Effect of Spatial Heterogeneity on the Natural Bioattenuation of Dissolved HydrocarbonsEPA Grant Number: R825418
Title: Effect of Spatial Heterogeneity on the Natural Bioattenuation of Dissolved Hydrocarbons
Investigators: Barlaz, Morton A. , Borden, Robert C.
Institution: North Carolina State University
EPA Project Officer: Chung, Serena
Project Period: October 28, 1996 through October 27, 1999 (Extended to April 30, 2000)
Project Amount: $449,052
RFA: Environmental Fate and Treatment of Toxics and Hazardous Wastes (1996) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management , Safer Chemicals
Description:Natural bioattenuation processes have a profound influence on the fate and transport of many hazardous contaminants in the subsurface. These processes can result in complete biodegradation of hazardous organic contaminants, eliminating any risk to the public and environmental receptors. However, bioattenuation processes are not included in most risk assessments because of the tremendous gaps in our knowledge of these processes.
In a recent study, Borden et al., demonstrated that the USEPA Protocol for Estimation of Anaerobic Microbiological Transformation Rate Data (Fed. Reg. Vol. 53, No. 115) yielded rates that were 10-100 times higher than field rates. If these rates were used in a risk assessment, then we would overestimate the extent of biodegradation and underestimate the risk to downgradient receptors. Before the effects of natural bioattenuation can be incorporated into risk assessments, an accurate and reliable method is needed to estimate field-scale bioattenuation rates.
The overall objective of this research is to improve our understanding of anaerobic bioattenuation processes in groundwater. Specific objectives are: 1) develop and validate a field technique for measuring in-situ biodegradation rates over small vertical intervals; 2) measure small-scale variations in biodegradation rates in two petroleum contaminated aquifers. Relate variations in biodegradation rates to differences in sediment composition, geochemistry, and microbial population; 3) using sediment from two petroleum contaminated aquifers, determine: (a) if spatial variations in contaminant biodegradation are due to large-scale spatial variations in the composition of the microbial community; and (b) if spatial variations in microbial populations correlate with the lag period prior to compound biodegradation in laboratory microcosms; and 3) evaluate the effect of large- and small-scale variations in biodegradation rates on field- scale plume behavior.
A test cell protocol will be developed to measure in-situ biodegradation rates at discreet vertical intervals with minimal disturbance of the subsurface ecosystem. This protocol will then be used to measure large-scale horizontal and small-scale vertical variations in biodegradation rates in two petroleum contaminated aquifers: Rocky Point and Pope Air Force Base. At each site, spatial variations in contaminant biodegradation rates, sediment characteristics, and microbial populations will be related to field-scale plume behavior. Changes in microbial population over time in anaerobic microcosms will be examined to identify the cause of the extended lag period often observed in microcosms constructed with sediment from petroleum contaminated aquifers. Results from this work will improve our ability to: 1) estimate the effect of natural bioattenuation processes on the fate and transport of hazardous organics in groundwater; and 2) estimate the risk of these contaminants to the public and environmental receptors. We will also develop recommendations to improve laboratory and field protocols for estimating field-scale bioattenuation rates.