Plant-Assisted Bioremediation of Trimethylbenzene Isomers in Soil at a Former Petroleum Oil Refinery, South-Central Michigan, by Harding, Barry J. and Jeffrey D. Spruit; #90031 (2004)

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

Harding, Barry J.¹ and Jeffrey D. Spruit²
¹Earth Tech, Grand Rapids, MI
²Michigan 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.