Shelby, North Carolina
Shelby, NC — 2015-Present
Chlorinated volatile organic compounds (CVOCs) and 1.4-dioxane in shallow soils and groundwater (0 to approximately 25 feet below ground surface).
To evaluate the potential for utilizing phytoremediation in to control the subsurface migration of CVOCs.
The TreeMediation implementation consisted of 150 TreeWell units which were installed in 20 by 20 foot spacing at approximately 25 feet below ground surface in May, 2015. Alternations of willow, London plane, and tulip poplar trees were planted in each unit. Nine piezometers were installed for the utilization of transducers to capture water level, and eight camera tubes were installed to capture root data. In spring of 2016, 42 willow and poplar trees were planted to replaced the 30% of poplar and London planes which had suffered mortality in the fall of 2015. In the spring of 2017, an additional 10 willow and 6 river birch trees were planted to replace the remainder of the tulip poplars.
Results to Date:
Aside from the 2015 mortality of the poplars (caused by improper storage and a delay in planting due to excessive rainfall), tree growth and viability were observed to be “very good” for the remainder of the TreeWell study. In 2017, an infestation of imported willow leaf beetles consumed most of the leaves of willow trees, which has not affected the overall growth or vitality. However, any reduction of leaf area or early leaf drop has the potential to reduce the hydraulic function of the system. Due to early spring 2019 detection of the Willow Leaf Beetle, followed by a timely insecticide treatment, there was no additional beetle damage to the Willow trees. The height and canopy of most of the trees in the TreeWell units have continued to increase. Trees are displaying vigorous growth and, based on hydrogeologic monitoring data, are providing hydraulic capture. Preliminary hydrogeologic data suggest they are on track to perform as designed. Assessment results are summarized below: