Carlyss, LA — 2015-Present
Benzene, chlorobenzene, toluene, diphenyl ether, and phenol; and lower concentrations of several other VOC constituents in shallow soils and groundwater (0 to approximately 30 feet below ground surface).
To evaluate the potential for utilizing phytoremediation in highly contaminated areas and evaluate the remedial and hydraulic impact of the TreeWell system on VOCs in the groundwater.
The TreeMediation implementation consisted of 90 TreeWell units among three different locations in Carlyss, Louisiana. TreeWell units were installed in 20 by 20 foot spacing at 25 feet below ground surface. In December 2015, a set of hackberry, Russian olive, live oak, and black locust trees were planted in each of the 18 TreeWell units during Phase I in the first Carlyss location. One set of units was filled with engineered soil with organic matter amendments, a second set was filled with a mixture of soil and zero-valent iron (ZVI), and a third set was filled with a mixture of soil, ZVI, and Daramend® (a proprietary electron donor). Phase II began in June 2017, when black locust and willow trees were planted in the 18 close-bottomed liner straw TreeWell units which were installed in a second Carlyss location. The straw TreeWell units were divided into zones with targeted depths of 44-115 feet below ground surface. One set of shallow units were filled with a mixture of soil and ZVI, and the second set of shallow units and set of deep units were filled with engineered soil with organic matter amendments. Finally, in December 2019, Phase III of the project commenced as 51 additional straw TreeWell units were installed in the third Carlyss location, with 35 willow and 25 black locust trees were planted in March 2020. A monitoring network consisting of piezometers and camera tubes were installed to monitor the effectiveness of the TreeWell system to enhance biodegradation of the COC in shallow soils and groundwater and exert hydraulic influence on shallow groundwater.
Results to Date:
For the 2016-2021 growing seasons, tree growth and viability were observed to be “very good” for the entire TreeWell unit plantation. The vertical profile of groundwater VOC concentrations within the TreeWell units show that VOCs are attenuating within all the TreeWell units. Units with ZVI or ZVI and Daramend in the backfill exhibited slightly more attenuation than units with only loam soil in the backfill. The tree health assessments do not show any significant indicators of plant stress. The height and canopy of most of the trees in the TreeWell units have continued to increase. Overall, the TreeWell units are performing as designed. The backfill media is reducing VOC concentrations as designed and to date, there are no obvious signs of VOC phytotoxicity. Additionally, the straw wells are functioning as designed to transmit target groundwater into the TreeWell units.