Aromatic Hydrocarbons In Groundwater Research Articles

Levels, distribution, origins, and human health risk evaluation of polycyclic aromatic hydrocarbons in groundwater around a petroleum depot wastewater discharge point

This study is an attempt to assess the influence of the oil storage depot discharges on proximate water sources in Ibadan, southwest Nigeria. Fifteen priority polycyclic aromatic hydrocarbons (PAHs) were examined in a total of 15 water samples (10 groundwater +4 surface water samples) utilizing gas chromatography–mass spectrometry, after extraction of the waters with dichloromethane and clean-up of the extracts. Results revealed that values of overall PAHs in groundwater (GW) and surface water (SW) varied from 0.01 to 3.45 mg/L (mean = 0.42 mg/L) and 0.01 to 0.09 mg/L (mean = 0.05 mg/L), correspondingly. The highest value of ∑15 PAHs (3.45 mg/L) was observed at 24 m to the discharge point. The ring wise distribution pattern of the PAHs in collected water samples follows the order: 2–3 rings >5–6 rings >4 – ring PAHs and low molecular weight (LMW) PAHs accounted for 90.73% relative to HMW (9.27%) in groundwater samples. The diagnostic ratios suggested that the PAHs pollution in water were likely from incomplete combustion of fossil fuels, vehicle emissions and released petroleum effluents from nearby depot. The concentration of carcinogenic PAHs in GW and SW ranged from 1×10−2to 9×10−2 mg/L and 1×10−2to 7×10−2 mg/L, correspondingly, which highlights possible human health risks. The values of hazard index (HI) for the studied samples via the oral ingestion and dermal exposure pathways are less than unity, suggesting no adverse non-carcinogenic health effects. The calculated incremental lifetime cancer risk (ILCR) for adults and children are in the 10−2–10−3 range, implying noteworthy possible carcinogenic health effects to human beings, with children being the most susceptible. Correspondingly, dibenzo [a, h] anthracence (DahA) and Benzo [a] pyrene (BaP) were established to be of greater carcinogenic threats in the waters taken from the study location. The study advocates complete discontinuance of discharge release into the neighboring environment.

Seasonal distribution, source apportionment and risk assessment of polycyclic aromatic hydrocarbons in groundwaters in Owo, Southwestern Nigeria

Abstract The study focused on evaluating the seasonal distribution, source apportionment, and probabilistic risk assessment of polycyclic aromatic hydrocarbons (PAHs) in groundwater. Groundwater samples were obtained from Owo, southwestern Nigeria and subjected to liquid–liquid extraction and quantified using gas chromatography–mass spectrometry. Total PAH concentrations varied from about 180 to 23,600 ng/L during the dry season. The wet season, on the other hand, exhibited a wider range, from about 1,550 to 150,000 ng/L. Seasonal variations were also found in PAH types and concentrations, with relatively higher concentrations recorded during the wet season. Diagnostic ratios and positive matrix factorization indicated that coal/biomass combustion and traffic-related vehicular emissions were the prevalent sources of PAHs in groundwater. Health risk assessment indicated potential carcinogenic risks (incremental lifetime cancer risk (ILCR) > 1E − 04), while ecological assessment suggested medium (RQNC < 800 and RQMPC ≥ 1) and high ecological risks (RQNC ≥ 800 and RQMPC ≥ 1). The study reflected the need for effective mitigation strategies.

Evaluating the potential of wax impregnated reactive components for long-term acenaphthene removal

