Natural attenuation of chlorinated solvents at Area 6, Dover Air Force Base: groundwater biogeochemistry

Monitored natural attenuation (MNA) has recently emerged as a viable groundwater remediation technology in the United States. Area 6 at Dover Air Force Base (Dover, DE) was chosen as a test site to examine the potential for MNA of tetrachloroethene (PCE) and trichloroethene (TCE) in groundwater and aquifer sediments. A "lines of evidence" approach was used to document the occurrence of natural attenuation. Chlorinated hydrocarbon and biogeochemical data were used to develop a site-specific conceptual model where both anaerobic and aerobic biological processes are responsible for the destruction of PCE, TCE, and daughter metabolites. An examination of groundwater biogeochemical data showed a region of depleted dissolved oxygen with elevated dissolved methane and hydrogen concentrations. Reductive dechlorination likely dominated in the anaerobic portion of the aquifer where PCE and TCE levels were observed to decrease with a simultaneous increase in cis-1,2-dichloroethene (cis-DCE), vinyl chloride (VC), ethene, and dissolved chloride. Near the anaerobic/ aerobic interface, concentrations of cis-DCE and VC decreased to below detection limits, presumably due to aerobic biotransformation processes. Therefore, the contaminant and daughter product plumes present at the site appear to have been naturally atteuated by a combination of active anaerobic and aerobic biotransformation processes.     

Sequential anaerobic-aerobic treatment of an aquifer contaminated by halogenated organics: field results

In situ, sequential, anaerobic to aerobic treatment of groundwater removed perchloroethene (PCE, 1.1 microM) and benzene (0.8 microM) from a contaminated aquifer. Neither aerobic nor anaerobic treatment alone successfully degraded both the chlorinated and non-chlorinated organic contaminants in the aquifer. After the sequential treatment, PCE, trichloroethene (TCE), vinyl chloride (VC), chloroethane (CA), and benzene were not detectable in groundwater. Desorption of residual aquifer contaminants was tested by halting the groundwater recirculation and analyzing the groundwater after 3 and 7 weeks. No desorption of the chlorinated contaminants or daughter products was observed in the treated portion of the aquifer. Sequential anaerobic to aerobic treatment was successful in remediating the groundwater at this test site and may have broad applications at other contaminated sites. Over the 4-year course of the project, the predominant microbial environment of the test site varied from aerobic to sulfate-reducing, to methanogenic, and back to aerobic conditions. Metabolically active microbial populations developed under all conditions, demonstrating the diversity and robustness of natural microbial flora in the aquifer.     

Metal accumulation in aquatic macrophytes from southeast Queensland,Australia

To determine the extent of metal accumulation in some aquatic macrophytes from contaminated urban streams in southeast Queensland, plants were sampled from six sites, along with contiguous sediments. In all, 15 different species were collected, the most common genera being Typha (Cattails or Bulrushes) and Persicaria (Knotweeds). Before heavy metal analysis, plants were further separated into various morphological tissues, and five selected samples were separated into various physiological tissues. The cadmium, copper, lead and zinc content of the plants were analysed using flames AAS. In general, plant roots exhibited higher metal concentrations than the contiguous sediments. Of the metals of interest, only for zinc was there a relatively clear pattern of increasing accumulation in aquatic macrophytes with increasing sediment metal concentrations. Comparison between morphological tissues of the sampled plants found that roots consistently presented higher metal concentrations than either the stems or leaves, however unlike previous studies, this investigation revealed no consistent trend of stems accumulating more metals than the leaves. For Typha spp., metal concentrations followed the order of roots > rhizomes > leaves, while for Persicaria spp. the order was roots > leaves > stems. The submerged species Myriophyllum aquaticum accumulated the highest levels of metals overall (e.g. Zn 4300 micrograms g-1 dry weight and Cd 6.5 micrograms g-1), and the emergent macrophytes also exhibited relatively high metal contents in their roots. The leaves of the submerged and floating-leafed species collected contained relatively high quantities of the four metals of interest, compared with the leaves of emergent aquatic macrophytes. In the Typha rhizome and Persicaria stem samples analysed for internal variation in metal content, there was a pattern of increasing metal concentrations towards the external sections of the stem, both for subterranean stems (rhizomes) and above-substrate stems. For Persicaria stems, no clear pattern was observed for cadmium and lead, the two metals investigated that are not required by plants for survival.     

