Treatment of BTEX Compounds and MTBE in Ground Water Resulting from Hydraulic Fracturing

Mark Aylward

Emanuel Pacheco

Josh Rusk

Mike Robidoux

Abstract

The presence of harmful contaminants following Hydraulic Fracturing for natural

gas is a growing concern in the United States. The compounds causing this contamination

include VOC’s such as MTBE and BTEX which must be effectively removed or reduced to an

acceptable level to provide potable and palatable water for human and agricultural use.

This report illustrates that the contamination of BTEX and MTBE from Hydraulic

Fracturing can be effectively reduced in a single modular in situ remediation system

combining Chemical Oxidation, Soil Vapor Extraction, Air Sparging, and that this combined

technique is favorable to any of these processes alone as well as Activated Carbon

Treatment or Biodegradation.

Table of Contents Page Number

1. Introduction ............................................................................................................................................... 1-1

2. Hydraulic Fracturing…………………………………………………………………………...…………..……2-1

3. Remediation Techniques. ..................................................................................................................... 3-1

3.1. Activated Carbon .......................................................................................................................... 3-1

3.2. Air Sparging .................................................................................................................................... 3-8

3.3. Biodegradation…………………………………………………………………………………………..3-13

3.4. Vapor Phase Extraction………………………………………………………………………………3-14

3.5. Chemical Oxidation…………………………………………………………………………………….3-16

4. Analysis ....................................................................................................................................................... 4-1

5. Conclusion……………………………………………………………………………………………………….….5-1

Appendix ................................................................................................................................................................... i

A-A. Group Member Contributions ............................................................................................................ i

B-B. Typical System Flow Scheme ............................................................................................................ ii

C-C. Tables and Figures……………………………………………………………………………………………….iii

References……………………………………………………………………………………………………………………..v

1-1

1 Introduction-

Hydraulic Fracturing (Hydro-Fracking) is the process in which water, sand, and often

chemicals are used under pressure to increase the output of a well. The wells in which

Hydro-Fracking is used are mostly for the production of oil and gas as an industrial

application and water in residential, commercial, and industrial applications. There have

been many reports in numerous states (Alabama, New Mexico, Virginia, and Wyoming)

where residents have reported changes in water quality with Hydro-Fracking near their

homes. Many articles report MTBE, BTEX, diesel fuel, natural gas, and other chemicals have

been found in well water.

MTBE is the abbreviation for the compound methyl tertiary butyl ether. This

compound is a colorless liquid at room temperature and atmospheric pressure. MTBE is

manmade and thus its presence in water indicates that man made contamination exists in

the recharge area of the well. MTBE degrades very slowly, is highly soluble in water, has a

very small molecular structure, and has very low taste and odor thresholds. Though no

known health problems have been directly related to MTBE, it is believed to cause a

multitude of long term noncancerous problems.

BTEX is an acronym that stands for benzene, toluene, ethyl-benzene, and xylene. These

compounds are volatile organic compounds that are found in petroleum. These

compounds are known to cause skin and sensory irritation, central nervous system

depression, and ill effects on the respiratory system. Prolonged exposure to these

compounds also affects these organs as well as the kidney, liver, and blood systems.

Determining an effective process to remove these harmful chemicals is the focus of this

report, but this cannot be done without fully understanding the hydraulic fracturing

process, the chemicals, and physical processes used to remove the harmful compounds.

Once this is analyzed, the proper remediation techniques can be determined and applied to

remediate the contaminated water from a source making it potable and palatable again.

2-1

2 Hydraulic Fracturing-

As already stated, Hydro-Fracturing is the process in which water, sand, and some

added chemicals are used under pressure to increase the output of a well. These wells in

most cases had been running at normal outputs, however over time, the underground

channels that allow deposits of gas, oil, and water can become clogged with sediments.

Introduction of the sand, water, and chemical solution under pressure into the well can

open and widen the preexisting channels and allow the well to produce again. This

application has been used for the increasing production of oil and gas wells since the

1960’s and has been used for water since the 1980’s.

The process of Hydro-Fracking for water wells involves first installing an inflatable

packer which is placed at least 40 feet below the well seal casing and at least 60 feet below

the ground surface to insure that the well is not contaminated by the surface during

fracturing. Once the packer is inflated, water and sand solution is introduced under

pressure (usually in the range of 500-3000 psi) into the well bore hole.

