The Sampling Protocol Site was created as a field test site for tracer experiments aimed at determining appropriate methods for groundwater sampling in fractured porous media. The site is underlain by the Cambrian interbedded shales and limestones of the Nolichucky Shale, which have been intensely folded and fractured by post-depositional deformation. Competent bedrock occurs at depths of 15-25 ft (5-6 m), and is overlain by saprolite and a moderately thick soil cover. Porosity in similar materials near this site varies from a few percent in the bedrock to more than 30% in the weathered saprolite. While matrix permeability is low, rapid flow and transport occurs within fracture zones that account for only a small percentage of the overall porosity, resulting in velocities of > 40 m/d.
The site is instrumented with an injection/pumping well, screened from 20-70 ft (6-20 m), and three sets of well pairs, screened from 20-70 ft (5-7 m) and 60-70 ft (18-20 m) in all cases. These well pairs are oriented updip, downdip, and along strike of the injection well. In addition, three multilevel wells (Fig. 1) have been installed adjacent to the screened well pairs to facilitate direct comparison of samples obtained from multilevel versus screened wells. Each multilevel contains 5 sampling ports whose locations have been determined by extensive borehole testing to determine the active flow zones (Fig. 2). The injection well is currently instrumented with a passive gas injection system for an ongoing SF6 tracer test. A solar-powered data logging system (Fig. 3) has been installed at the site to allow continuous water level monitoring in all of the wells and multilevel ports. Continuous water level monitoring devices suitable for installation in the small-diameter multilevel ports are under development. Dimensions of the site are 40 ft by 60 ft (12 × 18 m), but it can be expanded in all directions to include a larger network of existing screened wells and well pairs.
A large number of data sets have been obtained from this field site, and data are continuing to be accumulated through ongoing studies. These data, collected under ambient and stressed conditions, have allowed investigators to test hypotheses about flow and transport processes in fractured rocks and how structure and stratigraphy, variable flow conditions, well construction, and purge procedures affect the representativeness of a groundwater sample. Data sets include piezometric data from six pumping tests and from unstressed conditions documenting seasonal and storm-related changes, analyses from helium, bromide, SF6, and colloid tracer tests (Fig. 3), continuous core from three locations, electromagnetic borehole flowmeter measurements, point dilution test data, mineralogical data, field parameters, and geochemical analyses.