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ATSDR's PHAs are exposure, or contact, driven. A release of a hazardous wastedoes not always result in human exposure. Rather, people are exposed to acontaminant such as those identified at the INEEL site only if they come in contactwith it; they might be exposed by breathing, eating, or drinking a substancecontaining the contaminant, by skin contact with a substance containing thecontaminant, or from close proximity to gamma emitters. ATSDR concentrated itsreview on the time period 1987-2000. Exposures prior to 1987 are being estimated by the CDC dose reconstruction project.

This section evaluates the estimated exposure doses for contaminants of concern forcompleted and potential exposure pathways for potentially affected populations. Inthese evaluations, ATSDR considered the frequency and duration of the estimatedexposures. For populations affected by more than one pathway, ATSDR alsoconsidered the combinations of contaminants and exposure routes. This section alsopresents the potential health effects from each contaminant of concern in a completedpathway.

ATSDR considered characteristics of the exposed populations–such as age, sex,nutritional status, genetics, lifestyle, and health status–that influence how a personabsorbs, distributes, metabolizes, and excretes contaminants. Where appropriate,ATSDR includes these characteristics in the contaminant-specific discussions.

In evaluating public health hazards, ATSDR first tries to determine exposure by carefullyevaluating the elements of an exposure pathway that might lead to human exposure.These elements include (1) a source of site-related contamination, such as drums or wastepits; (2) an environmental medium in which the contaminants might be present or fromwhich they might migrate, such as groundwater or soil; (3) points of human exposure,such as drinking water wells or gardens; (4) routes of exposure, such as breathing, eating,drinking, or touching a substance containing the contaminant; and (5) a receptorpopulation. (Figure 4 explains exposure pathway evaluation in more detail.) ATSDR thenidentifies an exposure pathway as completed or potential, or else eliminates that pathwayfrom further evaluation. A completed exposure pathway exists if all elements of humanexposure link the contaminant source to a receptor population. A potential pathway is onethat ATSDR cannot rule out, even though one of the necessary elements is not apparent.

If a completed or potential exposure pathway exists, ATSDR then considers whetherchemicals of concern were present, are present, or are expected to become present. (Nomatter how much of a contaminant of concern is present, a public health hazard existsonly if people come in contact with, or are otherwise exposed to, harmful levels of thatcontaminant.)

Following the strategy outlined above, ATSDR identified completed and potentialexposure pathways by which the public could be exposed to contamination specificallyassociated with INEEL. All of these involve workers and visitors drinking INEELdrinking water. The following table (Table 5) shows all of the exposure pathways. Adiscussion about which pathways are completed, potential or eliminated begins on Page41.

Table 5.

Exposure Pathways Evaluation Table
Pathway Name Exposure Pathway Elements Comments
Point of Exposure Route of Exposure Potentially Exposed Population Time Frame of Exposure
Completed Exposure Pathways
Groundwater/ Drinking Water Taps served by wells at the CFA Ingestion On-site workers and sporadic visitors Past Past: Elevated levels of tritium were detected in well CFA#1 during the mid- to late-1980s. Workers and visitors who drank water supplied by these wells could have been exposed to radionuclides, but not at high enough levels to make them sick. Currently, the INEEL water supply meets safe drinking water standards.
Potential Exposure Pathways
Groundwater/ Drinking Water Drinking water supply wells and distribution system Ingestion On-site workers and sporadic visitors Past Past: Monitoring since the 1970s has revealed that the groundwater beneath the site is contaminated with a variety of non-radiological contaminants and radionuclides. ATSDR did not review groundwater and drinking water data for early years of operation. Therefore, it is not known with certainty whether people at the INEEL could have been exposed to contaminants when they drank water in the past (before the 1970s).
Eliminated Pathway
Groundwater/ Drinking Water On-site wells and off-site private drinking wells Ingestion, skin contact, and inhalation On-site workers and off-site residents Current and potential future On-site production well water is being and will be monitored to ensure that water delivered to the taps is safe for drinking. Any groundwater contamination is expected to be greatly diluted before reaching off-site areas.
Surface Waters Surface water Ingestion and dermal contact Workers or off-site residents No likely past or current exposure, or potential future exposure On-site surface water is not used for recreation. Surface water from on site does not directly affect surface water off site, because surface water flow is directed toward INEEL. Low levels of radionuclides, not specifically related to INEEL, have been detected in off-site surface water at levels below CVs. Infrequent and brief contact should not cause health effects.
Soils Potential contact with soils during a site visit or hunt Ingestion, dermal contact, and inhalation Workers, occasional site visitors, or hunters Limited past worker exposure. No likely current or potential future exposure Public access is restricted at all facility operation sites. ATSDR assumes that workers in these areas are protected from high exposure by guidelines mandated by the Occupational Safety and Health Administration (OSHA). Minimal soil contamination is expected in the limited areas of public access. Low levels of radionuclides, unrelated to INEEL, have been detected in off-site soil. Brief, infrequent contacts are not hazardous.
Air On-site work areas Air On-site workers, sporadic visitors, nearby off-site residents Limited past worker exposure. No likely current or potential future exposure The Draft Historical Dose Reconstruction for Air Releases from the ICPP, found that the ICPP contributed only a fraction of the thyroid dose as that from the Nevada Test Site. Air pollutants have been detected at several facilities on site. No public exposure has occurred or is occurring, because access is restricted at all facility operation sites. ATSDR assumes that workers in the area are protected from high exposure by OSHA-mandated guidelines. Very low levels of non-radiological contaminants and radionuclides, unrelated to INEEL, have been detected in off-site ambient air. Brief, infrequent contacts are not hazardous.
Ambient Radiation Off-site work areas, off-site locations Whole body On-site workers, sporadic visitors, nearby off-site residents Possible past worker exposure. No likely current or potential future exposure Gamma radiation readings were high near certain INEEL facilities. The public is restricted from these areas, and ATSDR assumes that workers are protected from high exposure by OSHA-mandated guidelines. Off-site levels do not vary greatly between nearby and distant locations nor from estimated natural background effective doses, and the levels are insufficient to affect public health.
Biota Off-site work areas Ingestion Residents of neighboring residential areas No past, current, or potential future Radionuclides have been detected in crops grown off the site and also in the muscles of livestock raised at the site and game grazing there. The levels of radionuclides were similar between nearby and distant locations and consistent with background concentrations.

