mercury contamination and bioaccumulation from historical gold mining in the sierra nevada – site...
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![Page 1: Mercury Contamination and Bioaccumulation from Historical Gold Mining in the Sierra Nevada – Site Characterization and Remediation Charles N. Alpers, Ph.D](https://reader035.vdocument.in/reader035/viewer/2022070307/551a2eab550346545e8b4952/html5/thumbnails/1.jpg)
Mercury Contamination and Bioaccumulation from Historical
Gold Mining in the Sierra Nevada – Site Characterization and
Remediation
Charles N. Alpers, Ph.D.
U.S. Geological SurveyCalifornia Water Science Center
Placer Hall6000 J Street
Sacramento, CA
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Cooperating AgenciesFederal
State
Local
Hydraulic mining, Placer County, CA
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Outline of Presentation• Background
– Review of mining history and mercury use in gold mining
• Environmental geochemistry of mercury in the Bear, Yuba, and American River watersheds, California– Water Quality– Sediment– Biota– Importance of seasonality in Hg cycle
• Remediation of 3 Hg-contaminated placer mine sites• What have we learned? • What information gaps remain?
Casci Creek, Nevada Co., CA
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HISTORICAL MINING:
Gold & Mercury
• More than 100,000,000 kg mercury (Hg) produced from 239 mines in California
• Approx. 33,000,000 kg Hg lost to atmosphere from furnaces at Hg mines
• Approx. 12,000,000 kg Hg used in Calif. gold mining
(Churchill, 2000)
box
USGS Fact Sheet 2005-3014
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GOLD MINING AND MERCURY USE IN THE
NORTHERN SIERRA NEVADA
• Highest intensity of hydraulic mining (placer gravel deposits) in Bear-Yuba watersheds
• Approx. 5,000,000 kg of mercury lost during gold processing in Sierra Nevada (USGS, 2000; Churchill, 2000)
• Significant gold dredging in all rivers draining Sierra Nevada
USGS Fact Sheet 2005-3014
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Hydraulic mining, Malakoff Diggins,
Nevada County, CA, circa 1880
Hydraulic mine, ground sluice system,
Scott Valley mine, Siskiyou County, CA
circa 1870s
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Sluice Tunnels
• Sluices recovered gold. • Mercury was used to amalgamate fine gold.• Mercury was lost during sluicing.• Mercury is still found in sluices and their foundations today. Photos: Rick Humphreys, SWRCB
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UNDERCURRENT
SLUICE BOX Sluice and undercurrent,Oro Fino mine,
Siskiyou County, CACirca 1855
Sluice–undercurrent system,
Spring Valley mine, Butte County, CA,
Feather River watershed
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Hg beads in sediment
South Fork American River, Lotus Camp (near Coloma)
Photo by R. Humphreys
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USGS Fact Sheet 2005-3014
Mercury Loss to the Environment in Hydraulic Mining
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Cleaning amalgam from stamp mill, Empire Mine, Cleaning amalgam from stamp mill, Empire Mine, Nevada County, California, 1900Nevada County, California, 1900
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Abandoned bucket-line dredge, Yuba Goldfields, CA
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TRANSPORT AND TRANSFORMATION OF MERCURY
ENVIRONMENTS: • Hydraulic and hardrock gold mines – Sierra Nevada• Mercury mines – Coast Ranges• Mountain streams above reservoirs• Foothill reservoirs• Rivers below reservoirs – gold dredging environments• Floodplain deposits• San Francisco Bay-Delta estuary
USGS Fact Sheet 2005-3014
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The Mercury Cycle in Aquatic The Mercury Cycle in Aquatic SystemsSystems
AIR
WATER
SEDIMENT
CH3Hg+
Hg(II)
Hg(II)
Particles
Hg0
HgCl2
HgCl42-
Runoff
Hg(II)
CH3Hg+
Hg0
DOM
Hg0
Hg(II)CH3Hg+ Hg0
Particles
Hg0
atmospheric transport
phytoplankton
zooplankton
lightlightmicrobes
microbes microbes
abiotic rxn.
