Active lime treatment system:
-- Acid rock drainage (ARD) and acid mine drainage (AMD) are neutralized using lime to precipitate dissolved iron, other metals, and oxy-hydroxides.
-- Influent flows into a reaction tank where it is mixed with lime slurry. The process solution then flows through a 4,000 Liter (L) flash/floc mixing tank where polymer flocculent is added. The solution then flows into a 40,000 L clarifier for floc settling and thickening. Solids are periodically pumped from the clarifier into a 550 L-capacity batch filter press for dewatering.
-- The system operated in two modes: monophasic and biphasic. The monophasic mode is a single stage process that treats a combined flow of ARD and AMD. The biphasic mode consists of two stages where only AMD is treated. During biphasic mode, the AMD flow passes through two sets of reaction tanks, flash/floc mixing tanks, and clarifiers.
-- The monophasic mode of the system treated ARD/AMD flows up to 250 liter per minute (L/min) while the biphasic mode treated AMD flow up to 720 L/min.
-- Forty-five percent lime slurry was added to the AMD at a rate of up to 1.3 L/min for biphasic mode and to the ARD/AMD at 0.35 L/min for monophasic mode.
Semi-passive alkaline lagoon treatment system:
-- ARD with low arsenic concentration is neutralized using lime to form hydroxide precipitate.
-- The semi-passive system operates as a continuous flow lime contact system.
-- ARD influent passes through three 4,000 L air sparge/lime contact tanks where initial precipitation occurs. Forty-five percent lime slurry is added to each contact tank at a combined rate of 0.16 L/min. The tanks are sparged with compressed air to mix the ARD and lime. The ARD/lime solution then flows through a series of six, spun fabric bag filters where approximately 60 percent of the precipitate is captured. Effluent from the bag filters then flows into a 5.4 million L multi-cell settling lagoon. Treated ARD is periodically discharged from the settling lagoon into the Leviathan Creek.
-- The system treats low ARD flows of approximately 120 L/min with relatively low arsenic content.
Edward Bates, EPA Project Manager
U.S. Environmental Protection Agency
National Risk Management Research Laboratory
Office of Research and Development
26 West Martin Luther King Jr. Drive
Cincinnati, OH 45268
Kevin Mayer, EPA Remedial Project Manager
U.S. Environmental Protection Agency Region 9
75 Hawthorne Street, SFD-7-2
San Francisco, CA 94105
Roy Thun, Project Manager
BP Atlantic Richfield Company
6 Centerpointe Drive, Room 6-164
La Palma, CA 90623
State of California Contact:
Richard Booth, Project Manager
California Regional Water Quality Control Board
2501 Lake Tahoe Blvd.
South Lake Tahoe, CA 96150
Average active lime treatment biphasic operation influent AMD concentrations:
-- Heavy metals: Aluminum (Al) (381,000 ug/L), Copper (Cu) (2,383 ug/L), Iron (Fe) (461,615 ug/L), Nickel (Ni) (7,024 ug/L)
Average active lime treatment monophasic operation influent ARD/AMD concentrations:
-- Heavy metals: Al (107,800 ug/L), Cu (2,152 ug/L), Fe (456,429 ug/L), Ni (2,560 ug/L)
Average semi-passive alkaline lagoon treatment influent ARD concentrations:
-- Heavy metals: Al (31,988 ug/L), Cu (13.5 ug/L), Fe (391,250 ug/L), Ni (1,631 ug/L)
Copper and sulfur mining activities.
Type/Quantity of Media Treated:
In monophasic mode, the active lime treatment system treated 17.4 million liter of combined AMD and ARD using 23.8 dry tons of lime over 6 months. During the biphasic mode the active treatment system treated 28.3 million liter of AMD using 125 dry tons of lime over 6 months.
The semi-passive alkaline lagoon treatment system treated 12.3 million liters of ARD using 19.4 dry tons of lime over 6 months.
