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B.8 Leviathan Mine Case Study

Alpine County, California

Acknowledgements

The mining team would like to acknowledge Dr. Nirupma Suryavanshi, Cal EPA, who submitted this Biochemical Reactors Case Study.

B.8.1 Site Information

Contact

Dr. Nirupma Suryavanshi

Cal/EPA-DTSC

5796 Corporate Avenue Cypress, CA 90630

714-484-5375

[email protected]

 

Name, Location, and Site Description

The Leviathan Mine is the former site of intermittent mining operations dating back to the 1860s, and open pit sulfur mining operations from the 1950s through the 1960s. A pilot scale bioreactor was first installed at the Leviathan Creek seep in 1993, and transferred to the Aspen Creek seep in the late 1990s. In 2003, Atlantic Richfield Company and researchers from the University of Nevada-Reno (UNR) and the U.S. Environmental Protection Agency (USEPA) installed a full-scale compost-free sulfate reducing bioreactor system (SRB) to treat acid rock drainage (ARD). Over an evaluation period of 20 months, from late 2003 to summer 2005, the bioreactor was able to achieve a target-metal removal efficiency of 95 percent. All target metals, except iron, were reducedIn chemistry, having gained electrons. Often gaining electrons is accompanied with gaining protons (hydrogen). As an example, when O₂ reacts with H₂, the oxygen is reduced, forming H₂O. to concentrations below the USEPA interim discharge standards. The compost-free bioreactor system also raised the pH of the ARDacid rock drainage from 3.0 to 7.0 and treated influent flows up to 30 gallons per minute (gpm) year-round. This case study looks at the effectiveness of the sulfate-reducing bioreactor treating ARD from the Aspen Seep at Leviathan Mine.

The Leviathan Mine is located in Alpine County, California near the California-Nevada border. The disturbed land comprises approximately 250 acres at the 7,000-foot elevation on the eastern slope of the Sierra Nevada. Mining operations commenced in the 1860s, but the mine was inactive from 1872 to 1935. The mine operated intermittently until the Anaconda Company purchased the property in 1951 and extracted sulfur by open pit mining from 1952 to 1962. No significant mining activities have occurred since Anaconda ceased operations in 1962 and sold the property.

Major environmental damage occurred at the mine, which is surrounded by the Humboldt-Toiyabe National Forest, during the period of open pit mining. Snowmelt, rain, and groundwater interact with the waste rock, creating sulfuric acid, which in turn leaches additional contaminants from the native minerals such as arsenic, copper, cadmium, nickel, zinc, chromium, aluminum, selenium and iron. Manganese is a secondary contaminant. The resulting ARDacid rock drainage flows into the Leviathan Creek system at numerous points, eventually joining the East Fork of the Carson River. For most of the year, roughly half of the flow in Leviathan Creek is composed of ARDacid rock drainage. The affected media include soil, sediment, surface water (stream, rivers, runoff, and drainage), surface pool water (lakes, ponds, and pools), and groundwater.

Leviathan Mine was added to the National Priority List (NPL) in May 2000 to address contamination of surface water from acid mine drainage (AMD)A low pH, metal-laden, sulfate-rich drainage originating from a mined area that occurs where sulfur or metal sulfides are exposed to atmospheric conditions. It forms under natural conditions from the oxidation of sulfide minerals and where the acidity exceeds the alkalinity. See also acid rock drainage. and ARDacid rock drainage. USEPA identified two problems requiring immediate attention: (1) an evaporation pond, known as Adit Drain (AD), collecting highly contaminated acid drainage, which overflows into the Leviathan Creek during the spring snowmelt; and (2) three seeps of acidic drainage causing contamination to enter Leviathan Creek and Aspen Creek (Figure B.8-1). One of these seeps, Aspen Seep (AS), originates from dumped overburdenGeological term for the material above solid rock. Sometimes called "soil". and flows into Aspen Creek. A sulfate-reducing bioreactor (SRB) designed and operated by Atlantic

 

Figure B.8-1. Leviathan mine disturbed area with major known ARDacid rock drainage points including Aspen Seep.

