--> Abstract: The Integration of Hydrochemistry and Sequence Stratigraphy to Identify a Groundwater Contaminant Plume: A Case Study from the Dominguez Gap Area of the West Coast Basin, Southern California, by W. L. Neal, K. D. Ehman, and R. S. Cramer; #90935 (1998).

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Abstract: The Integration of Hydrochemistry and Sequence Stratigraphy to Identify a Groundwater Contaminant Plume: A Case Study from the Dominguez Gap Area of the West Coast Basin, Southern California

NEAL, WILLIAM L., GeoChem Applications, El Dorado Hills, CA;KENNETH D. EHMAN, and RICHARD S. CRAMER, Groundworks Environmental, Inc., Santa Clara, CA

The Wilmington-Long Beach area, California, has a long history of environmental problems associated with oil production and industrial waste disposal. In this area, aquifers are impacted by many different sources. Identifying individual contaminant plumes by hydrochemistry alone is difficult due to the widespread contamination and complex hydrostratigraphy. By integrating hydrochemical data into a sequence stratigraphic framework for a contaminated site in the Dominguez Gap area, a contaminant plume from a liquid-waste disposal site was identified.

Soil and groundwater data collected in support of a remedial investigation for the site indicates that most contaminants are either "fixed" in the unsaturated zone or confined to the shallow, semiperched, water-bearing zone. However, some contaminants are mobile and have traveled significant distances in the saturated zone. Through evaluation of on-site versus off-site data, the hydrochemical "signature" of the contaminant plume was identified. To differentiate the site plume from other plumes in the region, the following performance criteria were applied: 1) the contaminant must be consistent with the site plume signature; 2) the contaminant must be connected to the source via a flow path as defined by the sequence stratigraphic model; and 3) the presence of the contaminant must be consistent with fundamental transport and attenuation mechanisms. Using these criteria developed through the integration of hydrochemistry and sequence stratigraphy, the contaminant plume (which extends for more than one mile downgradient of the site) was identified using data from only twelve off-site wells.

AAPG Search and Discovery Article #90935©1998 AAPG Pacific Section Meeting, Ventura, California