Abstract: Untitled

Eve Huggins, Antonio Buangan, June Oberdorfer, Marc Yalom

The purpose of this investigation was to define the site hydrogeology as part of the closure of a former petroleum-waste treatment facility. Continuous coring of the alluvium and bedrock, continuous packer-testing of bedrock boreholes, and completion of multi-depth paired piezometers permitted the determination of vertical and lateral variations in hydraulic conductivity, hydraulic head, and geochemical characteristics.

Located in the eastern margin of the southern Coast Ranges, the Coalinga facility is underlain by shale of the Tertiary Kreyenhagen Formation. Three distinct permeability zones occur which correspond directly to the degree of weathering of the shale. Groundwater flows primarily laterally through the high-permeability, shallow, weathered zones. Quaternary alluvium and terrace deposits fill the valleys to either side with fine-grained material and appear to act as discharge zones for shallow groundwater. Downgradient of the site, permeable sandstone units of the complexly-interbedded Tertiary Etchegoin Formation act as a sink for groundwater which is no longer present in the overlying alluvium.

Groundwater in the area is predominantly sodium-sulfate in composition and the high total dissolved solids content, including upgradient of the site, make it unsuitable for most beneficial uses. Similarity of the groundwater chemistry in the shallow zones, independent of the geologic unit, indicates the continuity of the shallow flow paths. The groundwater of the deeper, low-permeability zones often has a distinct geochemical signature, indicating the isolation of these zones from the major flow paths.

AAPG Search and Discovery Article #90958©1995 AAPG Pacific Section Meeting, San Francisco, California