GARVEY, TIMOTHY P., PETER J. RAFTERY, and STEVEN A. CATLIN, Groundwater Technology, Inc., Ventura, CA

ABSTRACT: Alternatives for In-Situ Remediation for Crude Oil in Soil and Groundwater

Releases of crude oil from production equipment, pipelines, and storage facilities may enter vadose zone sediments and penetrate to groundwater. Cleanup of the resultant subsurface crude oil may be mandated by governmental regulations or may be desired to satisfy landowner-specific requirements. Alternatives for in-situ cleanup or remediation of crude oil in the shallow subsurface may be placed in one of three categories: (1) remobilization and removal, (2) enhanced degradation, and (3) containment or stabilization.

Types of remobilization and removal technologies include (1) manual bailing of liquid crude from recovery wells, and (2) liquid product pumping, with or without groundwater table depression. The latter option may include enhancement by water, steam, or surfactant injection. These technologies may recover significant quantities of crude oil, but will leave residual saturations of at least 30%. Also, remobilization remedial processes may introduce crude oil into subsurface zones where it was not present previously.

Enhanced in-situ degradation stimulates or augments metabolic and reproductive processes of hydrocarbon-utilizing bacteria or fungi. This is accomplished by introducing liquid or vapor-phase "nutrients" (i.e., oxygen, nitrogen, and phosphorous compounds) into crude oil-containing areas. Uniform distribution of the nutrients is required for the process to be effective; this can be difficult to achieve due to subsurface heterogeneities.

Crude oil within and below the vadose zone can be contained or stabilized by physical, chemical, or biological processes. Containment generally involves the "interception" or "blocking" of migrating crude oil. Stabilization involves in-place "fixation" of the subsurface crude oil. Stabilization of a subsurface crude oil plume will occur naturally once the oil has migrated or attenuated such that gravitational equilibrium is reached and residual saturation is attained In the affected sediments.

Selection of an appropriate alternative for in-situ remediation of crude oil within or below the vadose zone is dependent upon a number of site-specific considerations, including site physiography and hydrogeology, type and amount of crude oil present, applicable regulatory requirements, and proposed future land uses. All remedial alternatives presently proven result in some residual saturation of sediments within the original crude oil-containing zones.

AAPG Search and Discovery Article #90992©1993 AAPG Pacific Section Meeting, Long Beach, California, May 5-7, 1993.