Organic Compounds In Groundwater Research Articles

Indicadores geoquímicos de contaminação por compostos orgânicos voláteis em águas subterrâneas da Bacia do Rio Lucaia, Salvador, Bahia

Geochemical indicators of contamination by volatile organic compounds in groundwater on Lucaia's River Basin, Salvador, Bahia, Brazil. This work investigated the groundwater contamination of the Lucaia's River Basin, Salvador, Brazil, for petroleum hydrocarbons leaking from fuel tanks. The concentrations of benzene, toluene, ethylbenzene and xylenes ― BTEX ―, sulfate, nitrate and iron (II) was determined in 17 samples of groundwater. The concentration of BTEX ranged from 0.2 to 185.7 µg.L -1 and the concentrations of sulfate, nitrate and iron (II) were correlated with levels of BTEX undergoing natural degradation. In only two points BTEX levels were observed far above the permitted by CONAMA Resolution no 396/2008, while the others were below the detection limit.

Methane Production and Isotopic Fingerprinting in Ethanol Fuel Contaminated Sites

Biodegradation of organic compounds in groundwater can be a significant source of methane in contaminated sites. Methane might accumulate in indoor spaces posing a hazard. The increasing use of ethanol as a gasoline additive is a concern with respect to methane production since it is easily biodegraded and has a high oxygen demand, favoring the development of anaerobic conditions. This study evaluated the use of stable carbon isotopes to distinguish the methane origin between gasoline and ethanol biodegradation, and assessed the occurrence of methane in ethanol fuel contaminated sites. Two microcosm tests were performed under anaerobic conditions: one test using ethanol and the other using toluene as the sole carbon source. The isotopic tool was then applied to seven field sites known to be impacted by ethanol fuels. In the microcosm tests, it was verified that methane from ethanol (δ¹³C = -11.1‰) is more enriched in ¹³C, with δ¹³C values ranging from -20‰ to -30‰, while the methane from toluene (δ¹³C = -28.5‰) had a carbon isotopic signature of -55‰. The field samples had δ¹³C values varying over a wide range (-10‰ to -80‰), and the δ¹³C values allowed the methane source to be clearly identified in five of the seven ethanol/gasoline sites. In the other two sites, methane appears to have been produced from both sources. Both gasoline and ethanol were sources of methane in potentially hazardous concentrations and methane could be produced from organic acids originating from ethanol along the groundwater flow system even after all the ethanol has been completed biodegraded.

Focus on sensors and detectors

Focus on sensors and detectors

Degradation of carbon tetrachloride in the presence of zero-valent iron

Efforts to achieve the decomposition of carbon tetrachloride through anaerobic and aerobic bioremediation and chemical transformation have met with limited success because of the conditions required and the formation of hazardous intermediates. Recently, particles of zero-valent iron (ZVI) have been used with limited success for in situ remediation of carbon tetrachloride. We studied a modified microparticulate product that combines controlled-release carbon with ZVI for stimulation of in situ chemical reduction of persistent organic compounds in groundwater. With this product, a number of physical, chemical, and microbiological processes were combined to create very strongly reducing conditions that stimulate rapid, complete dechlorination of organic solvents. In principle, the organic component of ZVI microparticles is nutrient rich and hydrophilic and has high surface area capable of supporting the growth of bacteria in the groundwater environment. In our experiments, we found that as the bacteria grew, oxygen was consumed, and the redox potential decreased to values reaching -600 mV. The small modified ZVI particles provide substantial reactive surface area that, in these conditions, directly stimulates chemical dechlorination and cleanup of the contaminated area without accumulation of undesirable breakdown products. The objective of this work was to evaluate the effectiveness of ZVI microparticles in reducing carbon tetrachloride under laboratory and field conditions. Changes in concentrations and in chemical and physical parameters were monitored to determine the role of the organic products in the reductive dechlorination reaction. Laboratory and field studies are presented.

