PUBLIC HEALTH ASSESSMENT
MONTICELLO MILL TAILINGS (DOE)
AND
MONTICELLO RADIOACTIVELY CONTAMINATED PROPERTIES
(aka MONTICELLO VICINITY PROPERTIES)
There are two National Priorities List (NPL) sites in Monticello, San Juan County, Utah: the Monticello Mill Tailings Site (MMTS) and the Monticello Vicinity Properties (MVP). Both sites are associated with the Monticello Uranium Mill.
The Monticello Mill Tailings Site is a former uranium and vanadium processing mill. It is divided into three distinct operable units: the mill site tailings and mill site property; the peripheral properties; and surface water, groundwater, and contaminated sediments in Montezuma Creek Canyon. The mill posed a public health hazard when it was operating. The tailings that remain on the mill site would be a public health hazard today if the public had access to the mill site. However, access is strictly controlled: the mill site, therefore, does not pose a threat to area residents.
The Monticello Vicinity Properties are off-site residential and commercial properties. Land use of most of these properties is residential housing. The community will continue to be exposed to low-level radiation until remediation is complete. The remedial actions will eventually remove most of the contaminated soils within the residential community, thereby eliminating concerns about long-term exposure.
For the purpose of this public health assessment, on site describes the actual mill site itself and off site describes all other areas (vicinity and peripheral properties).
There are several sources of contamination in soils and buildings throughout the city of Monticello: the mill tailings which, in the past, were windblown into the city, were prevalent throughout the southeastern quadrant, and were also taken from the mill site and used as fill for open lands; backfill around water, sewer, and electrical lines; and sand mix in concrete, plaster, and mortar. As a result, residents have been exposed to low levels of radium-226 and radon-222. Department of Energy (DOE) representatives have surveyed and recommended for clean-up inclusion a total of 449 vicinity and peripheral properties (420 vicinity and 29 peripheral). Three hundred eighty-nine vicinity properties and 11 peripheral properties have been remediated.
Agency for Toxic Substances and Disease Registry (ATSDR) staff members believe that exposures were greater in the past than they are today. Industrial hygiene surveys of the mill performed when the mill was operating reported that conditions were very dusty and that many workers were exposed to levels of radioactive dusts above allowable concentrations. Analysis of the available health outcome data show that San Juan County has the highest rate of renal failure among women in the state, and limited evidence suggests that there is an increased risk of dying of lung cancer in Monticello compared with the risk for the rest of the county. There is no supporting information connecting these incidences to the mill site.
The largest risk to the general public stems from exposure to direct gamma radiation from unremediated soils in Montezuma Creek Canyon. However, this risk is relatively low and direct gamma radiation exposure exists mostly at or near natural background levels. The contamination of Montezuma Creek by surface runoff of tailings from the mill site creates a potential exposure pathway. The most likely exposure would occur if hunters consumed game animals that had entered the mill site or the Montezuma Creek floodplain and eaten vegetation or drunk water from either one of the areas. However, such exposures, if any, would have been intermittent and highly unlikely to have resulted in adverse health effects. In the fall of 1996 the Environmental Protection Agency (EPA) and Utah Department of Environmental Quality (UDEQ) staff conducted a study of the body burden of contaminants in tissues and organs of deer and cattle that consumed water and vegetation from the Montezuma Creek floodplain. Cattle and deer from a background reference area were also sampled. The meat, liver kidney, and ribs are being analyzed for radionuclides and nonradionuclide contaminants. Although the analyses have not yet been completed, preliminary results indicate little or no contaminant uptake in cattle or deer above the uptake in the reference area animals. Since 1993, drainage controls on-site have nearly eliminated surface water run-off contamination. Surface water run-on has been eliminated by a series of ditches that divert water around the mill site. Surface water on-site is collected and routed to a pond for treatment before release. The major contribution to surface water contamination is leachate in groundwater that enters Montezuma Creek downgradient from the mill site. Also, the shallow alluvial aquifer is contaminated with uranium-234 and uranium-238 at levels of public health concern, but there are no known private wells associated with the aquifer and currently in use. ATSDR representatives recommend that local ordinances be established to prevent future installation of wells into the contaminated alluvial aquifer.
Monticello is in the geographic center of San Juan County. San Juan County covers a very large and sparsely populated area of southeastern Utah. With a total area of more than 7,800 square miles, the county is slightly larger than New Jersey, but its 1990 population was only 12,621. At 2.74 square miles, Monticello is the largest town in the county in terms of its area. More than half the population of San Juan County is Native American. Monticello's 1990 population was slightly more than 1,800.
The off-site area, the vicinity and peripheral properties, is being considered for follow-up public health actions. Exposure to contaminants from past and current activities at the MMTS suggests the need for health studies and further education efforts. ATSDR staff will conduct a needs assessment as a basis for determining the appropriate preventative health education plan for the sites. We will identify the public health problems, community concerns, health professional and community-specific needs, and primary target populations for health education. Special needs groups, such as children, minorities, and the elderly, will be noted. ATSDR staff plan to collaborate with state and local health departments.
A. Site Description and History
The Monticello Mill Tailings Site is a 110-acre abandoned uranium and vanadium processing mill in the city of Monticello, San Juan County, in southeastern Utah. The Monticello Vicinity Properties are off site residential and commercial properties. Both of the sites are associated with the Monticello Uranium Mill. The United States Department of Energy (DOE) owns the mill site (see Appendix F, Figure 1). The City of Monticello, private residents, and the state of Utah Highway 191 right-of-way own the land that borders the mill site. No residences are within the mill site boundary, but residences are adjacent to the north and east edges of the mill site (1).
Operating History
The Vanadium Corporation of America opened a vanadium ore-buying station at Monticello in late 1940 and began mill construction in 1941. In 1943, Vanadium Corporation began producing a uranium-vanadium sludge for the Manhattan Engineer District (1).
Construction of the Monticello plant, in addition to the mill proper, included the development of an adequate water supply, installation of a power plant, and construction of two large housing projects for workers. The staff town site, on the hill opposite the mill, consisted of a staff house for 12 men, a manager's house, and 14 4-room family dwellings. The other housing project consisted of 32 2-room family houses and a bunkhouse and boardinghouse for 32 men (2).
Intermediate owners and operators of the Monticello Mill Tailings Site included the War Assets Office; the Atomic Energy Commission (AEC); American Smelting and Refining Company; Galigher Company; Lucius Pitkin, Inc.; National Lead Company; the Bureau of Land Management (BLM) (acquired the mill site by means of a land transfer, never operated the mill); and the DOE. Mill operations were terminated on January 1, 1960. The ore-buying station remained open until March 1962 . Remediation work on the site is still being done today (1).
Milling processes used at Monticello during the 11 years of AEC operation included raw ore carbonate leach, low-temperature roast/hot carbonate leach and salt roast/hot carbonate leach until 1955, acid leach resin-in-pulp and raw ore carbonate leach from 1955 to 1958, and a carbonate pressure leach resin-in-pulp process from 1958 until mill closure in 1960 (1).
The mill tailings were stabilized between 1961 and 1962, and the plant was dismantled in 1964. Removal of contaminated soils from the ore-buying stations occurred between May 1974 and August 1975 (1, 3).