The Figure 2.1 shows the first stage of the Hydro-Fracking process. The water channel

is colored in blue and shows the “obstruction” that is impeding water from flowing into the

well. The inflatable packer is the shown just below the lower soil layer where it meets

bedrock. The pressurized water is then pumped into the well and kept at the required

pressure based upon the stone that is being fractured. Higher density stone such as granite

requires higher pressure whereas shale, which is less dense than granite, requires less

pressure.

2-2

(Figure 2.1 – Clogged Water Channels Prior to Hydraulic Fracturing) (www.goclearwater.com)

Once Hydro-Fracking water is introduced, the pressure will gradually rise as the

rock interface and obstruction resist the flow of pressurized sand and water mixture. Then

suddenly, the pressure will drop and then will stabilize at a lower pressure that indicates

that the channels have stop resisting flow and are allowing the fracturing solution to clear

the obstructions as well as slightly enlarging the preexisting channels. Water under this

pressure is allowed to flow for about 10 to 30 minutes at a rate of 50 to 80 gallons per

minute. Once this pressurization sequence is completed, the inflatable packer is lowered

and the process is repeated a second time.

It is most common for two sequences of Hydro-Fracking to be utilized to increase

the output of the well. After the second sequence, the well will have the same flow that it

had when it was new; this is a result of the reopening and typical extension of underground

waterways, improving water flow. This application is generally used for residential

applications but has been used in some commercial and industrial projects to restore well

2-3

output. When Hydro-Fracking is applied to water extraction wells, the depth of interest

typically ranges from 400 to 700 feet below the ground surface. At this depth, the rock and

sediment encountered generaly have densities far below that of the rock and sediment

found in the deeper gas drilling applications. This being the case, little to no chemical

addition is needed to improve process efficency.

The use of Hydro-Fracking for the drilling oil and gas extraction wells is different

than that of water extraction wells due to the typical depth of interest, as previously stated.

The depth of interest in this application can range from 1 to 4 miles below the ground

surface. The pressure required to fracture rock and sediment at these depths is much

higher than required for fracturing in water extraction wells; this brings about the need for

the addition of chemicals such as solvents to increase the efficiency of the process to an

economically justifiable level.

The exact percentages and chemicals used to achieve this goal is in very heated

debate recently since many reports state that these chemicals can and have contaminated

local aquifers and water supplies throughout the process. The gas drilling companies that

employ Hydro-Fracking in this way state that roughly 95% of the solution under pressure

is sand and water and the 5% of chemicals used are mild (salts, ceramics, citric acid). The

injection of hazardous materials into the pressurized solution to increase the effectiveness

of breaking through the rock layers to increase well outputs during Hydro-Fracking by the

gas and oil industries is currently allowed by the EPA. These chemicals and other chemicals

found in the fluid mixtures have been found in local water supplies and private wells

located near and in the area of natural gas drilling sites.

The potential contamination comes from the “used water” that is stored on site and

used in Hydro-Fracking for natural gas. This “used water” is the water that is put under

pressure and pumped into the ground to fracture the rocks and sediment during the

sequences to draw natural gas to a well. New water is pumped into the well with sand and

chemicals as the “used water” is pumped into a holding pit where it is removed and

disposed of. There is a potential for these chemicals found in the “used water” leaking or

seeping into the surrounding underground water supply and then being carried to drinking

2-4

water supplies; this has brought rise to many concerns regarding the proper holding,

disposal, and treatment of the resulting “used water.” These natural gas drilling sites are

typically located in remote areas (not near major cities) and residents usually have artisan

wells to provide them with drinking water. Many reports and articles have found and cited

the presence of MTBE, BTEX, diesel fuel, natural gas, and other chemicals in the water that

is drawn from these wells following Hydro-Fracking. In some cases, people who have

contaminated wells have been told not use their wells, resulting in the need to purchase

water from an outside source and store it in holding tanks they have needed to install on

their property.

Environmental effects such as having dead wildlife and livestock in and around local

streams in contaminated areas have also been widely documented. The natural gas

companies state that the chemicals used are in very low quantities and that the

contaminants found in the water is not from the Hydro-Fracking process. The following

figures (Figure 2.2 and 2.3) show the difference between Hydro-Fracking for natural gas

and for water in a residential application. When sites employ improper holding pit

techniques, the used water in the pit can leak into the surrounding soil matrix. This could

lead to chemicals migrating into local and surrounding aquifers.

