Monitoring the Effectiveness of Phytoremediation and Hydrogeologic Response at an Agricultural Chemical Facility

Background – Phytoremediation offers the prospect of using biotechnology to degrade or sequester contaminants from soil and groundwater, and/or slow the movement of shallow groundwater. Sequestration of heavy metals and degradation of petroleum hydrocarbons and volatile organic compounds is well documented; however, the fate of many pesticides is unclear. If groundwater movement can be slowed, possibly so will the movement of contaminants off-site, and therefore, a greater likelihood they will be degraded by biotic or abiotic processes, or be sequestered by plants.
The study site, located near Bancroft, Wisconsin, has a history of soil and groundwater degradation. Dinoseb (2, sec-butyl-4,6-dinitrophenol) is the primary contaminant of concern and this soil is unacceptable for conventional landfill disposal or landspreading. Sandy soil, shallow groundwater, and other factors make this a prime site to study the effects of phytoremediation. In June 2000, a mixture of
834 hybrid poplars, willows, and cottonwoods were planted in an effort to degrade and/or retard the movement of pesticides.

Objectives – The objectives of this research were:

1) Assess mortality and biomass production of the established trees at the site as they begin tapping into the capillary fringe of groundwater.
2) Correlate hydrologic response to transpiration rates at various times through the project duration (both daily and seasonal changes). Calculate radius of influence based on water table observations and correlate the results with a capture-zone model.
3) Determine changes in groundwater contaminant profile through the plots. Perform biannual testing on select monitoring wells (12 from the current project and three from the ACCP). Analyze a total of 32 samples per year on selected wells and piezometers. Install three to four piezometers with 2-foot screens to help assess the vertical extent of contamination.