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PUBLIC HEALTH ASSESSMENT

IDAHO NATIONAL ENGINEERING AND ENVIRONMENTAL LABORATORY (U.S. DEPARTMENT OF ENERGY)
[a/k/a IDAHO NATIONAL ENGINEERING LABORATORY (USDOE)]
IDAHO FALLS, BUTTE, CLARK, JEFFERSON AND BIN COUNTIES, IDAHO


SUMMARY

ATSDR's PHAs are exposure, or contact, driven. A release of a hazardous waste does not always result in human exposure. Rather, people are exposed to a contaminant such as those identified at the INEEL site only if they come in contact with it; they might be exposed by breathing, eating, or drinking a substance containing the contaminant, by skin contact with a substance containing the contaminant, or from close proximity to gamma emitters.

Site Background

Idaho National Engineering and Environmental Laboratory (INEEL) is situated on the upper Snake River Plain in southeastern Idaho. The site spans Butte, Bingham, Bonneville, Clark, and Jefferson Counties, encompassing 890 square miles. INEEL is owned by the federal government, managed by the US Department of Energy (DOE), and operated by Bechtel BWXT.

In the 1940s, the federal government began using the site to test refurbished naval guns and other ordnance and to research and develop nuclear reactors and related equipment. In 1975, the site was designated a national environmental research park to advance the science and technology related to environmental characterization and restoration of sites previously used for nuclear operations. DOE made INEEL the lead laboratory in developing new environmental technologies for DOE site cleanup and waste management.

As a result of past operations and disposal practices, chemical and radiological materials have been released to the environment. Since 1986, about 500 potentially contaminated sites have been identified at INEEL under an Environmental Restoration Program. The sources of the contamination include spills, abandoned tanks, septic systems, percolation ponds, landfills, and injection wells. Because of the presence of certain contaminants at INEEL, the US Environmental Protection Agency (EPA) added INEEL to its National Priorities List in November 1989. Site investigations and remediation are underway.

ATSDR Conclusions

According to the information reviewed by ATSDR, under normal operating conditions, INEEL poses no past, current, or future apparent public health hazard for the surrounding community from groundwater, surface water runoff, soil, biota Exiting ATSDR Website, or air. ATSDR has focused its review on data generated from 1987 to 2000. For exposure prior to 1987, the National Center for Environmental Health (NCEH) of the Centers for Disease Control and Prevention (CDC) is conducting a dose reconstruction. ATSDR will review the information, when the dose reconstruction is complete.

In drawing its conclusion about potential public health hazards now or in the future, ATSDR considered the following:

Community Concerns

In collecting and evaluating residents' public health concerns, ATSDR obtained the assistance of the INEEL Health Effects Subcommittee, the Idaho Bureau of Environmental Health and Safety, and the Cancer Data Registry of Idaho. The public health concerns obtained to date and ATSDR's response to them are presented and analyzed in the main body of this public health assessment.

On-Site Drinking Water

For potential public health hazards in the past, ATSDR determined that visitors could have been exposed to VOCs and tritium when they drank water drawn from certain INEEL drinking water wells. This exposure, however, would not have caused any adverse health effects. INEEL continues to test the water supply to ensure that it meets safe drinking water requirements.

Health Outcome Data

Residents raised questions about excessive cancer rates and the occurrence of birth defects, both of which they believed to be related to environmental releases from the site in six counties in the vicinity of INEEL (Bannock, Bingham, Bonneville, Butte, Clark and Jefferson). ATSDR's evaluation of cancer rates for the counties of concern indicated that the types of cancers commonly associated with radiological and chemical exposures are within the range of what would be expected according to comparisons with cancer rates in the state of Idaho as a whole. Rates of certain cancers, cases, or deaths were less than expected, while some were greater than expected. In most instances, the differences were not statistically significant. Most of the increases in cancer rates were likely a result of random variability, since there did not appear to be any consistent increases across counties or within counties (e.g., although breast cancer incidence was significantly increased in Clark County, it was significantly decreased in the more populous Bingham County, compared to the incidence in the rest of the state). ATSDR obtained the assistance of the INEEL Health Effects Subcommittee, the Idaho Division of Health (Bureau of Environmental Health and Safety and the Center for Vital Statistics and Health Policy), and the Cancer Data Registry of Idaho.

1961 SL-1 Reactor Accident

Public concern was also voiced about a nuclear accident on January 3, 1961, which resulted in an air release at the site's Reactor Testing Station. The cause of the accident was most likely operator error. Three employees were exposed to radiation at lethal levels (all of the employees actually died from immediate non-radiation physical trauma). According to calculations conducted at the time, approximately 99.99% of the total fission product inventory in the core was retained inside the reactor building, even though it was not designed as a containment facility. Therefore, elevated air levels of fission products have not migrated off-site and have not resulted in radiation exposures or doses to the public above levels that would cause adverse health effects. ATSDR has not received reports of health effects related to this accident; however, if data become available suggesting that health effects did occur, the agency will reevaluate the need for follow-up activities.


BACKGROUND

Site Description and History

INEEL is on the upper Snake River Plain in southeastern Idaho, at an average elevation of 4,900 feet above sea level. The site spans 890 square miles in Butte, Bingham, Bonneville, Clark, and Jefferson Counties, extending 39 miles from north to south, with a 36-mile width at the southern boundary. INEEL is bordered on the north and west by three mountain ranges and on the south by three large buttes. Only about 6% of the property contains buildings or other structures; the remaining 94% of the site is undeveloped and open land. Figure 1 shows the location of INEEL (ESRF 1998).

INEEL is owned by the federal government, but it is operated by Bechtel BWXT for the DOE (INEEL 2001a). Other administrators of the site are or have included DOE's Idaho Operations Office (DOE-ID), the Idaho Branch Office of Pittsburgh Naval Reactors (IBO), and DOE's Chicago Operations Office (DOE-CH), whose supporting contractors are Bechtel BWXT, Westinghouse Electric Corporation (WEC), and Argonne National Laboratory (ANL), respectively. DOE-ID is responsible for environmental control and management of INEEL.

The site was used by the federal government in the 1940s to test refurbished naval guns and other ordnance. In 1949, the site was designated as the National Reactor Testing Station by the Atomic Energy Commission (AEC). INEEL's mission was to conduct nuclear reactor research and to develop nuclear reactors and related equipment. Over the years, scientists constructed 52 test reactors at INEEL. Most test reactors were phased out when their missions were completed. Three reactors still operate at INEEL: the Advanced Test Reactor (ATR) in the Test Reactor Area (TRA), which produces a large amount of the nation's medical and industrial isotopes; the ATR Critical Flux in the TRA; and the Neutron Radiograph in the Argonne National Laboratory-West facility.

During the past 50 years, INEEL has also been used for radioactive waste disposal and storage. Some of the waste has been created at INEEL as part of its ongoing operations, and some has been shipped to INEEL from other US sites (DOE 1999).

In 1974, the National Reactor Testing Station was renamed the Idaho National Engineering Laboratory. DOE designated the site as the lead laboratory for developing new environmental technologies for DOE site cleanup and waste management. On January 29, 1997, the site was renamed the Idaho National Engineering and Environmental Laboratory to reflect the growing environmental program.

Today, DOE uses INEEL to "develop, demonstrate, deploy, and transfer advanced engineering technology and systems to private industry" (INEEL 2001a). The following are a few of the major DOE programs currently ongoing at INEEL:

Environmental Restoration and Management

INEEL's mission has focused on providing research and engineering support to the military, commercial, and governmental segments of the US economy. Over the years, this mission has meant applying nuclear power to commercial and naval use; reprocessing spent nuclear fuel; storing nuclear waste; and currently, remediating and managing waste generated at INEEL.

Some site operations have released non-radiological and radiological materials to the surrounding soil or air. Some of this contamination has reached the underlying groundwater.

Monitoring activities were initiated at INEEL to provide information about the pathways that might expose INEEL workers and the general public to site contaminants. Because of the nature of the activities at INEEL, radionuclides were the major contaminants analyzed during the early monitoring efforts. In 1984, DOE and EPA agreed to establish a non-radiological and radiological environmental monitoring program to further protect human and environmental health and ensure compliance with applicable federal, state, and local regulations (LMITCO 1998).

An Environmental Restoration Program was established at INEEL to clean up environmental contamination and decommission facilities that are no longer supporting INEEL's mission. Cleanup is conducted under a Federal Facility Agreement and Consent Order agreed upon by DOE, EPA, and the State of Idaho, in accordance with the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA), also known as Superfund (DOE 1995). Since 1986, about 500 potentially contaminated sites have been identified under the Environmental Restoration Program. Sources include spills, abandoned tanks, septic systems, percolation ponds, landfills, and injection wells. Because of the presence of certain contaminants, EPA added INEEL to its National Priorities List in November 1989 (ESRF 2000).

INEEL Site Location
Figure 1. INEEL Site Location

Location of INEEL and Selected Facilities
Figure 2. Location of INEEL and Selected Facilities

INEEL is divided into 10 Waste Area Groups (WAGs), each containing multiple operable units (OUs) and solid waste management units (SWMUs), some of which may overlap. An OU is a group of previously identified hazardous waste sites that share similar environmental media and geographic distributions. Eighty-three OUs have been identified at INEEL. Nine of the WAGs correspond to INEEL's major facilities. The tenth WAG includes the aquifer underlying the site and other miscellaneous areas (see Figure 2). Appendix C describes the WAGs in greater detail, and Table 1 summarizes the primary chemicals used at each WAG (DOE 1995).

