columbia basin gwma subsurface geologic mapping and hydrogeologic assessment project progress report...
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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)
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