Abstract
In September 2010, a research consortium led by
scientists from Utah State University began drilling the first of
three continuously cored boreholes on the Snake River Plain
in southern Idaho. The goals of this effort, the Snake River
Scientific Drilling Project, are to study the interaction between
the Earth's crust and mantle, to identify potential geothermal
energy sources, and to track the evolution of the Yellowstone
hotspot on the Snake River Plain.
The first borehole, located near Kimama, Idaho, is about
50 miles southwest of the U.S. Department of Energy's Idaho
National Laboratory. Because geohydrologic data are scarce
for that area of the central Snake River Plain, the Kimama
borehole, completed in January 2011, provided a unique
opportunity to collect geophysical and water-chemistry
data from the eastern Snake River Plain aquifer system,
downgradient of the laboratory. Therefore, in conjunction
with the Snake River Scientific Drilling Project, scientists
from the U.S. Geological Survey's Idaho National Laboratory
Project Office conducted geophysical logging and collected
water samples at the Kimama site. Wireline geophysical
logs were collected for the diverging borehole, Kimama-1A
and -1B, from land surface to 976 and 2,498 feet below land
surface (BLS), respectively. Water samples were collected
from Kimama-1A at depths near 460 and 830 feet BLS, and
from the Kimama Water Supply (KWS) well located about 75
feet away.
Geophysical log data included a composite of natural
gamma, neutron, gamma-gamma dual density, and gyroscopic
analysis for boreholes Kimama-1A and -1B. Geophysical logs
depicted eight sediment layers (excluding surficial sediment)
ranging from 4 to 60 feet in thickness. About 155 individual
basalt flows were identified, ranging from less than 3 feet
to more than 175 feet in thickness (averaging 15 feet) for
borehole Kimama-1B (0 to 2,498 feet BLS). Sediment
and basalt contacts were selected based on geophysical
traces and were confirmed with visual inspection of core
photographs. Temperature logs from the water table surface
(about 260 feet BLS) to the bottom of borehole Kimama-1B
(2,498 feet BLS) were nearly isothermal, ranging from about
62 to 64 degrees Fahrenheit. Gyroscopic data revealed that
borehole Kimama-1B begins to separate from borehole
Kimama-1A near a depth of 676 feet BLS. Drillhole azimuth
and horizontal deviation at total logged depth for boreholes
Kimama-1A and -1B were 172.6 and 188.3 degrees and
25.9 and 82.0 feet, respectively.
Water samples were collected and analyzed for common
ions; selected trace elements; nutrients; isotopes of hydrogen,
oxygen, and carbon; and selected radionuclides. One set of
water samples was collected from the KWS well and the two
other sample sets were collected from borehole Kimama-1A
near 460 and 830 feet BLS. With one exception, data for all
three zones sampled near Kimama generally indicated that the
water chemistry was similar. The exception was found in the
deepest zone in borehole Kimama-1A (830 feet BLS) where
concentrations probably were affected by the drilling mud.
A comparison of the inorganic, organic, and stable chemistry
data between the KWS well and the 460-foot zone in borehole
Kimama-1A indicated similar chemistry of the aquifer
water, except for some variability with nitrate plus nitrite,
orthophosphate, iron, zinc, and carbon-14. Radionuclide
concentrations were either less than reporting levels or at
background levels for the eastern Snake River Plain aquifer.
