PUBLIC HEALTH ASSESSMENT
Evaluation of Leviathan Mine Site
MARKLEEVILLE, ALPINE COUNTY, CALIFORNIA
The Leviathan Mine Site is located on the eastern slope of the Sierra Nevada in Alpine County, California, at approximately 7,000 feet above sea level. The site was originally mined for copper sulfate in 1863. In the 1950s and 1960s, the site was mined for sulfur by open-pit, strip-mining methods. Approximately 22 million tons of crushed rock containing high levels of sulfur ore was spread over the site. The waste rock is the major source of contaminants from the Leviathan Mine. Liquids flowing from the waste piles and tunnels at the site are best described as acid mine drainage (AMD). AMD is generally acidic and contains elevated metal concentrations.
AMD-contaminated water from Leviathan Mine has caused significant contamination and ecological impact to Leviathan, Aspen, and Bryant creeks, as well as the River Ranch Irrigation Channel. Elevated concentrations of aluminum, arsenic, cadmium, iron, manganese, nickel and thallium have been detected in surface water and sediment downstream from the mine. The contaminated waters and sediment are the source of two completed exposure pathways and eight potentially completed pathways.
The Washoe Tribe of Nevada and California has expressed concern that contaminated waters from Leviathan Mine may be affecting their lands downstream from the mine. Their concerns included impacts on culture, health, environmental damage, remediation, monitoring and testing, posting of health advisories, drinking water, health effects on pregnancy, cancer and public outreach.
Past and present consumption of surface waters in areas downstream of Leviathan Mine are considered completed exposure pathways because of the health risks from exposure to arsenic contamination. Swimming and wading are also considered completed exposure pathways because of the health risks from past or present exposure to arsenic. These two pathways are also considered completed in the future in Leviathan and Aspen creeks, but are considered potentially completed in areas further downstream of the mine (Bryant Creek & River Ranch Irrigation Channel) due to improving surface water conditions.
Potentially completed exposures include consumption of fish, plants and wild game collected near Leviathan Mine, eating beef raised on the River Ranch, inhalation of dust near the mine, and future exposure to surface water and sediments via drinking, swimming and wading in Bryant Creek and the River Ranch Irrigation Channel.
The available data indicate that the completed pathways could result in cancerous and non-cancerous health effects. The estimated cancer risks from these exposures range from no apparent increased risk to moderate increased risk of cancer depending on where, when, and how long the exposures occur. Arsenic represents the most significant risks to individuals exposed to surface water and sediment impacted by Leviathan Mine.
In general, the closer one gets to Leviathan Mine, the greater the probability that concentrations of contaminants will present a health risk. Avoiding contact with mine tailings, surface water, and sediments in Leviathan, Aspen, and Bryant creeks, as well as the River Ranch Irrigation Channel, will reduce health risks associated with exposure to contaminants from Leviathan Mine. Based on the completed pathways, the estimated exposure doses and the eight potentially completed exposure pathways, the Leviathan Mine Site is considered a public health hazard.
The Environmental Health Investigations Branch (EHIB), within CDHS, under a cooperative agreement with the Agency for Toxic Substances and Disease Registry (ATSDR), is conducting a public health assessment (PHA) at the Leviathan Mine Site in Alpine County, California. The site was nominated to the U.S. Environmental Protection Agency (EPA) National Priorities List (NPL) in October 1999. This PHA is intended to adhere to the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) legislation.
This PHA examines contaminants that have migrated from the Leviathan Mine Site into adjacent creeks and downstream surface waters. Data collected between 1954 and 2002 was used to prepare this PHA. Although a variety of documents and associated data were used in this assessment, the majority of risk estimation associated with the site utilized data summarized in Tables 1 through 5. This assessment of the Leviathan Mine Site is based on information available to CDHS at the time this health assessment was written.
The PHA differs from the EPA Risk Assessment that will be produced for the site in the future. The PHA focuses more on past and current exposures, whereas the risk assessment focuses more on current and future exposures. The PHA takes into consideration the specific health concerns of the community affected by the site and determines if people are exposed to contaminants at levels that could cause health problems. The EPA Risk Assessment is geared toward determining what areas need to be remediated and to what levels.
Leviathan Mine is located on the eastern slope of the Sierra Nevada in Alpine County, California. The mine is located approximately 6 miles east of the town of Markleeville, California, and approximately 2.5 miles west of the California/Nevada state border (Figure 1). Leviathan Mine is at an elevation of approximately 7,000 feet above sea level and located on the U.S. Geological Survey (USGS) Heenan Lake Quadrangle 7.5 minute series topographic map.
In 1863, Leviathan Mine was originally worked for copper sulfate. In 1869, miners began to dig for copper on the site. By 1870, miners had extracted 500 tons of 30% to 50% copper ore from the mine. During this time, miners noted that there was an immense sulfur deposit beneath the existing mining operations. In 1935, the Calpine Corporation of Los Angeles began mining sulfur at Leviathan Mine and during this period a number of underground workings were constructed. In 1941, Calpine ceased operations at Leviathan Mine.
In 1951, Anaconda Mining Company purchased Leviathan Mine for sulfur mining by open-pit, strip-mining methods. Approximately 22 million tons of overburden materials containing significant levels of low-grade sulfur ore were spread over approximately 200 acres. Anaconda's overburden castings generated a 26-acre waste pile at the site (1). This pile of gravel-sized material represents a major source area for contaminants from the mine. The other source area at Leviathan Mine is the mine excavation itself and associated adits (nearly horizontal mine tunnels leading to or from a mine). The 26-acre waste pile at the Leviathan Mine Site is more than 130 feet high in some areas (1). Open-pit mining operations continued at the mine until 1962.
The liquids flowing from the waste piles and adits at the Leviathan Mine are best described as acid mine drainage (AMD). AMD generally has a very low pH (2-3) and elevated metal concentrations. AMD is the result of sulfur in the geology at Leviathan Mine being exposed to oxygen in the air and water. When water washes over the exposed sulfur rocks it takes some of the sulfur with it. The sulfur in the runoff lowers the pH of the water. The low pH of the runoff makes metals in the soil and rock more soluble. Thus, as low pH water passes over rock, through cracks and seeps in the rock and through soils, it leaches metals into solution and results in elevated metal concentrations in the runoff. This may be in the form of surface water runoff or as a seep that discharges directly out of the ground through cracks and fissures in the bedrock.
According to reports from the California Department of Fish and Game (CDFG), Bryant Creek below the confluence of Mountaineer Creek was unpolluted prior to summer 1954 and contained a significant number of trout (2). The first reported fish kill as a result of the Leviathan Mine came in 1952 when open-pit mining operations intercepted an existing mine shaft (2). This discharged a large volume of AMD into Leviathan Creek. The release killed fish in Bryant Creek and the East Fork of the Carson River (Figure 1).
The Anaconda Mining Company made attempts to decrease water pollution during their mining operations by diverting Leviathan Creek around the waste pile with an impervious ditch and capturing AMD in retention ponds and treating it with lime.
From June 24 to June 26, 1957, a fish survey was conducted in Bryant Creek. No fish or aquatic organisms were reported present in Leviathan Creek or Bryant Creek from the Leviathan Mine area to the East Fork of the Carson River (2). In 1959, a fish kill of 10,000 to 20,000 fish was reported along 10 miles of the East Fork of the Carson River (2). This was reportedly the result of the discharge of approximately 5 million gallons of AMD that were released when a dike broke. The dike had been holding AMD in storage ponds at the Leviathan Mine Site.
In 1961, the U.S. Public Health Service (USPHS) produced a document called Summary Report on Quality of Interstate Waters, Leviathan Creek. The brief report recognized that the Anaconda Mining Company was responsible for pollution of the interstate watershed. It noted that the deterioration of water quality interfered with fish and aquatic life and had the potential to impact agricultural irrigation (1).
The East Fork of the Carson River flows through Dresslerville, Nevada, on the Washoe Indian Reservation. A major western Nevada water supply source, the East Fork is relied on heavily by the Washoe Tribe and residents of Nevada and California for fish and wildlife habitat, fishing, recreation, and other uses. The Washoe Tribe harvests pine nuts and game in areas near Leviathan Mine. The Leviathan-Bryant Creek watershed and the East Fork Carson River are within the historical habitat for the Lahontan Cutthroat Trout (Onchorhynchus clarki henshawi), a federally listed threatened species (3).
In 1962, Anaconda stopped mining and sold the Leviathan Mine to William Chris Mann and Zella N. Mann of Woodfords, California (2). Also in 1962, the mine was purchased by Alpine Mining Enterprises. In January 1969, the CDFG conducted a detailed survey of Bryant Creek. This survey determined that the entire 9.3 mile length of stream from the Leviathan Mine to the point where the stream enters the East Fork of the Carson River is toxic to fish and aquatic life and has been totally destroyed as a fishery resource (2).
