South Korean and U.S. officials today collected groundwater samples near a U.S. army base here, widening their probe into the alleged burial of the toxic defoliant Agent Orange by American troops about three decades ago.

Samples were taken from 10 wells and streams near Camp Carroll by experts from South Korea’s Environment Ministry, in the presence of U.S. military officials. The two sides also discussed how they would proceed with the joint investigation, officials said.

The investigation began after former U.S. soldiers told a U.S. television station early this month that they buried large amounts of the dangerous chemical in 1978 at a heliport inside Camp Carroll in Chilgok, 300 kilometres southeast of Seoul. “The groundwater samples will be analysed by several environmental laboratories. It is expected to take more than two weeks for the analysis to produce results”, a ministry official said. From the next week, South Korea and the U.S. will jointly start monitoring sites at Camp Carroll, according to the official.

Lt Gen John D Johnson, commander of the 8th US Army and lead investigator into the allegations said yesterday that ground-penetrating radar devices will be mobilised next week to identify substances buried at Camp Carroll. “If we get evidence that there is a risk to health, we are going to fix it,” Johnson told a local radio station.

Earlier this week, U.S. Forces Korea (USFK) said a 1992 study showed that a “large amount” of pesticides, herbicides and solvents were buried at Camp Carroll in 1978, but were removed and taken to an unknown site during the following two years. It also said its review of records found “trace amounts” of dioxin in a 2004 test at the site, but the findings do not “directly” indicate that Agent Orange was buried there.

Agent Orange was a defoliant widely used in the Vietnam War and is suspected of causing serious health problems, including cancer, genetic damages and birth defects in children. The defoliant was contaminated by dioxin, a highly toxic substance.

Despite a pledge by U.S. commanders for a swift probe into the claims of Agent Orange burial, concerns over health or environmental risks are growing in Chilgok, a city of some 30,000 people.