2-5

(Figure 2.2 - Hydro Fracturing for Residential Water Use) (www.goclearwater.com)

(Figure 2.3 - Typical Natural Gas Hydro Fracturing Drilling Rig (holding pit))

(http://www.sheldrakepoint.com)

2-6

The gas companies insist that further regulations would lead to a loss of jobs and the

depletion of a clean energy source and would not be in the best interest of the public good

at large. Another concern is that these drill sites can be numerous in small areas, ruining

these and surrounding areas, and that they all could potentially be at risk.

In a worst case scenario following the application of Hydro-Fracking for natural gas,

we could be faced with a severe spreading contamination of the local GWT (ground water

table) with visible environmental and health effects presenting in the region. In this case,

the remediation of the contamination would need to be swift and effective. The choice and

application of the numerous remediation technologies that could be used must be carefully

considered.

3-1

3 Remediation Techniques-

In focusing on the remediation of the resulting BTEX and MTBE portions of the

contamination, we have many possible technologies that could be used. We will be

analyzing how the use of Activated Carbon, Air Sparging, Biodegradation, Vapor Phase

Extraction, and Chemical Oxidation could be used to achieve our goal.

3.1 – Activated Carbon

Activated Carbon (AC) is a form of carbon made from charcoal, peat, and most similar

carbonaceous material that has been processed to have a large surface area. AC is made by

injecting oxygen or another chemical into the charcoal remains of the carbonaceous

materials to open up pores. The processed charcoal usually has a surface area ratio 100

square meters to one gram. The large surface area creates small pores that help with the

filtration with two mechanism adsorption, a chemical process and filtration, a physical

process. Figure 3.1.1 is a picture of activated white carbon which is made of Holm Oak

under a 2030 times magnification, showing the surface area.

3-2

(Figure 3.1.1 - Holm oak activated carbon)

(http://sortofcoal.com/science)

There are many different types of activated carbon; powered activated carbon

(PAC), granular activated carbon (GAC), extruded activated carbon (EAC), impregnated

carbon, and polymer coated carbon (PCC). Powered activated carbon is ground carbon

particles usually less than 1.00 mm in diameter. Granular activated carbon is the most

common type of activated carbon; commonly being used for water, gas and vapor

treatment. Impregnated Carbon contains inorganic compounds and is commonly used for

air pollution. EAC is similar to PAC but a binder is added to the EAC. This binder increases

the strength of the activated carbon structure allowing to work under extreme pressures.

PCC is used to filter blood and is coated in a bio-compatible polymer.

3-3

Activated carbon works in three ways; adsorbing chemicals from the water to the

exterior walls, filtering through the pores, and substances adsorb to the interior walls. Van

der Waals forces, particularly London Dispersion forces, bind the substances to activated

carbon. Activated carbon is good for binding most organic compounds, but different types

of AC is better for different chemicals. AC is categorized by its iodine number, this number

describes the effectiveness of activated carbon in terms of micro-pore content.

The activated carbon treatment is applied to ground water contamination by

pumping the water out of the ground and filtering it through the AC achieving various a

desired level of purification. For AC to be properly applied, a good layout of the ground

water table should be understood to determine the direction of water flow and to select

acceptable locations for the in-fluent and effluent wells. The concentration and the type of

contaminant must be known to select the proper type of activated carbon. With BTEX and

MTBE compounds the best type of AC to use is granular activated carbon (GAC) due to its

cost effectiveness in comparison to other forms of AC.

(Figure 3.1.2 - Average Breakthrough Curve for AC)

(http://www.cee.vt.edu/ewr/environmental/teach/wtprimer/carbon/sketcarb.html)

3-4

Granular activated carbon can have a variety of permeability rates and follows some

basic rules of chemistry. GAC decreases in adsorption efficiency over time and can be

replaced or re-mediated; for this application it can only be replaced due to the carcinogenic

affects of BTEX compounds. This decrease in adsorption efficiency is often shown in a

breakthrough curve (Figure 3.1.2) shown above which is a curve showing concentration

versus time based off of isotherm equations. These isotherm equations determine the limit

that the AC can absorb a certain solute. Two isotherm equations commonly used for

Activated Carbon are the Langmuir (Equation 3.1.1) and Freundlich (Equation 3.1.2)

equations. Also we must consider that the AC will adsorb the BTEX and MTBE compounds,

but the harmful chemicals will still remain in the filter media to be disposed of. This media

must be disposed of by either land-filling it as a Class I compound or thermal regeneration,

which can bring vapor emission problems.

