EPA
500
G ,
B
92
001
4
United States
Environmental Protection
Agency
Solid Waste And
Emergency Response
(OS-420) WF
EPA500-C-B-92-001
March 1992
vxEPA Hyperventilate Users Manual
A Software Guidance System
Created For Vapor Extraction
Applications
Ground Surface
Pump
I
oi.
Well
Contaminated
ubte
Flame
Vapor Treatment
Unit
I
Printed on Recycled Paper
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*
j
SOFTWARE heW by Library I
Database Coordinator,
please inquire at Circulation Desk
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Hyperventilate
Users Manual
A Software Guidance System Created for Vapor Extraction Applications
A Practical Approach to the
Design, Operation, and
Monitoring of In-Situ Soil
Venting Systems
wnioa 1.01
» Hyj»rC«* Stick Cnitii ly:
Panic. Johnson, Pfc.D.
AmyJ. SUbeaan
Shen Development
WesthoDov Research Center
About This Stack
Go to First Card
Economics \_
System Monitoring
Field Teats •
System Design
-
Vapor f f
Treatment I
Vapor
Ptov
by
Paul C Johnson, Ph.D.
Shell Development
Westhollow Research Center
Environmental R&D
P. O. Box 1380
Houston, TX 77251
Apple® Macintosh™ HyperCard™
compatible version 1.01
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C'
JJ
Disclaimer
The Hyperventilate software package was completed under a Federal Technology Transfer
Act Cooperative Research and Development Agreement between EPA arid Shell Oil
Company, signed in 1990.
EPA is facilitating the distribution of Hyperventilate because the Agency has found the
software and manual to be helpful tools, especially in teaching users about in situ soil
venting and in guiding them through a structured thought process to evaluate the
applicability of soil venting at a particular site. EPA's Office of Underground Storage
Tanks advocates the use of innovative cleanup technologies, and in situ soil venting is
recognized as an effective remediation alternative for many underground storage tank sites.
Hyperventilate is based on the document titled, "A Practical Approach to the Design,
Operation, and Monitoring of Soil Venting Systems" by P. C. Johnson, C. C. Stanley, M.
W. Kemblowski, J. D. Colthart, and D. L. Byers, published 1990 by Shell Oil Company.
The program asks a series of questions and forms a "decision tree" in an attempt to identify
the limitations of in situ soil venting for soils contaminated with gasoline, solvents or other
relatively volatile compounds.
EPA and Shell Oil Company make no warranties, either express or implied, regarding the
Hyperventilate computer software package, its merchantability, or its fitness for any
particular purpose. EPA and Shell Oil Company do not warrant that this software will be
error free or operate without interruption. EPA and Shell Oil Company do encourage
testing of this product.
EPA will not provide installation services or technical support in connection with the
Hyperventilate computer software package. Neither will EPA provide testing, updating or
debugging services in connection with the enclosed computer software package.
The Hyperventilate computer software package and this manual are not copyrighted.
For sale by the U.S. Government Printing Office
Superintendent of Documents, Mail Stop: SSOP, Washington, DC 20402-9328
OQ
UJ
U-
HEADQUARTERS LIBRARY
ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, O.C. 20460
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-Hyperventilate Users Manual -
Disclaimer
Shell Oil Co. makes no warranties, either express or implied, regarding the
enclosed computer software package, its merchantability, or its fitness for
any particular purpose. Shell Oil Co. does not warrant that this software
will be error free or operate without interruption. The exclusion of implied
warranties is not permitted by some states. The above exclusion may not
apply to you. This warranty provides you with specific legal rights. There
may be other rights that you may have which vary from state to state.
Apple is a registered trademark of Apple Computer, Inc.
Macintosh and HyperCard are trademarks of Apple Computer, Inc.
f77.rl is a product of Absoft Corp
Comments/Suggestions?
Comments and/or suggestions about the usefulness of this program can be mailed to:
Paul C. Johnson
Shell Development
Westhollow Research Center
P.O. Box 1380
RoomEC-649
Houston, TX-77251-1380
Please do not call the author and/or Shell with questions about the use or
interpretation of results from this program.
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Foreword
Hyperventilate is a software guidance system for vapor extraction (soil venting)
applications. Initial development of this program occured under the Apple Macintosh
HyperCard environment, due to its programming simplicity, ability to incorporate text and
graphics, and interfacing with other Macintosh programs (such as FORTRAN codes, etc.).
The objective was to create a user-friendly software package that could be both educational
for the novice environmental professional, and functional for more experienced users.
Hyperventilate will not completely design your vapor extraction system, tell you exactly
how many days it should be operated, or predict the future. It will guide you through a
structured thought process to: (a) identify and characterize required site-specific data, (b)
decide if soil venting is appropriate at your site, (c) evaluate air permeability test results, (d)
calculate the minimum number of vapor extraction wells, and (e) quantify how results at
your site might differ from the ideal case.
Hyperventilate is based on the article "A Practical Approach to the Design, Operation,
and Monitoring of Soil Venting Systems" by P. C. Johnson, C. C. Stanley, M. W.
Kemblowski, J. D. Colthart, and D. L. Byers [Ground Water Monitoring Review, Spring
1990, p.159 -178]. The software performs all necessary calculations and contains "help
cards" that define the equations used, perform unit conversions, and provide
supplementary information on related topics. In addition, a 62-compound user-updatable
library (to a maximum of 400 compounds) is also included.
Hyperventilate version 1.01 for the Apple Macintosh requires an Apple Macintosh
(Plus, SE, SE/30, II, IDC, or portable) computer equipped with at least 1 MB RAM (2 MB
preferred) and the Apple HyperCard Software Program (v.2.0 or greater)
This manual is not intended to be a primer on soil venting (although the software is) and it
is assumed that the user is familiar with the use of an Apple Macintosh personal computer.
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-Hyperventilate Users Manual-
Table of Contents
Title
Page
I
II ,
in
IV
V
V.I
V.2
V.3
V.3.1
V.3.2
V.3.3
V.3.4
VI
Appendices
A
B
C
D
E
F
G
Disclaimer
Foreword
. Introduction
Definition of Some Terms Appearing in this Manual
Software/Hardware Requirements
Loading Hyperventilate Software
Using Hyperventilate ,
- Starting Hyperventilate,
- General Features of Cards
- Sample Problem Exercise
- Navigating Through Hyperventilate .
- Is Venting Appropriate?
- Field Permeability Test
-System Design
References
' "3
Soil Venting Stack Cards
Soil Venting Help Stack Cards
Air Permeability Test Cards
Aquifer Characterization Cards
System Design Cards
Compound List Update Cards
A Practical Approach to the Design, Operation, and Monitoring
Soil Venting Svstems
i
ii
2
4
4
4
5
5
7
8
8
12
22
26'
35
36
of In Situ
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- Hyperventilate Users Manual -
I. Introduction
In situ vapor extraction, or soil venting is recognized as an attractive remediation alternative
for "permeable" soils contaminated with "volatile" compounds. As Figure 1 illustrates,
vapors are removed from extraction wells, thereby creating a vacuum and vapor flow
through the subsurface. Until the residual contamination is depleted, contaminants will
volatilize and be swept by the vapor flow to extraction wells. While its use has been
demonstrated at service stations, Superfund sites, and manufacturing locations (see Hutzler
et al. [1988] for case study reviews), vapor extraction systems are currently designed more
by intuition than logic. In fact, many systems are installed at sites where the technology is
not appropriate.
"A Practical Approach to the Design, Operation, and Monitoring of In Situ Soil Venting
Systems" [Johnson et al. 1990a - see Appendix G] is a first attempt at creating a logical
thought process for soil venting applications. The article, which is based on earlier results
of Thornton and Wootan [1982], Marley and Hoag [1984], Johnson et al. [1990], and
discussions with several of these authors, describes a series of calculations for determining:
(a) if soil venting is appropriate at a given site, (b) limitations of soil venting, and (c)
system design parameters, such as minimum number of extraction wells and potential
operating conditions.
Hyperventilate is a software guidance system based on the Johnson et al. [1990a]
article. The software performs all necessary calculations and contains "help cards" that
define the equations used, perform unit conversions, and provide supplementary
information on related topics. In addition, a 62-compound updatable chemical library (to a
maximum of 400 compounds) is included. ,
Initial development of this program occured under the Apple Macintosh HyperCard
environment, due to its programming simplicity, ability to incorporate text and graphics,
and interfacing with other Macintosh programs (such as FORTRAN codes, etc.). The
objective was to create a user-friendly software package that could be both educational for
the novice environmental professional, and a functional tool for more experienced users.
The OASIS [1990] system created at Rice University for groundwater contamination
problems is another excellent example of the use of HyperCard as a technology transfer
tool.
This document is a users manual for Hyper Ventilate. It contains sections describing the
installation and operation of the software. During the development of Hyperventilate,
the goal was to create a guidance system that could be used with little or no instruction.
Experienced Apple Macintosh users, therefore, can load and explore the capabilities of this
program after glancing at the "Loading Hyperventilate Software" section. Those users that
are less comfortable about exploring software without a manual are encouraged to read
through it once, and work through the sample problem. It is intentionally brief, and a
beginner should be able to navigate through the system in less than a couple hours. It is
assumed that the user has some previous Macintosh experience. If not, consult a
Macintosh users manual for a quick tutorial.
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-Hyperventilate Users Manual -
Air Bleed
Vapor Treatment
Unit
Vapor
Flow
Pressure ^,
Gauge
J
_n
;
:
?
j
LJ
5
S
1
m
I Vacuum vvX*»X
?[| * S...S
— . | I O I IHIIIIB * ^^^ ' "
Flow f
Meter Flow
Meter
-*- Vapor Well
Contaminated -^ —
Soil — Vapor
Flow
Ground water Table
Figure 1. Schematic of a typical vapor extraction operation.
3
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II. Definition of Some Terms Appearing in this Manual
button - an object on a "card" that causes some action to be performed when
"clicked" on
card - an individual screen that you view on your monitor
click - refers to the pressing and releasing of the button on your mouse
drag - refers to holding down the mouse button while moving the mouse
field - a text entry location on a "card"
HyperCard - a programming environment created by Apple Computer, Inc.
mouse - the device used to move the cursor within your monitor
select - 'refers to "dragging" the cursor across a "field"
stack - a group, or file, of "cards"
III. Software/Hardware Requirements
Apple Macintosh HyperVentilate version 1.01 requires an Apple Macintosh (or
equivalent) computer equipped with at least 1 MB RAM (2 MB preferable), a hard disk,
and the Apple HyperCard Software Program (v 2.0). Check to make sure that your
system software is compatible with your version of HyperCard.
IV. Loading HyperVentilate Software
Hyperventilate is supplied on an 800 kB double-sided, double density 3.5" diskette.
Follow the instructions listed below to insure proper operation of the software.
1) Insert the HyperVentilate disk into your computer's floppy drive. The
HyperVentilate disk should contain the files:
- "Soil Venting Stack"
- "Soil Venting Help Stack"
- "System Design"
- "Air Permeability Test"
- "Aquifer Characterization"
- "Compound List Update"
- "HypeVent"
- "f77.rl"
2) Copy these files onto your hard disk. They must be copied into the folder
that contains the "HyperCard" program, or else the software will not
operate properly.
3) Eject the HyperVentilate disk
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- Hyperventilate Users Manual -
V. Using Hyperventilate
The authors of Hyperventilate intend it to be an application that requires little pre-
training for the user. It is mouse-driven and instructions are included on each card, so
please take the time to read diem when you first use Hyperventilate.
This section of the users manual is divided into three subsections. Start-up instructions are
given in the first, basic features of the cards are described in the second, and a sample
exercise is presented in the third. For reference, copies of all cards, as well as more details
on each are given in Appendices A through F.
V.I. Starting Hyperventilate
1) Those users with color monitors should use the "Control Panel" (pull down the
"ll" menu and select "Control Panel", then click on the "Monitors" icon) to set their
monitors to black and white, and two shades of grey.
2) To avoid unnecessary "card-flipping", set the "Text Arrows" option in your
"Home" stack "User Preferences" card to on. You can get to this card from within
any HyperCard application by selecting "Home" under the "Go" menu. This will
take you to the first card in the "Home" stack. At this point click on the left-
pointing arrow and the "User Preferences" card will appear on your screen. Then
click on the square to the left of "Text Arrows" until an "X" appears in the square.
3) Hyperventilate is started by double-clicking on the "Soil Venting Stack" file icon
' from the Finder (or Desktop), or by choosing "Open" under the "File" menu (Note
that using d more advanced version of HyperCard than the one under which this
system was developed (v 2.0) may require you to first "convert" each of the seven
HyperCard stacks contained in Hyperventilate).
4) Your monitor should display the card shown in Figure 2. Note that there are a
number of buttons on this card; there are two at the lower left corner, and then each
file folder tab is also a button (some cards may contain less obvious "hidden"
buttons; try clicking on the authors name on the title card for example). Clicking on
any of these will take you to another card. For example, clicking on the "About
This Stack" button will take you to the card shown in Figure 3, which gives a brief
description about the use of buttons and fields. Read this card well.
5) Explore for a few minutes. Try.to see where various buttons will take you, try
entering numbers in fields, or play with calculations: Again, just remember to read
instructions given on the cards.
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-Hyperventilate Users Manual -
Buttons
A Practical Approach to the
Design, Operation, and
Monitoring of In-Situ Soil
Venting Systems
vtnioa 1.01
91991 AnBffVf Butnftl
Bfell On Com)uy
Economics
k Hyj«rCw4 BUrft Ciutrf »y:
Paul C. Johnson, PlLD.
Amy 3. Strtenan
Shell Development
Wwthoflo v Research Center
About This Stack
Go to First Card
System Monitoring
Field Tests
Site Investigation
About SOU Venting
Sy'»m Sh«-Doim
System Design
Is Venting Feasible?
^
Vapor
Flov
\
Buttons
Figure 2. First Card of the "Soil Venting Stack" stack.
Help: Stack Information
Buttons
Buttons have been placed in each
card. Clicking on any button vill
perform an action, such as:
Go Home to first
«rt In Venting Stack
Oo to next card
Oo to Help cud
Ptintcartor
text field
Calculate) Perform«Calculation
When curious, click on Symbols,
Pictures or Text
Fields
Fields may contain information, or they may be
a place for you to input numbers.
Scrolling Field:
Click on arrow to move
text up or do vn
Boxed Data Field:
When you see an I-beam
cursor appear in a boxed
field, click the mouse in the
box to set the cursor. Then
you may enter data.
A button vffl then usually
be pushed to perform an
action or calculation.
Click on the arro vs , or
move the box up or do vn
vith the mouse.
In (his are*, you can
O
il
ilia;
Try this example:
Enter Number in B ox
I 11 inches
(Click for calculation)
2.54 centimeters
Figure 3. Card HI of the "Soil Venting Help Stack" stack.
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- Hyperventilate Users Manual -
V.2. General Features of Cards
Figures 4 and 5 are examples of cards from the "Soil Venting Stack" stack and "System
Design" stack. There are a few general features, of these cards that users should
understand:
a) Each card (with the exception of the first card of the "Soil Venting Stack" stack) has
been numbered for easy reference with the printouts given in Appendices A through
F. In the "Soil Venting Stack" these numbers appear in the bottom center of each
card (i.e. number "3" in Figure 4). In other stacks these numbers appear at either
the top or bottom corners of the card (i.e. "SD1" in Figure 5).
b) Arrow buttons are included at the bottom of some cards. Clicking on right-pointing
arrow will advance you to .the next card in the stack; clicking on the left-pointing
arrow will take you in the opposite direction.
c) The identifying card numbers in the "Soil Venting Stack" stack are also fields into
which text can be typed. You can skip to other parts of the "Soil Venting Stack"
stack by selecting this field, typing in the card number of your destination (within
the "Soil Venting Stack"), and then hitting the "return" key.
d) Many cards have a house button in the lower left corner. Clicking on this button
will take you to the first card of the "Soil Venting Stack" stack, which is the card
displayed at start-up (see Figure 2).
•••••i^^^^^^^^H^^^^^^HMWIIBBB^IBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBllMillMH^^^^^^^^^^^^H^^^RMHM^^^^^^^^^^^^H
In-Situ Soil Venting System Design Process
You can click on any block in this diagram to jet more information about that particular step. Or yau
can begin at the start of (he process by ctkking on either the "Leak or SpOl Discovered" box, or the '
right-directed arrov at the bottom of this card.
Clean"
Sits
Figure 4. Card 3 of the "Soil Venting Stack" stack.
V
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-HyperventilateUsers Manual -
Number of Venting Wells...
The procedure for estimating the required
number of extraction velb is similar tj (he
process used previously to determine if
venting is appropriate at a given site.
As fflusinteft at the right, ve vffl estimate
single vertical veil flffwiates, calculi* the
minimum vapor flov required, determine
Ow area! extent of influence, and then,
factor in any site-specific limitetiou. This
information then determines the necessary
number of extraction veils.
Just proceed to' foliov the steps dictated on
the foOoving cards—>
Plovrate
Maximum Removal
Rate
Requirement
Site-Specific
Limitations
Area of Influence
Requirement
Figures. CardSDl of the "System Design" stack.
V.3. Sample Problem Exercise
In the following a sample problem is executed in excruciating detail. Those not wishing to
work along with the example are encouraged to utilize Appendices A through F as
references for more details on the less obvious functions of some cards.
This "Sample Problem Exercise" is divided into to four subsections that address: navigating
through Hyperventilate (§V.3.1), screening sites to see if soil venting is an appropriate
technology (§V.3.2), interpreting air permeability test data (§V.3.3), and guidance for
designing soil venting systems (§V.3.4).
V.3.1 Navigating Through Hyperventilate
Step 1: Location: The "Desktop" or Finder.
Action: Start-up Hyperventilate by double-clicking on the "Soil Venting
Stack" icon, or click once on this icon and then choose "Open" from
the "File" menu.
Result: Hyperventilate will start-up and display the title card (Figure 2).
Step 2: Location: Tide Card of the "Soil Venting Stack" stack.
Action: Click on the "About This Stack" button.
Result: You are now at card HI of the "Soil Venting Help Stack" stack
(Figure 3).
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-Hyperventilate Users Manual -
StepS: Location: Card HI of the "Soil Venting Help Stack" stack.
Action: Play with the buttons and scrolling field. Practice entering a number
in the field in front of "inches". Place the cursor in the box. It will
; change from a hand to an "I-bar" as it enters the field. Hold down
the mouse button and drag the I-bar across the entry, which will
become hilited. Now type in another number, or hit the delete key.
Practice until you feel comfortable selecting text and entering
numbers. Then click on the "Click for Calculation" button. When
you are done practicing, click on the "Return" button.
Result: Return to the tide card of the "Soil Venting Stack" (Figure 2).
Step 4: Location: Title Card of the "Soil Venting Stack" stack.
Action: Click on the "Economics" file folder tab. ?
Result:. You are now at card 27 of the "Soil Venting Stack" stack. Take a
quick glance at this card, which is displayed in Figure 6. *
Step 5: Location: Card 27 of the "Soil Venting Stack" stack.
Action: Click on the "House" button in the lower left corner.
Result: You are back at the title card (Figure 2). • •
Step 6: Location: Title card of the "Soil Venting Stack" stack.
Action: Click on the "Go to First Card" button.
Result: You are now at card 1 of the "Soil Venting Stack" stack.(Figure 7).
Economics...
For typical service station sites,
clean-up costs can range from
$100K - $250K for the venting
operation alone, depending on
the complexity of the site, clean-
up time, permitting
requirements, and the type of
vapor treatment system used. .
The tvo major costs are
generally associated vith the
vapor treatment unit and
"Click" on any item belov (&
hold button dovn) to see costs
associated vita that item.
Figure 6. Card 27 of the "Soil Venting Stack" stack.
V
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-Hyperventilate Users Manual -
This HyperCard Stack vas created to help guide environmental scientists
through the thought process necessary to decide if and hov soil venting might
be applied to remediate a given site. The organization and logic of this stack
follow the paper:
'A Practical Approach to the Design, Operation,
and Monitoring of In-Situ Soil Venting Systems"
Uy:
P. C. Jonason, C. C. Stanley. M. W, KemtlovsH, J. D. Colttait, ft D. L. flyers
published in Ground Water Monitoring Reviev, Spring 1990, p. 159-178
If at ttis yoiai yo« to not feel comfortable vitk the use of the buttons, please
click once on *?" for moie info on the mechanics of this stack...
Figure 7. Card 1 of the "Soil Venting Stack" stack.
Step 7: Location: Card 1 of the "Soil Venting Stack" stack.
Action: Click on the right-pointing arrow.
Result: You are now at Card 2 of the "Soil Venting Stack" stack (Figure 8).
Step 8: Location: Card 2 of the "Soil Venting Stack" stack.
Action: Read the text, and click on the "down" and "up" arrows on the
displayed text field under "About Soil Venting..." to make the
field scroll. Then click on the left-pointing arrow at the card bottom.
