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BTEX -Contamination and Remediation

SEMINAR REPORT

BTEX-CONTAMINATION AND REMEDIATION

Submitted ByMANASY PURUSHOTHAMAN PILLAI

Guided ByMs. ANU CHERIAN

DEPARTMENT OF CIVIL ENGINEERINGMUSALIAR COLLEGE OF ENGINEERING AND TECHNOLOGY

PATHANAMTHITTA-6896452009-2010

Dept Of Civil Engg:, M.C.E.T, Pathanamthitta 1


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.



ABSTRACT

BTEX 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.



CONTENTS

LIST OF ABBREVIATIONS

LIST OF FIGURES

LIST OF TABLES

1. INTRODUCTION 1

2. BTEX 3

2.1 COMPONENTS OF BTEX

2.2 BTEX CONTAMINATION

2.3 BTEX HEALTH EFFECTS

3. DETECTION OF BTEX CONTAMINATION 9

3.1 RAMAN DIPSTICK METHOD

3.2 BIOASSAY METHOD

3.3 MICROCHIP INDUCED LASER FLUROSCENCE SENSOR

4. TREATMENT 16

4.1 ORGANOCLAY AND CARBON TREATMENT

4.2 DIRECT PUSH GROUNDWATER CIRCULATION WELLS

4.3 REMEDIATION USING IN SITU CHEMICAL OXIDATION

5. CONCLUSION 23

REFERENCES 24



LIST OF ABBREVIATIONS

NO ABBREVIATION EXPANSION

1. BTEX Benzene, Toluene, Ethylbenzene, and Xylenes

2. COC Chemical Oxidation Of Carbonates3. DO Dissolved oxygen4. DP-GCW Direct push groundwater circulation well5. EPA Environmental Protection Agency6. GCW Groundwater circulation well 7. ID Inside diameter8. ISCO In situ chemical oxidation9. LIF Laser-Induced Fluorescence10. MCL Maximum Contaminant Levels11. MTBE Methyl tertiary butyl ether12. PAH Polycyclic aromatic hydrocarbons13. PMT Photomultiplier tubes14. PPA Parts per million15. TDO Toluene Dioxygenase Coupling 16. TOSC Technical Outreach Services for

Communities17. TPH Total petroleum hydrocarbons18. UV Ultra violet



LIST OF FIGURES

Figure Name Page no

1.1 Sources of Groundwater Contamination 1

2.1 Components of BTEX in Gasoline 42.2 Different phases of contamination from a gas 5

Station2.3 Routes Of Pollutant Intake 63.1(a) Portable Raman spectrometer 93.1(b) A simplified diagram of a Raman spectrometer 9

Operation3.2 Schematic diagram of experimental apparatus 124.1 organoclay and carbon treatment 164.2 Typical in-well aeration application 174.3 Typical ISCO Injection 194.4 Injection System Process Flow Diagram 20

LIST OF TABLE



Table Name Page no

2.1 MCL set by the EPA for each compound in 7

drinking water



1. INTRODUCTION

1.1 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



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.



2. BTEX

2.1 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.



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.



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




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


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



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



ChemicalMCL

(mg/liter or ppm)benzene 0.005

toluene 1

ethylbenzene 0.7

xylene (total) 10


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.



3. DETECTION OF BTEX CONTAMINATION

Since 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



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 ‘dip-

stick’, 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 spectrometer’s operation



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 bio-

available 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 doesn’t oxidize xylene and ethylbenzene.


http://en.wiktionary.org/wiki/qualitative

http://en.wiktionary.org/wiki/organism


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.



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)



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

probe’s 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 probe’s 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 50Ω load. A personal computer is

used to control the monochromator grating and the oscilloscope.

A series of tests were performed to determine the sensor’s 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.



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.



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



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.


http://www.aquatechnologies.com/info_organoclay.htm

http://www.aquatechnologies.com/info_adsorption.htm


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.

4.2 DIRECT PUSH GROUNDWATER CIRCULATION WELLS



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)



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 μg/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.



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 GROUNDWATER USING IN SITU CHEMICAL OXIDATION

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.



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.



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.



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 high- concentration plumes.

Cost ineffective for low-concentration plumes.



5. CONCLUSION

BTEX 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.



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

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http://www.sciencedirect.com/science

http://www.itrcweb.org/gd_ISCO.asp

