Natural Attenuation of Aromatic Hydrocarbons at Former Manufactured Gas Plant Sites

Principal Investigator:

Say-Kee Ong, skong@iastate.edu (other projects)

Co-Principal Investigator:

• Greg Stenback, gastenba@iastate.edu (other projects)

Project Status: In Progress




Research Objective: Not available

Research Plan: Research is being conducted at several former manufactured gas plant sites and several former petroleum service stations in Iowa as part of a natural attenuation study. Geochemical data, including dissolved oxygen, nitrate, sulfate, iron and manganese, collected upgradient of, within, and downgradient of an aromatic hydrocarbon contaminant source area correlate reasonably well with expected geochemical zones providing evidence of increased biological activity within the dissolved contaminant plume. These findings provide indirect evidence for the possible biodegradation of hydrocarbon contaminants. Decreasing contaminant concentrations with time in some plume edge monitoring wells indicate the plume may be shrinking near these monitoring wells. However, the bulk of the dissolved contaminant plume shows temporal fluctuations, but appears to be relatively stable over the long term. Underground storage tanks and some subsurface source soils and materials were excavated and removed prior to this study. Subsequent soil and groundwater sampling indicate that an unknown amount of DNAPL and LNAPL contaminant source materials still persist at the site, however, the spatial distribution of these contaminant sources is not well defined. Natural attenuation processes, including sorption, dilution and degradation, appear to be acting to prevent the contaminant plume from expanding significantly beyond its current position. These findings indicate that the dissolved plume is not likely to change significantly in the near future without some level of active remediation.

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