The catalytic oxidation of acenaphthene (ANA) was investigated using a controlled-release persulfate candle (PSC) and Fe(II) candle (Fe(II)C) to provide long-lasting oxidation conditions during groundwater remediation. To the best of our knowledge, this study is the first attempt to compare the pseudo-first-order rate constant (kobs) and % removal of ANA oxidation using PSC/Fe(II)C, PS solution (PSaq)/Fe(II) solution (Fe(II)aq), PSC/Fe(II)aq, and PSaq/Fe(II)C systems. The kobs and % removal of ANA in the PSC/Fe(II)C system exceeded those in the other systems. The optimal degradation conditions used were 0.1 mM ANA; 3.08 mM equilibrium concentration of PS (Ce,PS) released from PSC (controlled-release rate constant, kcr = 7.731 day−1); 5.673 mM equilibrium concentration of Fe(II) (Ce,Fe(II)) released from Fe(II)C (kcr = 3.796 day−1); unadjusted pH (~7.0); and 25 °C. Radical scavenger studies and electron spin resonance (ESR) spectra showed that sulfate (SO4•−) and hydroxyl (•OH) radicals were involved in the ANA oxidation, but •OH was the dominant radical species in the PSC/Fe(II)C system. Cl−, SO42−, and HCO3− acted as radical scavengers. The introduction of hydroxylamine (HA) into the PSC/Fe(II)C system resulted in a notable enhancement of ANA removal efficiency, increasing it from 51.8 % to 82.6 % within 10 min. Additionally, the PSC/Fe(II)C + HA system exhibited a higher Fe(II) consumption efficiency of 96.6 %, surpassing that of the PSC/Fe(II)aq + HA system, which registered an efficiency of 88.6 %. Intermediate byproducts after 24 h of reaction were detected as non-toxic byproducts by liquid chromatography-mass spectrometry (LC-MS). The PSC/Fe(II)C system would be beneficial for the remediation of polycyclic aromatic hydrocarbons in groundwater due to the continuous supply of Fe(II) and PS for a long time.

Estimation of Polycyclic Aromatic Hydrocarbons in Groundwater from Campania Plain: Spatial Distribution, Source Attribution and Health Cancer Risk Evaluation.

The aim of this study was to evaluate the concentrations of polycyclic aromatic hydrocarbons (PAHs) in 1168 groundwater samples of the Campania Plain (Southern Italy), taken using a municipal environmental pressure index (MIEP), and to analyze the distribution of these compounds to determine source PAHs using ratios of isomers diagnostic. Lastly, this study also aimed to estimate the potential health cancer risk in groundwaters. The data indicated that the highest concentration of PAHs was found in groundwater from Caserta Province and the contents of BghiP, Phe, and Nap were detected in the samples. The spatial distribution of these pollutants was evaluated using the Jenks method; moreover, the data indicated that incremental lifetime cancer risk ILCRingestion ranged from 7.31 × 10-20 to 4.96 × 10-19, while ILCRdermal ranged from 4.32 × 10-11 to 2.93 × 10-10. These research findings may provide information about the Campania Plain's groundwater quality and aid in the development of preventative measures to lessen PAH contamination in groundwater.

Solubilization and remediation of polycyclic aromatic hydrocarbons in groundwater by cationic surfactants coupled nanobubbles: Synergistic mechanism and application

Polycyclic aromatic hydrocarbons pose a severe threat to groundwater and the soil environment. Improving the efficiency of the surfactant-enhanced remediation (SER) technique is a research hotspot. Nanobubbles (NBs) were introduced to enhance the solubilization effect of cationic surfactant dodecyltrimethylammonium bromide (DTAB) on phenanthrene (PHE). The interaction between NBs and DTAB was favorable in reducing the critical micelle concentration of DTAB. The equilibrium solubilization of DTAB to PHE was upgraded by up to 30.4% with the synergy of NBs. The effect of DTAB concentration on the stability of NBs was an essential reason for the different upgrade rates. The kinetic study showed that the process of equilibrium solubilization was accelerated, while NBs were “consumed”. Based on the classic DLVO framework, OH– and inorganic ions in groundwater can participate in the formation of micelles and change the double electric layer thickness of bubbles, which are the key factors affecting the stability of NBs. The results revealed the colloidal interface characteristics and the particle behavior of micelles with NBs, providing new insight into the combined application of micelles or vesicles with NBs.