In 1983, Alpine Mining Enterprises deeded the Leviathan Mine to the State of California (1). Currently, the Leviathan Mine Site is owned by the state of California and managed by the California Water Resources Control Board.
Since 1985, the LRWQCB has continued to make efforts to minimize AMD impacts on surface waters in the area. Activities undertaken by LRWQCB since 1985 include: installation of an AMD treatment system capable of treating approximately 10.5 million gallons of AMD; installing a nearly ½ mile long concrete channel at the mine site to further minimize AMD discharging into Leviathan Creek; grading the site and covering areas with impermeable membranes to further reduce erosion impacts on Leviathan Creek; and planting vegetation to further minimize erosion and runoff from the main excavation.
The Lahontan Regional Water Quality Control Board (LRWQCB) has made efforts to reduce, eliminate, or mitigate AMD impacts on the Leviathan Mine watershed. In 1985, as part of the LRWCQB's Pollution Abatement Project, five evaporation ponds were constructed at the Leviathan Mine Site. As of 1999, the ponds had the capacity to hold approximately 14 million gallons of contaminated water (4). However, in years with heavy precipitation, the evaporation ponds often exceeded their capacity in the spring during periods of high rainfall and snowmelt. This resulted in occasional releases of AMD to Leviathan Creek. The current capacity of the AMD ponds is 16 million gallons. As a result of the LRWQCB's program to treat pond water, pond overflow has not occurred since July 1999.
The Atlantic Richfield Company (ARC) is one of the parties responsible for cleaning up contamination at Leviathan Mine. ARC and its environmental division, ARCO Environmental Remediation, also have made efforts to reduce and minimize the impacts of the mine. In particular, ARC has conducted treatability studies to identify areas where AMD is continuing to discharge into Leviathan Creek from the main mine excavation. In 2001, ARC conducted capture and treatment efforts for the AMD seeps at the channel underdrain and at Aspen Creek. These efforts will continue throughout the remedial process until all mine drainage discharges are remediated to reduce the AMD impact from Leviathan Mine.
During the agricultural growing season, water from Bryant Creek is regularly diverted for irrigation purposes to the River Ranch. This diversion (River Ranch Irrigation Channel) is located immediately downstream of the Doud Springs inlet into Bryant Creek. The diversion is approximately 7.8 miles downstream from Leviathan Mine (1) and is located on the western side of Bryant Creek (Figure 2). The diversion runs along elevation contours similar to Bryant Creek in a northwest direction toward the East Fork of the Carson River and then makes a hard bend toward the southwest in the area where Bryant Creek meets the East Fork of the Carson River. This diversion channel, which appears to be unlined and runs for approximately 2 to 3 miles before reaching the River Ranch, has historically been used for agricultural irrigation and livestock consumption on the River Ranch. Frequently during the growing season, the entire flow of Bryant Creek is diverted to the River Ranch (2). The River Ranch has diversion rights for 2 cubic feet per second (cfs), which is sufficient to de-water Bryant Creek downstream of the diversion during low flow (dry) periods (5). Livestock pastured on the River Ranch might consume the irrigation water and feed on crops grown with the diversion water.
In 1968, William F. Jopling, sanitary engineering associate with the Bureau of Sanitary Engineering, State of California, Department of Public Health, produced, "The Effect of Leviathan Mine Drainage on Leviathan and Bryant Creeks, Alpine County." This report noted that both arsenic and iron exceeded USPHS Drinking Water Standards at the River Ranch Irrigation Channel (1).
There is another diversion from Bryant Creek located about ¼ mile above the mouth of Bryant Creek as it enters the East Fork of the Carson River. This diversion is used to irrigate River Ranch pasture land to the north of Bryant Creek, along the Carson River East Fork (2).
On July 31 and August 1, 2001, CDHS staff conducted a site visit of Leviathan Mine and creeks downstream of the mine. CDHS staff also met with representatives of EPA, LRWQCB, the Washoe Tribe, the USGS, and the Carson Water Subconservancy District.
Upon arrival at the site, CDHS staff observed warning signs posted at the gate at the entrance to the Leviathan Mine Site. However, no other warning signs were observed during the tour of the mine excavation and in the areas near the creeks. Upon arrival, site personnel provided a health and safety overview for the site. The entrance is at the end of Leviathan Mine Road, which originates from Route 89/Monitor Pass. The site is isolated and is located at approximately 7,000 feet above sea level in a forested area of the Eastern Sierras.
During the site visit, CDHS staff toured around the main excavation pit and the AMD storage ponds, the Leviathan Creek channelization, as well as some of the AMD treatment works and some ongoing remediation efforts. CDHS staff were also taken to a biological remediation project on the seeps near Aspen Creek. This system uses bacteria to convert sulfur in the AMD and precipitate out some of the metals.
CDHS staff traveled down the dirt road that goes to the lower reaches of Bryant Creek. CDHS personnel toured the junction of Aspen and Leviathan creeks, and the location where Leviathan and Mountaineer creeks join and form Bryant Creek. At this location, CDHS staff observed a small dirt parking area and a fire ring. The rocks of the fire ring were covered with soot, suggesting that the fire ring has had considerable use. Of all the locations observed along the length of the creeks downstream of Leviathan Mine, this location appears to be the most likely area of exposure to AMD-contaminated surface waters. It should be noted that surface waters observed in the vicinity of this area were all less than 10 inches deep and many of the stretches of the creeks observed during the site visit had less than 6 inches of water.
Continuing down the dirt road heading downstream, the road parallels the path of Bryant Creek, but is located at a higher elevation than the creek bed. From approximately the junction of Leviathan and Mountaineer creeks to 2 miles down the road, the elevation between the creek bed and the road increases to several hundred feet. This stretch of the area appears to be relatively rugged and difficult to access. There is a narrow road that visitors could use to go down to the creek bed.
CDHS staff visited the lower reaches of Bryant Creek via a road that travels along Doud Springs, which enters Bryant Creek very close to the location of the surface water diversion for the River Ranch. During the site visit, the lower stretch of Bryant Creek appeared completely dry. The entire volume of Bryant Creek was being diverted to the River Ranch Irrigation Channel.
On August 1, 2001, CDHS personnel returned to the creeks downstream of Leviathan Mine to search for areas where people might swim or wade. On the recommendation of EPA personnel, CDHS went to an area immediately downstream of the junction of Mountaineer and Leviathan creeks where there is a large box culvert that runs under the dirt road. On the downstream side of this culvert is a small pool of water that could be used for wading and swimming. The water depth observed by CDHS during this visit was approximately 14-18 inches. It should be noted that July and August are usually low flow months in the area. In addition, CDHS noted that the access to this location was somewhat difficult. Although it is close to a road, the entry is limited to the southwestern side of the culvert and is steep, unstable ground. CDHS personnel also observed two fish swimming in this pool. The fish were approximately 4 inches long and appeared to be trout.
Based on the information available to CDHS, the earliest community involvement for the Leviathan Mine Site came in 1960 when the owner of River Ranch expressed his concerns about the mine and Bryant Creek water quality to the Nevada State Health Department. The River Ranch owner believed many of his cattle died from drinking the water (2). On January 5, 1960, the Nevada State Health Department sent a letter to the Anaconda Mining Company stating that the owner of the River Ranch was concerned about the Leviathan Mine contamination and that cattle losses at River Ranch were higher than mortality in other areas (2). The owner of the River Ranch stated that the quality and quantity of pasture have continually declined since the overburden was placed in Leviathan Creek in 1954. A compilation of cattle deaths at River Ranch by the owner determined a total of 163 cattle died at the ranch between 1954 and the early 1970s, or an average of about 10 deaths per year (2). In 1968 alone, a total of 26 cattle died.
Although this is the earliest available record of public concern relating to the site, it is likely that others in the area were aware of the mine's impact before 1960. The Washoe Tribal Chairman has stated: "Since the late 1800s, we've had to endure the impacts of that mine. It is continuing to render certain parts of the reservation and tribal members' interests literally lifeless (6)." The lands of the Washoe Tribe of Nevada and California include areas downstream of the mine. The Washoe Tribe has expressed concern about the health of tribal members, wildlife, and the habitat they have used and nurtured for generations (6). The tribe also is very concerned about protecting their cultural heritage. There is concern within the tribe that their access and use of certain areas might be restricted or might cease entirely. The tribe has also expressed concern that contaminated waters from Leviathan Mine might be affecting the quality of water and natural resources in the Carson River and areas downstream.
