Trimethylbenzoic acids as metabolite signatures in the biogeochemical evolution of an aquifer contaminated with jet fuel hydrocarbons.

Evolution of trimethylbenzoic acids in the KC-135 aquifer at the former Wurtsmith Air Force Base (WAFB), Oscoda, MI was examined to determine the functionality of trimethylbenzoic acids as key metabolite signatures in the biogeochemical evolution of an aquifer contaminated with JP-4 fuel hydrocarbons. Changes in the composition of trimethylbenzoic acids and the distribution and concentration profiles exhibited by 2,4,6- and 2,3,5-trimethylbenzoic acids temporally and between multilevel wells reflect processes indicative of an actively evolving contaminant plume. The concentration levels of trimethylbenzoic acids were 3-10 orders higher than their tetramethylbenzene precursors, a condition attributed to slow metabolite turnover under sulfidogenic conditions. The observed degradation of tetramethylbenzenes into trimethylbenzoic acids obviates the use of these alkylbenzenes as non-labile tracers for other degradable aromatic hydrocarbons, but provides rare field evidence on the range of high molecular weight alkylbenzenes and isomeric assemblages amenable to anaerobic degradation in situ. The coupling of actual tetramethylbenzene loss with trimethylbenzoic acid production and the general decline in the concentrations of these compounds demonstrate the role of microbially mediated processes in the natural attenuation of hydrocarbons and may be a key indicator in the overall rate of hydrocarbon degradation and the biogeochemical evolution of the KC-135 aquifer.

Cokriging optimization of monitoring network configuration based on fuzzy and non-fuzzy variogram evaluation.

A number of optimization approaches regarding monitoring network design and sampling optimization procedures have been reported in the literature. Cokriging Estimation Variance (CEV) is a useful optimization tool to determine the influence of the spatial configuration of monitoring networks on parameter estimations. It was used in order to derive a reduced configuration of a nitrate concentration monitoring well network. The reliability of the reduced monitoring configuration suffers from the uncertainties caused by the variographer's choices and several inherent assumptions. These uncertainties can be described considering the variogram parameters as fuzzy numbers and the uncertainties by means of membership functions. Fuzzy and non-fuzzy approaches were used to evaluate differences among well network configurations. Both approaches permitted estimates of acceptable levels of information loss for nitrate concentrations in the monitoring network of the aquifer of the Plain of Modena, Northern Italy. The fuzzy approach was found to require considerably more computational time and numbers of wells at comparable level of information loss.

A probabilistic methodology to assess the risk of groundwater quality degradation.

An approach to assess the risk of groundwater quality degradation with regard to fixed standards. based on Disjunctive Kriging (DK) is presented. The DK allows one to evaluate the Conditional Probability (CP) of overriding a given threshold of concentration of a pollutant at a given time, and at a generic point in a considered groundwater system. The result of such investigation over the considered area can be plotted in form of maps of spatial risk. By repeating this analysis at different times, several spatial risk maps will be produced, one for each considered time. By means of non-parametric statistics, the temporal trend of the CPs can be evaluated at every point of the considered area. The trend index, assessed by means of a sort of classification of the trend values obtained as described above, can be superimposed on the most recent values of the spatial risk (i.e.: the most recent values of probability). Consequently a classification of the risk of groundwater quality degradation results with which to weigh both the spatial distribution and the temporal behaviour of the probability to exceed a given standard threshold. The methodology has been applied to values of nitrate concentration sampled in the monitoring well network of the Modena plain, northern Italy. This area is characterised by intensive agricultural exploitation and hog breeding along with industrial and civil developments. The influence of agriculture on groundwater results in a high nitrate pollution that limits its use for potable purposes.

In situ lifetimes and kinetics of a reductive whey barrier and an oxidative ORC barrier in the subsurface.

