BTEX Contamination and Remediation

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BTEX -Contamination and RemediationSEMINAR REPORT BTEX-CONTAMINATION AND REMEDIATIONSubmitted By MANASY PURUSHOTHAMAN PILLAI Guided By Ms. ANU CHERIAN DEPARTMENT OF CIVIL ENGINEERING MUSALIAR COLLEGE OF ENGINEERING AND TECHNOLOGY PATHANAMTHITTA-689645 2009-2010Dept Of Civil Engg:, M.C.E.T, Pathanamthitta1BTEX -Contamination and RemediationACKNOWLEDGEMENTI would like to extend my sincere thanks to Mr. A. Shihabudeen Prof & Head of the Department of Civil Engineering, MCET College o

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BTEX -Contamination and Remediation

SEMINAR REPORT BTEX-CONTAMINATION AND REMEDIATION

Submitted By MANASY PURUSHOTHAMAN PILLAI Guided By Ms. ANU CHERIAN DEPARTMENT OF CIVIL ENGINEERING MUSALIAR COLLEGE OF ENGINEERING AND TECHNOLOGY PATHANAMTHITTA-689645 2009-2010

Dept Of Civil Engg:, M.C.E.T, Pathanamthitta

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BTEX -Contamination and Remediation

ACKNOWLEDGEMENT

I would like to extend my sincere thanks to Mr. A. Shihabudeen Prof & Head of the Department of Civil Engineering, MCET College of Engineering and Technology, Pathanamthitta for his cooperation and encouragement. I express my profound gratitude to Ms. Anu Cherian (Lecturer, department of civil engineering) for her valuable guidance and wholehearted cooperation in preparation of this paper BTEX- Contamination and remediation. Without which this seminar would not have seen the light of day. I am greatful to Mrs. Sreejakunjamma (Advisor) Lecturer, department of civil engineering. Gracious gratitude to all the faculty of the Civil Engineering department & friends for their valuable advice. Above all, I thank the Almighty GOD without whose blessing; I would never have been able to complete this work successfully.

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BTEX -Contamination and Remediation

ABSTRACTBTEX contamination is a threat to the mankind as well as to animals and plants. Prolonged exposure to the compounds even in small quantities is highly fatal. Due to massive usage of petroleum products, BTEX contamination is considered as one of the major environmental pollution. They are highly toxic and soluble in water and its presence will be significant hazard for all forms of life on earth. There are different advanced techniques on detections and treatments that have been developed recently. BTEX presence can be alerted to avoid the usage of contaminated water by the public. This paper presents a detailed study on BTEX contamination with effective detection methods like microchip induced laser fluorescence (LIF). The treatment of BTEX contamination has become one of the challenging techniques. The different treatment like in situ chemical oxidation (ISCO) is one of the most well developed and widely used as it needs only relatively short remediation period compared to other methods.

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CONTENTSLIST OF ABBREVIATIONS LIST OF FIGURES LIST OF TABLES 1. INTRODUCTION 2. BTEX2.1 COMPONENTS OF BTEX 2.2 BTEX CONTAMINATION 2.3 BTEX HEALTH EFFECTS

1 3

3. DETECTION OF BTEX CONTAMINATION3.1 RAMAN DIPSTICK METHOD 3.2 BIOASSAY METHOD 3.3 MICROCHIP INDUCED LASER FLUROSCENCE SENSOR

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4. TREATMENT4.1 ORGANOCLAY AND CARBON TREATMENT 4.2 DIRECT PUSH GROUNDWATER CIRCULATION WELLS 4.3 REMEDIATION USING IN SITU CHEMICAL OXIDATION

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5. CONCLUSION REFERENCES

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LIST OF ABBREVIATIONS

NO 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.

ABBREVIATION BTEX COC DO DP-GCW EPA GCW ID ISCO LIF MCL MTBE PAH PMT PPA TDO TOSC TPH UV

EXPANSION Benzene, Toluene, Ethylbenzene, and Xylenes Chemical Oxidation Of Carbonates Dissolved oxygen Direct push groundwater circulation well Environmental Protection Agency Groundwater circulation well Inside diameter In situ chemical oxidation Laser-Induced Fluorescence Maximum Contaminant Levels Methyl tertiary butyl ether Polycyclic aromatic hydrocarbons Photomultiplier tubes Parts per million Toluene Dioxygenase Coupling Technical Outreach Services for Communities Total petroleum hydrocarbons Ultra violet

