Abstract  Soluble substrates (electron donors) have been commonly injected into chlorinated solvent contaminated plume to stimulate reductive dechlorination. Recently, different types of organic mulches with economic advantages and sustainable benefits have received much attention as new supporting materials that can provide long term sources of electron donors for chlorinated solvent bioremediation in engineered biowall systems. However, sorption capacities of organic mulches for chlorinated solvents have not been studied yet. In this study, the physiochemical properties of organic mulches (pine, hardwood and cypress mulches) were measured and their adsorption capacity as a potential media was elucidated. Single, binary and quaternary isotherm tests were conducted with trichloroethylene (TCE), tetrachloroethylene (PCE), trans-dichloroethylene (trans-DCE) and cis-dichloroethylene (cis-DCE). Among the three tested mulches, pine mulch showed the highest sorption capacity for the majority of the tested chemicals in single isotherm test. In binary or quaternary isotherm tests, competition among chemicals appears to diminish the differences in Q(e) for tested mulches. However, pine mulch also showed higher adsorption capacity for most chemicals when compared to hardwood and cypress mulches in the two isotherm tests. Based upon physicochemical properties of the three mulches, higher sorption capacity of pine mulch over hardwood and cypress mulches appears to be attributed to a higher organic carbon content and the lower polarity.

Abstract  Plumes containing more than one contaminant can be found in sites polluted by gasoline or chlorinated solvents. This study evaluated Fenton-like removal efficiencies when two contaminants were coexistent. Perchloroethylene, trichloroethylene, cis-1,2-dichloroethylene, methyl-t-butyl-ether, benzene, and toluene were mixed in pairs and degraded by the goethite-catalyzed Fenton-like reaction at neutral pH and low H2O2 doses. Results revealed that the amount of each compound removed in two-contaminant systems was less than that in one-contaminant systems. This decline in removal was related to the reactivity constant (k(HO center dot)), initial concentration (C-0), and number of double bonds of the compounds. In a solution that contained two compounds with similar k(HO center dot) values, the amount of each compound removed was related primarily to the C-0 ratio of two compounds. When the k(HO center dot) values of two compounds differed considerably, the one with the larger k(HO center dot) value or the higher C-0 reduced or inhibited the Fenton-like reaction of the pollutant with the smaller k(HO center dot) or lower C-0. Compounds with few double bonds tended to be less competitive for Fenton-like removal. By adding H2O2 repeatedly, the removal of a compound that is less competitive for the Fenton-like reaction can be recovered.

Abstract  Control-release KMnO4 (CRP) technology has been recently developed as an improved, highly efficient option for treating dissolved contaminant plumes of trichloroethylene (TCE) in the groundwater. In this paper, the preparation of potassium permanganate encapsulated with stearic acid by oil phase separation method and the control-release mechanism of the encapsulated permanganate in the degradation of TCE were studied. At 1: 3 of the mass ratio of KMnO4 solid to stearic acid, solid KMnO4 could be loaded by stearic acid completely and only 30.9% KMnO4 was released into water from CRP after 240 h with well-controlled release efficiency. The influence of the initial TCE concentration, pH value, and inorganic oxidation agent on the release efficiency of CRP and the TCE decontamination by CRP oxidation were also investigated. Comparative study between raw permanganate and CRP has been performed to clarify the priority of control release technology in reducing the non-selective consumption of oxidant and improving the oxidation efficiency for remediation of TCE in groundwater. The experiments show that CRP could minimize non-selective consumption and self-losses, which improved the oxidant efficiency and decreased the amount of oxidant needed. The oxidant efficiency of CRP increased by 1.7-fold compared with that of aqueous KMnO4. CRP showed the well-controlled release property and high removal efficiency of TCE. The molar ratio between released KMnO4 and removed TCE ranged about 2.98-5.96, which is a little higher than the stoichiometric requirement of 2: 1. CRP could be used to control TCE pollution in groundwater over a large pH range. Complete dechlorination can be achieved by oxidation when the mass ratio of release KMnO4 to TCE exceeds 3: 1.

