1. SOW – 1240LU23Q0072 - Beal Selenium Attenuation Study.pdf

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Statement of Work Beal Mountain Mine Selenium Attenuation Study

August 31, 2023 (4 Pages)

Project Location:

The project is located at Beal Mountain Mine, a former open pit gold mine. The Mine is located approximately 16 miles west of Butte, Montana near the headwaters of German Gulch Creek. Access to the site is by turning south off County Road 441 (Fairmont Road) onto German Gulch Road near Fairmont Hot Springs and following the road to the Mine.

Background

Overburden from the Beal Mountain Pit and a small portion from the South Beal Pit was layered in the designated waste rock dump from 1989 until 1997. Two existing springs, Spring-5 and Spring-10A, were covered by the waste rock during construction of the dump. To minimize water infiltration and selenium mobilization from Spring 10-A percolating through the dump, a low permeability material was placed over the spring before construction of the final waste rock layer. The low permeability material, unfortunately, contained substantial amounts of selenium that is mobilized in water emanating from Spring- 10A and flows through the remainder of the waste rock dump. As a part of the closure plan for the Beal Mountain Mine, the U.S. Forest Service seeks a low-maintenance, cost-effective strategy to minimize the release of selenium into German Gulch which flows into the Clark Fork River via Silver Bow Creek.

Microorganisms with selenium reducing capabilities have been identified within material collected from the Beal waste rock dump. These preliminary observations demonstrate that biological reduction is a potentially feasible approach to selenium attenuation at Beal Mountain Mine.

Period of Performance

The Period of Performance shall begin October 1, 2023, and end on September 30, 2025.

Project Description

The purpose of this SOW is to assess the suitability of saturated rock backfill within the Main Beal pit for in-situ biological attenuation of selenium.

The proposed investigation will provide essential information on the applicability and optimization of a semi-passive approach to selenium management utilizing the saturated rock backfill at the Main Beal Pit. The rates of biological selenium reduction and attenuation will be determined using waste rock and water samples. If laboratory scale studies demonstrate that amendments support efficient selenium attenuation, this data could provide the basis for future work toward a full-scale semi-passive system.

Through completion of the following tasks, the contractor will evaluate the microbial community present within the saturated pit backfill to understand the extent and rate of existing selenium attenuation. The existing site water quality data base will be reviewed followed by development of a sampling and analysis plan (SAP). The SAP will guide site sample collection of water quality samples and microbial samples from site surface water and groundwater for organisms capable of selenium reduction within the backfilled pit. The contractor will conduct 500 feet of exploratory drilling for water quality monitoring and microbial community sampling within the pit and will obtain material samples for testing. Testing will be designed to understand the existing and potential rate and extent of selenium

2 | P a g e attenuation by existing microbial communities with the objective of identifying optimal dosage of supplements suitable for long term semi-passive in situ treatment.

Task No. 1: Project Administration and Technical Support

The purpose of Task No. 1 is to provide the necessary project documentation, management, and technical support to ensure project tasks are completed per this SOW, within project budgets and due dates.

• Technical support consists of providing oversight and managing the status of the project and subcontractors. This will include tracking ongoing work and submittals, answering Forest Service questions and requests for additional information, and discussing ongoing work and strategies relative to the project.

• Field visits may be required as part of the project support work to assess on the ground issues and questions related to ongoing work. For purposes of this statement of work, contractor should assume two separate meetings on site.

Task No. 2: Baseline Project Development and Sampling and Analysis Plan (Deliverable #1)

The contractor will be provided access to the Beal water quality database. The data will be thoroughly reviewed and used to develop and present the Forest Service with a sampling and analysis plan (SAP) detailing proposed activities.

During this task, research should be conducted into cost-effective and suitable supplement sources to support biological selenium attenuation.

Task No. 3: Field Sampling and Drilling

Site Visit and Water Sampling

Contractor will collect water samples from existing sampling points in and around the backfilled Main Beal Pit as defined in the SAP. A baseline survey of the microbial communities from surface and subsurface waters will be conducted using established protocols from the SAP.

Drilling

A proof-of-concept and optimization plan for in situ treatment require an exploratory drilling program to facilitate water monitoring within the saturated backfilled pit and the collection of waste rock samples for lab studies. Drilling will allow for the collection of waste rock from the saturated zone. Borings will be used to monitor future water quality and microbial activity within the treatment area. Important site-specific factors (e.g. hydrologic balance, water balance, process constraints) will be evaluated to develop optimal locations for amendments. The contractor and USDA-FS will cooperatively determine 2-3 optimal drilling locations. For the purposes of this statement of work, contractor shall assume a total of 500 feet of drilling.

