Columbia Basin GWMA Subsurface Geologic Mapping and Hydrogeologic

Assessment Project Progress Report

Groundwater Geochemistry

Dimitri VlassopoulosSS Papadopulos and Associates

Portland, Oregon

Presented at GWMA Board Meeting, Othello, WA January 22, 2009

Groundwater Geochemistry• Major ion chemistry

– Changes along flow path– Relative age– Recharge sources– Mixing

• Stable Isotopes– Water sources (precipitation/runoff, surface water)– Ancient (glacial) versus modern recharge

• Atmospheric tracers (groundwater age-dating) – Radiocarbon, tritium, CFCs, SF6

– Groundwater “age” (time since recharged)– Mixing of old and young water (pumping effects)

GWMA Well Sampling 2008

Groundwater Geochemistry, Age and Recharge• Geochemical data can

identify the source(s) of groundwater

– ancient groundwater

– surface water recharge (lakes, rivers, canals)

– irrigation water recharge

• Age-dating methods can be used to determine the length of time groundwater has been in the subsurface

• Direct information on the relative amounts of old and young water drawn by pumping wells

Canal

Apparent Groundwater Age

10,000 years 2,000 years

10 years old

10,000 years old

5,000 years old

Sediments

Basa

lt Aq

uife

rW

ater

-bea

ring

Zon

es

Canal

Apparent Groundwater Age

10,000 years 2,000 years

10 years old

10,000 years old

5,000 years old

Sediments

Basa

lt Aq

uife

rW

ater

-bea

ring

Zon

es

0

2

4

6

8

10

12

14

0% 20% 40% 60% 80% 100% 120%

Radiocarbon (percent modern)

Triti

um (T

U)

Irrigation Wells

Domestic Wells

Municipal Wells

Columbia River/Canals

Lakes

Increasing recharge age

Youn

g W

ater

(r

echa

rged

sin

ce 1

950s

)

Old Groundwater

15,000 10,000 5,000 2,000 1,000 0

Apparent Groundwater Age (Radiocarbon years)20,000

0

2

4

6

8

10

12

14

0% 20% 40% 60% 80% 100% 120%

Radiocarbon (percent modern)

Triti

um (T

U)

Irrigation Wells

Domestic Wells

Municipal Wells

Columbia River/Canals

Lakes

Increasing recharge age

Youn

g W

ater

(r

echa

rged

sin

ce 1

950s

)

Old Groundwater

15,000 10,000 5,000 2,000 1,000 0

Apparent Groundwater Age (Radiocarbon years)20,000

Royal City• Wells #1, #2

– Shallow-cased water supply wells completed in Wanapum– Static water levels steady– Mixture of older and “young” water (recharged since

1950s)– Recharge from Frenchman Hills sufficient to sustain

withdrawals

Apparent Age Radiocarbon Tritiumyears % modern TU

Royal City #1 1,300 38 5.45Royal City #2 < 50 61 10.6

Well

Moses Lake• Well #18

– Supply well completed in Wanapum (Frenchman Springs)– Static water levels stable– Mostly “young” water (post-1950’s)– Direct connection to East Low Canal through Roza/Upper

Frenchman Springs flow zones

Apparent Age Radiocarbon Tritiumyears % modern TU

Moses Lake #18 < 50 95 7.08

Well

Moses Lake• Well #17

– Supply well completed in upper Grande Ronde (Sentinel Bluffs)

– Static water levels declining– Mixture of old and “young” water (average recharge age

~6,000 years)– Recharge from “young” water component (<20 %) is too

small to offset withdrawals– Limited connection to surface recharge

Apparent Age Radiocarbon Tritiumyears % modern TU

Moses Lake #17 5,800 24 3.97

Well

Odessa• Irrigation well 20 miles east of Moses Lake

– Well completed in Lower Grande Ronde (Umtanum and Ortley)

– Static water levels declining– Old water (recharge age >10,000 years)– No present-day surface recharge sources

Apparent Age Radiocarbon Tritiumyears % modern TU

Odessa Irrigation Well 15,800 8 < 0.1Moses Lake #17 5,800 24 3.97

Well

Horseshoe Bend• Irrigation Wells

– Shallow (132’) well in use since 1948 (Roza/Alluvium)– Deeper (605’) well in basalt (Wanapum and uppermost Grande

Ronde)– Static water levels stable– Predominantly young water in shallow well, predominantly older

water in deeper well– Relatively low groundwater use area– Connection to surface recharge (Sprague Lake) sufficient to recharge

shallow well

Apparent Age Radiocarbon Tritiumyears % modern TU

HB 132 ft well < 50 87 2.58HB 600 ft well 7,900 18 < 0.1

Well

However…

• MOST of the groundwater in the Lower Grande Ronde aquifers is more than 10,000 years old

• The lower part of the basalt aquifer system has not been recharged since the end of the last ice age (!)

0

5

10

15

< 100 100 - 500 501 -1,000

1,001 -5,000

5,001 -10,000

> 10,000

Apparent Age (Years)

Freq

uenc

y