BioVent/Sparge In Situ Treatment of a Crude Oil Release

Problem

A pipeline rupture resulted in the release of 300,000 gallons of crude oil over an undetermined period. The upper stratigraphic unit consists of 25 feet of fractured caliches overlying a sandy aquifer with groundwater at approximately 28 feet bgs. A 3.0-acre crude oil NAPL plume ranging in thickness from 3 feet at the source to 6 inches at the leading edge has been analyzed and mapped. Because this is a leased property concerns of the landowner have resulted in a lawsuit challenging the corrective action plan developed for the site.

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Solution

Pelorus performed a supplemental site analysis and an in situ vent/sparge and respirometry test to determine the feasibility of enhanced bioremediation for remediation of the crude oil and volatile organic compounds (CVOC) distributed throughout this site. During this supplemental characterization, a product recovery system was installed to remove free product from the source area. Over a one-year period only 6,000 gallons of product have been recovered.

Due to the nature of the site conditions and poor product recovery yields, an in situ bioremediation system was designed around a pulsed vent/sparge concept. In principle, vent wells will be cycled off in one area of the plum while sparging is cycled on. The system is designed for the application of gaseous nitrogen and phosphate sources to the sparge air as a means of delivering oxygen, and nutrients simultaneously throughout the impacted groundwater and vadoze zone. Since the gaseous nutrients are organic, they will also have a tendency to partition into the hydrocarbon impacts resulting in a timed-release mechanism wherever the hydrocarbon migrates. After an optimum period of sparging, the venting system will cycle on to sweep oxygen and nutrients through the air permeable areas of the vadose zone. The vent/sparge cycling minimizes the volatile mass removed from the system, allowing it to serve as a food source and inducer of biodegradative enzymes. This is an important requirement in crude oil biodegradation as it sustains degradation of the heavier paraffinic hydrocarbons that are not otherwise degraded.

Preliminary bench scale column tests indicate that hydrocarbon degrading microbial populations of both the soil and groundwater increase by a minimum of 2 orders of magnitude. Commensurate with the increase in hydrocarbon specific degraders, there is an accelerated rate of biodegradation. High treatment efficiencies of the heavy paraffins has been observed in the vent/sparge cycling tests.

Pelorus EnBiotech Corporation has completed the total system design and specifications package for this project and is awaiting the disposition of legal matters and client approval to proceed with procurement and installation.

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