Risk assessment of exposure to volatile organic compounds in groundwater in Taiwan

The purpose of this study is to assess the risks from exposure to 14 volatile organic compounds (VOCs) in selected groundwater sites in Taiwan. The study employs the multimedia environment pollutant assessment system (MEPAS) model to calculate the specific non-cancer and cancer risks at an exposure level of 1 μg/L of each VOC for a variety of exposure pathways. The results show that the highest specific non-cancer risk is associated with water ingestion of vinyl chloride (VC) and that the highest specific cancer risk is associated with indoor breathing of VC. The three most important exposure pathways for risk assessment for both non-cancer and cancer risks are identified as water ingestion, dermal absorption when showering, and indoor breathing. Excess tetrachloroethylene (PCE), trichloroethylene (TCE), dichloroethylene (DCE), and VC are detected in the groundwater aquifers of one dump site and one factory. However, the study suggests that the pollutants in the contaminated groundwater aquifers do not travel extensively with groundwater flow and that the resulting VOC concentrations are below detectable levels for most of the sampled drinking-water treatment plants. Nevertheless, the non-cancer and cancer risks resulting from use of the contaminated groundwater are found to be hundred times higher than the general risk guidance values. To ensure safe groundwater utilisation, remediation initiatives for soil and groundwater are required. Finally, the study suggests that the current criteria for VOCs in drinking water might not be capable of ensuring public safety when groundwater is used as the primary water supply; more stringent quality criteria for drinking water are proposed for selected VOCs.

Low-Level Detections of Halogenated Volatile Organic Compounds in Groundwater: Use in Vulnerability Assessments

Concentrations of halogenated volatile organic compounds (VOCs) were determined by gas chromatography (GC) with an electron-capture detector (GC-ECD) and by gas chromatography with mass spectrometry (GC-MS) in 109 groundwater samples from five study areas in the United States. In each case, the untreated water sample was used for drinking-water purposes or was from a monitoring well in an area near a drinking-water source. The minimum detection levels (MDLs) for 25 VOCs that were identified in GC-ECD chromatograms, typically, were two to more than four orders of magnitude below the GC-MS MDLs. At least six halogenated VOCs were detected in all of the water samples analyzed by GC-ECD, although one or more VOCs were detected in only 43% of the water samples analyzed by GC-MS. In nearly all of the samples, VOC concentrations were very low and presented no known health risk. Most of the low-level VOC detections indicated post-1940s recharge, or mixtures of recharge that contained a fraction of post-1940s wate...

Process optimization using a kinetic model for the ultraviolet radiation-hydrogen peroxide decomposition of natural and synthetic organic compounds in groundwater

This paper discusses the application of ultraviolet radiation-hydrogen peroxide (UV-HP) process as an advanced oxidation process (AOP) in the treatment of source waters containing natural organic matter (NOM) and contaminated with a synthetic organic chemical (SOC) exemplified by alachlor, an acetanilide pesticide. Alachlor was chosen as the model compound owing to its hydrophobicity and propensity to complex with NOM, besides its classification as an endocrine disrupting chemical (EDC). The study examines the general principles, free-radical chemistry and reaction mechanisms of the UV-HP process from a kinetic modeling standpoint, and provides a systematic approach combining experimental data acquisition with modeling techniques for evaluating the influence of NOM and other free-radical scavengers such as the carbonate species on the contaminant degradation efficiency. The study proposes a kinetic model for predicting and/or simulating the UV-HP decomposition of alachlor in the presence of NOM and other free-radical scavengers under different water quality and operating conditions. The model incorporates additional and descriptive features such as pH decrease during oxidation (due to mineralization of NOM and SOC), and uses UV absorbance at 310 nm (UVA 310) as a surrogate parameter for NOM, accounting for changes in NOM structural composition attributable to hydroxyl radical attack and direct photolysis. The experimental data provide model validation and verification for alachlor degradation kinetics for NOM-free and NOM-containing waters. Although the model slightly overestimates the UV-HP process reaction rates for water containing NOM at low pH, it provides insight into the complex free-radical reactions, mechanisms and kinetics for process optimization toward economical and efficient decontamination.

Determination of Volatile Organic Compounds by Headspace Trap

A new analytical method for the determination of halogenated and aromatic volatile organic compounds in groundwater, mineral water, and drinking water at concentrations ranging between 1-10000 ng/L is developed. A new type of headspace sampler that combines static headspace sampling with a trap is used, yielding very low detection limits and good repeatability without carryover effects. An unexpected transformation of 1,1,2,2-tetrachloroethane into trichloroethene is observed and explained.

Optimization of analytical quality control for long-term monitoring of metals and volatile organic compounds in groundwater

Statistical analysis of historical results for matrix spikes (MS), matrix spike duplicates (MSD), and laboratory control samples (LCS) from aqueous samples analyzed for metals and volatile organic compounds was performed to determine whether the MS/MSD provided substantive information apart from that provided by the LCS. The statistical analysis showed that the mean recovery of all analytes from MS/MSD closely approximated the mean recovery of all analytes from the LCS. Average bias, skewness, and kurtosis were also assessed for both data sets. The evaluation provided strong evidence for the use of LCS recoveries as performance indicators of probable MS/MSD recoveries of metals and volatile organic compounds from groundwater.