(Equation 3.1.1-Langmuir Equation (Reynolds))

X - Quantity of contaminant adsorbed

m - Mass of the adsorbent

P - Pressure of adsorbate

k and n - Empirical constants for the given adsorbent-adsorbate pair at a specific temperature.

3-5

(Equation 3.1.2-Freundlich Equation (Reynolds))

In both equations 3.1.2 and 3.1.3

P - Partial pressure of the gas or the molar concentration of the solution

θ - Surface coverage

k - Rate constant at a given temperature

At very low pressures θ = KP

At high pressures θ = 1.

θ is difficult to measure experimentally. that is why it is usually estimated or the equation

is rearranged to a linier form shown below (Equation 3.1.3)

(Equation 3.1.3- Linear version of Freundlich equation (Reynolds))

Other equations used to determine the proper application of GAC is the Bernoulli

Equation (Equation 3.1.4) with a head loss through a filter predicted by either equation

developed from the Rose equation (Equation 3.1.5) or the Carmen Kozeny equation

(Equation 3.1.6).

3-6

(Equation 3.1.4 -Bernoulli Equation (Reynolds))

. P = Pressure,

V= water velocity

Z= height of water at point

g = gravity

h = head loss

γ= density of water

(Equation 3.1.5 – The Rose Equation (Reynolds))

This is the Rose equation that helps to predict head loss through porous media; the symbols from Bernoulli are the same.

ε - Porosity

D - Conduit diameter

θ- Shape factor

d - Diameter of the particle

3-7

(Equation 3.1.6 - Carmen- Kozeny equation (Reynolds))

This is the Carmen- Kozeny equation uses the same symbols as the Rose with

f - Dimensionless friction factor.

The removal effectiveness of this treatment depends largely on the individual system

design. Many studies have shown ninety percent or more reduction in BTEX compounds

and along with MTBE compounds. With the equations listed above a general idea for design

can be implemented with respect to the volume and the concentrations of the compound.

3-8

3.2 – Air Sparging

Air Sparging(AS), also known as “in situ air stripping” or “in situ volatilization” is a

remediation technology that is used to reduce concentrations of volatile petroleum

constituents dissolved in ground water and adsorbed in soils. This process often combines

Vapor Phase Extraction (VPE), Chemical Oxidation and Biodegradation to increase its

effectiveness. In the case where AS is combined with Biodegradation, it is often referred to

as Biosparging (BS).

The AS treatment is an in-situ process in which contaminant-free air is injected into a

saturated zone. This forces dissolved contaminants to move from their dissolved state to a

vapor state. Once these contaminants are in there vapor state they subsequently are

transported with the previously injected air to the unsaturated zone and removed from an

extraction well.

As is the case with many remediation processes, Air Sparging cannot completely

remove all of a contaminant but it does reduce the concentration to a manageable level, this

is illustrated in Figure 3.2.1.

3-9

(Figure 3.2.1: Air Sparging Results over Time) (VII-30,1994)

The key factors that determine the effectiveness of AS that we can measure and

quantify are the vapor/dissolved phase partitioning of the compounds and the

permeability of the soil. These factors will determine the rate in which constituents will be

removed from the soil and the number and location of sparge points.

Looking at the vapor/dissolved phased partitioning we will be concerned with the

constituent Henry's Law Constant, the fluid composition and boiling point, the compounds

vapor pressure, the overall concentration of the compounds and there solubility.

3-10

Henry's Law constant is a measure of the tendency of a constituent to transfer to

vapor phase and is needed to use Henry’s Law (Equation 3.2.1) which determines the

partial pressure of a constituent in the air.

(Equation 3.2.1 – Henrys Law)

(Reynolds)

-Partial Pressure in the air (atm)

- Henrys Law Constant (atm)

- Concentration of constituent (mole fraction)

A compound’s boiling point is a measure of how volatile it is. This can be used as a

parallel to determine Vapor/dissolved phase partitioning. Ideally this value should be

below 300 degrees Celsius to allow for an effective process.