Completed Exposure Pathways

Past Exposure of Workers to Tritium in INEEL Drinking Water

During the mid- to late-1980s, tritium was detected at levels above EPA's MCL–20,000pCi/L–in a supply well in the CFA. (Information is lacking on the concentrations thatmight have been in the distribution system that fed site taps during this period. Butbecause the distribution system was supplied by at least 2 wells, water from a wellexceeding a sample was always diluted by one or more wells that did not.) Workers andvisitors to this area who drank water from this supply were exposed to levels of tritium.The wells were never used by the general public nor by surrounding communities as adrinking water supply. Currently, the levels of tritium in the CFA wells (and distributionsystem) are safely below EPA's MCL.

Potential Exposure Pathways

Past Exposure of Workers to INEEL Drinking Water Contaminants

Elevated levels of a variety of non-radiological contaminants (primarily VOCs and metals) andradionuclides (primarily tritium and strontium-90) have been detected in on-site groundwater since theearly 1970s. Elevated levels of VOCs have also been detected in on-site production wells, but not insamples taken from the distribution system that feeds site taps. Because the groundwater has beencontaminated for a long time and the site water supply has relied solely on groundwater, ATSDR hasdetermined that on-site groundwater is a potential pathway of past exposure. Currently, no exposure toharmful levels of contaminants is occurring via the groundwater/drinking water pathway. INEEL monitorsits drinking water to ensure that it meets safe drinking water standards.

Eliminated Exposure Pathways

ATSDR has not identified any other complete or potential exposure pathways. For other pathways, (1) exposure to the general public has been prevented and/or (2) no site-related contamination is present and/or the measured levels are consistent with background concentrations. Specifically:

  • Current and future uses of drinking water: INEEL drinking water wells are tested and will continue to be tested to ensure that the water delivered to site taps is safe for drinking. No harmful levels of contamination are expected to reach off-site communities, now or in the future. Contamination found in groundwater at INEEL would take a very long time to reach the nearest community, at which point any contaminants would be greatly diluted.

  • Surface waters and surface soils: Public exposure to on-site surface water and surface soil is minimal, if it occurs at all, because the site is heavily guarded to restrict access. Monitoring has revealed that surface water samples collected from off-site area streams and rivers and soil samples collected from off-site locations contain only very low levels of radionuclides. The levels are within normal ranges observed worldwide.

  • Air: Emissions from several on-site facilities released non-radiological contaminants and radionuclides into the ambient air. Historical levels of non-radiological contaminants and radionuclides were much higher than current levels, but all levels have been within acceptable federal guidelines. The largest contribution to air would have been from diffuse sources of tritium at RWMC. Access restrictions prevent the public from entering on-site areas where the highest levels of airborne contamination have been detected. Radionuclides detected at off-site boundary and distant locations are within normal ranges observed worldwide. For the public, estimated radionuclide exposures along INEEL's southern boundary, where the nearest community is located, or along the eastern boundary, with the direction of wind flow from INEEL, are well below EPA radiation protection standards.

  • Biota/foodchain: Radionuclides have been detected in milk, crops, and livestock/game animals at very low levels (near the laboratory method detection concentrations). Concentrations found in on-site livestock/game animals are similar to concentrations detected in off-site areas over the years. The levels are also consistent with ranges observed in foodstuff worldwide. ATSDR does not expect people to get sick from eating foods containing the detected levels of radionuclides.