Permeable reactive barriers (PRB) are being used to engineer favorable field conditions for in-situ remediation efforts. Two redox adjustment barriers were installed to facilitate a 10-month research effort on the fate and transport of MTBE (methyl tert-butyl ether) at a site called the Michigan Integrated Remediation Technology Laboratory (MIRTL). Thirty kilograms of whey were injected as a slurry into an unconfined aquifer to establish an upgradient reductive zone to reduce O2 concentration in the vicinity of a contaminant injection source. To minimize the impact of contaminant release, 363 kg of oxygen release compound (ORC) were placed in the aquifer as a downgradient oxidative barrier. Dissolved oxygen and other chemical species were monitored in the field to evaluate the effectiveness of this technology. A transient one-dimensional advective-dispersive-reaction (ADR) model was proposed to simulate the dissolved oxygen transport. The equations were solved with commonly encountered PRB initial and constant/variable boundary conditions. No similar previous solution was found in the literature. The in-situ lifetimes, based on variable source loading, were estimated to be 1,661 and 514 days for the whey barrier and ORC barrier, respectively. Estimates based on either maximum O2 consumption/production or measured O2 curves were found to under- or overestimate the lifetime of the barriers. The pseudo-first-order rate constant of whey depletion was estimated to be 0.303/d with a dissolution rate of 0.04/d. The oxygen release rate constant in the ORC barrier was estimated to be 0.03/d. This paper provides a means to design and predict the performance of reactive redox barriers, especially when only limited field data are available.

An assessment of natural biotransformation of petroleum hydrocarbons and chlorinated solvents at an aquifer plume transect.

Field biogeochemical characterization and laboratory microcosm studies were performed to assess the potential for future biotransformation of trichloroethylene (TCE) and toluene in a plume containing petroleum hydrocarbons and chlorinated solvents at the former Wurtsmith Air Force Base in Oscoda, MI. In situ terminal electron accepting processes (TEAPs), contaminant composition and microbial phylogeny were studied at a plume transect 100 m downgradient of the source. The presence of reduced electron acceptors, relevant microbial communities, and elevated dissolved methane and carbon dioxide concentrations at the transect, as well as downgradient accumulation of BTEX metabolites and dechlorination products, indicated that past or current reductive dechlorination at the transect was likely driven by BTEX biodegradation in the methanogenic zone. However, TCE and toluene mineralization in sediment-groundwater microcosms without added electron acceptors did not exceed 5% during 300 days of incubation and was nearly invariant with original sediment TEAP, even following amendments of nitrogen and phosphorus. Mineralization rates were on the order of 0.0015-0.03 mumol/g day. After 8 months, microcosms showed evidence of methanogenesis, but CH4 and CO2 production arose from the degradation of contaminants other than toluene. Cis-dichloroethylene was observed in only one methanogenic microcosm after more than 500 days. It appears likely that spatially and temporally dynamic redox zonation at the plume transect will prevent future sustained reductive dehalogenation of highly chlorinated solvents, for during the course of a year, the predominant TEAP at the highly contaminated water table shifted from methanogenesis to iron- and sulfate-reduction. It is recommended that biotransformation studies combine considerations of long-term, spatially relevant changes in redox zonation with laboratory-scale studies of electron donor utilization and cometabolic substrate transformation to yield a more accurate assessment of natural bioattenuation of specific pollutants in aquifers contaminated by undefined organic waste mixtures.

Phospholipid compositional changes of five pseudomonad archetypes grown with and without toluene.

Bacterial physiological responses to toluene exposure were investigated in five reference pseudomonad strains that express different toluene degradation pathways: Pseudomonas putida mt-2, Pseudomonas putida F1, Burkholderia cepacia G4, Burkholderia pickettii PKO1, and Pseudomonas mendocina KR1. The intact phospholipids of these archetypes, grown with and without toluene, were characterized using liquid chromatography/electrospray ionization/mass spectrometry. All strains showed significant changes in phospholipid content and composition as an adaptive response to toluene exposure, as well as considerable diversity in response mechanisms. For example, the phospholipid content of toluene-grown PKO1, F1, and KR1 were 10.9-34.7% of that found in succinate-grown strains, while the phospholipid content of mt-2 and G4 increased by 56% and 94%, respectively, when grown on toluene. In addition, PKO1, F1, and mt-2 responded to the presence of toluene by synthesizing more phosphatidylglycerol, whereas G4 and KR1 synthesized phospholipids with polyunsaturated fatty acids (C18:2) on one or both of the sn-2 positions. These changes in phospholipid composition and concentration probably reflect the sensitivity and degree of tolerance of these strains to toluene, and suggest that different mechanisms are utilized by dissimilar bacteria to maintain optimal lipid ordering in the presence of such environmental pollutants.