Next, a compounds vapor pressure, another measure of volatility is needed. Vapor

Pressure is the pressure of a compound when it is in equilibrium with its pure liquid state,

so it measures a compounds tendency to evaporate and be transferred to a extraction well.

The higher the value of this, the more likely a compound is to evaporate; this value should

be above 0.5 mm Hg for Air Sparging to be effective.

The need for the compounds overall concentration can be seen by referencing

Figure 3.2-1. We see that it is not a linear relationship between contaminant removal and

time so, this number will give us an idea of how much of the contaminant we can remove

per mass over time.

Solubility is the maximum weight of a compound that can be dissolved in water.

This factor affects AS less than those previously mentioned but it is still needed. In addition

to the vapor/dissolved phase partitioning, solubility will give us some idea of the likelihood

of a compound to mobilize during the process.

3-11

Now looking at the permeability of a soil we must consider the soils intrinsic

permeability, structure and stratification and, the iron concentration of the ground water.

Intrinsic permeability (Equation. 3.2.2) measures a soils ability to transmit a fluid

through it. This value is possibly the most important for the overall design and varies

massively from site to site worldwide. If this value is above 10-9 cm2 we can be fairly certain

that AS will be effective. Similarly, if this is between 10-9 and 10-10 cm2 we would need to

evaluate the soil more closely; below these values AS would only be marginally effective.

This value is determined from the results of field tests done on a give site.

(Equation 3.2.2 – Intrinsic Permeability Equation) (VII-30, 1994)

k- Intrinsic Permeability (cm2)

K- Hydraulic Conductivity (cm/sec.)

- Viscosity of water (g-sec/cm)

- Density of water (g/cm3)

g- Acceleration due to gravity (cm2/sec)

A soils structure and stratification that is, the type of soil and its structures control

AS pressure and the flow of the air through the saturated zone. The soil structure can

create barriers blocking the contaminants from reaching extraction wells and can if not

carefully modeled and monitored, spread the contamination.

Dissolved iron lowers the permeability of a soil during AS operations. This happens

when dissolved iron reacts with injected oxygen precipitations out insoluble iron oxide

which clogs the soil pore spaces.

The modeling of this process has been attempted with varying degrees of success

from both a removal and flow rate standpoint. Many equations have been presented to

model these factors, these equations tend to be effective within very specific time periods

3-12

and contaminant levels. This can be attributed to the large number of unpredictable and

changing variables present (soil stratification, other contaminants, microorganisms, etc.).

Many of these equations are simply an application of Henry’s Law with various

assumptions. The Graph (Figure 3.2.2) shows the accuracy of this model with both

equilibrium and non-equilibrium assumptions VS. site test data.

(Figure 3.2.2 – Accuracy of remaining constituents model equations VS. Test Data) (Reddy, 2008)

Air Sparging is generally used in the case of BTEX compounds since they easily

transfer between dissolved and vapor phases, through an examination of chemical

properties, it can be noted that MTBE is not typically treated with classic AS systems alone,

to remedy this the addition of the Chemical Oxidation and SVE techniques can be integrated

into the overall design.

3-13

3.3 – Biodegradation

Biodegradation is a naturally occurring process which can be enhanced to treat

contaminated groundwater and soil through the biological breakdown of contaminants.

There are two ways in which organic material can be broken down, either aerobically or

anaerobically. Aerobic biological breakdown involves the breaking down of microbes

through the use of oxygen while anaerobic breakdown occurs without the use of oxygen.

All BTEX chemicals degrade aerobically, in the presence of oxygen. Through this

technique microorganisms are degraded from their organic parts to carbon dioxide and

water. The understanding of electron acceptors is essential in understanding which

methods are most effective in removing different BTEX and MTBE contaminants. If

removal of toluene is favorable, the introduction of nitrate into the groundwater would

promote an anaerobic degradation in the chemical.

Biodegradation can be extremely effective in this application as a removal process

since it’s a natural process which occurs with all BTEX and MTBE chemicals. Although the

decay rates of individual chemicals may vary, it is possible to increase the rate at which

these chemicals decay through the introduction of oxygen, nitrogen, sulfate or other

nutrients. Boosting the decay rate of an existing ongoing natural process enables us to

minimize the use of power generating mechanisms which may have alternately been

considered to remove contaminants. The natural process of biodegradation is typically the

most cost effective method in approaching larger scaled chemical spills.

