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