  • Ambient radiation: Ambient radiation exposure was measured at various facilities at INEEL. The exposure levels were greatest near source facilities. Much lower exposure would have occurred off site at boundary and distance locations. INEEL is restricted to the public, so no public exposure occurs on site. Off-site exposures from INEEL do not exceed estimated natural background exposures for the region and are within normal ranges observed worldwide.


Toxicological Evaluation

Non-Radiological Contamination

If a person is exposed to a contaminant, several factors determine the type and severity ofhealth effects associated with that exposure. These include exposure dose (how much ofthe substance is taken into the body), frequency (how often), and duration (how long); theroute of exposure (breathing, eating, drinking, or skin contact); and the multiplicity ofexposure (the combination of contaminants and pathways involved). Once exposure takesplace, characteristics such as age, sex, nutritional status, genetics, lifestyle, and healthstatus of the exposed individual influence how the individual absorbs, distributes,metabolizes, and excretes the contaminant. Together, those factors and characteristicsdetermine the health effects that might result from exposure to a contaminant.

After identifying exposure pathways, ATSDR considers information about exposures inlight of scientific information from the toxicological and epidemiologic literature.ATSDR may estimate exposure doses, which are estimates of how much contaminant aperson is exposed to on a daily basis. When estimating exposure doses, ATSDR looks atmany variables, including contaminant concentration, exposure amount, exposurefrequency, and exposure duration. For example, exposures in the workplace are differentfrom those in a residential setting.

ATSDR may compare estimated exposure doses to standard toxicity values. Fornoncancer effects, ATSDR uses ATSDR's minimal risk levels (MRLs) and EPA'sreference doses (RfDs) to eliminate exposures that are not expected to result in adversehealth effects. Chronic MRLs and RfDs estimate what level of daily human exposure to asubstance is likely to pose no appreciable risk of adverse noncancer effects over aspecified duration. Chronic MRLs and RfDs are values based on the levels of exposurereported in the literature that represent no-observed-adverse-effect levels (NOAELs) orlowest-observed-adverse-effect levels (LOAELs) for the most sensitive outcome for agiven route of exposure (e.g., inhalation, ingestion). Uncertainty (safety) factors areapplied to NOAELs or LOAELs to account for variation in the human population and theuncertainty involved in extrapolating human health effects from animal studies. ATSDRthen reviews toxicological and epidemiological literature to evaluate the weight ofevidence for adverse effects.

Comparison values and estimated dose comparisons allow ATSDR to decide whichsubstances are present at such low levels that they are not expected to cause harm, andfor which ATSDR can therefore confidently decline further evaluation. The substancesnot eliminated, and for which there are completed or potential pathways, are furtherconsidered in this section. When ATSDR evaluates a substance's potential to makepeople ill, the agency looks at site-specific factors that influence likely exposure doses.The agency also re-examines relevant scientific literature about the substance (andsometimes related substances) and how observations from the literature relate to theconditions of exposure at the site. ATSDR explores probable speciation,bioavailability, environmental fate and transport, cultural practices, the means by whichexperimental animals are exposed compared to how local populations might beexposed, how occupational levels and routes of exposure compare to levels and routesof exposure for the public, and many other factors.

ATSDR also evaluates the likelihood that site-related contaminants could cause cancer inpeople who would not otherwise develop it. To screen for the potential for cancer tooccur, ATSDR uses cancer slope factors (CSFs) that define the relationship betweenexposure doses and the likelihood of an increased risk of developing cancer over alifetime. But CSFs are developed by use of data from studies of animals or humansexposed to doses much higher than those typical of exposures to contaminated air, water,or soil. When evaluating the potential for cancer to occur, ATSDR must consider therelevance of such extrapolations from high exposure doses administered in animal studiesto the lower exposure levels typical of human exposure to environmental contaminants.

Built into the CSF derivation is the assumption of a linear-no-threshold (LNT) model thatassumes that the dose is proportional to the probability of cancer from the high dosesused in the laboratory down to the doses encountered in the environment. LNT assumesthat natural defenses are not effective against cancer at lower doses. A CSF represents theupper-bound estimate of the probability of developing cancer at a defined level ofexposure. CSFs tend to overestimate the actual risk in order to be protective in screeningand to avoid the risk of missing potentially significant exposures that should beevaluated.

ATSDR also considers the cancer effect levels (CELs) reported in the literature. ACEL is the lowest dose of a chemical in a study or group of studies that was found toproduce increased incidences of cancer (or tumors).

Consumption of Volatile Organic Compounds in Drinking Water at INEEL in thePast

In the past, TCE and carbon tetrachloride (both volatile organic compounds, or VOCs) insome INEEL production wells (RWMC #1, TSF #1, and TSF #2) exceeded ATSDR CVsand EPA MCLs for drinking water. The production wells fed into a facility , but not site-wide distribution system in which the water from each production well was diluted by thewater from other production wells. The diluted water in the separate distribution systemswas used for drinking. There are no data showing that contamination in any of the facilitydistribution systems exceeded ATSDR CVs or EPA MCLs for drinking water.

