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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