As part of an expansion of the Hawaii Refinery complex and due to the potential presence of voids underlying concrete and/or natural soils within various locations at the refinery complex, SEI was retained to conduct a GPR Survey at the site.  The objective of the GPR survey was to document the lateral continuity of shallow, subsurface strata beneath the concrete, asphalt, and ground surface for the purpose of identifying anomalous reflections consistent with those expected from soil cavities or areas of subsurface erosion.  SEI had previously been retained by Chevron Products Company for conducting a similar survey at the site in approximately 2001.

The GPR survey was performed within eight (8) separate units which included a total of 17 separate sites contained within the units.  The total area surveyed as part of this study was approximately 71,000 square feet in size.  The GPR survey was performed using a Subsurface Interface Radar System 3000 (SIR 3000) digital control unit utilizing a 500-Megahertz (MHz) antenna.  The GPR equipment is manufactured by Geophysical Survey Systems, Inc, New Hampshire.  The 500-MHz antenna provided moderate to high resolution and moderate depth of penetration and was specifically selected based upon the target depths of the anticipated voids and discontinuities which were potentially present at the site.

The results of the GPR survey revealed the presence of apparent soil voids within 11 of the sites surveyed and the presence of apparent buried utilities identified within four (4) of the sites.  The project was completed within approximately one week of project initiation of the field work at the refinery site.  Therefore, the project was completed within the proposed time frame and within budget.