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LIST OF FIGURES

Figure 1.1 2.1 2.2 2.3 3.1(a) 3.1(b) 3.2 4.1 4.2 4.3 4.4

Name Sources of Groundwater Contamination Components of BTEX in Gasoline Different phases of contamination from a gas Station Routes Of Pollutant Intake Portable Raman spectrometer A simplified diagram of a Raman spectrometer Operation Schematic diagram of experimental apparatus organoclay and carbon treatment Typical in-well aeration application Typical ISCO Injection Injection System Process Flow Diagram

Page no 1 4 5 6 9 9 12 16 17 19 20

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LIST OF TABLE

Table 2.1

Name MCL set by the EPA for each compound in drinking water

Page no 7

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1. INTRODUCTION1.1 GENERAL As we plunge into the new millennium our environment is being polluted by different man made activities. One of the major source of water is the groundwater which is considered to be consumable without much treatment. There are numerous chemicals associated with federal, commercial, industrial, and agricultural operations that are considered hazardous to humans, animals, plants, and the ecological environment. Groundwater becomes contaminated when hazardous chemicals leak into the ground and drain through the soil matrix into aquifers. Once they reach the aquifer, chemicals either float or sink depending on their specific gravity (i.e., whether they are lighter or heavier than water). Gradually, the chemicals dissolve into groundwater and flow down gradient to impact additional aquifers, water reservoirs, land, and sea, expanding the risk to human health and the environment.

Fig1.1 Sources of Groundwater Contamination

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BTEX -Contamination and Remediation Petroleum has been recognized as a potential environmental contaminant since shortly after the beginning of the Twentieth Century. Organic compounds can be a major pollution problem in groundwater. Their presence in water create hazard to public health and the environment. The term BTEX reflects that benzene, toluene, ethylbenzene and xylenes are often found together at contaminated sites. Because they are all highly toxic and soluble in water, they represent a significant hazard for humans.The main source of BTEX contamination is the leakage of gasoline from faulty and poorly maintained underground storage tanks. They are considered one of the major causes of environmental pollution because of widespread occurrences of leakage from underground petroleum storage tanks and spills at petroleum production wells, refineries, pipelines, and distribution terminals.

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2. BTEX2.1 GENERAL

Benzene, Toluene, Ethyl Benzene and Xylene (BTEX) are the volatile components commonly associated with petroleum products. Benzene, toluene and xylenes are found naturally in petroleum products like crude oil, diesel fuel and gasoline. Ethylbenzene is a gasoline and aviation fuel additive. Because of the high concentration of BTEX compounds in petroleum and the massive use of petroleum products as energy source, as solvents and in the production of other organic chemicals, their presence in water creates a hazard to public health and the environment. Contamination of groundwater with the BTEX compounds is difficult to remedy because these compounds are relatively soluble in water and can diffuse rapidly once introduced into an aquifer.

2.2 COMPONENTS OF BTEX

BTEX is the abbreviation used for four compounds found in petroleum products. The compounds are benzene, toluene, ethylbenzene and xylenes. These organic chemicals make up a significant percentage of petroleum products like crude oil, diesel, gasoline etc. Ethylbenzene is a gasoline and aviation fuel additive. They are also used extensively in manufacturing processes. Benzene is used in the production of synthetic materials and consumer products, such as synthetic rubber, plastics, nylon, insecticides and paints. Toluene is used as a solvent for paints, coatings, gums, oils and resins. Ethylbenzene may be present in consumer products such as paints, inks, plastics and pesticides. Xylenes are used as a solvent in printing, rubber and leather industries.

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BTEX -Contamination and Remediation The BTEX chemicals are present in a standard gasoline blend in approximately 18%(w/w), and the group is considered to be the largest one that is related to any health hazards.

Fig. 2.1 Components of BTEX in Gasoline (Source: Publication of hazardous substance research centers, TOSC publications) Naphthalenes make up only 1%(w/w) of gasoline. Benzene, which is recognized as the most toxic compound among BTEX, represents 11%, toluene represents 26%, ethylbenzene 11% and xylene 52% of the total BTEX fraction in gasoline.

