# Presentation: 081192

## 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. Eberts
- John Karl Böhlke
- Leon Kauffman
- USGS National Water
- Quality Assessment Program
- (NAWQA)

- U.S. Department of the Interior
- U.S. Geological Survey

**Notes:**
Mention SCTX helps to make 10 TANC study areas

## 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

## APPARENT AGES MAY NOT BE SUFFICIENT TO FORECAST SUPPLY WELL SUSCEPTIBILITY

- 25 yrs

- High Plains

- Central Valley

- High Plains

- Floridan

- Glacial deposits

- Preliminary – Subject to Revision

**Notes:**
Mention goes beyond vulnerability assessment for individual aquifer system / public supply wells but that the study unit level investigations are the foundation for the ultimate synthesis products

Also mention ... to provide foundation for assessing the vulnerability of the Nation’s supply wells

## SELECTED ENVIRONMENTAL TRACERS USED TO INFER GROUND-WATER AGE

- SELECTED ENVIRONMENTAL TRACERS USED TO INFER GROUND-WATER AGE

- Cook and Böhlke, 2000

- Age: Time Elapsed Since Recharge ToThe Water Table

- Tracer-Based Ages    Are Apparent Ages
- Tracer-Based Ages    Are Model Dependent

## AGE INTERPRETATION -- Piston Flow Model Assumption --

- 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 --

## AGE INTERPRETATION -- Lumped Parameter Models for Ground-Water Mixtures --

- a     	PFM = piston-flow model
- b, c, d  	EM = exponential model
- e	EPM = exponential piston-                      flow model
- Additional models
- 	LM = 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 --

-   b    c

- d

-  e

## AGE INTERPRETATION-- Tracer Plots --

- 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

- Piston Flow
- Exponential Mixing
- Binary Mixing

## AGE INTERPRETATION -- Flow Model Calibration and Simulation of Age Distributions --

**SF****6**
- Flow-WeightedParticle Tracking:
- 4.14 pptv
- Supply-WellSample:
- 4.53 pptv
**3****H**
- Flow-WeightedParticle Tracking:
- 1.98 TU
- Supply-WellSample:
- 2.1 TU

- Floridan Aquifer SystemPublic-Supply Well

- Preliminary – Subject to Revision

- Crandall, written commun., 2006

## AGE DISTRIBUTIONS IN GROUND WATER MIXTURES-- Implications for Susceptibility --

- AGE DISTRIBUTIONS IN GROUND WATER MIXTURES-- Implications for Susceptibility --

- 0

- 10

- 20

- 30

- Age, In Years

- Fraction of Sample

- 0.00

- 0.10

- 0.20

- TRACERMODEL3 (Böhlke, 2006)

- Water Samples With Identical Mean Ages

## FLORIDAN AQUIFER SYSTEM -- SIMULATED AGE DISTRIBUTION IN SUPPLY WELL --

- Recharge to Well,
-  In Percent

- Age, In Yrs

- 0.35

- Preliminary – Subject to Revision

- Not to Scale

-    BINARY MIXTURE:    Piston Flow (v. young)    and Exponential Piston Flow (older)

- Crandall, written commun., 2006

## 3H, TU

- 0.6

-           0.8

- FLORIDAN AQUIFER SYSTEM -- AGE TRACER DATA --

- TRACERMODEL1b; _[http://](http://water.usgs.gov/lab/)__[water.usgs.gov](http://water.usgs.gov/lab/)__[/lab/](http://water.usgs.gov/lab/)_** **

- 1.0

- 3H, TU

- 0.2

- 0.0

-    5.0

- Public Supply Well

- 0.0

- 1.0

- 4.0

- Preliminary – Subject to Revision

- 3H/3H(0), TU

## CENTRAL VALLEY AQUIFER SYSTEM -- SIMULATED AGE DISTRIBUTION IN SUPPLY WELL --

-  In Percent

- Age, In Yrs

- CENTRAL VALLEY AQUIFER SYSTEM -- SIMULATED AGE DISTRIBUTION IN SUPPLY WELL --

- Preliminary – Subject to Revision

- Not to Scale

- Exponential Piston Flow

- 0

- 50

- 100

- 150

- 200

- 250

- 300

- 350

- 0

- 0.01

- 0.02

- 0.03

- 0.04

- 0.05

- 0.06

- 0.07

- Burow, written commun., 2006

## SF6, pptv

- 0.8

- SF6, pptv

- 0.2

-    6.0

- 0.0

- 1.0

- 0.0

- 0.6

- CENTRAL VALLEY AQUIFER SYSTEM -- AGE TRACER DATA --

- Preliminary – Subject to Revision

-    5.0

- 1.0

- Public Supply Well

- 3H/3H(0), TU

- TRACERMODEL1b; _[http://](http://water.usgs.gov/lab/)__[water.usgs.gov](http://water.usgs.gov/lab/)__[/lab/](http://water.usgs.gov/lab/)_** **

## GLACIAL DEPOSITS -- SIMULATED AGE DISTRIBUTION IN SUPPLY WELL --

- Recharge to Well,
-  In Percent

- Age, In Yrs

- Preliminary – Subject to Revision

- Not to Scale

-    BINARY MIXTURE:    Exponential ( v. young)    and Piston Flow (older)

- 0

- 10

- 20

- 30

- 40

- 50

- 60

- 70

- 80

- 90

- 100

- Glacial deposits

- Starn, written commun., 2006

## 3H/3H(0), TU        

- 0.8

- 3H/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://](http://water.usgs.gov/lab/)__[water.usgs.gov](http://water.usgs.gov/lab/)__[/lab/](http://water.usgs.gov/lab/)_** **

-  20.

## 3H/3He; 4 Yrs

- 0.25

- 0.20

- 0.15

- 0.10

- 0.05

- 0.00

- Floridan

- Apparent Age:
- 3H/3He;** **4 Yrs
- SF6; 6 Yrs

- Preliminary – Subject to Revision

- COMPARISON OF SIMULATED AGE DISTRIBUTIONS IN SUPPLY WELLS

- Glacial deposits

- Age, In Yrs

- Recharge to Well, In Percent

- 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

- 100

- Central Valley

- Apparent Age: 3H/3He; 38 yrs
- SF6 25; Yrs

- 0.35

## CONCLUSIONS

-     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

- _[http://](http://oh.water.usgs.gov/TANCweb/NAWQATANC.htm)__[oh.water.usgs.gov/TANCweb/NAWQATANC.htm](http://oh.water.usgs.gov/TANCweb/NAWQATANC.htm)_

**Notes:**
Mention goes beyond vulnerability assessment for individual aquifer system / public supply wells but that the study unit level investigations are the foundation for the ultimate synthesis products

Also mention ... to provide foundation for assessing the vulnerability of the Nation’s supply wells