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AOC 36 - Mustard Gas Investigation Report
Section 6.0 - Foerster Ferex Magnetometer Survey
A magnetometer survey was conducted in the area of interest delineated during the location survey, as well as in the area 150 feet north which had been identified by former CSSA personnel, to locate buried metal. The sweep was conducted by ordnance experts from UXB International, Inc. These ordnance experts are all former U.S. military explosive ordnance detachment (EOD) personnel who received ordnance training at the U.S. Naval Explosive Ordnance School at Indian Head, Maryland and who have at least three years of active duty experience.
UXB personnel are practiced in the skill of identifying ordnance and ordnance related scrap on the ground surface and underground. Underground ordnance is identified through use of a magnetometer. Since magnetometers have no ability to differentiate between ordnance items and ordinary solid waste (large nails, nuts and bolts, other metal waste), each magnetic anomaly must be excavated to determine if it is caused by ordnance.
The magnetometer survey was conducted on 26 February 1997 using a Foerster Ferex (Mk-26) Ordnance Locator magnetometer. This type of magnetometer is a military-approved locator and is in use by U.S. military EOD teams. The Foerster Ferex locator is a hand-held unit which uses two fluxgate magnetometers aligned and mounted a fixed distance apart to detect changes in the earth’s ambient magnetic field. These changes in the magnetic field can be due to ferrous metal or magnetic disturbances in the soil. Both an audio and metered signal is provided to the operator. The metered signal indicates whether the disturbance is geodetic or metal related.
According to its manufacturer, the Foerster Ferex Locator identifies large ferrous objects to a depth of 18 feet. As described in Section 2.0, mustard gas shells were likely more than 2 feet long (26.78 inches), and more than 6 inches in diameter (155-mm). Containing only 11.7 pounds of mustard gas each, their total weight of 95 pounds consisted primarily of metal casing. Objects this size can effectively be identified to a depth of 18 feet using the Foerster instrument.
The Foerster Ferex is also capable of identifying anomalies within a horizontal radius of 3 to 5 feet. To ensure adequate coverage, a grid with a spacing of three feet was used to guide the Foerster Ferex magnetometer survey. UXO specialists assembled in line formation, one per search lane, and advanced in a slow, continuous pace, visually inspecting the surface for UXO, evidence of mustard gas shells, and evidence of ordnance compounds in the soils (stains); simultaneously, they searched for subsurface anomalies with a magnetometer. This process continued until each search lane was completed. Each time the instrument indicated an anomaly, the operator placed a pin flag next to the highest obtainable reading from the instrument. Once all detectable anomalies were marked, UXO personnel conducted anomaly excavation procedures, as described in Section7.
Flags marking buried magnetic anomalies at suspected mustard gas burial area.
Because the suspected mustard gas disposal area is located within SWMU B-28, a unit used to dispose of solid waste and metallic debris in trenches, numerous anomalies were identified during this sweep. Many of the anomalies were caused by metal debris on the ground surface. Those anomalies which were visible at the surface and did not require invasive work were immediately removed. Each of these items were examined to determine if they were UXO or mustard gas shell fragments. Metal items determined to be free of explosives were placed in a roll-off container for recycling. UXO items were segregated for later disposal.