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Bancroft, a community of approximately 450 people, lies within the
Gem Valley of Southeastern Idaho (Figure 1).
Their domestic water supply is derived from two wells which
contain elevated fecal coliform and nitrate concentrations.
In addition to water quality issues, these wells are located
within the Federal Emergency Management Agency’s 100-year floodplain.
A well located within this floodplain has an increased risk of
surface contamination during runoff events.
The purpose of the project was to provide geologic and
hydrogeologic information to the city officials enabling them to take
the proper course of action regarding the future of their domestic water
supply. The study included
an evaluation of the current supply wells and a possible target for a
new well.
Figure
1
: Location of the Bancroft study area.
Research consisted
of obtaining data from a variety of sources including well logs from the
Idaho Department of Water Resources, well static water levels from the
United States Geological Survey, Source Water Assessment Reports from
the Idaho Department of Environmental Quality, a research dissertation,
and field work verifying the data. As
a result of our research, we found:
- Current
supply wells’ location and design are the causes for current water
quality problems.
- The
best available target for ground water development is the same
aquifer the current supply wells are deriving water from.
- Ground
water flow direction is in a northwesterly direction from the Bear
River and Last Chance Canal to the Portneuf River (Figure 2).
- A
clay layer lies below the city of Bancroft and above the aquifer
which can minimize potential contamination to the drinking water
supply.
- Location
of a new well should be located south of Bancroft avoiding potential
contamination from within the town (Figure 2).
- The
new well should consider the depth to the clay layer and proper well
sealing to reduce potential contamination to the well.
Figure
2
: Ground water flow direction and new
well target area.
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