC site since 2004 in order to evaluate the application of seismic and electrical geophysical methods to characterize large-scale geologic structures and fault zones that cross the site.

Seismic Methods

OGW BG tested an innovative seismic surface-wave method to characterize a shallow fault at the NAWC site. The work was performed through a cooperative research agreement with the Kansas Geological Survey and included the multi-channel analysis of surface waves (MASW) seismic method.

The MASW seismic method was used to delineate a fault zone and gently dipping sedimentary bedrock overlain by several meters of regolith. Seismic data were collected rapidly and inexpensively using a towed 48-channel land streamer and an accelerated weight drop seismic source. The MASW results image the subsurface to a depth of about 20 meters and allowed detection of the overburden, gross bedding features, and fault zone. The fault zone was characterized by a lower shear-wave velocity (Vs) than the competent bedrock, consistent with a large-scale fault, secondary fractures, and in-situ weathering. The MASW two-dimensional (2D) Vs section was further interpreted to identify dipping beds consistent with local geologic mapping.

2D Resistivity

2D direct-current (DC) electrical resistivity surveys were conducted across the suspected thrust-fault along transects previously surveyed using shear-wave seismic refraction and surface-wave imaging techniques. The location and dip of a conductive anomaly observed in the 2D-resistivity data are consistent with previous MASW interpretations of a southeast-dipping fault at the site.

Results & Conclusions

Applied surface geophysical research at NAWC is ongoing. Initial results and conclusions include the following:

Although collected and processed independently, the 2D-resistivity and MASW seismic method interpretations are generally consistent. Both methods identify similar depth to bedrock, shallow northward dipping stratigraphic layers, and a steep southward dipping fault whose trend projects toward the NAWC site.
Overall, the MASW method better resolves the bedrock surface than the 2D-resistivity method. However, the 2D resistivity imaged deeper into the subsurface, thus improving interpretation of the fault dip.
A complete MASW land streamer data acquisition and processing system was designed and procured. The system is available to support USGS programs.[an error occurred while processing this directive] (USGS Programs and Offices can learn more.)
The data collection proved to be rapid and cost effective.
The surface geophysical methods proved effective for delineating large-scale geologic structures, including fault characteristics and lithologic changes. Because the two geophysical methods used for this study measure different physical properties (electrical resistivity and seismic shear-wave velocity, respectively), their combined use to characterize a site can improve interpretational confidence.
This work provides an example of the benefit of using surface geophysical methods to characterize geologic structure and stratigraphy, and their potential for identifying fluid and chemical migration pathways, refining site conceptual models, and for optimizing the location of characterization and sampling boreholes.

Support & Collaboration

This research was funded by the USGS Toxic Substances Hydrology Program. A MASW land streamer data acquisition and processing system was designed and procured in cooperation with the USGS Groundwater Resources Program.

Collaborators include:

Publications

Ivanov, J., Miller, R.D., Lane, J.W., Jr., and Lacombe, P.J., 2006, Mapping a shallow fault zone and dipping layers using MASW technique with a landstreamer: Geophysics, v. 71, no. 5, p. A39-A42.

Johnson, C.D., White, E.A., Ivanov, J., and Lane, J.W., Jr., 2006, Use of electrical resistivity and surface-wave seismic imaging methods to characterize the geologic framework of the NAWC site, West Trenton, New Jersey [abs.]: Geological Society of America Abstracts with Programs, v. 38, no. 7, p. 528, Paper no. 219-9.

Related Sites

For more information:

For more information on this project, please contact John W. Lane, Jr. (Chief, USGS OGW Branch of Geophysics) or Carole Johnson (Hydrologist, USGS OGW Branch of Geophysics), or call the Branch of Geophysics at (860)487-7402.

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USGS Programs and Offices can learn more about geophysical equipment available for USGS use and training and support from OGW BG.