Remediation Activities
In 1978, the United States Department of Energy (DOE), under the authority of the Atomic Energy Act, initiated the Surplus Facilities Management Program to assure safe caretaking and decommissioning of government facilities that had been retired from service but still had radioactive contamination. The Monticello Mill Tailings Site was accepted into the Surplus Facilities Management Program in 1980. The Monticello Remedial Action Project was then established to restore the government-owned mill site to safe levels of radioactivity, to dispose of or contain the tailings in an environmentally safe manner, and to perform remedial actions on off-site vicinity properties that had been contaminated by radioactive material from the mill operations.
In 1983, remedial activities for vicinity properties were separated from the Monticello Remedial Action Project with the establishment of the Monticello Vicinity Properties Project. The Grand Junction (Colorado) Projects Office of the Department of Energy conducts both the Monticello Remedial Action Project and the Monticello Vicinity Properties Project (1).
There are two National Priorities List (NPL) sites in Monticello, the Monticello Mill Tailings Site (MMTS) and the Monticello Vicinity Properties (MVP). Both sites are associated with the Monticello Uranium Mill. The Environmental Protection Agency (EPA) formally included the MVP and the MMTS on the NPL on June 10, 1986, (4) and November 16, 1989, respectively (3). The sites are being remediated in accordance with the Monticello Vicinity Properties Project November 1989 Record of Decision and the Monticello Mill Tailings Site August 1990 Record of Decision.
Mill tailings and associated contaminated material remain on the mill site as a result of milling ore to recover uranium and vanadium. Tailings particulate material has been blown by the wind and carried by surface water to off-site properties, over time. The tailings piles have been covered and vegetated to prevent further windblown dispersion of contaminants.
The MMTS is divided into three distinct operable units:
| Operable Unit I Operable Unit II Operable Unit III |
Mill Site Tailings and Mill Site Property Peripheral Properties Surface Water, Groundwater, and Contaminated Sediments in Montezuma Creek Canyon (4, 5) |
The remedial actions planned for these operable units are interdependent.
The August 1990 Monticello Mill Tailings Site Record of Decision addresses the remedial actions for Operable Units I and II. A record of decision will be prepared for Operable Unit III after remedial actions for Operable Units I and II are initiated and additional monitoring data for groundwater and surface water are collected.
The mill site consists of the former locations of the mill and residential areas, covering 32 acres, the tailings-impoundment area, covering 68 acres, and the former BLM property, covering 10 acres. The land that the BLM occupied was originally part of the mill site, but that land was deeded back to DOE in 1992. An estimated 100,000 cubic yards of contaminated material has been identified in the mill area, and approximately 1.4 million cubic yards (2 million tons) of tailings, contaminated soil, by-product material, and contaminated building material is located in the tailings-impoundment area (4). Appendix F, Figure 2, depicts the mill site property, associated buildings, and tailings piles.
The tailings are stored in four piles:
The peripheral properties are adjacent to the DOE property but are owned by other individuals or entities. During the period of mill operation, mill operators leased private land north and south of the existing mill site to stockpile ore. The former ore-stockpile areas and other adjacent areas contaminated by windblown and water-borne tailings cover approximately 300 acres around the mill site and contain most of the estimated 300,000 cubic yards of peripheral property material to be remediated. Peripheral properties also include the bed and banks of a 3.3-mile reach of Montezuma Creek between the city of Monticello and Vega Creek (4).
The Monticello Vicinity Properties (MVP), also referred to as the Monticello Radioactively Contaminated Properties, are off-site residential and commercial properties. Land use of most of these properties is residential housing. Adjacent land usage includes heavy and light commercial use and a "controlled" zoning district that allows a mix of agricultural, residential, industrial, and commercial use (3).
Throughout the operating period of the Monticello Uranium Mill, mill tailings from the mill site were windblown into the city of Monticello or used in construction in the city of Monticello. Windblown tailings contamination is prevalent throughout the southeastern quadrant of the city. The tailings were used as fill for open lands; backfill around water, sewer, and electrical lines; sub-base for driveways, sidewalks, and concrete slabs; backfill against basement foundations; and sand mix in concrete, plaster, and mortar. The total tonnage of uranium mill tailings removed from the mill site for construction purposes was never documented. However, contaminated material from the vicinity properties is estimated at 156,000 cubic yards. The removal of contaminated tailings from the mill site was restricted in August 1975, when a fence was erected around the mill site to prevent unauthorized access and the ore-buying stations were cleaned up. Appendix F, Figure 3, outlines the MVP project area and shows the adjacent mill site location (3).
Remediation began in 1984, and Appendix F, Figure 4, depicts the status of the Monticello Vicinity Properties as of February 1995.
According to the EPA Region VIII Hazardous Waste Management Division Five-Year Review (Type Ia) document, 420 individual properties were included in the Monticello Vicinity Properties (MVP) Site as of December 1996. This document covers the first 5-year review period from 1991 through 1996. DOE is the responsible party for remediating the MVP and is further responsible for certifying that the remediation is completed at each of the properties. These 420 individual properties are grouped into eight operable units, designated A through H. These operable units are defined for administrative convenience and, except for Operable Unit E, do not imply geographic proximity of individual properties to each other. For fiscal year 1996, 14 remedial actions were completed and by the end of 1996, 389 properties were remediated on the MVP Site. There are an additional 29 peripheral properties. As of May 1997, 11 peripheral properties were remediated (5, 6).
The MVP is divided into 8 distinct operable units (OU):
Operable Unit B. OU B consists of 243 properties. As of December 13, 1996, construction was complete at 237 properties; 3 properties were under construction; and 3 properties did not require remedial action.
Operable Unit C. OU C consists of 34 properties. Contamination is traceable to uranium milling at Dry Valley, Utah, or to other sources not associated with the Monticello Uranium Mill. As of December 13, 1996, construction was complete at 32 properties; 1 property was scheduled to be remediated; and 1 property did not require remedial action.
Operable Unit D. OU D consists of six properties. These are properties on which nonradiological hazardous substances are known or suspected to exist. As of December 13, 1996, construction was complete on three properties and three properties were under construction.
Operable Unit E. OU E consists of eight properties. These properties are crossed by Halls' Ditch, an irrigation ditch that passes through the mill site. As of December 13, 1996, remedial action was in progress on these properties.
Operable Unit F. OU F consists of ten properties. As of December 13, 1996, construction was completed on 4 properties. Owner negotiations are complete on 3 of the properties. The remaining 3 properties are still in negotiation.
Operable Unit G. OU G consists of ten properties. As of December 13, 1996, construction was completed on 3 properties. Remediation will not be required on one property because contamination does not exceed standards. The remaining 6 properties are either in design or scheduled for construction.
Operable Unit H. There are five properties being considered for supplemental standards within the MVP site. One of the properties is privately owned and the owner has requested DOE not to proceed with the remedial action due to the environmental degradation that will result from the cleanup work. Four of the properties are associated with the Highway 191 embankment where the cost of remediation may be excessive compared to the reduction in risk achieved by remediation. Supplemental standards are also being considered for city streets and utilities within the MVP site boundary. On December 23, 1996, EPA and Utah Department of Environmental (UDEQ) concurred, with comment, on the use of supplemental standards at the proposed properties. Negotiations on specific issues are under way (5, 6, 7).