Polycyclic aromatic hydrocarbons in groundwater of oil-rich regions of upper Brahmaputra Valley, India: linkages of colloidal transport

Polycyclic aromatic hydrocarbons in groundwater of oil-rich regions of upper Brahmaputra Valley, India: linkages of colloidal transport

Distribution, source and ecological risk assessment of polycyclic aromatic hydrocarbons in groundwater in a coal mining area, China

The impact of exposure to polycyclic aromatic hydrocarbons (PAHs) on the ecological environment has aroused widespread concern in coal mining areas. Coal mining and solid waste accumulation are among the main reasons for the widespread occurrence of PAHs in groundwater in mining areas. In this study, the PAH content in groundwater in a coal mining area in northern Anhui, China, was determined via gas chromatography–mass spectrometry (GC–MS). The seasonal variation, composition, spatial distribution and sources of PAHs were analyzed, and their potential ecological risks were evaluated. The concentration of ∑PAHs in groundwater ranged from 15.04 to 449.13 ng/L, mainly including 2- and 3-ring PAHs. There were obvious differences in the PAH distribution in groundwater, and higher PAH concentrations were detected in groundwater near industrial parks and solid waste dumping areas. Diagnostic ratio analysis indicated that the PAHs mainly originate from the combustion of coal, biomass and petroleum. The positive matrix factorization (PMF) results revealed that coal and biomass combustion, traffic emissions, coking emissions and oil leakage contributed 46.59%, 20.06%, 18.70% and 14.65%, respectively, to the detected PAHs. The ecological risk assessment results indicated that this area experienced a moderate ecological risk, and the mean ecological risk values during the wet season were lower than those during the dry season.

Evaluation and risk assessment of polycyclic aromatic hydrocarbons in groundwater and soil near a petroleum distribution pipeline spill site, Eleme, Nigeria

Evaluation and risk assessment of polycyclic aromatic hydrocarbons in groundwater and soil near a petroleum distribution pipeline spill site, Eleme, Nigeria

Sources and pollution path identification of PAHs in karst aquifers: an example from Liulin karst water system, northern China

Karst water, with constituting major sources for water supply worldwide, is vulnerable and prone to be polluted. In this study, it is reported that karst water polycylic aromatic hydrocarbons (PAHs) pollution is caused by the infiltration of surface runoff in the bared carbonate areas, which is of universal significance for the protection of groundwater resources in karst region. Hydro-geochemistry, stable isotopes (δD, δ18O and 87Sr/86Sr) and characteristic ratio method were conducted together to illustrate the concentration, distribution, sources and pollution path of polycyclic aromatic hydrocarbons in groundwater in the Liulin karst water system of northern China. The results showed that total concentration of polycyclic aromatic hydrocarbons ranged from 39.25 to 16,830 ng/L in groundwater, with Naphthalene being the dominant component, and the median value increased gradually along the flow path. The highest polycyclic aromatic hydrocarbons concentrations in karst water were mainly observed in the coal mining and the discharge areas. Based on the characteristic ratios, the polycyclic aromatic hydrocarbons in the study area mainly come from local incomplete combustion of woods, fossil fuels, coal and liquid fuels. The slight shift of δD and δ18O and moderate 87Sr/86Sr ratios suggest that the polycyclic aromatic hydrocarbons in karst water is mainly polluted by surface runoff during rain events in the bared karst region. The leakage of river water may partly contribute to the polycyclic aromatic hydrocarbons in some karst water, which normally located close to the karst water - river water mixing line. This study provides a new technical method for tracing the sources and identifying the pollution paths of organic pollution in a karst water system.