Richfield Company and University of Nevada-Reno (UNR) and USEPA researchers, treats the drainage from the Aspen Seep. More traditional lime-based treatment systems are currently being used to treat the other two contamination sources (Delta Seep/Channel Underdrain and Adit Drain) at the Leviathan Mine site. The overflow water is treated by chemical precipitation to mitigate human health and ecological risks. The full-scale treatment process, used seasonally since 2005, includes lime neutralization, aeration, and oxidation of reducing metals with the rotating cylinder treatment system (RCTS). The quantity being treated ranges between 3 million and 20 million gallons annually. The final, long-term remedy for this site has not been selected.

Figure B.8-2. Aerial view of the Leviathan Mine.

B.8.2 MIW chemistry

ARDacid rock drainage released from the Aspen Seep into Aspen Creek contains elevated levels of four primary metals: aluminum, copper, iron, and nickel. Each of these metals has historically exceeded USEPA interim discharge standards by over 500 times. Secondary metals of concern include selenium and zinc. Fish and insect kills in Leviathan Creek, Bryant Creek, and the East Fork of the Carson River have been attributed to the release of metal-laden ARDacid rock drainage. ARD, at pH 3, flows from the Aspen Seep at rates ranging from 8 to 30 gallons per minute (gpm). Table B.8-1 shows average concentrations of these primary metals, the pH prior to treatment, and compares the concentrations to the USEPA Interim Discharge Standard for Leviathan Mine.

 

Table B.8-1. Discharge criteria

Water Quality Parameter

Maximum2

Average4

pH 1

Between 6.0 and 9.0 SU

 

Arsenic (dissolved)

0.34 mg/l

0.15 mg/l 3

Aluminum (dissolved)

4.0 mg/l

2.0 mg/l

Cadmium (dissolved)

0.009 mg/l

0.004 mg/l

Chromium (dissolved)

0.97 mg/l

0.31 mg/l

Copper (dissolved)

0.026 mg/l

0.016 mg/l

Iron (dissolved)

2.0 mg/l

1.0 mg/l

Lead (dissolved)

0.136 mg/l

0.005 mg/l

Nickel (dissolved)

0.84 mg/l

0.094 mg/l

Selenium (total recoverable)

Not Promulgated

0.005 mg/l

Zinc (dissolved)

0.21 mg/l

0.21 mg/l

1. pH measurement based on 24_hour (single day) average discharge.

2. Concentrations based on daily grab samples, each grab sample field-filtered and acid fixed promptly after collection.

3 All average concentrations based on four daily grab samples, each grab sample field-filtered and acid fixed promptly after collection.

4 If the concentration detected by the contract laboratory is less than the detection limit, detection limit is used in calculating the average concentration.

 

USEPA 2008 Discharge Criteria in Table 1 are based on Applicable or relevant and appropriate requirements. Performance criteria include measuring the contaminant concentrations in the effluent water discharged to Leviathan Creek to ensure compliance with Environmental Protection Agency and state of California regulatory objectives.

B.8.3 BCR Design

The State of California, the site owner and therefore partially responsible for cleanup, had funded a bioreactor treatment system at the Leviathan Mine since the early 1990s. The system started as a simple one-cellAn individual unit in a treatment system., pilot-scale bioreactor with a manure substrateEither (a) a chemical which reacts or (b) a solid surface or (c) an electron donor.. The system continued to evolve throughout the late-90s but did not take its current form until the site was listed on the NPLNational Priority List. After the site became final on the NPL, USEPA directed Atlantic Richfield to prevent ARDacid rock drainage discharge from the Aspen Seep and several other discharge points. The State of California wanted the bioreactor system to be part of the Atlantic Richfield responsibility for cleanup. Atlantic Richfield saw promise in the system but felt it needed some improvements. The USEPA Office of Research and Development (ORD), Atlantic Richfield, the State, and UNR researchers convened for a design session to offer different approaches and ideas for constructing and implementing a full-scale bioreactor treatment system at the site. As a team, they proposed a system design, and the full-scale, compost-free bioreactor system was constructed in 2003. As constructed, the system requires 0.75 acres.

