application of ground-water dating techniques for evaluating the susceptibility of aquifers and...
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APPLICATION OF GROUND-WATER DATING TECHNIQUES FOR EVALUATING THE
SUSCEPTIBILITY OF AQUIFERS AND PUBLIC-SUPPLY WELLS TO CONTAMINATION
National Water Quality Monitoring Council Meeting
May 9, 2006
Sandra M. EbertsJohn Karl BöhlkeLeon Kauffman
USGS National Water Quality Assessment Program
(NAWQA)
U.S. Department of the InteriorU.S. Geological Survey
TALK OUTLINE
• Considerations For Interpretation Of Environmental-Age Tracers In Public-Supply Wells
• Tracer Concentrations & Age Distributions In Selected Aquifers And Public-Supply Wells
• USGS NAWQA Transport of Anthropogenic & Natural Contaminants (TANC) to Supply Wells Study
GROUND-WATER DATING STUDY AREAS
Central Valley aquifer system
High Plains aquifer
Glacial deposits
Floridan aquifer system
Transport of Anthropogenic and Natural Contaminants (TANC) to Supply Wells Study
Rio Grande aquifer system
Edwards-Trinity aquifer system
1,1,1 trichloroethane
cis-1,2 dichloroethenetrichloroethene
tetrachloroetheneMTBE
freon-11arsenic
uranium
7 yrs
APPARENT AGES MAY NOT BE SUFFICIENT TO FORECAST SUPPLY WELL SUSCEPTIBILITY
25 yrs
chloroformtrichloroethenearsenicuranium
5 yrs
High Plains
bromoformchloroform
tetrachloroethene
nitrate
atrazineDEAdiuronarsenicuranium
cis-1,2 dichloroethenetrichloroethene
tetrachloroethenenitratearsenic
uranium
20 yrs
Central Valley
High Plains
Floridan
Glacial deposits
Preliminary – Subject to Revision
SELECTED ENVIRONMENTAL TRACERS USED
TO INFER GROUND-WATER
AGE
Cook and Böhlke, 2000
Age: Time Elapsed Since Recharge ToThe Water TableTracer-Based Ages
Are Apparent Ages
Tracer-Based Ages Are Model Dependent
a PFM = piston-flow model
A water sample is a mixture of waters from all flow lines that reach the sampling point.
If the flow lines are associated with a narrow range of ages, the apparent age of the sample may reasonably represent the travel time from the point of recharge.
AGE INTERPRETATION -- Piston Flow Model Assumption --
a
Zuber, 1986
a PFM = piston-flow model
b, c, d EM = exponential modele EPM = exponential piston- flow model
Additional modelsLM = linear
LPM = linear-piston DM = dispersion
Lumped-parameter models … simple mathematical functions that describe age distributions for various combinations of recharge area, aquifer geometry, and sample type (Zuber, 1986)
AGE INTERPRETATION -- Lumped Parameter Models for Ground-Water Mixtures --
a
b c
d
e
Modified from Plummer, written commun., 2006
AGE INTERPRETATION
-- Tracer Plots --
Can Be Used To Recognize Cases Of Piston Flow And Binary Mixing With Tracer Free Fraction (Dilution)
Elimination Of Some
Mixing Models 0 200 400 600CFC-12 Concentration, pptv
0
10
20
30
40
3H
Dec
ayed
to
Yea
r 1
999,
TU
1990
19801960
19951975
1970
15
100
200
1050
20
1985
1999
Piston FlowExponential Mixing Binary Mixing
AGE INTERPRETATION -- Flow Model Calibration and Simulation of Age Distributions --
SF6Flow-WeightedParticle Tracking:4.14 pptv
Supply-WellSample:4.53 pptv
3HFlow-WeightedParticle Tracking:1.98 TU
Supply-WellSample:2.1 TU
Floridan Aquifer SystemPublic-Supply Well
Preliminary – Subject to Revision
Crandall, written commun., 2006
0.00
0.10
0.20
0 10 20 30
Age (yr)
Fra
ctio
n o
f s
amp
le
PF tau = 10.0
DM tau = 10.0
EM tau = 10.0
EPM tau = 10.0
AGE DISTRIBUTIONS IN GROUND WATER MIXTURES-- Implications for Susceptibility --
0 10 20 30
Age, In Years
Fract