The Washoe Tribe of California and Nevada have expressed concern that their natural environment and resources have been affected by operations at Leviathan Mine. The Washoe Tribe also has expressed reluctance to specifically identify resources near the mine that tribal members use or areas where tribal members collect plants, fish, and game for consumption or for cultural practices. Because Washoe Tribal Members are the most likely visitors to the area and most likely to utilize the resources near the mine, detailed information about use patterns would normally be acquired to assess health risks. However, this information is not currently available for this site.
CDHS respects the Washoe Tribe's decision to refrain from describing how they use areas near Leviathan Mine. However, this makes assessing the health risks fairly difficult. Because of the limited information about usage in the area and the fact that some people might be using the area for subsistence hunting and gathering, CDHS used very conservative estimates about frequency of contact and length of contact to natural resource areas near the mine that might seem elevated compared to normal risk assessments. This approach is taken for two reasons. First, the Washoe Tribe has lived in the area since well before the impacts of the mine occurred and have been subsistence hunters and gatherers for many generations. Subsistence hunters and gatherers are likely to visit areas near the mine more frequently and to spend longer periods of time in the area. Second, because limited use information is available for the area, CDHS has tended to be conservative in estimating risk to avoid underestimating health risks to people who use the area.
The Washoe Tribe harvests pine nuts, plants, and game in areas near Leviathan Mine. The impact of the mine and its contamination threatens the heritage of the tribe because it affects their subsistence way of living and makes it more difficult to maintain. The Washoe Tribal Chairman has summarized this concern saying that the mine "has an impact on our cultural resources. Our Washoe pharmacology has been impacted. There are traditional healing processes which are dependent on the bounty and richness which the natural landscape provides us. There is still significant involvement by the Washoe people with regard to those methods and processes of traditional healing (6)."
In May 1997, the Washoe Tribe of Nevada and California petitioned EPA to investigate ongoing concerns about the Leviathan Mine Site. It was hoped that EPA could provide assistance with the management of wastes generated at the site, particularly the existing evaporation ponds as well as reducing or eliminating the release of AMD from the ponds.
In 1997, EPA funded a 2-year project with the Washoe Tribe that allows for the meaningful participation of the tribe in the collection of tribal data for subsequent remedial investigations and other studies relevant to the remediation of Leviathan Mine. The funding for the project has been extended through 2002 and an extension of the agreement through 2003 is under consideration.
CDHS disseminated a draft of this public health assessment for public comment from May 4 to June 18, 2002. Public notices about the availability of the PHA were placed in three print and online newspapers. The notices informed the public that the PHA could be obtained at various repositories near the Leviathan Mine Site. Two newspapers ran stories with photos about the Leviathan Mine public health assessment (PHA)--the Reno Gazette-Journal and the Douglas County Record-Courier.
CDHS held a public meeting on May 30, 2002. Verbal comments from the public meeting, in addition to those received via mail and in written form, are summarized below. Written comments received by CDHS are attached in Appendix D. The community meeting was announced through the same newspapers mentioned above. Notices were sent to over 1,200 individuals in the area, mostly Washoe tribal members. In addition, notices were sent to owners of tribal land allotments that are adjacent to the creeks downstream of the Leviathan Mine Site and to various environmental agency representatives. Thirty-eight people, most of whom were tribal members, attended the Leviathan Mine PHA public meeting.
Community health concerns expressed during the public meeting included impacts on culture, health, environmental damage, remediation and how long it would take, monitoring and testing, posting of health advisories, drinking water, health effects on pregnancy and cancer, and public outreach.
Tribal members were very concerned about the health of the environment. "To me, all living things are affected," said one member. Another asked, "Who speaks for the animals or the deer that live up there?" They wanted to know the extent of the damage from the mine and how it would affect trees and other plants. One community member said he noticed that a lot of trees were dying in the area.
Some wanted to know whether further testing and monitoring will be done to assess the damage and potentially completed exposures. "Who will monitor the fish, the plants, the livestock?" asked one tribal member. This PHA recommends the collection of fish tissue data to determine if contaminants from the mine are getting into the fish. Another community member wondered if the organs of deer killed by hunters could be sent to a state lab for testing. An EPA representative was concerned that testing could result in false negatives if the deer was not native to the area but was killed there.
Tribal members wanted to know about past exposure and how long the state and other agencies knew about the possible harmful effects of the contamination. They shared stories about cultural activities, including fishing, hunting, gathering, and swimming in the area near Leviathan Mine Site and were concerned that they might have been exposed. Adults were concerned that they might have been exposed as children and their own children and grandchildren might now be exposed. Also, community members were concerned about swimming and wading in the water. Tribal members wanted to know about the impacts on food and ceremonial items gathered in the area: fish, game, pine nuts, wild onions, and certain other plants. One person said he saw a dead bear in the area and wondered if it could be attributed to the contamination. In this PHA, CDHS recommends that people avoid eating fish from creeks near the mine and avoid contact with Leviathan mine tailings, surface waters, and sediments from creeks near the site. It is also recommended that people who collect plants gather them as far from the mine site as possible.
Community members wondered if advisories would or could be posted in the area or if people should be prohibited from entering the area. There was a strong sentiment that advisories should be posted in the area downstream from Leviathan Mine and not just at the mine site itself. In this PHA, CDHS recommends advisories be posted near the mine to warn visitors and users of the area about potential risks. One person indicated that he had been on the mine site in the past.
Contamination of the water and water clean-up standards were of high concern. Community members wanted to know how far downstream the creeks were contaminated. One community member indicated that many years ago River Ranch received irrigation water from the East Fork of the Carson River, not from Bryant Creek. In this PHA, CDHS recommends surface water and sediment sampling at the River Ranch to test for AMD contaminants.
The community wanted to know if the groundwater was contaminated. Based on limited information about the groundwater in the area, it appears unlikely that significant volumes of AMD from Leviathan Mine are migrating to deep groundwater and impacting groundwater great distances from the site. Most of the AMD that makes its way to the groundwater will likely discharge downgradient in Leviathan or Aspen creeks. One tribal member said that the standard for drinking water should be set for a pregnant mother's unborn child, and then the water should be cleaned up to that standard. Another tribal member said the acceptable minimum standard should be pure water. It was emphasized that participants were thinking about their future generations. One tribal member suggested community education efforts about the water. This PHA recommends community outreach about the findings of this health assessment and the potential health effects of Leviathan Mine.
Finally, participants of the community meeting wanted to know what were the health effects from long-term exposure to metals. They wondered if their health professionals were trained to look for this type of exposure and they were concerned about potential birth and developmental defects. Cancer was of concern, particularly because the mine first opened in 1863 and the Washoe people have always lived in and utilized the area near Leviathan Mine Site.
The meeting participants wanted to know if CDHS-EHIB will hold more meetings and if more feedback will be solicited on the PHA process. CDHS and other agencies will hold meetings as new information is available. There was some concern that the public comment period for the PHA was not long enough. In response, CDHS-EHIB extended the deadline for two additional weeks.
In order to assess the potential adverse health effects of environmental contamination on a nearby population, one must identify contaminants that are present at a high enough concentration to possibly cause adverse health effects. Those contaminants are called contaminants of concern (COC), and are identified as follows.
The concentration of the contaminant in a specific medium (soil, air, or water) is compared to a screening value for that contaminant in that medium. This screening value is the concentration of a specific chemical in a specific medium (soil, air, or water) at, or below which, a person could be exposed without expecting adverse health effects. These values are calculated using assumptions that are protective of health regarding the body weight and ingestion rate of the receptor population, so that if the concentration of the contaminant is below the screening value, one should feel confident that adverse health effects will not occur. If the concentration of the contaminant exceeds the screening value, then it is considered a COC. However, adverse health effects are not certain to occur if the concentration of a chemical exceeds its comparison value.
Comparison values are available for evaluating both cancer and non-cancer health effects. The non-cancer health effects will be evaluated relative to the comparison values called environmental media exposure guidelines, or EMEG values (developed by ATSDR). If the contaminant levels are less than the EMEG values, then a non-cancer adverse health effect is not likely, and that contaminant is not considered further. On the other hand, if the contaminant concentration exceeds the EMEG comparison value, the contaminant is considered a COC, and a more rigorous toxicological evaluation is necessary. If EMEG values are not available for certain chemicals, alternative comparison values may be used.
Contaminants that might cause cancer can be evaluated in terms of an increase in the risk of developing cancer. Such an increased risk can be assessed by comparing contaminant concentrations to the cancer risk evaluation guide (CREG) comparison values. These CREG comparison values use a decision point for screening purposes that is set at "one-in-a-million" (or 1 x 10-6). In other words, if the concentration of a specific contaminant is less than the CREG, then exposure to the contaminant at that concentration is not expected to increase the risk of cancer by more than one additional cancer case per 1 million people exposed. If the contaminant concentration exceeds the CREG, the contaminant is considered a COC, and it receives further toxicological evaluation
The majority of the surface water data collected near Leviathan Mine is dissolved metal data. However, surface water data from early sampling events did not typically specify whether the analyses performed were for total or dissolved metals. As a conservative measure, CDHS assumed the early samples were dissolved and that all of the metals detected in the surface waters were bioavailable. This may have overestimated the historical risks near the site. Paired sampling for total and dissolved metals in surface waters near Leviathan Mine would be useful to more accurately assess the upper and lower bounds of the risks these waters pose to those exposed to the surface waters downstream of Leviathan Mine.
