Transport Of Methyl Tert-butyl Ether Research Articles

Trends in Methyl tert-Butyl Ether Concentrations in Private Wells in Southeast New Hampshire: 2005 to 2015.

In southeast New Hampshire, where reformulated gasoline was used from the 1990s to 2007, methyl tert-butyl ether (MtBE) concentrations ≥0.2 μg/L were found in water from 26.7% of 195 domestic wells sampled in 2005. Ten years later in 2015, and eight years after MtBE was banned, 10.3% continue to have MtBE. Most wells (140 of 195) had no MtBE detections (concentrations <0.2 μg/L) in 2005 and 2015. Of the remaining wells, MtBE concentrations increased in 4 wells, decreased in 47 wells, and did not change in 4 wells. On average, MtBE concentrations decreased 65% among 47 wells whereas MtBE concentrations increased 17% among 4 wells between 2005 and 2015. The percent change in detection frequency from 2005 to 2015 (the decontamination rate) was lowest (45.5%) in high-population-density areas and in wells completed in the Berwick Formation geologic units. The decontamination rate was the highest (78.6%) where population densities were low and wells were completed in bedrock composed of granite, metamorphic, and mafic rocks. Wells in the Berwick Formation are characteristically deeper and have lower yields than wells in other rock types and have shallower overburden cover, which may allow for more rapid transport of MtBE from land-surface releases. Low-yielding, deep bedrock wells may require large contributing areas to achieve adequate well yield, and thus have a greater chance of intercepting MtBE, in addition to diluting contaminants at a slower rate and thus requiring more time to decontaminate.

Laboratory experiments and simulations of MTBE transport in layered heterogeneous porous media

Methyl tert-butyl ether (MTBE) has been considered as a typical volatile organic compound (VOC) in the subsurface environment, which can result in a significant risk to subsurface ecosystems and human health. As the awareness on groundwater quality is increasing, it is of great importance to identify the effect of heterogeneity on VOCs transport through subsurface porous media. Thus, experiments on transport through homogeneous and layered heterogeneous porous media were carried out. In this study, NaCl and MTBE were used as a nonreactive tracer and a VOC, respectively. The results of tracer tests in homogeneous sand columns indicate that the test values fit well with simulated values. The breakthrough curves of homogeneous porous media show that the flow velocity of MTBE is slower than that of the NaCl, which means MTBE has been seriously retarded during transport process. In addition, MTBE transport is greatly dependent on the heterogeneity of the porous media with higher retention in the layered heterogeneous media compared to homogeneous media, which refers to non-Fickian transfer. The results imply that the layered heterogeneity could weaken the contamination intensity, thereby retarding the contaminant transport and prolonging the contaminants contact time in the heterogeneous porous media.

Effects of Temperature and Acidic Pre-Treatment on Fenton-Driven Oxidation of MTBE-Spent Granular Activated Carbon

The effects of temperature and acidic pretreatment on Fenton-driven chemical oxidation of methyl tert-butyl ether (MTBE)-spentgranular activated carbon (GAC) were investigated. Limiting factors in MTBE removal in GAC include the heterogeneous distribution of amended Fe, and slow intraparticle diffusivetransport of MTBE and hydrogen peroxide (H2O2) into the "reactive zone". Acid pretreatment of GAC before Fe amendment altered the surface chemistry of the GAC, lowered the pH point of zero charge, and resulted in greater penetration and more uniform distribution of Fe in GAC. This led to a condition where Fe, MTBE, and H2O2 coexisted over a larger volume of the GAC contributing to greater MTBE oxidation and removal. H2O2 reaction and MTBE removal in GAC increased withtemperature. Modeling H2O2 transport and reaction in GAC indicated that H2O2 penetration was inversely proportional with temperature and tortuosity, and occurred over a larger fraction of the total volume of small GAC particles (0.3 mm diameter) relative to large particles (1.2 mm diameter). Acidic pretreatment of GAC, Fe-amendment, elevated reaction temperature, and use of small GAC particles are operational parameters that improve Fenton-driven oxidation of MTBE in GAC.

