Characterization and Source of Unknown “Tar-Like Material” and “Slag” in a Former Oil Field in Compton, California

Abstract

The discovery of “tar-like material” and “slag” within a ravine traversing a mobile home park and former oil field promulgated its remediation and a subsequent lawsuit brought by the park's owner against the former Dominquez Oil Field (Compton, CA) operator claiming these materials were derived from historic oil production operations. In this study, archived samples of these materials from the (remediated) ravine were characterized for their physical (density, microscopic character, magnetic properties, and float-sink behavior) and chemical properties, the latter including chemical fingerprinting of the total extractable hydrocarbons, polycyclic aromatic hydrocarbons, and petroleum biomarkers, to determine their nature and source(s). Physical testing confirmed the “slag” was iron and/or steel (ferrous) slag that had experienced variable cooling histories. A chemical fingerprinting comparison of the “tar-like material” and Dominquez Field (Monterey Formation) crude oil revealed that the crude oil—or its weathered equivalent—was not the source of the tar-like material. The tar-like material exhibited evidence of heating consistent with a distillation residuum—the heavy fraction(s) of a distilled crude oil produced during refining. The most likely source of the tar-like material is a refined petroleum asphalt. The co-occurrence of ferrous slag—a common road asphaltic concrete aggregate and road base—and petroleum asphalt in the site's ravine was reconciled as being most likely derived from recurrent road-paving operations that occurred at the mobile home park in the 1980s—and not from historic oil field operations.