The earliest data available for review on environmental media relating to the Leviathan Mine Site was compiled by the Anaconda Mining Company during their operations. Surface water data collected between 1968 and 1969 was included in a 1975 Regional Board staff report (2). This data is summarized in Table 1. Samples were taken above the mine, below the mine, from Bryant Creek below the confluence of Mountaineer and Leviathan creeks (approximately 2 miles downstream of the mine) and from Bryant Creek at the River Ranch Irrigation Channel (approximately 7.8 miles downstream of the mine). This data is significant because it indicates that water quality was adversely affected at least 7.8 miles downstream from the Leviathan Mine (Figure 2). It also provides a rough idea as to what users of downstream creeks might have been exposed to before the interventions implemented in 1985 by the LRWQCB.
The samples with the highest reported concentration of arsenic were collected on June 12, 1969, near the Leviathan Mine discharges. This sampling effort analyzed samples from upstream of the mine, at the mine, Leviathan Creek and the River Ranch Diversion for pH, sulfates, dissolved solids, boron, aluminum, copper, iron, manganese and arsenic. These samples had a concentration of 110 ppm arsenic. This is the maximum concentration of arsenic detected at the site. However, the data collected near mine discharges are listed in ranges instead of discrete concentrations. Presumably, there was at least one arsenic sample at 110 ppm, but it is not possible to discern because the data, as it is reported in the 1975 report only lists the date (6/12/69), the location (discharges), and the range of concentrations (0.52-110 ppm). No further information was available for these samples. The next greatest concentration of arsenic reported in surface waters from the site was a detection of 30 ppm, collected on April 23, 1982, from the seep at Leviathan Mine tunnel 35 (Table 2) (7).
Since the LRWQCB's involvement in 1984, surface water samples have been collected at a number of sites along the creeks downgradient and upgradient of Leviathan Mine (Table 1). There is at least partial water quality data for every year since 1984. However, the location of some of these samples varies from year to year and from one agency to another. In estimating health risks, CDHS made efforts to standardize locations as much as possible. However, it is not currently possible to definitively cross-reference all sample locations. Therefore, closest approximations of sample locations were used in assessing risks by location.
In 1998, SRK Consulting, a contractor for ARC Environmental Remediation, collected three rounds of total and dissolved surface water data from Leviathan Creek and Aspen Creek to the junction of the two creeks (8). This data is comparable to other sampling efforts near Leviathan Mine in that the contaminants most frequently detected at elevated concentrations are arsenic, cadmium, manganese, nickel, and thallium.
On April 5, 1999, the U.S. Fish and Wildlife Service collected surface water samples immediately downstream of the Leviathan Mine (3). These samples contained elevated metal concentrations. Aluminum, arsenic, cadmium, manganese, nickel, and thallium concentrations exceeded available comparison values. The most significant detection in this sample was a detection of 27 parts per billion (ppb) of arsenic. This concentration is approximately 10 times greater than the chronic EMEG for children of 3 ppb.
Arsenic concentrations are elevated in nearly every sample collected downstream of Leviathan Mine, and in some samples arsenic was detected at concentrations that could cause short-term health problems if someone were to consume those surface waters. Most of the very high concentrations detected were collected in the mine adits and pits. However, detections of arsenic in Leviathan Creek occasionally reached levels that could pose a health risk to people that drink water from the creek. Generally, the further downstream from the site that samples are collected, the lower the concentration of contaminants. However, as recently as April 1999, samples collected as far away as the East Fork of the Carson River have elevated concentrations for a variety of inorganic compounds.
The 2001 Leviathan Mine Site Draft Site Management Plan contains dissolved surface water data from Leviathan Creek upstream of the mine and from Aspen Creek to the headwaters of Bryant Creek collected between January 1998 and October 2000 (9). As in previous sampling efforts, arsenic concentrations represent the most significant health risk in these surface waters. Nickel, aluminum, and iron were also analyzed in these samples. Nickel had three detections at concentrations above the child RMEG of 200 ppb. Average aluminum concentrations collected from Leviathan Creek (27,000 ppb) were above the child intermediate EMEG of 20,000 ppb, but below the adult EMEG (70,000 ppb).
Iron concentrations were detected above background levels in many surface water and sediment samples. In some cases iron concentrations in surface waters exceeded the USEPA Region III Risk-based Concentration (RBC) for iron in tap water (11,000 ppb). Therefore, iron is considered a COC and is evaluated further in the toxicological evaluation section.
The LRWQCB has made regular sampling efforts an ongoing part of their assessment process for remedial activities at the site and in areas impacted by the mine. LRWQCB provided a compilation of the surface water data collected from Leviathan Mine and nearby areas from 1995 to present (Table 3).
During the summer of 2001, the combined efforts of the LRWQCB and ARC Environmental Remediation resulted in the treatment of the pond overflow at the mine site and the channel underdrain, two major sources of AMD to Leviathan Creek. While the 2001 treatment efforts were under way, there was significant improvement in Leviathan Creek. In August 2001, while treatment efforts were under way, dissolved arsenic in Leviathan Creek below the mine (just above the Leviathan/Aspen Creek confluence) was detected at a concentration of 4.4 ppb. In 1999, at the same location, the U.S. Fish & Wildlife detected arsenic at 27 ppb in 1999.
There is a trend in the surface water data indicating that concentrations of contaminants are slowly, but consistently, decreasing. It is likely that the completion of the 1985 abatement project and the elimination of the pond overflow as well as the treatment efforts at the channel underdrain flow and the seep at Aspen Creek are factors in the improvement of water quality near the Leviathan Mine. It is also likely that the capture of AMD on-site in the storage ponds is having a positive affect on downstream conditions. The LRWQCB, ARC and the University of Nevada at Reno (UN-R) with USEPA oversight, continue to make efforts to reduce, mitigate, and, if possible, eliminate contamination at the site and in affected waters. Therefore, it is possible that concentrations of surface waters in the future could go below levels that would cause a health concern. Based on this information, it appears likely that some of the currently completed exposure pathways will be considered potentially completed in the future as surface water and sediment concentrations diminish as a result of remedial interventions.
In the summer and fall of 1982, the USGS installed 57 test holes including 49 peizometers, four neutron-probe holes and four suction-lysimeter holes to collect groundwater information and help characterize hydrology and geochemistry of shallow groundwater at the site. In addition, USGS installed 26 shallow (< 14 feet deep) peizometers by hand at the base of the waste pile at Leviathan Mine. Some of this data was presented in the USGS Hydrologic Data for Leviathan Mine and Vicinity, Alpine County, California, 1981-1983 USGS Open File 85-160 (7).
USGS also produced a report entitled: "Shallow Ground Water Flow in the Vicinity of the Open Pit at Leviathan Mine in 1987 (10)." This document discusses some of the findings of the 1982 groundwater studies. USGS assessed the groundwater in the area on the assumption that several standard hydrologic theories apply to the area. In particular, USGS assumed that groundwater flows downward and laterally beneath hills and upward and laterally beneath major stream valleys. This assumption is the generally accepted theory on groundwater flow, unless there is compelling evidence to the contrary. The USGS also assumed that the saturated thickness of the groundwater in the area of Leviathan Mine is between 25 and 50 feet thick. USGS further indicated that groundwater levels in the Leviathan Mine area generally mimic the topographic contours in the area.
Based on this information the majority of shallow groundwater at the Leviathan Mine appears to travel toward Leviathan Creek and likely discharges in Leviathan and Aspen creeks. However, this study is not comprehensive and has not made any attempts to determine the condition or movement of deeper groundwater. Therefore, movement of Leviathan Mine contaminants downgradient of the mine site cannot be eliminated as a possibility.
Because Leviathan and Aspen creeks are natural discharge areas for surface waters and groundwater in the vicinity of Leviathan Mine, it appears unlikely that AMD from the mine would migrate far off site before discharging into the creeks. The elevation of the mine is approximately 7,000 feet above sea level. The approximate elevation at the junction of Leviathan and Aspen creeks is 6,600 feet above sea level. This approximately 600 foot drop in elevation takes place in approximately 1 mile, creating a fairly steep topographic gradient.
Considering that the approximately 50 foot thick shallow groundwater lense is subject to the gravitational force of the steep topographical gradient, it appears most of the AMD at the site will make its way towards the creeks and discharge into Aspen and Leviathan creeks. However, this gradient does not assure that AMD from the mine is not reaching into deeper groundwater or migrating in other directions from the site.