To determine whether drinking water containing carbon tetrachloride or TCE had thepotential to increase adverse health outcomes, ATSDR estimated exposure doses. Inestimating to what extent people might be exposed to contaminants, ATSDR usedassumptions about how much contaminated water they drank and how often they drank it.The assumption was that the average contaminant concentrations in people's drinkingwater were equal to the maximum detected concentrations in the wells, rather than thelower maximum concentrations found at drinking water taps. ATSDR assumed that anadult consumes 2 liters of water every day for 365 days each year. These assumptionsallowed ATSDR to estimate the highest relevant exposure dose and to determine whetherhealth effects could occur.

The estimated exposure doses for either a child or an adult were below its RfD forcarbon tetrachloride, 0.0007 milligrams per kilogram of body weight per day(mg/kg/day). The RfD for carbon tetrachloride was derived from a laboratory study thatfound a NOAEL of 1 mg/kg/day–more then 50,000 times greater than the dosesATSDR estimated (ATSDR 1994).

No chronic MRL or RfD currently exists for TCE. For this reason, ATSDR reviewed theavailable toxicologic literature to determine possible adverse effects associated withexposure at doses estimated for this pathway. On the basis of this review, the exposuredoses ATSDR estimated for TCE are several orders of magnitude lower than the lowestdoses that, according to the toxicologic literature, can produce noncancer effects inexperimental animals administered oral doses of TCE (ATSDR 1997).

Remember that ATSDR assumed that the water in the distribution system could haveaveraged as high as the maximum found in one well feeding the system and that peoplereceived all their drinking water from this system. This was an overestimate of actualexposure, because lower contaminant concentrations have been found in the affectedwells, the distribution system drew from uncontaminated wells in addition to thecontaminated ones, and people ingest water from many sources (e.g., prepackagedjuices, soda, water supplies at the workplace). Therefore, ATSDR concludes thatdrinking water containing the highest detected levels of TCE reported in the productionwells is not expected to result in adverse noncancer effects.

TCE has been shown to cause cancer in laboratory animals given large doses. The linkbetween cancer in humans and TCE in drinking water is controversial, however.Available studies are inconclusive, and the data are inadequate to establish a link. EPAis currently reviewing the scientific literature to determine how to classify TCE'scarcinogenicity.

ATSDR compared doses estimated for exposed workers or visitors to doses estimatednot to result in cancer. ATSDR assumed that people were exposed to the maximumdetected concentrations of carbon tetrachloride (5.5 ppb) and TCE (15 ppb) and thatexposure occurred daily over the entire exposure period. This is an overestimate ofactual exposure, for people would have also ingested water from other sources.

Using these exposure assumptions, ATSDR determined that the levels of VOCs found inthe drinking water supply systems did not pose a health threat to INEEL workers or thesurrounding community.

Radiological Evaluation

For radiological contaminants, ATSDR uses information on radiation exposure and its effects, as related toenvironmental levels. This information comes from federal agencies, including EPA, the US Departmentof Energy (DOE), and the Nuclear Regulatory Commission (NRC). ATSDR also uses other publiclyavailable data sources and recommendations on radiation dose limits. The National Council on RadiationProtection and Measurements (NCRP), the International Commission on Radiological Protection (ICRP),and the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) developthese sources.

Consumption of Tritium in Drinking Water at INEEL in the Past

People were exposed to tritium in drinking water from on-site water supply wells in the past; however,those exposures did not pose any health risk to workers or site visitors. Tritium concentrations indrinking water in the CFA were measured as high as 38,900 pCi/L in 1987. This was above EPA'sMCL of 20,000 pCi/L; therefore, ATSDR evaluated the estimated dose.

If a full-time worker in the CFA were to drink 2 liters of this water daily for 7 days per week and 52 weeksper year, that worker would receive less than 2.6 millirems of whole-body dose in that year, or about 2.0%of the whole-body radiation background dose. This dose estimate is very protective, because it wascalculated from the historic maximum tritium concentration and it assumes that the workers drank all theirwater from the contaminated well at the CFA. Any part-time worker or visitor to the site would receiveonly a small fraction of this already insignificant dose.

Health Outcome Data Evaluation

The ATSDR public health assessment process has not been able to find evidence of releases of substancesto the public at levels that might be expected to result in any ill health. However, to address communityconcerns, ATSDR evaluated data for six counties adjacent to INEEL for the occurrence of congenitalanomalies (birth defects) and for cancer incidence and mortality, comparing the data with data for the stateof Idaho as a whole. This comparison allowed ATSDR to determine whether certain health conditions areunusually common in the six counties, but it did not provide any information about the possible causes ofbirth defects and cancer.