2.3 BTEX CONTAMINATION

BTEX contamination of soil and groundwater can occur by the accidental spill of gasoline, diesel fuel and leakage from underground storage tanks in pumping stations. Once released to the environment, BTEX can volatilize, dissolve, attach to soil particles or degrade biologically. Volatilization occurs when chemicals evaporate, allowing them to move from a liquid into the air. Volatilization of the BTEX components of gasoline commonly occurs when you pump gasoline into your car, and is responsible for the characteristic odour. This phenomenon can also occur within the air pockets present in soils. BTEX can also dissolve into water, allowing it to move in the groundwater.

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BTEX -Contamination and Remediation Since BTEX can "stick" to soil particles, these chemicals move slower than the groundwater. BTEX can also dissolve into water, allowing it to move in the ground water. Because of their polarity and very soluble characteristics, BTEX will be able to enter the soil and groundwater systems and cause serious pollution problems. If oxygen is present in sufficient quantities, BTEX can also degrade biologically, though very slowly.

Fig. 2.2 Different phases of contamination from a gas station (Source: Publication of hazardous substance research centers, TOSC publications)

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BTEX -Contamination and Remediation 2.4 BTEX HEALTH EFFECTS

Exposure to BTEX can occur by ingestion, inhalation or absorption through the skin. Inhalation of BTEX can occur while pumping gasoline or while showering or bathing with contaminated water. Absorption of these chemicals can occur by spilling gasoline onto one's skin or by bathing in contaminated water. Acute exposures to high levels of gasoline and its BTEX components have been associated with skin and sensory irritation, central nervous system depression and effects on the respiratory system.

Fig 2.3 Routes Of Pollutant Intake (Source: Publication of hazardous substance research centers, TOSC publications)

These levels are not likely to be achievable from drinking contaminated water, but are more likely from occupational exposures. Prolonged exposure to these compounds causes the kidney, liver and blood systems disorder. According to the U.S. Environmental Protection Agency (U.S. EPA), there is sufficient evidence from both human and animal studies to believe that benzene is a human carcinogen. Workers exposed to high levels of benzene in occupational settings were found to have an increase incidence in leukaemia.

2.5 BTEX REGULATIONS

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The U.S. EPA has established permissible levels for chemical contaminants in drinking water supplied by public water systems. These levels are called Maximum Contaminant Levels (MCLs). To derive these MCLs, the US EPA uses a number of conservative assumptions, thereby ensuring adequate protection of the public. The MCL is set so that a lifetime exposure to the contaminant at the MCL concentration would result in no more than 1 to 100 (depending on the chemical) excess cases of cancer per million people exposed.

Table2.1 MCL set by the EPA for each compound in drinking water

Chemicalbenzene toluene ethylbenzene xylene (total)

MCL (mg/liter or ppm)0.005 1 0.7 10

(Source: Publication of hazardous substance research centers, TOSC publications)

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2.6 REDUCING EXPOSURE TO BTEX

The U.S. EPA recommends that exposure to BTEX be minimized. To avoid or reduce exposure to BTEX, people should use water supplies having concentrations of these compounds that are below the MCL or apply appropriate water treatment or filtration systems. If necessary, short-term reductions in exposure may be accomplished by using bottled water for food and beverage preparation and avoiding bathing or showering with the contaminated water. With in-home treatment processes, such as activated charcoal filtration, it is usually possible to remove sufficient BTEX from water to meet the MCL and thereby minimize health risks. If benzene is present above the MCL, treatment should be applied to all household water because of inhalation hazards.

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3. DETECTION OF BTEX CONTAMINATIONSince the BTEX compounds are very toxic to humans and aquatic life, their sensitive and rapid determination is of critical importance. There are many established methods for determining BTEX contaminants in water, namely liquid-liquid extraction, solid phase extraction, gas chromatography, air stripping etc. But these methods exhibit high levels of sensitivity and selectivity. So they require well-trained personnel for its successful operation. If a small error occurs during sampling, the analytical result obtained using the best instrument will be inevitably wrong. Most existing methods for detecting BTEX are time-consuming, complicated and very expensive for routine screening. Also these methods require skill for its operation. There has been a lot of development in this area recently and many advanced techniques for the detection of BTEX contaminations have been developed. The use of lasers and optic fibers are some among them.

Some advanced techniques of detection of BTEX contamination are: 1. Raman Dipstick method 2. Bioassay method 3. Detection using Microchip Induced Fluorescence Sensor

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3.1 RAMAN DIPSTICK METHOD

Raman dipstick method is the detection of BTEX contamination using long path length fiber optic Raman dipstick. Determination of BTEX components via optical remote sensing is attractive because eliminates many of the problems in other established methods. Samples are interrogated through the long-path length dip-stick. It is directly inserted into the liquid of interest or an extension hose is attached to the end of the dipstick, providing a low profile and more flexible means of sample interrogation.