2D-cell experiment on methyl tert-butyl ether transport in saturated zone of groundwater

As an additive of gasoline, methyl tert-butyl ether (MTBE) has a higher solubility in water, which is about 20 times as high as that of benzene. This characteristic results in MTBE dissolving out of the gasoline into the soil and groundwater. Due to relative unique physicochemical behavior of MTBE it would be an ideal candidate for use in environmental forensic investigations. In order to study the transport and distribution of MTBE in saturated zone of ground water, a two-dimensional experimental cell was setup to simulate the real environment of the groundwater flow. The effects of soil and groundwater flow velocity on the MTBE transport were investigated. The results show that the mobile distance of MTBE in vertical direction was smaller than that in horizontal direction paralleling with the groundwater flow. Because the main dynamics of groundwater flow direction was convection and dispersion, the movement of MTBE is also diffusion in the vertical direction. In addition, the transport of MTBE was more quick in high permeability porous media, and the increase of groundwater flow velocity can accelerate the MTBE plume development, but the irregularity and randomness of the plume are enhanced synchronously. These research results can give some helps for the investigation of MTBE movement in the groundwater, also can make some references for other petroleum contamination behavior.

Evidence for Phytodegradation of MTBE from Coupled Bench-Scale and Intermediate-Scale Tests

This paper presents methodologies and demonstrates the need to couple bench-scale and intermediate tree-scale experiments, to fully understand the transport and fate of organic contaminants, specifically methyl tert butyl ether (MTBE), in mature trees. Bench-scale experiments showed MTBE to be optimally taken up by small poplar saplings with a transpiration stream concentration factor of approximately 1, little or no degradation in soils and, nearly 100±20% recovery in the coupled water-plant-air system, indicating no measurable phytodegradation at the bench-scale. A large 14 ft tree chamber was designed to evaluate MTBE transport and fate through intermediate-scale ( 12 ft tall) poplar trees. Abiotic MTBE volatilization tests conducted in the tree chamber showed 100±20% MTBE mass recovery, thereby demonstrating the integrity of the large chamber and its air monitoring technique. In contrast, replicate intermediate-scale experiments conducted with large (12 ft) trees irrigated with a known mass of MTBE sh...

Sorption of methyl tert-butyl ether and benzene in fine-grained materials from northern Illinois and the Chalco Basin, Mexico

Methyl tert-butyl ether (MTBE) is a gasoline oxygenate additive used to enhance gasoline combustion by lowering carbon monoxide and hydrocarbon emissions, thus reducing air pollution. However, it has been identified as the second most common volatile organic contaminant of urban aquifers in the United States. Methyl tert-butyl ether has also been blended into two types of gasoline sold in Mexico by the state oil company (Petrleos Mexicanos) but is currently not monitored in groundwater. Early research on MTBE determined that it is unable to sorb to soils and sediments. The objective of this study is to determine if fine-grained materials with high organic matter (0.25–15.3%) have the potential for sorption of MTBE. The experiment consisted of sorption isotherms of loess from DeKalb, Illinois, and lacustrine sediments from Chalco, Mexico. Experiments were performed with various concentrations of MTBE and benzene (10, 50, 100, 500, and 1000 g/L) at 25C and 10C. Methyl tert-butyl ether showed a retardation factor (R) as high as 1.856 0.0130 for lacustrine sediments and 1.095 0.0010 for loess at 25C. Benzene showed retardation factors as high as 1.996 0.0150 in lacustrine sediments and 1.775 0.0050 in loess at 25C. These results showed that sorption, and therefore, the retardation of MTBE in groundwater, is possible in fine-grained materials especially with high organic matter. This research increases the understanding of the fate and transport of MTBE and improves the knowledge to implement the optimal remediation method for sites contaminated by MTBE.

Design of an MTBE Remediation Technology Evaluation

AbstractThis study examines the intrinsic variability of dissolved methyl tert‐butyl ether (MTBE) concentrations in ground water during the course of a pilot‐scale bioremedial technology trial in Port Hueneme, California. A pretrial natural gradient tracer experiment using bromide was conducted in an anaerobic test section of the aquifer to characterize hydrogeology. The results showed the presence of a complex velocity field in terms of vertical stratification and preferential flowpaths. The hydraulic conductivity at the test area varied by &gt;2 orders of magnitude, and the effects of vertical stratification were made apparent by the tracers’ detection pattern, which was predominately higher in the lower part of the aquifer. Since historically the lower portion of the aquifer significantly influenced MTBE transport, it was emphasized by increasing the sampling frequency for MTBE and tracers during the pilot test that involved the intermittent addition of oxygen and propane into the aquifer. A second tracer experiment using bromide and deuterated MTBE (2H12‐MTBE) was conducted at the onset of the technology trial and after the aquifer was made aerobic. The continuous metering of the tracer solutions into the test area was maintained for 300 d. The results showed that 2H12‐MTBE behaved as a conservative tracer since (1) its concentrations increased throughout the study approaching its designed injected level and (2) the pattern of its detection resembled that of bromide. On the other hand, 2H12‐MTBE, which was purposefully introduced into the aquifer, behaved differently from that of the existing dissolved MTBE plume that emanated from a non–aqueous phase liquid (NAPL) source over a decade ago, thereby undergoing years of diffusion. The data imply that a detailed understanding of the complexity of the flow field was not possible by observing the intrinsic MTBE data alone.