Result: You are now back at card 1 of the "Soil Venting Stack" (Figure 7).
Step 9: Location: Card 1 of the "Soil Venting Stack" stack.
Action: Click on the right pointing arrow.
Result: You are again at card 2 of the "Soil Venting Stack" stack (Figure 8).
By now you should feel comfortable using the left- and right-
pointing arrows to travel through the stack.
Step 10: Location: Card 2 of the "Soil Venting Stack" stack.
Action: Click on the "?" button in the lower right corner of the card. This
button indicates that there is a "Help" card containing additional
information.
Result: You are now at card H2 of the "Soil Venting Help Stack" stack
(Figure 9). Scroll through the list of references, then click on the
"Return" button to return to card 2 of the "Soil Venting Stack" stack.
At this point you shpuld feel comfortable navigating around in Ilyperyentjlate.
10
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- Hyperventilate Users Manual -
About Soil Venting...
Soil Venting (a.k.a. "in-situsoil
venting", "vacuum extraction", &
"in-situ vapor extraction") is
rapidly becoming one of the most
practiced soil remediation processes
for permeable soils contaminated
vilh relatively volatile
hydrocarbons.
The underlying phenomena that
influence the success of any soil
venting operation are easily
understood. By applying a vacuum
Vapor
Treatment Unit
Vicwim
Blover
Figure 8. Card 2 of the "Soil Venting Stack" stack.
Help: About Soil Venting
Mow information about sou venting can be found in the foBovmg articles:
M. C. Marie; and G. E. Hoaj, Induced Soil Venting for fee Recovery/Restoration of Gasoline
Hydrocarbons in the Vadoie Zone. NWWA/API Conference on Petroleum Hydrocarbons and
Organic Chemicals inOroundvater, Houston, TX, 1984.
P. C. Johnson, M. W. Kemblovsld, and J. D. Colthan, Practical Screening Models for Sofl
Venting Applications, NWWA/API Conference on Petroleum Hydrocarbons and Organic Chemicals
in Ground vater, Houston, TX, 1988.
H. J. Hutzler, B. E. Murphy, and J. S. Gierke, State of Technology Reviev: Sofl Vapor Extraction
System], U.S.E.P.A, CR-814319-OM, 1988.
D. J. Wilson, A. N. Clarke, and J. H. Clarke, Sofl Clean-up byin-situ Aeration. I. Mathematical
ModelKr*, Sep. Science Tech., 23:991-1037,1988.
Figure 9. Card H2 of the "Soil Venting Help Stack" stack.
11
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-Hyperventilate Users Manual -
V.3.2 Sample Problem Exercise - Is Venting Appropriate?
In §V.3.2. you will work through an example problem to illustrate how one might decide if
venting is appropriate at any given site. For the purpose of this example we will use the
example site information given in Figure 10.
10'
20,
30,
I 40_
~*
50,
60'
North
South
m
•^ •
•
•
•
— - <•
•
P
•
HE
i
-0.3
1
•0.2- -
j
•0.02
• 0.0
.0.0
i
-02- -
i
• 0.0
• 1.7
1
-24 ,
. 73
1
• 9.5
M7
, Vv*: . Tank
Sandy V;«:
•
Fine to
Coarse Sand
m
i
Silty Clay
&
Clayey Silt
f
•
>
Medium Sand
HI
•Ply
^L7y — — •
-512
-5.4
-8577 .
•341- — — •
•653
•3267
. 1237
• 23831
•
.3319
.1.7
MO H
- 0.8 -
^4.6- — — — .
.•0.3 -
. 8.2
. 214
--31— — — — •
.967
- 971
^28679
•
. 23167 .
3-5 H
- 0.31
-1.2-
" 0.44
- 0.17
• 8.8
.-0.63
. 1.5
- 0.86
• 23
-1.6'
- 3.2_ T
3-3
Static Ground
Water Table
SCALE (fl)
\ 1 1
10
20
Contamination Type: Weathered Gasoline
Figure 10. Sample site data (Johnson et al. [1990a]). Total petroleum hydrocarbons
(TPH) [mg/kg] values are noted for each boring.
12
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-Hyperventilate Users' Manual -
Using your newly developed navigational skills and the right pointing arrow located at the
bottom of each card, slowly step your way through the stack until you reach card 7 of the
"Soil Venting Stack" stack (Figure 11). Take your time to read the text and "Help" cards
associated with each card along the, way.
Step 1: Location: Card 7 of the "Soil Venting Stack" stack.
Action: Read this card. It explains the process that you will use to decide if
venting is appropriate. Then advance to card 8 of the "Soil Venting
Stack" stack.
Result: You are now at card 8 of the "Soil Venting Help Stack" stack
(Figure 12). .
Step 2: Location: Card 8 of the "Soil Venting Help Stack" stack.
Action: Read the instructions on this card. Take the time to read the
information on the two "Help" cards: "Info about Calculation" and
"About Soils (& Unit Conversions)".
Now we will evaluate the efficacy of applying in situ soil venting to
the lower soil zone (45 - 50 ft below ground surface) in Figure 10,
which is composed of fine to medium sands. It also is the zone of
highest hydrocarbon residual levels (>20000 mg/kg TPH in some
areas).
It Venting Appropriate?
Read This
i
Ptovmte
Estimation
At this point ve vill proceed through a
simple thought process to decide if soil
venting is a feasible alternative. As
mentioned earlier, the three main factors that
govern the success of a venting operation are:
- vapor flovrate
- vapor concentrations
- subsurface stratigraphy (or the location of
contaminants relative to the vapor
flovpath)
Maximum Vapor
Concentration
±
Maximum Removal
Ratt
Figure 11. Card 7 of the "Soil Venting Stack" stack.
13
324-235 O - 92 - 2 QL 3
-------
-Hyperventilate'
Flowrate Estimation:
O Medium Sand
® Fine Sand
O Silly Sand
O Clayey Silts
O Input Your Ovn Permeability Range
Permeability Range (darcy)
to
1) Choose Soil Type, or
Optional - Enter your oim permeability values (daicy)
2) EnterWellRadto(Ia)
3) Enter Radios of Influence (ft) & Interval TTucknew*
4) Optional- Enter your ovn veil vacuum (406 " = max)
5) Click button ID calculate Predicted Flovrate Ranees
L- i itor 10 i
Jin
Well Radius
Radius of Influence
Interval Thickness* L 6.6|ft
[ —>Calculate Flovrate Ranges-*— J
* tiickua of cenu«4 ixttrvtX ar
Ataut Soib (ft UrutConvopioM
Predicted Flovrate Ranges
Well Flovrate
Vacuum (SCPM)
Pw (single veil)
(inH20)
5
1QL
20
4Q
JiH
J2Q.
-2HQ.
0.33
0.66
1,30
2.54
3.71
6.83
1007
to
to
to
to
to
to
to
_ 3.32
13-02.
25.38
37.09
68.27
100.66
Info about Calculation
Figure 12. Card 8 of the "Soil Venting Stack" stack.
Step 3: Location: Card 8 of the "Soil Venting Stack" stack.
Action: Choose the "Fine Sand" soil type, and enter:
well radius = 2 in
radius of influence = 40 ft
interval thickness = 6.6 ft
user input vacuum = 200 in H2O
into the appropriate fields, then click on the
"~>Calculate Flowrate Ranges<~" button.
Result: The flowrate ranges are calculated and displayed. Your screen
should now look like Figure 12. The calculated values are estimates
of the flowrate to a single vertical well (and are only valid estimates
when your conditions are consistent with the assumptions built into
the calculation - see Johnson et al. [1990a, b] for more details).
Step 4: Location: Card 8 of the "Soil Venting Stack" stack.
Action: Click on the right pointing arrow to advance to card 9. Read the
information on this card, then advance to card 10
Result: You are now at card 10 of the "Soil Venting Stack" stack (see Figure
13).
Step 5: Location: Card 10 of the "Soil Venting Stack" stack.
Action: Assume that the soil temperature at our sample site is 18° C. Enter
this value in the appropriate field, then hit the "return" key. This
action clears all values from the other fields.
14
-------
- Hyperventilate Users Manual -
Vapor Concentration Estimation - Calculation
T") Type in Temperature (*C) (hit )
Click to Enter Composition of Contaminant
T) or
Choose one of the Default Distributions
v , '
T) Click to Viev Distributions, (optional)
T) Click to Perform Calculations
18
O Enter Distribution
O "Fresh" Gasoline
® "Weathered" Gasoline
C Viev Distributions'")
{§) Perform Calculations
Sum of Mass Fractions
Results: Calc. Vapor Pressure
Calc. Vapor Concentration
iMLHovDo I Measure a Dutnwrton? 1
[About Calculation!
Figure 13. Card 10 of the "Soil Venting Stack" stack.
Help: Compound List
[ Viev Only Mode \
t Compound Name
Mass
Fraction
Vapor
Molecular Preaanre (atm)
1
2
3
4
5
6
7
8
9
10
propane
isobutane , .
n-butane
trans-2-butene
cis-2-butene
3-methyl- 1-butene
isopentane
1-pentene
2-methyl- 1-butene
2-methyl- 1, 3-butadiene
0.00
0.00
0
0
0
0
0.0069
0.0005
0.0008
0.0000
44. .
58.
58.
56.
56.
70.
72.2
70.1
70.1
68.1
8.04673
2.75865
1.97431
1.84196
1.67019
0.88399
0.73146
0.64989
0.62093
0.60914
<5
iS
,i!l,!i
i
•%'
c-
a.
iii.fi
M-
'JLL
O
I D.99628 1= SuinofMeajFnctions
(should be -1)
Hov Do I Meaarne « Dfrmhntton?JHi Return to Vapor COM. Estimation Cart
Figure 14. Card H16 of the "Soil Venting Help Stack" stack.
~\5
-------
•Hyperventilate Users Manual -
At this site the residual hydrocarbon is a "weathered" gasoline, so
choose this selection from the three composition options listed. The
"Fresh" and "Weathered" gasoline selections correspond to pre-
programmed compositions that are useful for estimation purposes. >
If you knew the composition of your residual, then you could enter
it by selecting the "Enter Distribution" option. Click on the "View
Distributions" button to take a look at the compound library and the
pre-specified composition of "weathered" gasoline. -.
Result: You are now at card HI6 of the "Soil Venting Help Stack" stack
(see Figure 14).
Step 6: Location: Card H16 of the "Soil Venting Help Stack" stack.
Action: View the library and pre-specified composition; If you are
interested, explore some of the help cards. Then click on the
"Return to Vapor Cone. Estimation Card" button to return to card 10
of the "Soil Venting Stack" stack.
Result: You are now at card 10 of the "Soil Venting Stack" stack (Figure
13).
Step 7: Location: Card 10 of the "Soil Venting Stack" stack.
Action: Click on the "Perform Calculations" button.
Result: Hyperventilate calculates the maximum possible vapor
concentration corresponding to the specified composition and
temperature. The results are displayed in Card 10 of the "Soil
Venting Stack" stack, which should now look like Figure 13.
Step 8: Location: Card 10 of the "Soil Venting Stack" stack.
Action: Using the right-pointing arrow button, advance to card 11 of the
"Soil Venting Stack" stack. Take the time to read the text, then click
on the "Calculate Estimates" button
Result: You are at card 12 of the "Soil Venting Stack" stack. The calculated
flowrates and maximum possible removal rates are displayed along
with an updated list of the input parameters that you have entered.
Your screen should look like Figure 15, if you have chosen the
"Ib/d" units.
Step 9: Location: Card 12 of the "Soil Venting Stack" stack.
Action: Click on the right-pointing arrow button. You are now at card 13 of
the "Soil Venting Stack" stack. Read the text, then enter:
estimated spill mass = 4000 kg
desired remediation time = 180 d
Now click on the "~>Press to Get Rates<—" button
16
-------
-Hyperventilate Users Manual -
Maximum Removal
Rate Estimates
select your unit preference belov
<§> Ub/d]
O
Temperature CQ
°
Note:
These an "maximum
removal rates", and should
only be used as screening
estimates to determine if
venting is even feasible at a
given site. Continue on ID
the next card to assess if
these rates BIB acceptable...
WeU Radius (in)
Radius of Influence (fQ
Contaminant Type
Permeable Zone Thickness (ft)
Pv-Well FtoTOLte Estimates Max. Removal Rate Estimates
Vacuum [SCFM] [IWdJ
(inH20) • (single veil) (single veil)
. 5_
..10
2J_
..IP
...6..P
120
2QQ_
p 33
0.66
1.30 .
.... ___
.. 6,8.3 ....
10.07
to
to
to
to
to
to
to
3.32
6.59
13.02
25.38
......3LP8.
.....68.27.
100.66
12.,....,.
....2.5
52
~J78 "I
364
to
to
to
to
to
to
to
62
}24
251
517
799
J778
- 3636
Figure 15. Card 12 of the "Soil Venting Stack!' stack.
I* Soil Venting Appropriate? Enter
At this point, you compare the
maximum possible removal rate
vith your desired removal rate.
If the maximum removal rate •
does not exceed your desired
removal rate, then soil venting
is not likely to meet your needs,
and you should consider another
treatment technology, or make
your needs more realistic.
In the next cards, ve vill refine
the removal rate estimates, in
.D Estimated Spill Mass) 4DOO| Q |b
180| days
£j Enter Desired
Remediation Time
toeetRates<~
Single Vertical Veil Results
Desired Removal Rate:
Gauge Vacuum (in H2O):
Mia Flo-mate @ 200 inH2O
Max Fbiraate @ 200 inH2O
Max. Eat Removal Rate:
(lover estimate) - pei veil
(upper estimate) - per veH
Ekc'd]
[inHZO]
ISCFM]
JSCFM]
Figure 16. Card 13 of the "Soil Venting Stack" stack.
17
-------
-Hyperventilate Users Manual -
Result: Your screen should now look like Figure 16. Note that your desired
removal rate (=22 kg/d) is less than the estimated maximum removal
rates for a single vertical well (=165 to 1650 kg/d). At this point in
the screening exercise, therefore, soil venting still appears to be a
viable option.
Step 10: Location: Card 13 of the "Soil Venting Stack" stack.
Action: Click on the right-pointing arrow button to advance to card 14 of the
"Soil Venting Stack" stack. Read the text, then advance to card 15
of the "Soil Venting Stack" by clicking on the right-pointing arrow
button. Again, take the time to read the text, then advance to card 16
of the "Soil Venting Stack" stack. The focus of these cards is the
prediction of vapor concentrations and removal rates as they change
with time due to composition changes. It is important to try to
understand the concepts introduced in these cards.
Result: You are at card 16 of the "Soil Venting Stack" stack (see Rgure 17).
Step 11: Location: Card 16 of the "Soil Venting Stack" stack.
Action: This card is used to finalize your input data prior to calculating vapor
concentration and residual soil contamination composition changes
with time. Read the instructions in the order that they are numbered.
Note that the summary table in the upper right corner of the card
contains all the parameter values that you have input thus far. The
instructions describe how to change these values, but at this point
we will retain the displayed values. Because it is difficult to present
the behavior of each compound in a mixture composed of an
arbitrary number of compounds, the output is simplified by
reporting the behavior in terms of "boiling point" ranges. This
simply represents a summation of all compounds whose boiling
points fall between pre-specified values. Presented in this fashion,
the model results can be interpreted much more quickly. Click on
the "tell me more about BP ranges..." button, read the help card,
then return to card 16 of the "Soil Venting Stack" stack. Click on
the "~>Set Default BP Ranges<~" button. Your screen should now
look like Figure 17. Click on the "Generate Predictions" button
Result: The message "Sit Back and Relax..." will appear on your screen,
followed by a screen on which the following appears:
"Copyright © Absoft Corp 1988
Copyright © Shell Oil Co 1990
HANG ON YOU WILL BE RETURNED TO HYPERCARD...
# OF COMPOUNDS IN LIBRARY = 62"
Then card 17 of the "Soil Venting Stack" stack will appear.
18
-------
Motfel Predictions
To flit right fa a summary of the
data you hav« input If you Irish *
choice any of the info, men. clfck
on the parameter name, and redo
the calculations oathe card you vffl
be taken to. Press to Winking
•Return' button to come tack
The model returns output that
allo vs you to determine
residual amounts of
compounds faffing viihin 5
toiling point ranees. Type in
your ovn ranges, or choose
the default values.
Temperature
Son Type
Soil Permeability Ranee (darcy)
Well Radius (in)
Radius of Influence (ft)
Contaminant Type
Permeable Zone Thickness (ft)
"* Set DefM* BP Ranges
Boiling Point Range *2
BoUingP.omtB.aage.«.
.Boiling.P.oint_gaagB*i
Boiling Point Range *5
-5Q
-28...
80
111
J44_
to
to
to
Jo
2?
80
JJLL ...C.
-ill. ...£.
250 C
Generate Predictions
tell me more about BP ranges.
Figure 17. Card 16 of the "Soil Venting Stack" stack.
[mcO.]
FIRST PRESS THE IMPORT
DATA. BUTTON!
These are the results (or the
contaminant type mat you have
Q«M(0)
L-airf
g-iesidual
.00
.24
.57
.98
1.49
2.11
2.87
3,81
Vapor
Cone.'
!» Initial]
100.000
75.062
58.631
48.078
39.390
31.941
25.916
21.150
Residual
Level
[» Initial]
100.000
95.000
90.022
85.034
80.034
75.035
70.035
65.037
Sm Hl& T* tfil'H'Bfr^ ^Q
p, >9D» of Initial
III Temperana
^ Contunina]
BP«1
Residual
[* total]
.690
.123
.000
.000
.000
.000
.000
,000
BPI2
Residual
[« total]
11.650
9.263
6.755
4.512
2.632
1.222
.385
.068
Remove
Residual
«(*C):
MType:
BP*3
Residual
[* total]
24.010
23.982
23.474
22.403
20.771
18.503
15.556
12.053
128.48 | £„!£
18 |
We&thered Gasoline
BP84
Residual
[« total]
22.140
23.000
23.820
24.577
25.248
25.766
26.031
25.919
BPttS
Residual
[» total]
41.510
43.632
45.950
48.509
51.350
54.509
58.028
61.959
lal]
o
iiiin
Ittr'i!
>|l|l|l
Figure 18. Card 17 of the "Soil Venting Stack" stack.
V
-------
-Hyperventilate Users Manual -
Step 12: Location: Card 17 of the "Soil Venting Stack" stack.
Action: Read the instructions, then click on the "—>Import Data<—" button.
Result: Your screen should look like Figure 18. The table in the lower part
of the card lists model predictions: vapor concentration and residual
soil concentration (expressed as a percentage of their initial values),
as well as the composition of the residual (expressed as a percentage
of the total for each boiling point range) as a function of the amount
of air drawn through the contaminated soil. Note that as the volume
of air drawn through the soil increases, the vapor concentration and
residual soil levels decrease, and the composition of the residual
becomes richer in the less volatile compounds (BP Range #5). In
the upper right corner of the card are displayed the saturated, or
initial, vapor concentration and the minimum amount of air that must
be drawn through the soil per gram of initial contaminant to achieve
at least a 90% reduction in the initial residual level. This value is
used in future calculations as a design parameter.
Step 13: Location: Card 17 of the "Soil Venting Stack" stack.
Action: Click on the right-pointing arrow to advance to card 18 of the "Soil
Venting Stack" stack.
Result: You are at card 18 of the "Soil Venting Stack" stack, which should
resemble Figure 19. Read the text. A summary of your input
parameters appears on the right side of this card. At the bottom
appears two calculated values representing the range of the minimum
number of wells required to achieve a 90% reduction in the initial
residual level in the desired remediation time. These values
correspond to idealized conditions, however, they can be used to
gauge the efficacy of soil venting at your site. For example, in this
case the minimum number of wells ranges between 0.7 - 7, which is
not an unreasonable number for a site the size of a service station. If
the range had been 100 - 1000, then it might be wise to consider
other remediation options.
It is important to recognize that model predictions are intended to
serve as guidelines, and are limited in their ability to describe
behavior that might be observed at any given site. One should use
all the information available, in addition to idealized model
predictions to make rational decisions about the applicability of soil
venting.
-------
-Hyperventilate Users Manual -
Step 14: . Location:
Action:
Result:
Card 18 of the "Soil Venting Stack" stack.
Click on the right-pointing arrow button to advance to card 19.
You are now at card 19 of the "Soil Venting Stack" stack. This card
lists several phenomena that can cause one to achieve less than ideal
removal rates. Take the time to explore each of these options, then
return to card 19 of the "Soil Venting Stack", stack.
Is Venting Appropriate?
This is a complete summary
of the data and results.