Polychlorinated Biphenyls and Polycyclic Aromatic Hydrocarbons in Groundwater of Fuel-Impacted Areas in Ado-Ekiti, Nigeria

Polycyclic aromatic hydrocarbon (PAH) and polychlorinated biphenyl (PCB) congeners in groundwater samples from selected fuel stations in Ado-Ekiti, Southwestern Nigeria, were analyzed to investigate the impact of increased anthropogenic activities. Qualitative and quantitative evaluations of the PAHs and PCBs were done using gas chromatography coupled with appropriate detectors. The PAHs concentrations ranged from ND − 0.98 mg/L, while the PCBs ranged from ND − 164 µg/L. The study reflected that NNPC sampling point had the least contaminated with PCBs, whereas 5Os evinced the highest. The concentrations of the high molecular weight PAHs were generally high compared to low molecular weight PAHs. Using specific ratio distribution, PAH fingerprints suggest pyrogenic origin. Further statistical analysis revealed that 69.0% of the PCBs congeners showed significant difference among the sampling sites with RIHD and 5Os contributing values responsible for the significant levels, while Chi-square revealed no significant difference in the PAHs levels.

Influencing factors and health risk assessment of polycyclic aromatic hydrocarbons in groundwater in China

Polycyclic aromatic hydrocarbons (PAHs) are a group of persistent organic pollutants. This study investigated the occurrence of 16 PAHs in groundwater of representative regions of China (the cities of Lanzhou, Shijiazhuang, and Golmud and in Du’an County) using a gas chromatograph mass spectrometer. The total concentrations of 16 PAHs (∑PAHs) were in the range 0–29.06 μg/L (average: 594.8 ng/L). Acenaphthylene (Acy) and Naphthalene (Nap) had the highest detected frequency (74.56 %) and highest average concentration (632.7 ng/L), respectively. The average concentration of ∑PAHs in each study area exhibited the following trend: Lanzhou > Golmud > Du’an dry season > Du’an wet season > Shijiazhuang. The dominant PAHs in the study areas comprised mainly 2–4-ring PAHs, i.e., Nap (38.71 %; Shijiazhuang), BaA (40.09 %; Du’an wet season), Ace (16.84 %; Du’an dry season), Nap (43.51 %; Lanzhou), and BaA (57.43 %; Golmud). Overall, the PAHs of 101 samples were derived primarily from combustion and a small number of samples of PAHs originated from petroleum sources. Owing to strong adsorption in the vadose zone, the concentrations of PAHs in Shijiazhuang groundwater were lower than those in the groundwater of Golmud and Du’an. The groundwater in Du’an, Lanzhou and Golmud exhibits potential carcinogenic risk if consumed without further treatment.

Occurrence of polycyclic aromatic hydrocarbons in groundwater from rural areas in eastern China: Spatial distribution, source apportionment and health cancer risk assessment

Polycyclic aromatic hydrocarbons (PAHs) pollution in well water has become more widespread, especially in rural areas. The development of small workshops has brought economic growth; however, a sharp increase in the level of pollution due to combustion of fossil fuels has also been observed. A lack of effective measures to control environmental pollution and strict legislation in these regions can contribute to higher PAHs emissions. In the study, the distribution and level of 16 PAHs in well water in rural eastern China were reported. The total concentrations of 16 priority PAHs varied from 4 to 169 ng/L, and an arithmetic mean of 38 ± 25 ng/L. Moreover, the highest PAHs content was found in well water from Shandong Province, and the average concentration was 60 ± 48 ng/L. The distribution of total 16 PAHs illustrated a decreasing trend from north to south. However, the distribution of PAHs with 2-rings and 4-rings was found to be higher in Jiangsu and Hebei province, respectively. The PAHs source identification results showed that the dominant source was coal and biomass combustion, which was consistent with the local conditions. The values of health cancer risks (CRs) were calculated, and that indicated that hazard quotients of nine non-carcinogenic contaminants were lower than one and might not have negative health risks. However, for carcinogenic PAHs, CRs values of the dermal pathway were higher than 10−6, and those for benzo [a]pyrene (BaP) and dibenzo [a, h] anthracene (DbA) were even higher (>10−4), indicating significant high risks to children and adults.

