317/319 Phytoremediation Site Monitoring Report - 2004 Growing Season

摘要

In 1999, Argonne National Laboratory (ANL) designed and installed a series of engineered plantings consisting of a vegetative cover system and approximately 800 hybrid poplars and willows rooting at various predetermined depths. The plants were installed using various methods including Applied Natural Sciences TreeWell system. The goal of the installation was to protect downgradient surface and groundwater by hydraulic control of the contaminated plume by intercepting the contaminated groundwater with the tree roots, removing moisture from the upgradient soil area, reducing water infiltration, preventing soil erosion, degrading and/or transpiring the residual volatile organic compounds (VOCs), and removing tritium from the subsoil and groundwater. This report presents the results of the monitoring activities conducted by Argonnes Energy Systems Division (ES) in the growing season of 2004. Monitoring of the planted trees began soon after the trees were installed in 1999 and has been conducted every summer since then. As the trees grew and consolidated their growth into the contaminated soil and groundwater, their exposure to the contaminants was progressively shown through tissue sampling. Since the inception of the project, significant progress was made in the refinement and testing of the analytical method (for which no official method is available), the determination of the optimal tissue for sampling, and of the variability of the concentrations within a specific tree. An understanding has also been developed on background concentrations of VOCs, and how to discriminate between VOCs that are associated with plant tissue because of aerial or of soil/groundwater uptake pathways. Also, during the 2003 sampling campaign, core samples from tree trunks were collected for the first time (the trees were large enough to stand the procedure). Data collected from the French Drain area last year supported the hypothesis that a correlation was present between concentrations of VOCs in the soil and in corresponding branch tissue. During this year (2004), systematic data collection in the French Drain area further consolidated this correlation and indicated that trees are clearly in the condition to have reached the target rooting depth. Concentrations in the hundreds of ppb in branch and trunk samples confirm that uptake can be a quantitative way to remove VOCs from the contaminated media. Additionally, laboratory studies were conducted in 2004 to determine mass recoveries from leaves and branches using the headspace method, and to determine if we could further modify our sample pretreatment method to ensure optimal recovery. Results showed that the recovery of TCE in leaves and branches with our current method ranged between 98 and 138%, indicating that most of the TCE present in the samples is recovered during the analysis. Freezing and heating had variable results in recovery rates, which resulted in no significant changes being introduced to the current SOP.