In the fall of 1998, the U.S. Fish and Wildlife Service collected fish data from the East Fork of the Carson River (3). This sampling effort collected fish from the East Fork of the Carson River upstream of the Bryant Creek Inlet, near the Bryant Creek Inlet and downstream of the Bryant Creek Inlet. The only data collected during this effort relative to water quality in Bryant Creek was one mountain whitefish (Prosopium williamsoni) collected near the Bryant Creek inlet on the East Fork of the Carson River. Fish collected during this sampling effort were analyzed for metals. The fish from these three sites had elevated levels of several metals. However, due to the limited amount of data, it is not possible to assess the impact Leviathan Mine has had on fish. Further studies of fish tissue metal content would be required to determine if contamination from Leviathan Mine is getting into fish in the creeks downstream of the mine.
Also in fall 1998, CDFG conducted a fishery resource assessment in the Leviathan Mine area. CDFG collected fish distribution, species composition, density, and biomass data from 11 sites in the Leviathan-Bryant Creek watershed and the East Fork Carson River near the confluence with Bryant Creek. This study concluded that streams not affected by the discharge of AMD had very high densities of fish relative to those that were influenced by Leviathan Mine (3). The study also concluded that streams downstream of Leviathan Mine were either completely devoid of fish or had very low numbers (3). However, the downstream Mountaineer and Upper Leviathan Creeks do not receive discharges and contained large robust populations of Rainbow and Brook Trout (3). One Lahontan Cutthroat Trout was also caught in Upper Leviathan Creek. This collection suggests that if the mine were not having a negative impact on the ecosystem, waters downstream of the mine might be a habitat for the Lahontan Cutthroat Trout as well as Brook and Rainbow Trout.
In 1999, the U.S. Forest Service made an assessment of AMD impacts on creeks in the Leviathan Mine Watershed (11). This study determined that three of the creek sites closest to the mine showed clear and consistent impairment relative to reference sites. The reference sites as a group also showed higher performance measures of biological integrity than the series of downstream sites on Bryant Creek below Mountaineer Creek (4). The most prominent pattern was of poor biological performance measures due to low species diversity and density at the three sites closest to the mine source area (11).
The earliest sediment data collected from creeks impacted by Leviathan Mine was in 1983 as part of the USGS 1981-1983 hydrologic investigation (7). This data, summarized in Table 4, reported concentrations of aluminum and arsenic above health comparison values in sediments in Leviathan and Bryant creeks and near the River Ranch Irrigation Channel. Therefore, aluminum and arsenic are considered COCs.
Sediment data was collected by ARC from 10 locations downstream of Leviathan Mine including Leviathan, Aspen and Bryant creeks as well as from the River Ranch Irrigation Channel from September 21st to 24th 1998. These samples were analyzed for aluminum, arsenic, chromium, copper, iron, manganese, nickel and zinc and presented in the Data Report for Leviathan Mine (12). Arsenic was the only COC from this round of sampling. Average concentrations of arsenic in sediment exceeded the child RMEG of 20 ppm for all four sample locations. One fine sediment sample collected from the River Ranch Irrigation Channel had manganese concentrations (3333 ppm) slightly above the child RMEG of 3000 ppm. However, the average of the three samples from this sample location (2355 ppm) was below the child RMEG for manganese.
In 2000, USGS, in cooperation with the U.S. Fish & Wildlife Service and the Washoe Tribe of Nevada and California, released the report, "Data on Stream-Water and Bed-Sediment Quality in the Vicinity of Leviathan Mine," which had been produced in September 1998 (13). This report provides data on eight different sediment sampling locations in the Leviathan-Bryant Creek system. The data set (Table 5) was used for most of the site wading risk calculations because it has data from the four areas of concern (Leviathan, Aspen, and Bryant Creeks and the River Ranch Irrigation Channel) and has three samples collected at each location. The only COC from this round of sediment data is arsenic.
The Data Report for the Leviathan Mine Study produced by ENSR for ARC in December 1999 included sediment data collected between September 21st and 28th, 1999 (12). This sampling effort included collection of coarse and fine sediments at 10 locations along Leviathan and Bryant Creeks followed by analysis for total and dissolved metal concentrations of aluminum, arsenic, cadmium, chromium, copper, iron, lead, manganese, nickel and zinc. These samples had comparable concentrations to the USGS sediment data with the exception of manganese, which was higher in the ENSR report, and arsenic, which was lower in the ENSR report. Arsenic is the only COC in this sediment data.
On December 7, 2000, EPA released sediment data the agency and the Army Corps of Engineers had collected on September 28, 2000, from 14 different locations near the Leviathan Mine Site (14). Arsenic was detected in sediment at concentrations above available comparison values. Cadmium and thallium were not detected. This data also indicate that arsenic is the only COC.
The LRWQCB's 1996 Site Safety Plan summarizes air monitoring data collected on September 21, 1993. The 8-hour time-weighted average of exposure to dust at the site was below the California Occupational Safety and Health Administration (Cal/OSHA) Permissible Exposure Limit (PEL) for arsenic, cadmium, chromium, lead, and nickel dust in all four samples (15). Additional dust samples were collected at the mine site on June 25, 2001, and analyzed for arsenic. All five air samples collected during this round of sampling were below detectable concentrations one microgram per cubic meter (ug/m3) and well below the 10 ug/m3 PEL for arsenic in air (16).
Because dust generation is likely to be greatest at the mine site, these results suggest the dust exposure pathway in other areas where waste rock reportedly was used to build roads would not present a health risk for workers. However, because the PEL is meant to be protective of workers that spend a 40-hour work week at the site, the PEL is not designed to be protective of sensitive populations such as pregnant women, children, or the elderly or people that use the area more frequently, or in ways different than a worker. Review of non-occupational comparison values for arsenic in ambient air indicate the detection limits for samples collected at Leviathan Mine were too high to assess potential health impacts on non-occupational exposure scenarios. The ambient air CREG for arsenic is 0.0002 ug/m3. This value is well below the detection limit for arsenic in ambient air used at the site. Based on this information, further assessment of the dust pathway is warranted in the vicinity of Leviathan Mine. Specifically, areas outside of the mine excavation along the site access roads where waste rock might have been used during road construction should be evaluated for AMD contamination.
Ambient air samples have been collected only on the Leviathan Mine Site and no air samples have been collected along the road that, on the basis of anecdotal information, might have been improved or augmented with the use of waste rock from Leviathan Mine. Concern about the safety of the roadbed materials is compounded by the possibility that AMD was used on the roads. According to the LRWQCB's 1975 Report Leviathan Mine (2), "Water from the ponding of seepage is being used on the roads." This suggests that contaminants at the mine could be present on the roads in the area and further strengthens the argument for further assessment.
An appraisal completed in 1970 on the effects of contaminants on irrigation water taken from Bryant Creek on agriculture at the River Ranch was reported in the LRWQCB Leviathan Mine Five Year Workplan (1). This appraisal was based on water, soil and plant samples collected from the River Ranch on September 7, 1970. Soils were analyzed for iron, copper, manganese, zinc, cobalt and nickel. This assessment concluded that there were elevated concentrations of iron (845 ppm), copper (11.6 ppm), manganese (160 ppm), zinc (6.6 ppm), cobalt (14.5 ppm), and nickel (24 ppm) in soils at the ranch due to irrigation water. Though the plant analysis showed elevated levels of iron (315 ppm) and manganese (135 ppm), it did not indicate toxic levels of any metals (1).
Additional information about the impacts on River Ranch operations can be seen in data collected by the Lahontan RWQCB in 1968 and 1969. The 1968/1969 surface water data collected at the River Ranch Irrigation Channel indicate that if people were drinking these waters, they would likely have been adversely affected by elevated arsenic concentrations. This data also suggest that domestic animals or wildlife drinking this water also might have been exposed to metals that could be of some health concern. However, due to limited information about how these waters are used by the River Ranch, the uptake of contaminants in livestock and the exposures cattle might have had at River Ranch, an assessment of the risks presented by consumption of River Ranch beef cannot currently be completed.
For a population to be exposed (receptor population) to environmental contamination, there must be a way (mechanism) by which that contamination comes into direct contact with the target population. An exposure pathway is the description of this mechanism. An exposure pathway consists of five parts: a source of contamination at concentrations that might cause harm, a contaminated environmental medium and transport mechanism, a point of exposure, a route of exposure, and a receptor population (17).
