Plant-Assisted Bioremediation of Trimethylbenzene Isomers in Soil at a Former Petroleum Oil Refinery, South-Central Michigan

Harding, Barry J.¹ and Jeffrey D. Spruit^2
1 Earth Tech, Grand Rapids, MI
² Michigan Department of Environmental Quality – RRD, Kalamazoo, MI

1,2,4-Trimethylbenzene and 1,3,5-Trimethylbenzene (TMBs) are aromatic compounds found in crude oil and as un-recovered C-9 distillation fractions added to gasoline. They are frequently encountered in soils from an abandoned oil refinery in south-central Michigan. Total TMB concentrations in soils collected from a historical refined petroleum spill area ranged from approximately 2,500 ug/kg to 30,000 ug/kg.

An ex-situ Pilot Study using four technologies was implemented to evaluate the effectiveness of treating soils (50 cubic yard “cells”) contaminated with aromatic volatile compounds, including TMBs. The effectiveness of Plant-Assisted Bioremediation (or Enhanced Rhizodegradation), using prairie grasses was evaluated through chemical and biological monitoring and compared to alternative soil treatment technologies.

Soil analyses indicated a 90% TMB reduction in the Plant-Assisted Bioremediation Cell over a 28-week period, and a 99% mass reduction of TMBs after grasses were transplanted (approximately 22 weeks). Excavation of the Plant-Assisted Bioremediation Cell confirmed new grass root growth in oily soil to a depth of at least three feet. Rhizosphere degradation was further supported through increased heterotrophic bacteria counts from an average of 9.7 million colony-forming units the first 14-weeks to 11.8 million CFU, and counts as high as 21 million CFU the remaining weeks. While Soil-Vapor Extraction (SVE) (99% efficiency) Land Farming (97%), and Chemical Oxidation (87%) were promising, they are more costly soil treatment options. Future site re-development efforts will likely integrate the use of prairie grasses at target “contaminant polishing” areas of shallow petroleum contamination and at areas designated for recreational or nature park usage.

AAPG Search and Discovery Article #90031©2004 AAPG Eastern Section Meeting, Columbus, Ohio, October 3-5, 2004