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Mercury Contamination and Bioaccumulation from Historical Gold Mining in the Sierra Nevada – Site Characterization and Remediation Charles N. Alpers, Ph.D.

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Presentation on theme: "Mercury Contamination and Bioaccumulation from Historical Gold Mining in the Sierra Nevada – Site Characterization and Remediation Charles N. Alpers, Ph.D."— Presentation transcript:

1 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 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

5 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

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

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

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

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

12 Abandoned bucket-line dredge, Yuba Goldfields, CA

13 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

14 The Mercury Cycle in Aquatic Systems AIR WATER SEDIMENT CH 3 Hg + Hg(II) Particles Hg 0 HgCl 2 HgCl 4 2- Runoff Hg(II) CH 3 Hg + Hg 0 DOM Hg 0 Hg(II)CH 3 Hg + Hg 0 Particles Hg 0 atmospheric transport phytoplankton zooplankton light microbes abiotic rxn. Graphic: Mark Marvin-DiPasquale (USGS) SRB, FeRB

15 SAMPLING SITES, BEAR-YUBA, 1999

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

17 ( δ 15 N) 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

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

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

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

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 DW = Drinking water std. AL = Aquatic life std. (CTR) DW AL Source: Alpers et al. (2005) USGS SIR DW 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 Mercury vapor monitoringStabilizing the entrance Washing the floor Finished product Photos: R. Humphreys, SWRCB

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

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

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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