Exposure pathways are classified as completed, potential, or eliminated. A completed exposure pathway is one in which all five elements of the pathway are present. A potential pathway is a pathway in which one or more elements of the pathway are missing, but might be present later. A pathway might also be described as a potential exposure pathway if information on one or more of the elements of the pathway is missing. An eliminated exposure pathway is one in which one or more of the elements is missing and will not be completed in the future. For a population to be exposed to an environmental contaminant, a completed exposure pathway must be present (10). If any one or more of these elements are missing, then there is no exposure, though the presence of contamination might still be significant and require remediation. This is especially true if there is a possibility of an incomplete exposure pathway becoming complete in the future.
The source of the contaminants in all pathways for this site are the mine tailings and associated AMD at the Leviathan Mine Site and downstream of the site. AMD from the site has migrated off the Leviathan Mine Site as far downstream as the East Fork of the Carson River (approximately 10 miles). Media of concern include surface waters, sediment, fish, wild game and fowl, plants, and beef cattle raised on River Ranch.
CDHS has identified two completed pathways and seven potentially completed pathways in the vicinity of the Leviathan Mine Site. The completed pathways, summarized in Table 6, are briefly described below and evaluated further in the public health implications section. The potentially completed pathways are summarized in Table 7 and described below.
Based on current information and understanding about the Leviathan Mine, no pathways can be eliminated at this time.
The wading and swimming pathway is considered a completed exposure to adults and children wading or swimming in Leviathan, Aspen and Bryant creeks, as well as the River Ranch Irrigation Channel in the past, present, and future, except for future exposure at Bryant Creek and the River Ranch Irrigation Channel (see potential pathways).
The surface water consumption pathway is considered a completed exposure to adults and children that drink surface waters from Leviathan, Aspen or Bryant creeks, as well as the River Ranch Irrigation Channel in the past, currently, and in the future, except for future exposure at Bryant Creek and the River Ranch Irrigation Channel (see potential pathways). These pathways will be evaluated further in the toxicological evaluation section.
The consumption of plants contaminated by AMD from Leviathan Mine is currently considered to be a potentially completed pathway because there is insufficient information to determine if plants collected in the area accumulate metals from Leviathan Mine. Information in the scientific literature indicates that some plants accumulate certain metals. Further complicating this picture is the fact that the uptake of metals is very dependent on soil pH. As the soil becomes more acidic, the potential for metals to be absorbed by the roots of the plant increases (17). In addition, the floodplain of affected creeks could also be of some health concern because flooding by AMD-contaminated waters could contaminate soils and plants in the floodplain.
Information about plant use in the area is very limited mainly because the Washoe Tribe is reluctant to provide details about their collection practices in the area. The way the plants are used or consumed will affect the exposure dose that an individual receives from metals that might be in or on the plants. In addition, exposure to contamination from Leviathan Mine can result from soil or dust accumulated on the plants. In some instances the highest potential risk at sites contaminated with heavy metals is from eating soil or dust remaining on plants. Eliminating carryover soil from plant materials as well as from clothing and hands is an important step in preventing exposure to these contaminants (18).
Based on the limited information available, CDHS cannot currently assess the potential health risks from consuming or otherwise using plants collected from areas on which Leviathan Mine has had an impact. Therefore, the consumption of plants from areas affected by Leviathan Mine is considered a potentially completed pathway.
Because fish have the potential to accumulate some of the contaminants from the Leviathan Mine Site in their tissue, it is possible that AMD contaminants could get into fish tissue and then be consumed by humans and potentially cause adverse health effects. This pathway is of particular significance for those metals which might bioaccumulate (e.g., cadmium). Reported bioconcentration factors for cadmium range from 113 to 18,000 for invertebrates and from 3 to 4,190 for fresh water aquatic organisms (19). A bioconcentration factor is a value that describes the degree to which a chemical can be concentrated in the tissues of an organism
There is currently only one fish tissue sample pertaining to the Leviathan Mine Site. This sample was collected approximately 10 miles downstream of the site and is therefore not likely to represent concentrations of contaminants in fish in Bryant Creek and other creeks closer to the Leviathan Mine. Because of limited data, this particular pathway cannot be evaluated further at this time. Fish tissue data is required to make any assessment about possible health effects from AMD impacts on fish and fish consumption by humans.
Based on available information the majority of shallow groundwater at the Leviathan Mine appears to travel toward Leviathan Creek and likely discharges in Leviathan and Aspen creeks. However, current understanding of the local groundwater is not comprehensive and no investigations have determined the condition or movement of deeper groundwater in the area. Therefore, movement of Leviathan Mine contaminants downgradient of the site cannot be eliminated as a possibility. Therefore, the future consumption of groundwater from private wells is considered a potentially completed exposure pathway.
The beef consumption pathway refers to the potential for the migration of metal contaminants from Leviathan Mine AMD into the food chain through beef cattle raised at the River Ranch that drink contaminated waters and consume crops irrigated with AMD-contaminated water.
It is possible that some of the contaminants in the AMD have reached the ranch and have affected the cattle. Whether this has had a health effect on the cattle is unclear. Furthermore, the effect on humans who consume beef from cattle produced on the ranch is unknown because of a lack of data. Therefore, the consumption of beef raised at the River Ranch is considered a potentially completed exposure pathway.
The consumption of wild game and fowl pathway refers to the potential for the migration of contaminants from AMD into the food chain through deer and other wild game that drink contaminated waters and consume plants or other animals impacted by AMD-contaminated water. For example, if a deer were feeding on plants that grow in an AMD-contaminated floodplain, metals that might have made their way into plants could be absorbed by the deer. If the deer were then eaten by humans, those people could be exposed to the metals the deer consumed. Because of an absence of data on game uptake of metals from the mine and uncertainties about wildlife migration and feeding patterns, it is not currently feasible to assess the health risks that game and fowl might present to potential consumers. Therefore, this is considered a potentially completed exposure pathway.
The inhalation of dust from Leviathan Mine pathway is currently considered to be potentially completed because there is insufficient information to determine if contaminants near the mine are in the air at levels that could be a health concern. Although conditions at the site appear to be safe for site workers, the conditions off site have not been addressed. Some of the roads to the mine reportedly were built using rubble from the mine site. Arsenic is of particular importance for the inhalation pathway because it is an inhalation carcinogen. No air samples have been collected along the roads that provide access to the site and might have been improved or augmented with the use of waste rock from Leviathan Mine.
Concern about the quality of the roadbed materials is compounded by the possibility of AMD being used on the roads. According to the LRWQCB's 1975 Report on Leviathan Mine (2), "Water from the ponding of seepage is being used on the roads ". This suggests that contaminants at the mine could be present on the roads that provide access to the area. Without lower detection limits on sampling events and some assessment of potential risk from dirt roads, it is not currently possible to determine if the dust inhalation pathway is completed or eliminated for areas near the mine. Therefore, this is considered a potentially completed exposure pathway.
The wading and swimming pathway is considered a potentially completed exposure for adults and children wading or swimming in Bryant Creek and the River Ranch Irrigation Channel in the future because concentrations of contaminants are decreasing to levels that fall below health concern for these activities.
The surface water consumption pathway is considered a potentially completed exposure to adults and children that drink surface waters from Bryant Creek and the River Ranch Irrigation Channel in the future because concentrations of contaminants are decreasing to levels that fall below health concern for these activities.
In evaluating health effects, several factors determine whether harmful effects will occur and the type and severity of those health effects. These factors include the dose (how much), the duration (how long), the route by which people are exposed (breathing, eating, drinking, or skin contact), the other contaminants to which they might be exposed, and their individual characteristics such as age, sex, nutrition, family traits, lifestyle, and state of health.
The following sections include an analysis of the potential health impact, both cancerous and non-cancerous, to recreational users and Washoe Tribal Members who might drink surface water, wade, or swim in Leviathan, Aspen and Bryant creeks or the River Ranch Irrigation Channel. General discussion about exposures to the contaminants of concern is included in Appendix C- Toxicological Summaries for Chemicals.
The approach used to evaluate potential non-cancer health effects to an individual or population assumes that there is a level of exposure below which non-cancer, adverse health effects are not likely to occur, called the threshold level or toxicity value. This approach compares a dose estimate with the toxicity value. The dose estimate is a calculated estimate of the amount of contaminant in contact with, or taken up by, the exposed person and is expressed as milligrams of contaminant per kilogram of body weight per day (mg/kg/day). When the dose estimate for a contaminant exceeds the toxicity value for that contaminant, there might be concern for potential non-cancer, adverse health effects as a result of exposure to that contaminant.
In order to determine whether adverse health effects are possible as a result of exposure to a contaminant, an exposure dose must be estimated for each completed pathway. This exposure dose can then be compared with appropriate toxicity values in order to evaluate the likelihood of adverse health effects occurring. Toxicity values used to evaluate non-cancer adverse health effects include ATSDR's minimal risk level (MRL) and EPA's reference dose (RfD) for ingestion and reference concentration (RfC) for inhalation. The MRL and RfD values are estimates of daily human exposure (mg/kg/day) to a contaminant below which non-cancer, adverse health effects are unlikely to occur.