Table 1. Waste Area Groups at INEEL
WAG No. Location/Description Chemicals Used/Disposed Of
1 Test Area North (TAN) 10 operable units (OUs) and 63 solid waste management units (SWMUs) Acids, petroleum products, asbestos, fission products, organic wastes (including TCE), and heavy metals
2 Test Reactor Area (TRA), 13 OUs and 49 SWMUs Organic wastes, petroleum products, fission products, and heavy metals
3 Idaho Nuclear Technology Engineering Center (INTEC), 13 OUs and 66 SWMUs Organic wastes, petroleum products, fission products, transuranic radionuclides, asbestos, acid salts, and heavy metals
4 Central Facilities Area (CFA) 13 OUs and 38 SWMUs Ordnance, salts of acids, petroleum products, heavy metals, fission products, asbestos, and organic waste
5 Power Burst Facility/Auxiliary Reactor Area (PBF/ARA), 13 OUs and 43 SWMUs Fission products, petroleum products, heavy metals, and organic wastes
6 Experimental Breeder Reactor-1/Boiling Water Reactor Experiment (EBR-1) 5 OUs and 20 SWMUs Heavy metals, organics, fission products, and petroleum products
7 Radioactive Waste Management Complex (RWMC), 14 OUs Fission products, transuranic radionuclides, organic wastes, salts of acids, ordnance, and heavy metals
8 Naval Reactors Facility (NRF) 8 OUs and 54 SWMUs Heavy metals, organics, petroleum products, and radionuclides
9 Argonne National Laboratory-West (ANL-W), 4 OUs and 14 SWMUs Heavy metals, fission products, petroleum products, and dioxins/furans
10 Miscellaneous Units and Snake River Plain Aquifer (SRPA), 4 OUs and 13 SWMUs Salts of acids, fission products, organic wastes, and ordnance

INEEL's Environmental Restoration Program further identified 26 specific areas throughout the 10 WAGs as requiring environmental investigation. As of January 2000, environmental investigations have begun at 21 areas. DOE, EPA, and the State of Idaho have reached a final cleanup decision, known as a Record of Decision (ROD), at 19 of the areas, and they have completed cleanup at 12 (INEEL 2001b).

Numerous technologies are employed to remediate INEEL, including containment, immobilization, and physical, thermal, chemical, and biological processes. Some of the areas have yet to be investigated, including the buried waste at the RWMC (WAG 7), soil contamination at INTEC tank farms (WAG 3), and site-wide groundwater and SRPA contamination.

INEEL established an Environmental Surveillance Program to monitor the level and assess the impact of pollutants from INEEL operations on the environment (BWXT 2000). The management and operating contractor, currently Bechtel BWXT, is responsible for the on-site portions of the program. Two components exist within the Environmental Surveillance Program: the Waste Management Surveillance Program (WMSP) and the Site Environmental Surveillance Program (SESP). The WMSP monitors soils, ambient air, direct radiation, biota, and surface water at the Radioactive Waste Management Complex, the Waste Experimental Reduction Facility, the Mixed Waste Storage Facility, Test Area North, and the Organic Moderated Reactor Experiment, in compliance with DOE Order 435.1. The SESP monitors ambient air, soils, and direct radiation beyond the boundaries of the individual waste management facility sites but within the borders of INEEL, in compliance with DOE Order 5400.5 (ESRF 1998).

In addition to the DOE contractor for INEEL, four other organizations monitor the environment in and around INEEL. The other organizations are: the US Geological Survey, the Environmental Surveillance, Education and Research Program, the National Oceanic and Atmospheric Administration, and the State of Idaho Oversight Program (part of the Idaho Department of Environmental Quality). These organizations work independently of the DOE contractor to assess contaminant concern at INEEL. The results of their work provide quality assurance of and lends confidence to data collected by the site contractors (ESRF 2000).

Environmental Management

INEEL has managed waste from on- and off-site sources for about 50 years. Most of the waste and the resulting contamination was generated by Cold War activities (INEEL 2001b). The types of waste managed range from radioactive waste (including transuranic, high-level, and low-level radioactive waste) to hazardous waste and industrial waste. The Glossary in Appendix F includes definitions of the different types of radioactive waste stored/disposed of at INEEL. INEEL also handles DOE's spent nuclear fuel from the national nuclear weapons complex (INEEL 2001b).

Demographics and Land Use

When assessing a site, ATSDR seeks to identify the people in the site's vicinity who are more likely than usual to be exposed to contamination, as well as populations (such as young children and the elderly) that are especially sensitive to exposure. To do so, ATSDR uses demographic (or population) information and land use information. Demographics also provide details on residential history in a particular area–information that helps ATSDR assess time frames of potential human exposure to contaminants. Demographic information for the residential areas surrounding INEEL is presented in this section. (Note that proximity, in itself, is not an adequate indicator of exposure to site-related contaminants. Whenever possible, proximity measures must be supplemented with environmental pathway information to permit evaluation of exposed populations.)

Today, INEEL is the largest employer in the area, with a workforce of approximately 8,100 people (ESRF 2000, INEEL 2000). The workforce includes about 400 federal employees, most of whom work for DOE-ID. Most of the other, non-federal employees work for or have worked for DOE contractors, including Bechtel (BWXT), Westinghouse Electric Corporation, and ANL (ESRF 1998). There are no permanent residents at INEEL or within a 10-mile radius of the operational center of the INEEL site.

The varied land use at INEEL includes the following broad categories: facility operations, general open space, grazing, and infrastructure. While 6 % of the INEEL site is developed, only about one-third of the developed area is used for facility operations in support of energy research and waste management activities.

A large portion of the site is open space that creates a buffer zone between INEEL operational areas and the nearest neighbors. Cattle and sheep graze on 300,000 to 350,000 acres (about 60%) of this buffer zone (DOE 1995). For the purpose of limiting any potential radionuclide contamination, animals are not allowed within 2 miles of any nuclear facility, and dairy cattle are not permitted. INEEL is a National Environmental Research Park. Public tours of the general facility and of a National Historic Landmark (Experimental Breeder Reactor-I) are available, and controlled hunting within a half-mile of the boundary fence is allowed. INEEL has several quarries, from which sand, gravel, pumice, silt, clay, and aggregate are extracted. These materials are used to build and maintain roads, construct facilities, bury wastes, and landscape (DOE 1995). Public roads and utility rights-of-way cross INEEL. However, public access to operation sites is restricted by fences, guard stations, and patrols.

Lands immediately beyond the boundaries of INEEL are desert, but some are irrigated for agricultural use. The closest towns to the boundaries of INEEL are Atomic City (population 25), 1 mile beyond INEEL's southern boundary; Mud Lake (population 179); and Tereton (population 100). Larger centers, such as Idaho Falls (population 43,929) to the east and Pocatello (population 46,080) and Blackfoot (population 9,646) to the southeast, are at least 20 miles from INEEL boundaries, even further from areas of contamination at INEEL's operational areas.

Farming is largely concentrated 50 to 70 miles northeast of the site. Large areas of agricultural land are also farmed in the Snake River Valley to the east and south of the site, although those areas are more than 30 miles from INEEL's RWMC, the operational area closest to the INEEL southern boundary.

Table 2 contains the demographic statistics for areas within 1, 5, and 10 miles of the nearest INEEL facility or building. As Table 2 notes, no one resides within one mile of any INEEL facility or building. Approximately 427 people reside within 10 miles of any INEEL facility or building. This population includes 46 children aged 6 years and younger, 72 females aged 15 to 44 years, and 44 adults aged 65 and older. Figure B-1 (Appendix B) shows the total population density in 1-, 5-, and 10-mile increments from INEEL facilities or buildings, and Figure B-2 shows the population density in 5, 10, 25-, and 50-mile increments from INEEL site boundaries.

Table 2. INEEL Regional Demography
Demographic Variables Miles from Nearest INEEL Facility
1 5 10
Total Population 0 45 427
Racial Characteristics
White alone 0 45 385
Black alone 0 0 0
Am. Indian and Alaska Native alone 0 0 2
Asian alone 0 0 4
Native Hawaiian and Other Pacific Islander alone 0 0 0
Some Other Race alone     34
     Two or More Races     3
     Hispanic or Latino 0 1 44
Sensitive Populations
Children Age 6 and Younger 0 2 46
Females Age 15-44 0 4 72
Adults Age 65 and over Older 0 7 44
Other Variables
     Total Housing Units 0 29 188

Demographic Statistics Source: 2000 US Census.


ENVIRONMENTAL CONTAMINATION AND OTHER HAZARDS

What is exposure? ATSDR’s public health assessments are exposure, or contact, driven. Chemical contaminants disposed or released into the environment have the potential to cause adverse health effects. However, a release does not always result in exposure. People can only be exposed to a chemical if they come in contact with the chemical. Exposure may occur by breathing, eating, or drinking a substance containing the contaminant or by skin (dermal) contact with a substance containing the contaminant. When do health effects occur? Exposure does not always result in health effects. The type and severity of health effects that occur in an individual from contact with a contaminant depend on the properties of the chemical, the exposure concentration (how much), the frequency and/or duration of exposure (how long), the route or pathway of exposure (breathing, eating, drinking, or skin contact), and the multiplicity of exposure (combination of contaminants). Once exposure occurs, characteristics such as age, sex, nutritional status, genetics, life style, and health status of the exposed individual influence how the individual absorbs, distributes, metabolizes, and excretes the contaminant. Together, these factors and characteristics determine the health effects that may occur as a result of exposure to a contaminant in the environment.Introduction

This section presents an evaluation of environmental data collected for the INEEL site. ATSDR evaluated these data to determine whether any contamination exists at levels that necessitate further evaluation (which in turn would determine if that contamination could be a public health hazard to the general public). Figure 3 describes the conservative exposure evaluation process used by ATSDR.

