FIELD NOTE: IRRIGATION OF TREE STANDS WITH GROUNDWATER CONTAINING 1,4-DIOXANE

Abstract

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.

KEYWORDS:

• phytoremediation
• landfill
• 1
• 4-dioxane
• phytovolatilization
• manganese-toxicity

ACKNOWLEDGMENTS

We gratefully acknowledge Jeff Hodgen, Casey Anderson, Nickolee Zollinger, and Jean Kennedy (former employees of Phytokinetics, Inc., Logan, Utah) for their assistance with the greenhouse studies and the installation of the pilot plots. We thank Seth Ryan, Tareq Adham, Jen Musella, and Jennifer Cassada (ENSR, Raleigh, North Carolina) for helping with the landfill characterization project and the monitoring of the pilot plots. We also thank Dr. Lynn Dudley (Department of Geology, Florida State University) for carrying out the salinity modeling studies and Rob Hibbs (Measuretek, Inc., Albany, Oregon) for capable assistance with the pilot monitoring instrumentation.

Notes

^(a)May through end of September (mean ETo = 12.7 cm/mo).

^(b)October through end of April (mean ETo = 6.1 cm/mo).

^(c)October through end of February (mean ETo = 4.8 cm/mo).

^(d)March and April (mean ETo = 9.4 cm/mo).

^(e)Average precipitation in the area of the site, 8.4 cm/mo.

^(f)189 L/min = 29.2 cm/mo for the 2.8 ha deciduous stand. 7.4 cm/mo for the 11.2 ha coniferous stand (or 9.7 cm/mo when only 8.4 ha are irrigated).

^(g)The following equation was used (Ferro et al., 2003): V_T = ETo Θ LAI, where V_T = transpiration rate for the stand; ETo = reference evapotranspiration. ETo = (0.8) pan evaporation; Θ = water use coefficient. Θ = 0.66 for the deciduous stands; Θ = 0.4 for the coniferous stands. LAI = leaf area index. LAI = 6.0 for the deciduous stands; LAI = 10 for the coniferous stands. Values for V_T listed in the table are 75% of values estimated using the equation in order to account for plant stress resulting from salinity, Mn, landfill waste, landfill gas, etc.