3-14

3.4 – Vapor Phase Extraction

Vapor Phase Extraction (VPE), also known as “Soil Venting” and “Vacuum Extraction”

volatilizes contaminants in a given zone by applying high powered vacuum pressure along

the surface of a saturated zone. This vacuum pressure volatilizes contaminants and forces

them in to vapor phase. Once in vapor phase, the contaminants are pulled by the vacuum to

an extraction well where they can be removed and treated. Due to the increased air flow

created by the subsequent vapor transport, natural Biodegradation is often stimulated by

this process.

The application of vacuum pressure to the saturated zone (SZ) creates a negative

pressure gradient that forces the volatilized contaminates (BTEX and MTBE) to extraction

wells placed throughout the subsurface. Key factors that must be considered in the design

of this system include, Soil Permeability, Soil Structure, Soil Moisture, and the depth of

ground water.

Firstly, in cases where the ground water table (GWT) is located less than three feet

below the surface of treatment or below the top of the capillary fringe, VPE alone is

generally not effective. The capillary fringe causes a problem in extraction wells because

the screens on the well intake are submerged , this causes the air flow to the well to be

greatly reduced. To counter act this effect, the addition of depression pumps in the area

surrounding each extraction well can lower the depth of the local capillary fringe allowing

air to flow through the soil pores.

The soil permeability obviously affects the rate at which the air and vapor phase

contaminants travel to the extraction wells. In these systems we ideally want soil with a

high permeability to increase the effectiveness, this is however, not always possible from a

practical standpoint. Methods for determining soil permeability are illustrated in section

3.2.

The soil structure is of particular importance to us in this case more than others. The

structure of the soil plays a large role in determining the flow path of vapors created from

VPE much like in AS. In many cases VPE systems are preceded by a hydraulic fracturing

prior to implementation, in our case, the soil has already undergone this process.

3-15

Determining the structure of the soil that has resulted from hydraulic fracturing will help

us determine the most effective placement of our extraction wells.

The moisture content of soils can restrict air through soil pores. This being the case,

high soil moisture is not a desirable trait. In this regard, some soils will be affected more

than others; for example, finer grained soils will create a larger capillary fringe than coarse

grained soils, meaning simply, the coarser a soil, the less we need to be concerned with soil

moisture.

The flow rate expected from an extraction well can be estimated through an

application of Darcy's law (Equation 3.4.1), with A being the pore space of the soil in

question.

(Equation 3.4.1 - Darcy's law) (http://chemelab.ucsd.edu/sve/ProjSum.htm)

VPE has proven to be effective in removing Volatile Organic Compounds (VOC’s) and

many Semi-Volatile Organic Compounds (SVOC’s) from ground water. Typically, VPE is

more effective on lighter VOC’s, this category includes the compounds in question, BTEX

and MTBE contaminants resulting from hydraulic fracturing. In general, with the

application of VPE alone to a Saturated Zone we can achieve a 90% reduction in

concentration of contaminant's, anything above the 90% margin is difficult and impractical

without the addition of other technologies. This result generally can be achieved in 6

months - 2 years and provides minimal disturbance to the site above.

3-16

3.5 – Chemical Oxidation

Chemical Oxidation (ISCO) is a remediation technique that applies one or more

oxidizing agents to a saturated zone that converts contaminants into non-hazardous, stable

substances. This is typically achieved by placing an injection well in a saturated zone

(Figure 3.5.1) to release the chemical oxidizer. Currently there are four major oxidants

used to treat contaminants, these are ozone, persulfate, permanganate, and peroxide. The

stoichiometric equations for the oxidation of BTEX and MTBE compounds is presented in

Table AP-2 (Appendix C-C). For this application we will be looking at ozone due to its

ability to break down BTEX, MTBE and the beneficial oxygenation and bio-stimulation

resulting from its application.

(Figure 3.5-1: Chemical Oxidation Injection Wells) (http://www.envirologek.com/Chemical_Oxidation.htm)

3-17

The results, which come from chemical oxidation when treating BTEX contaminants

in an in-situ environment, have proved to be one of the most effective methods. One of the

major proponents to this method desirability is due to its reaction rates which occur

relatively quickly.

