Applied Research: Ground-water Contaminant Transport at Rocky Mountain Arsenal

In 1991, an experiment was conducted in a very complex contaminant plume at the Rocky Mountain Arsenal (RMA) near Denver, Colorado.  Extensive contamination of RMA groundwater had resulted from the Army’s manufacturing of chemical and incendiary weapons (e.g. mustard, lewisite, napalm) in the mid-1940s and the nerve agents VX and GB (Sarin) in the early 1950s.  From 1952-1982, Shell and predecessors leased facilities at RMA and manufactured a range of pesticides.  In the mid-1970s, contaminated groundwater was discovered flowing north and northwest beyond the base boundary and contaminants were found in groundwater production wells, surface water, and surface sediments leading to crop damage and livestock deaths. Since many of the contaminants would have been expected to move slowly compared to the groundwater flow due to their interactions with the soil, it had been speculated that those interactions were weakened and the transport of the contaminants “facilitated” by unknown processes within the plumes.  The goal of the experiment was to determine if facilitated transport was occurring and, if so, to find out why.  The experiment clearly showed that all monitored organic contaminants were migrating at the same rate as groundwater, and related laboratory tests suggested that properties of the plume were preventing sorption of the contaminants by the soil.