Two technical revisions at Homestake, Richmond Hill Mines in 2017

August 5, 2018

DEADWOOD — Other than the submission and approval of two technical revisions — one to a Homestake Mining Company conditional use permit (CUP) and one to a Richmond Hill Mine CUP, it was business as usual in 2017 at the two sites.

Mark Tieszen, environmental manager for Homestake/LAC Minerals addressed the Lawrence County Commission July 24 regarding five annual CUP reviews for Homestake Mining Company and LAC Minerals – Richmond Hill Mine.

A technical revision to place 875,000 tons of excavated rock from the Sanford Laboratory into the Homestake Open Cut was submitted to the commission Feb. 2, 2017 and approved March 14, 2017.

A technical revision to the Richmond Hill Mine permits to modify the site inspection frequency, modify the leakage response action plan, and to discontinue the neutron probe monitoring in the pit impoundment were submitted to the commission Feb. 9, 2107 and approved March 14, 2017.

As part of the Open Cut review, it was reported that reclamation has been completed at the waste rock facilities.

“Approximately 513 acres have been released. There are approximately 129 remaining affected acres. Reclamation is complete on all affected areas,” Tieszen said.

Other activities completed in 2017 included the construction of a new addition to the Yates Water Treatment Plant for a new caustic tank and backup generator and the completion of a petition for release of reclamation obligations for various reclaimed facilities.

“We constructed a new addition to the water treatment plant with separate adjacent areas for caustic tank and backup generator,” Tieszen said. “The existing 500-gallon caustic tank in the main plant was replaced with a 3,000-gallon tank in its own containment area construction in the new addition. A new natural gas-fired backup generator was also installed in the new addition.”

The petition for release of reclamation obligations has been submitted and includes a total of 41.77 acres including: Sawpit Borrow Area (16.81 acres); Sawpit Water Management Areas (3.45 acres); East Waste Rock Water Management Areas (2.61 acres); Open Cut Landfill Area (5.52 acres); Grenstiner Pond (0.40 acres); East Topsoil Stockpile Area (3.56 acres); East Low Grade Stockpile (9.42 acres).

“A reclamation inspection was conducted in September 2016,” Tieszen said. “Reclamation and release criteria have been met.”

He also reported that sustainable post-mining land uses have been achieved in their respective areas: wildlife habitat, rangeland, forest-planting and recreation-historic interpretive.

“The petition was approved by the Board of Minerals and Environment in January 2018,” Tieszen said.

Deadwood Creek monitoring results indicate the following: water quality meets all standards for coldwater marginal fish life propagation waters; habitat assessment, biological and water quality monitoring show no adverse impacts from the mine.

In regard to geotechnical monitoring, the Open Cut East Block is expected to fail on Homestake property within the pit boundaries.

“As I’ve reported for years, we expect this block to fail,” Tieszen said. “It’s approximately 350 feet on the east wall and won’t affect any areas off Homestake property.”

Failure will be on Homestake property within the pit boundaries.

Three new prisms were installed at the east block and two in a previous failure area in 2017.

In regard to the Open Cut conveyor area, six new prisms were installed around the Sanford Lab conveyor area in 2017 and four existing prisms will be lost.

Bobtail Gulch movement has slowed following the installation of a buttress and is expected to continue to slow.

“Movement is primarily relaxation of the fill,” Tieszen said. “Homestake will continue to monitor at the Open Cut and East Waste Rock Disposal facility.”

Gayville and East Ravine are showing signs of possible diversions.

Monitoring points 618, 619, and 645 in Gayville Gulch show possible divergence from past monitoring trends and monitoring points 648, 649, and 650 in East Ravine show possible divergence from their long-term trends. A tension crack exists at the crest of the 5,100 bench in Gayville Gulch.

“When we started looking at possible causes, apparent displacements may be the result of survey imprecision, using a different total station starting in October 2015 or movement of base stations/back sights. The tension crack appears to be associated with topsoil slumping,” Tieszen said. “What we did in response was resurvey monuments 618 and 648 to confirm movements, inspect areas around survey monuments monthly, visually monitor the tension crack at the crest of the 5,100 bench in Gayville Gulch at least quarterly, and install inclinometers in Blacktail Gulch, Gayville Gulch, and East Ravine. The new monitoring doesn’t show any movement.”

Planned Homestake Mining Company activities for 2018 include drill and install new inclinometers at the east waste rock facility, continue the water treatment agreement with the South Dakota Science and Technology Authority, and continue water treatment.

The reclamation acreage overview for the Richmond Hill Mine, as reported by Tieszen, includes: 265.94 total released acres; 75.09 total remaining affected acres; 73.33 un-reclaimed acres (for water treatment); .35 acres reclaimed in 2016; and 1.41 acres to be reclaimed in the short-term.

For 2017, activities at the Richmond Hill Mine included continued water management and treatment and continued monitoring activities.

Sitewide monitoring results indicate that water quality at the site is generally stable or improving.

“Cleopatra Creek water quality monitoring confirms there are no impacts from the Richmond Hill Mine,” Tieszen said. “Monitoring is continuing and site-specific performance criteria have been developed in consultation with DENR to ensure protection of the environment in post-closure. Aquatic biological monitoring results show healthy streams and no adverse impacts from the Richmond Hill Mine.”

Plans for 2018 at the Richmond Hill Mine include continued reverse osmosis and biological water treatment, as well as continued monitoring activities and reclaiming the original sludge basin.

No formal complaints for either entity were received in 2017.

Homestake and LAC Minerals, Richmond Hill Mine, each received the 2017 Operation and Maintenance Wastewater Treatment award from the Department of Environment and Natural Resources (DENR) for outstanding operation of the wastewater treatment system and environmental compliance with the state surface water discharge permit.

At the end of 2017, Homestake Mining Company employed 11 FTEs plus two contract employees and community contributions totaled $13,300 including $10,100 monetary and $3,200 non-monetary in the form of Homestake coins for charitable auctions.

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