The process which is used in treating an area subject to BTEX contamination is

simply the placement of injection wells which can be placed directly over the contaminated

source area as well as several locations around the source area. Once the wells are in place,

ozone or another oxidant is then pumped into the contaminated area or ground water. As

the ozone enters and makes contact with the contaminants, chemical oxidation reactions

occur which break down the chemicals into harmless, non-toxic byproducts such as water

and carbon dioxide. MTBE is also broken down in the presence of ozone, however

oxidation occurs at a much slower rate when compared to the oxidation rate of BTEX. As

these reactions take place heat is formed due to the oxidation process. Vapor pressure

withing the subsurface is then increased by the increase in temperature, making it easier

for extraction of VOC’s using a vapor extraction system.

Before selecting ozone as a treatment technique it is important to understand how

the chemical is created and utilized. Ozone is a gas which is created by exposing oxygen

molecules to a controlled high voltage electrical field. When multiple oxygen molecules

pass through a high voltage field many bonds are broken, leaving them as single oxygen

atoms. These atoms are then free to reunite with the O2 atoms whose bonds were not

broken while passing the voltage area, thus reforming and creating O3, (Figure 3.6.1) which

is known as ozone.

3-18

(Figure 3.6.1: Ozone Production) (http://www.h2oengineering.com/managed_files/cms/OZONE%20SPARGE%20TECHNOLOGY%20FOR

%20GROUNDWATER%20REMEDIATION.pdf)

Another great aspect of ozone treatment of BTEX and MTBE in groundwater is the

way in which it operates as opposed to other treatment technologies. Operation of an in

situ ozone treatment results in very little site disturbance unlike some other technologies.

Ozone equipment is designed specifically for each site and doesn’t require the use of

chemicals in large quantities. On site equipment, draws oxygen from the atmosphere by

using compressors, the air is then fed through a oxygen concentrator which is capable of

removing nitrogen from the air. Pure oxygen can then be fed to the ozone generator which

uses a high voltage electric field to convert that oxygen to ozone. Additional, unmodified

air is then combined with the ozone and pumped to the subsurface of the contaminated

area at rates typically ranging from 1 to 4 cubic feet per minute, the amount of ozone used

varies with site conditions.

There are numerous benefits in using ozone to treat large contaminated areas. By

using ozone it allows us to minimize the amount of waste materials since these by-products

are converted into oxygen and carbon dioxide by ozone. Bulky equipment and constant

transportation and storage of chemicals is unnecessary because oxygen can be drawn into

an ozone creating mechanism located on site.

3-19

When dealing with a contaminated site it is desirable to focus on one specific treatment

technique which is capable of treating a targeted area, especially in the case of larger sites.

The benefit of using ozone is that it has the ability to treat a wide range of chemicals. It is

also useful in the fact that it is equally effective in saturated and unsaturated zones. At this

time, ISCO (in-situ chemical oxidation) is cost effective in treating large areas of BTEX

contamination with high concentration but not cost effective at treating smaller

concentrations. Similar to vapor phase extraction, the process of using chemical oxidation

is currently estimated to be 90% effective. Overall, the results of chemical oxidation by

using ozone is one of the safest methods as it produces non-toxic end products after it’s

short reaction time and is typically considered for large contaminated areas. Under ideal

conditions this technique can prove to treat a saturated zone in 2 to 6 month.

4-1

4 Analysis-

We must take several factors into account when choosing which treatment technique is

best for our application. A summary of factors effecting our process, its application and

there level of importance can be found in Table 4.1.

Table 4.1: Factors Effecting Treatment of BTEX and MTBE Contamination

Resulting from Hydraulic Fracturing

Process Activated

carbon

treatment

Air

Sparging

Biodegradation

SVE Chemical

Oxidation

Factor

In situ No Yes Yes Yes Yes

Possible Spread of

contaminants

No Yes No No Yes

Other on Site

Applications

No Yes No Yes Yes

Presence of Mobile

Contaminant

0 10 2 7 2

GWT Location 4 6 6 10 6

Soil Permeability 0 8 8 8 8

Distance to Nearest

Inhabited Area

0 10 0 0 10

Soil Structure 0 9 6 7 6

Soil Moisture 0 6 4 8 2

Presence of Other

Contaminants

0 2 10 4 9

Cost 5 5 5 5 5

Results 10 10 10 10 10

*Importance of factors is rated from 0-10, 0 being unimportant, 10 being a critical factor.

*Factors with binary yes or no answers indicate if it is a concern or not and have no gauged values.

