Post on 31-Mar-2015
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
Cooperating AgenciesFederal
State
Local
Hydraulic mining, Placer County, CA
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
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
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
Hydraulic mining, Malakoff Diggins,
Nevada County, CA, circa 1880
Hydraulic mine, ground sluice system,
Scott Valley mine, Siskiyou County, CA
circa 1870s
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
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
Hg beads in sediment
South Fork American River, Lotus Camp (near Coloma)
Photo by R. Humphreys
USGS Fact Sheet 2005-3014
Mercury Loss to the Environment in Hydraulic Mining
Cleaning amalgam from stamp mill, Empire Mine, Cleaning amalgam from stamp mill, Empire Mine, Nevada County, California, 1900Nevada County, California, 1900
Abandoned bucket-line dredge, Yuba Goldfields, CA
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
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
SAMPLING SITES, BEAR-YUBA, 1999
Source: May et al. (2000)
USGS OFR 00-367
• (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
Data from:Alpers et al. (2008) USGS SIR 2006-5008
Camp Far West Reservoir, CA
Data from:Alpers et al. (2008) USGS SIR 2006-5008
Camp Far West Reservoir, CA
Stewart et al. (2008) CJFASCamp Far West Reservoir, CA
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
DW = Drinking water std.
AL = Aquatic life std. (CTR)
DW
AL
Source: Alpers et al. (2005) USGS SIR 2004-5251
DW
AL DW
Total mercury in sediment
Boston Mine
Source: Alpers et al. (2005) USGS SIR 2004-5251
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)
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
Clean-up Scenes – Sailor Flat
Tunnel and pit areas restored
Tunnel before excavation
Tunnel during excavation Photos: R. Humpheys, SWRCB
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
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
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