If exposure was or is possible, ATSDR then considers whether chemicals were or are present at concentrations that might be harmful to people. ATSDR does this by screening the concentrations of contaminants in environmental media (e.g., groundwater or soil) against health-based comparison values (CVs) (Appendix A). CVs are chemical concentrations that health scientists have determined are not likely to cause adverse effects, even when assuming very conservative/worst case exposure scenarios. Because CVs are not thresholds of toxicity, environmental levels that exceed CVs would not necessarily produce adverse health effects. If a chemical is found in the environment at levels exceeding its corresponding CV, ATSDR examines potential exposure variables and the contaminant toxicology. ATSDR emphasizes that a public health hazard exists only if contact with harmful levels of contaminated media occurs with sufficient frequency and duration for harmful effects to occur.

Some of the comparison values used for screening by ATSDR scientists include ATSDR's Environmental Media Evaluation Guides (EMEGs), Reference Dose Media Evaluation Guides (RMEGs), and Cancer Risk Evaluation Guides (CREGs), as well as EPA's Maximum Contaminant Levels (MCLs). MCLs are enforceable drinking water regulations developed to protect public health. CREGs, EMEGs, and RMEGs are non-enforceable, health-based comparison values developed by ATSDR as a way to screen environmental contamination for further evaluation. Appendix E discusses the basis for the comparison values used in this evaluation.

ATSDR's Exposure Evaluation Process
Figure 3. ATSDR's Exposure Evaluation Process

Media-Specific Contamination

ATSDR reviewed non-radiological (chemical) and radiological data collected for groundwater, surface water, soil, air, and/or food in support of environmental monitoring at INEEL. ATSDR also reviewed information on ambient ionizing radiation exposures at the site. The material reviewed included quarterly, annual, and supplemental environmental reports for the 1950s through 1999.

This subsection summarizes environmental monitoring data for the different media by non-radiological and/or radiological contamination, and for ambient radiation at INEEL. Data tables 3 and 4 in the following text, as well as the tables in Appendix A, are also provided for media containing contaminants at levels exceeding comparison values. When they are available, ATSDR also evaluates off-site monitoring data. To harm human health, environmental contaminants must have a way to reach people and expose them. These exposure pathways are discussed in the "Pathways Analysis" section and summarized in Table 5. The potential for contaminants of concern that can reach people to cause illness is then evaluated in the "Public Health Implications Section".

For more information, see the appendices. Appendix E explains the different types of comparison values (CVs), Appendix F is a glossary of terms, and Appendix G discusses radiation and radioactive material. ATSDR presents two systems of radiological units of measurements: the Conventional System and the Systeme International. These units, other symbols, and abbreviations used in this document in radiological discussion are noted in the key below:

System Unit Parameter/Description
Units of Radioactivity (Conventional Units) picocurie, pCi The curie (Ci) is the basic unit of radioactivity. The pCi is 1,000,000,000,000 times smaller than one Ci.
milliroentgens, mR Radiation exposure is expressed in terms of roentgens (R). One mR is 1,000 times smaller than one R.
mrem Dose is given in units "roentgens equivalent man", or rems. One mrem is 1,000 smaller than one rem.
Units of Radioactivity (Systeme International) becquerel, Bq The basic units of activity is the becquerel (Bq). The number of curies must be multiplied by 3.7 x 1010 to obtain equivalent number of Bqs.
millisievert, mSv The sievert (Sv) is the unit of dose equivalent. One mSv is 1,000 times smaller than one SV. One mSv = 100 mrem.


Feature Symbol Description
Uncertainty Measurements ± Radioactivity measurements are given with a range of uncertainty denoted by "±" because of the statistical nature of the decay events. Usually data from the INEEL are presented in the form of one standard deviation which gives one (1) confidence in 68 of 100 cases that the true level of radioactivity falls between the measured concentration plus the uncertainty value and the measured concentration minus the uncertainty value. In the past, the INEEL used two standard deviations (95 out of 100) as a criterion for determining whether the measured value was valid. The INEEL now uses three standard deviations as the criterion, which is 997 cases out of 1000. Uncertainty values are available for some radiological measurement but not for all–presented in this document.
Negative Numbers as Results   Negative results are presented where the measured result is less than the preestablished average background concentration. Reporting these values better enables a scientist to observe trends or bias in the data.

Groundwater

The Snake River Plain Aquifer (SRPA) underlying INEEL is one of the most productive aquifers in the United States, serving as the primary drinking water source for Southern Idaho. The aquifer–or water-saturated zone–lies between 200 to 1000 feet below ground surface. It is made up of rock units that consist primarily of basaltic lava flows and interbedded sedimentary deposits. Water in this aquifer moves rather fast compared to other aquifers, primarily in the south-southwest direction through fractures in the solidified basalt lava flows, at an estimated rate of about 6 to 10 feet per day. Some local groundwater flow beneath INEEL is more complex and variable, because it is influenced by production wells, recharge from the Big Lost River, by percolation and sewage ponds, by areas of low aquifer transmissivity, and possibly by pumping from the production wells. Ground water velocities on site range from about 0.5 ft/day around Test Area North (TAN) to greater than the 10 ft/day in the vicinity of the Idaho Nuclear Technology and Engineering Center (INTEC).

Approximately 470 billion gallons of water flow underneath INEEL annually. Current INEEL activities use an average of 1.6 billion gallons of water from the aquifer each year, or less than one half of 1% of the estimated volume of water passing beneath the site. Total INEEL water consumption from reasonably foreseeable activities, including waste processing activities, could increase by 189 million gallons per year. This consumption would be a 12% increase in water withdrawn from the SRPA, but the new amount would still be less than 1% of the water passing under the site (DOE 1999).

A significant amount of recharge to the SRPA at INEEL comes from the intermittent flows of the Big Lost River, of irrigation water, and of groundwater inflow from adjoining mountain drainage basins. Most of the groundwater is recharged in the uplands to the northeast before it moves southwest through the aquifer to be discharged to springs along the Snake River near Hagerman. Lesser amounts of water come from local precipitation on the plain. Part of the precipitation evaporates, but part infiltrates into the ground surface and percolates downward to the aquifer.

The vadose—or unsaturated—zone extends down from the ground surface to the water table (the top of the SRPA). The water table ranges from about 200 ft to over 900 ft below ground surface. The subsurface materials in the vadose zone are generally not saturated: they contain both air and water. It is believed that the vadose protects the underlying groundwater by filtering many contaminants through adsorption, slowing the transport of contaminants, or breaking down contaminants by natural decay processes (DOE 1995).

Perched water zones have formed beneath portions of INEEL. These are zones of groundwater that sit on relatively impermeable layers of sediment or clay (ESRF 2000). There are known perched water zones at four INEEL facilities: INTEC, TRA, TAN, and the RWMC. The systems formed over time from water trickling down through the percolation ponds and from the sewage treatment plant lagoons, precipitation, flooding events, and particularly during periods of dryness of the Big Lost River (DOE 1999). The perched water zones are too small ever to be tapped for drinking water, and they do not extend far enough from source areas ever to reach off-site communities or their drinking water supplies. Perched water zones sometimes protect the SRPA from contamination hot spots.

Groundwater serves as the primary source of drinking for INEEL. Currently, the water system at INEEL relies on 17 production wells and 10 distribution systems (ESRF 2000).

The US Geological Survey (USGS) began a groundwater monitoring network at INEEL in 1949, before nuclear-reactor testing facilities were developed at the site. During the early monitoring years, periodic water-level and water-quality data were collected from the network to describe the occurrence, movement, and quality of SRPA water, in order to characterize INEEL water resources before the development of nuclear reactor testing facilities (USGS 1997). The USGS has maintained a formal comprehensive groundwater monitoring program at INEEL to describe the type and amount of contamination in groundwater beneath the site.

The USGS INEEL Project Office currently oversees 125 aquifer monitoring wells located on-site in areas of detailed study, specifically the TRA, the Idaho Nuclear Technology Engineering Center (INTEC) [ formerly the Idaho Chemical Processing Plant (ICPP)], the RWMC, and the TAN, and off-site south, southeast, and southwest of the INEEL boundary. In addition, 55 sites between the southern site boundary and Hagerman are monitored (ESRF 1998). The wells installed in the SRPA are screened at different depths: from about 200 feet below ground surface in the northern part of INEEL to more than 900 feet below ground surface in the southeastern part. An additional 45 wells are available for sampling perched water zones. (Water samples from surface water sites at or near INEEL and from wells in perched groundwater zones are also analyzed to document the chemical quality of the water that recharges the aquifer.)

Today, USGS, DOE, and other organizations monitor groundwater from wells on and near INEEL on schedules ranging from monthly to yearly, depending on the information needed for specific areas (USGS 1997, INEEL 2000). The monitoring allows scientists to track plumes of contamination beneath the INEEL facility. Collected samples are then analyzed for 60 volatile organic compounds (VOCs), metals, trace elements, and radionuclides, as well as for selected chemical and physical parameters as needed. The various organizations conduct special studies to identify any problems with the groundwater of the SRPA at facilities within INEEL at which past releases are suspected (ESRF 1998).

INEEL established a centralized drinking monitoring water program (DWP) in 1988 at most on-site facilities. The DWP, as well as other organizations, monitors 17 production/drinking water wells and 10 distribution systems for radiological, non-radiological (chemical), and bacteriological contaminants (LMITCO 1998). The Naval Reactors Facility (NRF) and the Argonne National Laboratory-West (ANL-W) maintain separate drinking water monitoring programs (ESRF 1998).

The ESRF and the Oversight Program also monitor drinking water quarterly, semiannually, and annually at on-site locations and in off-site communities near the site boundary and at a distance. These samples are tested for gross alpha and beta radioactivity and tritium. With the use of gamma spectroscopy, they are also tested for Sr-90, Tc-99 and other selected ions (ESRF 2000).

