Mercury Contamination and Bioaccumulation from Historical Gold Mining

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

Cooperating Agencies Federal 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: box Gold & Mercury • More than 100, 000 kg mercury (Hg) produced from 239 mines in California • Approx. 33, 000 kg Hg lost to atmosphere from furnaces at Hg mines • Approx. 12, 000 kg Hg used in Calif. gold mining USGS Fact Sheet 2005 -3014 (Churchill, 2000)

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 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 1870 s

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

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

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

Mercury Loss to the Environment in Hydraulic Mining USGS Fact Sheet 2005 -3014

Cleaning amalgam from stamp mill, Empire Mine, Nevada 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 Systems AIR atmospheric transport Runoff Hg(II) Hg 0 Hg(II) Particles phytoplankton Hg. Cl 42 Hg. Cl 2 zooplankton CH 3 Hg+ Hg 0 light Particles DOM CH 3 Hg+microbes Hg(II) Hg 0 WATER SEDIMENT Hg 0 microbes Hg(II) abiotic rxn. Hg 0 SRB, Fe. RB CH 3 Hg+ microbes Graphic: Mark Marvin-Di. Pasquale (USGS)

SAMPLING SITES, BEAR-YUBA, 1999

Source: May et al. (2000) USGS OFR 00 -367

Food Web Study, Camp Far West Reservoir, CA • (δ 15 N) − Me. Hg slope similar other studies • similar rate of biomagnification of Me. Hg with increasing trophic level. Stewart et al. (2008) CJFAS

Data from: Alpers et al. (2008) USGS SIR 2006 -5008 Camp Far West Reservoir, CA

Stewart et al. (2008) CJFAS Camp 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 Me. Hg bioaccumulation • Mass load of Me. Hg inflow exceeds in-reservoir production (benthic flux and hypolimnion) • Me. Hg bioaccumulation in upper trophic levels (fish, invertebrates) dependent on Me. Hg uptake in plankton, which have strong seasonal cycles

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

Total mercury in sediment Boston Mine Source: Alpers et al. (2005) USGS SIR 2004 -5251

Remediation of mercurycontaminated placer gold mines • 2000: Polar Star Tunnel, Dutch Flat Mining District (USEPA), $1. 4 M, 150 m tunnel (~$9 K/m) • 2003: Sailor Flat Tunnel, Tom and Jerry Mining District (USFS), $300 K, 130 m tunnel (~$2 K/m) • 2006: Boston Mine Tunnel, Red Dog Mining District (BLM), $250 K, 60 m tunnel (~$4 K/m)

Stabilizing the entrance Washing the floor Mercury vapor monitoring Finished product Photos: R. Humphreys, SWRCB Clean-up Scenes – Polar Star Tunnel

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

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

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 Me. Hg loads in mining-affected watersheds – Quantify potential benefits from mine remediation – Seasonal variability – Information needed for TMDLs • Data on Hg and Me. Hg 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 Me. Hg 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