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"

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

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

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)

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

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

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

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

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

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

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

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

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

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

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

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

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

6/5/2019 Questions? 18 18