USING ARCGIS TO MONITOR WATER TABLE FLUCTUATIONS AND ITS AFFECT ON THE BEHAVIOR OF NON-AQUEOUS PHASE PETROLEUM

We have developed a conceptual model of light non-aqueous phase liquid (LNAPL) petroleum behavior in a heterogeneous aquifer system under an active petroleum refinery. Major Hydrogeologic Findings:

• Large amounts of residual LNAPL trapped by capillary forces below the water table are dramatically remobilized during periods of low water table conditions triggered by long-term droughts and increased groundwater pumping.

• Conversely, a reduction of LNAPL in wells and a shrinking of free product bodies have been observed during periods of elevated water table and flood conditions. Using ArcGIS:

To analyze and illustrate the effects that water table fluctuations have on the apparent product thickness in site monitoring and recovery wells, the Spatial Analyst extension in ArcGIS 9.1 was used to contour groundwater elevations and LNAPL thicknesses as recorded during gauging events. The charts and contour maps shown here were created in ArcGIS to compare groundwater elevation and product thickness data for the same month exactly two years apart (April 2000 and April 2002).

• Data from April 2000 was collected during a period of long-term high water table conditions.

• Data from April 2002 was collected during a period of long-term low water table conditions resulted from a severe regional drought.

We created a model using the 3-D Analyst extension in ArcGIS to help visualize the overall extent and thickness of the product plume across the site. We are using these visualizations of product behavior to anticipate seasonal and climatic changes in product recovery rates and design appropriate remedial systems.