Determine possible resurgence points of the oil at springs or surface streams using a dye trace investigation.
Scope of Work
The dye tracer study was to assist in characterizing groundwater flow in the carbonate rock formations beneath the leak site and to determine discharge points for groundwater from the site.
The Karst Hydrogeologic Inventory was performed to confirm the accuracy of the geologic map and identify monitoring locations. The survey was conducted under conditions ranging from moderate to high flow during a wet period when the dominant resurgence points were active. The survey was conducted by walking or floating all streams and associated impoundments (lakes/ponds) in the study area to visually identify karst features such as springs, soil springs, seeps, sinkholes, swallets, karst windows,sinking streams, and caves.
Receptors were deployed in the water flow of the streams and resurgence points to be monitored. Background fluorescence was measured for both a one and two week interval. The results of the monitoring were used to evaluate the appropriate dyes and dye concentrations to be used for the dye tracer investigation.
All accessible monitoring wells in the area were measured during a dry period and the depth to water subtracted from the ground surface elevation. The elevations of springs and selected points along streams were measured estimated from topographic maps. These elevations and terrain features, such as topography, sinkhole distribution, sinking streams, etc. were used to construct a map of the water table for the uppermost aquifer.
Although the dye traces were performed during wet weather conditions, the water table elevations and stream flow (or lack of stream flow) indicates the dye trace results should be the same for dye weather conditions. However, it is possible that large-volume pumping from water wells for irrigation, cattle watering, etc. during the dry months might create a cone of depression that could result in groundwater from the leak site being pulled to a water well.
The karst investigation and dye tracer study revealed groundwater flow direction identifying potentially impacted areas. Ideally, dye trace investigations are performed before construction or a contaminant spill so that emergency response plans can be created and implemented quickly should an event occur.