Purpose/Significance of Application:
The primary objectives of the SITE evaluation were to:
-- Determine the removal efficiencies for the target metals over the evaluation period
-- Determine if the concentrations of the target metals in the treated effluent are below the interim (pre-risk assessment and record of decision) discharge standards mandated in 2002 Action Memorandum for Early Actions at Leviathan Mine
The secondary objectives of the evaluation were to:
-- Document operating parameters and assess critical operating conditions necessary to optimize system performance
-- Monitor the general chemical characteristics of the AMD or ARD water as it passes through the treatment system
-- Evaluate operational performance and efficiency of solids separation systems
-- Document solids transfer, dewatering, and disposal operations
-- Determine capital and operation and maintenance costs
Regulatory Requirements/Cleanup Goals:
EPA Project Discharge Standards (Maximum):
-- Heavy metals: Al (4,000 ug/L), Cu (26 ug/L), Fe (2,000 ug/L), Ni (840 ug/L)
-- Both the monophasic and biphasic modes for active lime treatment were able to remove on average 93.1 to 100 percent of each metal contaminant, with the exception of lead, which had a removal percentage of 74.6 to 78.3 percent.
-- The semi-passive alkaline lagoon treatment system was able to remove on an average 88.5 to 100 percent of each metal contaminant, with the exception of lead (removal efficiency of 66.4 percent) and copper (removal efficiency of 58.3).
-- Despite the low average percent removal efficiency for lead and copper, all contaminant metal concentrations in the effluent were below the interim discharge standards for both systems.
The initial fixed costs to construct the lime treatment systems were:
-- Active lime treatment operated in monophasic mode: $1,021,415
-- Active lime treatment operated in biphasic mode: $1,261,076
-- Semi-passive alkaline lagoon treatment: $297,482
The initial fixed costs consisted of site preparation costs, permitting costs, and capital and equipment costs. Site preparation costs included system design, project management, and construction management. Capital and equipment costs included all equipment and materials used, delivery, and initial system construction. Equipment and materials included reaction tanks, settling tanks, piping, pumps, valves, pH control equipment, automation equipment and satellite phones to support communication in the remote location.
Variable costs to operate each system over the 6-month evaluation period were as follows:
-- Active lime treatment operated in monophasic mode: $200,022
-- Active lime treatment operated in biphasic mode: $224,813
-- Semi-passive alkaline lagoon treatment: $195,151
Variable costs included system startup and shakedown, consumables and rentals, labor, utilities, waste handling and disposal, analytical services, maintenance and system modification, and system winterization.
The Leviathan Mine is a former copper and sulfur mine located in Alpine County on the eastern slopes of the Sierra Nevada Mountain range. Mining activities since the 1860s has resulted in significant AMD and ARD contamination. In the 1950s, approximately 22 million tons of overburden and waste rock were removed from the open pit mine and distributed throughout the site.
The active lime treatment system was installed at the site in 1999 and the semi-passive alkaline lagoon treatment system was installed in 2001. The SITE evaluation was conducted from June 2002 to October 2003. Each system used lime to neutralize AMD and/or ARD. The initial fixed costs for active lime treatment were $1,021,415 and $1,261,076 for monophasic and biphasic treatment respectively, and $297,482 for the semi-passive alkaline lagoon treatment system.
Both treatment systems were able to remove an average of 88.5 to 100 percent of each metal contaminant from the influent, with the exception of lead for the active lime treatment system (both modes), and copper and lead for the semi-passive alkaline lagoon treatment system. Lead had an average removal efficiency percentage of 74 to 78 with the active lime treatment and 66 percent removal efficiency with the semi-passive alkaline lagoon treatment. Copper had an average 58 percent removal efficiency with the semi-passive alkaline lagoon treatment. Based on these results, both lime treatment systems were continued after the SITE evaluation, with the active lime treatment system operating in biphasic mode to treat AMD and the semi-passive alkaline lagoon treatment system treating ARD.