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California Water Science Center

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Presentation on theme: "California Water Science Center"— Presentation transcript:

1 California Water Science Center
Mercury Contamination and Bioaccumulation from Historical Gold Mining in the Sierra Nevada – Site Characterization and Remediation Charles N. Alpers, Ph.D. U.S. Geological Survey California Water Science Center Placer Hall 6000 J Street Sacramento, CA

2 Cooperating Agencies Federal State Local
Hydraulic mining, Placer County, CA

3 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

4 HISTORICAL MINING: Gold & Mercury box
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) USGS Fact Sheet

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

6 Hydraulic mining, Malakoff Diggins, Nevada County, CA, circa 1880
Hydraulic mine, ground sluice system, Scott Valley mine, Siskiyou County, CA circa 1870s

7 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

8 Sluice and undercurrent, Oro Fino mine, Siskiyou County, CA Circa 1855
SLUICE BOX UNDERCURRENT Sluice–undercurrent system, Spring Valley mine, Butte County, CA, Feather River watershed

9 Hg beads in sediment Photo by R. Humphreys South Fork American River, Lotus Camp (near Coloma)

10 Mercury Loss to the Environment
in Hydraulic Mining USGS Fact Sheet

11 Cleaning amalgam from stamp mill, Empire Mine, Nevada County, California, 1900

12 Abandoned bucket-line dredge, Yuba Goldfields, CA

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

14 The Mercury Cycle in Aquatic Systems
Hg0 Hg(II) Hg0 atmospheric transport Particles AIR Runoff phytoplankton HgCl42- Hg(II) CH3Hg+ Hg0 HgCl2 zooplankton light light CH3Hg+ Hg(II) Hg0 microbes Simplified Hg model in aquatic system Illustrates that the Hg cycle is complex Hg takes many forms (organic & inorganic) Hg(II) is readily absorbed to particles and transported to sediments Human and ecosystem health concerns when MeHg is formed and incorporated into the food chain We will focus on sediment processes Hg-methylation and MeHg degradation under anoxic conditions Particles DOM WATER microbes microbes CH3Hg+ Hg(II) Hg0 SEDIMENT abiotic rxn. SRB, FeRB Graphic: Mark Marvin-DiPasquale (USGS)


16 Source: May et al. (2000) USGS OFR

17 Food Web Study, Camp Far West Reservoir, CA
(δ15N) − MeHg slope similar other studies similar rate of biomagnification of MeHg with increasing trophic level. Stewart et al. (2008) CJFAS

18 Camp Far West Reservoir, CA
Data from: Alpers et al. (2008) USGS SIR Camp Far West Reservoir, CA

19 Camp Far West Reservoir, CA
Data from: Alpers et al. (2008) USGS SIR Camp Far West Reservoir, CA

20 Camp Far West Reservoir, CA
Stewart et al. (2008) CJFAS

21 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

22 Source: Alpers et al. (2005) USGS SIR 2004-5251
DW = Drinking water std. AL = Aquatic life std. (CTR) DW DW AL Source: Alpers et al. (2005) USGS SIR AL DW

23 Total mercury in sediment
Boston Mine Source: Alpers et al. (2005) USGS SIR

24 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)

25 Clean-up Scenes – Polar Star Tunnel
Stabilizing the entrance Mercury vapor monitoring Photos: R. Humphreys, SWRCB The tunnel entrance in the pit was located just below the pit high wall. The area was stabilized and the tunnel sediment and remenats of the sluice were brought out using mining equipment from the upstream end. After the removal was completed, the tunnel floor was washed with high pressure hoses and the floor was them cemented over. The mercury-rich sediment sluice lumber was hauled to a landfill. Cementing over the sluice floor isolated mercury left in bedrock crevices. Washing the floor Finished product

26 Clean-up Scenes – Sailor Flat
Tunnel before excavation Tunnel and pit areas restored Tunnel during excavation Photos: R. Humpheys, SWRCB

27 Clean-up Scenes – Boston Mine
Trommel and concentrator bowl Photos: R. Humphreys, SWRCB Tunnel outlet During remediation Spiral concentrator Slusher Panning mercury

28 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

29 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

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