The MRL and RfD only consider non-cancer effects. Because they are based only on information currently available, some uncertainty is always associated with the MRL and RfD. Uncertainty factors are used to account for the uncertainty in our knowledge about the hazards of a chemical. For example, many of these values are based on animal studies and a conservative safety factor is applied to assure that human populations are adequately protected. The greater the uncertainty, the greater the uncertainty factor and the lower the MRL or RfD.
MRLs are classified as either acute, intermediate, or chronic. Acute MRLs are developed for exposures of up to 14 days; intermediate exposures are between 15 and 364 days; and chronic exposures are greater than 365 days.
To evaluate the cancer risk posed by some chemicals, the increased lifetime cancer risk was calculated. This risk is called an increased risk because the value that is calculated represents an increase in the number of expected cases of cancer over and above the normal background cancer rate in the general population of 1 in 4 (25%, or 250,000 cancers per 1 million people). Thus, an increased lifetime cancer risk of 1 in 1 million (or 1 x 10-6) means that in a population of 1 million people, 250,001 cases of cancer would be expected, with only 1 case potentially caused by exposure to the COC.
The National Toxicology Program (NTP), the International Agency for Research on Cancer (IARC), and EPA have reviewed available information from human and/or animal studies to determine whether certain chemicals are likely to cause cancer in humans. The potential for cancer to occur in an individual or a population is evaluated by estimating the probability of an individual developing cancer over a lifetime as the result of the exposure. EPA has developed oral slope factor (OSF) values for many carcinogens. An OSF is an estimate of a chemical's potential for causing cancer.
IARC considers both arsenic and cadmium to be carcinogenic to humans. Arsenic was the only COC that was put through carcinogenic risk calculations because it is the only known carcinogen associated with Leviathan Mine that has an established OSF. Ingesting arsenic has been reported to increase the risk of cancer in the liver, bladder, kidneys, prostate, and lungs (20).
The Department of Health and Human Services (HHS) has listed nickel as reasonably anticipated to be a carcinogen. However, no OSF has been derived for nickel. Therefore, nickel was not assessed for potential cancerous risk. Studies with dogs and rats have found that ingestion of nickel at levels very much greater than levels normally found in food and water have caused lung disease and affect the stomach, blood, liver, kidneys, immune system, and reproduction and development in rats and mice (21).
Based on limited human data and studies on rats, HHS has determined that cadmium and cadmium compounds might reasonably be anticipated to be carcinogens. EPA has determined that cadmium is a probable human carcinogen by inhalation (19). Studies of humans and animals that eat or drink cadmium have not found increases in cancer. However, additional research is needed to be more certain that eating or drinking cadmium definitely does or does not cause cancer (19). Skin contact with cadmium is not known to affect the health of people or animals because virtually no cadmium can enter the body through the skin under normal circumstances (19). CDHS is currently unable to assess the cancer risks from exposure to cadmium detected in surface waters and sediment because there is no OSF for cadmium.
The increased lifetime cancer risk is calculated from the OSF for that chemical and the dose an individual or population is estimated to receive. A slope factor is an estimate of a chemical's potential for causing cancer. The OSF, in turn, is calculated from the slope of the dose-response curve for the chemical in question. The increased lifetime cancer risk from exposure to a given chemical is calculated by multiplying the daily dose of the chemical by the OSF (Tables 8 and 9). The total increased lifetime cancer risk is calculated by adding together the cancer risk for the individual chemicals.
The Children's Health Issues section is designed to emphasize both recognition of, and response to, the special needs of infants and children. This additional emphasis is given to children because they are at greater risk for certain exposures than adults. The greater risks faced by children are related to several differences between children and adults. For example, children are smaller, and therefore can be exposed to higher levels of contaminant per body weight. Also, permanent damage to children can result from exposures that occur during critical developmental and growth periods. In this health assessment, exposure doses to children are evaluated as a portion of the analyses for each completed exposure pathway. In particular, CDHS made efforts to incorporate child surface area exposed to sediments impacted by Leviathan Mine.
The pathway analyses identified two completed exposure pathways (Table 6). Based on a review of the concentrations of contaminants in surface water to comparison values, aluminum, arsenic, cadmium, iron, manganese, nickel, and thallium are all considered COCs. Therefore, the non-cancer health effects of exposure to these COCs and the cancer risk from arsenic are evaluated for exposure to surface waters and sediment for creeks affected by AMD from Leviathan Mine.
Because the majority of the surface water data collected near Leviathan Mine is dissolved data, CDHS made efforts to compare dissolved data through the years to be consistent and to utilize the most data possible. Additionally, dissolved metal concentrations more closely approximate the fraction of metal in the water column that is bioavailable (22), so CDHS used dissolved concentrations of contaminants whenever possible in the assessment of health effects as they relate to Leviathan Mine. However, surface water data from early sampling events did not typically specify whether the analyses performed were for total or dissolved metals. Therefore, historical exposure calculations might overestimate the actual historical risk. The cancer and non-cancer toxicological evaluations of the completed pathways are described below. See Table 8 and 9 for a summary of estimated exposure doses.
CDHS intentionally used conservative estimates and assumptions in the toxicological evaluation to ensure that any potential health hazards from COCs are recognized. For evaluation of the complete exposure pathways in this health assessment, the exposure assessment will assume:
- 30-year duration for non-cancer effects;
- 70-year duration for cancer effects;
- populations exposed to the mean concentrations presented in data Tables (1-10) unless otherwise indicated; and
- concentrations reported for surface waters represent concentrations that are completely bioavailable.
See Table 10 for additional parameters, assumptions, and values used in the risk evaluation.
The wading pathway involves dermal contact exposures from the contaminated surface waters and sediments. The direct contact of a chemical with the skin (dermal contact) can lead to adsorption of a chemical. The ability of a chemical to penetrate the skin is measured by the permeability constant (Kp). The ability of a chemical to penetrate the skin is also a function of the concentration of the chemical in the medium of interest, the surface area of the body which is exposed to the chemical, the part of the body exposed, and the length of time the chemical is in contact with the skin.
The International Agency for Research on Cancer (IARC) considers both arsenic and cadmium to be carcinogenic to humans. Arsenic was the only COC that was put through carcinogenic risk calculations because it is the only known carcinogen associated with Leviathan Mine that has an established OSF. Ingesting arsenic has been reported to increase the risk of cancer in the liver, bladder, kidneys, prostate, and lungs (20).
In the wading scenario, CDHS assumed that children and adults wade in streams near the site for 5 days per week of a 12-week-long summer when temperatures are highest and people are most likely to be in the water. However, this scenario is only one of many possible exposure scenarios because people might spend time in these waters at different times of the year. Currently, there is no way to define the average and maximum days of exposure because use patterns for the area are unknown. CDHS has made multiple attempts to get additional information about tribal uses in the area, but has not been successful.
Therefore, CDHS has made conservative estimates of how people might use the area. Based on these assumptions, CDHS estimated wading risk based on 60 days of wading exposure per year in surface waters downstream of Leviathan Mine. Wading calculations use the 50th percentile for adult surface area of the lower leg, feet, hands, and head (6160 cm2) (23). The surface area of the head is included in these calculations because, according to the Washoe Tribe representatives, Washoe Tribal Members that hunt and gather in the area practice bathing rituals with surface waters before they hunt that would usually include washing of the face. The wading calculations also assume that the lower legs and feet are exposed to sediment during wading.
In the past when concentration of contaminants were higher, the increased cancer risk for adults associated with the estimated exposure dose for arsenic via the wading pathway ranges from less than 1 additional cancer case in 1 million individuals from wading in Aspen Creek to 50 additional cancer cases in 1 million individuals from wading in Leviathan Creek. These exposures represent no apparent increased cancer risk to low increased cancer risk. However, when estimating risk based on the maximum detection of arsenic at the mine, the risks rise to 1,200 additional cancer cases in 1 million individuals, which would be considered a moderate increased cancer risk.
The estimated aluminum, arsenic, cadmium, manganese and nickel exposure doses for adults and children wading in surface waters near Leviathan Mine did not exceed their respective dermal MRLs. Thus, non-cancer health effects are not likely to occur in children and adults wading in Leviathan, Bryant, and Aspen creeks, as well as the River Ranch irrigation diversion from al arsenic, cadmium, manganese, and nickel exposure.