Graphic: Mark Marvin-DiPasquale (USGS)SRB, FeRB
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SAMPLING SITES, BEAR-YUBA, 1999
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Source: May et al. (2000)
USGS OFR 00-367
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• (δ15N) − MeHg slope similar
other studies
• similar rate of biomagnification of MeHg with increasing trophic level.
Stewart et al. (2008) CJFAS
Food Web Study, Camp Far West Reservoir, CA
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Data from:Alpers et al. (2008) USGS SIR 2006-5008
Camp Far West Reservoir, CA
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Data from:Alpers et al. (2008) USGS SIR 2006-5008
Camp Far West Reservoir, CA
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Stewart et al. (2008) CJFASCamp Far West Reservoir, CA
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Principal Findings – Seasonal Cycles in Camp Far West
Reservoir
• Fall-Winter phytoplankton bloom is triggered by phosphorus in inflowing water
• Spring is the key season for zooplankton growth and MeHg bioaccumulation
• Mass load of MeHg inflow exceeds in-reservoir production (benthic flux and hypolimnion)
• MeHg bioaccumulation in upper trophic levels (fish, invertebrates) dependent on MeHg uptake in plankton, which have strong seasonal cycles
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DW = Drinking water std.
AL = Aquatic life std. (CTR)
DW
AL
Source: Alpers et al. (2005) USGS SIR 2004-5251
DW
AL DW
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Total mercury in sediment
Boston Mine
Source: Alpers et al. (2005) USGS SIR 2004-5251
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Remediation of mercury-contaminated placer gold
mines• 2000: Polar Star Tunnel, Dutch Flat Mining
District (USEPA), $1.4M, 150 m tunnel (~$9K/m)
• 2003: Sailor Flat Tunnel, Tom and Jerry Mining District (USFS), $300K, 130 m tunnel (~$2K/m)
• 2006: Boston Mine Tunnel, Red Dog Mining District (BLM), $250K, 60 m tunnel (~$4K/m)
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Clean-up Scenes – Polar Star Tunnel
Mercury vapor monitoringStabilizing the entrance
Washing the floor Finished product Ph
oto
s: R
. H
um
ph
reys,
SW
RC
B
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Clean-up Scenes – Sailor Flat
Tunnel and pit areas restored
Tunnel before excavation
Tunnel during excavation Photos: R. Humpheys, SWRCB
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Clean-up Scenes – Boston Mine
Tunnel outlet During remediation
Slusher
Trommel and concentrator bowl
Spiral concentratorPanning mercury Ph
oto
s: R
. H
um
ph
reys,
SW
RC
B
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What have we learned?
• Mercury “hot spots” occur in Sierra Nevada– Tunnels and ground sluices at hydraulic mines
– Stamp mill sites (and downstream) at lode mines
• From limited post-remediation monitoring:– At Polar Star and Boston mine tunnels, persistent
contamination from upstream sources
– Difficult to demonstrate benefits of remediation
• Bioaccumulation depends on seasonal dynamics involving food web– Critical to sample seasonally for water and biota
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What information gaps remain?• Baseline data on Hg and MeHg loads in mining-affected watersheds
– Quantify potential benefits from mine remediation– Seasonal variability– Information needed for TMDLs
• Data on Hg and MeHg in reservoir sediments– Dam removal issues– Potential sites for Hg removal, sand-gravel-gold extraction
• Studies of Hg methylation and bioaccumulation– Controls on what makes reactive Hg(II) available to microbes– Controls on microbial methylation: S, C, Fe, nutrients– Food web studies– Effects of wetland restoration, wet/dry cycles– Effects of agricultural amendments (esp. S on rice and other crops)
• Wildlife health effects– Effects of MeHg exposure on salmon and steelhead – Very little information on mammals, reptiles, many bird species
• Modeling of mercury cycling in rivers and reservoirs– Improved understanding of biogeochemical and hydrologic processes – Management tools for testing scenarios, confirming results