Sonolytic degradation of halogenated organic compounds in groundwater: Mass transfer effects

Organic pollutants in liquid exposed to acoustic waves behave differently according to their physical and chemical properties. Laboratory batch experiments of sonication for the degradation of trichloroethylene (TCE) and ethylene dibromide (EDB) were carried out in groundwater at 20 kHz, and 12.5 and 35 W/cm 2. A theoretical model for the batch sonication system was derived to examine the mass transfer dependency of the ultrasonic degradation. Experimental results were supported with model predictions suggesting that both liquid phase diffusion coefficient and Henry’s law constant are important parameters for the sonolytic degradation of the halogenated organic compounds in groundwater. When compared with the effect of the diffusion coefficient, Henry’s constant exerts a greater influence on sonolytic degradation. When Henry’s constant exceeds a value of 1 (volume/volume ratio), however, it no longer has much influence on the degradation process. The results also suggest that degradation is enhanced with an increase in ultrasonic power probably due to a greater bubble residence time and the formation of larger bubble at high-energy intensities.

Degradation of halogenated organic compounds in ground water by heterogeneous catalytic oxidation with hydrogen peroxide

Catalytic oxidation with hydrogen peroxide is a reliable method for the treatment of polluted water. The conversion of a wide spectrum of components including aliphatic and aromatic hydrocarbons as well as halogenated organic compounds into non-toxic or minor-toxic substances and finally into carbon dioxide and water can be achieved. The degradation of chlorobenzene, 4-chlorophenol, 4-chloroaniline and 1-nitro-4-chlorobenzene was investigated. Several catalysts can be implemented into the catalytic process. It has been demonstrated that the type of catalyst and oxidation agent as well as the reaction parameters influence the degradation rate and has to be adjusted to the concrete waste water problem to be solved.

Analysis of methyl tert-butyl ether (MTBE) and tert-butyl alcohol (TBA) in ground and surface water

The fuel oxygenate methyl tert-butyl ether (MTBE) is one of the most frequently detected volatile organic compounds in groundwater and, thus, has become a priority groundwater pollutant over the last decade. Methods for the quantitative determination and for compound-specific isotope analysis (CSIA) of MTBE and its key degradation intermediate, tert-butyl alcohol (TBA), in ground and surface water are reviewed. These compounds are exclusively analyzed by gas chromatography (GC), mainly with mass spectrometric (MS) detection because of the requirements for selectivity and sensitivity. Sample introduction/enrichment based on direct aqueous injection, headspace analysis, solid-phase microextraction (direct immersion and headspace), and purge-and-trap is discussed. Specific advantages and disadvantages of these techniques are compared and criteria are given for choosing an appropriate method. Furthermore, it is shown that CSIA can be used to determine the isotopic composition of MTBE and related compounds in the low μg/L range and will therefore become an invaluable tool in the characterization of the environmental fate of such pollutants.

Monitoring of the antioxidant BHT and its metabolite BHT-CHO in German river water and ground water

The behavior of anthropogenic polar organic compounds in ground water during infiltration of river water to ground water was studied at the Oderbruch area on the eastern border of Germany. Additionally, waste water sewage treatment works (STWs) discharging their treated waste water into the Oder River and rain water precipitation from the Oderbruch area were investigated. The study was carried out from March 2000 to July 2001 to investigate seasonal variations of the target analytes. Samples were collected from four sites along the Oder River, from 24 ground water monitoring wells located close to the Oder, from one rain water collection station, from two roof runoffs, and from four STWs upstream of the Oderbruch. Results of the investigations of the antioxidant 3,5-di- tert-butyl-4-hydroxy-toluene (BHT) and its degradation product 3,5-di- tert-butyl-4-hydroxy-benzaldehyde (BHT-CHO) are presented. BHT and BHT-CHO were detected in all samples of the Oder River with mean concentrations of 178 and 102 ng l −1, respectively. BHT and BHT-CHO were also detected in effluent waste water samples from municipal STWs at mean concentrations of 132 and 70 ng l −1, respectively. Both compounds are discharged into river water directly via treated waste water. In the rain water sample, 308 ng l −1 of BHT and 155 ng l −1 of BHT-CHO were measured. Both compounds were detected in roof runoff with mean concentrations of 92 ng l −1 for BHT and 138 ng l −1 for BHT-CHO. The median values of BHT and BHT-CHO in ground water samples were 132 and 84 ng l −1, respectively. The chemical composition of ground water from parts of the aquifer located less than 4.5 m distant from the river are greatly influenced by bank filtration. However, wet deposition followed by seepage of rain water into the aquifer is also a source of BHT and BHT-CHO in ground water.

