The site was a petroleum tank farm from the early half of the 20th century. Contaminants on-site include petroleum hydrocarbons, benzene and ethylbenzene, and PAHs naphthalene and 2-methylnapthalene. Most contaminants are in subsurface and groundwater, with the exception of PAHs that extend from the surface to groundwater.

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The primary remedial objective of the phytoremediation system is to remove source zone contaminants from surface and subsurface zones, plus degradation of groundwater contaminants on site. The secondary remedial objective is to promote groundwater chemistry that encourages more effective natural attenuation in the downgradient and offsite plume where trees cannot be planted due to the presence of a highway.

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The installed phytoremediation system is the first and primary remedial action for this Site. The alternative remedial actions considered were capping with pavement and MNA, or just MNA. Phytoremediation was chosen because MNA over decades prior did not control further spreading of the offsite plume. Capping was ultimately not chosen because the client did not want the site to potentially extend into perpetuity (would also require annual pavement maintenance). Active systems were not considered due to cost and concerns over theft.

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167 trees and buffalo grass were inoculated and planted over a ¼-acre lot. Eight to Ten-foot-deep boreholes were augured and planted with 12-foot hybrid poplar tree poles to speed up root growth down to the 16 to 25 deep contaminated groundwater zone. Buffalo grass was inoculated and sown on contaminated surface soils - that did not otherwise support plant growth - to degrade surface PAHs.

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After one year of growth, 85% of trees survived, and the inoculated buffalo grass thrived. Over half of the dead trees were replanted in hot spot locations, and all survived. The hybrid poplar trees have also taken on two hurricanes (one almost direct and another indirect) without incident. The phytoremediation system was installed in 2019 and is very successful in reaching the remedial action goals.

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Onsite groundwater monitoring well samples taken from within the planted area indicate major reductions in all contaminants on site. Between 2016 and 2019, TPH concentrations ranged from 5.95 mg/L to 786 mg/L; BTEX compounds ranged between 0.17 mg/L to 2.53 mg/L; and PAHs ranged between 0.31 mg/L to 3.2 mg/L. Q3 of 2020 and Q1 of 2021 now demonstrate concentrations below action levels for all contaminants.

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Offsite and downgradient of the planted area, groundwater plume contaminant concentrations are still above action levels, though concentrations are declining faster than previous MNA reports by as much as a tenfold reduction in the past year alone, and PAHs are now below action levels.

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The site is progressing rapidly and should hopefully meet our target of on-site remedial action goals within the expected 5- to 7-year timeframe.