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
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
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.
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BTEX -Contamination and Remediation
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
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BTEX -Contamination and Remediation
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
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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
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BTEX -Contamination and Remediation
Table Name Page no
2.1 MCL set by the EPA for each compound in 7
drinking water
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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
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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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BTEX -Contamination and Remediation
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.
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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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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
(Source: Publication of hazardous substance research centers, TOSC publications)
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ChemicalMCL
(mg/liter or ppm)benzene 0.005
toluene 1
ethylbenzene 0.7
xylene (total) 10
BTEX -Contamination and Remediation
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 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
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BTEX -Contamination and Remediation
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
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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.
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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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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.
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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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BTEX -Contamination and Remediation
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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BTEX -Contamination and Remediation
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
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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 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.
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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.
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BTEX -Contamination and Remediation
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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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 high- concentration plumes.
Cost ineffective for low-concentration plumes.
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BTEX -Contamination and Remediation
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.
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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/
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