Several ground-water monitoring wells on the
Mountain Home Air Force Base in southwestern Idaho
were constructed in February 2000 to replace existing
monitoring wells that became ineffective as a result of
declining water levels. Upon completion of the replacement
wells, borehole geophysical logs were collected,
including natural gamma radiation, electromagnetic
induction, caliper, fluid temperature, and resistivity.
A prototype borehole acoustic doppler velocimeter
(B-ADV) was used to make experimental three-dimensional
measurements of lateral and vertical flow in two
of the replacement wells, MW11–2 and MW3–2, each
450 feet deep, to better understand ground-water flow
in the basalt underlying this area.
Measurements indicated two independent flow
zones in each well: unit B, from about 380 to about
415 feet below land surface, and unit C, from about
415 to about 430 feet below land surface. In each well,
direction of flow in unit B was north-northwest toward
Canyon Creek and, in unit C, south-southwest toward
the Snake River. Measurements also indicated downward
intraborehole flow in both wells. Unit B appeared
to represent a local-scale flow regime; unit C appeared
to represent a regional flow regime.
This information suggests the existence of a
complex three-dimensional hydrogeologic setting that
cannot be discriminated easily on conventional waterlevel
maps. Although data from only two wells are
insufficient to construct a conceptual model of the
ground-water flow regime, these experimental results
demonstrate the capability of the B-ADV to obtain
detailed flow measurements that, combined with data
from other types of geophysical logs, discrete measurements
of hydraulic head, and water chemistry,
would aid in future studies and management of the
ground-water resources, including contaminant transport
and remediation.