Abstract  An analytical system composed of a cryofocusing trap injector device coupled to a gas chromatograph with mass spectrometric detection (CTI-GC-MS) specific for the on-line analysis in air of volatile chlorinated hydrocarbons (VCHCs) (dichloromethane; chloroform; 1,1,1-trichloroethane; tetrachloromethane; 1,1,2-trichloroethylene; tetrachloroethylene) was developed. The cryofocusing trap injector was the result of appropriate low cost modifications to an original purge-and-trap device to make it suitable for direct air analysis even in the case of only slightly contaminated air samples, such as those from remote zones. The CTI device can rapidly and easily be rearranged into the purge-and-trap allowing water and air analysis with the same apparatus. Air samples, collected in stainless steel canisters, were introduced directly into the CTI-GC-MS system to realize cryo-concentration (at -120 degrees C), thermal desorption (at 200 degrees C) and for the subsequent analysis of volatiles. The operating phases and conditions were customised and optimized. Recovery efficiency was optimized in terms of moisture removal, cold trap temperature and sampling mass flow. The injection of entrapped volatiles was realized through a direct transfer with high chromatographic reliability (capillary column-capillary column). These improvements allowed obtaining limits of detection (LODs) at least one order of magnitude lower than current LODs for the investigated substances. The method was successfully employed on real samples: air from urban and rural areas and air from remote zones such as Antarctica.

Abstract  Microbial reductive dechlorination of trichloroethene (TCE) and perchloroethene (PCE) in the vicinity of their dense non-aqueous phase liquid (DNAPL) has been shown to accelerate DNAPL dissolution. A three-layer diffusion-cell was developed to quantify this bio-enhanced dissolution and to measure the conditions near the DNAPL interface. The 12 cm long diffusion-cell setup consists of a 5.5 cm central porous layer (sand), a lower 3.5 cm DNAPL layer and a top 3 cm water layer. The water layer is frequently refreshed to remove chloroethenes at the upper boundary of the porous layer, while the DNAPL layer maintains the saturated chloroethene concentration at the lower boundary. Two abiotic and two biotic diffusion-cells with TCE DNAPL were tested. In the abiotic diffusion-cells, a linear steady state TCE concentration profile between the DNAPL and the water layer developed beyond 21 d. In the biotic diffusion-cells, TCE was completely converted into cis-dichloroethene (cis-DCE) at 2.5 cm distance of the DNAPL. Dechlorination was likely inhibited up to a distance of 1.5 cm from the DNAPL, as in this part the TCE concentration exceeded the culture's maximum tolerable concentration (2.5mM). The DNAPL dissolution fluxes were calculated from the TCE concentration gradient, measured at the interface of the DNAPL layer and the porous layer. Biotic fluxes were a factor 2.4 (standard deviation 0.2) larger than abiotic dissolution fluxes. This diffusion-cell setup can be used to study the factors affecting the bio-enhanced dissolution of DNAPL and to assess bioaugmentation, pH buffer addition and donor delivery strategies for source zones.

Abstract  The effectiveness of in situ treatment using zero-valent iron (ZVI) for nonaqueous phase or significant sediment-associated contaminant mass can be limited by relatively low rates of mass transfer to bring contaminants in contact with the reactive media. For a field test in a trichloroethene (TCE) source area, combining moderate-temperature subsurface electrical resistance heating with in situ ZVI treatment was shown to accelerate TCE treatment by a factor of about 4 based on organic daughter products and a factor about 8 based on chloride concentrations. A mass-discharge-based analysis was used to evaluate reaction, dissolution, and volatilization processes at ambient groundwater temperature (~10 °C) and as temperature was increased up to about 50 °C. Increased reaction and contaminant dissolution were observed with increased temperature, but vapor- or aqueous-phase migration of TCE out of the treatment zone was minimal during the test because reactions maintained low aqueous-phase TCE concentrations.

