Inspection cores revealed an area containing voids in the concrete wall of a storm drain culvert.

The contractor believed that potential voids were localized to a small area however, the county inspectors required verification that voids are absent in the rest of the culvert walls.

Spectrum employed the GSSI SIR-10A+ with a 900 MHz antenna. Horizontal and parallel traverses, spaced one foot apart, were established on both walls and the deck using a chalk line.

Vertical markings were placed at 2-foot intervals for location control.

 Our geophysicists collected the GPR data pressing the antenna against the deck while the contractor's laborers slowly pushed the scaffolding along a pre-determined path.

Location marks were placed in the data as the antenna crossed vertical chalk lines.

A steady hand, keen eye-sight, and strong biceps were required to keep the antenna on track.

Monitoring data collection can be ardous work.

The real effort is in the processing and interpretation of the data.

As you can see, we use PCs to process geophysical data and Macs for graphic presentation.

Using the best of both computer worlds yields significant benefits to our clients.

Once the data is processed, it is printed and "hung" to allow for interpretation.

We keep most of our office walls blank just for this purpose.

After a careful review of the data, Spectrum determined that voids were localized only in a small 3 by 3-foot area.

The adjacent image is a sample profile from this area.