The Radiological Cleanup of Enewetak Atoll

Note: For information related to claims, call the Department of Veterans Affairs (VA) at 800-827-1000. For all other 

information, call the Nuclear Test Personnel Review (NTPR) Program at 800-462-3683.

Historical Background

The Enewetak Atoll has a total land surface area of about 2.75 square miles consisting of 40 islands surrounding a central 

388 square mile lagoon in the Pacific Ocean. Following World War I, the Treaty of Versailles awarded control of the 

atoll to Japan with the stipulation that the atoll could not be fortified. During World War II, Japan used the atoll as a 

strategic base in violation of the Treaty. In 1944, the U.S. military captured the atoll and used it as a support and staging 

area. After Japan surrendered, the United Nations agreed to the U.S. trusteeship of the atoll, which placed the atoll under

U.S. administration, legislation, and jurisdiction.

The Trinity Test, the first nuclear weapon detonation, in Alamogordo, New Mexico and then the use of nuclear weapons 

in Hiroshima and Nagasaki, Japan ushered in the nuclear age. With the advent of these new weapons of war, additional 

testing and development was necessary. The Enewetak Atoll was a desirable testing location since:

1. It was under the control of the U.S.

2. The area was uninhabited or subject to evacuation without imposition of unnecessary hardship on a large number 

of inhabitants.

3. It was within 1,000 miles of the nearest B-29 aircraft base, as it was expected that one test nuclear device was to 

be delivered by air.

4. It was free from storms and extreme cold.

5. It has a protected harbor at least six miles in diameter thereby being large enough to accommodate both target and 

support vessels.

6. It was away from cities or other population concentrations.

7. The local winds were predictably uniform from sea level to 60,000 feet.

8. The water currents also were predictable and not adjacent to inhabited shorelines, shipping lanes, and fishing 

areas which avoided contaminating populaces and their food supply.

The residents of the Enewetak Atoll had to be evacuated before the initiation of the nuclear weapons testing. To minimize 

the hardship to the residents, the U.S. Navy constructed a small village on the Ujelang atoll, 124 miles southwest of 

Enewetak and transported the residents to their new location on December 21, 1947.

The nuclear tests were primarily conducted in the atoll’s northern quadrant to minimize radioactive contamination to the 

base camps on the southern islands. In 1958, the U.S. ceased nuclear testing on Enewetak in response to a trilateral 

testing moratorium between the United Kingdom (U.K.), Soviet Union (U.S.S.R.) and U.S. This moratorium was short 

lived, but in 1963, the Limited Test Treaty was signed by the U.K., U.S.S.R., and U.S. that officially and effectively 

banned atmospheric weapons testing by the partner states.

In the early 1970s, the U.S. decided that control of the atoll was no longer necessary due to the cessation of nuclear 

weapons testing and decided it would be best to return control to the Trust Territory of the Pacific Islands. The U.S. felt 
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there was a moral and potentially legal obligation to remediate the atoll due to the debris, unexploded munitions, 

dilapidated buildings and radiological contamination. To evaluate the radiological conditions on the atoll an extensive 

pre-cleanup survey was performed in late 1972 through early 1973. Congress directed DOD to manage the cleanup 

operation and the Department of Energy to provide technical support. This three year remediation project commenced in

May 1977 and ended on May 13, 1980 when the final 45 cleanup personnel departed the Enewetak Atoll.

Today, all of the atoll islands and the lagoon are accessible with the exception of Runit Island. Runit Island was 

quarantined due to residual sub-surface soil contamination and the use of “Cactus Crater”. The crater was formed during 

a May 1958, 18 kiloton surface detonation on the northern tip of Runit Island. It now contains radiologically contaminated 

waste from the atoll cleanup. The concrete-lined crater containing waste was entombed by a concrete dome, completed in 

spring 1980.

In 1986, the U.S. government officially returned the atoll to the Marshall Island Republic (MIR) sovereignty and created a 

partnership with the MIR to provide continued annual personnel monitoring. Islanders maintaining a typical islander 

lifestyle that includes locally grown or caught food are found uniformly to have very little to no intake of residual 

radionuclides and their annual radiation doses are below U.S. averages.

Summary of the Radiological Cleanup of Enewetak Atoll

The DOD organized three separate efforts in support of the cleanup: Removal and lagoon-dumping of uncontaminated 

debris and structures, removal and crater-entombment of radiologically contaminated debris and structures, and excision 

and crater-entombment of radiologically contaminated soil from the islands.

The islands of the atoll were classified based on intended use which determines the acceptable soil contamination level, 

see Table 1. The contamination criterion was established to limit the annual lung and bone doses to a resident living the 

typical island lifestyle to 0.010 and 0.013 rem1 per year, respectively

Radiological surveys were used to identify which islands required decontamination and to develop the remediation and 

radiological safety plans. The soil plutonium concentration level was evaluated to determine the necessity and extent of 

soil remediation, which were divided into three categories.

• Level 1: Plutonium concentration was greater than 400 pCi/g – soil removal by scraping.

• Level 2: Plutonium concentration was between 40 and 400 pCi/g – individual case consideration.

• Less than 40 pCi/g did not require cleanup.

Table 1. Island contamination criteria based on intended use

Intended Use Contamination Criteria 

(pCi/g) Number of Islands

Residential < 40 30

Agricultural > 40 and < 160 7

Food Gathering < 160 2

Quarantined - 1

 1 A rem is a radiation protection unit of measure that quantifies the risk of biological effects resulting from exposure to ionizing 

radiation. Ionizing radiation is any radiation (gamma, x-ray, beta, neutron, or alpha) capable of displacing electrons from atoms or 

molecules, thereby producing ions. According to the National Council on Radiation Protection and Measurements (NCRP, Report 

No. 160, Table 1.1), the general U.S. population receives about 0.62 rem per year from natural background radiation sources (radon, 

cosmic rays, and rocks) and man-made radiation sources (medical diagnostic x-rays and consumer products). As a basis of 

comparison, a standard diagnostic chest x-ray delivers a radiation dose of about 0.02 rem.
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The radiological soil surveys identified 12 islands with plutonium concentrations greater than 40 pCi/g; however, not all 

of these islands required remediation since they were not intended for residential use. The Planned Use Condition, Final 

Qualification Condition and Final Soil Survey results are recorded in Table 2.

Table 2. Radiologically contaminated islands with respective contamination levels

Island Name Code 

Name

Average Final Soil Survey 

(pCi/g)

Planned Use 

Condition1

Final Qualification 

Condition1

Taiwel Percy 6 Food Gathering Residential

Bokenelab Mary 19 Food Gathering Residential

Mary's Daughter Fern 139 Food Gathering Food Gathering

Lujor Pearl 63 Agricultural Agricultural

Pearl's Daughter Gwen 123 Food Gathering Food Gathering

Aej Olive 54 Agricultural Agricultural

Billae Wilma 3 Food Gathering Residential

Alembel Vera 7 Agricultural Residential

Elle Nancy 52 Food Gathering Agricultural

Boken Irene 80 Food Gathering Agricultural

Bokoluo Alice 140 Food Gathering Food Gathering

Bokombako Belle 95 Food Gathering Food Gathering

Mijikadrek Kate 20 Food Gathering Residential

Kidrinen Lucy 77 Food Gathering Agricultural

Louj Daisy 43 Food Gathering Agricultural

Bokinwotme Edna 33 Food Gathering Residential

Edna's Daughter - 103 Food Gathering Food Gathering

Kirunu Clara 65 Food Gathering Agricultural

Elelron Ruby 8 Food Gathering Residential

Aomon Sally 7.5 Agricultural Residential

Sally's Child Zoe 21 Food Gathering Residential

Bijire Tilda 7 Agricultural Residential

Enjebi Janet 20 Residential Residential

Runit Yvonne Permanently Quarantined
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Table 2. Radiologically contaminated islands with respective contamination levels (cont’d)

Island Name Code 

Name

Average Final Soil Survey 

(pCi/g)

Planned Use 

Condition1

Final Qualification 

Condition1

Boko Sam 0.3 Food Gathering Residential

Munjor Tom 0.3 Food Gathering Residential

Inedral Uriah 0.2 Food Gathering Residential

- Van 0.2 Food Gathering Residential

Jinedrol Alvin 0.3 Food Gathering Residential

Ananij Bruce 0.2 Agricultural Residential

Jinimi Clyde 0.15 Food Gathering Residential

Japtan David 0.2 Residential Residential

Jedrol Rex 0.2 Food Gathering Residential

Biken Leroy 2.5 Food Gathering Residential

Kidrenen Keith 0.3 Food Gathering Residential

Boken Irwin 0.4 Food Gathering Residential

Ribewon James 0.2 Food Gathering Residential

Mut Henry 0.4 Food Gathering Residential

Ikuren Glenn 0.2 Food Gathering Residential

Bokandretok Walt 0.2 Food Gathering Residential

Medren Elmer 0.3 Residential Residential

Enewetak Fred 0.5 Residential Residential

Lojwa Ursula 1.9 Agricultural Residential

Radiation Protection Standards

The primary radiological contaminants of the soil on the northern islands were long-lived transuranic elements (plutonium 

and americium) and relatively short-lived radioisotopes cesium-137, strontium-90 and cobalt-60. The principle purpose 

of the cleanup was to reduce the long-lived transuranic elements to levels that did not pose a long-term hazard to the 

returning people of Enewetak.

Due to extensive surveys providing an understanding of the radiological environment of each of the islands, rigid control 

of access to contaminated islands was employed to minimize exposure to radiation. The personnel working on the 

contaminated islands were supervised by the Radiation Control Division and under constant surveillance of the Field 

Radiation Support Teams. These workers were tracked by island access cards, wore dosimetry, and in the likelihood of 

internal contamination, received a bioassay. The Field Radiation Support Teams issued personal protective equipment 

and established monitoring requirements based on potential exposure environments, conditions and work assignments.

Radiation Doses

Due to the time between the last nuclear test at the atoll and the start of the Enewetak Cleanup Project, much of the shortlived radioisotopes had decayed to levels that resulted in extremely low dose rates. Approximately 68% of the 12,248

film badge readings showed no detectable exposures with less than 0.03% exceeding 0.07 rem. 7,519 thermoluminescent 

dosimeters were also issued, 99.97% of the readings were less than 0.042 rem.

Air samples were taken to monitor for the possibility of internal radiological contamination due to inhalation. Of the 

5,204 air samples collected, 95% of the samples were less than 1% of the established limits with none of the samples 
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exceeding 10% of the limits. To verify workers in contaminated areas were not internally contaminated, bioassay (urine) 

samples were collected and analyzed for plutonium intake. The samples were overwhelmingly (99.97%) negative, which 

indicates that the controls in place were effective in protecting the workers from internal contamination.

More information regarding the 1980 Radiological Cleanup of Enewetak Atoll is available at the NTPR public webpage at 

http://www.dtra.mil/Home/NuclearTestPersonnelReview.aspx.

March 2018