According to the Washoe Tribe of Nevada and California, some Washoe Tribal Members spend considerable time in areas near the mine. Washoe Tribal representatives indicated to CDHS that individuals might spend as much as a month at a time in these areas and might do this more than once per year. This information suggests that individuals could spend as much as 60 days per year in areas around Leviathan Mine. Based on this information and the fact that some areas of the creeks are difficult to access and very shallow, CDHS estimated that most, if not all, visitors to the area would swim in creeks downstream of Leviathan Mine a total of 24 days or less per year. CDHS assumes the 24 days of swimming will occur in the warmest 3 months (12 weeks) of the year and that swimmers will average 2 swims per week (2 swims/week x 12 weeks/year = 24 swims/year). This estimate is considered very conservative because the national average for swimming is 7 days per year (24).
CDHS evaluated cancer and non-cancer effects to adults that might swim in Leviathan, Aspen, and Bryant Creeks and the River Ranch Irrigation Channel. Based on the estimates by CDHS, none of the child or adult doses from exposure to COCs from the mine site via swimming (sum of dermal contact with water + incidental ingestion) present non-cancer health concerns. All the estimates for doses are less than the associated MRL or RfD for the COCs (Tables 8 & 9).
The swimming pathway involves dermal contact exposures and incidental ingestion of contaminated water in Leviathan, Bryant, and Aspen creeks, as well as the River Ranch Irrigation Channel waters while swimming. CDHS assumed that most of the swimming would take place during the warmer summer months and that 100% of adult and child body surface areas were exposed to surface waters for 1 hour for each day of swimming for a total of 24 days.
Estimating swimming risk is complicated by the fact that many stretches of the creeks downstream of Leviathan Mine have are shallow (less than one foot deep), making swimming difficult. However, it should be noted that in the scenario where someone decided to swim in very shallow waters, the exposures and associated risks would be greater because of the exposure to sediment contaminants in addition to those in the water. Although many of the creeks CDHS observed during the site visit in summer 2001 had 10 inches of water or less. July and August are low flow periods for the creeks near Leviathan Mine. Thus, the observations made on the 2001 site visit are not necessarily representative of the creeks from month to month or from year to year. Therefore, CDHS chose to use conservative estimates about how the resources are used in the area and, specifically, how frequently people might swim in the area. Also, CDHS has not had the opportunity to survey the entire stretch of the creeks affected by Leviathan Mine contamination. CDHS is concerned about historical exposures, and because river beds change over time it is possible that areas that currently are fairly shallow might have had deeper pools in the past.
Risk calculations based on the maximum concentration of arsenic detected in surface water at the mine site (110 ppm) would represent a non-cancerous health risk. If someone were to swim at the mine site and were exposed to these levels of arsenic, the dose to a child (0.00681 mg/kg/day) and adults (0.00292 mg/kg/day) would greatly exceed the MRL for arsenic (0.0003 mg/kg/day) and non-cancerous adverse health risks could have occurred. However, this is true only in the mine adits and is not the case for downstream creeks.
Exposure to arsenic via swimming does present some cancer risks for areas downstream of the mine site. Based on average surface water concentrations from 1984 to 1995, the increased cancer risk for adults associated with the estimated exposure doses for arsenic via the swimming pathway (dose x oral cancer slope factor of 1.5) ranges from an estimated increase of 0.47 additional cancer cases in 100 million people for adults currently exposed to surface water at the River Ranch Irrigation Channel to 91.1 additional cancer cases in 1 million people for past exposure to surface water at Leviathan Creek (Table 5). These risks are considered no apparent increased risk of cancer to low increased risk of cancer.
The wading and swimming pathway considers the effects of both the wading and swimming in areas near Leviathan Mine. Because swimming in the creeks associated with Leviathan Mine is not possible without wading in the creeks, these two pathways were calculated separately and the risks added to more accurately represent the exposure.
When estimating the potential health risks from exposure to COCs via wading and swimming, CDHS assumed that every swim resulted in exposure to sediment. Because not every wading event would result in a swimming event, the swimming and wading exposures were calculated separately and then combined. Combining these exposures results in dose estimates to arsenic ranging from 0.00000043 mg/kg/day for adult exposure to current River Ranch Irrigation Channel waters to 0.000102 mg/kg/day for children exposed to historic arsenic exposure in Leviathan Creek (Tables 8 & 9). These exposure estimates are all below the MRL (0.0003 mg/kg/day) for arsenic. The other COCs were also below their respective MRLs and RfDs.
The carcinogenic risk from arsenic via the wading and swimming pathway ranges from 0.67 additional cancers in a population of 1 million for current adult exposures at the River Ranch Irrigation Channel to 246 additional cancers in a population of 1 million for historic exposures at Leviathan Creek (Tables 8 & 9). These risks are considered no increased risk for cancer and low increased risk for cancer, respectively.
The surface water consumption pathway involves exposures to adults and children that drink surface waters from Leviathan, Aspen or Bryant Creeks, as well as the River Ranch Irrigation Channel in the past, now, and in the future. According to the Washoe Tribe of Nevada and California, Washoe Tribal Members might spend as long as a month at a time in the vicinity of Leviathan Mine for hunting and gathering purposes. Based on this information, CDHS assumes that individuals in the area might drink surface waters affected by Leviathan Mine. As a conservative measure, CDHS assumed that individuals might drink surface waters affected by Leviathan Mine for every day during a 4-week (28-day) excursion in the area. This estimate is based on the likelihood that most people that use the area will not spend more than a month in the area and those that do will bring an alternate source of drinking water or will use surface water that has not been affected by the mine (e.g., Mountaineer Creek).
The risks associated with consuming surface waters varies depending on proximity to Leviathan Mine and when water was collected. Generally, exposures that occurred between the 1950s and 1985 appear to represent the greatest health risk because the AMD problems became more severe after open-pit mining operations began in 1951. Surface water conditions began to improve somewhat after the 1985 remedial interventions. The increased cancer risk for adults associated with the estimated exposure dose for arsenic via the drinking pathway ranges from 5.86 additional cancer cases in 1 million people for current consumption by adults of surface water at the River Ranch Irrigation Channel to 1,520 additional cancer cases in 1 million for children who drank surface water from Leviathan Creek in the past. These risks of cancer are considered to represent no apparent risk to moderate increased risk of cancer. Like all of the completed exposure pathways at the site, the closer one gets to Leviathan Mine, the greater the probability that concentrations of COCs will present a health risk.
Arsenic concentrations in surface waters at the mine site and in Leviathan Creek present exposure doses that are above the MRL for children and adults for current and historic exposures. Past and current exposure dose estimates for children and adults to arsenic are all estimated to be below the chronic MRL for arsenic (0.0003 mg/kg/day) for Aspen and Bryant Creeks and the River Ranch Irrigation Channel.
Arsenic damages many tissues including nerves, stomach, intestines, and skin. Non-carcinogenic health effects related to arsenic exposure might consist of nausea, vomiting, diarrhea, and irritation of the skin. See Appendix C for further information about arsenic and other COCs.
Based on CDHS estimations, concentrations of manganese in surface waters appear to present some non-cancerous health risks. CDHS estimates that current concentrations of manganese in Leviathan, Aspen, and Bryant creeks could present non-cancerous health risks. Exposure doses for adults and children are greater than the EPA acute RfD of 0.005 mg/kg/day for these locations and for historical exposure to manganese via drinking water pathway at Leviathan Creek (Tables 8 and 9).
Non-cancer health effects that one might experience from exposure to elevated levels of manganese include central nervous effects, respiratory irritation, and a condition called manganism. Manganism is characterized by feelings of weakness and lethargy, tremors, and speech disturbances.
Average aluminum concentrations collected from Leviathan Creek just below the mine site (27,000 ppb) were above the child intermediate EMEG of 20,000 ppb, but below the adult EMEG (70,000 ppb). However, upon further assessment, the concentrations of aluminum detected in surface waters do not represent a health concern.
Surface water samples collected between 1981 and 1983 had one detection of 4,400 ppb thallium at Leviathan Mine. This concentration would be of considerable health concern if people were drinking it and could cause cancerous and non-cancerous health risks. The average concentration of thallium detected between 1981 and 1983 was much lower (27 ppb). However, these concentrations would still be sufficient to cause an additional 3 to 4 cancers in a population of 100,000 people if these waters were being used for drinking water. This would be considered a very low increased risk of cancer. Exposure to concentrations of thallium above the MCL (2 ppb) for a short period of time can cause problems with the digestive and nervous systems. Exposure to concentrations of thallium above the MCL over a lifetime can cause hair loss, changes in blood chemistry, or damage to the liver, kidney, and digestive tract.
In some cases iron concentrations in surface waters exceeded the USEPA Region III Risk-based Concentration (RBC) for iron in tap water (11,000 ppb). However, upon review of potential exposure doses using the four weeks of surface water consumption exposure model, iron would not be expected to exceed the Region III provisional reference dose (0.3 mg/kg/day). Therefore, iron concentrations detected in surface waters near Leviathan Mine do not appear to present any health concern to occasional surface water consumers near Leviathan Mine.