The Animas River Toxic Spill: Using current events to teach Geology, Geochemistry, and Presentation skills to undergraduate Geology majors at Fort Lewis College, Durango, CO

Kenny, R., Bachrodt, M.D., Hedrick, E.A., Jiang, M.L., Kirkpatrick, A.J., Leysens, P.O., Martinez, R.L., Mason, J.A., Poisson, K.C., Vandervert, M.S., and Whidden, B.M.

Geosciences Department, Fort Lewis College, Durango, CO

Abstract

The toxic spill generated by the Gold King Mine (GKM) blowout north of Silverton, Colorado traveled ~60 river miles along the Animas River and reached the City of Durango by 8:00pm on August 6, 2015 carrying elevated levels of heavy metals as both dissolved load and colloids. On August 15, 2015, the EPA determined, based on on-going analyses of river samples that the water quality of the Animas River had returned to pre-spill levels. Contaminated water and colloid samples were collected by the authors using standard EPA protocol during peak spill and toxicity levels, from August 7-13, 2015. Water samples from six Animas River locations and sludge samples from eight river and canal locations, were independently analyzed at an EPA and State of Colorado Certified Laboratory with funding provided by Fort Lewis College (FLC) Provost Barbara Morris. Nine undergraduate geology majors, as part of an upper-level undergraduate Geology course, were charged with undertaking a comparative geochemical analysis of water quality data collected by the EPA and the Geosciences Department at FLC. Each student was assigned specific tasks; all students collaborated and worked together to produce a final PowerPoint® presentation. The students addressed the geologic setting of the Silverton Caldera, mining history, historic mine releases, water quality concerns, bulkhead construction and benefits, and generated suitable GIS maps. Field outings to the Silverton area were conducted in August to discuss and geochemically distinguish between AMD and ARD sites. Historic cross-sections and high wall plans of the GKM were graciously provided by the Colorado Division of Reclamation, Mining, and Safety (Abandoned Mines Division). Spatially-referenced data from ArcMap® was imported into MAPTEK (Vulcan)® software, and a 3D model of the GKM underground workings was generated: (1) to illustrate the geologic and hydrologic complexity of the mine; and, (2) to investigate possible hydrologic connectivity that could possibly explain the elevated flow volumes observed during the blowout. In addition to the educational benefits of the study, the goals of the study were to provide the public with a more complete understanding of the GKM, and help explain why metal concentrations in streams vary by sample location, discharge levels, and time of day. The students presented their work at public forums.

Discussion Points

Historic discharges for the Gold King Mine:

2007 (300 g/m) · 2008-2009 (200 g/m) · 2010-2012 (150 g/m) · 2015 (Pre Blowout: 70 g/m)

Estimated (initial) spill release was 3 million gallons (likely greater because 550 to 600 gallons/minute discharged –

unabated, for at least a week after the initial spill)

Possible reasons for the unexpected high volume discharge:

Water table increased behind debris dams; lower levels of the Gold King Mine flood

Disturbance by EPA causes debris dam in Level 7 (figure 6) to fail; loss of hydrostatic pressure from the disturbance leads to system collapse, multiple dam failures, and cascading fluids (figure 7).

Water samples were collected at six locations along the Animas River; sludge samples were collected at eight locations:

Water samples were all collected in accordance with EPA field sampling protocol

Samples were analyzed at Green Analytical Laboratories (an EPA and State of Colorado Certified Lab)

Results were compared with EPA data:

Dissolved solid values vary due to time of day (Diurnal Cycles), sample depth, river currents, pH changes,

temperature changes, discharge, etc. (figure 12)

Elevated heavy metal values were detected in the sediment (sludge; figure 13)

Opportunity to inform the public about wide range of concentration data reported by EPA

Hardness data proportional to Ca, Mg / MCLs for many toxic metals are hardness dependent

Chronic effects and concerns:

Sludge may still be present in irrigation canals / persists in Animas River sediments

Oral and accidental ingestion concerns remain

Chronic effect on organism trophic level remains unknown

Re-entrainment of sludge during Spring runoff.

Bulkheads as remediation tool (figure 5)

An engineered concrete wall (10 – 20 feet long) placed inside a mine opening to retain water inside the mine workings

Purpose. Control AMD and prevents blow-outs; used to impound water inside the mine workings

Problems include: Lifespan (< century?) / Leakage around bulkheads: American Tunnel (70 g/m) · Koehler (8 g/m)

Bulkheads can cause impounded water to preferentially flow out of a fault or fracture connected to surface.

Emplacement requirements. Geology must be advantageous for installation of bulkheads:

Bulkhead location requires solid, competent rock (minimally fractured, altered, jointed or bedded)

No significant natural groundwater-conducting structural pathways (faults, shear zones, bedding planes, etc.)

connecting to nearby mine workings or surface discharge points

Adequate overburden to hold hydrostatic pressure (figure 5)

Benefits: Groundwater returned to pre-mining levels, natural attenuation of metals under anoxic environment (figure 5)

Gold King Mine underground 3D Model created:

to aid in understanding complexity of the underground workings of the Gold King Mine / possible hydrologic connectivity

Brief Mining History

Figure 1. (A) Gold King Mine and discharge point into Cement Creek. Cement Creek is a tributary of the Animas River which flows through Durango, CO; the Animas River is a tributary of the San Juan River (northwestern NM). (B) Outline of the Silverton Caldera (~27Ma); faults & fractures related to caldera collapse provided pathways for hydrothermal fluids and mineralization.

