Evaluation of Intrinsic Biodegradation in Fractured Bedrock

Problem

After the Suez crisis, Sweden embarked on a program to stockpile fuel reserves for civil and military needs. Throughout Sweden subterranean caverns (i.e., 10,000 to 100,000 m3) were excavated in the granitic bedrock below the groundwater table to store fuel reserves. Product was stored in these caverns on water-beds controlled by extensive pumping of groundwater. In 1994 SOL began decommissioning these sites by selling off product and allowing the groundwater to fill the caverns and reestablish natural groundwater gradients. Environmental impacts associated with the residual hydrocarbon products has became a key regulatory issue in the closure of the 120 facilities resulting in a mandated program to define the fate and transport of dissolved constituents.

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Solution

Pelorus was contracted to support SOL in developing a program to evaluate fate and transport as well as remedial alternatives for the facilities. Teamed with the Swedish Geotechnical Institute Pelorus developed a detailed site evaluation program that included; fracture mapping, borehole geophysics, pump tests, borehole flow logging, seismic imaging and sampling and analysis for intrinsic biodegradation parameters.

Pelorus performed on-site evaluations of bioremedial processes for one of these sites to determine to what extent intrinsic biodegradation processes were occurring and whether or not these processes could be enhanced. A program was implemented to collect:

1. Field data on groundwater indicator parameters to describe the natural attenuation process;

2. Laboratory microcosm data to determine relative rates and extents of fuel hydrocarbon degradation.

Pelorus mobilized a specially configured gas chromatograph (Reducing Gas Detector) and other sampling and analysis equipment to Sweden for this program. Site specific sampling and analysis was performed at the Site in Bladinge, Sweden to collect data for documenting the occurrence of intrinsic biodegradation activity on hydrocarbon impacts in the groundwater. Because of the extensive fracturing in the basalt formation it was necessary to perform straddle packer injection tests and tracer injection tests to evaluate fracture connectivity and transmissivity. During these tests groundwater samples were collected and analyzed for; dissolved oxygen, methane, hydrogen, hydrocarbons, as well as the various potential electron acceptors.

Bench-scale microcosm studies were directed at identifying the levels of specific microbial populations using PLFA (phospholipid fatty acids analysis) and molecular tools such as specific genetic probes to determine the types of biodegradative activity potential present. These analyses required the development of specific sampling protocols for retrieval of sample, from the crystalline rock, at the fracture interfaces. In addition sampling had to be coordinated with the rock core drilling activities and procedures modified accordingly.
This is an on going program consisting of periodic field sampling and analysis, data evaluation, remedial technology screening and strategic planning.

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