Based upon these numbers, a
"minimum number of veils"
has been calculated, vhich
should give you some
indication of hov
appropriate venting is for
your application. Note that
this is the number of veils if
circumstances are ideal,
Temperature fC ]: • | 18. ~
Contaminant Type: [Weathered Gasolim
Soil Type: | Fine Sand"
Well Radius [in]: Z
Est. Radius of Influence [ft]: 40
Permeatle Zone Thickness [ft]: 6.6
ROTO* perWeE(120" V«> [SCFM] 6.83
Flovn* per Well (120" Vac) [SCFM] 68.27
Min. Vol. of Air [U|-residtial]: 128-48
Estimated SpfflMa»: 4DOO
Desired Remediation Time [dayj]: • I 180
Minimum t of Wells
I 0-72 K Based <|
on Tour Input Parameters
7.23
Figure 19. Card 18 of the "Soil Venting Stack" stack.
21
-------
-HyperventilateUsers[Manual-
Field Tests
Figure 20. Card 20 of the "Soil Venting Stack" stack.
V.3.3 Sample Problem Exercise - Field Permeability Test.
Note: It is recommended that you always plot and visually inspect your data prior
to attempting to fit it to any theory.
In this example, we use Hyperventilate to analyze air permeability test data from the site
pictured in Figure 10. We will focus on results from the lower fine to medium sand zone
(45 - 50 ft below ground surface). Advance to card 20 (Figure 20) of the "Soil Venting
Stack" stack to begin.
Step 1: Location: Card 20 of the "Soil Venting Stack" stack.
Action: Using the right-pointing arrow, advance to card 21 of the "Soil
Venting Stack" stack. Read the text, then click on the "Air
Permeability Test" button.
Result: You are at card AP1 of the "Air Permeability Test" stack.
Step 2: Location: Card API of the "Air Permeability Test" stack
Action: Read the instructions, then click on the "Show Me Set-up" button.
Take a look at the figure, then click the "Return" button to return to
card API of the "Air Permeability Test" stack. Now click on the
"Test Instructions" button.
Result: You are at card APS of the "Air Permeability Test" stack.
Step 3: Location: Card APS of the "Air Permeability Test" stack.
22
-------
-Hyperventilate Users Manual -
Action:
Read the text, look at the sample data (click on the "show me sample
data" button) then enter the following values for this example:
soil layer thickness
estimated radius of influence
air permeability test flowrate
= 6.6 ft
= 50 ft
= 15CFM
Result:
Click on the "~>Calculate<-" button to estimate how long the air
permeability test should be conducted.
Your results should match those displayed below in Figure 21.
Step 4: Location: Card AP3 of the "Air Permeability Test" stack.
Action: Click on the "Return" button to return to card API of the "Air
Permeability Test" stack. Then click on the "Data Analysis" button.
Result: You are now at card APS of the "Air Permeability Test" stack.
Step 5: Location: Card APS of the "Air Permeability Test" stack.
Action: Read the text, then step through cards AP6 and AP7, until you reach
card APS of the "Air Permeability Test" stack.
Result: You are now at card APS of the "Air Permeability Test" stack.
Air Permeability Test - Instructions
i)
Identify soil zones to be treated
2)
Install vapor extraction vell(s) in this
zone(s). Existing monitoring veils
may be used, vhen the screen interval
extends only into the zone to be treated. |
Note the extraction veil radius and
borehole size. Insure that the veil is
not "connected" to other soil zones
through the borehole (use cement/grout [
to seal annular borehole region).
[ shov me sample data
FOR Volume Estimation
Enter
1) Soil Layer Thfctaess [ft]:
2) Estimated Radius of Influence [ft]:
3) Air Perm. Test Ftovn* [CFM]:
6.6
50
15
\J—> Calculate
Pan Volume:
Time t> Extract * Pore Volume:
Figure 21. Card AP3 of the "Air Permeability Test" stack.
23
-------
-Hyperventilate Users Manual -
Step 6:
Location:
Action:
Card APS of the "Air Permeability Test" stack.
Read the text, click the "clear" buttons to clear any entries from
columns, then enter the following data:
r = 53 ft
r = 32.4 ft
Time
[mini
9
11
15
23
30
40
100
flowrate
screened
Gauge Vacuum
fin H^.Ol
0.1
0.2 .
0.2
0.4
0.7
1.3
2.8
Time
[min]
4
7
9
12
16
24
30
39
' 52
77
99
110
121
141
Gauge Vacuum
fin H?O1
1.2
3.0
4.3
5.5
6.9
9.9
11
13
16
20
21
23
24.5
25.5
= 15 SCFM
interval thickness
= 6.6 ft
Step 7:
While entering the data it is convenient to place the curser in the time
column, type in the time value, then use the "tab" key to advance to
the vacuum reading column. Enter the corresponding vacuum
value, then hit the "tab key again. As you see, this advances the
curser to the time column again. Now click the "~>CaIculate<—"
button.
Result: Your results should match those displayed in Figure 22. Soil
permeability values have been calculated by fitting the field data to
the theoretical model described in cards APS - AP7 of the "Air
Permeability Test" stack.
Location: Card APS of the "Air Permeability Test" stack.
Action: Review the results, then click on the "Explanation & Statistics"
button.. This advances you to card AP9 of the "Air Permeability
Test" stack, which lists correlation coefficients for the data fitting
process. These values give an indication of how well the model
describes the behavior observed in the field. Values approaching
unity indicate a good fit. Your results should match those given in
Figure 23.
-------
- Hyperventilate Users Manual -
Air Permeability Test - Data Analytic (coat.)
Eater radial
T) distances of
monitorine points
Inter measured—.
?) tines and gauge
Vacuums
3) Eater (optional):
ajflovrate
I 15 USCFM)
b) screened interval
thickness
6.6 J(TO
r- I 53 IffO
(nsin) (inH2O)
P-l 32.4 IffO
(mm) (inH20)
P=l 1(«
(min) (inH2O)
9
11
15
23
30
40
100
0.1
0.2
'0.2
0.4
0.7
1.3
2.8
4
7
9
12
16
24
30
39
52
77
1.2
3
4.3
5.5
6.9
9.9
11
13
16
20
Q
!!
it
..;....
1
'!PF
li
o
Figure 22. Card APS of the "Air Permeability Test" stack.
Air Permeability Test - Data Analysis (cont.)
On the previous Card (APS), the data, you input vere fit to the approximate exptession given on Caid
AP6. Ifvas analyzed \»»( both methods described on caid AP7, if you input values for the
eitraction veil flovrate (Q) and the stratum thkkneas (m). Betov each column, of data, the tvo
calculated penneabflity values an denoted by:
darcy(A) - refers to calculation method 1 (see Caid APT)
darey(B) - refers to calculation method 2 (see Card APT)
During the regression analyses, (he data expressed as
pain of points (ln(t), P') an fit to a BM. The '
"correlation coefficient", r, is a measure of bov veU
fee data conform to the theoretical curve. Asr-->l,the
data point* an fall on the theoretical curve. A.t the rif lit
ate jiven 0» correlation coefficient values for the three
data. sets. For more info on the mewnine of r, consult
any introductory Statistics book.
Correlation Coef.
data set tl [0-941158 |
data set 12 I 0-98602
da* set M I Ho Data |
Figure 23. Card AP9 of the "Air Permeability Test" stack.
v
-------
- Hyperventilate Users Manual -
System Design
Figure 24. Card 22 of the "Soil Venting Stack" stack.
V.3.4 Sample Problem Exercise - System Design
In this example we illustrate the use of Hyperventilate for system design guidance. As in
§V.3.2 and §V.3.3, we use the sample site presented in Figure 10. At this site gasoline
was detected in three distinct soil strata: a fine to coarse zone located 10 - 30 ft below
ground surface (BGS), a silty clay/clayey silt zone located 30 to 42 ft BGS, and a fine to
medium sand zone that extends from 42 ft BGS to the deepest soil boring (60 ft BGS).
Groundwater is detected in monitoring wells at about 50 ft BGS.
Advance to card 22 of the "Soil Venting Stack" stack to begin (Figure 24).
Step 1: Location: Card 22 of the "Soil Venting Stack" stack.
Action: Use the right-pointing arrow to advance to card 23 of the "Soil
Venting Stack" stack. Read the text, then advance to card 24 of the
"Soil Venting Stack" stack.
Result: Card 24 of the "Soil Venting Stack" stack, which appears in Figure
25, should be displayed.
Step 2: Location: Card 24 of the "Soil Venting Stack" stack.
Action: Read the text, explore using some of the options. You will find that
the options: "Well Location", "Well Construction", "Surface Seals",
"Groundwater Pumping System", and "Vapor Treatment" provide
some useful guidance information on aspects and components of a
soil venting system. Return to card 24.
Result: Card 24 of the "Soil Venting Stack" stack should be displayed.
26
-------
- Hyperventilate Users Manual -
System Design...
At the right is a list of the components
of a venting system design. Click on
each to conduct the indicated phase of
the design process
Remember: It is not our intention to provide a
generic recipe for vacuum extraction system
design; Instead v* suggest the folio vine « *
structured thought process. As you shall see,
even in a structured thought process, intuition
and experience play important roles. There is
no substitute for a good fundamental
understanding of vapor flov processes,
transport phenomena, and ground vater ftovl
O Number of Extraction Wells
O Veil Location
O Veil Construction
O Surface Seals
O Ground vater Pumping System
O Vapor Treatment
t«i mm
Figure 25. Card 24 of the "Soil Venting Stack" stack.
Number of Venting Wells...
The procedure for estimating the required
number of extraction veils is similar to the
process used previously to determine if
venting is appropriate at a given site.
As illustrated at the right, ve vill estimate
single vertical •veil flovrates, calculate the
minimum vapor ftov required , determine
the anal extent of influence, and fiun
factor in any site-specific Imitations. This
information then determines tile necessary
number of extraction veils.
Just proceed to folio v tile steps dictated on
the foDovng caids — >
<>
I
|
I
O
Ftovrate
Estimation
Maximum Removal
Rate
Minimum Volume
Regainment
Site-Specific
Limitations
Ana of Influence
Red uin ment
>A_ K«nft«r
l) • of
)>-J Brtractlon
j/y Wells
:Tkiiiliirr'tr Return ^r^^P^t*i"»«t,:aii^^^ gpi
Figure 26. Card SD1 of the "System Design" stack.
V
-------
-Hyperventilate Users Manual -
Step 3: Location: Card 24 of the "Soil Venting Stack" stack.
Action: Select "Number of Extraction Wells" from the list of options.
Result: Card SD1 of the "System Design" stack should be displayed, as
pictured in Figure 26.
Step 4: Location: Card SD1 of the "System Design" stack.
Action: Read the text, then use the right-pointing arrow to advance to card
SD2.
Result: Card SD2 of the "System Design" stack should be displayed.
Step 5: Location: Card SD2 of the "System Design" stack.
Action: Read the instructions on the card, enter the following values into the
table, then click on the "Update" button:
Parameter Medium Sand
subsurface interval (ft BGS)
description of contaminant
radial extent of contamination (ft)
interval thickness (ft)
average contaminant concentration
10-30
gasoline
20
20
100
Soil Zone
Clayey Silt
30-43
gasoline
20
13
1000
Fine Sand
43-50
gasoline
20
7"'
10000
Result: Card SD2 should now resemble Figure 27.
Step 6: Location: Card SD2 of the "System Design" stack.
Action: Use the right-pointing arrow to advance to card SD3 of the "System
Design" stack.
Result: Card SD3 of the "System Design" stack should be displayed.
Step 7: Location: Card SD3 of the "System Design" stack.
Action: Read the text. Note that "clicking" on many of the table headings
will take you to "help" cards. Take a few minutes to explore the
use of these, then enter the following information:
Parameter
permeability (darcy)
design vacuum (in HiO)
Well Construction:
Radius of Influence (ft)
Extraction Well Radius (in)
Extraction Well Screen Thickness (ft)
Medium
10-100
40
40
2
10
Soil Zone
Sand Clayey Silt
0.01 - 0.1
40 ,
40
2
5
Fine Sand
1-10
40
40
2
5
-------
-Hyperventilate Users Manual -
Design Input Parameters...
(soil stratigraphy & contaminant characteristics)
Please enter the required information for each distinct soil
layer, click on the "Update* button, and then proceed to
the neit card (i.e. click on right ano v at bottom).
fthe tab key can be used to mow between celta)
Description of
Soil Unit
._L
JL
3
4
5
*
7
a
Medium Sand ..
FtoeSand
-
Depth BOS*
[ft]
10
3,0.
43
to.
to
to
to
to
to
to
30
•s.
50
Description of
Contamination
easoUne
JCSffilto
easoline
"
• BdevGnwdftufiH
^_
Sebct the total mass
units that yon prefer
C Cleai All Entries i
Contaminant
Distribution
n&u
20
^ 2jp
20
•I
fciirwl
takkatis
mi
20
ti
7
kvtni*
coke.
100
Iflflfl.
10000
ow
Cak.
Tottl
Mass
J20,?.
-29§ Q.
4232:3
0.0
0.0
_ P.O.
0.0
r o.o
(Update)
rafl-gi'W 111 ^ ;;s •! 'mB + M-J-\>WM + jjaiT^Wi S-:;B?S;
Figure 27. Card SD2 of the ."System Design" stack. .
Design Input Parameters . . .
Please enter the muted information for
each distinct soil layer, and then proceed
to the next card.
Note: - click on any febfe heading «
jet more Mo
- use tab key to move
betveen cells
O Bitty *»*
Description of
Soil Unit
1
Medium Sand
Permeability* .
[darcyj
.DJ21
Design
Vacuum
(inH20)
100
Jft
40
.JQ.
40.
Extraction Wen
Cons traction
ntou
.....2
lent*
fftl
10
rUmof
mi
40
Critical
Volume of
Air**
[L/gl
128.48
...1.21
Efficiency
(96)
.159.
..1.09.
128 100
* Eatir or CAMM from BJ( it to) rijV
•B^B^BaBBBBVB^BlB^
Clear All Entries
•mm vohmi oCv&jorrtfvinlta ukicvt rutLtlutioa.
•^BBBBBBBBH
Return
Figure 28. Card SD3 of the "System Design" stack.
JJ7 . :
324-235 O - 92 - 3 QL 3
29
-------
- Hyperventilate Users Manual -
The "Critical Volume of Air" is calculated by the same procedure
used previously in §V.3.2 (steps 10 -13). To initiate this
calculation, "click" on the "Critical Volume of Air**" heading.
Result: Card SD5 of the "System Design" stack appears on your screen
(Figure 29).
StepS: Location: Card SD5 of the "System Design" stack.
Action: Read the text carefully. The focus of this card is the prediction of
vapor concentrations and removal rates as they change with time due
to composition changes. It is important to try to understand the
concepts introduced in this card. For more information, read the
reference article contained in the appendix. Click on the "Do a
Calculation" button to advance to card SD6 of the "System Design"
stack (Figure 30).
Result: Card SD6 of the "System Design" stack appears on your screen.
Step 9: Location: Card SD6 of the "System Design" stack.
Action: This card is used to finalize your input data prior to calculating vapor
concentration and residual soil contamination composition changes
with time. Read the instructions in the order that they are numbered,
then enter "18" for the temperature and select "weathered gasoline"
from the three composition options. Because it is difficult to present
the behavior of each compound in a mixture composed of an
arbitrary number of compounds, the output is simplified by
reporting the behavior in terms of "boiling point" ranges. This
simply represents a summation of all compounds whose boiling
points fall between pre-specified values. Presented in this fashion,
the model results can be interpreted much more quickly: Click on
the "tell me more about BP ranges..." button, read the help card,
then return to card SD6 of the "System Design" stack. Click on the
"~>Set Default BP Ranges<~" button. Your screen should now
look like Figure 30. Click on the "Generate Predictions" button
Result: The message "Sit Back and Relax..." will appear on your screen,
followed by a screen on which the following appears:
"Copyright © Absoft Corp 1988
Copyright © Shell Oil Co 1990
HANG ON YOU WILL BE RETURNED TO HYPERCARD...
# OF COMPOUNDS IN LIBRARY = 62"
Then card SD7 of the "System Design" stack will appear as shown
: in Figure 31.
30
-------
-Hyperventilate Users Manual -
Critical Volume Calculation...
typically observed In venting
operations.
The results an plotted in this vay to
emphasize that the degree of
remediation that can be achieved by
venting depends mainly on **
volume of vapor extracted divided
by the initial mass of residual
hydrocarbon. For the example
pictured at the right, approximately
100 liters of air must be vilMravn
from the subsurface in older to
remove about 90% of a single gram
QC/QC(t=0)
1
% Removed
100
Weathered Gasoline
T-20"C
10* moisture content
C(t=0) ~ 222
Return to Design
Figure 29. Card SD5 of the "System Design" stack.
100 200
Qtfm(t=0) (1/g)
Do a Calculation
300
Critical Volume
Predictions...
Simply ewer the temperature at
the iigh.t;*,and then specify'die
composition of your contaminant
If you an unsure about Has, click
on the 'About Composition... *
button located at the loirer right
The model returns output that
allovs you to determine
residual amounts of
compounds falling •within 5
boiling point ranges. Type in
your ovn ranges, or choose
fee default values.
Temperature (*C)
Contaminant
Composition
(choose one)
18
O Enter Distribution
O "Fresh" Gasoline,
® "Weathered" Gasoline
( VievDistributions)
[.—> Set Default BP Ranges <—J
Boilincr Point Ranse Jfl
Boiling Point Range 92
Boiling Point Range *3
Boiling Point Range *4
Boilincr Point Ranro *5
-5fl
?X
80
111
144
t?
to
to
to
to
_2?
??n
in
_m^
250
S
C
c
JL
c
1
Generate Predictions
ten me more about B P
nnges
About Composition...
Figure 30. Card SD6 of the "System Design" stack.
V
31
-------
-Hyperventilate Users Manual -
Step 10: Location: Card SD7 of the "System Design" stack.
Action: Read the instructions, then click on the "~>Import Data<—" button.
Result: Your screen should look like Figure 31. The table in the lower part
of the card lists model predictions: vapor concentration and residual
soil concentration (expressed as a percentage of their initial values),
as well as the composition of the residual (expressed as a percentage
of the total for each boiling point range) as a function of the amount
of air drawn through the contaminated soil. Note that as the volume
of air drawn through the soil increases, the vapor concentration and
residual soil levels decrease, and the composition of the residual
becomes richer in the less volatile compounds (BP Range #5). In
the upper right comer of the card are displayed the saturated, or
initial, vapor concentration and the minimum amount of air that must
be drawn through the soil per gram of initial contaminant to achieve
at least a 90% reduction in the initial residual level. This value is
used in future calculations as a design parameter.
Step 11: Location: Card SD7 of the "System Design" stack.
Action: Click on the "Return to System Design" button
Result: A dialog box will appear asking: "Transfer Critical Volume Value?".
Click on the "Yes" button. You will now be prompted by another
dialog box asking: "What soil unit # is this value for?". Enter "1"
into the appropriate place then click on the "OK" button. You will
now be transferred back to card SD3 of the "System Design" stack.
Note that the value "128.48" has been entered into the "Critical
Volume of Air**" column for the medium sand soil unit.
Step 12: Location: Card SD3 of the "System Design" stack.
Action: Enter "128" into the "Critical Volume of Air**" column for the
clayey silt and fine sand soil units. For this example problem enter
"100" for the efficiency in all three soil units
Result: Card SD3 should now resemble Figure 28.
$
Step 13: Location: Card SD3 of the "System Design" stack.
Action: Click on the right-pointing arrow at the bottom of the page to
advance to Card SD4 of the "System Design" stack.
Result: Card SD4 of the "System Design" stack should appear on your
screen.
Step 14: Location: Card SD4 of the "System Design" stack.
Action: Assume that you wish to remediate this site in 180 days. Enter
"180" in the "Time for Clean-up" column for each soil unit. Click
on the "Update" button.
Result: Hyperventilate calculates a range of flowrates to a single vertical
well, then uses this value and other input parameters to determine
the minimum number of wells required based on two approaches.
32
-------
-Hyperventilate Users Manual -
To read about these, click on the "Number of Wells" column
heading. Your card SIM should resemble Figure 32.
It is important to recognize that model predictions are intended to
serve as guidelines, and are limited in their ability to describe
behavior that might be observed at any given site. One should use
all the information available, in addition to idealized model
predictions to make rational, decisions about the applicability of soil
venting. ;
You can read about the effect of venting at this site in the article:
"Soil Venting at a California Site: Field Data Reconciled with
Theory", by P. C: Johnson, C. C. Stanley, D. L. Byers, D. A.
Benson, and M. A. Acton, in Hydrocarbon Contaminated Soils and
Groundwater: Analysis, Fate, Environmental Health Effects, and
Remediation Volume 7, P. T. Kostecki and E. J. Calabrese, editors,
Lewis Publishers, p.253 - 281,1991. .
-------
'Hyperventilate Users Manual -
Saturated Vapor lo 20S3E*03 I fmefl.1
Cow:«itiatlcm«tlme=a I0'2053"*03 I |m*'L1
FIRST PRESS THE IMPORT
DATABUTTON1
These an the results for the
contaminant type that you have
QtfM(0>
L-airf
g-RSidual
.00
.24
.57
.98
1.49
2.11
2.87
3.81
Vapor
Cone.
