Further validation of the fracture-network approach for predicting flow in a more sparsely fractured rock at a depth of 100 - 300m has been undertaken more recently. In addition, tracer migration experiments have been performed to examine transport of solutes and colloids through fracture networks. The aims of these tracer migration experiments were to examine processes such as hydrodynamic dispersion and to assess mobility of colloids.
 

The aims of this project were to build confidence in the use of NAPSAC (the fracture network flow model) by comparing model predictions with experimental measurements at field scale.

The hydrogeological experiments were undertaken at the Reskajeage field site in Cornwall. A statistical description of the fracture network was obtained through a combination of core logging, fracture impression logging of the borehole wall and outcrop mapping. Effective hydraulic apertures for individual fractures were obtained by means of constant head injection tests. The hydraulic apertures derived from the single-fracture data and the fracture network geometry data were then used in the program NAPSAC to predict the effective hydraulic properties of the rock on longer length scales. These predictions were then tested by means of larger scale single borehole and interborehole groundwater flow tests.
Comparison of fracture network model results with cross-hole testing results. Click to see larger image.