Fig3.1 (a) Portable Raman spectrometer

Fig3.1 (b) A simplified diagram of a Raman spectrometers operation

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BTEX -Contamination and Remediation

Fiber-optic spectroscopic techniques used for detection include visible absorption, infrared absorption, fluorescence and Raman spectroscopy. Of these techniques, Raman spectroscopy is particularly better method for detecting BTEX analytes in water because it offers a high degree of selectivity and is compatible with aqueous matrices. Even though this method is very simple and cheaper, practically a lot of problems are there. Turbidity of the sample could block collection of Raman scattering from the sample. Also the presence of interfering compounds can lead to diminished sensitivity. If the interfering compounds are fluorescent it will mask Raman signals.

3.2 BIOASSAY METHOD

Bioassays are typically conducted to measure the effects of a substance on a living organism. Bioassays may be qualitative or quantitative. This is a quantitative bioassay using Pseudomonas putida F1, which has been well characterized genetically and possesses a diverse metabolism of aromatic compounds. Detection of BTEX compounds using Toluene Dioxygenase peroxide coupling reaction is called bioassay method. It is simple, sensitive, whole-cell-based bioassay system for detection of bioavailable BTEX compounds based on a method developed for screening of oxygenase activity. Pseudomonas putida F1 is known to express TDO capable of oxidizing compounds i.e., it is involved in the conversion of aromatic compounds to their corresponding catechols. As pseudomonas putida is capable of both monooxygenation and Dioxygenase reactions a screening of oxygenase is provided using whole cell system. This bioassay system requires no sophisticated instruments and exquisite techniques. The bioassay has long term storage stability so that it can be used for field monitoring of BTEX compounds and its tracking in contaminated water. The convenience of multiple sample-handling makes this whole cell assay an attractive method to be developed as a field diagnostic method for on-site BTEX contamination. The main disadvantage of this method is that pseudomonas putida doesnt oxidize xylene and ethylbenzene.

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3.3 DETECTION USING MICROCHIP INDUCED FLUORESCENCE SENSOR

Most organic molecules when excited with ultra rays re emit less energetic optical radiation. This emitted radiation is known as fluorescence and is characterized by its intensity as a function of both time and wavelength. Since this information is linked to the physical characteristics of an individual molecular species, it provides a powerful means to perform chemical analyses. By the observation of wavelength and time we can detect, identify and quantify the chemical species within an aqueous solution.

The Laser-Induced Fluorescence (LIF) takes advantage of both time and wavelength information to investigate the contamination of BTX compounds in soil and water. The device provides excitation using a passively Q-switched microlaser pumped by fiber-coupled near-infrared diode laser and generates short pulses of 266nm radiation at a repetition rate near 10 kHz. The microchip laser focusing optics and collection system are very compact and the entire assembly can be placed in a monitoring well or contained within the shaft of a cone penetrometer. Thus the UV radiation necessary to excite fluorescence in environmental pollutants such as gasoline is generated at the point of contamination while the infrared diode pump laser remains above the ground. This configuration takes advantage of the excellent transmission of infrared energy through fiber optics cable and minimizes the ultraviolet attenuation.

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3.3.1 EXPERIMENTAL APPARATUS

The experimental apparatus used to evaluate the performance of the LIF probe includes spectroscopic hardware, a test cell and a data acquisition system.

Fig. 3.2 Schematic diagram of experimental apparatus (Source: Sinfield. J.V .et.al, 2007)