[» Initial]
100.000
75*062
58.631
48.078
39.390
31.941
25.916
21.150
Residual
Level
[» Initial]
100.000
95.000
90.022
85.034
80.034
75.035
70.035
65.037
H Hin Volume ID Bemove
>4)fm nf Tnftful B»«ttiMl
jjjjj Temperatun (*C):
O , Contaminant Type:
BP«1
Residual
[» total]
.690
.123
.000
.000
.000
.000
.000
.000
BPI2
Residual
[96 total]
11.650
9.263
6.755
4.512
2.632
1.222
.385
.068
BP«3
Residual
[» total]
24.010
23.982
23.474
22.403
20.771
18.503
15.556
12.053
128 48 ^"m>
g-
IfO.tO | mnHr.11
18 |
Weathered Gasoline
BPS4
Residual
[% total]
22.140
23.000
23.820
24.577
25.248
25.766
26.03t
25.919
BPS5
Residual
[» total]
41.510
43.632
45.950
48.509
51.350
54.509
58.028
61.959
&
'.
!¥!*)
III!)!
Hll)
o
Launch Excel
Return to System Desij
Figure 31. Card SD7 of the "System Design" stack.
Design Input Parameters.
Please enter (1) the desired time period for
remediation, (2) the design gauge vacuum, and
then (3) click the •update" button.
Note: - click on any table heading to get mote info
- use tab key to mon betveen cells
@ ( Update J
Minimum Number of Wells
Description of
Son Unit
Time for
Clean-up
[days]
Design
Vacuum
-------
'Hyperventilate Users Manual -
References
Hutzler, N. J., Murphy, B. EM and Gierke, J. S., State of Technology Review:
Soil Vapor Extraction Systems, U.S.E.P.A, EPA/600/2-89/024, June 1989.
Johnson, P. C., Kemblowski, M. W., and Colthart, J. DM Practical Screening
Models for Soil Venting Applications, NWWA/API Conference on Petroleum
Hydrocarbons and Organic Chemicals in Groundwater, Houston, TX, 1988.
Johnson, P. C., Stanley, C. C., Kemblowski, M., W., Byers, D. L., and
Colthart, J. D., A Practical Approach to the Design, Operation, and Monitoring of
In Situ Soil Venting Systems, to appear in Ground Water Monitoring Review,
Spring 1990.
Marley, M. C., and Hoag, G. E., Induced Soil Venting for the
Recovery/Restoration of Gasoline Hydrocarbons in the Vadose Zone, NWWA/API
Conference on Petroleum Hydrocarbons and Organic Chemicals in Groundwater,
Houston, TX, 1984.
Marley, M. C., Baehr, A. L., and Hull, M. F., Evaluation of Air-Permeability in
the Unsaturated Zone using Pneumatic Pump Tests: 1. Theoretical Considerations,
in review, 1990.
Thornton, J. S. and Wootan, W. L., Venting for the Removal of Hydrocarbon
Vapors from Gasoline Contaminated Soil, J. Environ. Scl Health, A 17(1), 31-44,
1982.
Newell, C. J., Haasbeek, J. F., and Bedient, P. B., OASIS: A Graphical Decision
Support System for Ground-Water Contaminant Modeling, Ground Water, 28 (2),
224 - 234, March - April 1990.
35
-------
-------
-Hyperventilate Users Manual -
Appendix A: "Soil Venting Stack" stack cards.
-------
-------
'Soil Venting Stack' Cards
A1
A Practical Approach to the
Design, Operrioa, ml
Uomtoring of In-Sita Soil
Venting Systems
This HyperCard Slack
through the thought p
created to help guide environmental nentists
y to decide if and bov toil renting might
ha applied to
foUomthe
TBnstte. Tha organization ml logic of this stack
P. C. miMM.C. C. twain,*- W. SLnUonU, J. ». CoMut. * D. L. Bjra
published in Ground Water Monitoring Reviev, Spring 1990. p. 159-178
In-Sitn Soil Venting System Design Process
AtoatSoilV*
Oijtra
en ta|B> M «• «n «« «• puna tycttcUif a ate «• tMk a Spffl Dbowm*- fcu. or «•
' - "• '
Soil Venting («.k.a. "uxinisoil
*ia-silu vapor mncbon') is
raptdJy bamming on of U» mo«t
influent* tbefueeen of toy »oil
wnUngopa
undentood.
Pralimiitmfy Site InvwHigation
orSfrll DucowumJ...
In U» foUoviagcardf vi vill aaumt
lhat * leak or ipill tea bam discovered,
andUeappropriataeiaErgencrreioni
B Tflfl i Tti'ffliaiytfK'H pr?i7iftfn tf fiftlff^lftTf
or (utpKtal, a, site invesngatton is conducted to
characterize and delineate Ua zone of soil and
groundviter contaminatioo. In general, tb> site
HOVVB will ctep through « logical
thought procanto dead* if »U Mtfiag
iiBppropriakiatthiia*). The preview
card display 00 flovcnnt that it tfae
basis (of tix) tbot^tt prouu. Clicking
vilhin any prootsf box via take you to
that action of the «»aci dealing vith
that aspect of d» tbougbt proaa.
uDnvdiaBi inyact on poutiilial huiuauaod
virocnnBBb) mton. and is conducted in a
nlatMy ihort period of hm{dayi). A dstailad
alia elm aHm uation than follow. Itspurpoa, like
tteanergencyrespomgxnl abatement phase, is to
dulHiuunv potoBbial nttgratioo pattivays and
til impact associated vith prennt
b Venting Appropriate?
Screen Treatment AltematiTes
With any oontanuntednki, one should
BinlorettafBanbilityofantreanM
procnns. After oompilm,} • list 01
At this pout m vill p
O IncinBranon
O Composting
O Land Farming
Oln-Situ
impte thought process to decide if soil
venting is a (eeahleallBmaliw. As
mentiotBd earlier, the three main factors thai
govern the succesi of a venting operation are:
be eKaUished, and than tna final
choices)
- vapor flovnte
- vapor *^""""*>
- subiurAcB Miaiig^&pby (or tfa§ loution of
QSolidifialionfilabilizalMD
OSohent ExtnctionSoil Washing
Soil Venting it meat likely tote
cuccBsdld VDB&joilf aremly and Ite
-------
•Soil Venting Stack* Cards
A2
Fknrnf* KHuamtaam:
1) Canon loBT)n, or
O Medium Sand
9 Fin Sod
OSiltySana
O Clayey Silt.
O Input Your Ovn Permeability Range
Permeability Range
i i i u> i in i
WellRaditB
Radios of Inftatoc*
Vapor Concentration Estimate
Tba
rate secure vlnumur tha vapon
renjpvBd by venting vs "saturated*
or in equilibrium vilh the
In the ani card you villc
ofyoureofBanuanl. JurtfoUov
fl> in-tructioni in tt» upper left
eoner of the not cent.
Vapor Concentration Estimation -
T) Type to Temperature (*C) (hit ) [~
Click to Enter Composition of C<
[2J or
ChMM one of the Default DiHributioni
(T) Click to Viev Dirtritaitionj, (optional)
[T) Click to PBrfonnCalculationi
O Enter Dirthbution
O "Fresh* Gasolin
( VievDirthbulioDi 1
OPafonDCakadaliooi
Removal Rate Estimates
J.UIDOV81 T***V OCCWS VDfiUf
Un vapon removed by venting j
'saturated' or in
equilibrium vith the
Extimztod
Removal - Vapor z Vapor
Rate Concentration Flovnte
Sum of Man Fraction
Calc. Vapor PTCBUT*
Tha 'Reoxmt Rate' i* (imply
the product «f tba Oovrate
tum IhB *ffltl"l' f^.HM.BBfrlrt17B
The TClu* yon iapiA on Cardf
(fclOvillaauMlto
vith jow dennd removal rata.
Enter Deand
RamdiatioB Time
ays
don not mad your danrad
removal rate, then Mil venting
if DM likely to matt your medi, I
and you ifaoukl oonnder another |
technology^ or Bosks
Singto Vntieal Will KmoOU
In the npl cards, ve vill refine \
*.[£•*
VeatiqgAfptoprimti? - &*fiaeJfrtim*ttt
The pnc8diQff cftuDstu m
useful only •> a •{Snteut*. and
should be refined if venting it
itill a potentially taribto
option.
Typically during foil venting.
tot metrured vapor
toe plot on the rigjtf
(vhen th> tote] vapor flovrate
ii relatively conttmi).
Man P**iMC*lcat*tx>a*
Pictml fltlbs r^gfaiw
resuHt of mnpifl ™r<**a*
predictionf,for«
, OOCjC(t-0)
Tn§ wuual ans nplttanni
•d
[C(tyC(t-0)l
or nonnaliad removal rates
total vdurnt of vapor
300
-------
•Soil Venting Stack" Cards
A3
Is Vejitiag Appropriate?
Other fltinridnntiba*
of to data and rente.
Based upon than number*, a
should g™ yousomt
Ilk]:
(uo* T«> i«cmi
appropriate wrtuig ii for
yourapplialion. Note that
Qas it tl» nmnter of valli if
Mia Vol alAfe |U|-mUMl|:
Lov Permeability Lenses
1b tan Aon •*. click
Field Tests
/•Mt/STfc
Prior to tba design or ai
obtaiii m&n rafiDBd ost
potential vapor flovrab
rft"**>¥>"'*f'> vapor cone
1 IB BtU toil Q
irabtoto
jnatejoftto
ability.
«, and
sntnttioDs. In
tyiluiu nffi1* te uBtaUod, tben
aquifer doracteristia nut also be
determund. -
Click on the button to OB rigB to
tarn about tlnse lasts, or to analyze
data that you hme already collected. O
. Air Pannaahility Tait
Aquifar Characterizatioa
System Design
-------
"Soil Venting Stack" Cards
A4
System Design...
AttharijtttifaltstoraBCMnpoamti
«f a venting fyjtamdaagn. Click on
t*ett to coaSiEt tte jwtimtiiii
OKwnftar of Ettnetira Wall*
O Wall
O
Q
O Vapor Treatment
System Monitoring..
Tto fttffotiDMDCB of •
luzu DQUA bo iQDQikWBd ilk onlsr
to mutt flfficiflEi ojMnEbon, and
to bBtp dfitenoiDB vbm to chut off
Tio
O Vapor Flow RUM
At t miiMiEua, tba itemt Ibtad to
UB ri^rt tbould be nwwimL
•Click' on My oaB to get mon
O Vapor ConcantralioBf k Compoatiom
OTonpamlun
OVatar TmblB Lmd
O Soil Gta Concutntion fc Coopoation
System Shut Down...
Target »c«I dasn-uj) tonb an
often nt on a ow-iy-ntB batii,
mdanbasadontteeftiniated
potential imp«rt that any
raniltal may bam on air
lity, ^oundvahr quality, or
otharhB«mutai>danJt.
O CmaHatiw Amaont Ramomd
O EaJr«Uon WaU Vapor Coocramiion
O EatraetioB Watt Vapor CompontioD
OSoilGaiData
QSoU Boring Data
Economics...
For typic&l ttrvm station sites,
HOOK - J250K for the wrting
oporvboD BOOB, dflpeoding on
UB oocnphrpty of Ibo sits,
dtMtHB) tine, pBnnitting
and Ite typn of
•Click- oo any itam belov (aV
hold boUoDdovn) long costi
•ncocirtad vitb that item.
Acknowledgements...
I
I*
-------
-Hyperventilate Users Manual -
Appendix B: "Soil Venting Help Stack" stack cards.
-------
-------
"Soil Venting "Help Stack* Cards
B1
Help: Stack Information
Help: About Soil Venting
ate iofanaiuii ataat ton vcnina on te fool m the fdooiaa sttMeK
in Oramiwuei, HOMEU, TX, 1984.
P. C lahoMB, M. W. Kcmblmnki. «ui I. D. CoUhul, Raaicii
VMI
ia O
N. J. Hacdn, 8. E. Mmpby. md J. S. Okrtt. Slue of Tcdmoloiy Rcvvw: Soil Vipoi Einraos
, IMt. "
D. J. Wilion, A. N. Oatte, mA J. R date. Soil Oun-up by mom
MafeUnf. Sep. Socnce Toct. 23591-1037. 19U.
Buttons
Biuuni have been placed in each
card. Clicking on any button will
pcitunu an action, neb as:
OoHomnGnl
cninVeBiiiaSw*
When curious, click on Symbols,
Picture or Text.
Fields
Reids may contain information, or they may be
a place for you 10 input munben.
Scrolling Field:
didc a smsi • aw
XcEcB lae sown, H
mow tm to» up or daw
win UK mouse.
Inihi»atM.TOiicm _
Boxed DaU Field:
Try this example:
Bpttr Number is Baa
I II inches
Help: fa-Situ Soil Venting System Design Process
Help: Preliminary Site Investigation
This i> the decision process that one must follow to:
1) decide if toil venting is applicable at a given rite
&
2) deaign an effective aoil venting system
It ia an abridged version of Figure 2 In M Practical Approach to rA* Duign,
OptnUUM.
-------
"Soil Venting Help Stack" Cards
B2
Help: In-Situ Biostimulation
Help: Solidification / Stabilization
Fnctit Dtterifttoit
Pnctit Diteriptio*
Treatment of groundwtter tad toil
contamination below the water able
(•saturated zone*) by iwitu
bioeumulition involves the iddition
of nutrients and/or O2 (usually aa
H2OZ or liquid O2) to to aquifer in
order to enJitnce the de0adstion of
die hydrocarbons by indigenous toil
microbes. The nutrient! tud
oxygen trc added tbove (round to
Stabilization ind solidification «re
Ubauiient processes designed lo
either improve waste handling and
physics! chjuacterisQcs, decrease
surface am scrota which potlutanU
an teach, or limit the solubility of
hazardous comuratati. When
discussing thiJ technology, the
following definition.!
Solidification.
Help: Solvent Extraction / Soil Washing
Proctti D€fcriptton
"Solvent 010*0100" it the process
by wnicn contaminants aits nnweu
from toil* or sludges by mixing
them with a solvent into which the
contaminants preferentially
partition. Which solvent is used for
any particular treatment it very
dependent upon the type of
contaminant present in the coil.
Ihe solvent ihould have * high
affinity for the contanuntm(t) of
Help: Soil Permeability
NaB fttfk den.*,
onta. while K
coqducivuy'. The Mo «• nttmt fcy:
Help: Decision Matrix
(1) - Offcrouconpouadi trill »aiy m
fteir«ssMtf
Help: Vapor Flowrate per Unit Well Thickness
veil li/aa-if] a (ami
t jOl a lO*»Aan» n-1 «n
Help: Unit Conversion (k and K)
Bad miai - <** for «dl olcaluioo!)
Convert Rcm
O cnvk
O Wd
® cm2
O darcy
Help: Compound List
Vkw Only Mode I
ConuMnnd Name
Friction WcifM
V.BW
1
2
3
4
J
6
7
8
9
10
propane
isotelane
it-butane
tnni-2^>utcnc
cis-2-butene
3-mwhyl-l-butene
isopentane
1-pentene
2Hnethyl-l-butene
2-methyJ- 1 J-buiadiene
0.00
0.00
0
0
0
0
0.0069
0.0005
0.0008
0.0000
f "1.00660 1
44.1
58.1
58.1
56.1
56.1
70.1
72.2
70.1
70.1
6S.1
IJ A
2JJ
2.11 I
\yi 1
I.W I
OM i
0.71 I
"•' 1
Oil 1
045 C
» torn «f Mist PrtcDoo.
(.bouUte-1)
-------
"Soil Venting Help Stack" Cards
B3
Summary Card: Site Characterization
Compound List Default Data
mult determine Ihe following:
SttbivrFacc Characteristics
Contaminant Delineation
• emt rf heftfoaK aydraibn
duncaaMiaof etsoaa nl kyot
teenwtiliiy «ejiii
Help: Data for Fortran Program
Help: How Do I Measure a Distribution?
V*nr
* Compound Name
i<'Q (Ana) SolulaSly DuL
Wat* 01 @T.
(em) An 20'C
Cocff Din.
BHB-I^ume
2-mabyi.l
44.1
31.1
58.1
5«.l
36.1
70.1
74£
70.1
70.1
M.I
8J
2.93
2.11
1.97
1.79
0.96
0.71
0.7
OJS7
OJS3
62
49
61
430
430
130
41
141
155
M2
73
537
944
204
204
708
1(62
710
923
323
OJ)0
OjOO
0
0
0
0
0.00«9
0.0005
0.000*
0.0000
ieriet cdtmibs clMin iltm (n-kuuB, n-penoa:.
Help: Calculate a Distribution
rlelp: About Calculation
In this estimation of equilibrium
mnted) vipor concenntioni,
we attume that the con&uninmu
Buerte*
1000
5000
7000
VOtt
OM
OM
0.00000
0.07C92
0.3*4«2
OJ3844
0.00000
0.00000
0.00000
0.00000
0.00000
0.00000
(>200 aiffeg TPH) DIM it is
distributed between vapor,
loitacd, diiiolved-in-wil-
moiraire, A fice-phasei. In thii
cue. the equation at the light
applia Oook for 'Raouli'f Uw*
A the "Ideal Cat UW in any
ttennodynamici textbook for
i[unij
M.
K
T
RT
Help: 6a) Dilution Effects [Bypassing]
Help; 6b) Liquid Layers
vqwrflow
flow
SU* View
View
Tlie figure above depict* tile ate where aome vapora bypaia* zone* of
anwmination, and Ihcrcfore the vtpon removed from Ihe euraction well
repreaeni a routrarc of 0ie vapon obtained from both contanunated and clean
vapor flowpuhf. One can roughly judge the amount of bypatnni by Ihe well
placement, icreoiing, t«i cocBaniinanJ diitribulion. Cenenlly, obterad
In Figure 6b, vapor flows parallel to, but not through, the zone of
contamination, and the significant maw transfer resistance i* vapor phase
This would be Ihe case for a layer of liquid hydrocarbon rating on
mpcnneable strati or the water table. This problem was
NWW,
ihotu Me Eauvllont
Return
left DO • Calculation
-------
"Soil Venting Help Stack* Cards
B4
Help: 6c) Low Permeability Lenses - Equations
Help: 6c) Low Permeability Lenses
Derivnuona for these
cqu>Uon> ire given in
Johnson, et al • "A Practical
Approach to the Design.
Operation and Monitoring
of In Situ Soil Venting
Systems" - 1990.
In the situation depicted above, vapor flows past, rather than through the
contaminated soil zone, such M might be the cue for a contaminated city ten
surrounded by sandy soils. In this cue vapor diffusion through the clay to the
flowinRVaoor limits the removal rate fthc removal rate actually become!
These Equations are valid
test's Do sj Calculation
Help: Default Boiling Point Ranges
Help: Boundary Layer Equations
The Fonnn program HYPEVEKT will report residual levels of compound!
Ailing between user specified boiling point ranges. The default value* have
been chosen 10-4 s>cm«
* nil pnBB«bil]iy n v^por flew [cm2]
a dacsm of smcacd ouov.1 [cm]
'= ndius of mnuracc of wnui well |cm)
|VcUn4iiiB(aBl
•an -1J161106 j/an-«Z
> il Itae VCBB>( «r<41 [fjcm42]
• ie(ioo m wluch c
Help: Boundary Layer Equations - Calculation
Help: Low Permeability Lenses - Calculation
3] C -> Calculate <-- J
T)Soll Tjtpt (choose one)
QSiHySjml
Q Input You Ova tamubi£9 Bmie
; ; I to I 10 I Idarcjrsl
T) ProccM Variables)
Jun enter valua into the
approprUtc field*, then click on
the "calculate" button.
The "Relative Efficiency" U the
ratio of the predicted removal
rate to the removal rale that
would be obtained if the euncied
vapon wen saturated, or in
equilibrium with the liquid
Relative Efficiency
(*)
Ground Water Table Upwelling
Date and Time...
During venting, the pressure
within the radius of influence of
the vapor extraction well is
lowered, due to fee applied
vacuum. This lowering of the
pnsnire affects the groundwater
level in this zone, and an
"upwclling", or local rise in the
water table will occur.
The local water table rise can be
u great as the gauge vacuum
applied at the extraction well
Generally, the DATE and TIME
Should be recanted along with any
uuremeni that is made. Given the
time scale for vcnting-relsted
processes, recording the time to the
nearest minute should be sufficient.
Sample devices are Rokex watches,
hour glasses, sun dials, and timers.
-------
-Soil Venting Help Stack* Cards
B5
Vapor Flow Rates...
Pressure/Vacuum Readings.
Vipor flow rates from ctdi
ounelion well and into my injection
welUihould be monitored.
Simple measuring device* include
pitol tubes, oriface plates and 4
rotameten. it "a important to have
cilibnted these devioet M Ibc field
operating prciiiini Mid temperature*
Pftsnu is/Vacuums should be
measured it each extraction and
injection mil. In addition. subsurfaee|
pressure distributions (measured with
vsdose zone installations) are useful
for determining the zone of influence
aid vapor flow pathi.