Abstract  At buildings with potential for vapor intrusion of volatile organic chemicals (VOCs) from the subsurface, the ability to accurately distinguish between vapor intrusion and indoor sources of VOCs is needed to support accurate and efficient vapor intrusion investigations. We have developed a method for application of compound-specific stable isotope analysis (CSIA) for this purpose that uses an adsorbent sampler to obtain sufficient sample mass from the air for analysis. Application of this method to five residences near Hill Air Force Base in Utah indicates that subsurface and indoor sources of tricholorethene and tetrachloroethene often exhibit distinct carbon and chlorine isotope ratios. The differences in isotope ratios between indoor and subsurface sources can be used to identify the source of these chemicals when they are present in indoor air.

Abstract  A numerical model of metabolic reductive dechlorination is used to describe the performance of enhanced bioremediation in fractured clay till. The model is developed to simulate field observations of a full scale bioremediation scheme in a fractured clay till and thereby to assess remediation efficiency and timeframe. A relatively simple approach is used to link the fermentation of the electron donor soybean oil to the sequential dechlorination of trichloroethene (TCE) while considering redox conditions and the heterogeneous clay till system (clay till matrix, fractures and sand stringers). The model is tested on lab batch experiments and applied to describe sediment core samples from a TCE-contaminated site. Model simulations compare favorably to field observations and demonstrate that dechlorination may be limited to narrow bioactive zones in the clay matrix around fractures and sand stringers. Field scale simulations show that the injected donor is expected to be depleted after 5 years, and that without donor re-injection contaminant rebound will occur in the high permeability zones and the mass removal will stall at 18%. Long remediation timeframes, if dechlorination is limited to narrow bioactive zones, and the need for additional donor injections to maintain dechlorination activity may limit the efficiency of ERD in low-permeability media. Future work should address the dynamics of the bioactive zones, which is essential to understand for predictions of long term mass removal.

Abstract  A preliminary study of the 20kHz sonoelectrochemical degradation of perchloroethylene in aqueous sodium sulfate has been carried out using controlled current density degradation sonoelectrolyses in batch mode. An important improvement in the viability of the sonochemical process is achieved when the electrochemistry is implemented, but the improvement of the electrochemical treatment is lower when the 20kHz ultrasound field is simultaneously used. A fractional conversion of 100% and degradation efficiency around 55% are obtained independently of the ultrasound power used. The current efficiency is also enhanced compared to the electrochemical treatment and a higher speciation is also detected; the main volatile compounds produced in the electrochemical and sonochemical treatment, trichloroethylene and dichloroethylene, are not only totally degraded, but also at shorter times than in the sonochemical or electrochemical treatments.

Abstract  Henry's Law constants (HLCs) of several common, subsurface hydrophobic organic pollutants (HOPs) including trichloroethylene (TCE), perchloroethylene (PCE) and benzene, toluene, ethylbenzene,and o-xylene (BTEX), were measured using a static headspace phase ratio (SHPR) method over a range of temperatures (35, 45, 55, and 65 degrees C) and experimentally and operationally relevant cyclodextrin (CD) concentrations (0, 10, 20,50,and 100g L(-1)). In aqueous CD solutions, HLC values decrease according to a power law relationship with increasing CD concentration due to an apparent solubility enhancement caused by HOP partitioning to the hydrophobic cavity of CO molecules. The temperature dependence of air-water partitioning under the influence of CD was well described by the van't Hoff equation for all HOPs tested. A three-phase equilibrium model was used to interpret air-water-CD partitioning data, treating CD as a pseudophase. Our results show that HOP CD-water partition coefficients decrease linearly with increasing temperature. CD-water partition coefficients were generally independent of CID concentration, with a few exceptions. Comparison of our results for hydroxypropyl-beta-CD and TCE to those from another study showed several major discrepancies, which were attributed to differences in the experimental methods employed. Our attempt to correlate CD-water partition coefficients with HOP chemical properties indicates that correlations based on individual chemical descriptors (e.g., aqueous solubility, octanol-water partition coefficient, molecular volume or E(T) (30) polarity index) will not be sufficient to obtain accurate estimates of HOP CD-water partition coefficients for other compounds with differing chemical structures.