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BTEX -Contamination and Remediation A diode laser pump attached to the microchip laser, mounted in the probe is pumped by a 1W continuous wave at 808nm. The UV thus generated is focused onto probes sapphire window through the excitation fiber. The sapphire window focuses the UV radiation to the specimen in the test cell. Molecular fluorescence excited by the UV microchip laser is imaged through probes sapphire window onto the tip of the return fiber. The output fiber is focused on the entrance slit of a 1/8m scanning monochromator. Silica beam splitter mounted within the monochromator to direct a small fraction of light as trigger signal to the trigger PMT and the rest is directed on to the detector PMT. The fast photomultiplier tubes used to detect the intensities of the light are operated approximately at 800V. Both the PMTs are connected to a 1.5 GHz digital storage oscilloscope. It is used as an analog-to digital converter to acquire fluorescence signals. The PMT output signal is measured across a 50 load. A personal computer is used to control the monochromator grating and the oscilloscope. A series of tests were performed to determine the sensors sensitivity to BTX compounds and its time-response. Each test involved recording the time-dependent fluorescence spectrum (from 275 to 350nm) of one of the BTX compounds at a particular concentration in water. Using this, profile was plotted and the spectra from each test were analyzed to determine: 1. The total fluorescence signal gathered from the test medium-by time and wavelength integration 2. The fluorescence lifetime of the compound in solution-by time and emission wavelength integration 3. The wavelength of the peak fluorescence emission-the highest intensity at any wavelength 4. The peak fluorescence intensity-the volume under wavelength-time-intensity profile The LIF sensor can accurately measure fluorescence lifetimes as short as 2.5 ns.

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3.3.2 ADVANTAGES AND DISADVANTAGES

3.3.2.1 Advantages

1. It is a very compact collection system. So it can be placed in a monitoring well or within a cone penetrometer. 2. LIF can be used for the detection of contamination both in water as well as in soil. 3. The intensity of fluorescence is a function of wavelength and time, which is linked to the physical characteristics of an individual molecular species, provides a powerful means to detect the contaminants. 4. It has the ability to detect the presence of a compound in solution or recognize a change in state, relative to background conditions. So it helps in finding leaks in landfill systems or indicates the presence of harmful agents in water. 5. Since it is possible to detect, identify and quantify the contamination, it is easy to select the type and extent of treatment to be given.

3.3.2.2 Disadvantages

1. It is very difficult to detect the presence of Benzene in water. Also Ethylbenzene cannot be detected at all. 2. The entire system is costly as it has sophisticated instruments.

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4. TREATMENT OF BTEX CONTAMINANTS

The field of Remediation was developed to address the growing and ongoing problem of subsurface contamination of land and water by hazardous chemicals. An interdisciplinary approach is employed during the remedial process involving various branches of science, such as geology and hydrology, chemistry, and sound engineering methods. The remedial process typically involves:

Site investigations to characterize the site geology and hydrology, geochemical conditions, and nature and extent of contamination.

Laboratory testing to identify potential applicable remedial methods. Pilot-scale testing onsite to verify effectiveness of chosen remedial methods and identify optimal conditions for full-scale implementation.

Full-scale remediation. Remediation methods can generally be divided into ex situ (i.e., contamination is extracted and treated aboveground) and in situ (i.e., treatment in place, below ground) methods with the latter having evolved and developed extensively over the past decade to provide more effective and efficient solutions.

The methods of treatment of BTEX contaminants are: 1. Organoclay and carbon treatment method 2. Direct push groundwater circulation well method 3. Remediation of groundwater using in situ chemical oxidation

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4.1 ORGANOCLAY AND CARBON TREATMENT

Organoclays differ from naturally occurring clay minerals in two basic characteristics: (1) the space between the layers (i.e., basal space) is increased producing additional space for the adsorption of large molecular petroleum compounds and (2) their nature is changed from a hydrophilic to an organophilic state due to their functional group among the quaternary ammonium cations. Different types of organoclay employed are organically modified bentonite, montmorillonite, vermiculite, smectite and illite, where the basic structure of these minerals had a 2:1 lattice. Organoclays are manufactured by modifying bentonite with quaternary amines. In groundwater, oil may be mechanically emulsified due to confining pressure. If time is of the essence, oil/water separators and dissolved air flotation systems can be used, followed by polishing with organoclay and activated carbon. This treatment is used after groundwater has been pumped out of the aquifer. The contaminated water is passed through the organoclay and carbon unit where the organics are adsorbed and collected. This is accomplished through the adsorption of the chemical substance onto a carbon matrix. A combination of organoclay/activated carbon can easily achieve non-detect levels of most organics. The effectiveness of this process is related to the quality of the organoclay and the properties of the contaminants. Antifreeze and aqueous cleaners are filtered through organoclay beds to remove oils and allow for reuse.

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Fig4.1 Organoclay and carbon treatment

Organoclays have found increased acceptance as pre-treatment for activated carbon adsorption systems in both groundwater and wastewater cleanup. In this fashion organoclays can remove 50% or more of their dry weight in oil, diesel fuel, PNAH's, PCBs and other chlorinated hydrocarbons. The main function of organoclays has been the prevention of fouling of activated carbon, ion exchange resins and membranes.

