Southern Louisiana

VOCs - CVOCs with petroleum Hydrocarbon

Managing Phytotoxic Concentrations

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Targeting Groundwater at Extreme Depths

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Managing Phytotoxic Concentrations --- Targeting Groundwater at Extreme Depths ---

Project Objective:
Evaluate the efficacy of a TreeWell® system for providing hydraulic control and remediation of groundwater impacted with high concentrations of VOCs including Dense Non-Aqueous Liquid (DNAPL) impacts. Target treatment depths ranged from 25 to 115 ft bgs.

Implementation:
The TreeMediation project included 90 TreeWell® units installed in three site areas over three phases.

  • Phase I (2015):
    18 TreeWell units were installed at 20x20 ft spacing to a depth of ~25 ft. Each was planted with hackberry, Russian olive, live oak, and black locust trees. The units were divided into three soil treatments:

    1. Engineered soil with organic matter

    2. Soil mixed with zero-valent iron (ZVI)

    3. Soil mixed with ZVI and Daramend® (a proprietary electron donor)

  • Phase II (2017):
    18 close-bottomed straw TreeWell units were added in another part of the site. Depths ranged from 44–115 ft.

    • One set of shallow units was filled with soil and ZVI.

    • The remaining shallow and all deep units used engineered soil with organic matter.

  • Phase III (2019–2020):
    51 straw TreeWell units were installed and planted in March 2020 with 35 willow and 25 black locust trees.

A monitoring network of piezometers and camera tubes was installed to track the system’s effects on contaminant biodegradation and groundwater flow.

Results:
From 2016 to 2021, the TreeWell® units supported healthy tree growth with no visible signs of stress or VOC-related phytotoxicity. Trees continued to thrive, with steady increases in height and canopy size—even in areas with high VOC concentrations.

Groundwater monitoring showed clear signs of in-situ VOC biodegradation. VOC levels consistently decreased as water moved upward through the TreeWell units. While backfill with ZVI or Daramend® slightly improved performance, even units with only loam soil showed effective VOC breakdown.

Importantly, the straw TreeWell units successfully reached groundwater at depths up to 115 feet, enabling deep contaminant treatment as designed.

Coastal Florida

1,4-Dioxane in Fractured Bedrock

Managing Phytotoxic Concentrations

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Underlying Clean Groundwater Zone

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Managing Phytotoxic Concentrations --- Underlying Clean Groundwater Zone ---

Objective:
Evaluate the efficacy of a TreeWell® system as a sustainable and cost-effective replacement for a costly and ineffective pump-and-treat system.

Site Conditions:
The source area remained active, and a plume of 1,4-dioxane was migrating offsite through a fractured bedrock aquifer. Shallow aquifer media (0–2 meters) consisted of clean, sandy soils, while the deeper zone (2–4.5 meters) contained contaminated groundwater within fractured bedrock.

Implementation:
To facilitate the installation of a targeted remediation system, a mature vegetative canopy was removed. A 154-unit TreeWell® system was subsequently installed to address groundwater contamination within fractured bedrock. The design focused on intercepting and treating a plume of 1,4-dioxane migrating offsite.

The system incorporated some native wetland tree species selected for their tolerance to site conditions and phytoremediation potential: Slash Pine (Pinus elliottii), Willow (Salix spp.), Sycamore (Platanus occidentalis), Cypress (Taxodium distichum), and Laurel Oak (Quercus laurifolia).

Results:

  • Eliminated high-cost pump-and-treat system, saving the client approximately $300,000 per year in operational costs.

  • Replaced ineffective UV/peroxide treatment with a TreeWell® System, delivering measurable contaminant reduction.

  • Achieved active remediation and hydraulic control of the impacted zone beneath clean groundwater, with low O&M requirements.

  • Secured regulatory closure in record time:

    • No Further Action granted within three years.

    • Site Rehabilitation Completion Order (SRCO) issued by the Florida Department of Environmental Protection.

  • Resolved a 20-year remediation challenge through nature-based, cost-effective intervention.