The bioreactor at the Leviathan Mine Aspen Seep relies on sulfate-reducing microbial organisms, such as Desulfovibrio sp., to reduce sulfate to sulfide. These organisms function at a critical pH 4.0 (Tsukamoto and Miller, 2005). ARDacid rock drainage from the Aspen Seep has pH 3.1 and, therefore, requires pretreatment before entering the compost-free bioreactor treatment system. In order to accommodate this requirement, a 25 percent sodium hydroxide solution (0.26 ml/L) is added to the influent in a pretreatment pond (1,000 ft3). The influent is effectively increased to pH 4.0 before it enters the compost-free bioreactor system. Ethanol (0.43 ml/L) is also added to the system to provide a carbon source for the sulfate-reducing microbes.

Figure B.8-3. Aspen Seep Bioreactor No. 2 lined with HDPEhigh density polyethylene and filled with river rock.

After addition of the sodium hydroxide solution and ethanol, ARDacid rock drainage flows to Bioreactor No. 1 to reduce sulfate to sulfide. Bioreactor No. 1 measures 12,500 ft3 in total volume and 5,300 ft3 in active volume, with a 22-hour hydraulic residence timeThe mean length of time a fluid element is in the volume of interest, usually determined by dividing the flow rate into the liquid volume. (HRT) at 30 gpm. The bioreactor is lined in 60 mil high-density polyethylene (HDPE) and is filled with 6- to 24-inch river rock. Along with supplying a substrate for the bacteria to grow on, the river rock also provides stable flow paths and allows precipitates to be flushed through the matrix. Sulfide generated in the first bioreactor is passed to the second bioreactor for additional metals removal. With a 13-hour HRThydraulic residence time at 30 gpm, Bioreactor No. 2 measures 7,000 ft3 in total volume and 3,000 ft3 in active volume (Figure3). Each bioreactor has three influent distribution lines and three effluent collection lines at different elevations to allow variable flow operations.

After passing through the bioreactors, a 25 percent sodium hydroxide solution is once again added to the effluent to increase the pH to a neutral condition. A continuous-flow pond, measuring 16,400 ft3 with a 68-hour HRThydraulic residence time at 30 gpm, collects the effluent from the second bioreactor for extended settling of metal sulfide precipitates. The effluent from this settling pond flows over a rock-lined aeration channel, measuring 150 feet long and two feet wide, to promote degassing of residual hydrogen sulfide prior to discharge.

Chemical reaction (addresses the citation in section 3.1 Alcohol bases) for sulfate-reducing bacteria using an alcohol carbon source:

4AH2 + SO₄2- + H+ = 4A2- + HS+ 4H₂O

H₂S + M2+ = MS + 2H+

AH2 is the carbon source and SO₄2- is the terminal electron acceptorThe molecule which is reduced during metabolism. In aerobic metabolism, oxygen is the electron acceptor, accepting two electrons and two protons to form water. in the electron transport chain of the sulfate-reducing bacteria. This causes an increase in pH. H2S reacts with metals and results in metal sulfide precipitate (MS).

The reduction of sulfate to sulfide:

H₂SO₄ + 8H+ + 8e- = H₂S + 4H₂O

Ethanol contributes 12 electrons per molecule oxidized.

3H₂O + CH₃OH → 12e- + 2CO₂ + 12H+

Electron counting enables determination of the amount of carbon source required to reduce sulfate

To prevent plugging of the rock matrix, precipitate slurry is flushed occasionally from the bioreactors. The slurry is settled in a flushing pond (18,000 ft3, 75-hour HRThydraulic residence time at 30 gpm). Occasionally, solids are pumped out of the settling and flushing ponds and dewatered using a 10- to 15-foot spun-fabric bag filter. Under California and Federal standards, the bag filter solids are not hazardous.

The total system HRThydraulic residence time is 107 hours at maximum design flow of 30 gpm.