Characterization of methanotrophic bacteria on the basis of intact phospholipid profiles.

The intact phospholipid profiles (IPPs) of seven species of methanotrophs from all three physiological groups, type I, II and X, were determined using liquid chromatography/electrospray ionization/mass spectrometry. In these methanotrophs, two major classes of phospholipids were found, phosphatidylglycerol (PG) and phosphatidylethanolamine (PE) as well as its derivatives phosphatidylmethylethanolamine (PME) and phosphatidyldimethylethanolamine (PDME). Specifically, the type I methanotrophs, Methylomonas methanica, Methylomonas rubra and Methylomicrobium album BG8 were characterized by PE and PG phospholipids with predominantly C16:1 fatty acids. The type II methanotrophs, Methylosinus trichosporium OB3b and CSC1 were characterized by phospholipids of PG, PME and PDME with predominantly C18:1 fatty acids. Methylococcus capsulatus Bath, a representative of type X methanotrophs, contained mostly PE (89% of the total phospholipids). Finally, the IPPs of a recently isolated acidophilic methanotroph, Methylocella palustris, showed it had a preponderance of PME phospholipids with 18:1 fatty acids (94% of total). Principal component analysis showed these methanotrophs could be clearly distinguished based on phospholipid profiles. Results from this study suggest that IPP can be very useful in bacterial chemotaxonomy.

Quantification and interpretation of total petroleum hydrocarbons in sediment samples by a GC/MS method and comparison with EPA 418.1 and a rapid field method.

Total petroleum hydrocarbons (TPH) as a lumped parameter can be easily and rapidly measured or monitored. Despite interpretational problems, it has become an accepted regulatory benchmark used widely to evaluate the extent of petroleum product contamination. Three currently used methods (GC/MS, conventional EPA 418.1, and a rapid field method PetroFLAG) were performed to quantify the TPH content in samples collected from a site contaminated by transformer oil. To standardize the method and improve the comparability of TPH data, crucial GC-based quantification issues were examined, e.g., quantification based on internal standards (ISTD) vs external standards (ESTD), single vs multiple ISTD, and various area integration approaches. The interpretation of hydrocarbon chromatographic results was examined in the context of field samples. The performance of the GC/MS method was compared with those of EPA 418.1 and PetroFLAG. As a result, it was observed that the ISTD quantification method was preferred to the ESTD method, multiple ISTD might be better than single ISTD, and three different area integration approaches did not have a significant effect on TPH results. Evaluation of the chromatograms between a reference sample and three unknown samples showed that the extent of contamination varied appreciably with sample depth. It was also found that there existed a good positive correlation between GC/MS and both EPA 418.1 and PetroFLAG, and that EPA 418.1 produced the higher overall estimate while GC/MS and PetroFLAG resulted in lower, more statistically comparable TPH values.

Microbial characterization of a JP-4 fuel-contaminated site using a combined lipid biomarker/polymerase chain reaction--denaturing gradient gel electrophoresis (PCR-DGGE)-based approach.

