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 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 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.
Radar 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.
Buried 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.
J
R Associates,
Ph: