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Underground Storage Tanks

UST-survey

Noggin 250 SmartCart grid survey to map USTs

Overview

Real estate transactions regularly create the need for an environmental site assessment. Confirming the presence or absence of underground storage tanks (USTs) can be a critical factor in contract closing. GPR reflection mapping surveys are commonly used to identify the presence of USTs. The example presented shows five storage tanks plus related pipes discovered at the site of a gasoline station.

Problem

Confirming the presence or absence of underground storage tanks (USTs) can be a critical factor in real estate contract closing. GPR reflection mapping surveys are commonly used to identify the presence of USTs.

GPR Solution

GPR has proven to be an excellent tool for environmental assessments, especially in locating and mapping active and abandoned Underground Storage Tanks (USTs).

A Noggin 250 SmartCart was used to map the location of USTs at a gas station. It was necessary to cordon off the work area for safety reasons but access to the gas pumps had to be maintained. To minimize disruption to the business, the area was broken into four grids and surveyed at separate times. The EKKO_Mapper software was used later, in post-processing, to stitch the grids into one large data set.

The GPR survey results have been presented in several ways:

Cross-Section: The cross-section clearly shows five USTs; four grouped together on the right and one further apart on the left. The hyperbolic response suggests that the tanks are round in shape and it is even possible to see the slight differences in burial depths. The tank on the far right is the shallowest at approximately 3 feet in depth. The leftmost tank is about 0.5 feet deeper. The reflector interpreted as the tank bed is clearly visible on the sides and between the tanks.

USTs
UST-cross-section

Noggin 250 GPR cross-section showing underground storage tanks.

Depth Slices: The position and length of the tanks are evident in the depth slice images. Data had to be collected around a pump island resulting in a blank area within the grid data. Product lines, leaving the island and going to another tank (not shown here), are also visible in the depth slices.

UST-depth-maps

Underground storage tanks and product lines visible on GPR depth slices.

3D: GPR grid data were exported from EKKO_Mapper in a 3D format and plotted with the Voxler 3D visualization software. All the GPR data collected in the separate grids could be displayed in a single view, making interpretations easier. Users can rotate and cut into the data volume or make weaker GPR signals translucent or invisible to highlight signals from strong reflectors.

UST-3D-image

3D visualization of the GPR data.

Google Earth: The EKKO_Mapper software automatically integrates GPS data and can export depth slices as Google Earth compatible KMZ files. This is a very powerful tool for plotting geo-referenced depth slices of buried utilities. Users launch Google Earth and immediately “fly” to the surveyed location. They can then view and toggle between multiple depth slices.

UST-GE (1)

Google Earth overlaying of GPR data.

Results & Benefits

This example of using GPR to assist on a SUE (Subsurface Utility Engineering) requirement illustrates how many GPR users are deploying systems to address such problems around the world. Key results to note:

  • GPR was a practical solution when no other method could locate these USTs.
  • SmartCart configurations are optimized for rapid grid surveying
  • the field crew were easily trained in the whole methodology in less than a day
  • Integrated operation of EKKO_Mapper software and field data acquisition makes on-site mapping quick and easy.
  • The whole project was completed by a two person crew in less than half a day.
  • CAD layer drawings were created to add to the engineering design.
  • GPR image mapping results can also help locate take-offs, bell-joints and laterals.

GPR responses can vary greatly depending on the type of target being sought and the host material properties. GPR variability can be challenging to first time GPR users. When learning about GPR, the best practice is to review several similar case studies to develop an understanding of variability. Check for other insightful information on the resources tab to learn more. Use Contact Us or Ask-the-Expert to reach our Application Specialists who can help you tap into Sensors & Software’s vast array of technical information.

 
 
 
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