ZINNI, EDWARD V., CNG Producing Company, New Orleans, LA

ABSTRACT: Seismic and Stratigraphic Study of Hazardous Waste Injection Reservoirs, St. John the Baptist Parish, Louisiana

The purpose of this paper is to establish the use of reflection seismic data for environmental impact studies. A recent study by Herbert and Hanson (1991) assessed the regional stratigraphic and structural nature of three injection reservoirs for hazardous waste and their relationship with the base of lowermost Underground Source of Drinking Water (USDW) in St. John the Baptist Parish, Louisiana. The authors determined that the downdip equivalent of the Covington Aquifer lies stratigraphically between two of the injection reservoirs and, based on geophysical well logs, these three intervals may be in stratigraphic/hydrologic communication.In order to help determine if communication is occurring, 135 miles of seismic data and additional well control are integrated into the previous stu y. Seismic control indicates that 4 previously undetected normal faults transect the 3 injection reservoirs and the Covington aquifer. The presence of these faults significantly increases the possibilities of communication by (1) acting a conduits and allowing vertical migration of fluids along the fault planes, or (2) causing juxtaposition of sand against sand and allowing leakage to occur across the fault planes.

Regional cross-sections indicate that the upper injection reservoir is part of a fluvial system that occasionally scours down into the Covington aquifer causing sand on sand contacts. This type of scour and fill deposition may allow stratigraphic/hydrologic communication between these intervals.

The injection of liquid hazardous waste at this location could jeopardize not only the water quality of the Covington aquifer but possibly other shallow freshwater aquifers should vertical migration occur along the fault planes. Without the use of seismic data the risk of contamination would not have been properly assessed.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.