Proactive Investigation of Hydrocarbons Released Into a Linked Groundwater-Surfacewater Hydrologic System: Chevron Estero Marine Terminal

Daniel Tormey, James Waldron, and Don Culbertson

When regulatory concern is high, it is critical to address potential ecological impacts early, and hence "close the door" on further unnecessary studies, as illustrated by the Chevron Estero Marine Terminal case study. Cutter stack (diesel-like hydrocarbons) leaked from a facility sump, reached the water table, and migrated laterally an unknown distance. Media reports led to heightened public and regulatory concern, and the information gap led to worst-case assumptions about the extent and impact of the release to the biota of a nearby creek (Toro Creek).

Chevron undertook a rapid assessment with two goals: define the extent of cutter stock in soil and groundwater, and close the door on expensive biological studies of Toro Creek. The assessment consisted of installing a large number of small-diameter soil borings and temporary well points, monitor wells, and analyzing soil, groundwater, and hydraulic gradient. The information gap was very rapidly filled with the following comprehensive picture: 1) the cutter stock had mixed with heavy crude oil, was highly adsorptive to soil and practically insoluble in water; 2) the cutter stock had not reached Toro Creek; 3) Toro Creek is always a losing a stream, hydraulically connected to groundwater beneath the Chevron facility; 4) the groundwater basin is isolated by bedrock boundaries. Early att ntion to Toro Creek and the Pacific Ocean, and open communication with concerned agencies effectively limited the investigation to soil and water.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California