Tank Release or Hydrocarbon Remobilization?

Oral Presentation

Prepared by J. Lu
AECOM, 3995 Via Oro Ave, Long Beach, CA, 90810, United States

Contact Information: jun.lu@aecom.com; 562-213-4120


At petroleum product terminals, inspections are conducted routinely to detect any potential leaks in the tanks and the systems. During such inspection at a petroleum product terminal located in the west coast of the United States, hydrocarbon staining was found in soil along the perimeter of a diesel fuel tank. As the observation was made a few days after a magnitude 5.1 earthquake in the general area of the terminal, the hydrocarbon staining in the soil was suspected to be a result of a leak from the tank. The observation triggered an immediate tank inspection, which included an examination of tank exterior, piping and connections, pressure testing, wall thickness gauging, and an inventory check. Results of the initial inspection suggested that there were no integrity issues with the tank.

Before more vigorous and more disruptive inspections were conducted, chemical fingerprinting was conducted to assess the nature of soil staining and potential connection with the “suspected” tank leak. Samples were collected from the site, including a diesel fuel sample from the tank, a light non-aqueous phase liquid (LNAPL) sample from the monitoring well in the immediate vicinity, and representative soil samples from the perimeter of and beneath the tank. A tiered laboratory analytical approach was taken, which included initial gas chromatography-flame ionization detector carbon chain analysis and final gas chromatography-mass spectrometry or detailed fingerprint analyses. Based on the results of initial inspection, knowledge of LNAPL mobility in response to earthquake seismic waves, and chemical fingerprints of representative samples, it was determined that the soil staining was not a result of suspected tank release but remobilization of hydrocarbons from the historically impacted soil beneath the tank to the soil along the perimeter of the tank. As a result of this study, an unnecessary remedial investigation was avoided for a non-existent “tank release”.