A Conceptual Model and Remediation Strategy for Volatile Organic Compounds in Groundwater in Unconsolidated Sediments: A Lawrence Livermore National Laboratory Case Study

Field data collected during the first 7 years of pump-and-treat remediation of groundwater containing volatile organic compounds (VOCs) at the Lawrence Livermore National Laboratory (LLNL) Superfund Site in Livermore, California, indicate that groundwater contaminant plumes at this site can be divided into two distinct parts: source areas and distal areas. In source areas, located in the immediate vicinity of the contaminant releases, the contaminants are distributed in relatively high concentrations throughout the vadose zone and below the water table in both fine-grained and coarse-grained sediments. In distal portions of the plume, downgradient of the source areas, the contaminants: 1) are primarily limited to coarse-grained zones, 2) are usually orders of magnitude lower in concentration than in the source areas, and 3) have slightly diffused into the bordering aquitards but should not significantly affect the approach to or achievement of cleanup goals. The cleanup strategy for this distribution of contaminants calls for the hydraulic isolation of the source area followed by aggressive remediation of both the source and distal areas of the plume as needed to achieve remediation objectives most efficiently. In contrast to some of the currently perceived limitations of pump-and-treat remediation, our data and analyses indicate that distal portions of contaminant plumes can be expeditiously remediated, perhaps in less time than it took the contaminants to be transported to their preremediation locations.

Online sensing of volatile organic compounds in groundwater using mid-infrared fibre optic evanescent wave spectroscopy: a pilot scale test

A prototype sensing system for in-situ monitoring of volatile organic compounds in contaminated groundwater was tested at a pilot scale plant. The sensor consists of a commercially available Fourier transform infrared spectrometer, connected to a 6 m long infrared transparent silver halide fibre optic cable. A 10 cm long core-only section at the centre of the fibre is mounted on a sensor head and coated with a hydrophobic polymer layer, while the remaining fibre is protected by Teflon tubing and thus not in contact with the surrounding media. The sensor head was immersed into the monitoring wells of the pilot plant testing the sensor system under circumstances close to field conditions and typical for in-situ measurements. The pilot plant consists of a 1 m3 cubic tank filled with gravel. A pump is used to circulate water horizontally through the tank, simulating a natural aquifer. The evolution of the concentration of analytes injected into the system is monitored with time using the developed prototype sensing system. The results are validated by corresponding sampling and analysis with headspace gas chromatography.

Groundwater pollution at a pulp and paper mill at Sjasstroj near Lake Ladoga, Russia

Abstract Lake Ladoga, situated in north-west Russia, is the main source of drinking water for more than 6 million people in the region of St Petersburg. During recent years eutrophication of Lake Ladoga has increased, with pollution of the lake water and sediments by heavy metals, phenols and chloro-organic substances. This paper reports the influence of effluents from a pulp and paper mill at Sjasstroj situated on the southern shore of Lake Ladoga. At Sjasstroj, contamination of a wide area of land, and the production of large volumes of wastewater requiring treatment and disposal, threaten the sustainability of surface and domestic well supplies and lake ecosystems. A tiered approach to risk assessment was adopted in this investigation beginning with a survey of historical data and an initial field reconnaissance followed by more detailed, targeted hydrogeological and hydrochemical investigations. Concentrations of dissolved organic carbon (DOC) as high as 44 mg 1 −1 and adsorbable organic halogens as high as 130 µg 1 −1 were found in groundwater samples. The detailed field reconnaissance survey contradicted toxicity index values for the wastewater, sludge and groundwater samples calculated using a Russian method of risk characterization, which would otherwise predict a high potential environmental pollution risk. In reality, there is good evidence for natural attenuation of organic compounds in groundwater, with as much as 40–50% removal of DOC. However, the residual DOC can be problematic when chlorination of raw surface and groundwaters creates organo-chlorine by-products in treated water.

A review of in situ measurement of organic compound transformation in groundwater.

