Special Utility of Flexible Liner Methods in Karst Formations

Karst formations are well known to be difficult to assess because of their highly permeable and tortuous flow paths.  Karst formations are also difficult for installation of monitoring wells because of the loss of the typical sealing grout to those same high flow channels.  The inadvertent sealing of the important flow paths with grout is a problem.  It is especially difficult to use straddle packers because of the high probability of bypass of the packer in the formation.   Furthermore, the high flow rate in karst formations makes an open hole a special risk of cross connection between contaminated zones and uncontaminated zones.

A study was performed of methods for karst characterization by a well known environmental contractor and it concluded that flexible liners had advantages over all other available monitoring methods, but that paper did not explain the details of the liner attributes.  This presentation describes the basis for the significant characteristics of flexible liners as applied to karst formations.  The liners are used to seal the borehole and to perform multi level sampling without the use of any grout.  Consequently there is no loss of the grout to the formation or the inadvertent sealing of significant flow paths or impact on the ground water chemistry.  The liner can also be used to assess the hydraulic conductivity if the conditions meet certain criteria.  There is no need to identify the proper location of straddle packers because the multi level sampling liner seals the entire hole.  No water is stored in the borehole which makes head measurements during pumping tests and the sampling for tracers much more effective.  Special eversion aids are used to overcome the potential for diversion of a liner into a large solution channel/cavern.  Installations through sonic casing are especially attractive for reasons that are explained.