Hydrologic Conditions in the Palouse Aquifer

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Hydrologic Conditions in the Palouse Aquifer

• Dale R. Ralston
• Professor Emeritus of Hydrogeology
• University of Idaho

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Talk represents research conducted at UI and WSU

• UI
• Professor John Bush and his students
• Professors Jim Osiensky and Jerry Fairley and
  their students
• WSU
• Professor Kent Keller and his students
• Professor Joan Wu and her students
• Palouse Basin Aquifer Committee (PBAC)
• Larry Kirkland

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Outline of talk

• General geologic setting
• Ground water management concepts
• Description of the Palouse aquifer
• Well development and water level decline
• Research and management activities
• Water management questions

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General Geologic Setting

• Subsurface geology of the Palouse basin is
  dominated by basalt with layers of sediment,
  mostly along the east margin
• Basalt and sediment overlie older rocks that
  make up Moscow Mountain and Paradise Ridge

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Description of Map Units
Columbia River Basalt Group From Oldest to
Youngest
Imnaha Formation
n
Grande Ronde Formation
n
Wanapum Formation
n
Saddle Mountains Formation
n
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Grande Ronde Formation R1, N1, R2 and units N2

• Grande Ronde basalt makes up the majority of the
  subsurface section in the Palouse basin and other
  locations in Eastern Washington and Northern
  Idaho
• Formation is divided into four units based on
  paleo-magnetism
• This formation hosts the lower aquifer in the
  Palouse basin and is the major water producer in
  Lewiston and in the Grangeville area

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Wanapum Formation Priest Rapids Member

• Wanapum Formation is the uppermost basalt unit in
  the Palouse basin
• Priest Rapids member is present in most areas
  with the Rosa member present west of Pullman
• This formation hosts the upper aquifer in the
  Palouse basin

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Folds and faults are Important relative
to Ground water movement
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Ground Water Management Concepts
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Long-Term Equilibrium - Recharge Equals Discharge
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Water levels are stable prior to development or
when pumping amount is small
Water Level
Time (years)
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Addition of Pumping Can Result in a New
Equilibrium
Withdrawal
INFLOW
STORAGE
OUTFLOW
Water levels decline until inflow outflow
withdrawal
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Development of well(s) with a constant pumping
rate can result in water-level decline leading to
a new equilibrium
Constant pumping rate
Aquifer water level
Time
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Development of wells with a increasing combined
pumping rate will result in continual water-level
decline
Increasing pumping rate
Aquifer water level
Time
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Description of the Palouse Aquifer
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WGS84 117º W
117.2º W
Pa
46.9º N
1500
Ringo Butte
C
Kamiak Butte
Smoot Hill
2000
Moscow Mountain
M
1000
P
500
Tomer Butte
1500
Bald Butte
Pre-basalt topography of Pullman-Moscow basin.
Interpreted from geophysical data (Klein, 1987)
modeling (Opatz, 2003), and geologic
cross-sections.
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WGS84 117º W
117.2º W
Pa
46.9º N
Ringo Butte
C
Kamiak Butte
Primary dip Extent of R1 flows Sedimentation
?
?
Smoot Hill
Moscow Mountain
M
P
Tomer Butte
Emplacement from SW
Bald Butte
Approximate extent of basalts at the end of R1
time of the Grande Ronde (approximately 15.3 Ma).
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WGS84 117º W
117.2º W
Pa
46.9º N
Ringo Butte
C
Kamiak Butte
Primary dip Extent of N1 flows Sedimentation
?
?
Smoot Hill
Moscow Mountain
M
P
Tomer Butte
Emplacement from SW
Bald Butte
Approximate extent of basalts at the end of N1
time of the Grande Ronde (approximately 15.5 Ma).
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WGS84 117º W
117.2º W
Pa
46.9º N
C
Ringo Butte
Kamiak Butte
Smoot Hill
Moscow Mountain
M
P
Basalt Flow Direction
Tomer Butte
SNAKE RIVER
Bald Butte
Emplacement of R2 flows
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WGS84 117º W
117.2º W
?
Pa
46.9º N
C
Ringo Butte
Kamiak Butte
Smoot Hill
Moscow Mountain
Basalt Flow Direction
M
P
Tomer Butte
SNAKE RIVER
Flow Direction
Bald Butte
Emplacement of N2 flows
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Area Hydrogeology - 1

