Lower Rebellion

Silver Dyke Adit

Currently Three Operable Units

Sih-Mem Creek

Carpenter Creek Snow Creek

Neihart Slope

Belt Creek

Boundaries are subject to change

Town of Neihart OU1 (red), Mine and Watershed OU2 (yellow), and Silver Dyke Complex OU3 (green)

Meeting Objectives

• Status of the OU01 Town of Neihart Cleanup • Brief overview of Silver Dyke Mining Complex and

work completed to date including the findings of remedial investigation as it pertains to Operable Unit 3 (Silver Dyke Mining Complex)

• What’s next for Carpenter Snow Creek?

Meeting Objectives

• Status of the OU01 Town of Neihart Cleanup • Brief overview of Silver Dyke Mining Complex and

work completed to date including the findings of remedial investigation as it pertains to Operable Unit 3 (Silver Dyke Mining Complex)

• What’s next for Carpenter Snow Creek?

Overview Silver Dyke Mining Complex

• Operated from 1923 – 1929• Block mined from below resulting in

glory hole• Averaged 170,000 tons ore/year• Problems with milling early on due

to oxide and sulfide minerals• Waste disposal problematic• Perennial discharge coming from

adit

Silver Dyke Mine Conceptual Model

Aquafix Study 1. Seasonal fluctuations in flow and water chemistry will make maintaining a constant pH very difficult. Can a semi-passive system be operated effectively year-round in a remote location with minimal operation and maintenance?

2. What are the annual costs?

3. How much sludge will be generated? Will sludge pass TCLP?

4. How much TSS and TDS is generated compared to baseline?

5. Are there improvements in water quality (SW & GW) downstream?

EPA’s removal program initiated a removal action at the Silver Dyke Tailings in 2014

Approximately 34,000 cubic yards of mine tailings removed and placed in MacKay Gulch Repository

Silver Dyke Tailings Impoundment

Post Removal 2016Some erosion controls and revegetation measures necessary

Mackay Gulch Repository- Slope grade less than 4:1- Contains 180,000 cys of cover and top soil

- Infrastructure improvement- 675,000 cubic yard capacity

- Waste - Adequate separation to gw- Easy Access- One property owner- Minimal preparation- 34,000 cys placed there in

2014

Silver Dyke Glory Hole Repository

- Infrastructure improvement- Headwall removal- 570,000 cubic yard capacity- Positive drainage- No cover or top soil- Adit discharge

- Public support- Adequate separation to gw- Fairly Accessible- One property owner- May reduce adit discharge

Silver Dyke Glory Hole Hydrogeologic Work

Remedial Investigation Report

• The RI Report currently undergoing Agency review is a comprehensive report for OU2 and OU3• Evaluates data collected through 2012

• Addresses mine waste piles; streamside/floodplain deposits; groundwater; seeps, adits & shafts; surface water; sediments; road beds; residential properties; and terrestrial/aquatic populations that may be impacted by Site waste

700,000 cys OU3

350,000 cysNeihart Slope

110,000 cys Snow Creek

Unknown volume Belt Creek & lower Carpenter Creek

150,000 cys OU01

Mine waste volume estimates by study area

OU3 Mine and Mine Related Locations

Carpenter Creek Tailings 9 Seasonal Residential Properties located along Carpenter Creek and another below glory hole

Lead ranges from 197 mg/kg to 6,280 mg/kg

Over 500,000 cys

An unknown quantity of tailings are in Carpenter Creek from the confluence with Snow Creek to Town of Monarch (approx 14 stream miles)

OU3 Groundwater Investigations

OU3 Adit Discharge Locations

Meeting Objectives

• Status of the OU01 Town of Neihart Cleanup • Brief overview of Silver Dyke Mining Complex and

work completed to date including the findings of remedial investigation as it pertains to Operable Unit 3 (Silver Dyke Mining Complex)

• What’s next for the Carpenter Snow Creek Site?

Fish BarrierDry Fork Belt Creek Fish Barrier

Westslope Cutthroat Trout Barrier

Fish Wildlife and Parks has secured funding to construct a fish barrier in Carpenter Creek

Mine Adit Treatability Testing

EPA’s Office of Research and Development has completed a laboratory bench scale test of Haystack Creek Mine and Big 7 Mine adit discharges

Results look promising for a sulfate reducing bioreactor – low flow (1 gpm); plenty of space; and adit discharge is acidic

Field implementation possible in 2017

Dewatered Compromise Shaft in October

Schedule

• 2017 - 2019: Remedial Action at OU01 Town of Neihart pending available funding –Infrastructure improvement on Carpenter Creek Road and placement of waste in the Mackay Gulch Repository. Multi-year remedial action

• 2017: The Remedial Investigation Report for OUs 02 and 03 - Expected to be finalized in mid 2017.

• 2017: Feasibility Study Report for OU3—Silver Dyke Mining Complex is expected to be finalized in mid 2017.

• 2017: Proposed Plan and ROD - A proposed plan for cleanup, a public comment period, and a ROD by end of year.

• 2018/2019: The Feasibility Study Report for OU2—Mines and watershed is expected to be finalized in late 2018/early 2019. This OU contains the mines on Neihart Slope, Snow Creek as well as streamside deposits in Carpenter Creek below OU3 to Monarch (approx. 15 creek miles).

• 2019: Remedial Design for OU03 – Following negotiations with Potentially Responsible Parties, the Remedial Design is expected to begin in 2019

• 2019: Proposed plan to clean up OU2 is scheduled to be completed in late 2019. This will be followed by a public comment period, and a ROD

Questions or Comments