Theme: 01. Remediation Technology Innovations

Topic Area: 1s. Phytoremediation

Formatted Title:

Pivot to Phytoremediation to Successfully Close a Legacy Chlorinated VOC Brownfield Site

Background/Objectives:

Endophyte-assisted poplar and willow trees were strategically installed at a former manufacturing facility in east-central Illinois to diminish chlorinated VOC groundwater impacts (TCE, TCA and related daughter products) to position the site for closure under Illinois EPA’s voluntary Site Remediation Program. The site has six defined source areas which have created two shallow groundwater plumes within a heterogenous geologic setting located up-gradient of an adjacent residential area.

Several interim treatment methodologies were utilized at the site historically, including in-situ injection of bio-augmented liquid activated carbon and construction of a zero valent iron permeable reactive barrier. Although successful as implemented to mitigate leading edge plume conditions, they were not designed to treat source areas in order to achieve final regulatory closure of the site.

Approach/Activities:

With approval from the Illinois EPA, treatment pivoted to the use of phytoremediation as the most efficient, sustainable and cost-effective method to capture and treat the impacted shallow groundwater within the two plumes.

Phytoremediation was deployed at the site in two separate plantings in 2018 and 2019 of approximately 300 trees each in 11 individual treatment plots covering a total area of approximately 1-acre within the 27-acre site. The planting consisted of 5- and 10-foot long poles with the majority of the treatment plots located within asphalt or concrete paved areas. These plots were designed to focus primarily on the six delineated source areas and to additionally provide control and treatment of the two groundwater plumes resulting from these sources. The survival rate for each planting was nearly 100% with significant growth noted despite many of the plots being installed within paved areas and in areas exhibiting elevated concentrations of chlorinated VOCs. At the time of the confirmation groundwater sampling in the summer of 2021 the tree height ranged from approximately 20-25 feet and the trees were 4 to 6 inches in diameter at breast height.

Results/Lessons Learned:

Performance monitoring of groundwater conditions at the site determined that by 2021 (within three years following the initial implementation of phytoremediation) the site had achieved risk-based remedial objectives and a remedial action completion report was submitted to Illinois EPA. Concentrations of total VOCs in source areas prior to the initiation of phytoremediation ranged up to 80 mg/L and measured reductions of up to 95% were achieved during the final confirmation sampling event. The inoculation of trees with proprietary bacterial endophytes appeared to allow several plots to survive and maintain effectiveness in what could otherwise have been considered potentially phytotoxic conditions.

The significant and sustained reductions in the measured concentration of compounds of concern combined with focused institutional controls resulted in achievement of risk-based remedial objectives and a determination of no further action by the Illinois EPA. The site has been purchased by the local city government with the intention of future redevelopment for industrial/commercial purposes.

Phytoremediation of the site received positive acceptance by stakeholders including the Illinois EPA, the local city government and nearby residents. The use of phytoremediation also served as a sustainable and viable means to remediate the site which limited the use of finite resources to achieve risk-based site closure. The local city government intends to maintain the trees before the property is redeveloped which will serve to not only further remediate groundwater at the site sustainably but will also provide for a visually aesthetic view of the currently unoccupied property from adjacent residential properties.

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Jinjun Wang