Phytoremediation as a Sustainable Remedial Alternative at a Hydrocarbon Contaminated Site

Presented by Brent Searcy, P.E. (ETIC Arcadia, Pleasant Hill, CA).
Coauthors: Sean Bowen, Tim Hendrickson, and Ryan Haughy (ETIC)

This presentation describes a phytoremediation project at a petroleum impacted site in California’s San Joaquin Valley. The project involves replacing a conventional groundwater pump-and-treat and soil vapor extraction system with a site-wide phytoremediation approach involving over 1,000 planted poplar and willow trees. The effectiveness of phytoremediation was based on the enhancement of microbial degradation of the contaminant due to the planted trees.

In order to measure the effects of phytoremediation on the rate of contaminant biodegradation, Natural Source Zone Depletion (NSZD) rate measurements based on surficial CO2 flux were conducted within the tree plot and at similarly impacted hydrocarbon impacted locations outside of the tree-planted plots (control areas). Measurements of NSZD rates were started during the initial tree planting pilot study in 2015, and were repeated afterwards twice a year, at the beginning and the end of the growing season. Measurements conducted in both spring and fall indicate that NSZD rates were enhanced by phytoremediation with respect to areas not treated. Measurements in the spring showed a 3 times increase in NSZD rates, while those in the fall increased up to 13 times with respect to the control areas.

NSZD rate measurements, together with regularly collected tree health parameters, and groundwater elevation data, indicate that the phytoremediation has been effective, achieving regulatory concurrence for a more sustainable remedy that achieves improved mass removal rates. The pump-and-treat and soil vapor extraction systems are currently being phased out in favor of phytoremediation.