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REPORT
OF GEOLOGIC/HYDROGEOLOGIC SERVICES
CITY
OF HUETTER
KOOTENAI
COUNTY, IDAHO
INTRODUCTION
The city of Huetter (Huetter)
is located approximately two miles west of Coeur d’Alene Idaho on the
north shore of the Spokane River in the northern panhandle portion of
Idaho as can be seen in Figure 1. According to Huetter personnel, the
well does not produce sufficient quantities of water, especially during
summer months and the city would like to increase the production rate.
Huetter has requested assistance in evaluating the increased drawdown of
the Huetter well for sizing a larger pump.
GEOLOGY
The oldest and most predominant
rock type in the study area is the Precambrian gneiss that is
approximately 1.5 to 2.5 billion years old. The Precambrian gneiss was
intruded by Cretaceous age granitic rocks that are approximately 70 to
80 million years old. Basalt
flowed north into the area about 15 million years ago and backed up
water flowing south into Lake Rathdrum resulting in the accumulation of
lacustrine silts and clays.
The Rathdrum Prairie area
was modified by glaciation during at least two ice ages with glaciers
that flowed south from Canada. The most recent glaciation (Cordilleran)
occurred approximately 10,000 to 15,000 years ago. The glaciers created
ice dams in the area east of Clark Fork Idaho that blocked the ancestral
Clark Fork river channel. Structural failure of the ice dam resulted in
the release of large quantities of water creating significant flood
events. Glacial flood deposits, mostly sand and gravel, were deposited
in what is now the Rathdrum Prairie.
The alluvium in the study area is most likely derived
predominantly from fluvial deposition of sediments derived from erosion
of the upland areas to the south and/or reworked glacial flood deposits
to the north.
HYDROGEOLOGY
General
The general hydrogeologic
setting for the Huetter area was based on review of selected water well
reports for the study area. The water well reports indicate the presence
of glacial flood deposist/alluvium. The glacial flood/alluvial deposit
aquifer is composed predominantly of sand and gravel with occasional
boulders. The thickness of the sand and gravel is largely unknown but
appears to be greater than 300 feet in areas as shown on the water well
reports. Wells completed in the Rathdrum Prairie aquifer typically have
relatively high yields.
The static water
elevation in the Huetter well is approximately 2,010 feet relative to
mean sea level (msl) and is representative of the other wells in the
area. The water elevation
of the Spokane River is approximately 2,122 feet msl with the elevation
of the river bottom at about 2,110 feet msl (Seitz and Jones, 1981). The
water table elevation of the aquifer penetrated by the Huetter well is
approximately 100 feet below the Spokane River. The relatively large
unsaturated section between the ground water table and the Spokane River
would indicate that the Huetter well is not hydraulically connected to
the Spokane River.
Aquifer Test and Analysis
A variable rate aquifer
test was conducted in the Huetter well on June 03, 2003. There is no
water well report available. The
transmissivity values were estimated using the Birsoy-Summers method (Kasenow,
1996) for confined aquifers. The Birsoy-Summers method allows for the
calculation of transmissivity with variable pumping rates.
Based on the result of the variable rate aquifer test the
transmissivity for the Huetter well is approximately 2,200 feet squared
per day (ft2/day).
The maximum quantity of
water that can be used by Huetter as described in Huetter’s claim to a
water right (Appendix B) is 0.18 cubic feet per second (cfs) (81 gpm)
for municipal use with a 0.12 cfs (54 gpm) for additional domestic and
commercial use outside the city limits. The drawdown in the well was
computed using the Theis equation for various pumping durations with the
transmissivity value of 2,277 ft2/day and an assumed
storativity value of 5.0E-2. The computed drawdown in the well at 0.30
cfs or 135 gpm after one-week of pumping is 15.6 feet. The 15.6 feet of drawdown represents about 43% of the 36 feet
of available drawdown. Additional drawdown will result from well and
aquifer losses. The entrance velocity of the water through the screen
cannot be evaluated with the slot-size unknown.
CONCLUSION
The maximum quantity of water
that Huetter can pump according to their water right claim is 0.3 cfs or
135 gpm. Based on the
results of the aquifer test and the 135 gpm flow rate the projected
drawdown in the well will be approximately 16 feet.
Additional drawdown may result from well and aquifer losses,
heterogeneity in hydraulic conductivity that decreases away from the
well and the presence of no-flow boundaries.
We would recommend the following:
- Huetter
should monitor and record water level and pumpage information in the
municipal well. The period between measurements should be
approximately every two weeks.
2.
The water level and pumpage data should be complied and reviewed
at least once per year.
3.
The water level and pumpage information be compiled in a
commercially available spreadsheet format.
The spreadsheet will allow 1) the water system operator to view
trends by graphing the information and 2) electronic storage of the
information for ease of distribution and the creation of backup files.
4.
Huetter should monitor water levels and adjust pump rates to
ensure sustained yield and proper operation of the submersible pump.
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