Superfund Site Profile

An investigation to delineate the extent of 1,4-dioxane in groundwater is currently underway. Following completion of the 1,4-dioxane investigation, a decision will be made by EPA and the state on how to address contamination that extends off-site. The site monitoring and mitigation plan will be updated accordingly.


The 160-acre Marshall Landfill site consists of two adjacent 80-acre landfills. The northern landfill is Marshall Landfill, and the southern landfill is Boulder Landfill. Marshall Landfill began operating in 1965 as a solid waste composting and disposal operation. Between 1969 and 1974, Marshall Landfill accepted municipal waste, unstabilized sewage sludge, and many unknown, potentially hazardous, wastes. In 1974, Boulder County discontinued use of Marshall Landfill when Boulder Landfill opened to the immediate south. Boulder Landfill closed in January 1992. Sources of contamination include areas of saturated refuse, waste disposal trenches, small areas where organic solvents were disposed and two unlined leachate lagoons. Landfill operations contaminated surface water and on-site shallow groundwater.

The site’s remedy included a groundwater collection and treatment system, landfill improvements and environmental monitoring programs. The remedy began operating in 1993. EPA placed the collection and treatment system on a stand-by mode in November 2004 after influent to the treatment system consistently met the discharge requirements for the main contaminants of concern. Operation and maintenance activities and groundwater monitoring are ongoing.