Adsorption of MTBE from contaminated water by carbonaceous resins and mordenite zeolite

Equilibrium and kinetic adsorption of methyl tert-butyl ether (MTBE) onto two carbonaceous resins and one zeolite was elucidated in this study. The Freundlich isotherm is adequate for describing the adsorption equilibrium of MTBE onto all the tested adsorbents in deionized water and natural waters. The resins of Ambersorb 563 and 572 have the highest adsorption capacity and almost twice the capacity of mordenite in deionized water. A different extent of NOM competition with MTBE was found for the carbonaceous resins in natural waters. For mordenite, no competitive adsorption was observed in natural water. The ideal adsorbed solution theory combined with equivalent background compound (IAST-EBC) model successfully described and predicted the adsorption of MTBE onto the carbonaceous resins in natural waters. The pore diffusion and micropore diffusion model fit the experimental data fairly well and successfully predicted the transport of MTBE within the adsorbent under different operating conditions. The small tortuosity factor between 1.2 and 2.3 of the resins for the diffusion of MTBE was observed, indicating a superior transport property for the carbonaceous resins in natural waters. The intracrystalline diffusivity of MTBE in natural water was much slower than that in deionized water, only 1/10 in STL and 1/3 in FS natural water, since the aperture entrances of mordenite was appreciably hindered by NOM.

Competitive and Hindering Effects of Natural Organic Matter on the Adsorption of MTBE onto Activated Carbons and Zeolites

Equilibrium and kinetic adsorption of methyl tert-butyl ether (MTBE) onto three coal-based activated carbons, one coconut-based activated carbon, and two zeolites are elucidated in this study. Natural organic matter (NOM) and MTBE competed for the adsorption of activated carbons to different extents. The ideal adsorbed solution theory (IAST) combined with the equivalent background compound (EBC) model can adequately describe the NOM competition and predict the isotherms of MTBE onto the activated carbons. No competitive adsorption was observed for one of the zeolites, mordenite, due to the molecular effect. Besides, the aperture size, and the SiO2/Al2O3 ratio of the zeolite may also play an important role in the adsorption of MTBE from the aqueous phase. The surface diffusion model accurately simulated the transport of MTBE within the adsorbents employed in different water matrices. For all the activated carbons tested, the surface diffusivity of MTBE in natural water was nearly equal to that in deionized water, indicating that no apparently hindering effect occurs. A much slower adsorption kinetic of mordenite in natural water was observed since the opening apertures on mordenite may be appreciably hindered and blocked by NOM.

A Screening Model for Evaluating the Degradation and Transport of MTBE and Other Fuel Oxygenates in Groundwater

Methyl tert-butyl ether (MTBE) has received high attention since it contributed to cleaner air but adversely contaminated thousands of underground storage tank sites. Because MTBE is very soluble in water, it is difficult to remove from solution by conventional remediation techniques, therefore, biodegradation of MTBE has become a remediation alternative. In order to understand the transport and transformation processes, in this paper, we present a closed form analytical solution, which can be applied as a screening tool. The possible reaction pathways of first-order reactions are described as a reaction matrix. The singular value decomposition is conducted analytically to decouple the partial differential equations of the multi-species transport system coupled by the reaction matrix into multiple independent subsystems. Therefore, the complexity of mathematical description for the reactive transport system is significantly reduced and the analytical expressions can be derived.