Abstract  Air-stripping is one of the most effective technologies for removing volatile organic compounds (VOCs) from surfactant solutions, although the presence of surfactant poses some unique challenges. This study evaluated the effect of a mixed surfactant system on the apparent Henry's law constant of tetrachloroethylene (PCE) and the efficiency of PCE removal from surfactant solutions using a lab-scale hollow fiber membrane contactor. Results show that the presence of surfactant significantly reduced the apparent Henry's law constant of PCE, and the reduction was proportional to the total surfactant concentration. PCE removal efficiency by membrane air-stripping (MAS) decreased as the surfactant system transitioned from solubilization to supersolubilization. Besides significantly reducing the apparent volatility of VOCs, the presence of surfactant brings additional mass transfer resistance in air-stripping, which makes it difficult to achieve high levels of contaminant removal, even at very high air/liquid (A/L) ratios. In contrast, multipass/multistage MAS operated at low A/L ratios could achieve near 100% contaminant removal because of less mass transfer limitation during each stripping pass/stage. Experimental results, together with model calculations demonstrate multipass (and multistage) air-stripping as a cost-effective alternative for removing VOCs from surfactant micellar solutions compared to the options of using large air strippers or operating at high A/L ratios. (C) 2009 Elsevier B.V. All rights reserved.

Abstract  C-2, - C-5, non-methane hydrocarbons (NMHCs) and methyl chloride in the remote maritime atmosphere over the western North Pacific are analyzed in regard to their variation of mixing ratio and C-13/C-12 ratio (delta(13)C), together with those in polluted urban (Nagoya and Yokohama) and coastal (Tokyo Bay) atmosphere in Japan. NMHCs show large atmospheric mixing ratio and reacts between urban (coastal) and maritime atmospheres probably due to emission from urban areas and degradation within the maritime atmosphere. Reflecting isotopic fractionation during the degradation within the maritime atmosphere, ethane shows large and systematic delta(13)C variation between urban (around -27 parts per thousand ethane Peedee belemnite (PDB)) and maritime atmosphere s (up to -22 parts per thousand PDB). Except for ethane, however, alkanes show small isotopic variation around delta(13)C = -27 +/- 2 parts per thousand PDB (lo) without systematic isotopic differences between urban and maritime atmospheres, suggesting br,th small delta(13)C: variation a ithin major emission sources and also little isotopic fractionation during atmospheric degradation for alkanes other than ethane. Alkenes show large delta(13)C variation from -37 to -12 parts per thousand PDB for ethylene and from -27 to -14 parts per thousand PDB for propylene. Combination of both large delta(13)C differences between major sources (especially between land and maritime sources) and large isotopic fractionation effect during atmospheric degradation call be suggested for alkenes. Methyl chloride also shows large isotopic variation from -44 to -30 parts per thousand PDB in spite of their similar atmospheric mixing ratios from 580 to 710 parts per trillion by volume (pptv), probably due to the contribution of highly C-13-depleted, anthropogenic methyl chloride especially to urban atmospheres, Thr general delta(13)C pattern of NMHCs and methyl chloride in polluted urban city air agrees s strongly with those of biomass (C-3 plant) burning plumes, suggesting that thermal breakdown of C-.3 plant (or related organic matter) is one of the representative sources of these hydrocarbons in urban atmospheres. Further investigations of the isotopic signature of source materials as well as laboratory studies of isotopic fractionation processes resulting from atmospheric degradation will improve our understanding of the sources, sinks, and atmospheric distributious of NMHCs and methyl chloride.