Waste disposal practices over the past 50 years have resulted in contaminants seeping down to the groundwater of the SRPA and forming localized contaminant plumes beneath portions of the INEEL site. The contaminants originated from wastewater that was discharged into injection wells or disposed of into unlined infiltration or evaporation ponds in certain operational areas of INEEL, including INTEC and TAN, and from leakage of buried waste at the RWMC. Some contamination has trickled down into the perched water zones, most notably in the TRA area (INEEL 2000). At the time of construction, the waste injection wells were thought to be the best means to reduce human contact with waste.

Increased concern about the environment prompted changes in disposal practices at INEEL. These changes included elimination of wastewater injection in 1986, wastewater monitoring, and improved wastewater treatment system, such as the use of infiltration ponds, which allow the wastewater to slowly move through soil before reaching the groundwater.

Through routine monitoring of its groundwater network, elevated levels of VOCs, metals, semivolatile organic compounds (SVOCs), and polychlorinated biphenyls (PCBs) have been measured in the SRPA and in the perched aquifers beneath INEEL. Table A-1 provides information about these contaminants, their maximum concentrations as detected in on-site monitoring wells, and the location of those detections.

What are VOCs ? Volatile organic compounds (VOCs) are a group of organic chemicals having similar physical properties. These chemicals were detected in high concentrations beneath certain areas of INEEL. VOCs easily evaporate when exposed to air. Chemicals in this group include trichloroethylene (TCE), benzene, tetrachloroethylene (PCE) and carbon-tetrachloride. At INEEL these chemicals were used as cleaning solvents for degreasing. Much of the VOCs in the waste areas were from off-site waste that had been brought in from other facilities such as Rocky Flats for disposal.Of the contaminants detected, the VOCs carbon tetrachloride, 1,1,1-trichloroethane (1,1,1-TCA), and trichloroethylene (TCE) were among contaminants detected most frequently and in the highest concentrations. The highest levels of VOCs were measured in groundwater samples collected from the RWMC, TAN, and TRA facilities at INEEL. Note that chemical constituents associated with INEEL operations have not migrated beyond INEEL boundaries. Groundwater contamination in the SRPA and the perched aquifers is discussed in greater detail below.

The RWMC is situated on 168 acres, of which 97 acres constitute the actual disposal site, called the Subsurface Disposal Area. The RWMC is in the southwestern portion of the INEEL site, about 6 miles from the INEEL southern boundary. Since its establishment in the early 1950s, the RWMC has served as a controlled area for storage of solid radioactive and chemical defense wastes. The facility is also home to research and development projects dedicated to shallow land burial technology and alternate ways of removing, reprocessing, and repackaging transuranic wastes.

Solid and liquid chemical and radioactive wastes were buried in trenches and pits within sections of RWMC. Drums containing degreasing solutions and solvents were also buried. Many of the drums have deteriorated, releasing their contents to the surrounding soil over time. It is estimated that about 88,400 gallons of waste were buried before 1970: about 24,400 gallons of carbon tetrachloride, 39,000 gallons of lubricating oil, and 25,000 gallons of other organic compounds, including 1,1,1-TCA, TCE, perchloroethylene, toluene, and benzene. Since 1970, a layer of sediment has been added to the trenches to help impede any waste constituents from leaching into the underlying groundwater (ESRF 1999).

Groundwater investigations have identified VOCs at levels above ATSDR's CVs and EPA's drinking water standards in the SRPA beneath the RWMC. For example, 1,1,1-TCA was detected at levels up to 6,800 parts per billion (ppb), above ATSDR's CV and EPA's MCL of 200 ppb. VOC concentrations had decreased by 1998; still, one well (90) contained TCE (360 ppb) and tetrachloroethylene (PCE) (50 ppb) at levels above their MCLs (ESRF 2000).

High levels of VOCs were also detected in the perched water samples collected 70 feet below the surface of Pit 9. The maximum concentration of carbon tetrachloride was measured at 8,900 ppb, but the level was below 1,000 ppb at the pit boundary and at trace amounts at wells further downgradient from the RWMC. No one is drinking from the perched aquifer contaminated with carbon tetrachloride because INEEL's perched aquifers are all too small to supply facilities with drinking water.

The Record of Decision (ROD) for the RWMC signed by DOE, EPA, and the State of Idaho in December 1994 selected vapor vacuum extraction with treatment as the most appropriate remedial action. The treatment was specifically intended to remove contamination from the vadose zone, the area between ground surface and the top of the water table. Since the treatment began in 1996, more than 78,000 pounds of VOCs have been removed or destroyed (ESRF 2000; INEEL 2000). Ongoing efforts continue to remove and treat VOCs extracted from the vadose zone.

The TAN, located approximately 12 miles from INEEL's eastern boundary, consists of several facilities designed for handling, storing, examining, and conducting research and development on spent nuclear fuel. The facilities supported research of the 1979 Three-Mile Island incident and include one of the world's largest storage pools. The major facilities at TAN include the Contained Test Facility (CTF), the Technical Support Facility (TSF), the Loss of Fluid Testing (LOFT) facility, and the Water Reactor Research Test Facility (WRRTF). From 1953 to 1972, chemical, low-level radioactive, and sanitary wastewater was discharged at the TAN into the aquifer through a 310-foot deep injection (disposal) well. In 1972, the injection well was replaced by a 35-acre infiltration pond.

USGS investigations revealed that high levels of VOCs had entered the groundwater beneath the TAN area. TCE and PCE were measured at levels up to 32,000 and 110 ppb, respectively, both above their ATSDR CVs of 5 ppb for each. A VOC plume has also contaminated drinking water wells used by TAN employees (ESRF 1998). (See the drinking water discussion below.)

DOE began cleaning up the injection well in 1993. In 1994, DOE initiated a pump-and-treat interim remedial action to remove TCE from the groundwater of the SRPA. Sludge had been removed in 1990, but not before TCE had settled into pools of dense, non-aqueous phase liquid (DNAPL) below the SRPA. After months of operations, however, the TCE levels were higher than expected. The DNAPL pools continued to feed TCE to the plume; however, the TCE concentration in the plume was kept from rising by biodegradation caused by microorganisms from the injection well sewage. A ROD signed in August 1995 called for reducing the contamination levels to below the MCL of 5 ppb within 100 years. As a separate interim action, the treatment plant has been used to provide hydraulic containment of the contaminants. Bacteria in the remaining injection well sludge continues to degrade the TCE, bringing the concentration closer to the MCL.

The TRA is located in the southwestern portion of INEEL, about 5 miles northwest of the CFA. The area was originally established in the early 1950s to conduct experiments associated with developing, testing, and analyzing materials used in nuclear and reactor applications. The TRA houses the Advanced Test Reactor (ATR), which produces a neutron flux that simulates radiation effects on materials and fuels.

Starting in the late 1950s and the early 1960s, chemical, low-level radioactive, and sanitary wastewater was discharged to infiltration and evaporation ponds at the TRA. Between 1964 and March 1982, non-radioactive wastewater from cooling-tower operations at the TRA was also injected into a disposal well in the SRPA. After March 1982, this wastewater was discharged to two cold-waste infiltration ponds, and the well has been used as an observation well.

A perched water system has formed beneath the TRA from water percolating down through the disposal ponds. The perched water is a groundwater zone that sits on a layer of clay located about 330 feet above the SRPA. This layer of clay ultimately impedes water from passing through (ESRF 1998). Note that perched water aquifers may not be large enough or permeable enough to be used as a major source of drinking water, but may still be tapped locally (a few households) for a drinking water source, and can still contain contaminants that may represent a future threat to the SRPA. Nevertheless, since 1993, various agencies have been routinely monitoring water quality of the perched aquifer to determine whether any actions are needed (ESRF 2000).

As discussed, SRPA groundwater beneath certain portions of the INEEL site has become contaminated with VOCs and metals. The DWP routinely tests drinking water from production wells and distribution systems at INEEL for chemicals, including VOCs and metals, to ensure that the water is safe for drinking. Monitoring to date has shown that the VOC contamination has affected several production wells at the RWMC and TAN facilities. Table 3 summarizes contaminant concentrations that exceed CVs/MCLs.

Table 3. Maximum Concentrations of Non-Radiological Contaminants in Drinking Water Supply Wells
Contaminant Drinking Water Wells ATSDR CV/ EPA MCL
Maximum Conc. Location Date
Carbon Tetrachloride 5.5 ppb RWMC #1 10/1995 5 ppb/5 ppb
Trichloroethylene 15 ppb TSF #1 9/1996 5 ppb/5 ppb

Source: ESRF 1996.
MCL = EPA's maximum contaminant level; ppb = parts per billion.

As Table 3 indicates, the VOC carbon tetrachloride was detected at levels up to 5.5 ppb (just slightly above ATSDR's CV and EPA's MCL of 5 ppb) in a sample collected in 1995 from the RWMC #1 well at the RWMC facility. The concentrations reaching consumers, however, were much lower than the concentration detected at the wellhead.

Water collected from RWMC #1 also contained 1,1,1-TCA (0.6 ppb) and TCE (1.8 ppb), but at levels below the screening comparison values (ESRF 1996). Carbon tetrachloride levels in RWMC #1 increased slightly in 1996 but in 1997 decreased to levels just below comparison values. Again, carbon tetrachloride levels in the RWMC distribution system were lower than levels in the well (ESRF 1998).

