Bioremediation treatments were evaluated on the microcosm scale for their effectiveness in removing petroleum hydrocarbons from soil. Three compositionally distinct crude oils were applied to native soils from their respective oil production areas. The crude oils varied in API gravity (21 to 31 at 60°F) and in hydrocarbon class distribution. A total of 8 treatment regimes that included the variables of moisture content, fertilizer application, tilling, and pH control were examined for their effectiveness in enhancing biodegradation rates over no action and sterile controls. The microcosms were monitored for 52 weeks.

The extent of biodegradation was determined by the total extractable hydrocarbon (TEH) concentrations, hydrocarbon class distributions, gas chromatography, C17/pristane and C18/phytane ratios, and hopane concentrations in the initial and final oils. The estimated half-lives of the crude oils were determined to be greater than two years under all but one treatment regime. A very rigorous treatment of monitoring and controlling soil pH, nutrient concentrations, and moisture content on a weekly basis reduced the half-life of a crude oil to 8 weeks. Half-lives were measured by TEH loss and confirmed by hydrocarbon class distribution changes and gas chromatography "fingerprints." Hopane concentrations were used to more accurately predict crude oil half-life.

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