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
The site for this project is a former waste disposal site and includes some waste lagoons and wetlands. This multi-phase project represents a robust demonstration of TreeWell® system performance, 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-free 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 remedial performance at depths ranging from 25 to 115 feet below ground surface (bgs).
Between 2015 and 2022, a total of 123 TreeWell® units were installed in four phases across multiple areas of a former waste disposal site that includes waste lagoons and adjacent wetland areas. Phase I (2015) included 18 TreeWell® units installed to approximately 25 ft bgs, planted with hackberry, Russian olive, live oak, and black locust trees. These were divided into three amendment groups: engineered soil with organic matter, soil with zero-valent iron (ZVI), and soil with ZVI plus Daramend®. Phase II (2017) added 18 close-bottomed straw TreeWell® units installed to depths ranging from 44–115 ft bgs; shallow units were amended with either soil and ZVI or engineered organic-rich soil, while deep units contained organic-rich soil. Phase III (2019) expanded the system with 51 straw TreeWell® units planted with willow and black locust to enhance uptake and resilience. Phase IV (2022) installed 33 TreeWell® units targeting shallow groundwater migrating toward a wetland area downgradient of Phase I. A comprehensive network of multi-depth piezometers and camera tubes facilitates ongoing monitoring of groundwater movement, plant health, and biodegradation performance.
The results were conclusive: TreeWell® units consistently supported vigorous tree growth—even in areas with high VOC concentrations (>100 milligrams per liter)—demonstrating the system's protective effect against phytotoxicity. VOC concentrations reliably declined as groundwater migrated upward through the TreeWell® soil 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® system’s natural function: creating a vertical treatment zone that protects plant health while encouraging contaminant breakdown. Data from this site clearly demonstrate that even under high loading, contaminants at phytotoxic concentrations 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.