• Upper aquifer occurs in the Wanapum Formation
• Lower aquifer occurs in the Grande Ronde
  Formation
• Depth to water in upper aquifer is about 60 feet
  while the depth to water in the lower aquifer is
  about 300 feet

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Area Hydrogeology - 2

• Recharge to upper aquifer occurs from
  infiltration of precipitation and stream loss
• Recharge to lower aquifer occurs primarily as
  downward leakage from upper aquifer
• Recharge to the upper aquifer is greater than to
  the lower aquifer although present estimates of
  recharge rates have large error band

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Well Development and Water-Level Decline
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History of well development in Moscow -- 1

• In Moscow, the upper aquifer water levels
  declined until 1960s when deep wells were
  drilled and withdrawal was shifted to lower
  aquifer water levels now have recovered to
  1940s levels
• City of Moscow now withdraws about 30 percent
  from the upper aquifer

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History of Well Development in Moscow -- 2

• Water level decline has been experienced in the
  lower aquifer in Moscow, Pullman and Palouse
• There is considerable evidence that these three
  cities obtain water from the same aquifer system

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Water Levels from Grande Ronde wells in Moscow
and Pullman
WSU test
M-8
M-9
UI-3
P-3
P-4
M-6
Moscow Wells
Pullman Wells

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Research and Water Management Activities

• Ground water model (1990)
• PBAC (Palouse Basin Aquifer Committee) formed and
  developed plan
• Pumping from the Grande Ronde aquifer has been
  stabilized
• Additional research on geology, water ages and
  water level patterns

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Ground Water Model (1990)

• Cooperative effort of USGS and UI
• Represent upper and lower aquifers
• Primary results
• Ground water levels will continue to decline if
  pumping amounts continue to increase
• Ground water levels will stop declining (within
  10 to 15 years) if pumping is stabilized

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Palouse Basin Aquifer Committee (PBAC)

• Includes cities, Universities and counties from
  both states
• First goal, to stabilize pumping from the lower
  aquifer, was accomplished in early 1990s
• In 1999, PBACs revised goal was to stabilize
  ground water levels in lower aquifer by 2020 by
  conservation and possible recharge enhancement
• PBAC has supported and encouraged water
  conservation and aquifer research

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Decline rate of about 1.4 ft/yr
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Water Age-Dating Research

• Water analysis allows estimation of how long
  water has been in the ground
• Grande Ronde aquifer water in Moscow has ages
  from 20,000 to 25,000 years
• Grande Ronde aquifer water in Pullman is younger
  (_at_10,000 years) near the top of the aquifer and
  older with depth

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Water Management Questions -- 1

• Is the deep aquifer in the Moscow area part of a
  larger aquifer system that includes Pullman and
  Palouse and possibly Colfax and Garfield? Yes
  the areas are hydraulically connected.
• Does this aquifer receive recharge? Yes
  although we do not know if the recharge rate is
  greater than or less than the combined pumping
  rate of the four entities.

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Water Management Questions -- 2

• Why is the water so old if the aquifer is
  receiving recharge? Vertical ground water
  movement is very slow, perhaps less than an inch
  per year in deep aquifers. Annual recharge to
  most ground water systems is a very small
  percentage of water in storage. This fits
  because water ages get greater with depth in the
  Pullman area.

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Water Management Questions 3

• Are we facing the loss of our water supply source
  in the near future? No the quantity of water
  still in storage in the aquifer is large.
  However, we need to continue to take action to
  insure that we have a sufficient water supply
  into the future.

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Water Management Questions -- 4

• Is water conservation a long-term solution for
  the aquifer problem? Water conservation is
  important but may or may not be enough to insure
  that the area has a stable water source for
  decades into the future.

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Water Management Questions -- 5

• What can we do if stabilizing pumping does not
  stabilize water levels? PBAC is now
  investigating recharge enhancement alternatives
  and encouraging entities to turn to alternative
  sources of water.

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Water Management Questions -- 6

• Should water management activities be done
  separately by each of the states or as a combined
  effort? Since the same aquifer underlies both
  states, it makes sense to have combined
  management of the resource.

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Thank you!!