Contractor shall determine in situ transmissivity and residence time within the pit, using methods approved in the SAP. During drilling, materials will be logged and collected for analysis of microbial community structure and rock mineralogy. Samples shall be properly preserved for laboratory-scale testing.

In-Situ Microbial Monitoring

Contractor shall assess the microorganisms capable of selenium reduction in the saturated portion of the Main Beal

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Pit using methods detailed in the SAP.

Microbial Community Characterization

DNA will be extracted from the microbial samples collected during Task 3 and used to identify the microbial species present in each of the samples along their functional potential.

Interim Technical Memo (Deliverable #2)

An interim memo, performed under Task No. 6 described below, shall include sampling and material collection details, processing results, microbial community results, and a summary of material characterization. The report will highlight functionally important microbial groups and their relative abundance in the water samples. The contractor will use these findings to inform subsequent laboratory work.

Task No. 4: Laboratory Microcosm Study

Successful implementation of semi-passive in situ selenium treatment depends on the activity of native selenium-reducing microorganisms in the waste rock. Those microorganisms will require sufficient supplements to support biomass growth and metabolic activity. Selection of proposed nutrient additives will be aided by the understanding of the microbial community gained in Task No. 3 and will need to be tested empirically prior to full scale implementation. Contractor will conduct a laboratory testing program to assess, over short period of time, several variables concurrently (i.e., varying levels of amendments). Given the USDA-FS goal of passive treatment, the contractor shall only evaluate potential nutrient sources that could serve as future low maintenance options for use at the site.

Solids and water collected during the exploratory drilling will be used to perform a matrix of test conditions to evaluate amendment options and combinations. Microbial community analysis will be performed at lab test commissioning and decommissioning to assess changes to the microbial community as a function of the various amendments.

Batch Study Memo (Deliverable #3)

An interim memo will be prepared that includes analysis and findings of the microcosm study. The memo will highlight selenium reduction capacity, and rates, as a function of amendment, functionally important microbial groups, and their relative abundance in water samples. These findings will inform subsequent column tests.

Task 5: Laboratory Column Study

Once appropriate amendments have been selected based on results of the microcosm study, their optimal dosage and suitability for long-term treatment will be assessed in a column test. The contractor shall regularly measure the column influent and effluent chemistry to assess amendment consumption and selenium reduction. The microbial community in the rock samples will be assessed at column commissioning and decommissioning to gain insights into selective pressures exerted by amendment dosing and to identify key microorganisms that are involved in chemical reduction. Furthermore, the columns will be used to evaluate system response to upsets such as geochemistry changes.

Columns will be constructed to allow for validation of results. Column operation and configuration should be described in the SAP and will be operated to test both steady-state operation and upset conditions that are relevant to the site.

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Biological selenium reduction can reduce organo-selenium compounds which are prone to bioaccumulation and toxicity. Contractor shall quantify the production of different reduced selenium-containing compounds, including organo-selenium, periodically throughout the course of testing by sending samples to a certified laboratory specializing in selenium speciation.

Task No. 6: Reporting

The reporting task includes preparation of two interim reports (Deliverables #2 and #3 above) and a final comprehensive report (Deliverable #4). The first interim report, described in Task No. 3, will document field sampling and exploration drilling, and baseline material and microbial community characterization. The second interim report, described in Task No. 4, will summarize the microcosm study, including geochemical data and microbiological data. A third and final comprehensive report will include a summary of field sampling, baseline characterization, batch test results, and an in-depth summary of community analysis findings and chemistry from the column tests (Task No. 5), including rates of chemical reduction. The report will place laboratory findings in the context of field data and will be used to inform future in situ passive treatment alternatives on site.

The FS will review and comment within fifteen (15) working days (unless otherwise agreed to) upon receipt of each of the four draft deliverable reports. Each report will then be edited to include FS comments and produce a final report.

Forest Service comments will be discussed with the contractor and any comments that are not incorporated will be agreed to by the FS. One electronic version (Microsoft Word format) of each draft report will be submitted to the FS.

One hard copy of each final report will be provided to the FS and one PDF electronic version will be saved to the project electronic archive.