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Dating a Release

One of the primary goals of an invasive environmental assessment of a automotive fueling station is to determine whether a release of hydrocarbons has occurred and has adversely impacted the subsurface.    This type of assessment is performed on a daily basis by environmental consultants  using direct push drilling and routine chemical analysis of soil and groundwater samples is fraught with pitfalls.  The conclusions of the assessment can be misleading or downright wrong due the inability of a consultant to date the occurrence of the release.

The inability to date a release or at least determine if a new release has occurred from an UST system at a fueling station may lead to unintended consequences: the issuance of a new leaking SUT designation from the State regulatory agency resulting in unnecessary assessment; the denial of a loan from a financial institution for un-addressed environmental concerns; or application of an environmental insurance claim, to name the more obvious scenarios.

A well-planned and executed environmental assessment should take into account the identification of the source and the timing of a release. Factors that should be considered are the general location of a fueling station or UST system on-site.  Is the station on a busy intersection shared with other service stations  where a release from an adjacent facility maybe detected that can be falsely attributed to the subject site?  Are there USTs that were historically placed on the site that had been removed  and a historic hydrocarbon release will be incorrectly attributed to the current UST system?

Often other factors regarding the operation of the UST system are ignored in the assessment.  A review of  historic release detection methods that should be incorporated in the assessment should include:

  • statistical inventory reconciliations
  • leak detection or  vapor monitoring alarms
  • presence of water in the USTs.

When a release has not been historically detected by these methods, the risk for an undetected fuel release could be low.

The release history of the site must be reviewed including:

  • Previous risk-based hydrocarbon closure conditions  Many of these older service station have had leaking petroleum storage tank (LPST) designations in the past where closures were granted without full clean-up.  Yet when the sites are re-assessed, historic hydrocarbons can be re-detected.
  • Comparisons of current versus historic contaminant concentrations may not be appropriate due to the variability of soil and groundwater contaminants.
  • UST systems that have been up-graded since the last assessment and the reason for the initial release never identified or repaired.  Therefore, the common sources for releases – overfill/overspills, leaky spill buckets, dispenser releases, underground storage tank corrosion or holes –  may have continued.
  • Tank-hold water that has been impacted by past minor leaks or overfills and has never been removed/disposed, which is required to be chemically analyzed during tank removal procedures can create the impression of a new release.

Can a historic hydrocarbon release be differentiated from a current UST system release or at least a post risk-based closure release?  Depending on the timing of original closure, there can be several assessment tools to use:

  •  Lead additives are not applicable due to the occurrence of releases after the late 1980s, long after leaded fuels were discontinued.
  • Chemical assessment of a release to the subsurface for the presence of ethanol or MTBE might be more helpful to date a release(1979 – 2005).
  • Presence of TBF and TBA in soils or groundwater, degradation products of MTBE might assist.
  • Ratios of compounds such as the addition of benzene and ethylbenzene as a ratio to toluene and xylene can be useful to differentiate a new release from an older plume or be used as evidence for the lack of a “new release”.

In conclusion, the forensic assessment of a site  is paramount in order to get a true picture of a release and its implications.  Otherwise, an assessment can lead to unnecessary effort and expense.