Abstract  Novel reactive materials for catalytic degradation of chlorinated organic compounds in water at ambient conditions have been prepared on the basis of silica-supported Pd-Fe nanoparticles. Nanoscale Fe-Pd particles were synthesized inside porous silica supports using (NH4)(3)[Fe(C2O4)(3)] and [Pd(NH3)(4)]Cl-2 or Pd acetate as reaction precursors. According to temperature programmed reduction (TPR) studies, Pd introduction decreased the reduction temperature of the supported Fen+ species and nearly complete reduction with H-2 was observed at 400 degrees C. The successful surface loading with Pd was confirmed by X-ray photoelectron spectroscopy (XPS) analysis. Characterization of the samples by X-ray diffraction (XRD) and X-ray absorption near-edge structure + extended X-ray absorption fine structure (XANES + EXAFS) verified the presence of highly dispersed Pd-0, PdxFe1-x and Fe-0 phases. Reduction of the supported precursors in hydrogen resulted in materials that were highly active in perchloroethene (PCE) degradation and 2-chlorobiphenyl (2-ClBP) dechlorination. It was found that highly dispersed amorphous Fe-Pd bimetallic nanoparticles on silica support showed superior catalytic activity against PCE dechlorination in comparison to the free-standing Fe-Pd nanoparticles. For the samples with the same Fe content, the conversion of chlorinated organics as well as the stability increased with the Pd loading, e. g., the most effective degradation of PCEs and 2-ClBP was achieved at a Pd loading of 2.3-3.2 wt. %.

Abstract  BACKGROUND:: Genetic and environmental factors are believed to contribute to the development of autism, but relatively few studies have considered potential environmental risks. Here, we examine risks for autism in children related to in utero exposure to monitored ambient air toxics from urban emissions.

METHODS:: Among the cohort of children born in Los Angeles County, California, 1995-2006, those whose mothers resided during pregnancy in a 5-km buffer around air toxics monitoring stations were included (n = 148,722). To identify autism cases in this cohort, birth records were linked to records of children diagnosed with primary autistic disorder at the California Department of Developmental Services between 1998 and 2009 (n = 768). We calculated monthly average exposures during pregnancy for 24 air toxics selected based on suspected or known neurotoxicity or neurodevelopmental toxicity. Factor analysis helped us identify the correlational structure among air toxics, and we estimated odds ratios (ORs) for autism from logistic regression analyses.

RESULTS:: Autism risks were increased per interquartile range increase in average concentrations during pregnancy of several correlated toxics mostly loading on 1 factor, including 1,3-butadiene (OR = 1.59 [95% confidence interval = 1.18-2.15]), meta/para-xylene (1.51 [1.26-1.82]), other aromatic solvents, lead (1.49 [1.23-1.81]), perchloroethylene (1.40 [1.09-1.80]), and formaldehyde (1.34 [1.17-1.52]), adjusting for maternal age, race/ethnicity, nativity, education, insurance type, parity, child sex, and birth year.

CONCLUSIONS:: Risks for autism in children may increase following in utero exposure to ambient air toxics from urban traffic and industry emissions, as measured by community-based air-monitoring stations.

Abstract  Selected volatile organic compounds (VOCs) emitted from commercial activities and industrial processes have been classified as hazardous air pollutants, posing a potential health risk in the urban environment. In this respect, perchloroethylene (PCE), a suspected human carcinogen, is the most noticeable compound because it is widely used in laundries and hotels as a dry-cleaning solvent. The objective of this paper was to quantify the emissions of PCE and other petroleum-based solvents from dry cleaning business in illustration of the regulatory infrastructure of reducing PCE exposure in the environment of Taiwan. Based on the Emission Factors (AP-42) method, the emissions of the non-methane hydrocarbons (NMHCs) from dry cleaning business had decreased from 5100 metric tons in 1997 to 2800 metric tons in 2007. The success of significant reduction of NMHCs in Taiwan has been ascribed to the fact that Taiwan established the relevant regulations at the end of the 1990s. From the data on the industrial/commercial demand for PCE and the emission inventories of NMHCs from dry cleaning business, the reduction of PCE emissions will show a declining trend in the near future.