B.8.3.1 Modifications to initial design

Although the system has experienced nearly constant tweaking, the following is a description of the three major bioreactor treatment system designs: manure substrate pilot-scale; two-cell bioreactor, and full-scale compost-free.

The original pilot-scale bioreactor developed by the UNR research team in the early 1990s was a simple system consisting of a manure substrate in a small, shallow pond (Tsukamoto and Miller, 2005). This organic substrate served as both the physical structure and the sole carbon source for the sulfate-reducing bacteria. However, once the carbon source was depleted, ARDacid rock drainage treatment slowed down. Additionally, ARD from the Leviathan Seep proved too acidic for the sulfate-reducing bacteria to function optimally, further reducing the efficiency of waste stream treatment. The drainage at Leviathan Creek was from waste rock, described as material containing less than 20 percent sulfur by mass. After the first year of operation, the researchers determined the bioreactor was ineffective in treating ARDacid rock drainage from the Leviathan Seep.

In order to address problems with the initial bioreactor design, the system experienced a facelift in 1998 (Tsukamoto and Miller, 2005). A new two-cell bioreactor was constructed at the Leviathan Mine Aspen Seep. The ARDacid rock drainage from the Aspen Seep, originating from dumped overburden, is a less acidic waste stream and enabled the microbes to have a better chance of survival. In addition to the location, key modifications implemented in the 1998 bioreactor included:

The use of alcohol as a carbon source provides an advantage over other organic substrates. Alcohol can be used for treatment over extended time periods, and it also maintains a liquid state under varying environmental temperatures. Finally, the addition of alcohol to a treatment system can be varied according to optimal operating conditions. Alcohol, specifically ethanol, is an ideal substrate for use at the Leviathan Mine Aspen Seep due to the remote nature of the site as it is only accessible for a few months out of the year (see Section 3.1 regarding influent variability and the advantages of liquid substrates, and also Section 6.2.3 regarding seasonal access).

Again in 2003, the system was redesigned and the compost-free bioreactor treatment system was constructed. The most recent design of the bioreactor uses a rock matrix in both bioreactor cells, includes a pretreatment pond, and has improved flow distribution and advanced sludgeA watery semi-solid. capture capability.

B.8.3.2 Operation mode: gravity-flow vs. recirculation

Over the first six months of evaluation, the 2003 bioreactor design operated under gravity-flow mode. Gravity-flow mode allowed metal precipitates to accumulate in both the bioreactors and the settling pond. This required the system operators to flush the system frequently, in turn disturbing the bacteria in the bioreactors. In order to avoid the need to flush the system so frequently, the researchers transferred the system into recirculation mode for the remaining 14 months of the evaluation period. In recirculation mode, untreated ARDacid rock drainage is mixed with a 25 percent sodium hydroxide solution and sulfide-rich water from Bioreactor No. 2. The mixture then flows into the settling pond where the high pH and high sulfide concentrations encourage precipitation of metal sulfides. This prevents the metals sulfides from precipitating in the bioreactors. The pH of the water moving through the bioreactors is nearly neutral, presenting ideal conditions for the sulfate-reducing bacteria. The system required 17 percent less sodium hydroxide while operating under recirculation mode.

B.8.4 BCR Performance

The 2003 compost-free bioreactor was evaluated between November 2003 and July 2005 as part of the Superfund Innovative Technology Evaluation (SITE) program. This effort was possible through the cooperation of the USEPA National Risk Management Research Laboratory (NRMRL), USEPA Region IX, the State of California, Atlantic Richfield, and UNR.

Table B.8-2. Bioreactor Treatment System Removal, Full-scale Compost-free Bioreactor

 

Gravity-flow Mode (11/2003 – 4/2004)

     Recirculation Mode (5/2004 – 7/2005)

USEPA Interim Discharge Standard (mg/L)

 

  Influent (mg/L)

     Effluent (mg/L)  

       Influent (mg/L)

Effluent (mg/L)   

 

pH

3.1

7.2

2.9

7.6

-

Al

37.5

0.1

40

0.05

2.0

Fe

 117

4.9

116

2.7

1.0

Ni

 0.49

0.07

0.53

0.07

0.094

Cu

 0.69

0.005

0.79

0.005

0.016

Sulfate

 1502

1222

1530

1170

-

The system achieved an increase in waste stream pH from 3.0 to over 7.0 during treatment. Additionally, although the influent concentrations of the target metals were up to 580-fold greater than USEPA interim standards, effluent concentrations were up to 43-fold below the standards. The system was also able to reduce the sulfate concentration in ARDacid rock drainage by more than 17 percent.

