ISOTOPE TRACERS AND GROUNDWATER FLOW FROM

ABANDONED MINES IN A FRACTURED ROCK SETTING

Mark Williams

Jen Hazen

Bob Michel

INSTAAR, Stratus Engineering, USGS

END OF PIPE TREATMENT STRATEGY

Millions of dollars to install

Expensive to operate Operate for long-term 70,000 abandoned

mines in West Need low-cost

alternatives

TRACERS IN HYDROLOGY

HYDROLOGY Age Origin Pathways Not used because seen as too complex, too costly, too

difficult

MINE REMEDIATION Tracers are under-utilized to even a much

larger extent than in hydrology.

ISOTOPES IN HYDROLOGY

What are environmental isotopes?Environmental isotopes of an element are part of the natural environment. They are ideal for use as fingerprinting tracers since they are already present in the system.

Why would you use environmental isotopes?

The identification of fluid sources and pathways is often aided by the use of environmental isotopes. For example, waters from different areas may contain different isotopic fingerprints allowing the identification of the source, age, and pathway.

CHALK CREEK MINE:GROUNDWATER SOURCE

CONTROLSDEMONSTRATION PROJECT

EPA VIII 104(b)3 Program

SUPPLEMENTAL FUNDING REQUEST

Assistance Agreement MM998404-02

ZINC and HYDROGRAPH

HYDROGRAPH AND ISOTOPES OF ADIT

ISOTOPES OF INTERIOR STREAMS

HYDROGRAPH SEPARATION

Sulfur-35 (35S) IN THE ENVIRONMENT

Radioactive isotope of sulfate Half-life of about 87 days Produced by spallation of argon atoms in the

atmosphere by cosmic rays

18ArN=22 O2 SO2

SO4-2

Cosmic Rays

35SO42- 35SO4

2-

16 SN=16

35S: APPLICATIONS FOR MINE REMEDIATION

1. ESTIMATE AGE OF WATER

• Very effective for time scale less than one year

• Few other environmental tracers can do this

2. DISCRIMINATE “NEW” vs. “OLD” WATER SOURCES

• Particularly good for identifying snowmelt in mine discharge

3. DATE AGE OF SULFATE

• Date age of atmospheric –deposited sulfate less than one year old

4. DISCRIMINATE ATMOSHPERIC FROM GEOCHEMICAL SOURCES OF SULFATE

35S: UNITS AND VALUES

UNITS: Generally reported asmillebecquerels per Liter (mBq/L)

millebecquerels per mgSO4 (mBq/ mgSO4)

CONCENTRATIONS:

Snowfall 60 mBq/L

Snowmelt 20 mBq/L because of decay of snowpack

Rain(Summer) 100 mBq/L

FACTORS- extent of atmospheric mixing of stratospheric air into

troposphere; greatest in summer

35S: Collection and Analysis

Sample Collection Need 1-20 Liters of sample pass sample through ion exchange resin in the field elute SO4

2- from resin with barium chloride final volume 100 ml

Sample Analysis Liquid scintillation counting Count twice, about 4 months apart as part of QA/QC

35S RESULTS: The MVN3 stream has high zinc and the GTFI site is fracture flow

with little zinc

Isotope GTFI MVN-335S (mBq/L) 10 120

35S (mBq/ mgSO4) 0.3% <0.1%

Atmospheric Sulfate 2.4% <0.1%

18O (‰) -16.2 -18.1

New Water (%) 3% 80%

These results suggest that the MVN stream is characterized by new water and old SO4

2-. In contrast, the GTFI site has old water and a low but much greater percentage of atmospheric (new) SO4

2-.

FLOWPATHS; OLD AND NEW WATER

18O

3H

35S 35S

3H 18O

ISOTOPE COSTS

Isotope Waterloo INSTAAR USGS

D $39 $20 ---

18O $33 $20 ---

3H $135 --- $100

35S --- --- $200

15N18O3 $150 --- ---

RECOMMENDATIONS FOR ADDITIONAL RESEARCH

Sample Analysis Reason

[1] all samples 18O and Zn

[2] 35S -separate ppt from groundwater

-700’ level

-other interior streams

-Chalk Creek

-methods development

[3] 3H -age groundwater streams

-interior streams

-Chalk Creek

[4] 15N18O3

- -source of NO3

-interior streams

-Chalk Creek

-precipitation

[5] Discharge

-Hydrometric analysis

-interior streams

[6] Graduate Student -does the work

SUMMARY

Reconsider concept of saturated zone and water table in fractured rock settings

D and 18O underutilized surface – groundwater interactions

35S very promising 35S may constrain 3H/3He dating