Abstract  BIOSIS COPYRIGHT: BIOL ABS. RRM WATER POLLUTION WASTEWATER TREATMENT

Abstract  Chlorinated solvents are among the most common groundwater pollutants globally. A common method to remediate this groundwater pollutant is through bioremediation. One of the most important bacteria that remediation workers use in this remediation is Dehalococcoides ethenogenes, which are the only dehalogenating bacteria with the capacity to break down these contaminants to the non-chlorinated compound, ethylene. While much is known about these bacteria in the laboratory, little is known about their natural habitat. In this experiment, eight sites on Dover Air Force Base were selected based on the larger CERCLA Closeout project; 2.54 cm wells were installed and groundwater samples were collected. These sites monitored groundwater quality parameters: temperature, pH, dissolved oxygen, and oxidative reduction potential. Additionally, samples were also analyzed for the contaminants: tetrachlorethylene, trichloroethylene, and vinyl chloride. The presence of vinyl chloride is an indicator of Dehalococcoides ethenogenes. Soil samples from the aquifer level were taken from each site as well and soil particle texture was assessed using the Bouyoucos hydrometer method. The objective of this experiment was to determine if there was a relationship between clay particles at the aquifer level, groundwater quality, and the presence of Dehalococcoides ethenogenes.

Abstract  Office devices can release volatile organic compounds (VOCs) partly generated by toners and inks, as well as particles of paper. The aim of the presented study is to identify indoor emissions of volatile halogenated organic compounds into the office workspace environment. Mixtures of organic pollutants emitted by seven office devices, i.e. printers and copiers, were analyzed by taking samples in laboratory conditions during the operation of these appliances. Tests of volatile organic compound emissions from selected office devices were conducted in a simulated environment (test chamber). Samples of VOCs were collected using three-layered thermal desorption tubes. Separation and identification of organic pollutant emissions were made using thermal desorption combined with gas chromatography coupled to mass spectrometry. Test chamber studies indicated that operation of the office printer and copier would contribute to the significant concentration level of VOCs in typical office indoor air. Among the determined volatile halogenated compounds, only chlorinated organic compounds were identified, inter alia: trichloroethylene - carcinogenic - and tetrachloroethylene - possibly carcinogenic to human. The results show that daily exposure of an office worker to chemical factors released by the tested printing and copying units can be variable in terms of concentrations of VOCs. The highest emissions in the test chamber during printing were measured for ethylbenzene up to 41.3 μg m(-3), xylenes up to 40.5 μg m(-3) and in case of halogenated compounds the highest concentration for chlorobenzene was 6.48 μg m(-3). The study included the comparison of chamber concentrations and unit-specific emission rates of selected VOCs and the identified halogenated compounds. The highest amount of total VOCs was emitted while copying with device D and was rated above 1235 μg m(-3) and 8400 μg unit(-1) h(-1) on average.