Using exposure data covering the period 1987-2000, ATSDR has not identified any populations nearINEEL that were or are being exposed to levels of contaminants that would be expected to result in acuteor chronic health effects. However, to address community concerns about various health outcomesreported in the vicinity of INEEL, and to consider latency periods for potential past exposures, ATSDRevaluated health outcome data from several existing vital records and disease surveillance databases. Aspart of the evaluation process, ATSDR reviewed vital record and birth defect information from the IdahoDepartment of Health and Welfare's Center for Vital Statistics and Health Policy. ATSDR obtained theassistance of the INEEL Health Effects Subcommittee, the Idaho Division of Health (Bureau ofEnvironmental Health and Safety and the Center for Vital Statistics and Health Policy), and the CancerData Registry of Idaho.

ATSDR examined records for 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 thatthe types of cancers commonly associated with radiological and chemical exposures are within the range ofwhat would be expected on the basis of comparisons with the state of Idaho. Rates of certain cancers,cases, or deaths were less than expected, and some were greater than expected. In most instances, thedifferences were not statistically significant. Most of the small increases in cancer rates were likely a resultof random variability, since there did not appear to be any consistent increases across counties or withincounties (e.g., although breast cancer incidence was significantly increased in Clark County, it wassignificantly decreased in the more populous Bingham County, compared to the incidence in the rest of thestate).

Community Health Concerns

ATSDR identified community health concerns through meetings with community members, state and local officials, and INEEL personnel. ATSDR also reviewed site documents, including Community Relations Plans. Concerns raised during these interviews are discussed and addressed below: transuranic waste, operations of an incinerator, high cancer rates, Pit-9, the SL1 Reactor accident, contaminated on-site water supply wells, and reburial of plutonium over the aquifer.

Operations of a Transuranic Waste Incinerator

DOE has placed a moratorium on construction and operation of incinerators, pending an evaluation of alternative technologies. If INEEL incinerates transuranic wastes in the future, it will do so at its advanced mixed waste treatment plant. If that happens, health and safety issues will be addressed: the incinerator's emission control system will be set up to filter ultrafine particles of plutonium.

Choices about particular remedial actions at particular sites are made by federal and state regulatory agencies other than ATSDR. These agencies must consider public health implications along with other risk management considerations. If requested, ATSDR can review the actual trial burn data (stack emissions data) and/or ambient air monitoring data to evaluate the potential public health implications of this facility. ATSDR's "Public Health Overview of Incineration as a Means to Destroy Hazardous Waste" is available at ATSDR's webpage at:

While ATSDR does not endorse or promote the use of any particular technology, ATSDR believes that properly designed and operated incinerators can destroy or decontaminate certain kinds of hazardous wastes (primarily organic contaminated wastes) in a manner that is protective of public health. Incinerators are neither inherently safe nor unsafe.

High Cancer Rates in the Counties Surrounding INEEL

ATSDR's evaluation of cancer rates for the counties surrounding INEEL found that certain cancer types occurred more often than expected. Sometimes the differences were statistically significant. On the other hand, other types of cancer occurred less often than expected, and sometimes these differences were also statistically significant.

For males, significant increases in cancer rates in a single county were seen for bone and joint cancers, prostate cancer, and acute lymphocytic leukemia. For women, significant increases were seen in brain and breast cancer rates in a single county. Significant decreases in the incidence of certain cancers for men (total leukemia and acute lymphocytic leukemia) and for women (thyroid and breast cancer) were observed for a single county when compared to the state's experience. There were also significant decreases in rates for certain cancers (e.g., lung and bronchus cancer) among men and women across multiple counties. Overall, both men and women had higher rates for some cancers and lower rates for others compared to the state's rate, with some bias toward negative deviations.

Status of Cleanup Measures at Pit 9

Figure 4 Pit-9 Aerial ViewPit 9 was operated as a waste disposal pit from November 1967 to June 1969. (See Figure 4. Pit 9 Aerial View.) It was used to dispose of approximately 110,000 cubic feet of transuranic waste from the Rocky Flats Plant and additional low-level wastes from waste generators located at the INEEL. The total volume of the pit is approximately 250,000 cubic feet of overburden, 150,000 cubic feet of packaged waste, and 350,000 cubic feet of soil between and below the buried waste. Most of the transuranic waste consists of drums of sludge (contaminated with a mixture of transuranic waste and organic solvents), drums of assorted solid waste, and cardboard boxes containing empty contaminated drums.

Lockheed Martin Advanced Environmental Systems (LMAES), the subcontractor chosen for Pit 9 cleanup, was terminated for default on June 1, 1998, by INEEL contractor Lockheed Martin Idaho Technologies Company. The Pit 9 interim action was intended to provide information about methods for retrieval and treatment of buried transuranic waste and information on the status of contaminant migration and waste characteristics. After LMAES began its work slowdown in the summer of 1997, it became clear that a contingency plan was needed to assure that these objectives could be met. The litigation regarding LMAES has negatively impacted implementation of the contingency plan.

