Geochemical Characterization of Shallow Groundwater near the

Animas River, New Mexico

B. Talon NewtonEthan Mamer

Stacy TimmonsWith funding

from NM Environment

Department

Animas River: Long term monitoring groundwater quality

• Element 7 of the NMEDs Long-term monitoring plan

• Funded by U.S. EPA Clean Water Act, Section 106 through NMED

• Goals:– Set up long-term

monitoring using existing wells

– Evaluate groundwater chemistry, geochemical processes, and possible groundwater quality changes as a result of GKM

Gold King Mine Spill

• August 5, 2015• ~3 million gallons of mine waste water

released into the Animas near Silverton, CO• MESSY issue

– Impacts to environment, wildlife and people– Political impacts on relationships between local,

state and federal agencies (That is why I am whispering…)

NM Bureau of Geology and Mineral Resources

Did the Gold King Mine Spill impact groundwater quality in

shallow alluvial aquifer adjacent to the Animas River

in New Mexico?

NM Bureau of Geology and Mineral Resources

How does river water get into the aquifer?

NM Bureau of Geology and Mineral Resources

Groundwater/Surface Water Interactions

Losing Stream

Gaining Stream

NM Bureau of Geology and Mineral Resources

The Animas River in NM is mostly a gaining stream

• Stream flow data during base flow shows larger flow rates at downstream locations

• Groundwater level elevations are mostly higher than the river surface

• Stable isotopes of oxygen and hydrogen – During base flow conditions, river water

isotopically resembles groundwater

NM Bureau of Geology and Mineral Resources

NM Bureau of Geology and Mineral Resources

Groundwater sampling

Chemical analyses• Field parameters

– Temperature– pH– Specific Conductance– Dissolved Oxygen (DO)– Oxidation Reduction Potential

• Major Cation and Anions• Trace Metals• Environmental Tracers

– Stable isotopes of oxygen and hydrogen– Tritium– Carbon - 14

NM Bureau of Geology and Mineral Resources

Controls on Groundwater Chemistry

NM Bureau of Geology and Mineral Resources

Water – Mineral Interactions• Dissolution of different rocks that make up the

aquifer– Limestone - CaCO3 Ca2+ + HCO3

-

– Dolomite - CaMg(CO3)2 Ca2+ + Mg2+ + 2HCO3-

– Gypsum – CaSO4 Ca2+ + SO42-

– Halite – NaCl Na+ + Cl-

• Cation exchange– Na-Clay +Ca2+ Ca-Clay + Na+

NM Bureau of Geology and Mineral Resources

Geochemical Characterization

Geochemical controls on groundwater chemistry

• Mineral dissolution

• Mixing with older waters

• TDS values should increase along the flow path.

NM Bureau of Geology and Mineral Resources

Tracing the influence of River water• Samples with

DO < 3 mg/L exhibit higher range in TDS

• River water is saturated wrtDO (~10 mg/L)

• River water usually has lower TDS than groundwater

NM Bureau of Geology and Mineral Resources

Tracing the influence of river water

• Low DO groundwater exhibits higher values at lower elevations

• High DO water exhibits lower TDS values over same elevation range

NM Bureau of Geology and Mineral Resources

Tracing the influence of river water

• Box and Whisker Diagrams shows data set distribution

• River water TDS levels are much lower than groundwater TDS levels

• River water DO values are much higher than groundwater DO values

NM Bureau of Geology and Mineral Resources

Tracing the influence of river water

• More high DO samples than low DO samples

• Many wells exhibit high and low DO concentrations at different times

NM Bureau of Geology and Mineral Resources

Tracing the influence of river water

• Low DO samples exhibit no TDS trend with time

NM Bureau of Geology and Mineral Resources

Tracing the influence of river water

• High DO samples exhibit a TDS trend with time

• Lower TDS values during irrigation season

NM Bureau of Geology and Mineral Resources

Tracing the influence of river water

• Wells with both high and low DO waters show river input during irrigation season

NM Bureau of Geology and Mineral Resources

Source of high metal concentrations

• Some wells exhibit manganese and iron concentrations that are above EPA or state standards

• Can we use DO to determine the source of high manganese and iron concentrations?

NM Bureau of Geology and Mineral Resources

Source of high metal concentrations

NM Bureau of Geology and Mineral Resources

Source of high metal concentrations

Source of high metal concentrations

Preliminary Conclusions• Groundwater geochemical controls

– Dissolution of calcite and gypsum– Cation exchange– Mixing with older water from the Nacimiento and Ojo Alamo

aquifers

• Dissolved oxygen as an indicator of river water input– DO < 3 mg/L – No river input– DO > 3 mg/L – Positive for river input

• River water input associated with irrigation is observed in several wells

• River input cannot easily be linked with observed high manganese and iron concentrations in some wells

NM Bureau of Geology and Mineral Resources

Acknowledgements

• NM Environment Department and EPA for funding

• Trevor Kludt, Scott Christenson, Kitty Pokorny, Brigitte Felix - NMBGMR

• Dennis McQuillan, Diane Agnew – NMED

NM Bureau of Geology and Mineral Resources NM Bureau of Geology and Mineral Resources