Abstract  Long-term monitoring (LTM) of groundwater remedial projects is costly and time-consuming, particularly when using phytoremediation, a long-term remedial approach. The use of trees as sensors of groundwater contamination (i.e., phytoscreening) has been widely described, although the use of trees to provide long-term monitoring of such plumes (phytomonitoring) has been more limited due to unexplained variability of contaminant concentrations in trees. To assess this variability, we developed an in planta sampling method to obtain high-frequency measurements of chlorinated ethenes in oak (Quercus rubra) and baldcypress (Taxodium distichum) trees growing above a contaminated plume during a 4-year trial. The data set revealed that contaminant concentrations increased rapidly with transpiration in the spring and decreased in the fall, resulting in perchloroethene (PCE) and trichloroethene (TCE) sapwood concentrations an order of magnitude higher in late summer as compared to winter. Heartwood PCE and TCE concentrations were more buffered against seasonal effects. Rainfall events caused negligible dilution of contaminant concentrations in trees after precipitation events. Modeling evapotranspiration potential from meteorological data and comparing the modeled uptake and transport with the 4 years of high frequency data provides a foundation to advance the implementation of phytomonitoring and improved understanding of plant contaminant interactions.

Abstract  The hydrofluoroolefin 2,3,3,3-tetrafluoropropene (HFO-1234yf) has been introduced to replace 1,1,1,2-tetrafluoroethane (HFC-134a) as refrigerant in mobile, including vehicle, air conditioning systems because of its lower global warming potential. HFO-1234yf is volatile at ambient temperatures; however, high production volumes and widespread handling are expected to release this fluorocarbon into terrestrial and aquatic environments, including groundwater. Laboratory experiments explored HFO-1234yf degradation by (i) microbial processes under oxic and anoxic conditions, (ii) abiotic processes mediated by reactive mineral phases and zerovalent iron (Fe-0 ZVI), and (iii) cobalamin-catalyzed biomimetic transformation. These investigations demonstrated that HFO-1234yf was recalcitrant to microbial (co)metabolism and no transformation was observed in incubations with ZVI, makinawite (FeS), sulfate green rust (GR(SO4)), magnetite (Fe3O4), and manganese oxide (MnO2). Sequential reductive defluorination of HFO-1234yf to 3,3,3-trifluoropropene and 3,3-dichloropropene with concomitant stoichiometric release of fluoride occurred in incubations with reduced cobalamins (e.g., vitamin B-12) indicating that biomolecules can transform HFO-1234yf at circumneutral pH and at ambient temperature. Taken together, these findings suggest that HFO-1234yf recalcitrance in aquifers should be expected; however, HFO-1234yf is not inert and a biomolecule may mediate reductive transformation in low redox environments, albeit at low rates.

Abstract  This paper presents a full-scale thermal remediation of a brownfields site near San Francisco, California. In Situ Thermal Desorption (ISTD) was used for treatment of chlorinated solvents in a tight clay below the water table. The site had contaminants in concentrations indicating that a tetrachloroethene (PCE)-rich DNAPL was present. A target volume of 5097m(3) of subsurface material to a depth of 6.2m was treated for a period of 110d of heating. Energy was delivered through 126 thermal conduction heater borings, and vapors were extracted from a combination of vertical and horizontal vacuum wells. Approximately 2540kg of contaminants were recovered in the extracted vapors by the end of treatment. The PCE concentration in the clay was reduced from as high as 2700mg/kg to an average concentration of 0.012mg/kg within 110d of heating (a reduction of >99.999%). Similar effectiveness was documented for TCE, cis-1,2-DCE, and vinyl chloride. A total of 2.2million kWh of electric power was used to heat the site. Approximately 45% of this energy was used to heat the subsurface to the target temperature. Another 53% was necessary to boil approximately 41% of the groundwater within the treatment zone, creating approximately 600 pore volumes of steam by the end of the 110-d heating and treatment period. Steam generation thus occurred within the clay. Partitioning of the contaminants into the steam and its removal comprised the dominant remedial mechanism. The steam migrated laterally toward the ISTD heaters, where it encountered a small dry region adjacent to each of the heaters, which served as a preferential pathway allowing the steam to migrate upward along the heaters to the more permeable vadose zone. There the steam was captured by a system of vertical and horizontal vacuum extraction wells. This vapor removal strategy facilitated effective thermal treatment of the tight clays located below the water table. Features of a robust design are extension of the heaters at least 1.2m deeper than the treatment depth, and the installation of shallow horizontal vapor collection wells which allow for establishment of pneumatic control.