In January 1996, DOE proposed to the regulators to remediate soils in the upper part of Montezuma Creek Canyon, and to perform risk assessments to determine the need for remediation in the middle and lower parts of the canyon. These actions will remove the primary source of risk to human health in the canyon. DOE, EPA, and UDEQ decided to defer the decision for remedial action of the upper canyon until the risk assessments are finalized.
All surface contaminants posing an unacceptable risk to human health and the environment will be placed in the permanent repository immediately south of Monticello. In late May, 1997, DOE began placement of approximately 2.3 million cubic yards of mill tailings and other contaminated materials in the recently completed repository. Excavation has begun on the Carbonate Tailings Pile on the north side of the former mill site. The excavation and transportation of the tailings should be in full swing by June 20, 1997. The excavation and hauling will be conducted 7 days per week, 12 hours per day. The excavation activities will be completed by November 1998.
The Agency for Toxic Substances and Disease Registry (ATSDR) released the Monticello Mill Tailings and Monticello Radioactively Contaminated Properties (aka Monticello Vicinity Properties) Public Health Assessment for public comment on December 20, 1996. The official comment period ended on February 21, 1997. Several new DOE documents have been released and become available during the finalization of this public health assessment. ATSDR scientists requested, received, and reviewed these documents. These documents did contain in-depth valuable information. ATSDR updated the conclusions and recommendations of this document to reflect this more recent information.
Following is a synopsis of the newly released documents:
Operable Unit III Baseline Human Health Risk Assessment, March 1997--This document illustrates that when the risk is characterized in terms of the potential numbers of persons exposed, added cancer mortality associated with exposure to Operable Unit III contaminants is unlikely and would be indistinguishable from the background cancer mortality rate (8).
Operable Unit III Alternatives Analysis, Draft, May 1997--The purpose of this alternatives analysis is to identify and evaluate remediation alternatives for soil and sediment in the vicinity of Montezuma Creek, which is part of Operable Unit III of the Monticello Mill Tailings Site. This report is being prepared to support a non-time-critical removal action. A removal action is being pursued so an expedited remediation decision can be made for soil and sediment. Recommended removal actions for each reach of Montezuma Creek (Upper, Middle, and Lower) will be included in the future draft final and final versions of the document. The state will review the draft Alternatives Analysis Report and provide input on the alternatives. Input from the state will be incorporated under "State Acceptance" in the Draft Final Alternatives Analysis Report. DOE staff will then hold a landowner briefing to get input on the alternatives from the property owners. After input from the state and the landowners is incorporated into the Alternatives Analysis Report, the risk managers (i.e., DOE, EPA, and the state of Utah) will select recommended removal actions for soil and sediment in Upper, Middle, and Lower Montezuma Creek and present the information at a public meeting (9).
Operable Unit III Ecological Risk Assessment, Draft, June 1997--Only the aquatic community may be of "possible concern," although actual risks may be of "no concern." There is little likelihood that the Operable Unit III contaminants of concern are harming the other receptors. This conclusion is substantiated by the tissue sampling done for the cliff swallows (surrogate for the southwestern will flycatcher) and mule deer, which indicated that concentrations of contaminants of concern concentration in these tissues are not elevated. These findings need to be contrasted to short-term and long-term impacts to these receptors and their ecosystems that would occur during remediation. The potential impacts from remediation will be discussed in the alternative analysis for Operable Unit III soil and sediment (10).
ATSDR scientists will continue to review any future documents that become available. Should additional information become available that alters the findings of this public health assessment or addresses issues described herein, this public health assessment will be modified as needed.
ATSDR Activities
The Agency for Toxic Substances and Disease Registry (ATSDR) released a preliminary public health assessment for the Monticello Radioactively Contaminated Properties National Priorities List Site, more commonly referred to as the Monticello Vicinity Properties (MVP), in July 1988. The preliminary public health assessment concluded that the MVP site was of public health concern because of the risk to human health from exposure to hazardous substances. Assessors determined that people could be exposed during domestic uses of contaminated groundwater and by eating garden vegetables grown in contaminated soil. The document recommended that future environmental investigations be designed to address environmental and human exposure pathways.
ATSDR also released a site review and update (SRU) for the MVP in September 1992. The SRU concluded that although the community will continue to be exposed to low-level radiation until remediation is complete, the remedial actions will eventually remove most of the contaminated soils within the residential community, thereby eliminating concerns about long-term exposure from outside sources. However, there are properties in the community that may not be addressed by the current remedial actions for various reasons (i.e., properties whose owners have refused remediation, areas outside the 8-mile radius clean-up boundary, properties that contain naturally occurring radioactive materials (NORM), or properties where the brick veneer was left behind and, as a result, small sections of the community may continue to be exposed to low levels of radiation. The original clean-up boundary (6-mile radius) of the MVPs were those properties within the city limits. Peripheral properties generally lie outside the Monticello city limits. The new clean-up boundary extends to an 8-mile radius. DOE representatives, at the insistence of EPA and UDEQ, sent letters to all property owners within the 8-mile radius of the mill site. If owners suspected that tailings or materials from the mill site were on their property, they were requested to notify DOE. If contacted, DOE staff conducted radiological surveys of the property. Five additional properties have been included as a result of the surveys. Unless supplemental standards are approved, properties will be cleaned up to the 40 Code of Federal Regulation (CFR) 192.12 standard. EPA and UDEQ will consider supplemental standards (alternative clean-up levels including institutional controls) only if they are protective of human health and the environment. In November 1996, DOE released a draft final General Radiological Risk Assessment Methods document. The methods described in this document are intended for assessing exposure, dose, and risk for candidate supplemental standards properties. A risk assessment will be developed for each property using site-specific data, and these methods will be used to derive supplemental standards for evaluating response alternatives. If remedial actions are considered as a response alternative, the supplemental standards will serve as target performance goals. These methods provide supplemental standards that ensure overall protection of human health and the environment and compliance with applicable or relevant and appropriate requirements (11). EPA and UDEQ have no statutory requirement to clean up NORM. Property owners with such materials will be contacted and given the opportunity to have NORM disposed of in a repository.
The 1988 preliminary public health assessment discussed possible contamination of off-site groundwater and possible contamination of vegetables from home gardens as a concern at the MVP. The SRU concluded that groundwater contamination does not appear to be a problem at the MVP site, but does appear to be a concern at the MMTS. The Operable Unit III investigation addresses groundwater and surface water issues at the MMTS, and remediation of the soil should eliminate the possibility of contaminated vegetables. Currently, produce are not being grown within Operable Unit III or in the Montezuma Creek Canyon. The document recommended a health consultation to evaluate data on the disputed properties (disputed properties are no longer an issue, DOE representatives have agreed to remediate all properties inside the cleanup boundary), removal of tailings from the Monticello area, and naturally occurring radioactive materials such as rock collections. The document also recommended that workers for the City of Monticello use radiation detectors while conducting municipal improvements that require excavation of soils in areas where the soils have not been characterized for radioactivity (12).
ATSDR headquarters staff members and the ATSDR Region VIII representative conducted the first MMTS and MVP site visit July 20-24, 1992. They met with representatives of DOE; Chem-Nuclear Geotech; EPA Region VIII; other federal, state, and local environmental and health officials; and Monticello city officials. DOE and Chem-Nuclear Geotech staff members provided an overview and tour of the MMTS and the MVP.
