Bioremediation of Diesel-Contaminated Soils Using Biopiles

During construction of a new parking facility at KSC, a construction worker noticed a pungent, diesel-like smell emanating from the soil. The construction site, which was formerly a staging and maintenance area for heavy equipment in the 1960šs and 1970šs, was determined to have significant soil and groundwater contamination. In an effort to eliminate further leaching of petroleum products (No. 2 diesel fuel) from the soil to the groundwater, the contaminated soils (500 cubic meters) were removed from the site prior to installation of the asphalt surface. Based upon economic considerations, in situ bioremediation through the use of aerated biopiles was the selected remedial action. Alternatives such as thermal treatment were significantly more costly than bioremediation due to high transportation costs.

Biopiles are constructed similarly to windrow composting piles. Long rows of soil, approximately 1.5 to 2 meters in height, are placed on an impermeable barrier and are often covered as well by an impermeable barrier. An irrigation system and ventilation system are typically installed to augment biodegradation and sometimes volatilization. Ventilation systems are installed in a positive or negative pressure mode, depending on air quality requirements for the area. Biopiles are aerated and irrigated with water and nutrients until soils reach clean levels as defined by the regulatory agency (see the figure).

During the course of this remediation study, several parameters were monitored in the laboratory in an effort to prove biotic degradation pathways. Contaminant levels were analyzed weekly, and biological counts of diesel-degrading microbes were performed as well. In addition, biological community patterning, which monitors biological communities via their metabolic responses to a variety of carbon sources, was evaluated as an alternative technique to monitoring biological activity.

The importance of proving biotic degradation pathways stems from regulatory requirements. At the time of this re-medial effort (1994), bioremediation was still considered an innovative technology and was often reluctantly approved by regulators as a remedial technique. For this reason, proving that biotic, as opposed to abiotic degradation mechanisms, were dominant became paramount to the perceived success of the remediation.

In this study, bioremediation using biopiles was determined to be an effective remediation technique. Laboratory testing confirmed that biological degradation was the mechanism responsible for the contaminant reduction. Enumeration counts were up to 20 times greater in the biopiles than in a noncon-taminated background soil sample. Biological community patterning was also found to be an effective tool for correlating transitions in the biological community to contaminant degradation. The entire remedial process achieved clean soil [less than 10 milligrams/kilograms total recoverable petroleum hydrocarbons (TRPH)] within 12 weeks at a cost of $50 per cubic meter.

Key accomplishment:

• Achieved clean soil levels within 12 weeks of system activation.

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