Southern Louisiana
VOCs - CVOCs with petroleum Hydrocarbon
Targeting Groundwater at Extreme Depths
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Managing Phytotoxic Concentrations
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Targeting Groundwater at Extreme Depths 〰️ Managing Phytotoxic Concentrations 〰️
Project Summary: Evaluating TreeWell® Systems for Deep Groundwater Remediation
This multi-phase project represents a robust demonstrations of TreeWell® performance to date, offering a rare opportunity to observe its effects across a range of soil amendments, depths, and tree species in a DNAPL-impacted setting. The primary objective was to evaluate the efficacy of TreeWell® systems in hydraulically controlling and remediating groundwater contaminated with high concentrations of VOCs, including dense-phase impacts. The study focused on understanding how different soil amendments—including zero-valent iron (ZVI), Daramend®, and engineered organic-rich soils—contributed to overall performance at depths ranging from 25 to 115 feet below ground surface (bgs).
Over the course of three phases between 2015 and 2020, a total of 90 TreeWell® units were installed in three areas of the site. Amendments were used strategically: Phase I included units amended with ZVI, Daramend®, and unamended engineered soil; Phase II focused on deep straw units with either ZVI or organic-rich soil; and Phase III added 51 straw TreeWells planted with willow and black locust to maximize uptake and resilience. Importantly, backfill configurations were varied to allow comparison of amendment effects at different depths. A comprehensive monitoring network of multi-depth piezometers and camera tubes provided clear data on contaminant concentrations, groundwater movement, and plant health over time.
The results were conclusive: TreeWell® units consistently supported vigorous tree growth—even in areas with high VOC concentrations—demonstrating the system's protective effect against phytotoxicity. VOC concentrations reliably declined as groundwater migrated upward through the TreeWell columns, confirming in-situ biodegradation. While soil amendments like ZVI and Daramend® offered modest performance gains, their added cost did not significantly outperform unamended engineered soil. This project’s strongest value lay in its demonstration of the TreeWell’s natural function: creating a vertical treatment zone that protects plant health while encouraging contaminant breakdown. Data from Carlyss clearly show that even under high loading, contaminants did not reach the root zones of the trees—making this our best example to date of a TreeWell® system’s capacity to treat deep contamination while maintaining tree vitality.