4-2

With this data we first rule out Activated Carbon treatment since it requires a pump

and treat system and expensive transport of contaminants. Now we will look at the

possible results, we rule out biodegradation since it is widely affected by the presence of

other contaminants. Chemical Oxidation has the shortest treatment time for results similar

to that of SVE and Air Sparging. Next we look at the possible spread of contamination factor

for these three, where both Air Sparging and Chemical Oxidation are likely to result in the

spread of contaminants, the SVE system actually has the ability to control this factor, this is

another on site application of the SVE system. Chemical Oxidation also has post BTEX and

MBTE removal applications, for example the presence of NAH’s resulting from Hydraulic

Fracturing is common, this contamination could be treated with the system that is already

in place by changing the oxidizing agent. This being the case, it would seem that Chemical

Oxidation is our most viable option do to its results and flexibility as a treatment technique.

Now that we have chosen our technique we must address its issues, the spread of

contaminants, selection of an oxidizing agent and the subsequent delivery technique. The

first issue, the spread of contaminants can be solved by the implementation of a SVE

system in conjunction with the Chemical Oxidation process (Figure 3.5.1). Next we must

select an oxidizing agent, Table AP-1(Appendix C-C) shows us that Ozone (O3) is the best

choice for our compounds as all BTEX and MTBE compounds are susceptible to ozone. Next

we must find a way to apply the oxidizer to the saturated zone, with ozone we must be as

efficient as possible since the unstable nature of the compound causes it to react quickly

with a variety of compounds, in short, we must make sure the ozone is placed so it reacts in

the way we want it to. To this end, we can apply an air sparging system to inject the ozone

along its air stream at varying depths along the sparge well; this will provide a modular

application of ozone along a saturated zone. We will not need to be concerned with

modifying the soil structure since the area has already undergone hydro-fracking which is a

typical method used to improve this condition. Placing these sparge points throughout the

saturated zone should be effective in dispersing ozone in a controlled way. Finally we note

that before we implement our air sparging system we must remove all mobile

contaminants prior to application to avoid contamination of nearby aquifers.

5-1

5 Conclusion –

The Process of Hydraulic Fracturing for natural gas presents the problem of large scale

ground water contamination of varying degrees of severity and contents. We have

examined the remediation techniques of Activated Carbon, Air Sparging, Bioremediation,

Soil Vapor Extraction, and Chemical Oxidation in an effort to determine the most effective

and viable option for treating BTEX and MTBE contaminations commonly found following

this process. Due to the flexibility and impressive treatment time of Chemical Oxidation

systems, this technique was chosen; ozone was chosen as the oxidizer for its efficiencies in

removing all chemicals associated with BTEX and MTBE compounds.

In an effort to counteract the negative side effects of chemical oxidation a vapor phase

extraction system was also deemed necessary in the system. To provide a means to apply

the technique in situ we determined that a modified Air Sparging system would be most

effective. With this system we now have a viable way to not only treat the contamination of

BTEX and MTBE from hydraulic fracturing but a system can be modified to treat the

remaining hazardous contaminants resulting from the hydro-fracking without any new

installation or implementation costs.

i

Appendix A-A – Group Member Contributions

Josh Rusk

Josh was responsible for the research and writing of the Abstract, Air Sparging (3.2),

Vapor Phase Extraction (3.4), Analysis (4) and Conclusion (5) sections along with

report formatting.

Mark Aylward

Mark was responsible for the research and writing of the Activated Carbon (3.1)

section as well as the integration of the Introduction (1) and Hydraulic Fracturing (2)

sections into the report. Mark also created the “Typical System Flow Scheme” drawing

in Appendix B-B.

Mike Robidoux

Mike was responsible for the research and writing of the Introduction (1) and

Hydraulic Fracturing (2) sections.

Emanuel Pacheco

Emanuel was responsible for researching and writing the Biodegredation (3.3) and

Chemical Oxidation (3.5) sections.

In addition to the above tasks, all group members were responsible for the accuracy

and quality of the contents of this report and all slides pertaining to their sections.

ii

Appendix B-B – Typical System Flow Scheme

Figure B-B : Typical System Flow Scheme

iii

Appendix C-C – Tables and Figures

Table AP-1 – Criteria for selection of Chemical Oxidant (VII-30, 1994)

iv

Table AP -2 – Stoichiometric Oxidation Relationships (XIII, 2004)

v

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