Characterizing Exposure of Veterans to Agent Orange and Other Herbicides Used in Vietnam: Final Report (2003)

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MILITARY UNIT AND HERBICIDE SPRAYING DATABASES, AND EXPOSURE ASSESSMENT MODEL DEVELOPMENT 17 Vietnam for every military unit, down to the company level, for the duration of its assignment in South Vietnam. The primary problem in characterizing mobile units' locations was incomplete data. A critical issue was to determine whether data on a unit for particular dates were missing simply because the unit did not move and therefore did not report its continued residence at one location or whether the gaps are missing data. To develop statistical methods that could be used to evaluate the data in the entire database, the researchers studied patterns of movement of units on which substantial data already existed. That exercise yielded criteria for identifying data that indicated “short-term location stability” (where there may not have been consistent recording of location but there were not data gaps), which in turn helped to identify units for which “true” gaps existed. The researchers could then more reliably impute missing locations for these units. A preliminary cleaning and analysis of a large dataset of troop locations of Army combat battalions assigned to Military Region III13 suggested that data sources available in the National Archives (including Daily Journals, After-Action Reports, and Operation Reports-Lessons Learned) could be used to resolve most of the data problems encountered. That indicated to the researchers that it should be possible to assemble location databases for other mobile units—an important finding because such units are likely to have been among the most heavily exposed to herbicides. Herbicide Dispersion Data The Columbia University researchers determined that a major aspect of linking a military location with an exposure opportunity rests in the computerized records of herbicide application commonly known as the HERBS files. Records indicate that 95% of all herbicide used during the war were dispersed under Operation Ranch Hand, the US Air Force aerial spraying program (Stellman JM et al., 2003). Those records, although incomplete, are by far the most important 13 Military Region III, also known as the III Corps Tactical Zone (III CTZ), comprises a large area in the south of Vietnam surrounding Ho Chi Minh City (formerly Saigon). It was an area of heavy combat and wartime spraying. 

MILITARY UNIT AND HERBICIDE SPRAYING DATABASES, AND EXPOSURE ASSESSMENT MODEL DEVELOPMENT 18 records available for exposure-assessment purposes. In 1974, the National Research Council organized data into a file, known as the HERBS tape, that contained coordinate points for more than 6,200 missions flown by fixed- wing aircraft and included date, type of herbicide, gallons applied (gallonage), and purpose of mission (NAS, 1974). The data in the HERBS file are given in UTM coordinates; a mission is recorded as a series of turning points in the flight path. Algorithms were written to translate from UTM to Cartesian coordinates so that spray- mission data could be integrated with other geographic information. Other programs transformed the discrete turning points into continuous flight paths so that exposure potential could be evaluated over complete spray routes. Although herbicide operations in Vietnam began in August 1961, the HERBS file contains data only from 1965 on. During the course of their work, the researchers found additional information on pre-HERBS-file spraying in a variety of sources, including two early Air Force documents (Buckingham, 1982; CHECO, 1967), the Air Force Herbicide Project folders housed at the National Archives (which contain detailed information on the planning and execution of most Air Force herbicide missions), publications produced by the US Military Assistance Command, and information retrieved from the government of South Vietnam “202 Tasks Realized” report. In the early 1980s, ESG assembled a tape to supplement HERBS—the Services-HERBS tape—consisting of helicopter, backpack, truck, and other smaller-scale spraying data. The database also included some information on aborted spray missions, leaks, and other unintentional releases. The combined data from those two sources comprised over 8,800 individual military spray missions. However, several discrepancies existed between the two files. Many could be resolved by a careful comparison between consecutive legs with cross-referencing to the map of Vietnam or by reference to the Daily Air Activity Reports (DAARS). When discrepancies could not be resolved, a panel of military experts assembled by the contractor reviewed the missions and determined whether it was clear that the error was typographic and whether it was possible to resolve the differences. If it was impossible to resolve 

MILITARY UNIT AND HERBICIDE SPRAYING DATABASES, AND EXPOSURE ASSESSMENT MODEL DEVELOPMENT 19 a difference, the mission was flagged as questionable in the database so that it could be included or excluded at the discretion of the user. As a result of that exercise, the researchers developed a composite HERBS file that contains the date of spraying, coordinates of the spray mission, type of herbicide, number of gallons, mode of application, type of aircraft (if appropriate), and—where available—area sprayed. For missions flown with aircraft, the file also contains connectivity indicators that enable one to trace the path of spraying. During the researchers' reinspection of the DAARS, it became clear that individual missions were associated with particular targets and that identifying numbers (project numbers) were assigned to the targets. An earlier NAS report (1974) described how herbicide operations were organized into projects to be approved by various committees. In re-examining the original HERBS file obtained from NARA and ESG, the researchers found a field that could be related to the project numbers on the DAARS. When the HERBS file was grouped according to this field, all the Ranch Hand missions fell into specific projects. That was a major breakthrough in understanding the herbicide-spraying program because it allowed several thousand spray missions to be rationalized into a few hundred projects for analysis purposes. It is described in greater detail in a paper by the researchers that was featured on the cover of Nature on April 17, 2003 (Stellman JM et al., 2003). Combining and validating data from all those sources produced a final composite spraymission database that comprised 9,141 missions (19,977 sorties14) that dispersed 19,491,090 gal of herbicide in 1961–1971 (Stellman and Stellman, 2003). Depending on the assumptions used, the researchers estimate that the herbicides contained 487–807 lb (221–336 kg) of TCDD (Stellman JM et al., 2003). 14 A mission was executed by one to four aircraft. Each aircraft's flight was considered a sortie.