Abstract  Flow-through column experiments were conducted to estimate the change of the concentration of three chlorinated VOCs (chloroform, trichloroethylene and tetrachloroethylene) in two types of soil. The two soils were a terra rosa with organic carbon content of 1.32% and a sandy clay loam with organic carbon content of 0.26%. The experiments took place for 116 mu g/l single solutes in the absence and presence of humic acid (10 and 30 mg/l). Effluent concentrations depended on the individual compound, the carbon content of the soil, and the presence of humic acid. In the absence of humic acid, chloroform showed the highest effluent concentration. or equivalently the smallest extent of adsorption. When humic acid was added to the feed solution, the VOC effluent concentration increased. This was more severe for chloroform and trichloroethylene. The higher the concentration of humic acid in the feed solution, the higher the concentration of each of the VOCs in the soil bed effluent. The increased inability was attributed to the binding of the organic contaminants to the humic molecules affecting their solubility in the soil aqueous phase. In the case of tetrachloroethylene a small degree of biodegradation was also observed as indicated by the appearance of trichloroethylene. (C) 1998 Elsevier Science Ltd. All rights reserved.

Abstract  In many cities, dry cleaners using perchloroethylene are frequently located in multifamily residential buildings and often cause elevated indoor air levels of perchloroethylene throughout the building. To assess individual perchloroethylene exposures associated with co-located dry cleaners, we measured perchloroethylene in residential indoor air, and in blood and breath of adults and children residing in buildings with a dry cleaner as part of the New York City (NYC) Perc Project. We also measured perchloroethylene in indoor air, and in blood and breath of residents of buildings without a dry cleaner for comparison. Here, we evaluate whether an environmental disparity in perchloroethylene exposures is present. Study participants are stratified by residential building type (dry cleaner or reference) and socioeconomic characteristics (race/ethnicity and income); measures of perchloroethylene exposure are examined; and, the influence of stratified variables and other factors on perchloroethylene exposure is assessed using multivariate regression. All measures of perchloroethylene exposure for residents of buildings with a dry cleaner indicated a socioeconomic disparity. Mean indoor air perchloroethylene levels were about five times higher in minority (82.5 ug/m(3)) than in non-minority (16.5 ug/m(3)) households, and about six times higher in low-income (105.5 ug/m(3)) than in high income (17.8 ug/m(3)) households. Mean blood perchloroethylene levels in minority children (0.27 ng/mL) and adults (0.46 ng/mL) were about two and three times higher than in non-minority children (0.12 ng/mL) and adults (0.15 ng/mL), respectively. Mean blood perchloroethylene levels in low income children (0.34 ng/mL) and adults (0.62 ng/mL) were about three and four times higher than in high income children (0.11 ng/mL) and adults (0.14 ng/mL), respectively. A less marked socioeconomic disparity was observed in perchloroethylene breath levels with minority and low income residents having slightly higher levels than non-minority and high income residents. Multivariate regression affirmed that indoor air perchloroethylene level in dry cleaner buildings was the single most important factor determining perchloroethylene in blood and breath. Neither age, gender, nor socioeconomic status significantly influenced perchloroethylene levels in breath or blood. We previously reported that increased indoor air, breath, and blood perchloroethylene levels among NYC Perc Project child participants were associated with an increased risk for slightly altered vision. Thus, the disproportionately elevated perchloroethylene exposures of minority and low-income child residents of buildings with a dry cleaner shown here constitutes an environmental exposure disparity with potential public health consequences. Among residents of buildings without a dry cleaner, we observed some small increases in perchloroethylene breath and blood levels among non-minority or high income residents compared to minority or low income residents. These differences were not attributable to differences in indoor air levels of perchloroethylene which did not differ across socioeconomic categories, but appear to be associated with more frequent exposures dry cleaned garments.