Callahan Mine Superfund Site- Community Update July 2020

Callahan Mine Superfund Site -July 2020 Com m un it y Update

This is an update of the May 2020 Community Update Presentation for the Callahan Mine.

• Outline

• Background

• Activities completed through July 2020

• Activities planned for remainder of 2020.

:allahan Mine Superfund Site -July 2020 Community Update - Background

:all ahan Mine Cleanup Approach : EPA is managing the Callahan Mine leanup as three separate projects (called "Operable Units").

Legend

ISS:J Ar eas fo r O U 3 Re m ed i a l Action

Are as for OU1 Remedial Action

OUl: Cleanup of arsenic and lead contamination in residential properties and PCB contamination in the former Mine Operations Area was completed in September 2013.

OU2 (Groundwater, WRP#l and WRP#2) - No cleanup decision yet.

OU3 (Tailings lmpoundment, WRP#3, and sediments)• Installation of a horizontal drain was completed in 2015.• Stabilization of Tailings Dam and Cover system for Tailings

lmpoundment- current site activity.• Consolidation of waste rock and cont am inat ed sediments into

the former mine pit (CAD cell) to address ecological threats. Some waste rock may be capped in place or consolidated onto the Tailings lmpoundment.

• Ecological restoration.

Callahan Mine Superfund Site - Jul y 2020 Community Update - Background

ifhe OU3 cleanup is being implemented in three phases.

Phase 1: Installation of a Horizontal Drain and passive treatment system to facilitate dewatering of the Tailings lmpoundment (completed in 2015).

Phase 2: Tailings lmpoundment closure (current work).• Tailing Dam and Tailings lmpoundment will be stabilized by reducing the height of the rock wall and

installation of stabilization measures along to the toe of the Tailings Dam.• Tailings excavated as part of the Tailing Dam height reduction will be placed on the back portion

of the Tailings lmpoundment.• A cover system will be installed over the Tailings lmpoundment.

Phase 3: Dredging/excavation of contaminated sediments and placement in the former mine pit (Confined Aquatic Disposal - CAD cell). The Design for Phase 3 was completed in 2019.

Callahan Mine- Ope rable Units and PhasesOUl Residential Cleanup

Callahan Mine Superfund Site - Ju ly 2020 Community Update

• Activities completed through July 2020:

• Environmental Sampling of the following:• Surface water in Goose Pond and Goose Cove.

• Groundwater monitoring wells at the Site.• Surface water seepage along the toe of the Tailings lmpoundment and

Waste Rock Pile #3.

• Pumping tests were performed for the bedrock groundwater and overburden groundwater at the Tailings lmpoundment to better assess the inflow of groundwater into the Tailings lmpoundment.