Pollution characteristics of aromatic hydrocarbons in the groundwater of China

Much of the world's groundwater supply has been contaminated by aromatic hydrocarbons originating from anthropogenic sources. To study the occurrence and distribution characteristics of aromatic hydrocarbons in groundwater, 24 aromatic hydrocarbon compounds were selected: Five BTEX compounds (benzene, toluene, ethylbenzene, o-xylene, m-xylene, and p-xylene), 10 alkyl-substituted benzene, and 9 halogenated aromatics. These aromatic hydrocarbons were then analyzed from 355 samples collected from across China. Results indicated that aromatic hydrocarbons were detected in 59 out of 355 samples. Of the selected aromatic hydrocarbons, BTEX compounds were detected with high frequency and at low concentrations; comparatively, halogenated aromatics were detected with low frequency and at high concentrations. The aromatic hydrocarbon characteristics found in both karst and pore groundwater samples were then determined using their respective hydrogeological conditions and corresponding human activities. In karst groundwater, BTEX compounds were the most frequently detected aromatic hydrocarbon. The high detection frequencies of aromatic hydrocarbons were caused by their rapid migration, owing to the developed conduit system in the sampled karst area. The low concentrations of aromatic hydrocarbons in karst groundwater samples were caused by low-intensity human activity along with special hydrogeological conditions with higher redox potential and the unique compositions of aromatic hydrocarbons. Alkyl-substituted aromatics and halogenated aromatics were detected at higher concentrations in pore groundwater, owing to high-intensity human activity. Aromatic hydrocarbon pollution was gradually decreased along piedmont-alluvial plain-coast line, owing to a decrease in aquifer vulnerability. These were positively correlated with the size of the aquifer's particles. Samples with a high accumulative concentration of these aromatic hydrocarbons tended to occur in pore groundwater with a high concentration of either SO42− or Cl−.

Simultaneous determination of 16 polycyclic aromatic hydrocarbons in groundwater by GC-FID after solid-phase extraction

Groundwater contamination by polycyclic aromatic hydrocarbons (PAH) may pose a risk to human health, as these compounds are considered to be highly toxic, carcinogenic and/or mutagenic and bioaccumulative. The aim of this study was to evaluate and determine PAH levels in groundwater samples collected from tubular wells in a city of northern Brazil by gas chromatography with flame ionization detector (GC-FID) used by the population for consumption. Sample pre-treatment using solid-phase extraction cartridges was performed in order to promote an enrichment of the PAH fraction of interest and to remove interferences from the matrix to further determine PAH in samples by GC-FID. The results obtained showed that all groundwater samples studied presented PAH levels lower than maximum values allowed by MS 2914/2011 and CONAMA 396/2008. The developed procedure is characterized by low limits of detection and quantification, equal to 0.024–0.113 µg L−1 and 0.079–0.378 μg L−1, respectively, good linearity (r2 > 0.99). The recoveries obtained for 16 PAH by the addition and recovery method ranged from 85.4 to 105.7% with good precision (RSD < 5.0%). The results of this study showed that the method developed is fast, accurate and robust with high efficiency for identification and determination of 16 PAH in groundwater samples.

Adsorption and catalytic oxidation of organic pollutants using Fe-zeolite.

In this work, a natural zeolite, modified and loaded with iron (NZ-A-Fe) as a heterogeneous catalyst, was characterized for its suitability as a permeable reactive barrier (PRB) material for treatment of aromatic hydrocarbons in groundwater. Adsorption and oxidation processes were analyzed. Batch adsorption tests for benzene, toluene and xylene (BTX) aqueous concentrated solutions were performed at neutral pH. Kinetic adsorption was described with the pseudo-second-order model. Experiments were performed using a stirred batch reactor with near 11 mM initial BTX concentration applying NZ-A-Fe as solid catalyst and H2O2 as an oxidant. BTX removal reached 80% in 600 min in these experimental conditions. Catalytic oxidation was described with a pseudo-first-order kinetic model. No significant iron leaching was detected during all the experiences. These investigations show that coupling adsorption with catalytic oxidation with this novel system is a promising procedure to simultaneously remove BTX from moderately concentrated aqueous solution at neutral pH in groundwater.