Vapor Concentrations & Composition...
Temperature...
The vapor concentration and
composition from each extraction
well should be analyzed periodically.
Thit data is multiplied by the
extraction well flownte to calculate
the removal nte (i.e. IWdiy), and
cumulative amount of contaminant
removed.
By iuelf, vapor eoncentniion data
doe* not give a complete picture of
the system's performance. Decreaiei
TeJnBif
The soil and ambient tempcraoirei
can have a significant effect on the
performance of soil venting system!
The soil temperature affects the
contaminant vapor concentrations,
while the ambient temperature
contrail whether or not condensation,
or even freezing will be significant.
For future reference, therefore, it is
useful to record UK ambient and soil
tempefaoires.
-------
•Soil Venting Help Stack* Cards
B6
Extraction Well Vapor Composition...
Soil Gas Data...
EXTRACTION WELL VAPOR
COMPOSITION
when combined with vipor
concentrations ihif da* gives more
insight into the effectiveness of die
system. If the lout vipor
concentration dfrmiei without •
change in composition* it is
probably due to increased m«s
transfer retuuncc (water table
upwelling, drying-out of low
permeability looet, etc.). and is not
SOIL GAS DATA
this data 'a the most useful because
it yields information about the
residual composition snd extent of
Vspor concentntian can not, in
genera), be used to determine the
residual levd, except in the limit of
very low residual levels (when
vapor concentrations are
proportional to soil residual levels).
Soil Cat Monitoring
Installation Results
r.Sft
SOIL BORING DATA
Generally confirmation (oil barings
are taken once a system is turned
off, and these sie often analyzed for
TPH (total petroleum
hydrocarbons) and volatile
residuals.
One should keep in mind (hit TPH
results can often be misleading.
since they reveal nothing about the
composition of the residual or its
Bont
Bcfm
B-l
B-2
B-3
Ate
B-4
B-i
BJS
TPH
fmsAtl
1200
14OOO
S600
20
120
5
BTBX
(ni/ktl
20
120
400
ND
O.I
ND
-------
-HyperVentilate Users Manual -
Appendix C: "Air Permeability Test" stack cards.
-------
-------
"Air Permeability Stack" Cards
C1
Air Permeability Tests...
The purpose of an air permeability lest it
to obtain siie-spocific data Oat will be
used in the final system design. It is a
way to verify thai venting is an
appropriate remediation technique for
your site.
In particular, one typically tries to get a
better estimate of the soil permeability of
each distinct soil layer to be mated, and
a bcoer estimate of contaminant vapor
concenlrations
( Show Me Set-Upj
[ Test Instructions
Calculate <- J
•Hoc nEina a Pn> Volume:
fr"3
Air Permeability Test - Sample Data
• , ,
Pictured at file right are the
soil vacuum measurements
from an air permeability
tat conducted in a silly
The specific operating
conditions and site
characteristics arc described
in "A Practical Approach to
the Design, Operation, and
Monitoring of In Situ Soil '
Venting Systems-, by P. C
Time(nun)
Air Permeability Test - Data Analysis
The expected decrease in subsurface pressure (increase in gauge vacuum) P* is
predicted by: <*eJota«.B«l(l990)forcta1».»D>
F(r,t) =
4itm(k/|i)
f *•
J *.r
Air Permeability Test - Data Analysis (cont.)
For (r* cuH k Pi»» I) < 0.1, the governing equation can be approximated by the
expression:
.[ -0.5772 - I
ln(t)J
This Equation predicts that a plot of P1 -vs- ln(t) should be a straight line with slope
A and y-tntercept B equal to:
Air Permeability Test - Data Analysis (cont.)
The permeability, k, can men be calculated by one of two mohodi;
/yv The first is applicable when both Q (flowrate) and m (well icreen interval) are
^ known accurately. The calculated slope A is used:
The second approadi is used whenever Q or m are not known wilh confidence.
In ihiJ case. both, the slope, A, and intercept, B, are used:
t •.«* 0,5772 + £.)]
Air Permeability Test - Data Analysis (cont.)
-------
"Air Permeability Stack" Cards
C2
Air Permeability Test - Data Analysis (cont.)
4tf»jMil>pt>enliI»llBTOnaim»
-------
-Hyperventilate Users Manual -
Appendix D: "Aquifer Characterization" stack cards.
-------
-------
'Aquifer Characterization" Stack Cards
D1
Aquifer Characterization:
To achieve efficient venting, the
hydrocarbon-contaminated ml must
be exposed to air flow, therefore, in
most case* where the residual nil
contamination lies close to, or below,
the unrated toil zone (grouadwster
able), it will be necectaiy to
incoipontte a groundwater punping
system in the vapor cunoioo system
design*
A« mentioned previously, one mut
always be aware of the troundwater
Aquifer Characterization:
Since mod venting systems are installed tbove "phreatic squifen" (aquifen with
unconfraed upper tarlmctt), the two primary aquifer parameters needed for daign
K » hydraulic conductivity
S - effective porwity (or tpecifie yield)
The fint parameter repreienti a convenient combination of the fundamental
parameter*: permeability, deraity, and vitcoiity:
where;
Aquifer Characterization:
These parameters (K and S) can be estimated iving the result* of • nmoud traoiicnt
groundwaur pump ten with a connant punning me. The resuiu arc then compared
igainn nandard "type curve** for specific aquifer lituations (i.e. leaky, unconfmcd
iquifen, etc.).
Presa the "Reference!" button below for more information on dug tests, bail tens,
pump teat, and data analysis.
1 to Main Stack ]
Aquifer Characterization - References
}. Bear. "Hydraulics of Groundwater", McGraw-Hill, 1979. ISBN 0-07-004170-9,
p. 463-490.
R. A. freeze and I. A. Cherry, "Groundw.ter-. Premice-Hali, 1979. ISBN
0-13-365312-9, p. 339 - 35Z
-------
-------
- Hyperventilate Users Maraud -
Appendix E: "System Design" stack cards.
-------
-------
"System Design* Stack Cards
E1
h '
\j
Number of Venting Wells...
lumber of ettacBOB well* ia inaSar ID Of
ea'fanfxxialjilodctniBB
ipf«o"naa> « • •*•» "»»•
m Ot *Ufib»' btutoo. tad Ota poacd •>
i (i». dick Stl 0«t»»lt BP
Boilim Faint Raiwe »5
-5.0...
...at...
.8ft...
.UL.
...2ft..;
........
...Ul..
Removal Efficiency...
IBB mbuface ia difficiill n cbanocriae, aid
lanly oanf onaa to oar ttodan of a "auHlbta".
Tbaw an tme amend damoa of Btouicoa But
will caaac mliif nmtnal «Ea • BB baiBtaD
BMo pnotcM tat
-------
•System Design' Stack Cards
E2
Help: Well Parameters
Help: Minimum Number of Wells
a Nomber of Won.- ii c*lcBB«l by a» mv BKlbodi dimmed bdo«r
to pan* «r flaw dmmsk to ammamm* ne MYOB hm
MtenailamgrcoBiMiaMio^
teflBBM* if « aBKtiai «dl, few
Ri1
Contaminant Composition
Vttw only Mod«
CorapoiDd Nimc
Man
Fraclira
Molccibr
Wrijhl d) Ol II TC
I
2
3
4
S
6
7
8
9
10
propane
isobutftjK
n-buuae
tnin-Z-butcnc
c«-2-buteoe
3-methyl-l-buune
uopodine
1-pentene
2-nmhyl-l-buiene
2^n«hyl-l J-butadiene
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
44.1
58.1
58.1
S6.1
S6.1
70.1
72.2
70.1
70.1
68.1
" 2
193
111
1.97
1.79
0.96
0.78 |
0.7
0.67
0.65 C
Flow Do I Measure a Distribution?
Detamining ihe ejuet oompoeuoo of
u>iiykn mixtures
(nich u guoline) requtrei ipeciftlized
•nalytUal technique*. For the purpose of
cnimaimg the roponsc to vouing, however,
ipproximuc compoiitiaa on be tiled widi
voy good result*.
one mu*t unftyze the mixture by gu
nphic «n*ly»o. Prior to the
Butyia. ehoOK about 6-10 muter
ompoundt who«t proptrue* «ie wdl known.
Calculate a Distribution
aGCoatyica
0X10
OJOO
111)
OJOO
OM
OJDO
OM
OXK)
DM
0.00000
0.00000
1.00000
0.00000
0.00000
0.00000
0.00000
0.00000
To be able to nicceafuUy locate i
attraction well*, passive wells,
and surface seals one must have a
good undemanding of vapor flow
behavior. Wells locations should
be chosen to maximize vapor flow
through the contaminated zone,
while minimizing vapor flow
through other zones.
If one well is sufficient, it should
almost always be placed in the
geometric center of the
I
Well Construction
Surface Seals
Wells should be screened only
unless the permeability to vapor
flow is so low thst removal rates
would be greater if flow were
induced in an adjacent soil layer.
Removal rate estimates for various
msss-tzaosfer limited scenarios m
discussed elsewhere in this suck.
Based on predictive equations, the
dowrate is expected to increase by
15* what the extraction well
rvCFipe
Surface mil, such as
polymer-based linen and asphalt,
concrete, or clay ops, are
sometimes used to control the
vapor flow paths. Figure 12
illustrates the effect thai a surface
seal will have on vapor flow
patterns. For shallow ^*ffi^trrf
zones <
-------
"System Design" Stack Cards
E3
Groundwater Pumping Systems
In cue* wheie oonaminated toil*
lie jun above or below die water
table, (rouadwMcr pumping
ijrstena will be required to insure
tint contaminated aoila remain
espoied. In designing a
groundwiter system it u
irapomm to be awue itat
upwelling (draw-up) of the
groundwiter table will occur
when • vKuum it »ppUed it die
attraction weU
(tee the figure ai the right).
Vapor Treatment Systems
Currently there * four main
itmoit aroaeut* available:
VAPOR COMBUSTION UNITS:
Vapors are incinerated «nd
denrucuon efficiencies «re
typically >9S*. A supplenwnial
fuel, such u propane, it added
before combustion unlen
extraction well vapor
concentntions are on Ibe order of
-------
-------
-Hyperventilate Users Manual -
Appendix F: "Compound List Update" stack cards.
-------
-------
'Compound List Update' Stack Cards
F1
Compound List Update
Thi« cvd U provided u i utility Co let you »dd, or delete compound! from the
Compound Lift Du* B«e thit thii program uicx. You miy not delete or ohmge Ibc
properties of (he bnw <2 compounds, fince ttoe vc needed for the two definite
guoline cue odcuUtion (U. the "Frcih" and "Weathered* guolinet). If you wish
to chinge toy of the propertei of the idded chemicals, firet delete them, then
reiraert them into the Con^oand Lilt DtuBtte. Follow the direction below:
egftefbOmim:
(meanly 30
Ckcminl N»inc;lNe»Comg
otlcn)
Molcutor Wdikl [l/mot«]
Vmpor Pm»n «2IC J.titi)
8«Uli« Pei.l 01 aim (C|
-------
-------
-HyperventilateUsers Manual-
Appendix G: Reprint of:
"A Practical Approach to the Design, Operation, and
Monitoring of In Situ Soil Venting Systems"
-------
-------
Reprinted from the Spring 1990 Issue of
Ground Water Monitoring Review
A Practical Approach to the Design,
Operation, and Monitoring of In Situ
Soil-Venting Systems
by P.C. Johnson, CC. Stanley, M.W. Kemblowski, D.L. Byers, and J.D. Colthart
Abstract
When operated properly, in situ soil venting or vapor extraction can be one of the most cost-effective remediation
processes for soils contaminated with gasoline, solvents, or other relatively .volatile compounds. The components of
soil-venting systems are typically off-the-shelf items, and the installation of wells and trenches can be done by
reputable environmental firms. However, the design, operation, and monitoring of soil-venting systems are not
trivial. In fact, choosing whether or not venting should be applied at a given site is a difficult decision in itself. If
one decides to utilize venting, design criteria involving the number of wells, well spacing, well location, well construc-
tion, and vapor treatment systems must be addressed. A series of questions must be addressed to decide if venting
is appropriate at a given site and to design cost-effective in situ soil-venting systems. This series of steps and questions
forms a "decision tree" process. The development of this approach is an attempt to identify the limitations of in
situ soil venting, and subjects or behavior that are currently difficult to quantify and for which future study is needed.
Introduction
When operated properly, in situ soil venting or vapor
extraction can be a cost-effective remediation process
for soils contaminated with gasoline, solvents, or other
relatively volatile compounds. A "basic" system, such
as the one shown in Figure 1, couples vapor extraction
(recovery) wells with blowers or vacuum pumps to
remove vapors from the vadose zone and thereby reduce
residual levels of soil contaminants. More complex sys-
tems, incorporate trenches, air injection wells, passive-
wells, and surface seals. Above-ground treatment sys-
tems condense, adsorb, or incinerate vapors; in some
cases vapors are simply emitted to the atmosphere
through diffuser stacks. In situ soil venting is an espe-
cially attractive treatment option because the soil is
treated in place, sophisticated equipment is not
required, and the cost is typically lower than other
options.
The basic phenomena governing the performance of
soil-venting systems are easily understood. By applying
a vacuum and removing vapors from extraction wells,
vapor flow through the unsaturated soil zone is induced.
Contaminants volatilize from the soil matrix and are
swept by the carrier gas flow (primarily air) to the extrac-
tion wells or trenches. Many complex processes occur
on the microscale, however, the three main factors that
control the performance of a venting operation are the
chemical composition of the contaminant, vapor flow
rates through the unsaturated zone, and the flow path
of carrier vapors relative to the location of the contamin-
ants.
The components of soil-venting systems are typically
off-the-shelf items, and the installation of wells and
trenches can be done by reputable environmental firms.
However, the design, operation, and monitoring of soil-
venting systems is not trivial. In fact, choosing whether
or not venting should be applied at a given site is a
difficult question in itself. If one decides to utilize vent-
ing, design criteria involving the number of wells, well
spacing, well location, well construction, and vapor
treatment systems must be addressed. It is the current
state-of-the-art that such questions are answered more
by experience than by rigorous logic. This is evidenced
by published soil venting "success stories" (see Hutzler
et at. 1988 for a good review), which rarely include
insight into the design process.
In this paper, a series of questions are presented that
must be addressed to:
• Decide if venting is appropriate at a given site.
• Design cost-effective in situ soil-venting systems.
This series of steps and questions forms a "decision
tree" process. The development of this approach is an
attempt to identify the limitations of in situ soil venting,
and subjects or behavior that are currently difficult to
quantify and for which future study is needed.
The "Practical Approach"
Figure 2 presents a flow chart of the process dis-
cussed in this paper. Each step of the flow chart will be
discussed in detail, and where appropriate, examples
are given.
The Site Characterization
Whenever a soil contamination problem is detected
or suspected, a site investigation is conducted to charac-
-------
terize and delineate the zone of soil arid ground water
contamination. In general, the site characterization is
conducted in two stages. The emergency response and
abatement phase assesses the immediate impact on
potential human and environmental receptors, and is
conducted in a relatively short period of time (days). A
detailed site characterization then follows. Its purpose,
like the emergency response and abatement phase, is
to determine potential migration pathways and assess
the environmental impact associated with present condi-
tions and future migration of the contaminants. Often
the sequence of steps following initial response and
abatement is as follows:
• Background review: Involves assembling historical
records, plot plans, engineering drawings (showing
utility lines), and interviewing site personnel. This
information is used to help identify the contaminant,
probable source of release, zone of contamination,
and potentially impacted areas (neighbors, drinking
water supplies, etc.).
• Preliminary site screening: Preliminary screening
tools such as soil-gas surveys and cone penetrometers
are used to roughly define the zone of contamination
and the site geology. Knowledge of site geology is
essential to determine probable migration of conta-
minants through the unsaturated zone.
• Detailed site characterization: Soil borings are drilled
and monitoring wells are installed.
• Contaminant characterization: Soil and ground water
samples are analyzed to determine contaminant con-
centrations and compositions.
Costs associated with site investigations can be rela-
tively high depending on the complexity of the site and
size of the spill or leak. For large spills and complex
site geological/hydrogeologica! conditions, site investi-
gation costs may begin to approach remediation costs.
In addition, the choice and design of a remediation
system is based on the data obtained during the site
investigation. For these reasons it is important to ensure
that specific information is collected, and to validate the
quality of the data.
If it is presumed that in situ soil venting will be a
candidate for treatment, then the following information
needs to be obtained during the preliminary site investi-
gation:
• Subsurface characteristics — site geology: This
includes the determination of soil stratigraphy (va-
dose and saturated zone) and characteristics of dis-
tinct soil layers (i.e., soil type, permeability estimates).
While they are not essential, the moisture content,
total organic carbon, and permeability of each distinct
soil layer also provides useful information that can
be used to choose and design a remediation system.
* Subsurface characteristics — site hydrogeology:
Depth to ground water, and the ground water gradi-
ent must be known, as well as estimates of the aquifer
hydraulic conductivity.
• Contaminant delineation: The distribution of con-
taminants in the saturated and vadose zones needs
to be assessed. This includes the extent of the free-
phase hydrocarbon, residual hydrocarbon, and solu-
Vapor Treatment
Unit
Vapor
Flow
- Vapor Extraction Weil
Contaminated
Soil
Vapor
Flow
Free-Liquid
Hydrocarbon
Groundwater Table
Soluble
Plume
Figure. 1. "Basic" in silu soil-venling system.
Process
Output
Background Review
Sifp rhararfpi-Kfirs:
Sutmirfacf Cbaracfmitkft
* charactentnct of Aicinc! tod laycn
(pcrmeabiliiy estimates, icil typci)
• depth to groundwater
• {Toiindwaicx gradient
* aquifer permeability (estimate) '
• lutttilrface & ittaVc-gr-
j T7 — ~ — h
1
| Ground water Pump Test | *
^ -^
- removal rale alimxlc* 1
• vapof fiowrate euunatea I
* final Riidual fcvel* A. composition ]
- air pcnpcvtilitjr of difiinct 101) Mycn
• radius of influence of vapor wcljj
• initial vapor conc«rtntf ion»
• tadtux of influence ]
* pumping r»e decenninaiion |
number of vapor extraction w
vapor *d( ccfuituction
vapor well fpaaiy
maunoM tysem
(vieuuin) ipcdficaioni
|roundw*ia pumping lytiem ipecifici
v«iti«t iwovery mei
System Shut-Off
Figure 2. In situ soil-venting system design process.
-------
hie hydrocarbon. Soil samples should be analyzed to
determine which contaminants are present at what
levels (contaminant composition). Specific analytical
methods should be used to identify target compounds
(i.e., benzene, toluene, or xylenes) and total hydrocar-
bons present. For soil analyses these methods are:
EPA 8240. 8020, 8010 - volatile organic chemicals
(VOCs)
EPA 8270 - semivolatile organic chemicals
EPA 418.1 - total petroleum hydrocarbons (TPH).
The corresponding methods for water samples are:
EPA 8240, 8020, 8010 - volatile organic chemicals
{VOCs)
EPA 8270 - semivolatile organic chemicals
EPA 418.1 - total petroleum hydrocarbons (TPH).
With the current high cost of chemical analyses it
is important to intelligently select which analyses
should be performed and which samples should be
sent to a certified laboratory. Local regulations usu-
ally require that a minimum number of soil borings
be performed, and target compounds must be ana-
lyzed based on the suspected composition of the con-
tamination. Costs can be minimized and more data
obtained by utilizing field screening tools, such as
hand-held vapor meters or portable field gas chroma-
tographs (GCs). These instruments can be used to
measure both residual soil contamination levels and
headspace vapors above contaminated soils. At a
minimum, soil samples corresponding to lithology
changes or obvious changes in residual levels (based
on visual observations or odor) should be analyzed.
For complex contamination mixtures, such as gas-
oline, diesel fuel, and solvent mixtures, it is not prac-
tical or necessary to identify and quantify each com-
pound present. In such cases it is recommended that
a "boiling point" distribution be measured for a
representative sample of the residual contamination.
Boiling point distribution curves, such as shown in
Figure 3 for "fresh" and "weathered" gasoline samples,
can be constructed from GC analyses of the residual
soil contamination (or free product) and knowledge of
the GC elution behavior of a known series of compounds
(such as straight-chain alkanes). Compounds generally
elute from a GC packed column in the order of increas-
ing boiling point, so a boiling point distribution curve
is constructed by grouping all unknowns that elute
between two known peaks (i.e., between n-hexane and
n-heptane). Then they are assigned an average boiling
point, molecular weight, and vapor pressure. Use of
these data will be explained later.
