1. Geochemical Tracers for Discriminating Recharge and Subsystems in a CRBG Aquifer
Kyle Duckett
Master’s Student
University of Idaho
Department of Geologic Sciences
Graduate Advisor: Dr. Jeff Langman
-To start with, I'd like to thank you all for having me here today
- My name is Kyle Duckett; Masters Student; Uidaho; Advisor Jeff Langman
-Im going to tell you all a bit about the work Ive been doing throughout the year; More specifically "Geochemical Tracers, and how we can use them to discriminate recharge pathways and subsystems in a Columbia River Basalt Aquifer"

2. Acknowledgements:
This work would not be possible without funding and ongoing support from the Palouse Basin Aquifer Committee (PBAC)
Inspiration: Steve Robischon
Graduate Advisor: Jeff Langman
Collaborators: John Bush, Pamela Dunlap, Erin Brooks, Jeff Welker
Field Help: Kyle, Ricky, Gary, Meg, Gabi, Tom, Miki, Taylor
-So before I get into it, We would like to acknowledge PBAC for the funding to make this work and my education possible; With a special thank you to Steve Robischon as the motivating force behind this work
-My work involves a great deal of collaboration with John and Pam, as well as Erin Brooks from the University of Idaho; We have also been lucky enough to partner up with Jeff Welker from GNIP, who has shared alot of precipitation data with us.
-Tons of help in the field to make this possible

3. Moscow-Pullman Subbasin
6/5/2019
Moscow-Pullman Subbasin
Basement Rock
Moscow-Pullman Subbasin
Sample Well Locations
Palouse Range
(Moscow Mountain)
-As I said we are talking about a CRBG aquifer; On the left here we see the extent of columbia river flood basalts, in Washington, Oregon and Idaho.
-Same Definition as John Bush
-Now each blue dot is a sample location; this doesn't give you a lot of detail, but I would like to highlight to extent of our sample range from east to west through Moscow and Pullman
-What makes our subbasin unique is the fact that it lies on the eastern margin
Modified From Bush et al. 2017 3 3

4. Modified from Bush et al. (2017)
Basin Geology
Pullman
Moscow
-This is John's E-W cross section through the basin, which captures several of our sample wells
-Colored basalt units stretching across, through the sediments of Latah shown in yellow
-Flow tips meet the contact surrounding moscow to the east but also to the north and south; Water interacting with flow tips and sediment packages...
-Focus on Moscow, because the story is much more interesting N N
Modified from Bush et al. (2017)

5. Identifying Recharge Signals
6/5/2019
Identifying Recharge Signals
Age is difficult
Pathway Chemistry
Variation = “Signals”
Multiple Tracers Clarity
-Most common question; Hard to answer. New evidence from John, Dates are hard to accept
-Well we know that water chemistry is a product of water/rock interactions and travel time. Variation = Signals... Multiple methods brings clarity to the noise
-Insights on recharge locations and pathways
Bethke and Johnson, 2008
Geochemical Tracers
Recharge + Pathways 5 5

6. Identification METHODS
6/5/2019
Identification METHODS
28 wells have been sampled:
3 in the Latah
6 in Wanapum
1 Wanapum + Grande Ronde
18 wells in Grande Ronde
Analyses:
Field Parameters (pH, DO, Conductivity, Temperature)
Major + trace elements
Stable Isotopes (2H, 18O, 34S, 13C)
-Samples 28 wells; Production and private; locations predetermined by well locations
-Environmental parameters; Chemistry for identification of signals; Stable isotopes to enhance clarity/Support signals 6 6

7. Recharge sources/Signals
Eastern Signal: Surface Water
δ 18O (VSMOW)
R2 Zone
Northern Signal
Pullman Wells X
Groundwater Samples
Pullman Wells Average
Yellow = Enriched
RED = Depleted
-Distinct Signals; 4 different groupings
-R2 zone could be a mixed zone
-Pullman Wells look very similar to our R2 mixed zone
-Isotopes Can help bring clarity

8. Isotopes Are Just Signals
Water/Rock Interactions + Time Water Chemistry
Environmental Conditions + Source Isotopic Ratios
Variation in Signal = Variation in Conditions/Pathway
Multiple Signals = Clarity
-We've been talking about chemistry...
Water Isotopes
Elevation
Temperature
Carbon Isotopes
Modern Carbon Signal Emplaced during percolation
Sulfur Isotopes
Emplaced from sulfate in surface runoff
Modified by environmental conditions

