Grantee Research Project Results
1998 Progress Report: Effect of Spatial Heterogeneity on the Natural Bioattenuation of Dissolved Hydrocarbons
EPA Grant Number: R825418Title: 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: Hahn, Intaek
Project Period: October 28, 1996 through October 27, 1999 (Extended to April 30, 2000)
Project Period Covered by this Report: October 28, 1997 through October 27, 1998
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
Objective:
The overall objective of this research is to improve our understanding of processes controlling the anaerobic bioattenuation of dissolved hydrocarbons in groundwater. Field and laboratory studies will be conducted in two petroleum contaminated aquifers. The major groundwater contaminants at these sites are benzene--a known carcinogen, toluene, ethylbenzene, and xylene isomers (BTEX). At each site, we will measure spatial variations in contaminant biodegradation rates, sediment characteristics, and microbial populations, and relate these variations to field-scale plume behavior. 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.Progress Summary:
Field studies are underway at two sites contaminated with dissolved petroleum hydrocarbons. The first site is a former fire training area at Pope Air Force Base (Pope AFB) near Fayetteville, NC. The second site is an underground storage tank release near Rocky Point, NC.
Objective 1. | Develop and validate a field technique for measuring in-situ biodegradation rates over small vertical intervals. |
In year 1, we completed development and initial testing of a prototype in-situ chamber for measuring vertical variations in biodegradation rates. The system consists of a multilevel injection well installed in the center of a perforated 24-inch diameter steel casing. The perforation size and spacing were determined based on mathematical modeling of solute residence time in the chamber. Preliminary field tests have shown that we can install and monitor this system with minimal mixing between adjoining layers.
Objective 2. | Measure small-scale variations in biodegradation rates in two petroleum contaminated aquifers and relate variations in biodegradation rates to differences in sediment composition, geochemistry, and microbial population. |
This past year, we obtained all required permits and installed in-situ test chambers at both the Pope AFB and Rocky Point sites. The chambers were installed by excavating to the water table (approximately 5 ft below grade) and driving the 24 inch pipes into the aquifer using a vibratory hammer mounted on a large excavator. At both sites, the chambers were driven to a depth of 16 to 20 feet and then terminated because of increasing soil resistance. In the center of each chamber, a multilevel sampler has been installed and used to inject groundwater containing the problem contaminants (benzene, toluene, ethylbenzene, xylene isomers and trimethylbenzene isomers) and a non-reactive tracer (NaBr). Chemically inhibited controls are also being operated at both sites. Monitoring is underway to measure vertical variations in biotransformation rates. A detailed microbiological and geochemical characterization is being conducted at each site to correlate differences in biotransformation rates with differences in sediment characteristics, aqueous and solid phase geochemistry, and microbial populations.
Objective 3. | Use sediment from two petroleum contaminated aquifers to 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. |
Samples of contaminated aquifer material have been collected from several locations at the Pope AFB and Rocky Point sites and used to construct microcosms to determine spatial variations in biotransformation rates. These sediment samples have also been characterized to determine spatial variations in electron acceptors (O2, NO3, Fe(III), SO4, CO2) and important microbial groups. Results to date have shown important similarities and differences between sites. The Rocky Point aquifer is a relatively homogeneous fine sand with only a minor amount of clay. BTEX degradation in microcosms from this site is typically much more rapid than is observed in the aquifer. This aquifer also shows large spatial variations in microbial populations and high numbers of anaerobic protozoa. The Pope AFB aquifer is more heterogeneous and contains zones with a high clay content. BTEX degradation rates in microcosms from this site appear to be more consistent with field monitoring results. While there are significant changes in microbial populations throughout the aquifer, these shifts are more gradual and no anaerobic protozoa have been detected.
Objective 4. | Evaluate the effect of large- and small-scale variations in biodegradation rates on field- scale plume behavior. |
The monitoring systems at both sites are complete and are being sampled on a regular basis. These results are being used to calibrate the MODFLOW-MT3D-RT3D family of models to simulate large scale plume behavior. Once this is complete, the results from the laboratory microcosms and in-situ test chambers will be integrated with the modeling work to evaluate the effect of small and large-scale variations in biotransformation rates on plume behavior.
Future Activities:
The major focus for the coming year will be to improve our calibration of the groundwater flow, transport and biodegradation models, and then use these models to evaluate the effect of small and large-scale variations in biotransformation rates on plume behavior. We will continue monitoring the laboratory microcosms, in-situ chambers and multilevel sampling wells over the coming year to improve our estimates of biotransformation rates. Additional field work will be conducted this coming summer to obtain a more detailed characterization of spatial variations in the permeability distribution at both sites.Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 17 publications | 6 publications in selected types | All 4 journal articles |
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Type | Citation | ||
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Hunt MJ, Borden RC, Barlaz MA. Determining anaerobic BTEX decay rates in a contaminated aquifer. Journal of Hydrologic Engineering 1998;3(4):285-293. |
R825418 (1998) R825418 (Final) |
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Supplemental Keywords:
monitored natural attenuation, MNA, hydrocarbon, anaerobic, heterogeneity., RFA, Scientific Discipline, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, Contaminated Sediments, exploratory research environmental biology, Environmental Chemistry, Ecosystem/Assessment/Indicators, Chemical Mixtures - Environmental Exposure & Risk, Ecosystem Protection, Ecological Effects - Environmental Exposure & Risk, Ecological Effects - Human Health, Hazardous Waste, Ecological Risk Assessment, Groundwater remediation, Hazardous, Ecological Indicators, treatment residuals, ecological exposure, risk assessment, petroleum contaminants, ecological receptors, biodegradation, spatial heterogeneity, contaminated sediment, hazardous organic contaminants, dissolved hydrocarbons, bioattenuation, ecological impacts, risk assessments, aquifers, hydrocarbons, ecosystem impactsProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.