The Dye Tracing Pages

Emergency Response to an Oil Pipeline Leak

The investigation included the following: a) a review of literature b)field survey for the karst hydrogeologic inventory c) dye receptor placement retrieval, and analysis for the background fluorescence study d) and a potentiometric surface investigation.

HYDROGEOLOGIC INVENTORY

This field investigation was necessary to confirm the accuracy of the geologic map. 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.

DYE TRACE INVESTIGATION

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.

POTENTIOMETRIC SURFACE INVESTIGATION

All Accessible monitor 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.

POTENTIOMETRIC CONCEPTUAL MODEL

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 form the leak site being pulled to a water well.

Water surface elevations obtained from water wells during both wet and dry periods usually provide useful information about the water table surface. Howeve, particularly in the Ordivician Limestone of Middle Tennessee, one has to use caution in using hte data. Most of the wells are open borehole completed, and they often extend through several confining layers and aquifers. Some of the wells in the area even extend through the Ridley Limestone, the Pierce Limestone (confining layer), the Murfreesboro Limestone, the Wells Creek Formation (confining layer) into the Knox Dolomite confined aquifer. However, the water level elevation usually averages out to be approxiamatley the equivalent to the potentiometric surface of the uppermost aquifer (water table), but some wells to a lower aquifer, and some may be slightly too high due to water rising from a confined aquifer with a potentiometric surface higher than the water table. Also, low yielding wells may be pumped down during dry weather conditions an d yield water elevations that are lower than the actual water table. Sometimes these problems make it impossible to map the water table surface. However, in this area, these problems do not appear to be serious, and a reasonable estimate of the water table during both wet and dry periods was obtained.