Mining Impacts: A Case Study

Transcription

1 Mining Impacts: A Case Study Raymond K. Will William E. Motzer Tailings and Mine Waste 2008 Conference Colorado State University 2490 Mariner Square Loop, Suite 215, Alameda, CA

2 Jamestown Mine Site Location

3 Jamestown Mine, Tuolumne County N Scale in Feet Crystalline Pit DP-5 RSA TMF South Crystalline Pit DP-6 Harvard Pit PWRP DP-1 Based on vertical air photography taken June 30, 1993.

4 Introduction Historic underground gold mining district Jamestown mine reopened in 1978 Ore concentrated by froth flotation and gravity for free gold Concentrate hauled to leaching facility in Nevada Closure Plan accepted in 1994 Reclamation completed except tailings pile County of Tuolumne proposed alternative cap design Delays resulted in litigation and re-consideration

5 Containment Zone Regulation Amendments to policy of State Water Resources Control Board (SWRCB) Background water quality may not be achievable Revised cleanup levels Consistent with maximum benefit of state Implementation of CZ requires Cleanup and Abatement Order (CAO)

6 Rationale for CZ Designation Geology: hard metamorphic rock Slate, schist, diorite, gabbro Pit Lake creates a groundwater sink Groundwater pumped into detention ponds Constituents of concern

7 Jamestown Mine, Geologic Cross Sections Ql Tl Tm Jhb Jgb Jsp Jms Jl Jc gs ph, sl QAM LEGEND Quarternary Landslide Tertiary Latite Tertiary Mehrten Formation Jurrasic Hornblendite Jurassic Gabbro Jurassic Serpentinite Jurassic Mariposa Formation Jurassic Logtown Ridge Formation Jurassic Consumnes Formation Green Shist Phyllite and Slate Rocks formed by hydrothermal alteration

8 Harvard Pit

9 Profile A A 2000 A (SE) A' (NW) Woods Creek Orginial Ground Surface Harvard Pit Lake TDMW Water Table TDMW 22 Elevation(ft) pre mine post mine 600 Water Levels Distance (ft)

10 Detention Pond

11 Constituents of Concern Constituents of concern: Arsenic Sulfate Nitrate Magnesium Sodium Calcium TDS mg/l 150 2,000 mg/l mg/l mg/l mg/l mg/l 200 4,000 mg/l

12 Harvard Pit Lake Water Quality HCO3 SO Bicarbonate (mg/l) Sulfate mg/l Jan-88 Jan-90 Jan-92 Jan-94 Jan-96 Jan-98 Jan-00 Jan-02 Jan-04 Date

13 Groundwater TDS Concentrations, 2001 N Scale in Feet LEGEND Monitoring well Key mining area 375 Pit Lake TDS concentration in ppm TDS isoconcentration contour in ppm

14 Groundwater Flow Direction, Jamestown Mine LEGEND Monitoring well Groundwater contour Groundwater flow direction TDMW 22 Crystalline Pit DP-5 Rock Storage Area Key mining area Surface Water Drainage Flow TDMW 7 Tailings Management Facility South Crystalline Pit TDMW19 TDMW14 TDMW14 RSMW9A TDMW12 TDMW3 TDMW18 TDMW4 Harvard Pit (1204) RSMW8A TDMW16 TDMW15 N TDMW6 TDMW Scale in Feet 1200 Source: MWH (2003).

15 Woods Creek

16 Reclamation and Closure Storm water runoff detention ponds also wetlands wildlife habitats Crystalline Pits backfilled, re-contoured, topsoiled, planted Mill site facilities removed Tailings dam revegetated Leachate collection and recovery system managed by pumping and recirculating water Excess water: spray evaporation and revegetation Waste rock piles re-contoured and revegetated

17 Wildlife Pond

18 Tailings Dam

19 Tailings Pond

20 Reclaimed Waste Rock Pile

21 Revised Management Plan Water Monitoring Program surface water and groundwater Groundwater monitoring well installation sampling evaluation and reporting Domestic well analysis down gradient perimeter wells to be monitored Safety review and risk assessment Groundwater performance criteria and contingency plan Storm water management

22 Revised Management Plan (continued) Tailings management facility and process water retention pond closure Rock Storage Area re-grading of low grade ore stockpile Crystalline pits additional re-contouring, storm water controls Harvard Pit in-situ treatment to precipitate constituents of concern, primarily arsenic, sulfate, and TDS, treatment verification monitoring program

23 Harvard Pit Lake May 2007

24 Harvard Pit Lake TDS and Arsenic 2, ,600 TDS Arsenic TDS 1.6 1, As Jan-88 Jan-90 Jan-92 Jan-94 Jan-96 Jan-98 Jan-00 Jan-02 *Source: Tuolumne County Monitoring Report (2002) Date Jan-04 0

25 Rock Crushing Operation for Tailings Cover May 2007

26 Tailing Management Facility 2.0 ft Clay Cover May 2007

27 Summary The Jamestown Mine is slowly being transformed by careful planning, design and implementation of selected reclamation plans. The long term challenge is to control the migration of toxic concentrations of dissolved metals into the surrounding groundwater.

28 Acknowledgements California Regional Water Quality Control Board Shaw Environmental Sonora Mining Company Mr. William E. Motzer,, Senior Geochemist Mr. Alain Boutefeu, Technical Illustrator