Laboratory assessments of the rate of degradation of organic compounds in groundwater have been criticized for producing unrepresentative results. The potential for organic compounds to be transformed in groundwater has been measured using in situ methods, which avoid problems of attempting to duplicate aquifer conditions in the laboratory. In situ assessments of transformation rates have been accomplished using transport studies and in situ microcosms (ISMs); a review of these methods is given here. In transport studies, organic solutes are injected into an aquifer and the concentrations are monitored as they are transported downgradient. The change in mass of a solute is determined by the area contained under the breakthrough curve (plot of concentration versus time). ISMs isolate a portion of the aquifer from advective flow and act as in situ batch reactors. Experiments using ISMs involve removing water from the ISM, amending it with the solutes of interest, re-injecting the amended water, and monitoring the solute concentrations with time. In both transport and ISM studies, the loss of organic solutes from solution does not allow a distinction to be made between sorptive, abiotic and biotic transformation losses. Biological activity can be chemically suppressed in ISMs and the results from those experiments used to indicate sorption and abiotic loss. Transformation products may be monitored to provide additional information on transformation mechanisms and rates.

Monitoring Microbial Dechlorination of Tetrachloroethene (PCE) in Groundwater Using Compound-Specific Stable Carbon Isotope Ratios: Microcosm and Field Studies

The determination of compound-specific stable isotope ratios is a promising new tool to assess biodegradation of organic compounds in groundwater. In this study, the occurrence of carbon isotope fractionation during dechlorination of tetrachloroethene (PCE) to ethene was evaluated in a PCE-contaminated aquifer and in a microcosm that was based on aquifer material from the site. In the microcosm, all dechlorination steps were accompanied by carbon isotope fractionation. The largest fractionation occurred during dechlorination of cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC), resulting in a large enrichment of 13C in the remaining cDCE and VC. Stable carbon isotope ratios (δ13C) of cDCE and VC increased from −25.7 to −1.5‰ and −37.0 to −2.5‰, respectively. The δ13C of ethene was initially −60.2‰ and approached the δ13C of the added PCE (−27.3‰) as dechlorination came to completion. A similar carbon isotope pattern was observed for PCE dechlorination at the field site. Strong enrichment of 13C in cDCE and VC during microbial dechlorination may serve as a powerful tool to monitor the last two dechlorination steps, which frequently determine the rate of complete dechlorination of chlorinated ethenes at field sites undergoing intrinsic bioremediation.

Oxidative degradation and kinetics of chlorinated ethylenes by potassium permanganate

The oxidative treatment of chlorinated ethylenes in ground water using permanganate was investigated in a series of batch kinetic tests. Five chlorinated ethylenes including tetrachloroethylene (PCE), trichloroethylene (TCE), and three isomers of dichloroethylenes (DCEs) were examined. The degradation process was rapid with pseudo-first-order rate constants ranging from 4.5×10 −5 to 0.03 s −1 at MnO 4 −=1 mM. The rate increased with a decreasing number of chlorine substituents on the ethylene. The higher reactivity of trans-DCE ( k obs=30×10 −3 s −1 at MnO 4 −=1 mM) as compared to cis-DCE ( k obs=0.9×10 −3 s −1 at MnO 4 −=1 mM) is thought to be caused by a significant steric effect due to the formation of a large cyclic activated complex. TCE oxidation as a second-order reaction was confirmed and the rate constant, k=0.67±0.03 M −1 s −1, is independent of pH over the range of 4–8. The activity of both Cl − and hydrogen ions was monitored over time and suggests essentially complete dechlorination, making the degradation products less harmful than the parent compounds. Competition for MnO 4 − from other organic compounds in ground water or highly contaminated ground water was also evaluated in experiments. A simple and quick approach was demonstrated to estimate permanganate consumption by other organic compounds for field applications and to predict the TCE degradation rate in a system involving multiple contaminants. The modeling results suggest that the effect of autocatalysis by MnO 2 on TCE degradation is significant when the system contains high concentration levels of MnO 4 − and TOC.

Determination of Volatile Organic Compounds in Groundwater by GC: Comparison Between Headspace and Purge and Trap

Two methods for determining fuel contamination in groundwaters are compared. The first is based on headspace extraction, while the other utilizes purge and trap. Analyses, in both cases, are made by gas chromatography/flame ionization detection, with benzene, toluene, and xylene isomers as monitoring agents for fuel leaks. When compared, results show satisfactory agreement if we take into account the high levels of fuel contamination found in samples collected in control wells from a gas station in an urban site. Thus headspace/gas chromatography can be used, as an alternative technique, to monitoring of volatile organic compounds in groundwater. The main advantages when compared to purge and trap/gas chromatography are simplicity, low cost, and automatic sample handling. When a mass spectrometry detector was used, ethylmethylbenzene and trimethylbenzene isomers were detected in the water samples. These compounds could also be used as alternative tracers for fuel leak detection.