Facile modification of multi-walled carbon nanotubes–polymeric ionic liquids-coated solid-phase microextraction fibers by on-fiber anion exchange

In situ anion exchange has been proved to be an efficient method for facile modification of polymeric ionic liquids (PILs)-based stationary phases. In this work, an on-fiber anion exchange process was utilized to tune the extraction performance of a multi-walled carbon nanotubes (MWCNTs)-poly(1-vinyl-3-octylimidazolium bromide) (poly(VOIm+Br−))-coated solid-phase microextraction (SPME) fiber. MWCNTs were first coated onto the stainless steel wire through a layer-by-layer fabrication method and then the PILs were coated onto the MWCNTs physically. Anion of the MWCNTs–poly(VOIm+Br−) fiber was changed into bis(triflroromethanesulfonyl)imide (NTf2−) and 2-naphthalene-sulfonate (NapSO3−) by on-fiber anion exchange. Coupled to gas chromatography, the MWCNTs–poly(VOIm+Br−) fiber showed acceptable extraction efficiency for hydrophilic and hydrogen-bonding-donating alcohols, with limits of detection (LODs) in the range of 0.005–0.05μgmL−1; after the anion exchange with NTf2−, the obtained MWCNTs–poly(VOIm+NTf2−) fiber brought wide linear ranges for hydrophobic n-alkanes with correlation coefficient (R) ranging from 0.994 to 0.997; aromatic property of the fiber was enhanced by aromatic NapSO3− anions to get sufficient extraction capacity for phthalate esters and halogenated aromatic hydrocarbons. The MWCNTs–poly(VOIm+NapSO3−) fiber was finally applied to determine several halogenated aromatic hydrocarbons in groundwater of industrial park.

Assessment of microbial communities associated with fermentative-methanogenic biodegradation of aromatic hydrocarbons in groundwater contaminated with a biodiesel blend (B20).

A controlled field experiment was conducted to assess the potential for fermentative-methanogenic biostimulation (by ammonium-acetate injection) to enhance biodegradation of benzene, toluene, ethylbenzene and xylenes (BTEX) as well as polycyclic aromatic hydrocarbons (PAHs) in groundwater contaminated with biodiesel B20 (20:80 v/v soybean biodiesel and diesel). Changes in microbial community structure were assessed by pyrosequencing 16S rRNA analyses. BTEX and PAH removal began 0.7 year following the release, concomitantly with the increase in the relative abundance of Desulfitobacterium and Geobacter spp. (from 5 to 52.7 % and 15.8 to 37.3 % of total Bacteria 16S rRNA, respectively), which are known to anaerobically degrade hydrocarbons. The accumulation of anaerobic metabolites acetate and hydrogen that could hinder the thermodynamic feasibility of BTEX and PAH biotransformations under fermentative/methanogenic conditions was apparently alleviated by the growing predominance of Methanosarcina. This suggests the importance of microbial population shifts that enrich microorganisms capable of interacting syntrophically to enhance the feasibility of fermentative-methanogenic bioremediation of biodiesel blend releases.

Monitored Natural Attenuation of Manufactured Gas Plant Tar Mono‐ and Polycyclic Aromatic Hydrocarbons in Ground Water: A 14‐Year Field Study

AbstractSite 24 was the subject of a 14‐year (5110‐day) study of a ground water plume created by the disposal of manufactured gas plant (MGP) tar into a shallow sandy aquifer approximately 25 years prior to the study. The ground water plume in 1988 extended from a well‐defined source area to a distance of approximately 400 m down gradient. A system of monitoring wells was installed along six transects that ran perpendicular to the longitudinal axis of the plume centerline. The MGP tar source was removed from the site in 1991 and a 14‐year ground water monitored natural attenuation (MNA) study commenced. The program measured the dissolved mono‐ and polycyclic aromatic hydrocarbons (MAHs and PAHs) periodically over time, which decreased significantly over the 14‐year period. Naphthalene decreased to less than 99% of the original dissolved mass, with mass degradation rates of 0.30 per year (half‐life 2.3 years). Bulk attenuation rate constants for plume centerline concentrations over time ranged from 0.33 ± 0.09 per year (half‐life 2.3 ± 0.8 years) for toluene and 0.45 ± 0.06 per year (half‐life 1.6 ± 0.2 years) for naphthalene. The hydrogeologic setting at Site 24, having a sandy aquifer, shallow water table, clay confining layer, and aerobic conditions, was ideal for demonstrating MNA. However, these results demonstrate that MNA is a viable remedial strategy for ground water at sites impacted by MAHs and PAHs after the original source is removed, stabilized, or contained.

