Formatted Title
High Resolution Site Characterization and Forensic Methods to Characterize a Recent Petroleum Release from Multiple Historic Petroleum Releases
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, bulk petroleum and chemical storage/transfer facility for approximately 150 years. Multiple grades of petroleum products have been stored in aboveground storage tanks and various releases have occurred throughout the history of site operations. The site is located on a tidal estuary, with the down-gradient portion of the site separated from a surface water by a both a steel sheet pile bulkhead and a beach.
The shallow site soils consist of mixed sand, silt and gravel above a layer of clay. Historical soil impacts of petroleum compounds occur near the surface to approximately 15 to 20 feet below ground surface (bgs). Two historical light non-aqueous phase liquid (LNAPL) plumes have been previously identified in the area of the site that included mixtures of light distillates such as gasoline and naphtha, middle distillates such as #2 fuel oil and heavy petroleum such as #6 fuel oil. Each plume has undergone various amounts of weathering.
In 2019, LNAPL was identified seeping from the beach sand and discharging to the estuary. To evaluate the source of the discharge and whether it was a new release or mobilization of a historical plume, a study area consisting of approximately six acres has been investigated. The study area contains multiple environments including a bulk petroleum storage and transfer areas, an open uplands area, a vegetated uplands area and a beach area.
Approach/Activities
Investigations into the source of the LNAPL have been ongoing since 2019 utilizing multiple methods of LNAPL, soil, sediment and groundwater sampling; including high-resolution characterization using laser induced fluorescence (LIF) and hydraulic profiling (HP). Forensic evaluation of both LNAPL samples and soil samples has been completed using gas chromatograph flame ionization detection (GC/FID) chromatograms generated by forensic laboratories and standard extractable petroleum hydrocarbon (EPH) analysis. A tidal study was conducted using 32 groundwater data loggers deployed in a combination of temporary and permanent monitoring wells and one deployed in the estuary to develop a detailed map of groundwater flow at the site over the tidal cycle.
The LIF and HP were used to identify pockets of soil impacted with LNAPL. The locations and depth intervals containing LNAPL identified with the LIF were targeted for soil sampling for EPH analysis to determine the extent of the petroleum impacts to the area.
Evaluation of the LNAPL and LNAPL-impacted soil at the site was conducted to evaluate the samples for different types of petroleum and the extent of weathering. The forensic chromatograms were compared to the GC-FID chromatograms produced during analysis of EPH samples which were collected as part of the requirements to characterize the site. The samples evaluated were separated into different petroleum compounds and weathering extent.
Results/Lessons Learned
The LIF/HP identified extensive LNAPL across the study area. Co-location of soil borings and temporary monitoring wells with the LIF/HP locations allowed for verification of the LIF/HP results and provided information on the mobility of the LNAPL. The EPH chromatograms, when used as a supplement to the forensic chromatograms, provided a high-resolution forensic evaluation of the study area allowing for the recent release to be delineated within the historical releases present across the study area.