During the first six months of evaluation, while the system operated in gravity-flow mode, 2.44 million gallons of ARDacid rock drainage was treated. The system used 2,440 gallons of sodium hydroxide solution and 1,180 gallons of ethanol. Removal efficiency of target metals exceeded 94 percent.

Over the following 14 months, while the system functioned in recirculation mode, over 5.8 million gallons of ARDacid rock drainage was treated achieving a removal efficiency of target metals exceeding 96 percent. During this time, 5,280 gallons of sodium hydroxide and 2,805 gallons of ethanol were pumped into the system. The system operates year-round and treats up to 30 gpm in either mode.

The innovative two-phase lime treatment system to treat millions of gallons of the worst acid discharge that collects throughout the year in several large ponds on the mine site was developed. The treatment occurs during the summer months to maximize the pond storage capacity and prevent overflow of the ponds in the winter and spring. The California Regional Water Quality Control Board - Lahontan Region - continues to capture the highly acidic waste from the Adit Seep (AS) and Pit Under-drain (PUD) in the existing pond system and then treat the entire year's accumulation during an intensive one- to two-month period during the summer. Pond overflow, initially considered the most serious contaminant source, has been prevented since 1999. In the wet year of 2006, nearly 20 million gallons were treated during the spring and summer. In very dry years such as 2007 and 2009, only three million gallons or less must be treated to completely empty the ponds. Improvements in equipment, process efficiency and monitoring were constantly being implemented.

Atlantic Richfield Company, the successor to Anaconda, was capturing and neutralizing most of the remaining acid rock drainage as they develop long-term cleanup plans. A full-scale biological treatment system designed by the University of Nevada-Reno and constructed and operated by Atlantic Richfield has gained international attention for its remarkable success in treating one of the seeps year-round. Since 2003, the biological treatment system captured and treated all the acidic drainage captured at the Aspen Seep, typically more than three million gallons per year.

Atlantic Richfield has used various lime treatment systems to treat approximately six million gallons of acid mine drainage annually from the Delta Seep (DS) and Channel Underdrain (CUD), but only during the summer months.

Channel Underdrain (CUD), Delta Seep (DS) and Aspen Seep (AS) were included in the system. Atlantic Richfield Company attempted to design a system to treat all the known discharge sources for the entire year to reduce environmental damage, allow a more thorough evaluation of remaining risks to the downstream area and to assess the effectiveness and reliability of potential long-term treatment options. Difficulties were encountered during 2006 indicated that a lime treatment plant is not likely to be effective during the winter without very large investments in safe access and power at this remote mountain location. Improvements in the temporary lime treatment and biological systems, including a state-of-the-art High Density Sludge (HDS) lime treatment plant, were completed in 2009. The systems have improved efficiency with less waste generated and were also allowing an earlier commencement of the treatment season for the Channel Under-drain and Delta Seep. It was expected that the decision-making and design processes will continue for the next several years before a proposed plan for a long-term, year-round remedy is developed for public comment.

Atlantic Richfield’s contractor AMEC continued to operate the Aspen Seep Bioreactor (ASBR) in recirculation mode to treat AS discharge without significant modifications from 2010 operations. A belt filter press was used to dewater the ASBR sludge after AMEC determined a centrifuge mobilized to the site earlier in the year was not appropriate for dewatering ASBR sludge. The dewatering system consisted of a belt filter press, associated tanks for containment of raw sludge and dewatering effluent, and sludge and effluent pipelines.