Application of a fiber-optic NIR-EFA sensor system for in situ monitoring of aromatic hydrocarbons in contaminated groundwater

Interaction of analyte molecules with the evanescent wave of light guided in optical fibers is among the most promising novel sensing schemes that can be applied for environmental monitoring and on-line process analysis. By combining this measuring principle with the solid-phase extraction of analyte molecules into the polymer cladding of a fiber, it is possible to perform direct absorption measurements in the cladding, if the fiber is adapted to a conventional spectrometer/photometer. A big advantage of this arrangement is that the measurement is scarcely disturbed by matrix effects (background absorption of water in IR measurements, stray light due to turbidity in the sample). By using near-infrared (NIR) evanescent field absorption (EFA) measurements in quartz glass fibers coated with a hydrophobic silicone membrane it is possible to design and construct sensors for monitoring apolar hydrocarbons (HCs) in aqueous matrices. The paper presents a fiber-optic sensor system for the determination of aromatic HCs in groundwater or industrial wastewater. Generally, this instrument is suitable for quantitative in situ monitoring of pollutants such as aromatic solvents, fuels, mineral oils or chlorinated HCs with relatively low water saturation solubility (typically between 0.01 and 10 g l −1). The sensor probe is connected via all-silica fibers to a filter photometer developed at the IFIA, thus, allowing even remote analysis in a monitoring well. This portable instrument provides a total concentration signal of the organic compounds extracted into the fiber cladding by measuring the integral absorption at the 1st CH overtone bands in the NIR spectral range. In situ measurements with the sensor system were performed in a groundwater circulation well at the VEGAS research facility of the University of Stuttgart (Germany). The NIR-EFA sensor system was tested within the frame of an experiment that was carried through in a tank containing sandy gravel with a groundwater-saturated aquifer, where soil and groundwater were contaminated with technical grade xylene. The goal of this experiment was to model and optimize the groundwater circulation well used for the remediation of the aquifer and soil surrounding the well. The sensor proved to trace reliably the total hydrocarbon concentration in the process water pumped from the well to a stripper column. Measurements were performed continuously over 4 months with C8 HC sum concentrations in the process water between 80 mg l −1 down to the limit of detection, which is around 200 μg l −1. It could be demonstrated that the fiber-optic sensor system is a valuable tool for near-real-time control of a remedial action technique and verification and documentation of its success.

Using Ternary Diagrams to Characterize Transport and Attenuation of BTX

During the past decade or longer, large amounts of data on the concentrations of dissolved aromatic hydrocarbons have been obtained from routine monitoring of leaky underground storage tanks (USTs). Commonly, aromatic hydrocarbon concentration data is interpreted only within the context of regulatory maximum allowable concentration levels. We show in this paper how ternary diagrams can clearly characterize the physical and chemical controls governing the fate and transport of aromatic hydrocarbons in ground water from routine monitoring data. The results of type mathematical modeling experiments for BTX solute transport show that changes in BTX concentrations, when plotted as proportions on ternary diagrams, form clear “trajectories” documenting major attenuation or transport processes. For example, BTX concentrations affected by biodegradation form a trajectory from the source BTX location on the ternary diagram to the benzene apex. In contrast, BTX concentrations affected by volatilization form a trajectory trending from the source to the xylene apex. Ternary diagrams are easy and effective tools to determine from routine monitoring data (1) whether proposed natural attentuation processes are in fact present, and (2) the efficiency of different remediation efforts used to clean up UST sites.