Groundwater Geochemistry - Columbia Basin Ground Water

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Groundwater Geochemistry - Columbia Basin Ground Water
Columbia Basin GWMA
Subsurface Geologic Mapping and Hydrogeologic
Assessment Project Progress Report
Groundwater Geochemistry
Dimitri Vlassopoulos
SS 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
Apparent Groundwater Age
10,000 years
2,000 years
Canal
– surface water recharge
(lakes, rivers, canals)
Sediments
Water-bearing Zones
10 years old
Basalt Aquifer
– ancient groundwater
old
5,000 years
rs old
10,000 yea
– 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
Apparent Groundwater Age (Radiocarbon years)
20,000 15,000
10,000
5,000
2,000
1,000
0
14
Irrigation Wells
Domestic Wells
12
Municipal Wells
Lakes
er
t
a
8
d You
e
ix +
ng
Young Water
Tritium (TU)
10
W
M ter
6
d
Ol
4
u
ro
n
dw
a
G
(recharged since 1950s)
Columbia River/Canals
Old
Groundwater
2
Increasing recharge age
0
0%
20%
40%
60%
80%
Radiocarbon (percent modern)
100%
120%
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
Well
Royal City #1
Royal City #2
Apparent Age
years
1,300
< 50
Radiocarbon
% modern
38
61
Tritium
TU
5.45
10.6
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
Well
Moses Lake #18
Apparent Age
years
< 50
Radiocarbon
% modern
95
Tritium
TU
7.08
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
Well
Moses Lake #17
Apparent Age
years
5,800
Radiocarbon
% modern
24
Tritium
TU
3.97
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
Well
Odessa Irrigation Well
Moses Lake #17
Apparent Age
years
15,800
5,800
Radiocarbon
% modern
8
24
Tritium
TU
< 0.1
3.97
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
Well
HB 132 ft well
HB 600 ft well
Apparent Age
years
< 50
7,900
Radiocarbon
% modern
87
18
Tritium
TU
2.58
< 0.1
However…
• The lower part of the
basalt aquifer system
has not been
recharged since the
end of the last ice age
(!)
15
Frequency
• MOST of the
groundwater in the
Lower Grande Ronde
aquifers is more than
10,000 years old
10
5
0
< 100
100 - 500
501 1,000
1,001 5,000
5,001 10,000
Apparent Age (Years)
> 10,000

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