Hydrogeological Modeling of the Pullman-Moscow Basin Basalt Aquifer System, WA and ID

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Hydrogeological Modeling of the Pullman-Moscow
Basin Basalt Aquifer System, WA and ID

• Joan Wu, Farida Leek, Kent Keller
• Washington State University
• John Bush
• University of Idaho

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OUTLINE

• Introduction
• Hydrogeologic Setting
• Methodology
• GIS database development
• Ground-water flow modeling
• Results and Discussions
• Summary
• Position Announcement

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INTRODUCTION

• The aquifer system in the CRBG is the sole water
  supply source for the Palouse Basin
• The continuous water-level decline and the
  projected future development have led to serious
  public concerns
• PBAC a multi-stakeholder, multi-agency (city,
  county, university) organization promoting
  conservation and sound ground-water management
• The 2003 MOA with PBAC GIS database

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INTRODUCTION (contd)

• Past Studies on Hydrogeological Characterization
• Crosby and Cavin (1960)
• Foxworthy and Washburn (1963) Jones and Ross
  (1972)
• Bush and colleagues (1998, 2000, 2001, 2003)
• Past Studies on Groundwater Modeling
• Barker (1979), overly conservative
• Lum et al. (1990), overly optimistic
• Both models proved inadequate by year 2000

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INTRODUCTION (contd)

• Goal
• To develop a foundation for improved and informed
  Palouse Basin groundwater resources assessment
  and management
• Objectives
• To develop a hydrogeology GIS database for the
  Palouse Basin to improve data accessibility and
  data processing and analysis efficiency
• To develop a groundwater flow model for the
  basaltic aquifer system of the Pullman-Moscow
  area based on new spatial and temporal data

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HYDROGEOLOGIC SETTING

• Palouse loess
• Saddle Mts.
• Wanapum basalt
• Grande Ronde basalt
• Imnaha basalt
• Pre-basalt

CRBG
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HYDROGEOLOGIC SETTING (contd)

• Palouse loess rural domestic use
• Wanapum basalt major aquifer for Moscow till
  1960s
• Grande Ronde basalt source for more than 90 of
  water supply, with a recent construction of WSU 8

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• Occurred during late Miocene and early Pliocene
  (176 mya BP)
• Engulfing 1.6105 km2 of the Pacific Northwest
  between Cascade Range and Rocky Mt., covering
  parts of ID, WA, and OR
• Over 300 high-volume individual lava flows
  identified, along with countless smaller flows,
  with vents up to 150 km long
• Eventually accumulating to more than 1,800 m
  thick
• Tectonic origin (Hooper, 1997)
• Yellowstone hot spot
• Thinning of continental lithosphere due to
  spreading behind Cascade arc
• Proximity of fissure vents to tectonic boundary
  between accreted terranes and lithospheres of old
  N. Am. Plate

Source USGS, http//vulcan.wr.usgs.gov/
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Source ND Space Grant Consortium,
http//volcano.und.edu/
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METHODOLOGYI. GIS DATABASE DEVELOPMENT

• Data Collection
• Well log
• Groundwater level
• Pumpage
• Precipitation
• Geochemistry
• Data Compilation
• Digitizing into ArcGIS
• Processing existing and new coverages
• Topography
• Township and range to UTM conversion of well
  coordinates
• Stream network
• Land use
• Soil
• Watershed boundary

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Digitizing Processing Well Data
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Digitizing Processing Well Data contd
A
a
Well 15/46-31J1
Well 39N/5W-7ad2
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METHODOLOGYI. GIS DATABASE DEVELOPMENT

• Data Analysis
• Plot long-term hydrographs
• Separate vs composite
• Their relations with precipitation and pumpage
• Build structural contour maps
• To depict the shape of stratigraphic horizons
• Construct aquifer contour maps
• Wanapum
• Grande Ronde
• Develop hydrogeological cross-sections
• Across most of the basin
• In various directions

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RESULTS AND DISSCUSSIONI. GEOSPATIAL DATA
ANALYSIS
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Composite Hydrograph of Wells in the Palouse Basin
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Long-term Groundwater Pumpage from Two Aquifers
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Long-term Hydrographs