Figure 2. Miners working the Gold King Mine, near Silverton, CO in 1899.

• 1870-1930s

• Mine discharge directly into Cement Creek

• By 1991

• All mining operations (around 400) shut down due to falling prices

• 1991-present

• Unmitigated discharge flows:

• Cement Creek

• tributary of the Animas River in Silverton, Colorado (Thompson, 2015)

Lake Emma Drains

Acid Mine Drainage vs Acid Rock Drainage

Figure 3 (left). June 4, 1978, Sunnyside Mine operations bore too close to Lake Emma. Lake Emma drained into the Sunnyside Mine. An estimated 500 million gallons drained into the

Sunnyside Mine and discharged through the American Tunnel into Cement Creek.

Figure 4. (A) AMD greater metal loading/mine portal (discharge to Cement Creek)/more

available oxygen/Thiobacillus ferrooxidans bacteria catalyst/Schwertmannite precipitates. (B) ARD ferricretes (So. Mineral Creek; near neutral pH)/acid-tolerant

algae/goethite/oxides of Fe, Al, Mn/low metal loading/acidophyllitic mosses & algae/pH typically 3.2 to 5.5/ /amorphous oxyhydroxdides. Al oxyhydroxides [such as Basaluminite (Al₄(OH)₁₀·4H₂O) and Al(OH)3] precipitate in mixing zone (outlined by the yellow lines).

Gold King Mine: Dissolved Load and Colloids

Figure 11. (clockwise) Heavy metal contaminated dissolved load (ions in solution) at 32nd Street (Durango). Metal-rich colloid (sludge) deposits along a meander point bar north of Durango, Colorado (fresh geese tracks). Colloids were defined as

(FLC & EPA) Data Comparison: Dissolved Load and Colloids

Figure 12. (left) Dissolved solids data: Al, As, Fe, Pb all exceeded EPA Primary or Secondary Drinking water standards (August 7, 2015). Sunlight (leading to photosynthetic reactions), temperature, streamflow, pH changes, can result in concentration variations of solute loads.

Figure 13. (right) Sludge (sediment, colloid) data. Toxic sediment still exists along the banks of the Animas River. Pb values are elevated >1000 ppm. An appropriate risk exposure for residential citizens should be (at a minimum) <400 ppm.

Figure 9. 3D model (MAPTEK Vulcan) showing the American Tunnel beneath the seven Gold King Mine levels. Flow may come out of mine openings after emplacement of bulkheads. 3D models are critical for identification of possible hydrologic connections.

References

Bove, D., 2007, Alteration map showing major faults and veins and associated water-quality signatures of the Animas River Watershed headwaters near Silverton, southwest Colorado,Denver, Colo. : U.S. Geological Survey, 2007.

Church, S.E., Owen, J.R., von Guerard, P., Verplanck, P.L., Kimball, B.A., and Yager, D.B., 2007,The effects of acidic mine drainage from historical mines in the Animas River watershed,San Juan County, Colorado; what is being done and what can be done to improve waterquality? Reviews in Engineering Geology, v. 17, p. 47-83, doi: 10.1130/2007.4017(04).

Clark, C., 2015, Upper Gold King Mine Spill Still Not Cleaned up: valleydailypost.com/upper-gold-king-mine-spill-still-cleaned-up (accessed October 2015).

Gammons, C.H., Nimick, D.A., and Parker, S.R., 2015, Diel cycling of trace elements in streamsdraining mineralized areas-A review. Applied Geochemistry, v. 57, p. 35-44.

Simpson, Kevin. "Animas River: Long-term Impacts of Wastewater Spill Lie beneath theCurrent." Denver Post 18 August 2015

Thompson, J., 2015, When our river turned orange: Web Exclusive, p. 1, doi: August 9, 2015.

Acknowledgments

Mine portal photograph is in the public domain. Bulkhead photographs and diagrams modified from Kirstin Brown. We gratefully acknowledge help from Kirstin Brown, Chuck Baltzer, Lauren Heerschap, and MAPTEK. Geochemistry funds provided by FLC Provost Barbara Morris.

(Silverton

Standard)

B

Figure 8. American tunnel bulkhead #2 (bypass pipe lower left; pressure sampling pipe right).

A

Figure 6. Relationship of the American Tunnel to the Gold King Mine and level 7 portal.

Benefits of Bulkheads

Figure 5. Bulkheads: (a) Prevent formation of AMD and unintentional releases of water; (b) Minimize amount of water treatment necessary; (c) Return groundwater table to pre-mine levels; and, (d) Creates anoxic environment, minimizing oxidation. Adequate overburden is required to hold back the hydrologic pressures. Multiple bulkheads are installed. Sunnyside Mine workings have 12 bulkheads in place.

B

non-crystalline (determined by XRD), ultramicroscopic particles not easily separated out by filtering.

Figure 10. Gold King Mine portal.

Figure 7. Possible triggering mechanism for a catastrophic toxic mine discharge

Internal debris dam failure model leading to AMD.

Loss of hydrostatic pressure behind rockfalls and mine waste rock in the adit can lead to porous debris, dam failure

Pressure from cascading fluids can lead to system collapse & catastrophic discharge

A