Site visitors observed that small gardens are common in the community. Also, soils on and around the MMTS generally appeared to have some form of vegetation. The MVP locations were under remediation. The remediation debris from these off-site properties was being trucked to and then temporarily stored on top of the East Tailings Pile. Remediation workers were practicing dust-control measures to minimize redistribution of the contaminated material. City workers were improving the water system, and piles of soil marked areas where improvements were being installed throughout the community.
Staff members from the EPA's National Air and Radiation Environmental Laboratory (NAREL) and from Boston University (BU) accompanied ATSDR representatives on a second site visit, which took place from October 4 to 8, 1993. NAREL staff members helped ATSDR with radiation evaluation, and BU staff members helped to evaluate community health concerns and health outcome data. They met with representatives of DOE, RUST Geotech (formerly Chem-Nuclear Geotech), EPA Region VIII, and the UDEQ. ATSDR staff members also met with Monticello community members and city officials to gather community health concerns. ATSDR representatives performed an introductory orientation at two DOE-hosted public meetings. There were no significant observations other than those already mentioned in the background and history portions of this document.
ATSDR representatives conducted public availability sessions in Monticello and Blanding from December 7 to 8, 1993. ATSDR staff members met informally with individuals or small groups of community members during the trip and the public availability sessions, which helped to gather health information and collect community concerns. They interviewed approximately 160 community residents and concerned residents. A variety of questions and concerns were collected. Community members indicated that a group of concerned residents existed in the northwest quadrant of Monticello. These residents filed a lawsuit against the National Lead Company, the contractor that operated the Monticello Uranium Mill before the mill closed in 1960, for the multiple deaths of children from leukemia (13).
ATSDR and NAREL staff members provided information on radiation and health issues during
community information sharing sessions from April 24 to 27, 1995. They discussed what
radioactive materials, radiation, and contamination are; how we locate radioactive materials and
measure radiation; how we are exposed to radiation in our environment and from naturally
occurring radioactive materials inside the human body; the possible health effects of exposure to
radiation; and how we protect ourselves from radiation sources. They conducted 13 community
radiation and health information-sharing sessions in Monticello and Blanding. The audience
included community members, groups of students, Blue Mountain Dineh (Navajo), and White
Mesa Utes. Attendance at each session was as follows:
| Sessions 1 & 2 Session 3 Session 4 Session 5 Session 6 Session 7 Session 8 Sessions 9 & 10 Session 11 Session 12 Session 13 |
Blanding Elementary School = 650 students San Juan High School = 35 students Blanding Middle School = 10 students Blanding Community = 4 people Monticello High School = 40 students Monticello Community (Session A) = 4 people Monticello Community (Session B) = 6 people Monticello Elementary School = 325 students San Juan High School = 12 students Blue Mountain Dineh = 10 people White Mesa Utes = 2 people. |
C. Demographics, Land Use, and Natural Resource Use
Appendix A, Tables A1-A3, and Appendix F, Figures 5-9, present demographic information.
Monticello is in the geographic center of San Juan County, Utah. The city of Monticello was established in 1888 and was named for Thomas Jefferson's home in Virginia because of similarities in geography.
Data used in Appendix A, Tables A1-A3 and the following text are approximations from the 1990 Census of Population and Housing for San Juan County and Monticello (14). Figures 5-9 in Appendix F present demographic data extracted from the United States Bureau of the Census Topologically Integrated Geographic Encoding and Referencing (TIGER) system (15). The TIGER system was launched in 1983 to automate the mapping and other geographic activities required to support the bureau's censuses and surveys.
San Juan County covers a very large and sparsely populated area of southeastern Utah. With a total area of more than 7,800 square miles, the county is slightly larger than New Jersey, but its 1990 population was only 12,621. More than half the population of San Juan County is Native American. At 2.74 square miles, Monticello is the largest town in the county in terms of its area. Monticello's 1990 population was slightly more than 1,800. In contrast to the population of the county as a whole, more than 87% of Monticello's residents are white; 12.3% are of Hispanic origin. Persons of Hispanic origin may be of any race. Extraordinarily high percentages of the population for both the city, 41.4%, and the county, 43.3%, are under age 18.
There were 3.26 persons per household in Monticello in 1990, which is well above the national average of about 2.6 but is consistent with the town's large percentage of persons under age 18. (A household is an occupied housing unit, but the definition does not include such group quarters as military barracks, prisons, and college dormitories.) Nearly 80% of Monticello's households are owner-occupied, which suggests a stable, nontransient population. Homeowners tend not to move as often as do renters. The cost of housing in isolated rural areas is typically much lower than in metropolitan areas. What appears to be relatively low mean value of owner-occupied housing ($55,300) and rent paid for renter-occupied housing ($199 per month) in Monticello is consistent with that fact.
The median household income is $25,787, and the per capita income is $8,615 for Monticello. San Juan is one of the nation's poorest counties, with 36.4% of the population below the poverty level. Monticello has a poverty rate of 12.6%. More than three-fourths of Monticello residents aged 25 and older have a high school equivalency or higher educational background, which indicates a relatively well-educated community.
San Juan County, the largest county in Utah, comprises 5,045,760 acres, most of which is sparsely populated rangeland and forest. Most county land is managed by either the federal government or the Navajo Indian Nation. The U.S. Forest Service (Manti-La Sal National Forest), the Bureau of Land Management (San Juan District Office), and the National Park Service manage approximately 61% of the land in the county, and the Navajo Indian Reservation encompasses another 25% along the county's southern border. The state of Utah administers 6%, and less than 1% of that 6% is owned by cities and the county. The remaining 8% is privately owned land, located primarily in Monticello and Blanding (1).
Historically, the primary uses of county lands have been mining, farming/ranching, and recreation (e.g., camping, hiking, and hunting). Mining in Utah, as in other western states, is subject to supply and demand, and thus has been cyclical. Oil, gas, and uranium are the primary mineral resources of interest in the county. Utah is the fourth largest U.S. producer of oil and gas, although no major oil or gas fields are located in the immediate vicinity of Monticello (1).
Uranium ores have been found locally in approximately half of the county, including areas close to Monticello. However, the uranium market has been depressed since 1982, and White Mesa Mill is the only active uranium processing facility in the county (1). Since 1995, White Mesa Mill has been the only active mill in the United States.
Farming and ranching, the latter primarily cattle and sheep grazing, are common throughout the county. A total of 213 farms and ranches use approximately 8% of county land (411,693 acres) for agricultural purposes (1).
Most recreational use occurs in the many parks, forests, and proposed wilderness areas, a number of which are relatively close to Monticello. The largest of the parks is Canyonlands National Park. The South Unit entrance of Canyonlands is 15 miles north of Monticello. Lake Powell is approximately 100 miles southwest, with approximately 1,000 miles of its coastline in San Juan County (1).
Five zoning districts have been established within San Juan County: multiple-use, agricultural, rural residential, controlled, and Indian reservation. Within the city limits of Monticello, areas have been zoned for heavy and light commercial use and for residential use. Commercial zoning along the major thoroughfares of Monticello, U.S. Highway 191 and U.S. Highway 666, has established a central business district. Commercial growth has occurred to the north and east, radiating from the center of town along those routes. Heavy commercial (formerly industrial) zoning exists in the southeastern corner of the city. The mill site and tailings piles lie south of this area, within a controlled district that permits a mix of agricultural, residential, industrial, and commercial use. Several residences have been built east and immediately north of the mill site, but otherwise most of the land is nonresidential. Alfalfa for livestock feeding is grown immediately east of the mill site. Land to the south is marginal for grazing (11).