The cone penetrometer, which is essentially an
instrumented steel rod that is driven into the soil, is
becoming a popular tool for preliminary site screening
investigations. By measuring the shear and normal
forces on the leading end of the rod, soil structure
can be defined and permeability or hydraulic conduc-
tivity can be estimated. Some cone penetrometers are
also constructed to allow the collection of vapor or
ground water samples. This tool has several advan-
1.0
Cumulative
Weight og;
Fraction
0.6
. ' 0.4
0.2
O.O.-
Figure 3. Boiling point distribution curves for samples of
"fresh" and "weathered" gasolines.
tages over conventional soil boring techniques (as a
preliminary site characterization tool): (1) the subsur-
face soil structure can be defined better; (2) no soil
cuttings are generated; and (3) more analyses can be
performed per day.
• Temperature (both above and below ground surface)
Contaminant vapor concentrations are dependent on
temperature, and therefore, removal rates are
strongly influenced by subsurface temperatures.
Above-ground temperatures will influence the selec-
tion of materials and construction of the above-
ground vapor treatment system.
Results from the preliminary site investigation
should be summarized in contour plots, fence diagrams,
and tables in preparation for deciding whether venting
is appropriate, and for the final design of the system.
Deciding if Venting Is Appropriate
As previously stated, the three main factors govern-
ing the behavior of any in situ soil-venting operation
are the vapor flow rate, contaminant vapor concentra-
tions, and the vapor flow path relative to the contamin-
ant location. In an article by Johnson et al. (1988), simple
mathematical equations were presented to help quantify
each of these factors. Following it is illustrated how to
use these ."screening models"and the information col-
lected during the preliminary site investigation to help
determine if in situ soil venting is appropriate at a given
site. In making this decision the following questions will
be answered:
1. What contaminant vapor concentrations are likely
to be obtained?
2. Under ideal vapor flow conditions (i.e., 100 -1000
scfm vapor flow rates), is this concentration great
enough to yield acceptable removal rates?
3. What range of .vapor flow rates can realistically
be achieved?
4. Will the contaminant concentrations and realistic
vapor flow rates produce acceptable removal rates?
5. What residual, if any, will be left in the soil? What
-------
vapor composition and concentration changes will occur
with time? How do these values relate to the regulatory
requirements?
6. Are there likely to be any negative effects of soil
venting?
Negative answers to questions 2 or 4 will rule out
in situ soil venting as a practical treatment method.
What Contaminant Vapor Concentrations Are Likely
to Be Obtained?
Question 1 can be answered based on the results of
soil-vapor surveys, analyses of headspace vapors above
contaminated soil samples, or equilibrium vapor models
(Johnson et al. 1988). In some cases just knowing which
compounds are present is sufficient to estimate if venting
is feasible. In the absence of soil-vapor survey data,
contaminant vapor concentrations can be estimated.
The maximum vapor concentration of any compound
(mixture) in extracted vapors is its equilibrium or "satur-
ated" vapor concentration, which is easily calculated
from knowledge of the compound's (mixture's) molecu-
lar weight, vapor pressure at the soil temperature, resid-
ual soil contaminant composition, and the ideal gas law:
(1)
RT
where:
CC5l = estimate of contaminant vapor concentration
[mg/L]
Xi = mole fraction of component i in liquid-phase
residual (x, = 1 for single compound)
P;v = pure component vapor pressure at tempera-
ture T [atm]
Mw-i = molecular weight of component i [mg/mole]
R = gas constant = 0.0821 l-atm/mole-°K
T = absolute temperature of residual [°K].
Table 1 presents data for some chemicals and mix-
TABLE1
Selected Compounds and Their Chemical Properties (Johnson et al. 1988)
Compound
n-pentane
n-hexane
trichloroethane
benzene
cyclohexane
trichloroethylene
n-heptane
toluene
tetrachloroethylene
n-octane
chlorobenzene
p-xylene
ethylbenzene
m-xylene
o-xylene
styrene
n-nonane
n-propylbenzene
1,2,4 trimethylbenzene
n-decane
DBCP
n-undecane
n-dodecane
napthalene
tetraethyilead
gasoline1
weathered gasoline2
Mw
(g/mole)
72.2
86.2
133.4
78.1
84.2
131.5
100.2
92.1
166
114.2
113
106.2
106.2
106.2
106.2
104.1
128.3
120.2
120.2
142.3
263
156.3
170.3
128.2
323
95
111
Tb (1 atm)
(C)
36
69
75
80
81
87
98
111
121
126
132
138
138
139
144
145
151
159
169
173
196
196
216
218
dec.@200C
-
-
PV-20C
(atm)
0.57
0.16
0.132
0.10
0.10
0.026
0.046
0.029
0.018
0.014
0.012
0.0086
0.0092
0.0080'
0.0066
0.0066
0.0042
0.0033
0.0019
0.0013
0.0011
0.0006
0.00015
0.00014
0.0002
0.34
0.049
ces,
(mg/L)
. 1700
560
720
320
340
140
190
110
130
65
55
37
40
35
29
28
22.0
16
9.3
7.6
11
3.8
1.1
0.73
2.6
1300
220
'Corresponds to "fresh" gasoline defined in Table 2 with boiling point distribution shown in Figure 3.
'Corresponds to "weathered" gasoline defined in Table 2 with boiling point distribution shown in Figure 3.
Tb (1 aim) • compound boiling point at 1 aim absolute pressure.
Mw - molecular weight.
Ce« - equilibrium vapor concentration (see Equation 1).
Pv° (20 C), - vapor pressure measured at 20 C.
-------
lures accidentally released to the environment. There
are more sophisticated equations for predicting vapor
concentrations in soil systems based on equilibrium par-
titioning arguments, but these require more detailed
information (organic carbon content, soil moisture) than
is normally available. If a site is chosen for remediation,
the residual total hydrocarbons in soil typically exceed
500 mg/kg. In this residual concentration range most of
the hydrocarbons will be present as a separate or "free"
phase, the contaminant vapor concentrations become
independent of residua! concentration (but still depend
on composition), and Equation 1 is applicable (Johnson
et al. 1988). In any case, it should be noted that these
are estimates only for vapor concentrations at the start
of venting, which is when the removal rates are generally
greatest. Contaminant concentrations in the extracted
vapors wiH decline with time due to changes in composi-
tion, residual levels, or increased diffusional resistances.
These topics will be discussed in more detail.
Under Ideal Vapor Flow Conditions (i.e., 100 - 1000
scfm Vapor Flow Rates), Is This Concentration Great
Enough to Yield Acceptable Removal Rates?
Question 2 is answered by multiplying the concentra-
tion estimate Ccsl, by a range of reasonable flow rates,
O:
R«« = Cest Q (2)
Here Res, denotes the estimated removal rate, and
Cesi and Q must be expressed in consistent units. For
reference, documented venting operations at service sta-
tion sites typically report vapor flow rates in the 10 -
100 scfm range (Hutzler et al. 1988), although 100 -
1000 scfm flow rates are achievable for sandy soils or
large numbers of extraction weHs. At this point in the
decision process what is still being neglected is that
vapor concentrations decrease during venting due to
compositional changes and mass transfer resistances.
Figure 4 presents calculated removal rates Rcsl [kg/d]
for a range of Qj, and Q values. Ces, values are presented
in [mg/L] and [ppmCH-»] units, where [ppmcH4] represents
methane-equivalent parts-per-million volume/volume
(ppmv) units. The [ppmow] units are used because field
analytical tools that report [ppmv] values are often cali-
brated with methane. The [mg/L] and [ppmcm] units are
related by:
[ppmcH4J * 16000 mg-CH4/mole-CH4 * 10'*
[mg/L]=
(ppm.
-13.3
153000
(0.0821 l-atm/°K-mole) * (298 K)
(3)
For field instruments calibrated with other compounds
(i.e., butane, propane), [ppmv] values are converted to
[mg/L] by replacing the molecular weight of CH4 in
Equation 3 by the molecular weight [mg/mole] of the
calibration compound.
Acceptable or desirable removal rates Raccepiabic>can
be determined by dividing the estimated spill mass Mspiii.
by the maximum acceptable cleanup time T:
Racccpiable = Mspin/T (4)
For example, if 1500kg (•*• 500 gal) of gasoline had
been spilled at a service station and it was wished to
Removal
Rate
(kg/d)
(ppm,.
t
.1 1 10
Vapor Concentration (mg/1)
I ) * concentration in methftne-equivmlent ppm (vo) Aol.) units
100
Figure 4 In situ soil-venting removal rate dependence on
vapor extraction rate and vapor concentration.
complete the cleanup within eight months, then Raccepta-
b(e = 6.3 kg/d. Based on Figure 4, therefore, Cesl would
have to average >1.5 mg/L (2400 ppmCH«) for 6=2800
1/min (100 cfm) if venting is to be an acceptable option.
Generally, removal rates <1 kg/d will be unacceptable
for most releases, so soils contaminated with compounds
(mixtures) having saturated vapor concentrations less
than 0.3 mg/L (450 ppmCH4) will not be good candidates
for venting, unless vapor flow rates exceed 100 scfm.
Judging from the compounds listed in Table 1 , this corre-
sponds to compounds with boiling points (Tb)>150 C,
or pure component vapor pressures <0.0001 atm evalu-
ated at the subsurface temperature.
What Range of Vapor Flow Rates Can Realistically
Be Achieved?
Question 3 requires that realistic vapor flow 'rates for
the site-specific conditions be estimated. Equation 5,
which predicts the flow rate per unit thickness of well
screen Q/H [cm3 Is], can be used for this purpose:
[ 1 - (PA,n,/Pw)2]
(5)
where:
k = soil permeability to air flow [cm2 ] or [darcy]
p. = viscosity of air = 1.8 x 10* g/cm-s or 0.018 cp
Pw = absolute pressure at extraction well [g/cm-s2]
or [atm]
PAIOI = absolute ambient pressure °» 1.01 x 10* g/cm-s2
or 1 atm
Rw • = radius of vapor extraction well [cm]
RI = radius of influence of vapor extraction well
[cm].
-------
This equation is derived from the simplistic steady-
state radial flow solution for compressible flow (Johnson
ct al. 1988), but should provide reasonable estimates
for vapor flow rates. If k can be measured or estimated,
then the only unknown parameter is the empirical "ra-
dius of influence" Rj. Values ranging from 9m (30 ft)
to 30m (100 ft) are reported in the literature (Hutzler
et ai. 1988) for a variety of soil conditions, but fortun-
ately Equation 5 is not sensitive to large changes in R|.
For estimation purposes, therefore, a value of R|=12m
(40 ft) can be used without a significant loss of accuracy.
Typical vacuum well pressures range from 0.95 - 0.90
aim (20 - 40 in H2O vacuum). Figure 5 presents pre-
dicted flow rates per unit well screen thickness Q/H,
expressed in "standard" volumetric units Q*/H (= Q/
H(Pw/PA
-------
In Figure 6a a fraction <}> of the vapor flows through
uncontaminated soil. The fraction can be roughly esti-
mated by assessing the location of the well relative to
the contaminant distribution. In Figure 6a for example,
it appears .that roughly 25 percent of the vapor flows
through uncontaminated soil. The maximum removal
rate for this case is then:
R«. = (1-*)QC« (6)
In Figure 6b, vapor flows parallel to, but not through,
the zone of contamination, and the significant mass
transfer resistance is vapor phase diffusion. This would
be the case for a layer of liquid hydrocarbon resting on
top of an impermeable strata or. the water table. This
problem was studied by Johnson et al (1988) for the
case of a single component. The solution is:
Rest = *\Q Ces,
n = --
jtt
where:
tj
[ln(R,/Rw)/{PAlm -
= efficiency relative to maximum
removal rate
D = effective soil-vapor diffusion coeffici-
ent [cnf/s]
ft = viscosity of air = 1.8 x 10 4 g/crn-s
k = soil permeability to vapor flow [cm3]
H = thickness of screened interval [cm]
RI ' = radius of influence of venting well
[cm]
Rw ~ venting' well radius [cm]
PAI™ = absolute ambient pressure = 1.016 x
10* g/cm-s2
PW = absolute pressure at the venting well
[g/cm-s2]
RI < r < R2 = defines region in which contamina-
tion is present.
Note that the efficiency ^ is inversely proportional
to the screened interval thickness H because a larger
interval will, in this geometry, puil in unsaturated air
that has passed above the liquid-phase contamination.
D is calculated by the Millington-Quirk (Millington and
Quirk 1961) expression, which utilizes the molecular
diffusion coefficient in air D", the vapor-filled soil poros-
ity eA, and the total soil porosity eT:
= D°
where eA and eA are related by:
(8)
(9)
Here pb and 9M are the soil bulk density [g/cm'] and
soil moisture content [g-H2O/g-soil].
As an example, consider removing a layer of contam-
ination'bounded by sandy soil (k=l darcy). A 5.1cm (4
in) radius vapor extraction well is being" operated at
Pw=0.90atm (6.91 x 10* g/cm'-s'), and the contamination
extends from the region R! = Rw =? 5.1cm to R2 = 9m
(30 ft). The well is screened over a 3m'(10 ft)'interval.
Assuming that: •
•pb = 1.6g/cnV
6M = 0.10 .
D° = 0.087 cm'/s
eT = 0.30
RI = 12m ' • "
then the venting efficiency relative to the maximum
removal rate (Equation 2), calculated from Equations 7
through 9.is: .
T, = 0.09-9%., .
Figure 6c depicts the situation in which vapor flows
primarily past, rather than through the contaminated
soil zone, such as might be the case for a contaminated
day lens surrounded by sandy soils. In this case vapor-
phase diffusion through the clay to the flowing vapor
limits the removal rate. The maximum removal rate in
this case occurs when the vapor flow is fast enough to
maintain a low vapor concentration at the permeable/
impermeable soil interface. At any time t a contaminant-
free or "dried out" zone of low permeability will exist
with a thickness 6. An estimate of the removal rate Rcs,
from a contaminated zone extending from RI to R2 is:
= n(R22~Rf)Ces,D/8(t)
(10)
where D is the effective porous media vapor diffusion
coefficient (as calculated previously from Equations 8
and 9) and Ce^t is the estimated equilibrium vapor con-
centration (Equation 1). With time 5(t) wiil grow larger.
In the case of a single component system the dry zone
thickness can be calculated from the mass balance:
d5
pb Cs — = Cesl D/8(t) (11)
at
where Cs is the residual level of contamination in the
low permeability zone [g-contamination/g-soil]," and all
other variables have been defined. The solution to
Equations 10 and 11 yields the following equation that
predicts the change in removal rate with time:
8(0 =
2 Ces, D t
pbcs
(12)
As an example, consider the case where benzene (Cy =
3.19 x ]0~* g/cm3 @20 C) is being-removed from a zone
extending from RI = 5.1cm to R2 = 9m. The initial
residual level is 10,000 ppm (0.01 g-benzene/g-soil), pb
= 1.6 g/cm', D" = 0.087 cmVs, and eT = eA = 0.30. Figure
7 presents the predicted removal rates and "dry" zone
thickness 5(t) as a function of time. Note that it would
take approximately one year to clean a layer 1.5m (5
ft) thick, for a compound as volatile as benzene. Equa-
tion 12 predicts high initial removal rates; in practice,
however, the removal rate will be limited initially by
the vapor-phase diffusion behavior described previously
for Figure 6b.
Mixture removal rates for the situations depicted in
Figures 6b and 6c are difficult to estimate because
-------
changes in composition and liquid-phase diffusion affect
the behavior. Currently there are no simple analytical
solutions for these situations, but it can be postulated
that they should be less than the rates predicted previ-
ously for pure components.
The use of equilibrium-based models to predict
required removal rates will be discussed under the next
question.
What Residual, If Any, Will Be Left in the Soil?
What Vapor Composition and Concentration
Changes Will Occur With Time? How Do These
Values Relate to the Regulatory Requirements?
As contaminants are removed during venting, the
residual soil contamination level decreases and mixture
compositions become richer in the less volatile com-
pounds. Both of these processes result in decreased
vapor concentrations, and hence, decreased removal
rates with time. At low residual soil contamination levels
(<500.ppm) Equation 1 becomes less valid as sorption
and dissolution phenomena begin to affect the soil resid-
ual - vapor equilibrium. In the limit of low residual
contamination levels, contaminant equilibrium vapor
concentrations are expected to become proportional to
the residual soil contaminant concentrations. As venting
continues and residual soil levels decrease, therefore, it
becomes more difficult to remove the residual contami-
nation. It is important to realize that, even with soil
venting, there are practical limitations on the final soil
contamination levels that can be achieved. Knowledge
of these limits is necessary to realistically set cleanup
criteria and design effective venting systems.
The maximum efficiency of a venting operation is
limited by the equilibrium partitioning of contaminants
between the soil matrix and vapor phases. The maxi-
mum removal rate is achieved when the vapor being
removed from an extraction well is in equilibrium with
the contaminated soil. Models for predicting this maxi-
mum removal rate have been presented by Marley and
Hoag (1984) and Johnson et al. (1988). The former con-
sidered only compositions in a residual free-phase, while
the latter also considered the effects of sorption and
dissolution processes. A complete discussion of the
development of these models is not appropriate here,
but we will discuss the use of the predictions.
The change in composition, vapor concentration,
removal rate, and residual soil contamination level with
time are functions of the initial residual composition,
vapor extraction well flow rate, and initial soil contami-
nation level. It is not necessary to generate predictions
for every combination of variables, however, because
with appropriate scaling all results will form a single
curve for a given initial mixture composition. Figure 8a
presents the results computed with the model presented
by Johnson et al. (1988) for the "weathered" gasoline
mixture whose composition is given by Table 2. The
important variable that determines residual soil levels,
vapor concentrations, and removal rates is the ratio Qt/
M(t=0), which represents the volume of air drawn
through the contaminated zone per unit mass of conta-
1000,
10-
benzene (20 C'
200
"Dry" Zone
Thickness
5
(cm)
100
0 100 200 300 400 500
Time (d)
Figure 7. Estimated maximum removal rales for a venting
operation limited by diffusion.
Weathered Gasoline
T = 20°C
10% moisture content
cta^dta.*.,***» C<(=0) = 222 me/1
3 phuc tywoft
.0001
100
•80
% removed
60
40
20
100 ZOO
Qt/m(t=0) >ucK C(l=0) = 270 mg/t
S(*M«.!
Approximate Composition
100
•BO
% removed
60
40
100 200
Qt/m(i=0) (1/g)
300
Figure 8. Maximum predicted removal rates for a weathered .
gasoline: (a) full composition (b) approximate composition.
minant. In Figure 8, the scaled removal rate (or equiva-
lently the vapor concentration) decreases with time as
the mixture becomes richer in the less volatile com-
pounds.
While a detailed compositional analysis was availa-
ble for this gasoline sample, an approximate composi-
tion based on a boiling point distribution curve predicts
similar results. Figure 8b presents the results for the
approximate mixture composition also given in Table 2.
Model predictions, such as those shown in Figure 8
for the gasoline sample defined by Table 2, can be used
to estimate removal rates (if the vapor flow rate is speci-
fied), or alternatively the predictions can be used to
estimate vapor flow rate requirements (if the desired
removal rate is specified). For example, if we wanted
to reduce the initial contamination level by 90 percent,
-------
TABLE 2
Composition
Compound
Name
propane
isobuiane
n-butaoe
trans-2-butene
cis-2-butene
3-methyl-l-butene
isopentane
1 -pentene
2-methyl-l-butene
2-methyl-l ,3-butadiene
n-pentane
trans-2-pentene
2-methyl-2-butene
2-methyl- 1 .2-butadiene
3,3-dimethyl-l-butene
cyclopentane
3-methyl-l -pentene
2.3-dimethylbutane
2-methylpentane
3-methylpentane
n-hexane
methykyclopentane
2.2-dimethylpentane
benzene
cyclohexane
2,3-dimethylpentane
3-methylhexane
3-ethylpentane
n-heptane
2,2.4-trimethyIpentane
methylcyclohexane
2,2-dimethylhexane
toluene .
