Using geophysics to locate buried USTs

Determining if a site has old fuel tanks is a common problem. In this case study a land developer was considering purchasing a small strip mall shown below. The strip mall consisted of several buildings and a large parking area. There once was a gas station on the site. The station was demolished when the video store was built. It was assumed the station's tanks were removed during demolition but there was no documentation to prove it. The developer hired us to determine if the tanks had been removed.

Site MapSite Map

We collected magnetic data, radar data and performed limited utility locating. To avoid interference from surface metal, the survey was performed at night when the parking lot was almost free of cars. We began the survey with pipe and cable locating. Buried steel pipes create anomalies on magnetic contour maps. Pipes usually have characteristic anomalies that make them easy to spot. Occasionally they can produce anomalies that look like tanks. Pipe and cable locating was performed to avoid misidentifying pipe anomalies.

Next magnetic data were collect. Magnetic data were collected on ten-foot centers throughout the parking lot. The magnetic data were contoured to look for magnetic anomalies indicative of tanks. The location of buildings and buried pipes were superimposed on the magnetic map to aid interpretation.

Magnetic Contour MapMagnetic Map

The magnetic map of the site contained several anomalies. There were anomalies surrounding the three cars in the parking lot and above a buried pipe running between the shops and the video store. These anomalies were quickly attributed to known sources and were not investigated further. There was a large group of anomalies to the right of the video store. These anomalies were indicative of buried metal. It was not possible to tell from the anomalies alone what the buried metal was. It could have been buried tanks or it could have been the old foundation of the service station. To resolve the anomalies, a radar was used to image the buried metal. Radar scans were collected along traverses spaced five feet apart over the group of suspicious anomalies.

GPR Profile of TanksRadar Profile

Above is one radar profile collected adjacent to the video store. Three tanks can clearly be seen in the profile. The radar crossed over the center of two tanks and then went along the axis of a third. The tanks were buried approximately three feet beneath the asphalt parking lot. Additional profiles discovered a total of six buried tanks at the site.

Investigation ResultsBuried Tanks

The geophysical investigation showed that six buried fuel tanks were still at the site. The land developer renegotiated the price of the strip mall based on the new tank information. Our investigation saved the developer considerable expense in environmental costs.

J R Associates routinely performs magnetic and radar investigations to look for buried tanks, drums and other hazardous debris. Please contact us to discuss how our services could benefit you.

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J R Associates, 1886 Emory Street, San Jose, CA  95126

Ph: (408) 293-7390 Email: jra@Greatgeophysics.com