All domestic surface water resources for the Monticello area are upgradient from the mill site. The City of Monticello public water system draws from two sources: the springs located on the flanks of the Abajo Mountains and the Monticello Reservoir on South Creek 1 mile southwest of the mill site. The raw water from those sources is treated, stored, and used as the public drinking-water supply, with the current treatment capacity of the public water system at 1.2 million gallons per day. The municipal distribution system has 650 residential and commercial connections, serving 2,000 people (16).
Blue Mountain Irrigation District has a permit to irrigate approximately 1,000 acres with surface water diverted from South Creek. A ditch originating at South Creek upgradient of the mill site diverts water to irrigation sites east of Monticello. The irrigation season begins April 1 and ends around mid-July, when surface water ceases to flow in South Creek. Montezuma Creek runs through the mill site, and return flow of irrigation water to Montezuma Creek occurs downstream from the tailings area. Additional water rights permit downstream landowners to draw agricultural irrigation water from Montezuma Creek. The creek provides drinking water for livestock (1).
b. Groundwater
The source of potable water (water used for drinking, cooking, showering, etc.) for those people living outside the city of Monticello is predominantly groundwater. Private groundwater wells penetrate the Dakota Sandstone Aquitard (a geological formation that impedes groundwater flow from one aquifer to another) and draw water from the lower Burro Canyon Aquifer. The shallow (upper) alluvial aquifer is currently not used as a potable water source (16).
Groundwater is also used for irrigation in the Montezuma Creek area, which encompasses the entire Montezuma Creek drainage area as far as the creek's confluence with the San Juan River. Existing water rights permit irrigation of some 299 acres with groundwater as the sole supply and another 1,718 acres with groundwater as a supplemental supply. Groundwater is not currently being used for irrigation in the area immediately downgradient from the mill site (1).
D. Health Outcome Data Sources
Health outcome data for Utah and the vicinity of the Monticello Mill Tailings Site and the Monticello Vicinity Properties are available from a variety of sources. The sources reviewed for this public health assessment are described below.
We consolidated concerns collected from site visits, public meetings, public availability sessions, letters and phone calls to ATSDR, and site-related documents. When several people expressed the same or similar concerns, we consolidated those concerns but took care to maintain the integrity of the original concerns as expressed. Numbers in parentheses represent the number of times a given concern was reported.
Boston University staff members assembled a list of 66 individuals and organizations familiar with the Monticello sites; we contacted most of them during site visits or follow-up telephone calls. In addition, Boston University staff representatives reviewed 94 documents, scientific articles, or print media articles related to community concerns at the Monticello sites. We categorized concerns as follows:
A. Past Site-Related Exposures
B. Continuing Exposure Concerns Related to the Sites
C. General Health Outcome Concerns
D. Specific Health Outcome Concerns
There was also concern about a perception of elevated rates of cancers, particularly leukemia, in Blanding.
Appendix D contains information on community concerns categorized as procedural concerns and community health concerns not related to the mill site.
This section provides an historical perspective on radiation and discusses its effects on human health. In the 1890s, scientists learned how to produce a type of radiation they called x-rays, and they also found that certain naturally occurring elements emit particles and rays which they called radiation. Soon, radiation and radioactive materials were being used for medical purposes, both externally as well as internally, to diagnose and treat a host of medical conditions like ankylosing spondylitis, acne, and cancer. Commercial use of radioactive materials evolved and included making electron tubes, static eliminators, smoke alarms, and glow-in-the-dark watches. Radiation has been used for many purposes since its discovery but, like a double-edged sword, it has produced both good and bad effects as an historical review of its destructive side proves.
The effects of radiation were found to vary from one individual to the next, and with such factors as dose, dose rate, nonuniformity of dose distribution, type of radiation, gender, age, health status, portion of the body or organ involved, cell oxygen concentration, rate of cell division, density of ionization, and presence of carcinogenic promoting and radiation protective chemicals. In general, the effect increases with higher dose, higher dose rate, delivery of the dose in a shorter exposure period, larger portion of the body being exposed, the younger the individual (especially the embryo/fetus), and the higher the internal oxygen concentrations. To provide statistically useful information, it was necessary to select several large groups of individuals that had been exposed to large doses of radiation. Some of these groups included ankylosing spondylitis patients, radium dial painters, atomic bomb survivors, cancer therapy patients, and laboratory animal studies. Another group is the uranium miners where it was found that the ability of radon gas to produce lung cancer was enhanced by smoking and breathing silica dust and diesel fumes that were present inside the mines. The result is an understanding of the average and range of effects at high doses.
The reasons that individuals respond differently to radiation is complicated, but the reasons that radiation can affect an individual has been intensely studied. DNA is a two-stranded, twisted molecule inside cells that directs the formation on the proteins for human life. Radiation exposure can break one or both stands of the DNA molecule, break a bond that connects the two strands, or alter the sequence of the DNA building blocks. These processes can kill the cell, or allow it to produce nonfunctional tumor tissue or chromosomal abnormalities. The rate of these mutations would be higher than actually observed if it were not for repair mechanisms. A repair mechanism for broken strands cuts out the damaged section and reportedly regenerates it slowly and faithfully.
It would be useful to know the actual effects of radiation at the relatively low doses and low dose rates seen around Monticello. The effects at environmental levels, however, are too small to be seen directly, or perhaps, indirectly. Scientists calculate the effect from high dose studies and interpolate or estimate the effect at low environmental doses, or rely on epidemiologic studies that relate health incidence rates of a potentially exposed population with a control population. The extrapolation of effects from high doses to low has been considered by many to be linear with no threshold. This means that cutting the dose in half would reduce the effect by two, and there would be no dose below which there is no effect. Other possible dose-response charts have been suggested, but the linear-no-threshold model provides the basis for the most radiation protection practice. An example to the contrary is cataract formation, which clearly has a threshold and which is regulated with that in mind. Even though a threshold may exist for cancer production in humans, the production rate is so small at low doses that it is unlikely that the presence or absence of a threshold can be demonstrated.
Radiation protection recommendations and regulations have grown out of the need to protect patients, occupational workers, and the public from the potentially harmful effects of radiation, while allowing its beneficial use. Some beneficial uses include consumer products, various industries, and medical diagnosis and therapy. Even now, many people may just be starting to understand that the coal, natural gas, fertilizer, and other industries with no obvious relationship to radioactive material actually use and distribute large quantities of radioactive material. The doses of radiation in medical settings can be extreme, even when compared with either environmental or bomb survivor levels. The medical community recognizes that the potential harmful effects of radiation can be outweighed by the positive benefits of increased cancer cure rates, less need for surgery, and more effective diagnoses.
Radiological effects are usually classified in two groups (nondeterministic and deterministic) based on the statistical probability or determined certainty that they are due to radiation. The nature of how human biological quantities are changed distinguishes these. A short definition of each group, followed by an example, is provided below for explanation.
A nondeterministic effect is one that occurs at random, or purely by chance, and cannot be related 100% to any particular case. Most diseases associated with smoking are considered a nondeterministic effect. For example, a person might develop lung cancer from smoking cigarettes. If the same person had not smoked, that person could have developed lung cancer anyway. There is no way to determine whether a particular person's lung cancer resulted from smoking cigarettes; i.e., there is no proof of a cause-effect relationship. Similarly, exposure to radiation does not guarantee that an individual will develop a certain medical condition, but it does increase the likelihood. Cancer is a main somatic effect that may be caused by radiation exposure, and includes such types as thyroid, skin, bone, breast, liver, lung, and leukemia.