9. Alkalinity (mg/L CaCO3)
Source/signal mixing
Sulfate (mg/L)
δ 34S (CDT) X
Northern Signal
Eastern Signal
R2 Producing Zone
δ 18O (VSMOW)
Pullman Wells
Alkalinity (mg/L CaCO3)
δ 13C (VPDB)
Pullman Wells X
-I also mentioned Carbon and Sulfur Isotopes; Sulfate and Alkalinity are established during recharge; however here we are looking at things in solution instead of measuring the Hs and the Os of the water itself
-Distinct Signals
-Evidence of R2 zone
-Pullman looks like R2 with a little North

10. Source Mixing Recharge Sources Groundwater Samples δ 18O (VSMOW)
Yellow = Enriched
RED = Depleted
Summer Precipitation
Winter Precipitation
Creek
R2 Zone
δ 18O (VSMOW)
δ 2H (VSMOW)
Mountain, Northeast
-Water isotopes; Measurement of the water itself; Very powerful; Stable, not changing in the subsurface
-Same color regime as chemistry slide; Same signals are present
-Supports potential for mixing of surface water dominated signals and snow dominated signals
-R2 zone and northerly signal continuing west towards Pullman
Snow Pack
δ 18O (VSMOW)
GNIP database; Moravec et al. 2010

11. Water Isotope Signals In Moscow
Enriched Signal
Northern Signal
δ 18O (VSMOW)
Precipitation
Toyota
Creek
Paradise Creek
Creek Signal
Parker
Eastern
Eastern Signal
Sample Locations
Surface Water
Yellow = Enriched
RED = Depleted
-Map view; Moscow only; Each circle is a sample location; Yellow is surface water; red is lower temperature and higher elevation, correlating to snow pack
-Eastern signal; Northern Signal; Very enriched in connection with surface water/stream in Moscow
Northern
South Fork Palouse River
Snow Pack
Depleted Signal

12. Recharge Along the Eastern Margin (Potential Flow Paths)
North/Depleted
South Fork Palouse River
Paradise Creek
Moscow 9
UI 4
UI 3
δ 18O (VSMOW)
Sample Locations
Surface Water
Yellow = Enriched
RED = Depleted
Eastern/Enriched
-So again were in map view here; here we see some idealized flow paths, based on our observational data
-North signal; East Signal
-Creek Signal

13. Recharge Along the eastern Margin (Cont.)
δ 18O (VSMOW)
Toyota
UI 3
Parker
Wanapum Formation
Grande Ronde Formation
-This is a cross sectional view E-W similar to John's Cross Section
-Here you see sample wells; Each Red/Orange Object is the screened interval for that sample well
-Northern Signal dipping along the basement rock
-Eastern Signal pushing up under the Wanapum Fm
-R2 Producing zone; Potential mixing zone N2 N R2 N1 R1
Well Screened Interval

14. Signals Moving Into Pullman
Moscow
δ 18O (VSMOW)
Wanapum Formation
-Evidence of signals continuing over towards pullman; Chemistry, Carbon, Sulfur; Water isotopes shows some loss from Palouse River in P4, P5, P6, similar to in Moscow
-R2 Zone seems like major producing zone
Grande Ronde Formation N2 R2 N1 R1
Well Screened Interval

15. What is happening to the north?
Latah Formation
R2 Recharge Zone
Moscow Mountain
Grande Ronde Formation N1
-Only way to investigate is to look to the North
Pullman
Moscow
Latah Formation
Basement Rock

16. Age, Recharge, and Travel Time
6/5/2019
Age, Recharge, and Travel Time
Past investigations indicate primarily “Old Water”
Larson, 2000
Douglas, 2007
Depleted Isotopes
Temperature
Elevation
Dead Carbon
Wood
Peat
Required Flux
2cm/year
-I know ive been talking for a while; I want to tell you all a bit about our plans moving into the future
-We can prove these wrong...
-We plan to...
Basement Rock
Moscow-Pullman Subbasin
Larson, 2000
Bush et al., 2017
Sample Well Locations
Age Dates 10,000 – 30,000 Years???
Areas Without Data 16 16

17. Future Work Reevaluate carbon age dates for groundwater samples
6/5/2019
Future Work
Reevaluate carbon age dates for groundwater samples
Published 14C Data (Douglas, 2007)
Stabile Isotopes (13C)
Noble Gas Data (Ar, Ne, Kr, Xe, 4He, R/Ra)
Establish travel time estimates for aquifer recharge
-Noble gasses allow us to reinterpret ages; based on new evidence of carbon sources and flow paths... 17 17

18. 6/5/2019
Questions? 18 18