03
Nov

The remediation of petroleum spills to render a site ready for re-development may be very costly and lengthy because of the nature of the petroleum liquids involved, and their interaction with soils and groundwater.  The discharges of petroleum liquids, which are also known as Light Non-Aqueous Phase Liquids (LNAPLs), are common in oil terminals, tank farms, gas stations, and other oil processing or storing facilities. LNAPL-impacted sites are generally valuable real estate for warehousing or residential development because of their proximity to waterfronts, major highways (oil terminals and tank farms), or near city centers (gas stations).

 

If spilled in quantity, LNAPL floats to the top of the groundwater table and adsorbs to the soils. Free phase LNAPL may be in the form of floating phase on the ground water or in soils if detected above certain value as extractable petroleum hydrocarbon (EPH). In New Jersey, if a site investigation detects LANPL as free phase, it requires remediation. Given the constraints of the remedy and time it may take, choosing the proper remedy is key for the economic viability of the development project at an oil-impacted site.

 

Generally, the remedy of LNAPL consists of mass removal of the free phase followed by treatment of the dissolved residual phase in groundwater. There are several remedies commonly applied for the mass reduction of LNAPL including multi-phase extraction, recovery, thermal extraction, surfactant flushing, and excavation. The optimal remedy must consider the duration to achieve the remedial objectives and its implementation must have minimal delay on site improvement.  Implementation of certain remedies (i.e. thermal) may have major impact on the start of the development.  Certain remedies such as surfactant or multiphase extraction and recovery may not affect the start of construction.   However they may be long term remedies and, in many cases, may result in relatively small recoveries, which result in further extending the duration of implementation.  Excavation, depending on the depth of the water table, may be the most efficient remedy method because it removes contaminants from the site. Depth of the impact caused by an LNAPL discharge is limited to the depth of the groundwater. In areas where the groundwater table is shallow, the excavation of LNAPL and off-site disposal of the resulting soils may prove to be economic. In addition, excavation is a quick process and conducive to development especially if it is part of site preparation.

 

The characterization of the LNAPL is a key first step for a successful remedy. Determining the limits of what is considered free product in soil or groundwater pre-remedy will determine the time and effort to complete the remedy. The NJDEP has determined that the free product is a set EPH concentration in soils depending on the spilled oil category: either #2 fuel oil or diesel/all other types of oil. However, the level of EPH that defines the free product varies from site to site depending on the soil characteristics and the weathering of the discharged oil.

 

SESI used a laboratory test method to better estimate the free product LNAPL concentration from actual soil cores at two different sites. Laboratory tests were conducted, using a water drive method, to determine the residual fuel oil saturation. The tests were conducted by confining undisturbed soil samples in a flow cell. Once in the cell, the soil samples were slowly saturated with water in an up-flow mode to displace air from the soil and simulate imbibition of water at low flow rate. The results of the testing showed that weathered #2 fuel oil from the two sites were not mobile at EPH concentrations ranging from 14,900 mg/kg to 21,700 mg/kg, higher than the NJDEP mobility standard of 8,100 mg/kg for Category 2.  These high levels of EPH concentration for the oil mobility result in less soils requiring treatment and therefore savings in remedial costs.

 

SESI is familiar with the demands of remediating and redeveloping a site, and approaches every project as a partnership. Contact SESI to discuss LNAPL strategy for your project.

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