Production wells at the TAN were also affected by VOCs. TCE was detected in 1987 at levels averaging 6.1 ppb (exceeding EPA's MCL of 5 ppb) in wells TSF #1 and TSF #2. Even though distribution system concentrations were not found to exceed the MCL, bottled water was provided to the approximately 100 workers in this area as a precaution until an air-stripping system was installed in 1988. Concentrations at TSF #1 again exceeded the MCL throughout 1995 (at levels ranging from 7.8 to 12.9 ppb) and reached levels up to 15 ppb in 1996. The water samples from the distribution system, however, met safe drinking water standards. TSF #1 was taken off line during the third quarter of 1997. TSF #2 is still being used (ESRF 2000; LMITCO 1998).

Note again that water drawn from INEEL production wells is diluted when it is mixed and then fed into a system of pipes that leads to water taps on INEEL. Because of this dilution effect, drinking water reaching workers has never been found to contain VOCs at levels exceeding the MCL, even though water in the RWMC or TAN production wells has reached levels about 10% to 22% above the MCL. INEEL will continue to routinely monitor its production wells to ensure that the water meets safe drinking water standards.

Groundwater samples are collected annually to determine whether substances generated by INEEL facilities would migrate through the SRPA to the Snake River in the Twin Falls-Hagerman area. This Twin Falls-Hagerman area is referred to as the Magic Valley area. The SRPA supplies most of the water that supports the Valley's farming industry as well as most of the region's drinking water.

Monitoring to date has detected VOCs and nitrates in off-site wells, but at low levels. In all likelihood, this contamination has not originated from INEEL. Possible local sources of the low detected levels of VOCs and nitrates in the off-site groundwater samples include agricultural fertilizers, effluent from animal-feeding operations and food-processing industries, and septic tanks (ESRF 2000).

What radionuclides were detected in groundwater at INEEL? Tritium and strontium-90 are radionuclides that were frequently detected in groundwater at INEEL. These radionuclides were contained in wastewater that was disposed of in injection wells or into infiltration ponds at the INTEC, TRA, and/or RWMC facilities.Given what is known about the nature and extent of non-radiological contamination and the cleanup activities planned or carried out at INEEL, it is not expected that much contamination, if any, will ever reach the Valley in the future. Even if contamination did reach the area, it would be so diluted that the levels would be well below safe guideline values. If any contaminants traveled with groundwater off site, they would travel south-southwest from INEEL, toward Minidoka (which is not in the direction of the Magic Valley, but 50 miles east of the eastern boundary of the Magic Valley Area), which is 73 miles from the INEEL source (Johnson 2000). ATSDR’s estimates suggest that groundwater leaving INEEL would reach Minidoka in about 50 to 220 years, at which point its contaminants would be present at less than 0.02% of their original concentration and not at levels sufficient to make people sick.

Gross alpha and beta measurements are screened in groundwater as a general indicator of radiological contamination. Screening identified gross alpha and gross beta activity in groundwater beneath INEEL. High levels were found on-site at the INTEC area, where gross alpha (4,700 pCi/L, or 173 becquerels per liter [Bq/L])) and gross beta concentrations (949,000 pCi/L, or 35, 113 Bq/L) exceeded their respective MCLs.

Groundwater samples have been further analyzed to identify the specific radionuclides responsible for the elevated alpha and beta radioactivity. Table A-2 in Appendix A presents the maximum concentration of specific radionuclides detected at INEEL. Of the radionuclides exceeding ATSDR's CVs or EPA's MCLs, tritium and strontium-90 were detected most frequently and/or in the highest concentrations. The following discussion describes the occurrence of tritium and strontium-90 in the groundwater in greater detail.

Elevated tritium levels up to 75,000 pCi/L, or 2,793 Bq/L, were detected beneath the INTEC and TRA facilities. Tritium was injected with wastewater into a disposal well at INTEC and discharged, with the wastewater, to the infiltration ponds at INTEC and the TRA. Routine use of the disposal well ended in February 1984. Since that time most of the radioactive wastewater was discharged to the infiltration ponds (DOE 1999). Today, INEEL disposes of much less tritium in the infiltration ponds.

A large plume extends from the INTEC and TRA areas southwestward, in the general direction of groundwater flow. The plume has also spread under the CFA. Tritium is the plume's primary contaminant. The plume has decreased from 51 square miles (mi2) in 1985 to about 40 mi2 in 1991. Although the tritium concentrations have remained nearly unchanged since 1991, the higher concentration lines appear to have "receded" to the source areas at INTEC and the TRA (DOE 1999). Dilution and radioactive decay (tritium has a relatively short half-life of 12.5 years) have greatly reduced the contaminant concentrations at the edge of the plume, giving the impression that the plume has receded (INEEL 2000). Today, the plume is monitored, but it is not actively remediated. As long as no further contamination enters the groundwater, it is expected that natural attenuation, dispersion, and decay will reduce the tritium in the groundwater to safe levels within 100 years. Researchers are looking at ways to reduce contamination entering the groundwater, such as by reducing the amount of water that can seep into the ground at disposal areas. The plume will continue to be monitored to determine the need for future cleanup (INEEL 2000)

The USGS monitors wells (USGS wells 103, 105, and 108) along INEEL's southern boundary and downgradient of the tritium plume. Tritium in these wells has been detected in only trace amounts, well below EPA's MCL of 20,000 pCi/L, or 740 Bq/L (USGS 1997). Tritium concentrations in groundwater are expected to decrease further, because the INTEC disposal well is no longer used and less tritium is being disposed of at INEEL.

A strontium-90 plume has formed in the SRPA beneath the INTEC facility, extending southwest with the general direction of groundwater flow. Concentrations have reached 516,000 pCi/L, or 19.092 Bq/L (ATSDR 2000). Strontium-90 entered the groundwater as a consequence of past waste disposal practices. Between 1952 and 1995, about 24 Ci of strontium-90 were contained in wastewater injected directly into the SRPA through the INTEC disposal well and discharged to infiltration ponds (USGS 1997). In addition, 33 Ci of strontium-90 contained in wastewater were discharged into a pit at INTEC.

Scattered detections of strontium-90 have also been reported at the TRA, but at lower concentrations (up to 1.9 pCi/L [0.07 Bq/L] in SRPA groundwater samples and up to 179 pCi/L [6.6 Bq/L] in the perched aquifer) than at the INTEC facility. Strontium-90 in the TRA does not appear to be moving in a plume. Strontium-90 in the groundwater beneath the TRA is believed to be related to radioactive waste percolating down to the groundwater from the infiltration and evaporation ponds.

Until 1992, strontium-90 concentrations in groundwater were decreasing as a result of radioactive decay processes and dilution with water recharging from the Big Lost River. More recently, however, strontium-90 concentrations in most wells have remained relatively constant, between 2.6 ± 0.7 and 76 ± 3 pCi/L (compared to EPA's MCL of 8 pCi/L [0.3 Bq/L]). It is possible that the recharge entering the groundwater from the Big Lost River has decreased and that, therefore, the groundwater and associated contaminants are less diluted (USGS 1997).

Gross alpha and beta radioactivity levels have been routinely monitored in on-site production wells and distribution systems. The detected levels of gross alpha and beta are generally consistent with background concentrations and are below their EPA MCLs (15 pCi/L, or 0.6 Bq/L, for gross alpha and 5 pCi/L, or 0.2 Bq/L, for gross beta).

Over the years, monitoring has frequently detected tritium in certain on-site wells and distribution systems. While most of the detections have been at levels below EPA's MCL of 20,000 pCi/L (740 Bq/L), tritium levels in the CFA #1 well during the mid- to late-1980s reached levels up to 38,900 pCi/L, or 1,493 Bq/L, above EPA's MCL (ESRF 1988, 1989, 1990, 1991). Because the CFA lacks a source of tritium, it is believed that the tritium may have come from contaminated groundwater at the INTEC facility.

The CFA distribution system was not sampled before 1990; therefore, ATSDR does not know what levels of tritium might have been delivered to the taps. It should be noted, however, that water from well CFA #1 would have been mixed with water drawn from well CFA #2 during that time period, and that tritium levels in the CFA #2 well were safely below EPA's MCL. Since 1989, the tritium levels in the CFA #1 well have fallen below EPA's MCL (ESRF 1998). The tritium levels in both CFA wells and the CFA distribution system currently meet water quality criteria.

Production wells near the strontium plume originating at INTEC have also been regularly monitored for strontium-90. Strontium-90 has been detected at levels up to 1.1 pCi/L (0.04 Bq/L), below EPA's MCL of 8 pCi/L (0.3 Bq/L). Strontium-90 was not detected at all during most recent monitoring events.

Table 4. Maximum Concentrations of Radionuclides in Drinking Water Supply Wells
Radionuclide Drinking Water Wells in CFA EPA MCL pCi/L (Bq/L)
Maximum Concentration pCi/L (Bq/L) Location Date
Tritium 38,900 (1,439) CFA # 1 1987 20,000 (740)

Source: ESRF 1998.
Bq/L = bequerels per liter; pCi/L = picocuries per liter

Historical groundwater sampling has identified very low levels of three radionuclides beyond site boundaries: tritium, iodine-129, and chlorine-36. In 1985, tritium detection was reported for several monitoring wells located just south of the site boundary. The levels were below EPA's MCL of 20,000 pCi/L (740 Bq/L). By 1988, the leading edge of the tritium plume had receded to within site boundaries. In 1992, iodine-129 was reported in two wells about 4 and 8 miles from the southern site boundary. The detected levels were well below 1 pCi/L (0.04 Bq/L), EPA's MCL for iodine-1291. The U.S. Geological Survey (USGS) has identified chlorine-36 as being significantly above background in 1984 at well USGS 14. USGS 14 is located approximately seven miles south of the southern INEEL boundary and southeast of Big Southern Butte. The elevated chlorine-36 values at the well have been correlated to discharges at INTEC by evaluation of chlorine isotope data in other wells. These isotopes have not been detected in more recent samples.