• Each aquifer has a distinct pattern of
  water-level fluctuations in relation to pumping,
  climate, recharge
• Wanapum saw its groundwater level recovery since
  1960s when pumping shifted to the Grande Ronde
• Relatively more consistent pattern of fluctuation
  in Grande Ronde wells in Pullman than in Moscow
• 0.30.6 m/yr groundwater level decline observed
  at both pumping centers

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Contour Map of Top Altitude of Wanapum Formation
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Contour Map of Top Altitude of Grande Ronde
Formation
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Structural Contour Maps

• Wanapum
• Wanapum basalt is to the NW controlled by NW
  trending folds, and dips and thickens E and W
  away from Pullman
• Grande Ronde
• The top of GR drops in elevation E towards Moscow
  and W and NW away from Pullman
• Substantial lateral changes in the occurrence and
  nature of sediments exist between Pullman and
  Moscow

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Potentiometric surface contour map of the Wanapum
aquifer (1960s)
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Potentiometric surface contour map of the G.
Ronde aquifer (1990s)
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Potentiometric Surface Contour Maps

• Wanapum
• Hydraulic connection between Pullman and Moscow
  is weak
• General groundwater movement is to W and NW
• Grande Ronde
• Piezometric surface shows two cones of depression
  as a result of heavy pumping
• The open shape of cones of depression to the W
  and NW is possibly controlled by structural
  features

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METHODOLOGYII. DEVELOPING A NEW MODEL
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Water Release from a Confined Aquifer Water
Expansion Aquifer Compression
Source http//www.bae.uky.edu/sworkman/AEN438G/th
eiseq/theiseq.html
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Unsteady-State Flow in Ideal Aquifer Theis
(1935) Equation
The flow of ground water has many analogies to
the flow of heat by conduction. We have exact
analogies for thermal gradient,
thermal conductivity, and specific heatsolution
of some of our problems is probably already
worked out in the theory of heat conduction
Source http//www.olemiss.edu/sciencenet/saltnet/
theisbio.html
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Unsteady-State Flow in Ideal Aquifer The
Solution
Actually derived by a mathematician friend of
Theis, C.I. Lubin. Reportedly, Lubin declined
co-authorship of the paper because he regarded
his contribution as mathematically trivial.
Fetter, 1994
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Groundwater Flow Model Development

• Industry standard MODFLOW
• MODular 3-d finite-difference groundwater FLOW
  model
• Free source codes from the USGS and GUI versions
  available
• PEST (nonlinear parameter estimator) can be used
  with MODFLOW for optimal parameterization

Source http//water.usgs.gov/nrp/gwsoftware/modfl
ow2000/modflow2000.html
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Comparison of Model Domain and Structure
Barker (1979) Western BC at Union Flat Cr. One lumped basalt aquifer single-layer-cake
Lum et al. (1990) Western BC at Snake R. Palouse Loess two separate basalt aquifers, layers horizontal
New Model Western BC as in Barker (1979) Three model layers with actual top/bottom altitudes
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Comparison of Western Boundary Condition
Barker (1979) Dirichlet (head) at Union Flat Cr. for lumped aquifer
Lum et al. (1990) Cauchy (weighted head and flux) at Snake R. for all three aquifers
New Model Same as in Barker (1979) but for three distinct aquifers
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Comparison of Hydraulic Parameterization
Comparison of Hydraulic Parameterization
Barker (1979) Uniform hydraulic properties within zones Kh Kv 0.037.9 m/d, S 0.005
Lum et al. (1990) Uniform hydraulic properties within zones of each aquifer Loess Kh 1.5 m/d, Kv 0.02 m/d Wanapum Kh 0.10.2 m/d, Kv 2.43.610-4 m/d Grande Ronde Kh 0.13.7 m/d, Kv 3.17610-5 m/d S 0.001
New Model Apply inverse modeling to a wealth of historical head data for greatly improved parameterization
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Comparison of Recharge Distribution
Barker (1979) 17 mm yr-1 uniform across model domain
Lum et al. (1990) 71 mm yr-1 uniform across model domain
New Model Spatially varying following OGreen (2005) 3 mm yr-1 in 33 (near Moscow Mt.), 10 mm yr-1 in 37 (Pullman area), actual infiltration in 10 (valleys) of the basin area
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Management Alternatives
Given pumpage needs 2,400 MGY 9.1106 m3,
basin area 660 km2
Aerial Recharge Recharge needs 14 mm Winter wheat consumes up to 90 annual precipitation of 550 mm Winter runoff loss unavoidable from conventionally farmed fields Low permeability across Bovill sedimentWanapum basalt contact in places
Transporting Surface Water from Snake R. Economic feasibility low but of potential
Artificial Recharge Of greatest potential when using streams incised into Wanapum Ground-water modeling imperative in determining the effectiveness
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SUMMARY AND CONCLUSIONS