Phytoremediation of MTBE with Hybrid Poplar Trees

ABSTRACT This research investigates the fate and transport of methyl tert-butyl ether (MTBE) in phytoremediation, particularly the uptake and volatilization of MTBE in lab-scale hydroponic systems. The research reveals that MTBE was taken up by hybrid poplar cuttings and volatilized to the atmosphere. Volatilization of MTBE occurred through both stems and leaves. The concentration of MTBE in the transpiration stream declined exponentially with height, indicating that the uptake and volatilization along the stems are an important removal mechanism of MTBE in phytoremediation. Volatilization, via diffusion from the stems, has not been directly measured previously. No volatile MTBE metabolites were detected; however, mass balance closure and metabolite detection were not primary objectives of this study. The greatest amount of MTBE in plant biomass was associated with the woody stems from the previous year's growth, owing in part to the large biomass of stems. MTBE in the plant tissues appears to reach a steady state concentration and there does not appear to be an accumulation process that could lead to highly elevated concentrations relative to the groundwater source.

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

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

Plant Uptake of Methyl tert -Butyl Ether (MTBE) from Ground Water

Methyl tert-butyl ether (MTBE) is an important ground-water contaminant. Gasoline spills and leaks from pipelines, underground and aboveground storage tanks, and other transport modes are major sources of MTBE contamination. A six-channel system was set up and used to examine the effect of alfalfa plants on the fate and transport of MTBE. Contamination by MTBE was established by continuously feeding a solution of 0.84 mM MTBE into each channel at 1 L/day. The concentrations of MTBE in the channel ground-water effluent, at the channel soil surface, and within alfalfa plant stems were monitored. By incorporating plant water use with the concentrations of MTBE in plant water, the authors obtained the mass fluxes of MTBE transported by alfalfa plants grown in soil channels. Even with the same contaminant concentration in the growth channel, alfalfa plants took up MTBE nonuniformly. The more vigorous the growth of plants, the higher the MTBE concentration in the plant water, and the more MTBE removed by the pl...

Transport of methyl tert-butyl ether through alfalfa plants.

Concentrations measured in alfalfa plant stem segments indicated that plants grown in methyl tert-butyl ether (MTBE)-contaminated soil took up the chemical through their roots. Assuming a cylindrical shape for the plant stem, a mathematical model was developed to describe the transport of MTBE through the stems. Simulation results from uniform and nonuniform initial concentration distributions across the stem radius were compared with steady-state experimental data. With known values of plant stem radius, water usage, water content, and the distance over which the concentration decreased by 50%, the diffusion coefficient of MTBE radial transport across the plant stem was estimated with 95% confidence to be in the range of 8.43-16.2 x 10(-8) cm2/s with a mean of 1.23 x 10(-7) cm2/s. When the diffusion coefficient was calculated based on transient experimental data, the values with 95% confidence interval ranged from 4.14 x 10(-7) to 8.00 x 10(-7) cm2/s with a mean value of 6.07 x 10(-7) cm2/s. The difference between these two results can be reduced by more accurate estimation of the water flow velocity through plant stems. The model is applicable to other species including sunflowers and poplars upon substitution of appropriate parameters.

MTBE Transport Screening Analysis in Vadose Zone Risk and Liability Apportionment Assessment

The problem of allocating liability cleanup costs is an arduous task when more than one potentially responsible party has contributed to the groundwater plume. This problem is most likely to be encountered when dealing with methyl- tert -butyl-ether (MTBE) contamination, as MTBE is seen to travel large distances in underlying aquifers. There has been a signi®cant effort in the recent past to develop liability allocation methodologies that incorporate fate and transport behavior and toxicological characteristics of the contaminants. The application of such methods often requires estimation of contaminant input from the vadose zone into the underlying aquifer. A screening level analysis is presented here to develop preliminary insights on relative mass contributions arising from different source types. The analysis illustrates how different vadose zone conceptualizations lead to vastly different contaminant loadings. Parametric studies indicate that the contaminant flux into the aquifer is very sensitive to changes in water infiltration rates. Hence, a reliable estimate of this parameter is critical for equitable allocation of remedial costs. Conceptual model formulation, should focus on identifying whether the fuel present in the aquifer can flow as a separate phase. It is also important to obtain reliable estimates for fluid saturations at the site.

