Abstract: API's Decision Support System (DSS) Applied in a Site Assessment for Residual Crude Oil in Soil: Case Study in Kern County, California

Leslie A. Klinchuch, James M. Waldron

Historical crude oil leaks from a pipeline have impacted soil near a sensitive ground-water recharge area in Kern County, California. The residual crude oil in soil is confined to the vadose zone, and occurs from about 10 feet below ground surface (bgs) to a maximum depth of 80 feet bgs. The water table beneath the impacted soil is currently 159 feet bgs. The site is irrigated regularly for agriculture. Ground water has not been affected. Future ground-water recharge plans may raise the water table to 50 feet bgs near the area of the impacted soil. Fate and transport modeling with site-specific data was used to determine if the existing hydrocarbons in the soil pose a significant risk to ground water quality.

The computer models selected for this project are incorporated as modules in the American Petroleum Institute's (API's) Exposure and Risk Assessment Decision Support System (DSS). Transport of BTEX compounds was modeled using SESOIL for the unsaturated zone, coupled with AT123D for the saturated zone. The SESOIL model was calibrated using actual soil moisture measurements and ground-water recharge estimates based on applied irrigation. Peak BTEX concentrations in ground water predicted for the site are well below maximum contaminant levels. A sensitivity analysis affirmed that aerobic biodegradation significantly reduces BTEX compounds. Due to the high availability of dissolved oxygen in the ground water at this site, natural attenuation may be the most viable mechanism to remediate B EX compounds in the soil.

AAPG Search and Discovery Article #90958©1995 AAPG Pacific Section Meeting, San Francisco, California