Performance assessment of NAPL remediation in heterogeneous alluvium

Over the last few years, more than 40 partitioning interwell tracer tests (PITTs) have been conducted at many different sites to measure nonaqueous phase liquid (NAPL) saturations in the subsurface. While the main goal of these PITTs was to estimate the NAPL volume in the subsurface, some were specifically conducted to assess the performance of remedial actions involving NAPL removal. In this paper, we present a quantitative approach to assess the performance of remedial actions to recover NAPL that can be used to assess any NAPL removal technology. It combines the use of PITTs (to estimate the NAPL volume in the swept pore volume between injection and extraction wells of a test area) with the use of several cores to determine the vertical NAPL distribution in the subsurface. We illustrate the effectiveness of such an approach by assessing the performance of a surfactant/foam flood conducted at Hill Air Force Base, UT, to remove a TCE-rich NAPL from alluvium with permeability contrasts as high as one order of magnitude. In addition, we compare the NAPL volumes determined by the PITTs with volumes estimated through geostatistical interpolation of aquifer sediment core data collected with a vertical frequency of 5-10 cm and a lateral borehole spacing of 0.15 m. We demonstrate the use of several innovations including the explicit estimation of not only the errors associated with NAPL volumes and saturations derived from PITTs but also the heterogeneity of the aquifer sediments based upon permeability estimates. Most importantly, we demonstrate the reliability of the     

Using polymer mats to biodegrade atrazine in groundwater: laboratory column experiments

Large-scale column experiments were undertaken to evaluate the potential of in situ polymer mats to deliver oxygen into groundwater to induce biodegradation of the pesticides atrazine, terbutryn and fenamiphos contaminating groundwater in Perth, Western Australia. The polymer mats, composed of woven silicone (dimethylsiloxane) tubes and purged with air, were installed in 2-m-long flow-through soil columns. The polymer mats proved efficient in delivering dissolved oxygen to anaerobic groundwater. Dissolved oxygen concentrations increased from <0.2 mg l(-1) to approximately 4 mg l(-1). Degradation rates of atrazine in oxygenated groundwater were relatively high with a zero-order rate of 240-380 microg l(-1) or a first-order half-life of 0.35 days. Amendment with an additional carbon source showed no significant improvement in biodegradation rates, suggesting that organic carbon was not limiting biodegradation. Atrazine degradation rates estimated in the column experiments were similar to rates determined in laboratory culture experiments, using pure cultures of atrazine-mineralising bacteria. No significant degradation of terbutryn or fenamiphos was observed under the experimental conditions within the time frames of the study. Results from these experiments indicate that remediation of atrazine in a contaminated aquifer may be achievable by delivery of oxygen using an in situ polymer mat system.     

Preliminary background ozone concentrations in the mountain and coastal areas of Bulgaria

Urban and non-urban rural ozone (O3) concentrations are high in Bulgaria and often exceed the European AOT40 ecosystem as well as the AOT60 human health standards. This paper presents preliminary estimates to establish background, non-urban O3 concentrations for the southern region of Bulgaria. Ozone concentrations from three distinctly different sites are presented: a mountain site influenced by mountain-valley wind flow; a coastal site influenced by sea-breeze wind flow; and a 1700-m mountain peak site without 'local' wind flow characteristics. The latter offers the best estimate of 46-50 ppb for a background O3 level. The highest non-urban hourly value, 118 ppb, was measured at the mountain-valley site.     

Spatial characteristics of fine particulate matter: identifying representative monitoring locations in Seattle, Washington

This study investigates how PM2.5 varies spatially and how these spatial characteristics can be used to identify potential monitoring sites that are most representative of the overall ambient exposures to PM2.5 among susceptible populations in the Seattle, WA, area. Data collected at outdoor sites at the homes of participants of a large exposure assessment study were used in this study. Harvard impactors (HIs) were used at 40 outdoor sites throughout the Seattle metropolitan area. Up to six sites at a time were monitored for 10 consecutive 24-hr average periods. A fixed-effect analysis of variance (ANOVA) model that included date and location effects was used to analyze the spatial variability of outdoor PM2.5 concentrations. Both date and location effects were shown to be highly significant, explaining 92% of the variability in outdoor PM2.5 measurements. The day-to-day variability was 10 times higher than the spatial variability between sites. The site mean square was more than twice the error mean square, showing that differences between sites, while modest, are potentially an important contribution to measurement error. Variances of the model residuals and site effects were examined against spatial characteristics of the monitoring sites. The spatial characteristics included elevation, distance from arterials, and distance from major PM2.5 point sources. Results showed that the most representative PM2.5 sites were located at elevations of 80-120 m above sea level, and at distances of 100-300 m from the nearest arterial road. Location relative to industrial PM2.5 sources is not a significant predictor of residential outdoor PM2.5 measurements. Additionally, for sites to be representative of the average population exposures to PM2.5 among those highly susceptible to the health effects of PM2.5, areas of high elderly population density were considered. These representative spatial characteristics were used as multiple, overlapping criteria in a Geographic Information System (GIS) analysis to determine where the most representative sites are located.     