MTBE Transport Screening Analysis in Vadose Zone Risk and Liability Apportionment Assessment

The problem of allocating liability cleanup costs is an arduous task when more than one potentially responsible party has contributed to the groundwater plume. This problem is most likely to be encountered when dealing with methyl-tert -butyl-ether (MTBE) contamination, as MTBE is seen to travel large distances in underlying aquifers. There has been a significant effort in the recent past to develop liability allocation methodologies that incorporate fate and transport behavior and toxicological characteristics of the contaminants. The application of such methods often requires estimation of contaminant input from the vadose zone into the underlying aquifer. A screening level analysis is presented here to develop preliminary insights on relative mass contributions arising from different source types. The analysis illustrates how different vadose zone conceptualizations lead to vastly different contaminant loadings. Parametric studies indicate that the contaminant flux into the aquifer is very sensitive to changes in water infiltration rates. Hence, a reliable estimate of this parameter is critical for equitable allocation of remedial costs. Conceptual model formulation, should focus on identifying whether the fuel present in the aquifer can flow as a separate phase. It is also important to obtain reliable estimates for fluid saturations at the site.

Concentrations, Sources, and Fate of the Gasoline Oxygenate Methyl tert-Butyl Ether (MTBE) in a Multiple-Use Lake

Discovery of the fuel additive methyl tert-butyl ether (MTBE) in drinking water supplies is of concern to public health officials, water suppliers, and the public. Despite recent policy decisions, few published studies exist on the concentrations, sources, and fate of MTBE in surface waters. The purpose of this study was to determine (1) the relative contribution of motorized watercraft as a source of MTBE, (2) its seasonal distribution, (3) loss from the water column, (4) the extent of vertical transport, and (5) its persistence between years; this work was done in Donner Lake, California, a multiple-use lake in the Sierra Nevada Mountains. MTBE measurements were made at 9 individual depths from surface to bottom on 16 dates. Recreational boating was the most important source of MTBE. Statistically, 86% of the change in MTBE was explained by variation in motorized watercraft use. Neither highway runoff nor precipitation contributed significantly. MTBE concentration ranged from <0.1 μg·L-1 to a high of 12 μg·L-1. Between July 1 and 7, 1997, MTBE content rose dramatically from 115 to 365 kg. By January, levels had declined to a minimum of 15 kg, suggesting little interannual persistence. The major loss of MTBE appeared to be volatilization at the air−water interface characterized by two distinct periods. During the boating season, MTBE decline was 1.2 kg·day-1 (193 day half-life). At the end of the boating season, MTBE loss increased to 8.1 kg·day-1 (14 day half-life). Thermal stratification acted to retard MTBE transport to deeper depths.

The Urban Atmosphere as a Non-Point Source for the Transport of MTBE and Other Volatile Organic Compounds (VOCs) to Shallow Groundwater

Infiltration and dispersion (including molecular diffusion) can transport volatile organic compounds (VOCs) from urban air into shallow groundwater. The gasoline additive methyl-tert-butyl ether (MTBE) is of special interest because of its (1) current levels in some urban air, (2) strong partitioning from air into water, (3) resistance to degradation, (4) use as an octane-booster since the 1970s, (5) rapidly increasing use in the 1990s to reduce CO and O3 in urban air, and (6) its frequent detection at low microgram per liter levels in shallow urban groundwater in Denver, New England, and elsewhere. Numerical simulations were conducted using a 1-D model domain set in medium sand (depth to water table = 5 m) to provide a test of whether MTBE and other atmospheric VOCs could move to shallow groundwater within the 10−15 y time frame over which MTBE has now been used in large amounts. Degradation and sorption were assumed negligible. In case 1 (no infiltration, steady atmospheric source), 10 y was not long en...

Review of the environmental behavior and fate of methyl tert‐butyl ether

AbstractA review of pertinent equations and current research indicates that when gasoline oxygenated with methyl tert‐butyl ether (MTBE) comes into contact with water, large amounts of MTBE can dissolve. At 25°C, the water solubility of MTBE is about 5,000 mg/L for a gasoline that is 10% MTBE by weight, whereas for a nonoxygenated gasoline, the total hydrocarbon solubility in water is typically about 120 mg/L. Methyl tert‐butyl ether sorbs only weakly to subsurface solids; therefore, sorption does not substantially retard the transport of MTBE by ground water. In addition, MTBE generally resists biodegradation in ground water. The half‐life of MTBE in the atmosphere can be as short as 3 d in a regional airshed. In the air, MTBE tends to partition into atmospheric water, including precipitation. However, the washing out of gas‐phase MTBE by precipitation will not, by itself, greatly alter the gas‐phase concentration of the compound in the air. The partitioning of MTBE to precipitation can nevertheless result in concentrations as high as 3 μg/L or more in urban precipitation and can contribute to the presence of MTBE in surface and ground water.