Many scientists use the "linear no-threshold" assumptions to determine nondeterministic effects from radiation exposure. "No threshold" means that any exposure, no matter how small, may be harmful. "Linear" means that the probability of the development of an effect doubles as the exposure doubles.
Our present knowledge of science, radiation, and human anatomy suggests that a single change in just one of our body's cells can produce cancer or genetic defects. The body's cells are divided into two classes: somatic cells and germ cells. The majority of cells that make up our tissue, organs, and other parts of our body structure are somatic. The germ cells (sperm or ovum) are used for reproduction. Damage to the chromosomes (a small part of the cell), whether it comes from a single radiation particle such as an alpha or beta particle, an x-ray, or a gamma photon, can initiate the process. It is very important to realize that when considering nondeterministic effects even the smallest amount of exposure to radiation may carry an associated risk, and exposure to more radiation does produce a higher probability of a person acquiring certain medical conditions than no exposure at all.
Nondeterministic effects can be cumulative in a way that is additive, synergistic, or antagonistic. Additive effects are those where the total risk of acquiring cancer is the sum of the risks from all insults, such as receiving two doses of radiation in a short time period. Synergistic effects are those where the total cancer risk is greater than the sum of the individual risks, such as with smoking and breathing radon gas. In this case, the risk from doing both is more than the risk from smoking plus the risk from breathing radon. Antagonistic effects are those where the total risk is less than the individual risks. An example would be receiving two doses of radiation separated by a long period of time, during which the body's defense mechanisms provide partial repair before the second exposure is received.
Deterministic effects do not occur at random but have a direct cause and effect relationship. Intoxication from drinking alcohol is considered a deterministic effect. For example, a person consuming alcohol might appear normal. After too many drinks, the person will appear a little woozy. If the person had not consumed alcohol he or she should not show signs of intoxication. So there appears to be proof of a cause-effect relationship between drinking and showing signs of intoxication.
Some radiation effects, including cataract formation, embryonic malformations, and radiation sickness, are deterministic. They have time and quantity thresholds, just as do the deterministic effects for alcohol. Individuals exposed to very high radiation doses in a short period of time do show a response. Normally, the more radiation exposure the individual experiences and the faster the exposure occurs, the more pronounced the biological effects will be and the sooner they will become evident. However, at low exposure rates, adverse health effects may not be noticed. At this point the radiation dose is below the threshold level. Exposures to uranium mill workers and populations surrounding mill tailings sites would have been well below the threshold level for deterministic effects.
The amount of exposure, or dose, primarily determines whether radiation effects are nondeterministic or deterministic. Very high levels of radiation exposure, which are far above environmental levels, cause acute health effects, such as radiation sickness. Initial symptoms and the median acute dose that cause them include anorexia (97 rads), nausea (140 rads), fatigue (150 rads), vomiting (180 rads), and diarrhea (230 rads) (17, 18). The rad is the traditional measurement unit for radiation absorbed dose. The larger the dose, the quicker the symptoms and signs develop. Blood syndrome occurs rapidly at 100 to 250 rads, gastrointestinal tract syndrome at more than 1,200 rads, and central nervous system syndrome at more than 3,000 rads. The clinical symptoms of blood syndrome are bleeding in various organs and decreased blood pressure, of gastrointestinal tract syndrome are nausea and vomiting, and of central nervous system syndrome are convulsions and disorientation. Other clinical symptoms related to high levels of radiation exposure are loss of hair (2,000 to 3,000 rads), skin reddening (850 rads), skin damage (2,000 rads), and sterility as discussed later (18). These dose estimates can vary widely among individuals. At higher doses, the symptoms can indicate the onset of disease; for example, a highly upset stomach can indicate total destruction of cells lining the gastrointestinal tract. These types of health effects are readily noticeable--the radiation effects are deterministic, i.e., the effect is proportional to the dose. Immediate and continuing low-level exposures may produce later health effects. These are known as chronic or delayed health effects.
We have identified six areas of concern: cancer, mutations, infertility, degenerative effects, life shortening, and cataracts.
A large amount of data concerning cases in which humans experienced exposure to high levels of radiation has been collected (19). For those cases, it is not the acute health effects discussed earlier that are important, but the delayed health effects. Several questions are relevant. For instance, if a person were exposed, did the person develop cancer, how long after exposure, was the source of radiation inside or outside the body, what type of cancer, and how old was the person at the time of exposure? There is normally a latent period of about 10 to 15 years before any clinical signs or symptoms of carcinogenic effects appear. A lengthy plateau period, during which the risk of acquiring a late or delayed health effect exists, follows latency. However, leukemia caused by high radiation doses like those at Hiroshima and Nagasaki, Japan, is an exception. Its effects have been observed much earlier than with other forms of cancer, within a few years after exposure (20, 21).
A plateau period may last about 20 to 30 years. The risk of developing cancer is constant during the entire plateau period. Also, the higher the risk coefficient, the greater the probability that a person will develop cancer. The person's age at irradiation is also important. Evidence from human studies shows that a person's age at time of exposure can be a major determinant of radiation-induced cancer risk; the younger an adult is, the lower the risk of developing cancer becomes. However, unborn babies and children have a higher risk of developing cancer related to radiation exposure than exposed adults have.
Although cancer is probably the most important somatic radiation hazard, three of the other concerns merit brief discussion: degenerative effects, life shortening, and cataracts. Degenerative effects are failures of body organs to function properly. This does not necessarily imply complete failure, but it does indicate some amount of permanent impairment of the organ. Life shortening is believed to occur because of radiation-induced malignancies (cancer, tumors, etc.)--not because of any acceleration of the aging process. Cataracts, or vision-impairment of the eyes' lenses, normally occur after a long latent period. The threshold for lens opacity is 200 rads, and doses of 10 rads per year over many years should not affect the vision (18).
Effects discussed to this point have involved high radiation doses and the resulting damage to cell systems, i.e., injury to several cells or groups. Radiation exposure to a single cell may also produce damaging health effects. High doses of radiation to a single germ cell could lead to a variety of genetic defects in humans if the defect was passed on to the next generation. If the dose is received during pregnancy, defects could be observed in the developing fetus. Although the relationship between radiation exposure and probability of mutations is unclear, some clinically observable human defects, not necessarily related to radiation exposure, are point mutations (a single gene disorder), multiple point mutations (many gene disorders), chromosomal aberrations (e.g., Down syndrome), and spontaneous abortions.
Infertility is normally attributed to gamma-ray radiation of the human gonads. The amount of exposure, or dose, determines the probable effect. For males, a dose of 10 rads received within a short time period (hours to days), may cause a brief period of sterility, and 500 to 950 rads causes permanent sterility. For females, it takes 150 to 640 rads for temporary and 200 to 1,000 rads for permanent sterility depending on age (18). These values are thousands of times greater than the doses around Monticello (22).