Toxicity of methyl tert-butyl ether to marine organisms: ambient water quality criteria calculation

In response to increasing concerns over the detection of methyl tert-butyl ether (MTBE) in groundwater and surface water and its potential effects in aquatic ecosystems, industry and the United States Environmental Protection Agency (USEPA) began to collaborate in 1997 to develop aquatic toxicity databases sufficient to derive ambient water quality criteria for MTBE consistent with USEPA requirements. Acute toxicity data for seven marine species, chronic toxicity data for an invertebrate, and plant toxicity data were developed to complete the saltwater database. The species tested were Cyprinodon variegatus, Gasterosteus aculeatus, Callinectes sapidus, Mytilus galloprovincialis, Palaemonetes pugio, Rhepoxynius abronius, Americamysis bahia, and Skeletonema costatum. The toxicity tests were conducted in accordance with USEPA and American Society for Testing and Materials testing procedures and Good Laboratory Practice guidelines. Data developed from this study were consistent with existing data and showed that MTBE has low acute and chronic toxicity to the marine species tested. Based upon measured MTBE concentrations, acute effects were found to range from 166 mg MTBE/l for the grass shrimp to 1950 mg MTBE/l for marine mussel. The no-observed effect concentration for the reproduction and growth of mysids was 26 mg MTBE/l during the life cycle test. The toxicity of MTBE to saltwater organisms is comparable to its toxicity to the freshwater species tested. Reported MTBE concentrations in coastal waters are several orders of magnitude lower than concentrations observed to cause effects in marine organisms.     

Induction of PAH-catabolism in mushroom compost and its use in the biodegradation of soil-associated phenanthrene

This paper describes the induction of phenanthrene-catabolism within Phase II mushroom compost resulting from its incubation with (1) phenanthrene, and (2) PAH-contaminated soil. Respirometers measuring mineralization of freshly added 14C-9-phenanthere were used to evaluate induction of phenanthrene-catabolism. Where pure phenanthrene (spiked at a concentration of 400 mg kg(-1) wet wt.) was used to induce phenanthrene-catabolism in compost, induction was measurable, with maximal mineralization observed after 7 weeks phenanthrene-compost contact time. Where PAH-contaminated soil was used to induce phenanthrene-catabolism in un-induced compost, induction was observed after 5 weeks soil-compost contact time. Microcosm-scale amelioration of soil contaminated with 14C-phenanthrene (aged in soil for 516 days prior to incubation with compost) indicated that both induced (using pure phenanthrene) and uninduced Phase II mushroom composts were equally able to promote degradation of this soil-associated contaminant. After 111 days incubation time, 42.7 +/- 6.3% loss of soil-associated phenanthrene was observed in the induced-compost soil mixture, while 36.7 +/- 2.9% loss of soil-associated phenanthrene was observed in the uninduced-compost soil mixture. These results are notable as they indicate that while pre-induction of phenanthrene-catabolism within compost is possible, it does not significantly increase the extent of degradation when the compost is used to ameliorate phenanthrene-contaminated soil. Thus, compost could be used directly in the amelioration of contaminated land i.e. without pre-induction of catabolism.     

Potential role of fire retardant-treated polyurethane foam as a source of brominated diphenyl ethers to the US environment

Five tetra- to hexabrominated diphenyl ether (BDE) congeners (BDE-47, -99, -100, -153 and -154) are the most frequently reported in wildlife and humans. The commercial penta-BDE product, used predominantly to flame-retard polyurethane foam, consists primarily of these same congeners. In 1999, North American demand accounted for 98% of the total global penta-market of 8500 metric tons. Frogs, housed with flame retardant-treated polyurethane foam as a dry substrate, accumulated 10,100 microg/kg (wet weight) of the above BDEs. Crickets kept therein as food contained 14,400 microg/kg. The crickets are believed to have browsed directly on the foam and, in turn, were consumed by the frogs. BDE congener composition in all three matrices matched that of the penta-commercial product. Similar congeners were also observed in soil and stream sediments collected near a polyurethane foam manufacturing plant. Summed concentrations of BDE-47, -99 and -100, the dominant congeners observed in these samples, ranged from < 1 to 132 microg/kg (dry weight basis). Sunfish fillets obtained from a nearby, off-site pond contained a total of 624 microg/kg (lipid basis). Sewage treatment plant (STP) sludge exhibited these same congeners at 1370 microg/kg (dry weight). BDE-209, the fully brominated congener predominant in the commercial deca-BDE product, was also present at 1470 microg/kg. While no known polyurethane foam manufacturers discharged to this plant, the distribution pattern of the low brominated congeners in the sludge matched that of the penta-product. After four weeks of exposure to ambient outdoor conditions, the surface of flame-retarded polyurethane foam became brittle and began to disintegrate. Subsequent dispersal of these penta-containing foam fragments may be one mechanism by which these BDEs reach the environment.