The impact of pollution on soil microbial communities and subsequent bioremediation can be measured quantitatively in situ using direct, non-culture-dependent techniques. Such techniques have advantages over culture-based methods, which often account for less than 1% of the extant microbial community. In 1988, a JP-4 fuel spill contaminated the glacio-fluvial aquifer at Wurtsmith Air Force Base, Michigan, USA. In this study, lipid biomarker characterization of the bacterial and eukaryotic communities was combined with polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis of the eubacterial community to evaluate correlation between contaminant (JP-4 fuel) concentration and community structure shifts. Vadose, capillary fringe and saturated zone samples were taken from cores within and up- and down-gradient from the contaminant plume. Lipid biomarker analysis indicated that samples from within the plume contained increased biomass, with large proportions of typically gram-negative bacteria. Outside the plume, lipid profiles indicated low-biomass microbial communities compared with those within the initial spill site. 16S rDNA sequences derived from DGGE profiles from within the initial spill site suggested dominance of the eubacterial community by a limited number of phylogenetically diverse organisms. Used in tandem with pollutant quantification, these molecular techniques should facilitate significant improvements over current assessment procedures for the determination of remediation end-points.

Statistical trends in ground-water monitoring data at a landfill Superfund site: A case study.

This paper describes the use of statistical regression models to characterize temporal trends in groundwater monitoring data collected between 1980 and 1990 on 15 wells and 13 parameters (195 cases in all) at the KL Avenue landfill site in Kalamazoo County, Michigan. This site was used as a municipal landfill prior to 1980, then was placed on the Superfund site list in 1982 after ground-water contamination was found.Six temporal regression trend models were defined using linear and quadratic regression models. These trends were used to classify each of the 195 cases as: improving, deteriorating, or stable over the 1980-1990 time period. Using these classifications it was determined that there were more than twice as many improving cases as deteriorating conditions at the KL site during this time period. These models provide a method for visualizing and interpreting trends in ground-water quality at individual well locations within the contaminant plume and for assessing the chemical trend behavior of the overall plume. The improving, deteriorating, and stable trend categories were developed for two purposes. The first purpose is to facilitate comprehension of information contained in large amounts of water quality data. The second is to assist communication among the many different groups of people who recommend actions, including remediation responsibilities at Superfund sites, like the KL site.A normal probability model was used in the trend classifications. This model contained provisions to accommodate nondetect data and other 'abnormal' laboratory determinations which can influence the trend selection process. The robustness of this classification procedure was examined using a lognormal probability model. The overall conclusions about the KL site using the lognormal model were similar to those obtained using the normal model. However, some individual trend indications were different using the lognormal model. The Shapiro-Wilk test was used to check the adequacy of both the normal and lognormal models. The lognormal model was found to be a somewhat more adequate model for fitting the KL site data, but was not found to be superior to the normal model for each case.The normal and lognormal models were both found to be suitable for determining overall trend conditions at this site. Both models are recommended for these purposes assuming an understanding of the statistical constraints and hydrochemical context. However, it is recommended that the search for more adequate trend models continues.

Network design factors for assessing temporal variability in ground-water quality.

Benchmark major ions and nutrients data were collected biweekly for about two years at 12 wells at two sites in a shallow sand and gravel aquifer in west-central Illinois. The purpose of the study was to explore the time series properties of ground-water quality data collected at a relatively high sampling frequency. A secondary purpose was to determine the relative magnitudes of natural and sampling-related sources of variance in ground-water quality time series. The absence of this kind of information has severely hindered the design of ground-water sampling programs in the past.An autocorrelation analysis showed that the median sampling frequency for which the predicted ratio of effective independent sample size to total sample size was 0.5 (50% sampling redundancy) ranged from 6 to 14 samples per year. For a predicted ratio of effective independent sample size to total sample size of 0.9 (10% sampling redundancy) the sampling frequency ranged from 3 to 6 samples per year. This suggests that, for the wells sampled, sampling frequencies much higher than monthly can result in considerable loss of information, and may not be cost effective. Care was taken in the design of the field and laboratory sampling protocol to minimize the effects of measurement error. The data analysis confirmed that this goal was accomplished. In most cases considerably less than five percent of the total variability could be attributed to sampling and analytical error. Because of the relatively short duration of the study (42 biweekly sampling occasions at most wells) it was not possible to identify the magnitude of seasonal variations reliably.