Formatted Title

What’s New: Delineation of a Release to a Historically Impacted Area

Background/Objectives

First developed in the late 1800s within a highly industrialized area, the site has been continuously operating under various owners as a refinery and bulk petroleum storage/transfer facility for approximately 150 years.

Light non-aqueous phase liquid (LNAPL) was recently discovered in a septic tank located proximate to active underground petroleum pipelines within a relativity high-traffic area of the site. The source and extent of the LNAPL were characterized through numerous field investigations, which were hampered by the occurrence of historical petroleum hydrocarbon impacts.

Given that this is an active facility, an approach has been taken to address recent releases to the extent practicable given presence of facility infrastructure and not extend the remediation of new releases into areas of historical impacts. The investigation of this current release was guided by petroleum hydrocarbon forensic evaluations with the ultimate goal of implementing a source area remedy (i.e., LNAPL collection) such that groundwater quality downgradient of the source area is no longer impacted by comparison to upgradient groundwater quality.

Approach/Activities

Investigations into the source and extent of the recent LNAPL release have been conducted through the collection of soil and LNAPL samples from borings and temporary wells.  Petroleum hydrocarbons within LNAPL and soil samples have been analyzed using high resolution capillary gas chromatography with a flame ionization detector. This method allows for the identification and quantification of up to 88 separate peaks comprised of normal alkanes, isoprenoids, aromatics, polycyclic aromatic hydrocarbons, and oxygenate compounds. While this method is semiquantitative, it is relatively reproducible such that identified peaks reported as a percentage of the entire chromatogram are comparable between different samples.

Calculation of various diagnostic ratios, carbon ranges (gasoline, diesel, residual), as well as implementation of principle component analysis, were used to delineate the impacts (i.e., extent of mixing) of the recent release within an area which contains historical petroleum hydrocarbon impacts.

Results/Lessons Learned

The evaluation of petroleum hydrocarbon forensic data allowed for the delineation of the recent release, and also identified at least three potentially separate historical releases.  Further complicating investigation efforts, as well as LNAPL remedy implementation, was the discovery of numerous, and conflicting, historical underground piping mapping data. These mapping data, when taken as a whole, provide some rational of the spread of the release, but also suggest some volume of recent LNAPL might still be contained within these suspected piping networks, presenting a long-term LNAPL and dissolved phase groundwater source. The majority of recoverable recent LNAPL also exists within a high traffic area; therefore, the implementation of LNAPL recovery needed to account for active site conditions.