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ISOTOPE TRACERS AND GROUNDWATER FLOW FROM ABANDONED MINES IN A FRACTURED ROCK SETTING

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

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ISOTOPE TRACERS AND GROUNDWATER FLOW FROM ABANDONED MINES IN A FRACTURED ROCK SETTING

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  1. ISOTOPE TRACERS AND GROUNDWATER FLOW FROM ABANDONED MINES IN A FRACTURED ROCK SETTING Mark Williams Jen Hazen Bob Michel INSTAAR, Stratus Engineering, USGS

  2. 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

  3. 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.

  4. 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.

  5. CHALK CREEK MINE:GROUNDWATER SOURCE CONTROLSDEMONSTRATION PROJECT EPA VIII 104(b)3 Program SUPPLEMENTAL FUNDING REQUEST Assistance Agreement MM998404-02

  6. ZINC and HYDROGRAPH

  7. HYDROGRAPH AND ISOTOPES OF ADIT

  8. ISOTOPES OF INTERIOR STREAMS

  9. HYDROGRAPH SEPARATION

  10. 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 18Ar N=22 16 S N=16 Cosmic Rays O2 SO2 35SO42- 35SO42- SO4-2

  11. 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

  12. 35S: UNITS AND VALUES UNITS: Generally reported as millebecquerels 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

  13. 35S: Collection and Analysis Sample Collection • Need 1-20 Liters of sample • pass sample through ion exchange resin in the field • elute SO42- 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

  14. 35S RESULTS: The MVN3 stream has high zinc and the GTFI site is fracture flow with little zinc These results suggest that the MVN stream is characterized by new water and old SO42-. In contrast, the GTFI site has old water and a low but much greater percentage of atmospheric (new) SO42-.

  15. FLOWPATHS; OLD AND NEW WATER  18O  18O  3H  3H  35S  35S

  16. ISOTOPE COSTS

  17. 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

  18. 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/3Hedating

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