ion
of
Sam
ple
0.00
0.10
0.20
TRACERMODEL3 (Böhlke, 2006)
Water Samples With Identical Mean Ages
FLORIDAN AQUIFER SYSTEM -- SIMULATED AGE DISTRIBUTION IN SUPPLY WELL --
Rech
arg
e t
o W
ell,
In
Perc
en
t
0.000.05
0.100.15
0.200.25
0 10 20 30 40 50 60 70 80 90 100
Age, In Yrs
0.35
Floridan
Preliminary – Subject to Revision
Not to Scale
BINARY MIXTURE:
Piston Flow (v. young) and Exponential Piston Flow (older)
0.25
0.20
0.15
0.10
0.05
0.00
0 10
20
30
40
50
60
70
8 0 90
10
0
Crandall, written commun., 2006
0.6
0.8
FLORIDAN AQUIFER SYSTEM -- AGE TRACER DATA --
TRACERMODEL1b; http://water.usgs.gov/lab/
1.0
3H
, TU
0.2
0.0
5
.0
Public Supply Well
0.0
1.0
4.0
Surficial Aquifer
Binary Mixing ModelExponential Mixing Model
Piston Flow Model
Exponential Piston Flow Model xP/xE = 15Samples
Preliminary – Subject to Revision
3H/3H(0), TU
Confining Unit
Shallow Upper Floridan
Deep Upper Floridan
Rech
arg
e t
o W
ell,
In
Perc
en
t
Age, In Yrs
CENTRAL VALLEY AQUIFER SYSTEM -- SIMULATED AGE DISTRIBUTION IN SUPPLY WELL --
Preliminary – Subject to Revision
0
0.01
0.02
0.03
0.04
0.05
0.06
0.070 50
100
150
200
250
300
350
Not to Scale
Exponential Piston Flow
0
50
10
0
15
0
20
0
25
0
30
0
35
0
Central Valley
0
0.01
0.02
0.030.04
0.05
0.06
0.07
Burow, written commun., 2006
0.8
SF 6
, p
ptv
0.2
6
.0
0.0 1.0
0.
0
0.6
CENTRAL VALLEY AQUIFER SYSTEM -- AGE TRACER DATA --
Preliminary – Subject to Revision
5
.01.
0
Public Supply Well
3H/3H(0), TU
Binary Mixing ModelExponential Mixing Model
Piston Flow Model
Exponential Piston Flow Model xP/xE = 0.6Samples
TRACERMODEL1b; http://water.usgs.gov/lab/
GLACIAL DEPOSITS -- SIMULATED AGE DISTRIBUTION IN SUPPLY WELL --
Rech
arg
e t
o W
ell,
In
Perc
en
t
Age, In Yrs
Preliminary – Subject to Revision
0.00
0.05
0.10
0.15
0.20
0.250 10
20
30
40
50
60
70
80
90
100
Not to Scale
BINARY MIXTURE:
Exponential ( v. young) and Piston Flow (older)
0.25
0.20
0.15
0.10
0.05
0.00
0 10
20
30
40
50
60
70
80
90
10
0
Glacial deposits
Starn, written commun., 2006
0.83H/3H(0), TU
3H
, TU
0.2
25.
0.0 1.0
0.
0
Public Supply Well
0.6
GLACIAL DEPOSITS -- AGE TRACER DATA --
Preliminary – Subject to Revision
TRACERMODEL1b; http://water.usgs.gov/lab/
Binary Mixing ModelExponential Mixing Model
Piston Flow Model
Exponential Piston Flow Model xP/xE = 3.0Samples
20.
0.00
0.05
0.10
0.15
0.20
0.25
0
10 20 30 40 50 60 70 80 90
100
0.25
0.20
0.15
0.10
0.05
0.00
0 10
20
30
40
50
60
70
80
90
10
0
Floridan
Apparent
Age:
3H/3He; 4 Yrs
SF6; 6 Yrs
Preliminary – Subject to Revision
COMPARISON OF SIMULATED AGE DISTRIBUTIONS
IN SUPPLY WELLS
0.00
0.05
0.10
0.15
0.20
0.25
0
10
20
30
40
50
60
70
80
90
100
0.00
0.05
0.10
0.15
0.20
0.25
0
10 20 30 40 50 60 70 80 90
1000 10
20
30
40
50
60
70
80
90
10
0
Glacial deposits
Age, In Yrs
Rech
arg
e t
o W
ell,
In
Perc
ent Apparent Age:
3H/3He; 7 Yrs
0.25
0.20
0.15
0.10
0.05
0.00
0 10
20
30
40
50
60
70
80
90
10
0
Central Valley
Apparent Age:
3H/3He; 38 yrs
SF6 25; Yrs1,600 gal/min
660 gal/min
72 gal/min0.25
0.20
0.15
0.10
0.05
0.00
0.35
• Age Distributions Are More Useful Than Apparent Mean Ages For Understanding Susceptibility
• Ground-Water Flow Models Calibrated To Age Tracer Concentrations Can Be Used To Simulate Age Distributions
• It May Be Possible To Describe Age Distributions In Public-Supply Wells Using Lumped-Parameter Models (Simple Mathematical Functions)
• Tracer-Tracer Plots Can Sometimes Provide Insight Into Age Distributions In Public-Supply Wells
CONCLUSIONS
http://oh.water.usgs.gov/TANCweb/NAWQATANC.htm