The clean-up of Pit 9 has recently been fast tracked. On July 30, 2002 workers began bolting and welding together a steel shoring box to be fitted around the perimeter of the dig zone in a small portion of Pit 9. In April of 2002, the DOE agreed with the state of Idaho and the EPA to start construction at Pit 9 by Nov. 30, 2002.

Much of the plutonium-contaminated waste in Idaho came from the fabrication of plutonium weapons parts at the Rocky Flats Plant near Denver, Colorado, and other weapons facilities. Waste that is stored above ground will eventually be moved to the Waste Isolation Pilot Plant (WIPP) near Carlsbad, New Mexico. Disposal of the waste that was buried before 1970 will be addressed under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). Currently, the reburial of plutonium is on hold.

ATSDR, in its consultation on the Pit 9 remedial action plan dated September 1993, recommended not going through with the planned action, because the cleanup levels would not be protective of public health.

Exposures That Resulted from the SL-1 Reactor Accident

The Stationary Low-Power Reactor No. 1's (SL-1's) mission was to provide power to radar stations along the northern perimeter of North America; a series of such stations was known as the Defense Early Warning Line. The design work was done by Argonne National Laboratory in 1955-1956 under the name Argonne Low Power Reactor. The Army's designation for the plant, SL-1, indicates that the plant was a stationary, low-power reactor and that it was the first of its kind.

SL-1 and its planned successors did not include a conventional reactor containment structure. Because they were designed for deployment in remote areas, it was not thought to be necessary. Instead, the reactor building was a simple steel cylinder with quarter-inch-thick walls. It was 48 feet high and 38.5 feet in diameter. No special provisions were made to ensure that the building would be airtight.

The accident occurred on January 3, 1961, at the Atomic Energy Commission's National Reactor Testing Station near Idaho Falls, Idaho. The cause of the accident was most likely operator error. A technician must have manually withdrawn one of the control rods; rapid boiling of water in the channel caused the rod to be ejected with great force. The result was a power excursion, fuel failure, and release of fission products.

Three technicians were working at SL-1 that night. They all died, making this the first fatal accident caused by a nuclear fission reactor outside the former Soviet Union. There was a fatality associated with the September 1983 accident at the RA-2 reactor in Argentina. Though the victims all received lethal doses of radiation, two died from other injuries before they could die from the radiation. Monitoring for radiation releases from the site began almost immediately. Calculations, completed later, indicate that approximately 10 curies had been released by early morning on January 4, 20 curies by the morning of January 5, and a total of 50 more curies between January 6 and January 30, 1961.

According to calculations conducted at the time, about 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. During the recovery period, 23 people received radiation doses greater than 3 rem. Of those, three received total whole body doses in excess of 25 rems, but none received enough to display any near-term symptoms (Thompson 1973).

Potential Health Threats Posed by Contaminated Water Supply Wells

In the past, VOCs and tritium were detected in INEEL drinking water supply wells at levels above screening comparison values, but drinking the water at INEEL would not pose any health risks to on-site workers or to the sporadic visitor. One reason is that people did not drink directly from the drinking water well, but rather from drinking water distribution systems in which the water from the contaminated well was diluted by water from uncontaminated wells. Comparison values are designed to be very protective of people (including children) over a lifetime of drinking water. Because of a large margin of safety built into the comparison values, the worker's or sporadic visitor's lifetime intake would be much lower than the levels shown to cause health effects.

Monitoring to date has confirmed that no contamination has migrated to any off-site drinking water supply wells. Groundwater moves south-southwest from INEEL toward Minidoka, about 73 miles away (Johnson 2000). It would take between 50 and 220 years for the groundwater to reach the town, at which point the concentrations in the plume would be greatly diluted–less than 0.02% of the original value.

Exposure to Plutonium That Is Being Reburied over the Snake River Aquifer at INEEL

All reburial activities at INEEL are in landfills monitored for leakage. The only plutonium that would be permitted for reburial on site would be at concentrations below the WIPP acceptance criteria of 100 nanocuries per gram. Plutonium was once thought to be insoluble and not likely to migrate through soil. We now realize that colloids of plutonium tend to move through soil more readily than previously thought. This is still not a health threat, because the plutonium is not in a bio-available form.

Child Health Considerations

ATSDR recognizes that the unique vulnerabilities of infants and children demand special emphasis in communities faced with contamination of their water, soil, air, or food. Children are at greater risk than adults from certain kinds of exposures to hazardous substances emitted from waste sites and emergency events. In general, children are more likely to be exposed because they play outdoors and they often bring food into contaminated areas. They are shorter than adults, which means they breathe dust, soil, and heavy vapors close to the ground. Children are also smaller, so they receive higher doses of chemical exposure proportional to their body weight. The developing body systems of children can sustain permanent damage if toxic exposures occur during critical growth stages. Most importantly, children depend completely on adults for risk identification and management decisions, housing decisions, and access to medical care.