When the ASBR operates in recirculation mode, sodium hydroxide is added to the AS influent which is then mixed with sulfide-rich water and sodium hydroxide from bioreactor cell 2 in the Settling Pond (Pond 3) for precipitation of metal sulfides. Water is pumped from the opposite end of the Settling Pond back to the pretreatment pond at approximately three times the system influent rate. The ASBR is operated in this mode because recirculated water has lower metals content and higher pH than raw AS water. These parameters are ideal for biological treatment in the bioreactor cells. Ethanol is added to the recirculated water to provide a carbon source for the sulfate-reducing bacteria. The Settling Pond (Pond 3) discharges to the next Settling Pond (Pond 4) from which bioreactor effluent is discharged along a rock-lined aeration channel to an infiltration pond adjacent to and above Aspen Creek. The recirculation pumps are powered by propane generators.

Approximately 7.2 million gallons of water from the AS bioreactor were treated and discharged to Aspen Creek during 2011. The AS flow rate during 2011 was higher than the 2010 AS flow rate. Details of the bioreactor performance are summarized in Atlantic Richfield’s year-end summary report.

Field parameter measurements showed the ASBR was effective at increasing the pH overflows from the northeastern corner of the infiltration pond down a steep slope into Aspen Creek and reducing the oxidation state of Aspen Seep discharge. Burleson measured ASBR effluent pH between 6.5 and 7.0 during the 2011 treatment season. The pH of ASBR effluent appears to have remained relatively stable during 2011. ORP is another key indicator of bioreactor performance. Burleson measurements show a decreasing trend in ASBR effluent ORP from June through September. The lowest ORP measurement coincides with bioreactor flushing.

The following improvements were made to the ASBR during 2011:

Discharge of ASBR effluent from the infiltration pond to Aspen Creek continued during 2011. Discharge seeps through the downslope infiltration pond berm into Aspen Creek. Water also overflows from the northeastern corner of the infiltration pond down a steep slope into Aspen Creek.

Significantly above average precipitation was measured at Monitor Pass during the winter of 2010-2011. Discharge rates from the acid drainage sources on site during 2011 were similar to those observed during 2006, and historical flow rates, considering the amount of precipitation.

The range of pH measurements at the CUD and DS in 2011 was similar to the pH range observed during treatment seasons between 2001 and 2010. These pH trends may reflect flushing of oxidation products from the variably saturated volume of the subsurface materials during the high rainfall years (such as 2005 and 2006) and increased retention of material above the water table during drier years (such as 2007 and 2008).

Visual observations were recorded during 2011 water quality monitoring to supplement field screening data. Visual observations included creek water clarity, the presence of unusual materials within the creek, and the presence of aquatic life.

High flows that occurred throughout the late winter and spring during 2011 were cloudy and turbid in comparison to the clearer water of Mountaineer Creek that is not affected by Leviathan Mine.

The visual appearance of Leviathan Creek began to improve in late May 2011 after Atlantic Richfield began capturing CUD and DS discharge, and run off declined. Flow in Leviathan Creek downstream became clearer, and orange chemical staining in the creek bed began dissipating.

Seepage from the east bank of Leviathan Creek below and immediately up and downstream from the DS collection tank was observed since 2008 continued through the 2011 treatment season. Seepage flowed freely into Leviathan Creek for about 10 feet along the stream bank, and red staining was evident in the stream bank sediment. The presence of the seep suggests that shallow, acidic seepage is present that is not intercepted by the DS collection system.

Aquatic life in Leviathan and Bryant Creeks was documented during 2011 oversight visits. Trout was observed in the pool within Leviathan Creek at Station 17. Aquatic life observations were qualitative; thorough documentation of aquatic communities was outside the scope of oversight tasks. A separate ongoing aquatic macro-invertebrate study includes sampling in the Leviathan Mine watershed in the spring and late summer each year. The macro-invertebrate study quantifies the health of the aquatic community downstream from the mine.

Water treatment by the Regional Board and Atlantic Richfield in 2011 led to seasonal improvements in Leviathan Creek water quality downstream from the mine. Water quality monitoring and visual observations suggest that conditions in Leviathan Creek at the end of the 2011 treatment season were generally similar to conditions at the end of the 2010 treatment season. This summer was the eleventh consecutive season of CUD capture and treatment, and fifth consecutive season of DS partial capture and treatment.

