Paper No. 2
Presentation Time: 2:00 PM
ON THE EFFICACY OF MONITORING WELLS IN KARSTIC CARBONATE AQUIFERS
Monitoring wells are specified by law in virtually every case where contaminants may be or have been released, and they are placed using criteria appropriate only for granular aquifers. However, the results of three academic studies and five investigations performed at contaminated sites demonstrate that monitoring wells and piezometers installed in karstic carbonate aquifers often yield unreliable data and lead to incorrect conclusions concerning aquifer properties, groundwater flow, and contaminant movement. The following cautions are indicated when assessing karst aquifers.
- Monitoring wells may be unreliable in detecting contaminant release.
- A monitoring well that detects a contaminant is unlikely to provide appropriate data regarding the quantity of the release or the speed and direction of the contaminant movement.
- Water levels measured in wells often give erroneous indications of groundwater flow direction.
- Well water levels taken at traditional calendar intervals give little insight into the frequency and magnitude of true fluctuations that may occur in the well.
- Head fluctuations in wells in response to nearby pumping do not necessarily indicate flow connections.
- Traditional well tests in carbonate aquifers typically do not sense the most important elements of the permeability structure.
- Virtually every well in a carbonate aquifer is influenced by a unique suite of permeability and recharge elements.
The highly anisotropic and heterogeneous nature of karst aquifers requires different monitoring methods. Alternative and more appropriate means of aquifer assessment and monitoring in these aquifers are available, including wells augmented with tracer investigations and the use of springs and other access points to the conduit elements of the porosity system. In the words of my late colleague Dr. James Quinlan: “A well that has not been proven to be related to the site of interest by a tracer investigation is not a monitoring well.”