The USGS and the Idaho Department of Water Resources, in cooperation with DOE, have sampled select off-site private wells and water sources. These wells are between the southern boundary of INEEL and the Hagerman area, and they tap into the SRPA. They include domestic wells, irrigation wells, springs, dairy wells, and stock wells. The wells have been analyzed for selected radionuclides. Monitoring indicates that no radionuclides have exceeded the established MCLs for radionuclides in drinking water.

During monitoring in 1998, ESRF collected 28 samples from the off-site drinking water locations and analyzed the samples for gross alpha and beta radioactivity particles and tritium. No samples contained detectable concentrations of gross alpha or tritium. Gross beta activity above the minimum detectable concentration was present in many of the drinking water samples at levels between 3.0 ± 2.0 pCi/L and 8.0 ± 3.0 pCi/L, but at levels below EPA's MCL (50 pCi/L) for drinking water. Concentrations in this range are normal. They are attributed to the decay of naturally occurring potassium-40, thorium, and uranium, which dissolve with water as it trickles down through the soil (ESRF 1999).

As noted in the on-site groundwater discussion, groundwater moves south-southwest from INEEL toward Minidoka, located 73 miles away. It could take between 50 and 220 years for the water in the groundwater plume to reach the town, at which point the contamination is expected to be greatly diluted.

Surface Waters

INEEL is located in the Pioneer Basin, also known as the Mud Lake-Lost River Basin. Because this is a closed drainage basin, surface water does not flow off site. Instead, precipitation and inflowing surface water infiltrate the groundwater underneath INEEL or the water evapotranspires. Flooding is a concern at INEEL: facilities have been affected in the past by a combination of rapid snow melts, heavy rains, and frozen soil thawing. To prevent flooding, a diversion dam was installed in 1958 (and expanded in 1984) near the southwestern boundary to divert water to a series of natural depressions and spreading areas (DOE 1995).

Three rivers could possibly flow onto INEEL: Big Lost River, Little Lost River, and Birch Creek. Big Lost River, the major surface-water body, enters INEEL in the southwest corner of the site and travels northeast into an area of natural infiltration basins (also known as playas) in the northwest corner of the site. It drains more than 1,400 mi2 of mountainous area that includes parts of the Lost River and the Pioneer Ranges (USGS 1997; LMITCO 1998). Little Lost River drains about 705 mi2 of land, and Birch Creek drains an additional 750 mi2 of land to the north and west of INEEL (DOE 1995). Little Lost River and Birch Creek are frequently used as sources of irrigation before they reach the site boundary, and therefore their waters rarely reach INEEL. However, when there is a heavy rainfall or rapid snow melt, water from these two rivers may enter INEEL from the northwest and recharge the groundwater aquifer. Intermittent streams are also present during periods of high rainfall.

Only limited surface water monitoring has been done at or near INEEL. This pathway is not considered a viable route for off-site contaminant transport. First, INEEL does not withdraw or use surface water for its operations, nor does it discharge liquid waste, or effluent, into natural surface waters. Liquid effluents generated by INEEL are discharged to on-site sewage lagoons, seepage ponds, industrial waste ponds, industrial waste ditches, and sewage treatment facilities (ERSF 1998). Second, contaminants are not expected to be transported off site with surface water, since rivers and creeks seldom flow beyond site borders. As noted, most inflowing surface water and precipitation at INEEL infiltrates into groundwater. The previous section discusses groundwater quality.

Some of the information available comes from special studies by USGS of non-radiological (purgeable organic) compounds in water. The USGS data collected from six sites at or near INEEL indicated that the surface water quality met the applicable non-radiological water quality standards (DOE 1999, ESRF 2000) and has remained fairly constant over the years of testing.

More in-depth surface water sampling was done in the Magic Valley area (near Twin Falls) located southwest—slightly west of the general direction of groundwater flow—of the site (ESRF 1995). This sampling was done largely to determine whether contaminants in the Snake River Plain Aquifer were resurfacing in surface water downgradient of and at a distance from INEEL operational areas. Samples were collected quarterly from the Snake River in that study area and analyzed for gross alpha and beta activity and tritium.

The monitoring results indicate that concentrations of radionuclides in the surface water samples have generally been lower than their EPA MCLs for drinking water. Detection of radionuclides in groundwater was likely related to naturally occurring sources for the region. During recent sampling in 1998, eight samples from surface water locations showed no detectable concentrations of gross alpha or tritium. Gross beta activity above the minimum detectable concentration was present in a total of 32 of the 36 off-site groundwater and surface water samples at concentrations ranging from 3.0 ± 2.0 pCi/L to 8.0 ± 3.0 pCi/L, all below the MCL of 50 pCi/L (ESRF 2000). Concentrations detected in this range are normal and are attributed to decay of naturally occurring radionuclides, which dissolve in the water as it trickles through soil.

Soils

Past spills and former waste management practices at certain INEEL facilities have resulted in contamination being released to the surrounding surface soil. Under WMSP, surface soil samples have been collected from the Radioactive Waste Management Complex, the Stored Waste Experimental Pilot Plant, and the Waste Experimental Reduction Facility every 3 years. Under SESP, soil from eight WAGs is analyzed for radionuclides once every 7 years (ESRF 1998).

Monitoring revealed that non-radiological contaminants have been released to surface soil at INEEL. Detected contaminants include metals (arsenic, cadmium, and mercury), SVOCs [benzo(a)pyrene and DEHP], one explosive (2,4,6-trinitrotoluene), and PCBs (Aroclor 1254 and Aroclor 1260). Contaminants identified at levels above comparison values include arsenic, mercury, benzo(a)pyrene, DEHP, 2,4,6-trinitrotoluene, and Aroclor 1260, a PCB. These substances will be evaluated in the Public Health Implications section of this PHA. Table A-3 in Appendix A summarizes non-radiological contaminant concentrations.

Radiological contamination has been detected in surface soil in restricted access areas of INEEL. Some of the highest levels reported include americium-241 at 3,200 pCi/g (118,400 Bq/kg) and strontium-90 at 38,000 pCi/g (1 × 106 Bq/kg) in the TRA area; cesium-137 at 30,400 pCi/g ( 1.1 x 10-6 Bq/kg) in the TSF; and radium-226 at 11.9 pCi/g (440.3 Bq/kg) in the ARA.

ATSDR does not have soil comparison values for many radionuclides. In the absence of comparison values, ATSDR analyzed the maximum concentrations of radionuclides in on-site surface soil using the National Council on Radiation and Protection Measurements (NCRP) Report No. 129 Recommended Screening Limits for Contaminated Surface Soil and Review of Factors Relevant to Site-Specific Studies.

What is background radiation? Background radiation comes from cosmic sources, from naturally occurring radioactive materials, and from global fallout. In the United States, the average annual dose from background radiation is 300 mrem, of which 200 mrem comes from the natural decay of radon. More detailed explanations can be found in Appendix G Radiation and Radioactive Material.Following this guidance, ATSDR derived screening estimates of exposure doses. Because INEEL is in the middle of the Arco Desert, ATSDR derived screening estimates of doses for the sparsely vegetated pasture use scenario. ATSDR then compared the screening dose estimates to the International Commission on Radiological Protection (ICRP) guidance level. Currently, ICRP recommends that the general public be exposed to no more than 100 millirems (mrems) of radiation (or 1 millisievert) above background per year of exposure, based on a chronic exposure over a 70- year life span.

Background doses vary for several reasons, including naturally occurring sources (e.g., uranium and radon) and elevation. At sea level, the annual background dose from external sources is 100 ± 10 mrem (Eisenbud 1997). At higher elevations (INEEL is at approximately 4,900 feet), the background dose is expected to be higher because there is less atmosphere to provide shielding from solar and cosmic radiation.

How do we know if airborne contaminants originating from INEEL have traveled offsite ? Wind-borne contamination could spread eastward from the INEEL site. To monitor possible off-site migration, INEEL collected soil, air, and biota samples at locations near the INEEL perimeter (or boundary locations), as well at locations further away from the site (or distant locations). Boundary locations include communities near the INEEL boundary, including Atomic City, Arco, Monteview, Taber, and Terreton. While ATSDR refers to these communities as boundary communities, there is a buffer of at least 6 miles between any boundary community and the nearest INEEL facility or Waste Area Group. Distant locations include communities further away, such as American Falls, Blackfoot, Carey, Dietrich, Idaho Falls, and Minidoka. ATSDR compared the boundary and distant samples to samples collected at INEEL as a means of better distinguishing between possible INEEL contributions from other sources (e.g., worldwide fallout, long-lived natural radioactivity). Contamination originating at INEEL would be expected to decrease with distance from the source, or between boundary and distant locations.Table A-4 lists the maximum concentrations of radionuclides detected at INEEL, the locations and years of the detections, and the screening estimate of doses based on the maximum detected concentrations. As the table shows, exposure dose estimates based on the maximum detected concentrations exceeded the ICRP guideline of 100 mrem for americium-241 (88 mrem), cesium-137 (65,238 mrem), radium-226 (251 mrem), and strontium-90 (632,700 mrem). As noted, the highest levels of americium-241 and strontium-90 were found in the TRA, and the highest level of cesium-137 was found in the TSF. These concentrations are most likely related to hot spots of contamination caused by past operations. The high concentrations of radium-226 may be natural: INEEL's activities did not call for radium at the parts of the site where radium was found in soil.

