Investigation of Alternative Groundwater Sampling Systems for Use in Fractured Rock Aquifers

Groundwater sampling in open boreholes tapping fractured bedrock aquifers is particularly challenging because of mixing of water within the borehole from multiple fractures. To alleviate this problem, a packer-pump assembly can be employed to isolate flow from discrete fractures or fracture sets. Groundwater is then extracted at a rate commensurate with flow produced by the identified fracture. While this procedure has long been recognized as a standard procedure to collect samples from discrete fractured zones, it can be time consuming and logistically difficult.

This study is investigating alternative (without the use of a packer assembly) sampling systems that can be used to extract representative groundwater samples from boreholes adjacent to discrete fractures with less equipment and at a reduced cost. A patent-pending system has been developed that utilizes hydraulic containment to extract representative groundwater samples in open boreholes. Representative samples are obtained by minimizing mixing of borehole water with fracture water. Therefore, a key component of the system is the confirmation of favorable borehole flow patterns during sampling. A variety of tools have been used to track borehole flow patterns, including flowmeter and novel tracer deployment procedures. Preliminary results indicate that fracture water can be effectively isolated from stagnant borehole water with the new sampling system.