These effects occur at doses resulting from higher exposures or doses than existed around
Monticello. At doses below 10 rem, delivered over many years, epidemiologic studies do not
appear to show any adverse health effects. This may be the result of the body's own defense and
repair mechanisms at work, or because the effects are too small to detect. The health effects
from acute radiation doses are summarized in Table 1.
| Table 1. Summary of Radiation Health Effects From Acute Doses | ||
| Radiation Dose | Effect (Varies with factors like age, gender, and physical condition) | |
| Gray (Gy) | Rads | |
| 0.1-0.5 Gy to unborn child |
10-50 rads | May cause leukemia |
| 0.1 Gy to the testes |
10 rads | Brief period of sterility |
| 0.25-0.5 Gy | 25-50 rads | Appearance of blood changes |
| 1 Gy | 100 rads | Lowest dose observed to cause leukemia in Nagasaki atom bomb survivors |
| 1-2.5 Gy | 100-250 rads | Blood syndrome occurs starting in this range. Includes nausea and vomiting within hours, loss of appetite, fatigue, temporary loss of hair in 2-3 weeks, and possible death in 1-2 months |
| 2 Gy to the lens of eye |
200 rads | Lens opacity threshold for total dose (not dependent on exposure time) |
| 1.5-6.4 Gy to the ovaries |
150-640 rads | Temporary female sterility |
| 2-10 Gy to the ovaries |
200-1,000 rads | Permanent female sterility |
| 5-9.5 Gy to the testes |
500-950 rads | Permanent male sterility |
| 8.5 Gy to the skin |
850 rads | Skin reddening |
| 12 Gy or more | 1200 rads | Gastrointestinal syndrome occurs at this dose from desquamation of the intestinal epithelium. The symptoms are severe nausea, vomiting, and diarrhea almost immediately after exposure, and death within 1-2 weeks. |
| 20-30 Gy | 2,000-3,000 rads |
Permanent hair loss |
| 30 Gy or more | 3,000 rads | Central nervous system syndrome occurs due to damage of the central nervous system. Disorientation and unconsciousness occur within minutes and death within hours to several days. |
| NOTE: Table 1 includes the following definitions:
Gray (Gy) = International unit of measurement for radiation absorbed dose (1 Gy = 100 rads) | ||
Possible adverse health effects of radiation exposure (whether internal or external) are numerous and quite complicated. Such factors as a radionuclide's toxicity, its decay scheme, the pathway into the human body, and the amount of dose play an important role. Cosmic rays and natural terrestrial radioactivity from uranium, thorium, and their decay products also potentially affect one's health. Because of the city's high altitude, residents of Denver, Colorado, receive around 100 milliRoentgen equivalent man (mrem) a year more than residents of such sea-level cities as Miami, Florida (18). For comparison, a typical chest x-ray can deliver a dose of 20 mrem. Using the linear-no-threshold model in ICRP 60 and NCRP 91, one would conclude that in geographical areas with high radiation exposure rates, the health risk from radiation to the general public is greater than in areas where radiation exposure rates are lower. However, the health risk at such doses does not correlate well with the observed effect, possibly because other insults to the body can be more significant (23, 24).
There are three principal ways for radioactive materials to leave a mill site during processing of uranium or ore: airborne radioactive dust and radon-222 gas, water-soluble radionuclides, and mill tailings (both fine and coarse) (25). All of the radionuclides leaving the mill site are naturally occurring.
A radioactive series originates with a long-lived heavy element, eventually decaying by a number of emissions to a stable element marking the end of the series. Four series of naturally occurring radioactive elements exist in nature: the thorium series, neptunium series, uranium series, and actinium series. The uranium series (uranium-238 to lead-206) and the thorium series (thorium-232 to lead-208) are most likely to present biological hazards to people (26). The isotopes of both the uranium and thorium series--particularly radium-226 (radium), radon-222 (radon), thorium-234, and thorium-230 from the uranium decay series, and radium-228 (mesothorium), radium-224, radon-220 (thoron), thorium-232, and thorium-228 (radiothorium) from the thorium series--are of most concern to human health. Because the radionuclides in these series are naturally occurring, they are present throughout the environment. These radionuclides, along with other sources of radiation, such as cosmic radiation, all contribute to radiation levels that exist naturally. This natural radioactivity level is called the background radiation level.
Uranium-bearing ores removed from the earth contain between 0.1-0.2% uranium (28). The uranium in the Colorado Plateau ores is primarily in the form of hydrated oxide uranium minerals. These include carnotite (K2O • 2UO3 • V2O5 • 3H2O) and tyuyamunite (CaO • 2UO2 • V2O5 • 8H2O). Mined ores are shipped to a uranium mill, where the uranium is separated from the rock. There, the uranium is purified into yellow cake. Yellow cake is the name conventionally used for uranium ore concentrates. Depending on the separation process, carbonate or acid leaching, the yellow cake contains 85% or more of uranium oxide (U3O8), a small percentage of red cake (vanadium pentoxide [V2O5]), and other compounds (25, 29). The acid process, in particular, tended to release gaseous reaction products such as CO2 (carbon dioxide), H2 (hydrogen), and H2S (hydrogen sulfide). The process would have also released unreclaimed sulfuric and hydrochloric processing acids. However, these are chemical effluents and are not radioactive.
B. Uranium and Vanadium Production Methods at Monticello
The Monticello Uranium Mill used three extraction processes: salt roast, carbonate leach, and acid leach-resin pulp. The first operation in all three processes was crushing, grinding, and screening to produce fine sand. The salt roast process produced red cake (vanadium pentoxide [V205]) by mixing the sand with a sodium salt, roasting, washing out with water, precipitation, and heating under pressure. The other two processes took the fine sand and added liquid and chemicals to suspend the particles in the liquid. This leached or washed the uranium and vanadium out of the particles, and the useful liquid was then filtered. The carbonate leach process began next. Chemicals were added to the liquid, and the uranium compounds were precipitated. These uranium solids were filtered and steamed to make hard yellow cake (uranium oxides). Finally, in the acid leach process, chemicals were added to the remaining liquid to precipitate the vanadium compounds. These vanadium oxide solids were removed on filters, pressed to form red cake, and heated to make black cake (29, 30).
The Monticello Uranium Mill, like all chemical plants, produced several wastes. The first was residual ore material left along the roadways and at the ore-buying station. This material came from trucking the ore to the station, segregating it, and moving it to the mill. Other wastes produced at the mill site were in the form of dusts, fumes, gases, liquids, and solids.
Dust. The second waste produced was dust from the crusher and grinder. The crusher took the ore rock and made 1-inch gravel, and then the ball mill turned the gravel into fine mesh sand. The ball mill was the dustiest operation at Monticello. The coarse dust settled out near the grinder and was a breathing hazard to the operators. Uranium concentrates in the fine dust particles, which can be carried farther than coarse materials by the wind. A large portion of the dust particles were 1 to 10 microns (0.001 - 0.01 millimeters) in diameter (31). This size is respirable, meaning it can enter and lodge in the deep, air-exchange regions of the respiratory tract. Once there, it has the potential to cause biological damage from the radiation it emits or the chemicals it contains. If the particles are insoluble, they are partitioned so that some remain in place and produce damage by exposing the surrounding tissue to radiation; most others are coughed up and swallowed, exposing the stomach and intestines to radiation as they pass out of the body; and a small fraction may even pass directly into the bloodstream. If the particles are soluble, some will enter the bloodstream; others are coughed up and can enter the bloodstream via the intestines.