In all likelihood, the greatest part of a person's time would not be spent on soil containing the highest detected concentrations of radionuclides. ATSDR therefore further analyzed the levels of americium-241, cesium-137, radium-226, and strontium-90 in on-site soil by using the geometric mean of the soil concentrations. (A geometric mean is used when data show a wide range of concentrations.) The geometric mean and the estimated doses are presented in Table A-5. As noted, the screening doses based on the geometric mean concentrations (americium-241, 0 mrem; cesium-137, 5 mrem; radium-226, 41 mrem; strontium-90, 43 mrem) are below the ICRP guidance value of 100 mrem.

Since the 1970s, INEEL has monitored surface soil at boundary and distant off-site locations and analyzed samples for specific radionuclides. (From 1970 through 1976, samples were collected annually—except in 1972—and from 1978 on, samples have been collected biannually.)

Radionuclides were detected much less frequently and in much lower concentrations (sometimes by as much as several orders of magnitude) in off-site samples than in on-site samples. Of the radionuclides analyzed, americium-241 (up to 0.09 pCi/g, or 3.3 Bq/kg), cesium-137 (up to 1.2 pCi/g, or 44.4 Bq/kg ), plutonium-238 (0.0027 pCi/g, or 0.1 Bq/kg), and plutonium-239/-240 (up to 0.035 pCi/g, or 1.3 Bq/kg) were detected (ATSDR 2000). Off-site concentrations typically varied little by location (boundary versus distant) or by sampling year (ESRF 1999).

Contamination leaving INEEL would be expected to decrease with distance from the source. But concentrations were nearly uniform, with no consistent correlation with distance from the INEEL boundary. Similarly, INEEL-derived contamination should have been highest shortly after the times of INEEL's greatest release. But again, off-site concentrations varied little from year to year. It is possible that radionuclides detected off-site are the result of fallout from worldwide nuclear weapons testing.

ATSDR further analyzed the maximum concentrations of radionuclides in off-site surface soil using the NCRP Report No.129 Recommended Screening Limits for Contaminated Surface Soil and Review of Factors Relevant to Site-Specific Studies, then compared the screening dose estimates to the ICRP recommended value of 100 mrem. The estimates, which assumed exposure to the maximum off-site concentration of radionuclides, were much lower than the ICRP guideline of 100 mrem: americium-241, 0 mrem; cesium-137, 3 mrem; plutonium-238, 0 mrem; plutonium-239/-240, 0 mrem; strontium-90, 10 mrem.

Air

Non-radiological air pollutants have been emitted from INEEL facilities and operations. INEEL monitors relevant INEEL facilities for (1) criteria pollutants (such as nitrogen dioxide, sulfur dioxide, carbon monoxide, and ozone); (2) toxic air pollutants (such as benzene, carbon tetrachloride, formaldehyde, fluorides, ammonia, and hydrochloric and sulfuric acids); and (3) particulate matter. Combustion activities (e.g., boilers and emergency generators) and chemical processing operations at INEEL emit mostly gaseous and vaporous pollutants. Waste management processes, construction, and excavation activities mostly generate particulate matter (DOE 1995).

Pollutants of particular interest are two oxides of nitrogen, nitrogen oxide (NO) and nitrogen dioxide (NO2), which are collectively referred to as NOx. Other substances monitored include sulfur oxides (primarily in the form of sulfur dioxide, or SO2) and particulates greater than 10 and 2.5 micrometers in diameter( PM-10 and PM-2.5). VOCs and NOx are evaluated for their potential to contribute to ozone formation.

NO2 was monitored at Van Buren Avenue and the Experimental Field Station (EFS) through 1998. At Van Buren, quarterly mean concentrations ranged from 1.9 micrograms per cubic meter (µg/m3) to 3.4 µg/m3, with an annual mean of 2.7 µg/m3 (1.5 ppb). This annual concentration is 3% of the EPA air quality standard of 100 µg/m3 for NO2. The maximum 24-hour concentration measured was 7.1 µg/m3 (3.8 ppb) on December 15. Quarterly means at EFS sampling ranged from 2.3 µg/m3 during the fourth quarter to 16.1 µg/m3 during the first quarter. For 1998, the mean concentration was 7 µg/m3 (3.9 ppb), 7% of the EPA standard. The maximum 24-hour average concentration occurred on January 14, when a value of 19.2 µg/m3 (10.2 ppb) was recorded.

EFS is thought to be affected by the New Waste Calcining Facility at INTEC, the largest single source of NO2 at INEEL. The Experimental Field Station (EFS) is about 3 miles in the prevailing wind direction from INTEC. NO2 concentrations observed there may indicate some effect from this facility on ambient concentrations. All quarterly concentrations have remained below 50% of the annual standard from 1990 though 1998 (time period of monitoring). Except in 1993, all annual NO2 levels remained below 20 µg/m3. 1993 levels peaked at approximately 50 µg/m3.

SO2 was monitored at the Van Buren Avenue location. The mean SO2 concentration for 1998 was 7.5 µg/m3 (2.8 ppb), 9% of EPA's annual primary air quality standard of 80 µg/m3. In 1998, the maximum recorded 24-hour SO2 concentration at Van Buren was 25.6 µg/m3, which did not approach the EPA secondary primary air quality standard of 365 µg/m3. In addition to the two primary standards, there is a secondary ambient air quality standard for SOx that cannot be exceeded more than once per year. The highest 3-hour concentration was 33.3 µg/m3 (12.5 ppb), approximately 2.6% of the secondary standard of 1,300 µg/m3.

Mean SO2 concentrations have decreased in the past decade. In 1989, INEEL's mean concentration was 17 ± 2 µg/m3. In 1998, the mean concentration was 8 ± 1 µg/m3. LMITCO gathered INEEL particulate concentrations in 1996; its maximum reading–which came from the RWMC–was 35 µg/m3 (ESRF 1997), less than the maximum 24-hour concentration of 150 µg/m3.

In addition, INEEL monitored for specific chemical contaminants at the CFA and the RWMC (ATSDR 2000). Nineteen of the listed contaminants exceeded ATSDR's CVs (see Table A-6), but these were actually measurements of subsurface vapor concentration and not ambient air. The only two chemicals that did not exceed their comparison values were benzene and trans-1,2-dichloroethene, which were detected at the CFA. For 14 of the 21 chemicals monitored, the maximum concentrations were detected at the RWMC. At this location, the values ranged from 4,520 milligrams per cubic meter (mg/m3) of toluene to 20,800,000 mg/m3 of carbon tetrachloride. At the CFA, the concentrations ranged from 31.7 mg/m3 of trans-1,2-dichloroethene to 18,600 mg/m3 of 1,1-dichloroethene.

Even though certain non-radioactive airborne contaminants have been detected at elevated concentrations on the INEEL site, concentrations are expected to decrease greatly by the time they reach the INEEL boundaries, six miles away. Still, the DOE measured particulate matter, nitrogen dioxide, and sulfur dioxide at off-site locations around INEEL. Results of the monitoring indicate the levels are within air quality standards set by the EPA (INEEL 2000). Over the years, particulate concentrations have generally been higher at boundary and distant locations than at INEEL. For example, in 1998, the annual means of total suspended particulate concentrations ranged from 5 µg/m3 at INEEL's ARA to 40 µg/m3 at Arco.

Small radioactive particles can be carried in the air. Therefore, DOE established an ambient radiological air monitoring program at INEEL in 1952 with monitoring of the RWMC area. The program was intended to determine worker safety and identify contamination controls at points of releases. Airborne particulate radioactivity and specific radionuclides are also now routinely monitored by a network of stations located on site, around the site (upwind and downwind of the site), and at boundary and distant locations. The sampling locations are selected to provide information on possible migrating pollutants before they can become a concern for off-site residents.

Particulates are monitored continuously on the INEEL site by use of a network of low-volume air samplers at on-site stations, boundary locations, and distant locations. INEEL selected on-site sampler locations to give adequate coverage in the event of releases of radioactivity from INEEL facilities and to give adequate time to protect the off-site public in the event of releases. Each low-volume air sampler is made up of a set of filters consisting of a 1.2-micrometer (µm) pore membrane filter followed by a charcoal cartridge. The filters are 99% efficient for airborne particulate radioactivity and iodides (ESRF 1999).

The filters from the low-volume air samples are collected and analyzed weekly for gross alpha and gross beta activity. If any traces of radionuclides are detected, the filters are then individually analyzed for gamma-emitting radionuclides. The particulate filters are also composited by location at the end of each quarter; all on-site composites are analyzed for gamma emitters by gamma spectroscopy, and one third of off-site composites are analyzed for specific radionuclides, which include americium-241, plutonium-238, and strontium-90.

Annual average concentrations of gross alpha and gross beta through 1998 have remained relatively low, below their respective DOE-derived concentration guides (DCGs) of 2 × 10-15microcuries per milliliter ( µCi/mL)2 and 3 × 10-15 µCi/mL. DOE's DCGs are derived for members of the general public based on the most restrictive alpha and beta emitters resulting in an effective dose equivalent of 100 mrem per year. Airborne tritium possibly related to activities at INEEL has been detected, but at levels below DOE's DCG of 10-15 µCi/mL. Particulate matter detected in certain areas, such as the RWMC and INTEC, may be attributed to the slightly contaminated soil suspended in the air during construction activities.

During recent sampling (1998), gross alpha was present in on-site samples (annual mean concentration of [1.1 ± 0.1] × 10-15 µCi/mL), in boundary samples (annual mean concentration of [1.2 ± 0.1] × 10-15 µCi/mL), and in distant samples (annual mean concentration of [1.5 ± 0.1] × -15 µCi/mL). Likewise, gross beta was measured in on-site samples (annual mean concentration of [24 ± 1] × 10-15 µCi/mL), in off-site boundary samples (annual mean concentration of [23.1 ± 1] × 10-15 µCi/mL), and in distant off-site samples (annual mean concentration of [21 ± 1] × 10-15 µCi/mL). All detected concentrations were below DOE DCGs for gross alpha and gross beta. The detected levels of airborne radioactivity for on-site, boundary, and distant locations were similar throughout the year, suggesting that no one area was being impacted by airborne contributions from specific sources, such as the INEEL facility (ESRF 1999).