Contaminants have been detected in INEEL drinking water wells in the past. Children probably never visited the operational portions of INEEL served by the affected wells. People did not drink directly from the drinking water wells, but from drinking water distribution systems in which the water from contaminated wells was diluted by water from uncontaminated wells. A child who visited the area could have had only sporadic, indirect exposure to drinking well water. Comparison values that may have been exceeded in drinking water are designed with a large margin of safety to protect people (including children) from prolonged, continuous exposure for a lifetime of drinking water 24 hours per day, 7 days per week, and 52 weeks per year. A child visiting the site would be expected to take in far less than the protected intake rates. Because of the margins of safety built into the comparison values, the child's lifetime dose would be orders of magnitude below doses shown in the scientific literature to cause harm to the most sensitive species.

ATSDR also attempted to identify populations of children in the vicinity of INEEL and any public health hazards threatening these children. Approximately 73 children under the age 6 and younger live within 10 miles of the INEEL facilities. ATSDR determined, however, that harmful exposures are not expected to occur, because children cannot access areas of concern or locations of contamination at INEEL and no harmful exposures associated with INEEL are specific to children at boundary community schools, residential areas, or recreational areas. Following a careful evaluation of these pathways as they relate to children, ATSDR determined that no harmful exposures have occurred in the past, nor are they likely to occur either now or in the future. These potential exposure pathways are discussed in the "Pathways Evaluation" section of this document.


On the basis of our evaluation of available environmental information, for the period1987-2000, ATSDR categorized the exposure situations at INEEL as "no apparent publichealth hazard". ATSDR concluded that although there have been exposures in the past,no adverse health effects are expected. Conclusions regarding specific health concerns areas follows:

  1. No site-related contaminants are currently accessible to the public, on oroff site, at levels known to cause adverse health effects. Therefore, no adverse healtheffects are expected, given current conditions. If conditions change, ATSDR will reviewits conclusion.

  2. Elevated levels of VOCs and tritium have been detected in certain INEELdrinking water wells in the past. No contamination has migrated to off-site drinking watersupplies. ATSDR evaluated exposure to the levels of contaminants in the INEEL wellsand the drinking water distribution system supplied by the wells and determined thatdrinking from INEEL's water supply would not harm workers or increase their risk ofdeveloping adverse health effects. INEEL continues to monitor the water supply to ensurethat it meets state and federal drinking water standards.

  3. Elevated county cancer rates (when compared to state averages) wereprobably the result of random variability, because they did not appear to be consistentincreases within the counties.

  4. Fission products reaching the atmosphere as a result of the 1961 SL-1reactor accident did not cause any health problems. Although an estimated 80 curies werereleased to the atmosphere, 99.99% of the fission product inventory was contained in thereactor building and did not reach the atmosphere.


  • If future non-radiological and radiological sampling data or land usemodifications change exposure scenarios, ATSDR will review those data and respondappropriately.

  • Where needed and requested, undertake an environmental health educationprogram to provide information to community members on health outcome datapresented in the Idaho National Engineering and Environmental Laboratory public healthassessment.


The Public Health Action Plan for the INEEL contains a description of actions to betaken by ATSDR and other government agencies at and in the vicinity of the site after thecompletion of this public health assessment. The purpose of this Public Health ActionPlan is to ensure that this public health assessment not only identifies public healthhazards but also provides a plan of action designed to mitigate and prevent adversehuman health effects from exposure to hazardous substances in the environment. Ifadditional information for the INEEL site becomes available, that may change theconclusion of this PHA, human exposure pathways should be reevaluated, and theseconclusions and recommendations should be amended, as necessary, to protect publichealth.

  • INEEL staff will notify ATSDR immediately if environmentalcontamination either is detected off site or has the potential to migrate off site. Upon suchnotification, ATSDR will determine appropriate public health actions.

  • ATSDR is working with the INEEL Health Effects Subcommittee todetermine appropriate community health education.

  • ATSDR will continue to address new health concerns as they arise,through health consultations.

  • The Cancer Data Registry of Idaho will continue to collect cancerincidence data for the state of Idaho, including the six counties involved near INEEL.

  • ATSDR has developed a "Public Health Overview of Incineration as aMeans to Destroy Hazardous Waste", which is available on the ATSDR webpage at: If incineration is ever selected as aremediation technology, ATSDR can be requested to review trial burn data (stackemissions data) and/or ambient air monitoring data and evaluate the potential healthimplications of the facility.

  • After Completion of activities for the dose reconstruction, beingconducted by CDC/NCEH, ATSDR will determine if the agency needs to do furtherevaluation of past exposures (before 1986).



