Field note: irrigation of tree stands with groundwater containing 1,4-dioxane

Coniferous and deciduous tree stands totaling 14 ha were recently planted on a closed landfill, and when mature, the stands are expected to be part of a natural treatment system for recovered groundwater. The trees would be irrigated at the rate of 189 L/min year-round with water containing 1,4-dioxane (< 10 mg/L), a compound that would be taken up and phytovolatilized by the trees. The water is moderately saline and contains elevated levels of manganese. This paper describes a concurrent series of preliminary studies, performed prior to the full-scale planting, to assess the feasibility of the phytoremediation system. Greenhouse experiments were carried out to identify tree species that can take up 1,4-dioxane and are tolerant of the water. Estimates were made of the area of the tree stand necessary to transpire the irrigation water plus precipitation. The landfill matrix was characterized in terms of its percolation rate and water holding capacity and based on those results salinity-modeling studies were carried out to estimate the fate and leaching potential of the various inorganic species that would accumulate in the root-zone of the trees. A pilot study, currently in progress on the landfill, suggested that the landfill cap is a suitable matrix for the establishment of large trees, and that the stands could be irrigated without the production of excess drainage.