This study examined the effect of weathering on hydrocarbon biodegradation and toxicity at a former oil field near Guadalupe, California. Soil and groundwater at this site contains residual diesel-range hydrocarbons formerly used to dilute the viscous crude oil to facilitate pumping (Lundegard and Garcia, 2001). Natural attenuation is being considered at this site as a means of remediating residual hydrocarbons in soil and groundwater. To provide the lines of evidence required for use of natural attenuation at this site, this research was undertaken to determine if the hydrocarbons continue to be biodegradable after extensive weathering in the field. Observed hydrocarbon biodegradation rates were directly proportional to initial total petroleum hydrocarbon (TPH) con-centration, suggesting first-order kinetics. Highly weathered hydrocarbons most distant downgradient from the source zones exhibited slightly lower biodegradation rate con-stants. Microtox® toxicity decreased rapidly during 20 days of biodegradation in laboratory microcosms.


Civil and Environmental Engineering

Number of Pages


Publisher statement

Publisher's website: http://www.battelle.org.



URL: http://digitalcommons.calpoly.edu/cenv_fac/92