2,3,4-trimethyipentane
3-melhylheptane
2-methylheptane
n-octane
2,4,4-trimethylhexane
2,2-dimethylheptane
ethylbenzene
p-xylene
m-xylene
3,3,4-trimethylhexane
o-xylene
2,2,4-trimethylheptane
n-noname
3,3,5-trimethylheptane
n-propylbenzene
2,3,4-trimethylheptane
1 ,3,5-trimethyIbenzene
1 ,2-4-trimethy Ibenzene
n-decane
methylpropylbenzene
dimethylethylbenzene
n-undecane
1 ,2,4,5-tetramethylbenzene
1 ,2,3,4-tetramethylbenzene
1 ,2,4-trimethyl-5-ethylbenzene
n-dodecane
napthalene ' • • •
n-hexylbenzene . .
methylnapthalene
Total
(Mass Fractions)
Mw
44.1
58.1
58.1
56.1
56.1
70.1
72.2
70.1
70.1
68.1
72.2
70.1
70.1
68.1
84.2
70.1
84.2
86.2
86.2
86.2
86.2
84.2
100.2
78.1
84.2
100.2
100.2
100.2
100.2
114.2
98.2
114.2
92.1
. 114.2
114.2
114.2
114.2
128.3
128.3
106.2
106.2
106.2
' 128.3
106.2
142.3 -
128.3
142.3
120.2
142.3
120.2
120.2
142.3
134.2
134.2
156.3
134.2
134.2
148.2
170.3
128.2
162.3
142.2
of Fresh and
Fresh
Gasoline
0.0001
0.0122
0.0629
0.0007
0.0000
0.0006
0.1049
0.0000
0.0000
0.0000
0.0586
0.0000
0.0044
0.0000
0.0049
0.0000
0.0000
0.0730
0.0273
0.0000
0.0283
0.0083
0.0076
0.0076
0.0000
0.0390
0.0000
0.0000
0.0063
0.0121
0.0000
0.0055
0.0550
0.0121
0.0000
0.0155
0.0013
0.0087
0.0000
0.0000
0.0957
0.0000
0.0281
0.0000
0.0105
0.0000
0.0000
0.0841
0.0000
0.0411
0.0213
0.0000
0.0351
0.0307
0.0000
0.0133
0.0129
0.0405
0.0230
0.0045
0.0000
0.0023
1.0000
Weathered Gasolines
Weathered
Gasoline
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0069
0.0005
0.0008
0.0000
0.0095
' 0.0017
0.0021
0.0010
0.0000
0.0046
0.0000
0.0044
. 0.0207
0.0186
0.0207
0.0234
0.0064
0.0021
0.0137
0.0000 .
0.0355
0.0000
0.0447
0.0503
0.0393
0.0207
0.0359
0.0000
6.0343
0.0324
0.3000
0.0034
0.0226
0.0130
0.0151
0.0376
0.0056
0.0274
0.0012
0.0382
0.0000
0.0117
0.0000
0.0493
0.0707
0.0140
0.0170
0.0289
0.0075
0.0056
0.0704
0.0651
0.0000
0.0076
0.0147
0.0134
1.0000
Approximate
Composition
0.
0
0
0
0
0
0.0177
0
0
0
0
0
0
0
0
0.0738
0
0
0
0
0
0
0
0
0.1761
0
0
0
0
0
0
0
0.1926
0
0
0
0
0
0
0
0
0.1641
0
0
0
0
0
0.1455 -
0
0
0
0
0
0.0534
0
0
0.1411
0
0
0
0.0357
0
1.00000
-------
then Figure 8 predicts that •* 100 1-air/g-gasoline will
be required. This is the minimum amount of vapor
required, because it is based on an equilibrium-based
model. The necessary minimum average vapor flow rale
is then equal to the spill mass times the minimum
required vapor flow/mass gasoline divided by the
desired duration of venting. Use of this approach is
illustrated in the service station site example provided
at the end of this paper.
Figure 8 also illustrates that there is a practical limit
to the amount of residual contaminant that can be
removed by venting alone. For example, it will take a
minimum of 1001-vapor/g-gasoline to remove 90 percent
of the weathered gasoline defined in Table 2, while it
will take about 200 1-air/g-gasoline to remove the
remaining 10 percent. In the case of gasoline, by the
time 90 percent of the initial residual has been removed,
the residual consists of relatively insoluble and non-
volatile compounds. It is important to recognize this
limitation of venting, and when setting realistic cleanup
target levels, they should be based on the potential envi-
ronmental impact of the residual rather than any specific
total residual hydrocarbon levels. Because mandated
cleanup levels are generally independent of the remedia-
tion method, this also indicates that soil venting will
often be one of many processes used during a given site
remediation. It is not difficult to envision that in the
future soil venting may be followed or coupled with
enhanced biodegradation to achieve lower cleanup
levels.
It is appropriate to mention at this point that the.
mathematical models presented in this paper are being
used as "tools" to help plan and design venting system.
As with any models, they are mathematical descriptions
of processes that at best approximate real phenomena,
and care should be taken not to misapply or misinterpret
the results.
Are There Likely to Be Any Negative Effects of Soil
Venting?
It is possible that venting will induce the migration
of off-site contaminant vapors toward the extraction
wells. This may occur at a service station, which is often
in close proximity to other service stations. If this occurs,
one could spend a lot of time and money to unknowingly
clean up someone else's problem. The solution is to
establish a "vapor barrier" at the perimeter of the con-
taminated zone. This can be accomplished by allowing
vapor flow into any perimeter ground water monitoring
wells (which often have screened intervals extending
above the saturated zone), which then act as passive air
supply wells. In other cases it may be necessary to install
passive air injection wells, or trenches, as illustrated in
Figure 9a.
As pointed out by Johnson et al. (1988), the applica-
tion of a vacuum to extraction wells can also cause a
water table rise. In many cases contaminated soils lie
just above the water table and they become water satur-
ated, as illustrated in Figure 9b. The maximum rise
occurs at, or below the vapor extraction well, where the
water table rise will be equal to the vacuum at that point
a)
Vapot Extraction
Well
C
Off-She
Contamination
Passive Air Injection Well
or
Perimeter Grouitdwaier Monitoring Well
b)
L'nsaturated
Soil Zone
Vapor Extraction
Well
Water Table Upweltmg
Caused by Vacuum
Figure 9. (a) Use of passive vapor wells to prevent migration
of off-site contaminant vapors, (b) Water table rise caused by
the applied vacuum.
expressed as an equivalent water column height (i.e.. in
ft H2O). The recommended solution to this problem is
to install a dewatering system, with ground water pump-
ing wells located as close to vapor extraction wells as
possible. The dewatering system must be designed to
ensure that contaminated soils remain exposed to vapor
flow. Other considerations not directly related to vent-
ing system design, such as soluble plume migration con-
trol and free-liquid product yield, will also be factors in
the design of the ground water pumping system.
Design Information
If venting is still a remediation option after answer-
ing the questions above, then more accurate information
must be collected. Specifically, the soil permeability to
vapor flow, vapor concentrations, and aquifer charac-
teristics need to be determined. These are obtained by
two field experiments: air permeability and ground
water pumping tests, described briefly next.
Air Permeability Tests
Figure 10 depicts the setup of an air permeability
test. The object of this experiment is to remove vapors
at a constant rate from an extraction well, while monitor-
ing with time the transient subsurface pressure distribu-
tion at fixed points. Effluent vapor concentrations are
also monitored. It is important that the test be conducted
properly to obtain accurate design information. The
extraction well should be screened through the soil zone
that will be vented during the actual operation. In many
cases existing ground water monitoring wells are suffici-
ent, if their screened sections extend above the water
table. Subsurface pressure monitoring probes can be
-------
Pressure Vapor flowmeter
Gauge
Vapor Treatment
Vapor Sampling
Pod
Vapor
Flow"
Pressure Sampling Probes
Figure 10. Air-permeability test system.
driven soil-vapor sampling probes (for <20 ft deep con-
tamination problems) or more permanent installations.
Flow rate and transient pressure distribution data
are used to estimate the soil permeability to vapor flow.
The expected change in the subsurface pressure distribu-
tion with time P'(r,t) is predicted (Johnson et al.) by:
P' —
Q
4jtm(k/u)
/"V
*
dx
(13)
For (r e|a./4kPAlmt)<0.r Equation 13 can be approxi-
mated by:
P1 =
4jcm(k/n) I
[-0.5772 - in 1-^- } + ln(t)l (14)
I UkPAtm / J
Here:
P' = "gauge" pressure measured at distance r
and time t
m = stratum thickness
r = radial distance from vapor extraction well
k = soil permeability to air flow
|x = viscosity of air = 1.8 x 104 g/cm-s
« = air-filled soil void fraction
t = time
Q = volumetric vapor flow rate from extraction
well
PAI™ = ambient atmospheric pressure = 1.0 atm =
1.013x 10"g/cm-s:.
Equation 14 predicts a plot of p'-vs- In(t) should be a
straight line with slope A and y-intercept B equal to:
A =
B =
4jtm(k/u.)
-0.5772-In
/ r en
\4kPy
Atm
(IS)
The permeability to vapor flow can then be calculated
from the data by one of two methods. The first is applica-
ble when Q and m are known. The calculated slope A
is used:
k =
4A,m . <16)
The second approach must be used whenever Q or m
is not known. In this case the values A and B are both
used:
reu. -B
k = - - exp(- + 0.5772)
HV
4P
(17)
AUB
Equation 13 can also be used to choose the locations
of subsurface pressure monitoring points before con-
ducting the air permeability test, given an estimation of
k and the flow rate to be used.
Vapor samples should be taken at the beginning and
end of the air permeability test, which should be con-
ducted for a long enough time to extract at least one
"pore volume" VP of vapor from the contaminated soil
zone. This ensures that all vapors existing in the forma-
tion prior to venting are removed. The vapor concentra-
tion-at the start of the test is representative of the equi-
librium vapor concentration, while the concentration
measured after one pore volume has been extracted
gives, an indication of realistic removal rates and the
mixing or diffusional limitations discussed in association
with Figure 6. The time Vp for one pore volume to be
removed is:
TP = Vp/Q = €A
H/Q
.(18)
where R, H. eA, and Q are the radius of the zone of
contamination, vertical thickness of the zone of contami-
nation, air-filled void fraction, and volumetric vapor
flow rate from the extraction well. For example, consider
the case where R=12 m, H=3 m. eA=0.35, and Q=0.57
m3 /min (20 ft' /min). Then rp=475 m 70.57 m' /min=833
min=14 h.
Ground Water Pumping Tests
To achieve efficient venting, the hydrocarbon-con-
taminated soil .has to be exposed to air flow, which in
turn requires that the water table be lowered to counter-
act the water upwelling effect caused by the decreased
vapor pressure in the vicinity of a venting well (Johnson
et al. 1988) and to possibly expose contaminated soil
below the water table. Thus the ground water pumping
system has to have a sufficient pumping rate and be
operated for a long enough time period to obtain the.
required drawdowns. Because most venting systems are
installed above phreatic aquifers, two aquifer parame-
ters are needed for the design: average transmissivity T'
and storage coefficient S. These parameters can be esti-
mated using the results of the standard transient ground
water pumping test with a constant pumping rate (Bear
1979). Using the estimated values, the required pumping'
rate may be calculated as follows:
Q .= 4-nT S(r,t)/W(u)
(19)
where: W(u) is the well function (Bear 1979) of u = Sr/
-------
4Tt, and s(r,t) is the required drawdown at distance r
and pumping time equal to t.
System Design
In this section the questions that must be answered
in order to design an in situ soil-venting system will be
discussed. It is not the authors' intention to provide a
generic "recipe" for soil-venting system design; instead,
a structured thought process to guide in choosing the
number of extraction wells, well spacing, well construc-
tion, etc. is suggested. Even in a structured thought
process, intuition, and experience play important roles.
There is no substitute for a good fundamental under-
standing of vapor flow processes, transport phenomena,
and ground water flow.
Choosing the Number of Vapor Extraction Wells
Three methods for choosing the number of vapor
extraction wells are outlined in the following text. The
greatest number of wells from these three methods is
then the value that should be used. The objective is to
satisfy removal rate requirements and achieve vapor
removal from the entire zone of contamination.
For the first estimate residual contaminant composi-
tion and vapor concentration changes with time are neg-
lected. The acceptable removal rate Raccepiabie is calcu-
lated from Equation 4, while the estimated removal rate
from a single well Rest is estimated from a choice of
Equations 2,6,7, or 12 depending on whether the speci-
fic site conditions are most like Figure 6a, 6b, or 6c.
The number of wells Nwcns required to achieve the
acceptable removal rate is:
- Racceplable'Rest
(20)
Equations 2,6, and 7 require vapor flow estimates, which
can be calculated from Equation 5 using the measured
soil permeability and chosen extraction well vacuum Pw.
At this point one must determine what blowers and
vacuum pumps are available because the characteristics
of these units will limit the range of feasible (PW,Q)
values. For example, a blower that can pump 100 scfm
at 2 in. H2O vacuum may only be able to pump 10 scfm
at 100 in. H2O vacuum.
The second method, which accounts for composition
changes with time, utilizes model predictions, such as
those illustrated in Figure 8. Recall that equilibrium-
based models are used to calculate the minimum vapor
flow to achieve a given degree of remediation. For exam-
ple, if we wish to obtain a 90 percent reduction in resid-
ual gasoline levels, Figure 8 indicates that ==1001-vapor/
g-gasoline must pass through the contaminated soi!
zone. If our spill mass is 1500kg (=500 gal), then a mini-
mum of 1.5 x 10s 1-vapor must pass through the conta-
minated soil zone. If the target cleanup period is six
months, this corresponds to a minimum average vapor
flow rate of 0.57 m* /min (=20 cfm). The minimum num-
ber of extraction wells is then equal to the required
minimum average flow rate/flow rate-per-well.
The third method for determining the number of
wells ensures that vapors and residua) soil contamina-
tion are removed from the entire zone of contamination
Nmin- This is simply equal to the ratio of the area of
contamination Aconlamina,i0ni to the area of influence of
a single venting well irR|2:
Nmin =
^contamination
KR
(21)
This requires an estimate of RI, which defines the zone
in which vapor flow is induced. In general, R[ depends
on soil properties of the vented zone, properties of sur-
rounding soil layers, the depth at which the well is
screened, and the presence of any impermeable bound-
aries (water table, clay layers, surface seal, building
basement, etc.). At this point it is useful to have some
understanding of vapor flow patterns because, except
for certain ideal cases (Wilson et al. 1988), one cannot
accurately predict vapor flow paths without numerically
solving vapor-flow equations. An estimate for RI can
be obtained by fitting radial pressure distribution data
from the air permeability test to the steady-state radial
pressure distribution equation (Johnson et al. 1988):
P(r) = Pw [l + (i _ ( *!E
lp(r/R-> 11/2
ln(Rw/R,)J
(22)
where P(r), PAlm, Pw, and Rw are the absolute pressure
measured at a distance r from the venting well, absolute
ambient pressure, absolute pressure applied at the vapor
extraction well, and extraction well radius, respectively.
Given that these tests are usually conducted for less
than a day, the results will generally underestimate RP
If no site-specific data are available, one can conserva-
tively estimate R( based on the published reports from
in situ soil-venting operations. Reported RI values for
permeable soils (sandy soils) at depths greater than
20 feet below ground surface, or shallower soils beneath
good surface seals, are usually 10m - 40m (Hutzler et
al. 1988). For less permeable soils (silts, clays), or more
shallow zones R| is usually less.
Choosing Well Location, Spacing, Passive Wells, and
Surface Seals
To be able to successfully locate extraction wells,
passive wells, and surface seals one must have a good
understanding of vapor flow behavior. Well locations
should be chosen to ensure adequate vapor flow through
the contaminated zone, while minimizing vapor flow
through other zones.
If one well is sufficient, it should almost always be
placed in the geometric center of the contaminated soil
zone, unless it is expected that vapor flow channeling
along a preferred direction will occur. In that case the
well should be placed so as to maximize air flow through
the contaminated zone.
When multiple wells are used it is important to con-
sider the effect that each well has on the vapor flow to
all other wells. For example, if three extraction wells
are required at a given site, and they are installed in
the triplate design shown in Figure lla, this would result
-------
a>
a)
b)
vapor flow f
lines
injection
well
_ . extraction
"" ,' wells
c)
Figure 11. Venting well configurations
in a "stagnant" region in the middle of the wells where
air flow would be small in comparison to the flow
induced outside the triplate pattern boundaries. This
problem can be alleviated by the use of "passive wells"
or "forced injection" wells as illustrated in Figure lib
(it can also.be minimized by changing the vapor flow
rates from each well with time). A passive well is simply
a well that is open to the atmosphere; in many cases
ground water monitoring wells are suitable. If a passive
or forced injection well is to have any positive effect, it
must be located within the extraction well's zone of
influence. Forced injection wells are simply vapor wells
into which air is pumped rather than removed. One
must be careful in choosing the locations of forced injec-
tion wells so that contaminant vapors are captured by
the extraction wells, rather than forced off-site. To date
there have not been any detailed reports of venting
operations designed to study the advantages/disadvan-
tages of using forced injection wells. Figure 1 Ic presents
another possible extraction/injection well combination.
As illustrated in Figure 9, passive wells can also be used
as vapor barriers to prevent on-site migration of off-
site contamination problems.
For shallow contamination problems (<4m below
ground surface) vapor extraction trenches combined
with surface seals may be more effective than vertical
wells. Trenches are usually limited to shallow soil zones
because the difficulty of installation increases with
depth.
Surface seals, such as polymer-based liners and
asphalt, concrete, or clay caps, are sometimes used to
control the vapor-flow paths. Figure 12 illustrates the
effect that a surface seal will have on vapor-flow pat-
"open" soil fuif
b)
impermeable sol
Figure 12. Effect of surface seal on vapor flow path.
a)
cement cap
stoned pipe
b)
air-Tight monitoring well
cap/water sensor assembly
coarse packing
"*" material
pressure gauge
connection
wire lo i
double ictton
inner scpu ical
well cap
i
Figure 13. (») Extraction well construction, and (b) air-tight
ground water level measuring system.
terns. For shallow treatment zones (<5m) the surface
seal will have a significant effect on the vapor flow paths,
and seals can be added or removed to achieve the
desired vapor flow path. For wells screened below 8m
the influence of surface seals becomes less significant.
Well Screening and Construction . .
Wells should be screened only through the zone of
contamination, unless the permeability to vapor flow is
so low that removal rates would be greater if flow were
induced in an adjacent soil layer (see Figure 6). Removal
rate estimates for various mass-transfer limited sce-
narios can be calculated from Equations 7 and 12.
Based on Equation 5, the flow rate is expected to
-------
increase by 15 percent when the extraction well diameter
is increased from 10cm (4 in) to 20cm (8 in). This implies
that well diameters should be as large as is practically
possible.
A typical well as shown in Figure 13a is constructed
from slotted pipe (usually PVC). The slot size and num-
ber of slots per inch should be chosen to maximize the
open area of the pipe. A filter packing, such as sand or
gravel, is placed in the annulus between the borehole
and pipe. Vapor extraction wells are similar to ground
water monitoring wells in construction but there is no
need to filter vapors before they enter the well. The
filter packing, therefore, should be as coarse as possible.
Any dust carried by the vapor flow can be removed by
an above-ground filter. Bentonite pellets and a cement
grout are placed above the filter packing. It is important
that these be properly installed to prevent a vapor flow
"short-circuiting." Any ground water monitoring wells
installed near the extraction wells must also be installed
with good seals.
Vapor Treatment
Currently, there a four main treatment processes
available:
* Vapor combustion units: Vapors are incinerated and
destruction efficiencies are typically >95 percent. A
supplemental fuel, such as propane, is added before
combustion unless extraction well vapor concentra-
tions are on the order of a few percent by volume.
This process becomes less economical as vapor con-
centrations decrease below «• 10,000 ppmv.
• Catalytic oxidation units: Vapor streams are heated
and then passed over a catalyst bed. Destruction effi-
ciencies are typically >95 percent. These units are
used for vapor concentrations <8000 ppnv More con-
centrated vapors can cause catalyst bed temperature
excursions and meltdown.
• Carbon beds: Carbon can be used 10 treat almost any
vapor streams, but is only economical for very low
emission rates (<100 g/d)
• Diffuser stacks: These do not treat vapors, but are
the most economical solution for areas in which they
are permitted. They must be carefully designed to
minimize health risks and maximize safety.
Ground Water Pumping System
In cases where contaminated soils lie just above or
below the water table, ground water pumping systems
will be required to ensure that contaminated soils
remain exposed. In designing a ground water pumping
system it is important to be aware that upwelling (draw-
up) of the ground water table will occur when a vacuum
is applied at the extraction well (see Figure 9b). Because
the upwelling will be greatest at the extraction wells,
ground water pumping wells should be located within
or as close to the extraction wells as possible. Their
surface seals must be airtight to prevent unwanted short-
circuiting of airflow down the ground water wells.
System Integration
System components (pumps, wells, vapor treating
units, etc.) should be combined to allow maximum flexi-
bility of operation. The review by Hutzler et al. (1988)
provides descriptions of many reported systems. Specific
requirements are:
• Separate valves, flow meters, and pressure gauges for
each extraction and injection well.
• Air filter to remove particulates from vapors
upstream of the pump and flow meter.
• Knock-out pot to remove any liquid from vapor
stream upstream of the pump and flow meter.
Monitoring
The performance of a soil-venting system must be
monitored in order to ensure efficient operation, and
to help determine when to shut off the system. At a
minimum the following should be measured:
• Date and time of measurement.
• Vapor flow rates from extraction wells and into injec-
tion wells: These can be measured by a variety of
flow meters including pilot tubes, orifice plates and
rotameters. It is important to have calibrated these
devices at the field operating pressures and tempera-
tures.
• Pressure readings at each extraction and injection
well can be measured with manometers or magnahelic
gauges.
