The inability of the TPH analytical method (8015) to quantify all hydrocarbon components of petroleum in a given sample is well established but not widely appreciated by regulators, scientists, and remediation managers (e.g., API Publication 4709). A case where this shortfall became particularly impactful was a release of approximately 3,000 barrels of heavy (API 19) crude oil from a buried pipeline. During cleanup, the State of California required that soil samples be analyzed using EPA Method 8015 to quantify the oil concentration in the soil, which was then used to calculate the volume of oil present. However, the volume of oil calculated using this method did not match the volume of oil expected based on visual and other evidence. It was suspected that the analytical method was not quantifying all the hydrocarbons, largely, but not solely, related to those components larger than C44. To test this hypothesis, three pure oil samples from the release were sent to two separate labs for quantification following the same procedures as the soil samples. Lab 1 quantified only 30 to 36% and Lab 2 only 38 to 41% of the hydrocarbons present. Therefore, it was determined that the lab analyses for all the soil samples quantified on average only 33% of the oil present in the soil samples and approximately 66% of the oil had gone unreported. Subsequently, a “correction factor” was developed to account for this under-reporting. This “correction factor,” based on the average of three pure oil samples analyzed, was used to convert the Method 8015-determined oil concentrations into a more accurate oil volume estimate. The “corrected” oil volume better matched the volume expected based on visual evidence. Such correction factors may be applicable to other remediation data sets.
Primary Author / Conference Presenter:
Dr. Kristin Robrock
Oakland, California, USA
Dr. Paul Boehm, Exponent, Maynard, MA