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The communities of
Bloomington and Paris lie along the west side of the Bear Lake
valley in southeastern Idaho Figure 1). Both communities derive
domestic water from springs that issue from sedimentary rocks to
the west, in the Bear River mountain range. The IWRRI Community
Water Project team completed a study in year 2002 that provides
the communities with hydrogeologic assistance to address a
number of concerns regarding their water supplies. The study
achieves the following goals:
- Evaluate the hydrogeology of the
primary water supply springs
- Delineate recharge areas for the
springs
- Locate potential alternate groundwater
sources
- Delineate the recharge zones for the
alternate water supplies
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The dominant rock types in the Bear River range
include limestone and sandstone, deposited in an ancient, Paleozoic sea
(Figure 2). Later, during Mesozoic time, regional compression folded and
thrust faulted the rocks. The deformed strata were exposed and deeply
eroded at land surface during Tertiary time by regional uplift. A thick
pile of fine-grained sediments then accumulated above the old erosional
surface. These sediments, called the Salt Lake formation, consist, in
part, of material eroded from the older strata. Most recently, formation
of the Bear Lake valley resulted from renewed faulting. Many of these
faults show recent movement. The conceptual model describing
ground-water flow involves precipitation entering the hydrologic system
primarily in the mountains, melting in the spring, flowing through the
limestone, and discharging through springs in the Bloomington formation
just above a shale unit (Figure 2). The shale acts as a barrier to
ground water flow and forces most of the ground water out of the
limestone aquifers through springs. Some water seeps through the shale
into the Brigham formation that lies above a thrust fault. The fault
acts as a barrier to ground water flow, forcing ground water to
discharge from springs in the Brigham formation. Most of the high
yielding wells in the valley completed in gravels within the Salt Lake
formation, suggest this rock unit forms a viable target as well.
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Based on these
interpretations potential target rock units include: 1) the Salt
Lake formation 2) the Bloomington formation and 3) the Brigham
formation (Figure 2). The gravelly portion of the Salt Lake
formation hosts numerous high-yielding wells, suggesting a
priority target that occurs close to both communities. This
aquifer may be isolated, however, from potential recharge areas,
and wells developed in the gravel will require an engineered
screen. The Bloomington formation contains several high-volume
springs, and connects directly to a recharge area. Fracture and
cave distribution controls water flow in the Bloomington
formation; therefore, a well must intersect these features to
yield significant water. The Brigham formation contains water,
however, the Lead Bell Shale apparently limits recharge.
Geochemical analyses of water issuing from springs in the
Brigham indicate that the aquifer does not connect to a regional
ground-water flow system. Also springs and wells in the Brigham
formation typically yield less than 40 gpm.
The following list prioritizes
exploration targets for additional ground water sources. It is
based on the relative merit of each target from an
ease-of-discovery versus a risk-of-failure point of view.
- Salt Lake formation
- Brigham formation
- Bloomington formation
We recommend drilling a test well prior to
drilling a production well to determine the suitability of the
target aquifer. The city should initiate a routine water level
monitoring plan once the new well is on line, to plan water
usage and development. |
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