Fumes. The next waste was fumes released from the roaster stack at the end of the production cycle. For the purpose of this public health assessment, a fume is considered a process chemical that is added or formed during plant operation and released into the discharge air. This waste stream included chlorine and hydrogen chloride gas and an estimated 1,182 kilograms (2,600 pounds) of fine particles each day. These particles contained 0.363% uranium oxide and 1.52% vanadium pentoxide (32). Although the size distribution of particles was not reported, they were likely small enough to be carried far by the wind and would penetrate deeply into the lungs of people who inhaled them. Even after such particles settle out, they can later be resuspended by the wind and vehicles and be inhaled.
Gases. In this public health assessment, a gas is considered to be any item in the process that is normally a gas. Radon gas is considered to be the primary gaseous waste, and it came from all parts of the operation. This inert gas is formed during the natural radioactive decay of uranium and thorium, and produces human exposure primarily through inhalation. Radon was released from essentially all parts of the milling operation, and is still being released from the tailings piles and locations where tailings are still present. Measurements taken in 1983 and 1984 showed that the concentrations of radon gas on site, at the boundary, and at various locations off site exceeded the administrative limit of 0.90 picocuries per liter (pCi/L). Remediation efforts appear to be successfully reducing the levels off site.
Liquids. Liquid tailings were the leftover processing liquids. The waste resulted from milling and leaching the ore, and from washing the filtered oxides. The main chemicals it contained were chlorides, sulfates, carbonates, and bicarbonates of sodium and other metals. Nitrates were added to this list late in the plant's operating history when ammonium nitrate was added as a process chemical. The liquid effluents flowed into a tailings pond and finally into Montezuma Creek, which runs through the mill site. The water with dissolved and suspended pollutants then became available for watering livestock and for irrigating crops and pasture grass.
Solids. Solid tailings were the leftover solid process wastes. They contain the original ore and the chemicals added during extraction, less most of the uranium and vanadium. The tailings were placed into four separate piles: the Carbonate Pile, Vanadium Pile, Acid Pile, and East Tailings Pile. The damp material normally stayed in place, but as it dried, the wind blew it off the mill site, contaminating some of the nearby land. By 1962, Atomic Energy Commission (AEC) representatives had covered the piles with earth and seeded them to reduce the public health risk. Rain and creek water, however, continue to wash some tailings downstream. Currently, the rate at which radon gas is being released from the tailings piles exceeds the EPA recommended limit of 20 picocuries per square meter second (pCi/m2s). Radon gas consists of both Rn-220 and Rn-222, but the short 51.6 second half-life of Rn-220 makes Rn-222 the isotope of concern in health evaluations. Therefore, exposures to Rn-220 would not be of health concern. Radon gas also is released from the piles at elevated levels, but the levels are lower than levels present when the piles were uncovered.
The radioactive materials in the gas, liquid, and solid waste streams were mainly thorium and daughters of thorium and uranium. Radionuclides created when uranium or thorium decays toward a stable element and emits radiation are called "daughter" products. Tables 2 and 3 show the decay series for the uranium series and thorium series, respectively. Note that radium and radon gas are in those decay chains. Because the mill had removed most of the uranium, the tailings are less radioactive than the original ore.
Each table has 4 columns: element number, isotope, half-life, and energy. The element number is the atomic number of the atom as listed in the Periodic Table of the Elements. Each element may have many radioactive isotopes--same atomic number but different mass numbers (left superscript). The half-life is the time it takes for one-half of the atoms of an isotope to decay. Longer half-lives indicate a more stable radionuclide. Column 4 indicates the energy of the decay particle. Usually the higher the particle or photon energy, the more ionizing power it has.
Radioactivity involves the spontaneous decay of an unstable atomic nucleus accompanied by the
emission of a particle or photon or both. There are basically three different types of decay
products of interest: alpha (
), beta (
), and gamma (
) rays. An alpha particle is a positively
charged helium atom. Alpha radiation is the least penetrating of the three, subject to being
stopped by a mere sheet of paper or a few centimeters of air. It is not normally considered
dangerous, except when the alpha-emitting substance has been ingested or inhaled (33). Beta
particles are electrons, either positively or negatively charged. Beta particles are easily stopped
by a thin sheet of metal or a few feet of air. Beta radiation may cause skin burns, and a beta
emitter is harmful inside the body. Gamma rays are high-energy photons, somewhat higher in
energy than x-rays. Gamma radiation frequently accompanies alpha or beta emission and is the
most penetrating of all three.
D. Uranium and Thorium Decay Schemes
| Table 2. Uranium Series (34) | |||
| Element Number |
Isotope and Types of Emission* |
Half-Life | Energy (MeV) (Most Prominent) * |
| 92 | uranium-238 , |
4.5 x 109 years | 4.19 ; 0.05 |
| 90 | thorium-234 , |
24.1 days | 0.19 ; 0.06 |
| 91 | protactinium-234m ** protactinium-234 , |
1.14 minutes 6.7 hours |
2.3 ; 1.0 0.48 ; 0.17 |
| 92 | uranium-234 , |
250,000 years | 4.7 ; 0.05 |
| 90 | thorium-230 , |
75,400 years | 4.68 ; 0.07 |
| 88 | radium-226 , |
1,622 years | 4.78 ; 0.19 |
| 86 | radon-222 , |
3.8 days | 5.49 ; 0.58 |
| 84 | polonium-218 |
3.1 minutes | 6.0 ; 0.5 |
| 82 | lead-214 , |
26.8 minutes | 0.67 ; 0.35 |
| 83 | bismuth-214 , |
19.9 minutes | 3.3 ; 0.61 |
| 84 | polonium-214 |
0.000164 seconds |
7.68 ; 0.8 |
| 82 | lead-210 , |
22.3 years | 0.02 ; 0.047 |
| 83 | bismuth-210 |
5.0 days | 1.16 |
| 84 | polonium-210 , |
138.4 days | 5.3 ; 0.8 |
| 82 | lead-206 | stable | - |
| * = alpha particle, = beta particle, and = gamma ray ** m = The m on 234m means this is an excited or metastable state of protactinium-234 | |||
| Table 3. Thorium Series (34) | |||
| Element Number |
Isotope and Types of Emission* |
Half-Life | Energy (MeV) (Most Prominent)* |
| 90 | thorium-232 , |
1.4 x 1010 years | 4.00 ; 0.059 |
| 88 | radium-228 , |
5.8 years | 0.039 ; 0.014 |
| 89 | actinium-228 , |
6.1 hours | 1.2 ; 0.9 |
| 90 | thorium-228 , |
1.9 years | 5.42 ; 0.08 |
| 88 | radium-224 , |
3.6 days | 5.68 ; 0.24 |
| 86 | radon-220 , |
55.6 seconds | 6.28 ; .055 |
| 84 | polonium-216 |
0.15 seconds | 6.77 ; 0.8 |
| 82 | lead-212 , |
10.6 hours | 0.33 ; 0.24 |
| 83 | bismuth-212 , , |
60 minutes | 6.08 ; 2.2 ; 0.7 |
| 84 | polonium-212 |
2.98 x 10-7 seconds |
8.78 |
| 81 | thallium-208 , |
3.1 minutes | 1.79 ; 2.6 |
| 82 | lead-208 | stable | - |
| * = alpha particle, = beta particle, and = gamma ray | |||
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