--> Abstract: Conjunctive Use of Downhole Geophysical and Traditional Mapping Methods to Improve Site Characterization for Remedial Planning from a Petroleum Hydrocarbon Release Site, by Raymond L. Knox, Tim McKinsey, and Misti Benchabbat; #90078 (2008)

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Conjunctive Use of Downhole Geophysical and Traditional Mapping Methods to Improve Site Characterization for Remedial Planning from a Petroleum Hydrocarbon Release Site

Raymond L. Knox, Tim McKinsey, and Misti Benchabbat
Schnabel Engineering, West Columbia, SC

Removal of an underground storage tank system revealed no saturated conditions above bedrock (metamorphic Carolina Slate Belt) and no evidence of a release. Subsequent monitoring of the site public water supply well in response to taste and odor complaints indicated the presence of MTBE. Bedrock monitoring wells contained other petroleum constituents (BTEX).

A variety of techniques were used to determine best monitoring well locations and predict contamination fate. Continuous recording of water levels in monitoring wells was used to determine possible hydraulic connection to water supply well.

Fracture trace analysis using aerial photographs, topographic maps, and outcrops was used to propose additional monitoring well locations. Downhole acoustical televiewer logs were used to determine fracture zones and orientations.

Passive diffusion bags (PDB) were placed in wells opposite fracture sets identified by the geophysical logs to identify specific fracture sets and orientations contributing contaminants to the wells.

Contaminant distribution maps were compared to predicted fracture locations and orientations. Results suggest PBD samplers were inadequate for determining zones of contribution. Traditional surface mapping techniques were sufficient for determining dominant fracture orientation and oblique secondary fracture orientation. Acoustical televiewer logs suggested the secondary fractures had minimal impact on potential flow at the site. Water level response in only one well suggested connection to impacted supply well. Additional monitoring of the site is being performed before a final closure decision is made.

 

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas