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Eastern Snake Plain Aquifer Model Boundary Analysis
“The Idaho Department of Water Resources has placed a strong emphasis on the
development, use and refinement of scientific tools,” reads the final modeling report written by
members of the East Snake Plain Aquifer (ESPA) modeling committee (Cosgrove V). The ESPA
model has recognizable flaws. These flaws are in the minds of the scientists involved in the
model’s creation, and in the minds of those affected by the decisions made based on these types
of models. This model is the basis for groundwater mitigation required by water right disputes.
These disputes involve large amounts of money which can greatly affect the livelihoods of many
individuals. Research has been done that is not currently in use in the model’s calculations
regarding the model boundary. Because the model is a basis for solutions to legal water right
disputes, it must be as scientifically sound as possible. This means that research should be
ongoing and when completed, it must be immediately used for model boundary enhancement.
The ESPA is the main source of water for millions of dollars worth of agricultural
products grown in the state of Idaho (“2007 Census”). As water is critical to crop growth, its
availability can be an issue that people will fight over. Water rights are issued to owners of wells
according to the date their well was drilled and registered with the Idaho Department of Water
Resources (IDWR). In cases of shortages where a senior, or older water right, holder charges
younger water right holders of taking his water, a computer generated model funded by the
IDWR is used to mitigate.
Mitigation, in this case, is the distribution of costs between younger water right owners
who have a direct effect on the pumping done by the senior water right holder. If a senior water
right holder believes his well or spring is producing less than he is allotted through his water
right, he may file suit against all water rights whose date of registration is younger than his.
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Mitigation may take the shape of a decrease in irrigated acres, recharge of aquifer through
injection wells or other injection sites, intermittent pumping and so forth. And thus the model has
the potential power to give or take.
Models used to describe the ESPA were created as early as 1974, and many subsequent
variations of original, yet differing models have been created since. The model in question was
derived from a series of previous models created by the United States Geological Survey (USGS)
with updates based on new technologies as well as better understanding and research of the
ESPA. In 1999, the IDWR and University of Idaho modified existing models to incorporate a
new mathematical code based on software called MODFLOW. MODFLOW uses a code that is
an industry standard so to say. This code is implemented in many ground water flow modeling
programs even today. The model currently in use by the IDWR began its most recent renovation
in the year 2000, and small modifications have been made since then by the IDWR and
University of Idaho’s Idaho Water Resources Research Institute IWRRI (Cosgrove 8-9).
The model is essentially a series of mathematical equations used to describe water flow.
It incorporates precipitation events, stream and river recharge due to leakage, stream discharge
directly from the aquifer at various locations, pumping habits, water level data, soil and rock
types, and many other factors that potentially affect groundwater flow. These mathematical
equations are completed through use of various computer software programs including ArcGIS,
MODFLOW, and others. In the end, the model is used to show effects of one factor related to
groundwater flow on another. Thus, the effects that few or many pumping wells have on any
given stream’s discharge or even their effects on water levels in other wells can be seen. As
explained above, these outputs of the model can then dictate the severity of the mitigation
required.
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The geographic boundary of the model is an important factor in determining participants
of mitigation. For better understanding, the characteristics of the Oakley fan area will be
considered. The Oakley fan tributary basin receives its water from snowfall in the mountains.
Water pumped from the ground can be traced back to the surrounding mountains. The model
boundary follows foothills that run east-west along the Snake River Plain (Whitehead). This can
be justified by the fact that there is a geologic boundary of impermeable met with permeable
layers along these foothills. This means that from the foothills south to the mountains, water flow
is restricted by the type of rock that lies underneath the soil. Thus, it can be assumed that the
ESPA terminates at the foothills and there is no aquifer beneath the foothills and the mountains
to the south. The boundary follows the foothills from the Raft River area (I-80 Pocatello-Salt
Lake junction) to Declo where a discrepancy occurs. The geologic layer for which the boundary
is defined in that stretch continues following the foothills south towards Oakley; however, the
boundary chosen to represent the ESPA for the model breaks from the geologic layering and cuts
across the Oakley fan area to meet up with the same geologic layer along the foothills west of
Burley. This border implies that there is a distinct boundary between the water originating in the
mountains south of and surrounding Oakley and the water of the ESPA, but shows no evidence
of a geologic boundary.
In this lack of evidence, there lies a problem. This boundary that stretches across the
Oakley fan (just south of Burley) allegedly determines which wells are taking water from the
ESPA and those that are taking water from an aquifer beneath the Oakley fan. In certain
instances, this boundary suggests that wells which are less than a mile from each other are
pumping water from an entirely different source. Although there is no scientific reason to believe
that these wells pump water from different sources, a price must be paid in mitigation for the
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well that is located on the ESPA side of the boundary and not for the well which lies outside of
the boundary.
The source of logic behind the boundary creation in such locations as the Oakley fan can
be traced back to a report written by R.L. Whitehead cited by S. P. Garabedian, who wrote a
report on the ESPA, which was then cited by the Modeling committee in their Final Model
report. The map which accompanies the report written by Whitehead entitled “Geologic
Framework of the Snake River Plain, Idaho and Eastern Oregon” shows the boundary and gives
an explanation of those areas where the boundary location seems to have no rhyme or reason.
The text on the right hand side of the map, third paragraph down, last sentence reads, “Where
rocks equivalent in age to those in the plain extend beyond the plain’s boundary, a topographic
contour was chosen arbitrarily to define the boundary.” For the purposes of the report created by
Whitehead, a topographic contour was sufficient. For the purposes of a model created to
distribute mitigation on all those within its boundaries, arbitrary is not sufficient.
Tributary basins that include few or no irrigation wells may be cut off with arbitrary lines
because of the minimal effect they impose; however, when hundreds of wells in a single tributary
basin are left out of mitigation because of an arbitrary line, justice is not being served. The same
applies to those inside the boundary and included in mitigation whose water may not come from
the ESPA. Science must dictate the placement of such boundaries.
Many scientific approaches may be taken to find the true boundary of the ESPA in such
locations. Returning to the Oakley fan situation, two distinct techniques were implemented by
Water Well Consultants Inc. to find a meaningful boundary where water from the Oakley fan
meets the ESPA. Water Well Consultants Inc. (WWC) was contracted by the Southwest
Groundwater District in Burley, Idaho, to consult the district regarding every aspect of mitigation
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and water problems in the region, including the model boundary situation. WWC proposed water
chemistry and potentiometric surface analyses to genuinely locate said boundary.
A potentiometric surface map is similar to a topographic map in that the lines on the map
display represent certain elevations. In the case of a potentiometric surface map, the lines
represent different elevations of the water table, or top of the aquifer. Water level data was
collected by the USGS and IDWR as well as WWC themselves from over 100 wells stretching
from the city of Oakley north to the city of Minidoka, west to Bliss and south to Twin Falls.
These water levels were plotted on a large map and a potentiometric map was then created.
The potentiometric surface map displayed the suspicions of WWC owner and
professional geologist Brian Higgs. Water coming from the upper part of the ESPA (American
Falls area) met with the water flowing from the Oakley Fan almost head on. A sort of trough in
the aquifer was created just south of the city of Burley and from that trough the water flowed
NW to the area towards the river and on northward to Thousand Springs. The significance of this
trough shown was immense. The boundary used in the ESPA model is 7 to 10 miles north of the
trough. This suggests that if there were a distinct boundary between the waters of the Oakley fan
and the ESPA, it would have to be at the trough, as water cannot flow up-gradient. This also
suggests that hundreds of farmers to the south of the trough are paying high prices to buy water
in north-eastern Idaho or cutting back production and water usage to mitigate for acres that
shouldn’t legally be within the boundaries of mitigation disputes. If the boundary were to be
moved to where the trough lies, nearly 300 wells and 60,000 acres would be excluded from
current mitigation.
WWC also completed a water chemistry analysis to understand better the chemical
difference between the water of the ESPA and the Oakley fan. Water samples were taken north
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of the city of Minidoka where groundwater flows southwest from the desert region of Idaho
National Laboratories. These samples were used to represent the common ESPA water coming
from an area unaltered by irrigation and domestic effects. Samples were also taken of the Snake
River at Milner Dam and the Cottonwood Creek which originates in the mountains directly west
of Oakley. The Oakley fan was divided up into sections and a grid was created. Water samples
were taken from irrigation wells across the grid. The samples were logged and sent to a
hydrologic lab for testing.
Results of the testing are documented and analyzed in “Chemistry of the Waters
Recharging the Aquifers of the South West Irrigation District.” In this report and an
accompanying report written by Thomas Higgs P.E., it is suggested, backed by a series of
statistical analysis procedures, that the water coming from the Oakley fan has a 15% correlation
with ESPA water and with the water recharging the ESPA through the Snake River (Higgs, B 8).
This leads to the conclusion that if in fact the Oakley fan water does have an effect on pumping
wells in portions of the ESPA, the effect is minimal. If indeed those individuals pumping Oakley
fan water are required to mitigate, this percentage should be incorporated into the calculation of
their required mitigation.
These two different approaches taken by WWC, to scientifically determine the boundary
of a tributary basin of the ESPA, could be reproduced in nearly every other contributing tributary
basin where the aquifer boundary was chosen arbitrarily. Situations may vary; however, the
science would remain constant and more information would enhance the model greatly.
Opposition to immediate model change is mainly fueled by unwillingness to put forth the
financial resources required. In a meeting with the South West Irrigation District and
representatives from the IDWR, the director of the department Dave R. Tuthill mentioned that a
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committee formed to create the model would be legally required to meet and discuss the
proposed changes. As the members of the committee reside in all parts of the state, a special
meeting would be necessary, or the discussion would have to wait until a previously scheduled
meeting. Cost to the department for the traveling and accommodations of the members of the
committee must be considered. He also mentioned that a state judge would be required to
approve proposed changes. This requires funds as well as legal processing and preparation time.
Along with legal costs, labor cost for the modification must be considered. Fees charged
by modelers and total cost of research may in some minds outweigh the benefits of modification.
Modelers charge anywhere from 50 to well over 100 dollars an hour and many hours at a time
may be spent on modification.
Taking into view all arguments supporting and opposing immediate action in aquifer
boundary change, few possible solutions can be reached. I propose a fix-it-as-it-comes approach.
This means that immediate action must be taken; however, the boundary may move as funds for
research become available and as the research is completed. In the cases of such tributary basins
as the Oakley fan, the information is available and immediate action should be taken to
incorporate this information into the existing model. As for other tributary basins, research
money is nearly always available through government grants and budgets as well as from private
individuals and corporations. The costs of research can be low as in the case of the research
completed by WWC. Workers included two field data collectors, one lab worker, and an
engineer for statistical analysis. Costs were kept low and reliable data was produced.
This approach would keep modelers from being overwhelmed with large loads of data
awaiting input, as it would be the case if all basins were researched simultaneously. This also
allows modification to take place even as research is being done. As shown before through the
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example of only one tributary basin, the Oakley fan, financial burdens would decrease while
production and fairness would exist. And the Oakley fan is only one of more than eight
contributing tributary basins! A one to two year time frame is not feasible, but a goal of 5-10
years is more than obtainable and if finances drive the argument, time is money and thus the
sooner the better. Taking this approach would allow science to dictate rather than guesswork,
which is the most important benefit of all. When large quantities of citizen’s money and assets
are at stake, science is the only legitimate way to deal with a problem such as this.
As thousands of farmers across the East Snake Plain now worry about their mitigation
costs for the coming years, it is only fair to them that the governmental agency in charge of their
mitigation demonstrates that every step is being taken to insure equal distribution of fault. The
present process has been proven insufficient and a solution to these insufficiencies has been
proposed. With all due respect, I submit that as a government agency the Idaho Department of
Water Resources has the obligation to arrive at decisions based on complete and accurate data.
Where data is not available and the lack of it inhibits fairness to the individuals involved, the
agency must show probable cause for lack of action or present evidence of continuing research
and development directed toward the betterment of decision-making tools. And thus, I propose
immediate action with respect to “development, use and refinement of” the Eastern Snake Plain
Aquifer Model with respect to its representation of the ESPA boundary.
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Works Cited
"2007 Census Publications." Agricultural Statistics Service. 02/03/2009. United States
Department of Agriculture. 13 Feb 2009 <
http://www.agcensus.usda.gov/Publications/2007/Full_Report/Volume_1,_Chapter_2_Co
unty_Level/Idaho/st16_2_001_001.pdf >.
Garabedian, S.P. Hydrology and Digital Simulation of the Aquifer System, Eastern Snake River
Plain, Idaho: Regional Aquifer -System Analysis. Washington D.C.: USGPO, 1992.
Cosgrove, D.M., B.A. Contor, and G.S. Johnson. Enhanced Snake River Plain Aquifer Model
Final Report. Moscow, ID: IWRRI, 2006.
Hydrology, Idaho Technical Committee on. Upper Snake River Basin Study. Boise: IDWR,
1997.
Whitehead, R.L. Geohydrologic Framework of the Snake River Plain, Idaho and Eastern Oregon.
Denver: U.S. Department of the Interior, 1986.
Higgs, Brian. Chemistry of the Waters Recharging the Aquifers of the South West Irrigation
District. Idaho Falls: SWID, 2008.
Higgs, Thomas. Stochastic Analysis of the Water Flows in the Oakley Fan Area. Idaho Falls:
WWC, 2008.
David Tuthill. South West Irrigation District meeting. Twin Falls, ID, 20 August 2008.