• Vapor concentrations and compositions from extrac-
tion wells: total hydrocarbon concentration can be
measured by an on-line total hydrocarbon analyzer
calibrated to a specific hydrocarbon. This information
is combined with vapor flow rate data to calculate
removal rates and the cumulative amount of contam-
inant removed. In addition, for mixtures the vapor
composition should be periodically checked. It is
impossible to assess if vapor concentration decreases
with time are due to compositional changes or some
other phenomena (mass transfer resistance, water
table upwelling, pore blockage, etc.) without this
information. Vapor samples can be collected in evacu-
ated gas sampling cylinders, stored, and later ana-
lyzed.
• Temperature: ambient and soil.
• Water table level (for contaminated soils located near
the water table): It is important to monitor the water
table level to ensure that contaminated soils remain
exposed to vapor flow. Measuring the water table
level during venting is not a trivial task because the
monitoring well must remain sealed. Uncapping the
well releases the vacuum and any effect that it has
on the water table level. Figure 13b illustrates a moni-
toring well cap (constructed by Applied Geosciences
Inc., Tustin, California) that allows one to simulta-
neously measure the water table level and vacuum in
a monitoring well. It is constructed from a commer-
cially available monitoring well cap and utilizes an
electronic water level sensor.
Other valuable, but optional measurements are:
t Soil-gas vapor concentrations and compositions:
These should be measured periodically at different
radial distances from the extraction well. Figure 14
-------
1/g" OD Teflon Tubing
Ground Surface
^>sx<^ Bo* Containing Vapor Sampling
^"Ss. Ports ^Thermocouples
PPVCPipe
coarse packing
ceriient/behtonite
Figure 14. Vadose zone monitoring well installation.
shows the construction of a permanent monitoring
installation that can be used for vapor sampling and
subsurface temperature measurements. Another
alternative for shallow contamination zones is the use
of soil-gas survey probes. Data from soil-gas probes
are valuable for two reasons: (1) by comparing extrac-
tion well concentrations with soil-gas concentrations
it is possible to estimate the fraction of vapor that is
flowing through the contaminated zone <)>=Cextrac,iori
weii/Qoii gas* and (2) it is possible to determine if the
zone of contamination is shrinking toward the extrac-
tion well, as it should with time. Three measuring
points are probably sufficient if one is located near
the extraction well, one is placed near the original
edge of the zone of contamination, and the third is
placed somewhere in between.
These monitoring installations can also be useful for
monitoring subsurface vapors after venting has ceased.
Determining When to Turn Off the System
Target soil cleanup levels are often set on a site-by-
site basis, and are based on the estimated potential
impact that any residual may have on air quality, ground
water quality, or other health standards. They may also
be related to safety considerations (explosive limits).
Generally, confirmation soil borings, and sometimes
soil-vapor surveys are required before closure is
granted. Because these analyses can be expensive and
often disrupt the normal business of a site, it would be
valuable to be able to determine when confirmation
borings should be taken. If the monitoring is done as
suggested previously, then the.following criteria can be
used: ' , •
• Cumulative amount removed: Determined by inte-
grating the measured removal rates (flow rate x con-
centration) with time. While this value indicates how
much contaminant has been removed, it is usually
•not very useful for determining when to take confix
mation borings unless the original spill mass is known
accurately. In mostcases that information is not avail-
able and cannot be calculated accurately from soil-
boring data.
* Extraction well vapor concentrations: The vapor con-
centrations are good indications of how effectively
the venting system is working, but decreases in vapor
extraction well concentrations are not strong evidence
that soil .concentrations have decreased. Decreases
may also be due to other phenomena such as water
table level increases, increased mass transfer resist-
ance due to drying, or leaks in the extraction system.
• Extraction well vapor composition: When combined
with vapor concentrations these data offer more
insight into the effectiveness of the system. If the total
vapor concentration decreases without a change in
composition, it is probably due to one of the phe-
nomena mentioned previously, and is not an indica-
tion that the residual contamination has been signific-
antly reduced. If a decrease in vapor concentration
is accompanied by a shift in composition toward less
volatile compounds, on the other hand, it is most
likely due to a change in the residual contaminant
concentration. For residual gasoline cleanup, for
example, one might operate a venting system until
benzene, toluene, and xylenes were not detected in
the vapors. The remaining residual would then be
composed of larger molecules, and it can be argued
that these do not pose a health threat through volatili-
zation or leaching pathways.
• Soil-gas contaminant concentration and composition:
These data are the most useful because it yields infor-
mation about the residual composition and extent of
contamination. Vapor concentrations cannot, in gen-
eral, be used to determine the residual level, except
in the limit of low residual levels (note that Equation 1
is independent of residual concentration). It is important
to consider the effect of continued soil-venting system
operation on soil-gas sampling results. Results taken
• during operation, or immediately after shutdown, can
be used to assess the spatial extent of contamination
and composition of the vapors. After the system is
shut down, vapors will begin to migrate away from
the source and equilibrate on a larger scale. True soil-
vapor concentrations can be measured once equilib-
rium concentrations are attained in the sampling
/one; at least two sampling times will be required to
, determine that equilibration has occurred. Due to the
diffusion of vapors, samples taken after shutdown are
not good indicators of the spatial extent of the conta-
minated zone:
Other Factors
Increased Biodegradation
It is often postulated that because the air supply to
the vadose zone is increased, the natural aerobic micro-
biological activity is increased during venting. While the
argument is plausible and some. laboratory data are
available (Salanitro et al. 1989), conclusive'evidence
supporting this theory has. yet to be .presented. This is
due in part to the difficulty in making such a mea-
surement. A mass balance approach is not likely to be
useful because' the initial spill mass is generally not
known with sufficient accuracy. An indirect method
would be to measure CO2 levels in the extraction well
-------
vapors, but this in itself does not rule out the possibility
that O2 is converted to CO2 before the vapors pass
through the contaminated soil zone. The best approach
is to measure the O2/CO2 concentrations in the vapors
at the edge of the contaminated zone, and in the vapor
extraction wells. If the CO2/O2 concentration ratio
increases as the vapors pass through the contaminated
soil, one can surmise that a transformation is occurring,
although other possible mechanisms (inorganic reac-
tions) must be considered. An increase in aerobic mic-
robial populations would be additional supporting evid-
ence.
In Situ Heating/Venting
The main property of a compound that determines
whether or not it can be removed by venting is its vapor
pressure, which increases with increasing temperature.
Compounds that are considered non-volatile, therefore,
can be removed by venting if the contaminated soil is
heated to the proper temperature. In situ heating/vent-
ing systems utilizing radio-frequency heating and con-
duction heating are currently under study (Dev et al.
1988). An alternative is to reinject heated vapors from
catalytic oxidation or combustion units into the con-
taminated soil zone.
Air Sparging
Due to seasonal ground water level fluctuations, con-
taminants sometimes become trapped below the water
table. In some cases ground water pumping can lower
the water table enough to expose this zone, but in other
cases this is not practical. One possible solution is to
install air sparging welts and then inject air below the
water table. Vapor extraction wells would then capture
the vapors that bubbled up through the ground water.
To date, success of this approach has yet to be demon-
strated. This could have a negative effect if foaming,
formation plugging, or downward migration of the resid-
ual occurred.
i" ' i" '
Application of the Design Approach
to a Service Station Remediation. :,
In the following, the use of the approach discussed
previously and outlined in Figure 2, is demonstrated for
a service station remediation.
Preliminary Site Investigation
Prior to sampling it was estimated that 2000 gallons
of gasoline had leaked from a product line at this operat-
ing service station site. Several soil borings were drilled
and the soil samples were analyzed for total petroleum
hydrocarbons (TPH) arid other specific compounds
(benzene, toluene, xylenes) by a heated-headspace
method utilizing a field GC-FID. Figure 15 summarizes
some of the results for one transect at this site. The
following relevant information was collected:
• Based on boring logs there are four distinct soil layers
between 0 - 18m (0 - 60 ft) below ground surface
(BGS). Figure 15 indicates the soil type and location
of each of these layers.
• Depth to ground water was 15m, with fine to medium
sand soils.
VU77
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23131
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• OJ
. OJ
. 1.2
, 214
• H7
• 971
.2X79
, ma
•OJI
- 0.44
• 0.17
• I.S
. u
.»«
•2}
• J.2 "
HB-10y HB-5 HB-3
/ BB-23
fVvnr
HB-21
[Ground Wucr
. Recovery WcllJ
Recovery Well]
Figure 15. Initial total hydrocarbon distribution [mg/kg-soil]
and location of lower zone vent welL
• The largest concentrations of hydrocarbons were
detected in the sandy and silty clay layers adjacent
to the water table. Some residual was detected below
the water table. Based on the data presented in Figure
15 it is estimated that = 4000kg of hydrocarbons are
present in the lower two soil zones.
• Initially there was some free-liquid gasoline floating
on the water table: this was subsequently removed
•. by pumping. A sample of this product was analyzed
and its approximate composition (=20 percent of the
compounds could not be identified) is listed in
Table 2 as the "weathered gasoline." The corre-
sponding boiling point distribution curve for this mix-
ture has been presented in Figure 3.
• Vadose zone monitoring installations similar to the
one pictured in Figure 14 were installed during the
preliminary site investigation.
Deciding if Venting Is Appropriate
For the remainder of the analysis the contaminated
soils located just above the water table will be the focus.
• What contaminant vapor concentrations are likely to
be obtained?
Based on the composition given in Table 2, and using
Equation 1, the predicted saturated TPH vapor concen-
tration for this gasoline is:
Cest = 220 mg/L
Using the "approximate" composition listed in Table
2 yields a value of 270 mg/L. The measured soil-vapor
concentration obtained from the vadose zone monitoring
well was 240 mg/L. Due to composition changes with time,
this will be the maximum concentration obtained during
venting.
• Under ideal flow conditions is this concentration great
enough to yield acceptable removal rates?
-------
Equation 4 was used to calculate Racceptabie- Assum-
ing Mspm = 4000kg and T = 180 d, then:
Racccpubie = 22 kg/d
Using Equation 2, CCSI = 240 mg/L, and Q = 2800 V
min (100 cfm):
Res, = 970 kg/d
which is greater than Raccepubie-
• What range of vapor flow rates can realistically be
achieved?
Based on boring logs, the contaminated zone just
above the water table is composed of fine to medium
sands, which have an estimated permeability 1< k < 10
darcy. Using Figure 5, or Equation 5, the predicted flow
rates for an extraction well vacuum Pw = 0.90 atm are:
0.04 < Q < 0.4 m'/m-min Rw = 5.1cm, R! = 12m
0.43 < Q < 4.3 ftVft-min Rw - 2.0 in, RI = 40 ft.
The thickness of this zone and probable screen thickr
ness of an extraction well is about 2m (6.6 ft). The total
flow rate per well through this zone is estimated to be
0.08
-------
zone will be discussed. A ground water pumping well was
installed to maintain a 2m drawdown below the static water
level. Its location is also shown in Figure 15.
System Monitoring
Three vadose monitoring wells similar in construc-
tion to the one pictured in Figure 14 were installed so
that the soil temperature, soil-gas concentrations, and
subsurface pressure distribution could be monitored at
three depths. One sampling port is located in the zone
adjacent to the aquifer. The vapor flow rate from HB-
25 and vapor concentrations were measured frequently,
and the vapor composition was determined by GC-FID
analysis. In addition, the water level in the ground water
monitoring wells was measured with the system pictured
in Figure 13b. The results from the first four months of
operation are discussed in following text
In Figure 17a the extraction well vacuum and corre-
sponding vapor flow rate are presented. The vacuum
was maintained at 0.95 atm (20 in H2O vacuum), and
the flow rate was initially 12 scfm. It gradually decreased
to about 6 scfm over 80 d. For comparison, Equation 5
predicts that Q=12 cfm for k=8 darcys. Increasing the
applied vacuum to 0.70 atm (120 in H2O vacuum) had
little effect on the flow rate. This could be explained
by increased water table upwelling, which would act to
decrease the vertical cross section available for vapor
flow. The scatter in the flow rate measurements is prob-
ably due to inconsistent operation of the ground water
pumping operation, which frequently failed to perform
properly.
Figure 17b presents the change in vapor concentra-
tion with time. Fifteen specific compounds were identi-
fied during the GC-FID vapor analyses; in this figure
the total concentration of known and unknown com-
pounds detected between five boiling point ranges are
presented:
methane - isopentane (<28 C)
isopentane - benzene (28 - 80 C)
benzene - toluene (80 - 111 C)
toluene - xylenes (111 - 144 C)
>xylenes (>144 C).
There was a shift in composition toward less volatile
compounds in the first 20 days, but after that period
the composition remained relatively constant. Note that
there is still a significant fraction of volatile compounds
present. Within the first two days the vapor concentra-
tion decreased by 50 percent, which corresponds to the
time period for the removal of the first pore volume of
air. Comparing the subsequent vapor concentrations
with the concentrations measured in the.vadose zone
monitoring wells indicates that only (80 mg/L)/(240 mg/
L)* 100=33% of the vapors are flowing through contamin-
ated soil.
Figure 18a presents calculated removal rates (flow
rate x concentration) and cumulative amount (1 gal =
3 kg) removed during the first four months. The
decrease in removal rate with time is due to a combina-
tion of decreases in flow rate and hydrocarbon vapor
concentrations. After the first four months approxi-
mately one-fourth of the estimated residual has been
a)
HB-25
Vacuum
(in H O)
140 - ' - -
120
100
80
60-
40
6.
f 1^ v— ,
. 1—- n».
<ȣ
\ A.
\?\>^>
.-,. ..••/
'» A
\ * *
V
„;•/>
V V'
^
Flowratc
(SCFM)
•10 '
•5
20 40-60 80 100 120
Time (d)
(in H.O| denote vacuums expressed as equivalent water column height]
b)
20 40 60 80 100 120
Time (d)
Figure 17. Soil-venting results: (a) vacuum/flow rate data,
(b) concentration/composition data.
a)
Removal
Rate
(kg/d) 30-|
20
10-1
0
400.
200
Cumulative
Recovered
(gal)
100
20 40 60 80 •' 100 120
Time (d)
b)
ftH.,0
Time (min)
1ft HO] denote vacuums expressed as equivalent water column heights
Figure IS. Soil-venting results: (a) removal rate/cumulative
recovered, (b) water table, rise.
removed from this lower zone.
On day 80 the vacuum was increased from 20 - 120
in H2O vacuum and the'subsequent increase in subsur-
-------
face vacuum and water table upwelling was monitored.
Figure 18b presents the results. Note that the water
table rise paralleled the vacuum increase, although the
water table did hot rise the same amount that the
vacuum did.
Figure 19 compares the reduced measured TPH
vapor concentration C(t)/C(t=0) with model predic-
tions. C(t=0) was taken to be the vapor concentration
after one pore volume of air had passed through the
contaminated zone (=80 mg/L), m(t=0) is equal to the
estimated spill mass (=4000 kg), and V(t) is the total
volume of air that has passed through the contaminated
zone. This quantity is obtained by integrating the total
vapor flow rate with time, then multiplying it by the
fraction of vapors passing through the contaminated
zone <|> (=0.33). As discussed, the quantity was esti-
mated by comparing soil-gas concentrations from the
vadose zone monitoring installations with vapor concen-
trations in the extraction well vapors. There is good
quantitative agreement between the measured and pre-
dicted values.
Based on the data presented in Figures 15 through
19 and the model predictions in Figure 8, it appears that
more extraction wells (= 10 more) are needed to reme-
diate the site within a reasonable amount of time (< 2
years).
Conclusions
A structured, technically based approach has been
presented for the design, construction, and operation
of venting systems. While an attempt has been made to
explain the process in detail for those not familiar with
venting operations or the underlying governing phe-
nomena, the most effective and efficient systems can
only be designed and operated by personnel with a good
understanding of the fundamental processes involved.
The service station spill example presented supports the
validity and usefulness of this approach.
There are still many technical issues that need to be
resolved in the future. The usefulness of forced or pas-
sive vapor injection wells is often debated, as well as
other means of controlling vapor flow paths (impermea-
ble surface covers, for example). A well-documented
demonstration of the effectiveness of soil venting for
the removal of contaminants from low-permeability
soils is also needed. It is clear from the simplistic model-
ing results presented in this paper that venting will be
less effective in such situations. Without a comparison
with other viable treatment alternatives, however, it is
difficult to determine if soil venting would still be the
preferred option in such cases. Other topics for future
study include: enhanced aerobic biodegradation by soil
venting, the possibility of decreasing residua! contami-
nant levels in water-saturated zones by air sparging/
vapor extraction, and optimal operation schemes for
multiple vapor extraction well systems.
References
Bear, J.1979. Hydraulics of Groundwater, McGraw-Hill.
Dev, H., G.C. Sresty, I.E. Bridges, and D. Downey,
weathered gasoline
m(t=0)-4000kg
0.0
01234567*9 JO
V(t)/m(t=0) (1/g) .,
•Figure 19. Comparison of model predictions and measured
response.
1988. Field test of the radio frequency in situ soil
decontamination process. In Superfund '88: Proceed-
ings of the 9th National Conference, HMCRI, Novem-
ber 1988.
Hutzler, N. J., B.E. Murphy, and J.S. Gierke. 1988. State
of Technology Review: Soil Vapor Extraction Sys-
tems, U.S EPA, CR-814319-01-1.
Johnson, P.C., M.W. Kemblowski, and J.D. Colthart.
1988. Practical screening models for soil venting
applications.. In Proceedings ofNWWA/API Confer-
ence on Petroleum Hydrocarbons and Organic Chem-
icals in Ground Water, Houston, Texas.
Marley, M.C, and G.E. Hoag. 1984 Induced soil venting
for the recovery/restoration of gasoline hydrocarbons
in the vadose zone. In Proceedings of NWWA/APl
Conference on Petroleum Hydrocarbons and Organic
Chemicals in Ground Water, Houston, Texas.
Millington, R.J. and J.M. Quirk. 1961. Permeability of
Porous Solids, Trans. Faraday Soc., 57:1200-1207.
Salanitro, J. P., M.M. Western, and M.W. Kemblowski.
1989. Biodegradation of aromatic hydrocarbons in
unsaturated soil microcosms. Poster paper presented
at the Fourth National Conference on Petroleum
Contaminated Soils, University of Massachusetts,
Amherst, September 25-28.
Wilson, D. J., A.N. Clarke, and J.H. Clarke. 198& Soil
Clean-up by in situ aeration. I. Mathematical Modell-
ing, Sep. Science Tech., voj. 23 pp. 991-1037.
Biographical Sketches
Paul C. Johnson, Ph.D., joined Shell
Development Co.'s (Westhollow Research Center,
Room EC-649, P.O. Box 1380, Houston, TX 77251-
1380) Environmental Science Department in 1987 after
earning his B.S. in chemical engineering from the Uni-
versity of California, Davis, and his Ph.D. in chemical
engineering from Princeton University. His current
areas of research include the development and evalua-
tion of soil treatment processes, modeling and measur-
ing transport phenomena in porous media, and the
development of transport models for predicting emis-
sions and exposures used in envvironmental risk
-------
assessments.
• Curtis C. Stanley received his degree in geology with
an engineering minor from North Carolina State Uni-
versity in 1979. He is currently a senior hydrpgeologist
for Shell O.il Co. (Westhollow Research Center, 2236
Two Shell Plaza, Houston, TX 77082) and is responsi-
ble for hydrogeologic response at Shell's retail facilities.
Stanley is a Certified Professional Geological Scientist
and also a Certified Ground Water Professional with
the NWWA's Association of Ground Water Scientists
and Engineers. He is also a member of API's Ground
Water Technology Taskforce and is an EPA Peer
Reviewer.
Marian W. Kemblowski, Ph.D., is a senior research
engineer in the Environmental Science Department at
Shell Development Co. (Westhollow Research Center,
Houston, TX 77082) where he has worked since 1985.
He obtained his M.S. degree in civil engineering from
the Technical University of Warsaw, Poland, in 1973
andhisPLD. in ground water hydrology from the Insti-
tute for Land Reclamation in Warsaw, Poland, in 1978.
In 1980 - 1981 he was a visiting hydrologist in the New
Mexico School of Mining and Technology. From 1981
to 1985 he worked as an assistant scientist at the Uni-
versity of Kansas. His principal research interests are
in the areas of numerical analysis, transport in porous
media, and ground water monitoring systems.
Dallas L. Byers is a technical associate in the Envi-
ronmental Science Department at Shell Development.
After receiving his B.S. degree in zoology from the Uni-
versity of Nevada, Las Vegas, he was employed by the
Texas Water Quality Board as a quality control chemist
for 3'/2 years. In 1977 he joined Shell (Westhollow
Research Center, Houston, TX 77082) where he cur-
rently is providing technical assistance and support for
research in the fate of chemicals in soil and gorund
water.
James D. Colthart, Ph.D., has been in a variety of
R&D and technical planning positions since joining
Shell (Westhollow Research Center, Houston, TX
77082) in 1966. He has a B.E. from Yale University
and a Ph.D. from Rice University, both in chemical
engineering. Currently he is the research manager of
Shell Development Co. Air, Waste, and Groundwater
Group.
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