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Direct push groundwater circulation wells (DP-GCW) are a promising technology for remediation of groundwater contaminated with dissolved hydrocarbons and chlorinated solvents. In these wells, groundwater is withdrawn from the formation at the bottom of the well, aerated and vapor stripped and injected back into the formation at or above the water table. Previous field studies have shown that: (a) GCWs can circulate significant volumes of groundwater; and (b) GCWs can effectively remove volatile compounds and add oxygen. This induces a circulating flow field that carries clean water and oxygen throughout the contaminated regions of the aquifer

Fig4.2 Typical in-well aeration application (Hinchee, 1994)

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BTEX -Contamination and Remediation The GCWs were constructed with No. 20 slotted well screen (2.4 cm ID) and natural sand pack extending from 1.5 to 8.2 m below grade. Air is introduced at 7.5 m below grade via 0.6 cm tubing. Approximately 15% of the vertical length of the air supply tubing is wrapped in tangled mesh polypropylene geonet drainage fabric to provide surface area for biological growth and precipitation of oxidized iron. These materials were selected to allow rapid installation of the GCWs using 3.8 cm direct push Geoprobe rods, greatly reducing well installation cost.

The system was tested in a petroleum contaminated aquifer. The contaminant plume there is approximately 10 m deep, 50 m wide and contains up to 4 mg/L total BTEX and 75 mg/L dissolved iron. An extensive pilot test was first performed to estimate the zone of influence for a single well. At this site an air injection rate of 1.2 L/min resulted in a water flow rate of 1 to 2 L/min based on bromide dilution tests in the GCW. The GCW increased the dissolved oxygen concentration in the discharge water to between 6 and 8 mg/L and reduced contaminant concentrations to less than 20 g/L total BTEX. Monitoring results from a 73 day pilot test were then used to define the zone of influence for a single DP-GCW and to design a full scale barrier system.

While a variety of types of groundwater circulation wells are available, the use of direct-push technology to install these wells enables a substantial reduction in the cost and complexity compared to other GCW types presently available. This advantage comes with the limitations of direct-push technology, including poor utility in soils containing large amounts of rock or basalt. Direct push technology also has limitations on the depth that can be reached, but because BTEX contamination from motor fuels is typically found in the upper extent of an aquifer the hundred foot depth that direct push technology (in particular, Geoprobe) can reach should be adequate for many sites.

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BTEX -Contamination and Remediation A series of direct-push groundwater circulation wells (DP-GCW) had to be arranged across the width of a BTEX plume to substantially remediate the plume. The wells used in this study were made of small diameter (0.8 inch inside diameter) slotted PVC well screen. This material is inexpensive and readily available. The use of such small wells achieved two goals: it allowed the use of the direct push technology to install the wells, and it required only a small air flow rate to generate an acceptable liquid pumping rate in each well. For the field test, about 1.2 L/min of air was sparged into each well, generating about 1 L/min of water circulation; this is low compared to the circulation rates of other published GCWs.

4.3 REMEDIATION OF CONTAMINATED USING IN SITU CHEMICAL OXIDATION

GROUNDWATER

One of the most well developed and widely used in situ remediation technologies for soil and groundwater contaminated with organic compounds is in situ chemical oxidation (ISCO). Various chemical oxidants are commercially available. The four major oxidants used for soil and groundwater remediation are: permanganate, persulfate, peroxide, and ozone. Additional differences between the oxidants include the required oxidant dosage (mass and volume); location, number, and type of required injection points; logistics involved in mixing and delivering the oxidants to the subsurface; and health and safety considerations.

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Fig4.3 Typical ISCO Injection ISCO involves the delivery of chemical oxidants directly to the subsurface contamination source zones and down gradient groundwater contamination plumes. This is commonly achieved by either temporary injection points or permanent injection wells. Upon direct contact with organic contaminants, a chemical oxidation reaction occurs, which mineralizes the contaminant compound and produces non-toxic end products such as carbon dioxide (CO2) and water. The contaminants susceptible to chemical oxidation include total petroleum hydrocarbons (TPH) (i.e., fuels), polycyclic aromatic hydrocarbons (PAHs), oxygenates (e.g., MTBE), chlorinated solvents, phenols, and pesticides.

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BTEX -Contamination and Remediation 4.3.2 Treatment of ground water

The apparatus consist of mixing tank, air compressor, pipes and pumps.