Above average precipitation resulted in increased accumulations of water in on-site ponds compared to the accumulations observed the last couple of drier years, and resulted in increased discharge rates from acid sources during the 2010-2011 winter as compared to earlier years. The resulting increase in pond water levels did not restrict either the Regional Board or Atlantic Richfield from treatment system operations. Free-board capacity in Ponds 2, 2N, 2S and 3 was preserved, and overflow to Leviathan Creek prevented, by Spring Season treatment using an RCTS (Rotating Cylinder Treatment System) system. The storage capacity at Pond 4 was increased during the treatment season by removal of sludge.

The Regional Board treated all of the available water from Ponds 2N and 2S and Pond 1. The Pond Water Treatment System (PWTS) operated 24 hours per day, 7 days per week for the 43 day operating period in 2011. The switch to use of imported lime slurry in the PWTS resulted in increased truck traffic necessary to support treatment activity at Pond 1 during 2011 field activities.

Atlantic Richfield captured and treated CUD and DS discharges for 166 days in 2011, which led to noticeable improvements in Leviathan Creek. Atlantic Richfield initiated capture of the CUD and DS flows on May 4, 2011 prior to observation of significant decrease of water quality at Station 15. The HDS treatment system was commissioned, and operated into early November before demobilization. At Aspen Seep, sludge was removed from the bioreactors, and dewatering via belt filter press was completed.

Following actions for the 2012 treatment season were recommended:

Figure B.8-4. Aspen Seep bioreactor settling pond: Note black sludge in middle-left. View to West. June 3, 2011.

Figure B.8-5. Aspen Seep bioreactor infiltration pond: View to North. June 3, 2011.

Figure B.8-6. Aspen Seep bioreactor sludge dewatering equipment:  View to Northeast. July 13, 2011.

 

Figure B.8-7. Aspen Seep bioreactor settling pond prepared for sludge removal. August 18, 2011.

 

Figure B.8-8. Ponds at Leviathan Mine full of acid mine drainage during winter (with overflow pipes).

Acidic mine waste flows from at least four separate discharge locations. Sulfuric acid with dissolved metals and arsenic enter Leviathan and Aspen Creeks unless it can be captured and treated. Since the eastern slope is fairly arid, even the relatively low flow rates of the acid mine drainage have devastated the stream system as far away as the Carson River, nine miles downstream. Atlantic Richfield will conduct a feasibility study that will include an estimate of power needs for a long-term remedy. The Leviathan Mine project will require active remediation for a very long time. Because the site is remote and many miles from power lines, diesel or other fuel must be trucked into the site to power any cleanup activity. Snowfall and wet winter conditions limit large vehicle access on the steep mountain road to only about half the year during the dry summer months. Using renewable energy instead could potentially allow treatment of the acid drainage for longer periods of the year, would be a much greener cleanup option, and would reduce stress on local roads.

B.8.5 Regulatory Challenges

Most tribes have established Environmental Departments funded primarily by USEPA. As with states, USEPA can delegate programmatic authority to tribes for Environmental programs, including regulatory authority under the Clean Water Act, if the tribe applying for such authority has an established Environmental Department and satisfies other USEPA requirements. Consequently, many tribes have developed enforceable Water Quality Standards. Although the tribe has developed its own Water Quality Standards, they are not yet enforceable until the tribe receives programmatic authority from USEPA. However, the tribe has been in close communication with those designing the Creek area BCR regarding the tribe’s Water Quality Standards which reflect the tribe’s priorities in addressing surface water contaminants (although the BCR may have the effect of treating water that meets Water Quality Standards, the tribe may not view the resulting water quality as being protective of the tribe, considering the tribe’s more intensive use of water and water related resources).

