--> Abstract: Hydrostratigraphic Analysis of a Complex Fluvial Depositional System, Sacramento County, California, by J. E. Sciacca; #90935 (1998).

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Abstract: Hydrostratigraphic Analysis of a Complex Fluvial Depositional System, Sacramento County, California

JOHN E. SCIACCA, International Technology Corporation, Martinez, California

A comprehensive stratigraphic analysis process was implemented as part of the environmental restoration program at Mather Air Force Base in Sacramento County, California. The base is underlain by a complex series of Pleistocene fluviai deposits and facies of the ancestral American River. Previous subsurface interpretations had not incorporated an adequate working depositional model in their analysis, resulting in inconsistent and often confusing relationships between lithologic units. In addition, the existing monitoring well network had not screened certain channel sequences with potential for enhanced contaminant transport.

The stratigraphic analysis process included the drilling and wireline geophysical logging of stratigraphic boreholes at strategic locations selected for monitoring. Characteristic electrofacies were identified on the geophysical logs and incorporated into a stratigraphic cross-section network. The cross-sections were correlated by evaluating the electrofacies and tying unconformities, particularly the basal boundaries of channel sequences. Hydraulic and chemical data were also plotted on the sections to evaluate groundwater flow and hydraulic communication.

The analysis resulted in the identification of a distinctive stacked channel sequence extending for over four miles in the dip direction and interpreted within the context of a bedload dominated fluvial model. A time stratigraphic equivalent mixed load channel sequence was also delineated in the southern portion of the facility. The mixed load sequence extended for over three miles along dip. Both channel sequences were found to be preferential pathways for transport of chlorinated hydrocarbon plumes, some extending for over two miles in length.

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