• GIS database has in the first time brought
  together the various scattered data pertinent to
  PBA hydrogeology and placed it in uniform and
  easily accessible form
• Such database facilitates efficient data
  retrieval and analysis and allows continuous
  updating and refinement, forming a solid
  foundation for future trans-boundary
  hydrogeolocial investigation
• A great deal has been learned from this newly
  available digital temporal and spatial data
• Development of an improve basin-scale groundwater
  flow model is underway

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THANK YOU !
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Pullman-Moscow Cross-section

• Pullman-Moscow Cross-section
• Pullman side
• Less sedimentary interbedding
• Loess is in direct contact with the basalt
• Wanapum is unproductive
• Moscow side
• More sedimentary interbeds
• Wanapum is highly productive
• Current hydraulic gradient and ground-water flow
  in Grande Ronde between Pullman and Moscow is
  minimal, reflecting good hydraulic connection and
  lack of dike barrier as suggested by some
  scientists

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Long-term Hydrographs Revisit

• Relatively consistent pattern of fluctuation in
  Grande Ronde wells in Pullman
• Aquifer is shown to have been depressurized!
• Greater fluctuation in Grande Ronde wells in
  Moscow due to
• Multi-layered sediment system
• Proximity to low-permeability boundaries created
  by non-basaltic rocks
• Confined nature of aquifer
• All these factors tend to cause longer recovery
  period for the wells to reach equilibrium

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Pullman-Albion-Colfax Cross-section

• Fracture patterns and degree of weathering
  dominantly control the productivity of wells
• Grande Ronde dips eastward towards Colfax with a
  hydraulic head drop of 150 m
• Intrusion of low-permeability pre-Tertiary rocks
  are considered to form barriers between Pullman
  and Colfax and cause the drastic change in
  hydraulic head
• Certain previous pump test results may be
  questionable substantial ground-water flow from
  Pullman to Colfax appears unlikely

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PullmanUnion Flat CreekSnake River

• Significant difference (460 m) exists in
  hydraulic heads of the Wanapum and Grande Ronde
  near the Snake R. this sudden change in head may
  be related to the dip of the basalt flows to the
  NW away from the Snake R.
• Cross-sections and potentiometric surface maps
  suggest a major flow direction of NW along the
  Snake R. significant seepage along the canyon
  walls of the Snake R. from the Grande Ronde
  aquifer is unlikely
• Geochemistry data from previous studies (Larson
  et al., 2000) also indicates a lack of Grande
  Ronde discharge to the Snake R.

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SUMMARY AND CONCLUSIONS (contd)

• Long-term trends of the hydrographs indicate weak
  vertical hydraulic connection between the two
  basalt aquifers, consistent with pervious isotope
  geochemistry studies
• Each aquifer exhibits a distinct pattern of
  water-level fluctuation as affected by pumping,
  climate and recharge, with the top basalt aquifer
  seemingly receiving Holocene precipitation
  recharge and the bottom aquifer pre-Holocene
  recharge

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SUMMARY AND CONCLUSIONS (contd)

• Potentiometric surface contour maps of the basalt
  aquifers display a general pattern with the
  ground-water level dipping SNW along the ancient
  basalt flow
• Existing structural features (monoclines,
  anticlines and synclines) tended to create local
  areas with rapid changes in water levels in the
  approximate direction of their major axis
• Previous modeling studies using Snake R. as a
  Cauchy boundary and forced high recharge may have
  been the key causes of the model failures

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SUMMARY AND CONCLUSIONS

• Geologic and hydrogeologic conditions at the two
  cities of Pullman, WA and Moscow, ID in the
  Palouse Basin are rather different yet the
  hydraulic connection appears strong
• The nature and position of stratigraphic units
  and their inherent spatial heterogeneity together
  with geologic structures have significant effects
  on the ground-water flow regime in a fractured
  complex basalt system, which should be carefully
  taken into account in future modeling efforts