Mercury transport and transformation at the Black Butte Mine Superfund Site

Transcription

1 Mercury transport and transformation at the Black Butte Mine Superfund Site Eckley, CS 1, Luxton, T 2, Schenk, L 3, McKernan, J 2, Goulet, J 1, Lynch, K 1, Muza, R 1 1. EPA R EPA ORD National Risk Management Research Lab 3. USGS OWSC Acknowledgments: CDM Smith (R-10 Contractor): Scott Coffey, Mary Lou Fox, Steve Dent, Kevin Lee, Mark Jusayan EPA R-10 & Manchester Lab: Jennifer Crawford, Katie Adams & Theresa McBride All data presented is preliminary 1

2 Site History Black Butte Mine: Deposit: primarily cinnabar Operation timeframe: 1890 to late 1960s 1990s: purchased by Land & Timber Company Mine: underground mine; surface waste rock & tailings Ore Processing: elemental mercury was produced on the site by heating crushed ore in a furnace. New furnace constructed in Black Butte Mine Production: ~635,000 kg of Hg Black Butte Mine Adit Black Butte Ore Processing Furnace 2

3 Site Characteristics Park Source: Park and Curtis, 1997 Environ. Contam.& Tox. Cottage Grove Reservoir ~15km downstream of mine Fish Hg public health advisory since 1979 Most fish >0.3 µg/g; some older fish >1 µg/g Hg levels of reservoir fish are main driver for site remediation 3

4 Site History: Removal Action Since the mid-1990s, Oregon Department of Environmental Quality (ODEQ) and the EPA have conducted site assessments and investigations of the Black Butte mine Summer EPA Removal Action to reduce tailings transport to surface water through slope stabilization (re-grading) & capping tailings 4

5 Site History: Post removal stream monitoring Summer 2008 (1 year following Removal): Loading assessment study 21 locations measured during base-flow conditions (Oregon Dept of Env. Quality ODEQ) Major finding: Dennis Creek: 10 ng/l Furnace Creek: 19,850 ng/l Furnace Creek could contribute 50-75% of the mass of mercury entering the reservoir. 2010: Black Butte added to the National Priorities List (Superfund) 5

6 Discharge m3/min Initial Superfund Sampling: Storm event Objective: provide a better understanding of surface water fluxes *data are preliminary* Dennis Creek Discharge Furnace Creek Discharge Gauging stations installed at 4 locations (2 shown) Storm event sampled (29 mm) Dennis Creek Furnace Creek 0 10/18/12 12/7/12 1/26/13 3/17/13 5/6/13 Date 6/25/13 8/14/13 10/3/13 6

7 Discharge m3/min THg ng/l Initial Superfund Sampling: Storm event Large increase in particulate-hg during storm event (>85% of total load) The conc. of Hg on mobilized particles is fine sediment conc in creek 5.0 Discharge 4.5 THg--Dissolved THg--Particulate Dennis Creek ± 0.8 µg/g 6.7 ±1.6 µg/g Fine sediment Conc *data are preliminary* 0 3/3/13 3/4/13 3/5/13 3/6/13 3/7/13 Date 3/8/13 3/9/13 3/10/13 7

8 Discharge m3/min THg ng/l Initial Superfund Sampling: Storm event Large increase in particulate-hg during storm event (>80% of total load) The conc of Hg on mobilized particles is > fine sediment conc in creek *data are preliminary* Discharge THg--Dissolved THg--Particulate 455 µg/g Furnace Creek ± 7 µg/g Fine sediment Conc /3/13 3/4/13 3/5/13 3/6/13 3/7/13 Date 3/8/13 3/9/13 3/10/13 8

9 Discharge m3/min THg ng/l Initial Superfund Sampling: Storm event Large increase in particulate-hg during storm event (>80% of total load) The conc of Hg on mobilized particles is > fine sediment conc in creek *data are preliminary* Discharge THg--Dissolved THg--Particulate Precip THg: 3.1 ng/l ~800 ng/l /3/13 3/4/13 3/5/13 3/6/13 3/7/13 Date 3/8/13 3/9/13 3/10/13 9

10 Site Characteristics: Cottage Grove Reservoir Several unknowns regarding connection between current THg releases from the mine & MeHg accumulation in reservoir fish: How bioavailable for methylation is the current inorganic Hg released from the mine? How much historic Hg is the reservoir is re-suspended & available for methylation? What is the role of watershed land-use activities on mobilizing Hg, carbon & sulfate? How does reservoir management influence methylation?? THg MeHg 10

11 Black Butte Mine: Reservoir Study Objective: Identify the influence of reservoir water-level changes on methylmercury production. Fall & Winter Low pool Spring & Summer High pool 11

12 Black Butte Mine: Reservoir Study 12

13 Black Butte Mine: Reservoir Study Design Methods/Measurements: Surface Water (THg, MeHg, DOC, Sulfate, Sulfide, TSS, ph) Sediment (THg, MeHg, Organic Carbon, Sulfide) Porewater (THg, MeHg, DOC, Sulfide, Sulfate, ph) Rationale for porewater measurements: Porewater Hg is more bioavailable for methylation Hg/MeHg trends in porewater are different than sediment Porewater sulfate/sulfide represents microbial activity/redox Porewater MeHg more available for benthic invert. uptake Porewater MeHg diffusion into overlying water 13

14 Black Butte Mine: Reservoir Study Design USGS Sample Locations USGS 14

15 Reservoir Depth (m) Sample Events Black Butte Mine: Reservoir Study Design Spring Summer Sample Event Winter 4 Fall 2 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month 15

16 Reservoir Study: Porewater Methodology Piezometer/Henry Sampler 16

17 Reservoir Study: Porewater Methodology Pore water squeezer Problems encountered: Filters clogged (fine grain size) Porewater flow within the core unsure what depth is being sampled Potential oxidation of redox sensitive species 17

18 Porewater Methodology Centrifuge/Filtration Some constituents redox sensitive; Perform work in anoxic chamber requires lab space EPA Mobile Lab 18

19 Porewater Methodology Centrifuge/Filtration Centrifuge sample to separate sediment and water 19

20 Porewater Methodology Centrifuge/Filtration Filter porewater Vacuum pump filtration improves throughput Clean & dirty glove chambers increase efficiency 20

21 Depth above sediment (m) Depth above sediment (m) Reservoir Study: Initial Results No thermal stratification in water column D.O. lower in the summer; but no anoxic hypolimnion THg & MeHg levels similar with depth Summer results show slightly more MeHg Winter Spring Summer Fall Winter Spring Summer Fall THg-W (ng/l) MeHg-F (ng/l) *data are preliminary* 21

22 Reservoir Study: Initial Results The %MeHg-F (MeHg-F/THg-F) of the upstream, reservoir and outflow water clearly show an increase during the summer months Data are provisional and subject to revision. Do not cite or distribute. *data are preliminary* 22

23 Reservoir Study: Initial Results Methylation activity is higher in sediment subjected to wet/dry conditions from water level fluctuations *data are preliminary* 23

24 Reservoir Study: Initial Results Sediment: Central pool site has the highest THg & MeHg Porewater: Wetland site has the highest THg & MeHg *data are preliminary* Central pool Wetland area 24

25 Summary Mine Site Initial results: elevated THg load during stormevents loads dominated by particulate transport stormwater Hg may originate from internal sediment resuspension and/or terrestrial erosion Reservoir Initial results: water level changes appear to increase methylation activity 25

26 Questions? 26