Fig 4.4 Injection System Process Flow Diagram A pilot study was conducted. The purpose of the study was to evaluate the efficiency of ISCO using persulfate for treating groundwater contaminated with free- and dissolved-phase petroleum hydrocarbons and chlorinated solvents. Persulfate was chosen due to its reactivity with a wide range of organic contaminants including the COCs. Groundwater occurs at approximately 15 meters below ground surface. The study was performed in two phases. During first phase, batches of persulfate were hydrated, mixed, and injected into the injection well. During Phase II of the study, air was continuously injected below the contaminated zone (i.e., air sparging) for the purpose of enhancing the distribution of persulfate in groundwater. A total of 3,800 kilograms of sodium persulfate were hydrated with 26,000 liters of water and injected into groundwater via the injection well.

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4.3.3 ADVANTAGES AND DISADVANTAGES

Advantages

Disadvantages

relatively short remediation period

Effectiveness dependant upon ability to disperse oxidant in aquifer.

Non-toxic byproducts.

health and safety risk to workers handling oxidants.

minimized waste generation.

Temporary mobilization of metals.

minimized site disturbance.

potential secondary drinking water

impact (taste, odor).

Cost effective for source areas and highconcentration plumes.

Cost ineffective for low-concentration plumes.

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5. CONCLUSIONBTEX contamination is a threat to the mankind as well as to animals and plants. Prolonged exposure to the compounds even in small quantities is highly fatal. The reason why the BTEX entering our soil and groundwater system, are considered such a serious problem is that they all have some acute and long term toxic effects. Benzene is carcinogenic to humans. So the detection of these compounds is of utmost importance.

There are a lot of advanced methods of detection BTEX contamination emerging nowadays. Three advanced techniques are studied in this paper. Among the three, detection using laser induced fluorescence (LIF) is found to be more effective. LIF is a very compact system. This method detects contaminants relative to a baseline or background. This method of detection is quick compared to the other methods which are time consuming. Since it is possible to detect, identify and quantify the BTX contamination, it is easy to select the type and extent of treatment to be given. Though this method is a bit costly, it provides a powerful, accurate and reliable means to detect the contaminants in both water and soil.

Various treatment techniques are also implemented nowadays. Three remediation methods are studied in this paper. Among the three, remediation of contaminated groundwater using in situ chemical oxidation (ISCO) is found to be safer. ISCO is one of the most well developed and widely used. This method needs only relatively short remediation period compared to other methods. In this method chemical oxidation reaction produces non-toxic end products such as carbon dioxide (CO2) and water. This method is cost effective for high-concentration plumes. The inert final product provides a safe means of treatment of contaminants in both soil and water.

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BTEX -Contamination and Remediation

REFERENCES

1. Aggarwal. I.D, Sleltman. C.M, Determination of BTEX contaminants in water via long path length fiber optic Raman dip stick, Sensors and Actuators B: Chemical, vol.53, 1998, pp 173-174. 2. Bloch. B, Germaine. , J.T, Hemond, H.F., Johnson. B, Sinfield, J.V, Contaminant Detection, Identification, and Quantification Using a Microchip Laser Fluorescence Sensor, ASCE journal of Environmental Engineering, vol.133, 2007, pp 346-351 3. BTEX Contamination, A Publication of the Hazardous Substance Research Centers Technical Outreach Services for Communities (TOSC) program, 2003, pp 1-2. http://www.toscprogram.org/ 4. Interstate Technology & Regulatory Council. 2005. Technical and Regulatory Guidance for In Situ Chemical Oxidation of Contaminated Soil and Groundwater, 2nd ed. ISCO-2. Washington D.C.: ITRC ISCO Team. Web link:

http://www.itrcweb.org/gd_ISCO.asp. 5. PART1,From the Lab to the Field - Recent Developments in Polymer Coated ATR Sensing for the Determination of Volatile Organic Compounds A Thesis Presented to The Academic Faculty by Manfred Karlowatz, Georgia Institute of Technology, May 2004 6. http://www.aquatechnologies.com/info_btex.htm 7. http://www.envirotools.org/factsheets/btex.doc 8. http://www.epa.gov 9. http://www. sciencedirect.com/

Dept Of Civil Engg:, M.C.E.T, Pathanamthitta

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BTEX -Contamination and Remediation

Dept Of Civil Engg:, M.C.E.T, Pathanamthitta

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