Michael Brooks, MSHP, CHP
Senior Health Physicist, Lead Health Assessor
Federal Facilities Assessment Branch
Division of Health Assessment and Consultation

Jo A. Freedman, Ph.D., D.A.B.T.
Federal Facilities Assessment Branch
Division of Health Assessment and Consultation

Steve Martin, M.B.A.
Data Analyst, Federal Facilities Information Management System
Office of Program Operations and Management
Information Resources Management Branch


Sandra Isaacs
Chief, Federal Facilities Assessment Branch
Division of Health Assessment and Consultation

Rita Ford
Chief, Energy Section
Federal Facilities Assessment Branch
Division of Health Assessment and Consultation

ATSDR Region X Representative

Richard W. Robinson
Environmental Protection Specialist
Seattle, WA

Peer Reviewers

James E. Watson, Ph.D.
University of North Carolina at Chapel Hill
Professor, Department of Environmental Sciences and Engineering

Sydney W. Porter, CHP
Porter Consultants, Inc.
Ardmore, PA

David J. Tollerud, M.D., M.P.H.
University of Louisville
Associate Director, Institute for Cellular Therapeutics
Director, Specimen Repository Core Facility
Clinical Professor, School of Medicine


Ackerman DJ. 1991, Transmissivity of perched aquifers at the Idaho NationalEngineering Laboratory, Idaho. US Geological Survey, Water-ResourcesInvestigation Report 91-4114, DOE/ID-22099.

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Agency for Toxic Substances and Disease Registry. 2001.. Toxicological profile onCesium. (Draft for Public Comment July 2001.) Atlanta: US Department of Health andHuman Services.

Bechtel BWXT (BWXT). 2001. 2000 Environmental monitoring program report forthe Idaho National Engineering and Environmental Laboratory.

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Environmental Science and Research Foundation, Inc.1988. DOE. Idaho NationalEngineering and Environmental Laboratory site environmental report for calendar year1987. Environmental Science and Research Foundation, Inc. May 1994.

Environmental Science and Research Foundation, Inc. 1989. DOE. Idaho NationalEngineering and Environmental Laboratory site environmental report for calendar year1988. Environmental Science and Research Foundation, Inc. June 1989.

Environmental Science and Research Foundation. 1990. DOE. Idaho NationalEngineering and Environmental Laboratory site environmental report for calendar year1989. Environmental Science and Research Foundation, Inc. June 1990.

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Environmental Science and Research Foundation. 1997. DOE. Idaho NationalEngineering and Environmental Laboratory site environmental report for calendar year1996. Environmental Science and Research Foundation, Inc. July 1997.

Environmental Science and Research Foundation. 1998. DOE. Idaho NationalEngineering and Environmental Laboratory site environmental report for calendar year1997. Environmental Science and Research Foundation, Inc. July 1998.

Environmental Science and Research Foundation. 1999. DOE. Idaho NationalEngineering and Environmental Laboratory site environmental report for calendar year1998. Environmental Science and Research Foundation, Inc. 1999.

Environmental Science and Research Foundation. 2000. DOE. Idaho NationalEngineering and Environmental Laboratory site environmental report for calendar year1998. Environmental Science and Research Foundation, Inc. July 2000.

Garabedian SP. 1992. Hydrology and digital simulation of the regional aquifer system,Eastern Snake River Plain, Idaho. Washington DC: US Geological Survey ProfessionalPaper 1408-F.

Idaho National Engineering and Environmental Laboratory (INEEL). 2000. 2000Oversight and overview. A synopsis of activities and issues related to the INEEL fromthe state agency charged with overseeing the site on behalf of the citizens of Idaho. 2000.

Idaho National Engineering and Environmental Laboratory (INEEL). 2001a. INEELOverview. Available at . January2001.

Idaho National Engineering and Environmental Laboratory (INEEL). 2001b.INEEL Environmental activities at INEEL. Available at . January 2001.

Johnson T M, Roback R C, October 2000, Groundwater "fast paths" in the SnakeRiver Plain aquifer: Radiogenic isotope ratios as natural groundwater tracers: Geology;v. 28; no. 10; p. 871-874.

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Miller E C, and Varvel M D. 2001. Reconstructing past disposal of 743 Series wastein the subsurface disposal area for Operable Unit 7-08, organic contamination in theVadose Zone. INEEL/EXT-01-00034, Rev. 0, Idaho National Engineering andEnvironmental Laboratory, Bechtel BWXT, Idaho, LLC, Idaho Falls, Idaho.

Plastino M. 1998. Coming of age: Idaho Falls and the Idaho National EngineeringLaboratory.

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US Department of Energy. November 2000. Draft proposed plan for Operable Unit 1-07Bfinal remedial action at the TSF Injection Well (TSF-05) and surrounding groundwatercontamination (TSF-23). Idaho Operations Office: US. Department of Energy..

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US Department of Energy.April 16, 2002. Operable Unit 7-08 volatile organic compoundvapor monitoring results from selected wells at the Radioactive Waste ManagementComplex, Supplement 2001. Idaho Falls Operations Office: US Department of Energy,INEEL/EXT-2000-00040, Supplement 2001, EDF-ER-126, Rev 0.

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