Stabilization of Mercury in Waste Material from the Sulfur Bank Mercury Mine, Lake County, California

Site Name:

Sulfur Bank Mercury Mine Superfund Site

Location:

Lake County, California

Period of
Operation:

November 15, 2000 to April 29, 2001

Cleanup
Type:

Bench Scale

Technology:
Three stabilization technologies were used for immobilizing mercury in sulfide mine waste materials from the Sulfur Bank Mercury Mine (SBMM) site. The three technologies are listed below:

ENTHRALL Technology:
-- Developed by E & C Williams, Inc.
-- Uses inorganic sulfide reagent to target heavy metals. The treatment forms permanent bonds between the reagent surface and heavy metals.
-- Used a proprietary sonic drilling rig to inject the reagent. Two rigs were used concurrently to inject the reagent directly into the waste pile at 15-foot intervals.

KEECO’s Silica Micro Encapsulation (SME) process:
-- Developed by Klean Earth Environmental Company (KEECO).
-- Encapsulates metal in an impervious microscopic silica matrix, which eliminates the adverse effects of the metal on human health and the environment.
-- A modified ex situ process in which material is removed from its location for treatment at an adjacent on-site facility. The material is mixed with the reagent at the on-site facility and then returned to the site where it is replaced and compressed in place.

Generic Phosphate treatment:
-- Forms insoluble phosphate salts containing the contaminant.
-- Phosphates stabilize metals by chemically binding them into new stable phosphate phases, such as apatites, and other relatively insoluble phases in the soil.

Cleanup Authority:
-- EPA’s Superfund Innovative Technology Evaluation (SITE) program
-- Mine Waste Technology Program (MWTP)

Contacts:
U.S. Environmental Protection Agency Contacts:
Ed Bates
National Risk Management Research Laboratory (NRMRL)
26 W. Martin Luther King Dr.
Cincinnati, OH 45268
(513) 569-7774

Roger Wilmoth
Mine Waste Technology Program
National Risk Management Research Laboratory (NRMRL)
26 W. Martin Luther King Dr.
Cincinnati, OH 45268
(513) 569-7509

Technology Vendor Contacts:
E & C Williams, Inc.
Charlie Williams
Project Manager
120 Varnfield Dr, Ste. A
Summerville, SC 29483
(843) 821-4200

Klean Earth Environmental Company
Amy Anderson
Project Manager
19023 36th Ave. West, Ste. E
Lynnwood, WA 98036
(425) 778-7165

Contaminants:
Heavy Metals
-- Mercury: Mercury concentrations ranged from 312 to 1360 milligrams per kilogram (mg/kg) in the mercury ore and 130 to 447 mg/kg in the waste rock.

Waste Source:
Historic mining activities at the site.

Type/Quantity of Media Treated:
Waste Material (quantity not provided)

Purpose/Significance of Application:
To determine the effectiveness of three stabilization technologies for immobilizing mercury in waste rock material, thereby reducing leachable mobile mercury in the effluent.

Regulatory Requirements/Cleanup Goals:
To achieve a 90% reduction in the total mass of mercury leached from each treatment (relative to the control) over a 12-week continuous column leaching study.

Results:
E&C William's ENTHRALL Technology:
-- The ENTHRALL Technology was not effective in reducing levels of mobile mercury in the mercury ore columns.
-- The total mass of mercury in both the particulate and dissolved fractions were similar to the control column.

KEECO's SME Technology:
-- The SME process was applied both ex situ and in situ and was effective in reducing mobile mercury (< 25µm).
-- The in situ process reduced leachability by 88% and the ex situ process by 86%, when compared to the control.
-- Both the in situ and ex situ treatments achieved a 99% reduction in particulate-associated mercury, relative to the control.
-- There was however a significant increase in the mass of mercury in the dissolved fraction (< 0.45 µm). The in situ applications showed a 198% increase in comparison to the control, and the ex situ showed a 238% increase.

Generic Phosphate:
-- The phosphate treatment increased the levels of both the particulate and dissolved fractions (< 0.45 µm) over the course of the 12-week study.
-- The mass of mercury leached was high during the first two weeks or monitoring.
-- The treatment accelerated the breakdown of the mercury ore material matrix and facilitated the release of particulates.
-- The rise in leachable mercury invalidates this treatment as a possible remedial alternative for the materials at the SBMM site.

Cost Factors:
E&C William's ENTHRALL Technology:
-- Estimated total operating cost for remediating the SBMM piles was $59,807,000. No cost for residual handling was presented because the technology does not produce residuals.
-- The largest cost component, the chemical reagents, was $57,008,000 (93.5% of the total cost).
-- The second highest cost, equipment, was $1,633,500 (2.7% of the total cost).
-- The remediation cost per ton of material is $27.82.

KEECO's SME Technology:
-- Estimated total operating cost for remediating the SBMM piles is $35,690,000. No cost for residual handling was presented because the technology does not produce residuals.
-- The largest cost component, the chemical reagents, was $26,700,000 (68% of the total cost).
-- The KEECO technology requires residual handling, which costs $1,283,000 and constitutes the second highest cost item.
-- The remediation cost per ton of material is $16.60.

Generic Phosphate:
-- Full-scale treatment costs were not provided. Based on the study results, further experimentation and product modifications are required before the reagent can be considered for use at the SBMM site.

Description:
The Sulfur Bank Mercury Mine (SBMM) Superfund site is located on the south shore of Oaks Arm of Clear Lake, in Lake County, California. SBMM was mined periodically from 1865 to 1957, with open pit mining beginning in 1915. Starting in the late 1920s, heavy earthmoving equipment was used on a large-scale basis, which dramatically increased the environmental impacts of the mining. Various mining activities over the years have deposited large amounts of mercury in the Clear Lake ecosystem.

Two innovative in situ stabilization technologies and one generic phosphate stabilization treatment were evaluated in a treatability study, using material from the SBMM. The two innovative technologies were the ENTHRALL, developed by E&C Williams, Inc., and the Silica Micro Encapsulation (SME) process, developed by the Klean Earth Environmental Company.

The ENTHRALL technology uses an inorganic sulfide reagent, which forms a permanent bond between the reagent and the heavy metals. The reagent is injected using a proprietary sonic drill. The SME process encapsulates the heavy metals in an impervious microscopic silica matrix. The process can be conducted ex situ by first excavating the material and mixing it with the reagent at an adjacent on-site facility. The material is then returned to the site and compressed into place. The generic phosphate treatment stabilizes the heavy metals by chemically binding them into stable phosphate phases, such as apatites, and other relatively insoluble phases in soil.

The ENTHRALL technology was not effective in reducing levels of mobile mercury in the mercury ore columns. The SME process was applied both ex situ and in situ and was effective in reducing mobile mercury. Both the in situ and ex situ treatments achieved a 99% reduction in particulate-associated mercury, relative to the control, but there was a significant increase in the mass of mercury in the dissolved fraction. The phosphate treatment increased the levels of both the particulate and dissolved fractions. The rise in leachable mercury invalidates this treatment as a possible remedial alternative for the materials at the SBMM site.

The estimated total operating cost for the ENTHRALL and SME process technologies were $59,807,000 and $35,690,000, respectively. Residual handling costs were not included in these costs because the technologies do not produce residuals. Full-scale treatment costs were not provided for the generic phosphate treatment.