A tracer methodology for identifying ambient flows in boreholes

Maurice, L., Barker, J.A., Atkinson, T.C.., Williams, A.T. and Smart, P.L. (2011) A tracer methodology for identifying ambient flows in boreholes. Ground Water, 49 (2), 227-238. (doi:10.1111/j.1745-6584.2010.00708.x).

Abstract

Identifying flows into, out of, and across boreholes is important for characterizing aquifers, determining the
depth at which water enters boreholes, and determining the locations and rates of outflow. This study demonstrates
how Single Borehole Dilution Tests (SBDTs) carried out under natural head conditions provide a simple and cheap
method of identifying vertical flow within boreholes and determining the location of in-flowing, out-flowing, and
cross-flowing fractures. Computer simulations were used to investigate the patterns in tracer profiles that arise
from different combinations of flows. Field tracer tests were carried out using emplacements of a saline tracer
throughout the saturated length of boreholes and also point emplacements at specific horizons. Results demonstrated
that SBDTs can be used to identify flowing fractures at the top and bottom of sections of vertical flow, where
there is a change in vertical flow rate within a borehole, and also where there are consistent decreases in tracer
concentration at a particular depth. The technique enables identification of fractures that might be undetected by
temperature and electrical conductance logging, and is a simple field test that can be carried out without pumping
the borehole.

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