To identify specific radionuclides that might have contributed to elevated concentrations in 1998, particulate filters were composited by location at the end of each quarter and analyzed for plutonium-238, americium-241, and strontium-90. Of the specific radionuclides analyzed by this method, only americium-241 and strontium-90 were detected. Americium-241 was measured during the first quarter of the year at two off-site locations, Blackfoot ([1.9 ± 1.5] × 10-15 µCi/mL) and Arco ([2.1 ± 1.5] × 10-18 µCi/mL), and then during the third quarter at one on-site location, ANL-W ([10 ± 5.71] × 10-18 µCi/mL). Strontium-90 was detected during the second and third quarters at on-site locations at concentrations up to (16 ± 7.7) × 10-11 µCi/mL (at the TRA) and during the third quarter at off-site locations at concentrations up to (13 ± 8.5) × 10-11 µCi/mL (at Blackfoot). All these levels are below DOE DCGs.

Contamination from INEEL should decrease with distance from the source. But concentrations in the ambient air and particulate samples showed little variation with distance from the INEEL boundary. Similarly, INEEL-derived contamination should have been greatest just after the times of INEEL's greatest release, but off-site concentrations varied little from year to year. Sources other than INEEL, such as worldwide fallout, may be the origin of the detected radionuclides (ESRF 1999).

Atmospheric moisture samples and precipitation samples are collected during certain years and evaluated for the presence of tritium. Detected tritium concentrations have generally been low, within normal ranges observed worldwide, and have varied little by location. During recent sampling in 1998, 31 atmospheric samples were taken at four off-site locations (Atomic City, Blackfoot, Idaho Falls, and Rexburg). Only five of these samples indicated any positive detects for tritium (up to [4.9 ± 2.0)] × 10-15 µCi/mL). Tritium was also detected (up to [4.9 ± 1.1] × 10-7) µCi/mL) in 4 of 49 samples taken from two on-site locations (weekly sampling at EFS and monthly sampling at CFA) and from one off-site location (monthly sampling at Idaho Falls). Again, measured levels were within acceptable ranges, suggesting that the tritium's presence could have resulted from natural production in the atmosphere or from worldwide fallout (ESRF 1999). (See Appendix G for a description of radiation and worldwide fallout.)

Biota/Foodchain

Contaminants released from INEEL to air may accumulate in plants and animals, which are collectively referred to as biota. Many of these plants and animals are important sources of human nutrition, but people who consume them may be potentially exposed to chemical and radiological substances.

INEEL is home to a broad range of wildlife. Game species seen at INEEL include deer, moose, and elk. Other large animal species include coyotes and bobcats. In addition to these mammals, INEEL supports a large variety of smaller animals and some species of fish, such as kokanee salmon and rainbow trout, which are present when the Big Lost River flows onto the site as a result of heavy rains or melting snow runoff (DOE 1995). Controlled hunting is permitted at INEEL one-half mile inside the site boundary. The hunting helps the Idaho Department of Fish and Game reduce crop damage caused by foraging wildlife. Cattle and sheep graze on 300,000 to 350,000 acres of INEEL buffer zone (DOE 1995), but the animals are not allowed within 2 miles of any nuclear facility, and dairy cattle are not permitted to graze on any of the buffer zone. Several farms and commercial and single-family dairies at off-site locations grow crops and raise dairy cows.

Surveillance of biota is conducted at INEEL in select facilities (e.g., RWMC and WERF) and off-site. Most of the monitoring is for radionuclides, with limited monitoring of selected metals in some vegetation, wildlife, and other biota. ATSDR has evaluated the results of metals analyses for certain types of vegetation, primarily sagebrush, and animals, such as rabbits, mice, and insects. The samples did not contain high enough levels of metals to make people ill (ATSDR 2000). Off-site sampling of biota and locally grown foods conducted by ESRF has focused exclusively on radionuclides.

Cows graze over large areas of pasture or range, and their milk tends to concentrate radioactive iodine. As such, small levels of radioactive particles can translate to high concentrations in milk. Children are particularly vulnerable to the effects of iodine in milk: they drink more milk than adults, their thyroids glands are smaller (where iodine concentrates), and children tend to be more sensitive to contaminants than adults. Sampling of milk from dairies near the INEEL border and distant from INEEL, however, show that iodine-131 was within levels seen in the environment and that no other radionuclides were present (ESRF 2000). Milk samples are also analyzed for strontium-90 and tritium.

Other biota routinely analyzed for radioactivity and specific radionuclides are wheat and garden lettuce. Potatoes have also been sampled during selected years.) Samples have been collected from both boundary locations near the site and from distant locations further away. Boundary samples have been compared to distant samples to identify possible influences from INEEL operations. Tissue samples from sheep and game that graze at INEEL have also been analyzed (ESRF 1999). Radionuclide concentrations in foodstuff have been low, with little variation between sampling locations (boundary versus distant) or between years (from 1988 through 1998). Of the radionuclides tested, strontium-90 was detected most frequently in the tested crops. As with the other radionuclides, strontium-90 concentrations in crops did not vary greatly from boundary to distant sampling locations or by year (ESRF 1999).

Cesium-137 was the most commonly detected radionuclide in tissue samples taken from sheep and local game animals. Cesium-137 concentrations detected in 1998 in three of the four tissue samples from sheep measured between (4.1 ± 3.4) × 10-9 µCi/g and (7.0 ± 3.5) × 10-9 µCi/g, and were similar to those found at both on-site and off-site control samples during recent years (1994 through 1997). Concentrations in samples collected from game animals (elk, pronghorn antelope, mule deers) ranged from (2.3 ± 2.1) × 10-9 µCi/g to (16.9 ± 2.6) × 10-9 µCi/g. The Cs-137 concentrations appear to be higher than the DOE DCG of 4 x 10-10 uCi/mL for class D (DOE Order 5100.5, 2-8-90, page III-14). ATSDR's Toxicological Profile for Cesium identifies cesium-137 levels in Alaskan caribou meat, in the range of (7 to 63) x 10-7 µCi/g (ATSDR 2001). Levels measured at INEEL could be considered as being attributable to ambient levels from previous atmospheric nuclear detonations.

Contamination from INEEL would be expected to decrease with distance from the source, but concentrations in the samples showed little variation with distance from the INEEL boundary. Similarly, INEEL-derived contamination should have been greatest just after the times of INEEL's greatest release, but off-site concentrations varied little from year to year. Sources other than INEEL, such as worldwide fallout, may be the origin of the radionuclides in the biota tissue samples.

Ambient Radiation

Atmospheric transport is a viable pathway by which people in the surrounding community could be exposed to radionuclides released from INEEL. Measuring devices called thermoluminescent dosimeters (TLDs) were placed at and near INEEL and monitored for radiation exposure by INEEL and independent researchers at ESRF (ESRF 2000).

The type of radiation that the TLDs measure is known as external radiation. This classification is an important distinction, because the total dose of radiation a person might incur includes both doses from external sources and doses from internal sources. External doses result from radioactive sources outside the body; internal radiation doses result from exposure to radioactive sources inside the body. Whether an exposure contributes to a person's external or internal dose depends primarily on the type of radiation. Alpha particles cannot travel far, and the skin prevents them from entering the body. Therefore, exposures to alpha particles would not contribute to a person's external dose; if an alpha particle source is within the body, it would contribute to a person's internal dose. Beta particles also may be responsible for both internal and external doses, but they do not penetrate body tissue as easily as gamma rays, limiting the dose from external sources. Gamma rays can travel long distances and can easily penetrate body tissues; therefore, people can be exposed to gamma rays through external or internal sources.

The external radiation that TLDs check could have many sources–natural radioactivity in the air and soil, cosmic radiation from space, fallout from nuclear weapons tests, radioactivity from fossil fuel burning, or radioactive effluents from INEEL operations and other industrial processes. TLD cards were placed 3 feet above the ground at 135 locations along facility perimeters, largely in areas likely to show the highest gamma radiation readings. The cards at each TLD location are replaced twice a year to provide semi-annual cumulative external gamma radiation measurement. More recently, cards have also been placed at 13 off-site locations (ESRF 2000).

Radiation dose measured by the TLDs is expressed in millirem (mrem). Gamma radiation measurements at on-site TLDs have generally stayed below 200 mrem/year. Occasionally, there were high readings near on-site radioactive material storage areas at the INTEC facility, near the TRA, and near a former radioactive disposal pond (ESRF 1995). In 1998, on-site TLD readings were highest at the INTEC facility (233 ± 9 mrem), at the RWMC (231 ± 8 mrem), and at the TRA (up to 574 ± 58 mrem) (ESRF 2000).

Lower measurements have been recorded at off-site TLDs. The average dose of external radiation at boundary locations was equivalent to about 126 mrem and is consistent with background. The expected annual background dose from external (terrestrial and cosmic) sources is roughly 140 ± 15 mrem, because the area is about 4,900 feet above sea level and there is less atmosphere to shield from solar and cosmic radiation than at sea level. At sea level the annual background dose from external sources is closer to 100 ± 10 mrem (Eisenbud 1997).

1 Iodine-129 has a very long half-life of 15.7 millions years, suggesting that it may remain present in the environment for a long time. For this reason, scientists are interested in tracking iodine-129 concentrations in groundwater. Data, however, are too limited at this time to show contaminant trends.
2 1 × 10-9 µCi/mL = 1 pCi/L = 1,000 pCi/m3.

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