B.8.6 Stakeholder Challenges

Most Native American tribes have a different perception of environmental protection and remediation than that of western European or modern American societies. Therefore, it is very important to approach the tribe(s) that may be affected by the proposed BCR, and initiate a consultation process before beginning even the conceptual design. Federally Recognized Tribes and USEPA have jointly developed consultation policies and procedures to be used before environmental regulations or actions, that may affect tribes, are initiated. Therefore, it is highly recommended that those proposing BCRs on, or near, tribal lands or in areas of tribal jurisdiction, contact the appropriate USEPA Regional office and ask for office of the USEPA tribal liaison official who will likely offer detailed guidance on the appropriate tribal consultation procedures.

B.8.7 Other Challenges and Lessons Learned

A bioreactor treatment system, ranging from pilot-scale to full-scale implementation, has been operating at the Leviathan Mine since 1993. The technology has experienced many changes since its inception. In its current form, this treatment technology operates year-round and is compliant with USEPA discharge standards for all target metals except iron.

As the site remedial project manager explains, initially designed with simplicity in mind, the Aspen Seep SRB (Sulfate Reducing Bioreactors) has required more operator involvement than originally anticipated because pumping is required to keep the system operating properly. Although the system has proven to be both effective and reliable, it has also required more maintenance than originally planned.

The remote nature of the site and the surrounding environment are impacting system operations. The climate is also influencing the system with slower biological activity during the winter months. Winter snowpack limits access to the site for eight months out of the year requiring operating materials such as sodium hydroxide, ethanol, and diesel fuel to be stored in bulk before the winter. Similarly, equipment replacement, sludge dewatering, and sludge transfer are all performed during the summer months.

This technology can now be implemented at other sites. The bioreactor system at Leviathan Mine successfully addressed problems related to carbon availability and sulfate reductionThe stripping of oxygen atoms from sulfate (SO₄²⁻), most often yielding sulfide (S²⁻) as an ultimate product.. However, due to the unique characteristics of each site, the dose for base and ethanol would need to be determined through a simple bench test

The capitol costs for construction of the gravity-flow operation amounted to $836,600 and changing to the recirculation mode added nearly $30,000, for a total of $864,100. Operating at an average flow rate of 10 gpm, the operation and maintenance costs of the system are $15.73 per 1,000 gallons of treated ARDacid rock drainage. The compost-free sulfate-reducing bioreactor at the Aspen Seep is the first of its kind. The project was labor intensive because the operating conditions at the site were continually altered to stress and test the system. The system also included many optional features, such as controlling and routing flows, that would not normally be used in most systems. Because of these factors, the final costs are likely to be higher at Leviathan than the cost of operating and maintaining the system at other sites.

The capital cost of the rotating cylinder treatment system (RCTS) was less than $100,000. The cost of operation and maintenance depends on the volume of water treated each season. Overall treatment cost of all technologies applied at the Leviathan site is reported as follows:

Unpredictable amounts of acid mine drainage from year to year make budgeting and contracting processes very uncertain.

B.8.8 References

Tsukamoto, T.K. and Miller, G.C. 2005. “Semi-Passive Bioreactors at the Leviathan Mine.” http://www.unr.edu/mines/mlc/presentations_pub/presentations/Tim%20Ts.%20Semi-Passive%20Bioreactors%20at%20the%20Leviathan%20Mine.PPT#353,2,Slide 2

U.S. Environmental Protection Agency (USEPA). 2001. “Leviathan Mine Superfund Site: Update on Cleanup Activities.” San Francisco, CA. http://yosemite.epa.gov/r9/sfund/r9sfdocw.nsf/91f8ceee903fc0f088256f0000092934/0bdfb95fe5a4b9b788 2570070063c2f9/$FILE/levi11_01.pdf

U.S. Environmental Protection Agency (USEPA). 2004a. “Leviathan Mine Superfund Site: Proposal for Year-Round Treatment System.” San Francisco, CA. http://yosemite.epa.gov/r9/sfund/fsheet.nsf/024bc4d43f9aa0f48825650f005a714e/469733799e2ce6a0882 56e8400686547/$FILE/Leviathan%20Mine_apr_04.pdf

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Publication Date: November 2013

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