United States Environmental Protection Agency Solid Waste And Emergency Response (OS-420) WF EPA510-R-93-001 January 1993 Hyperventilate Users Manual (v1.01 and v2.0) A Software Guidance System Created For Vapor Extraction Applications Vapor Treatment Unit Pump lllllll Ground Surface Wcll Contaminated Soil IBM EPA 510 R 93 001 c.2 Printed on Recycled Paper ------- ------- Hyperventilate Users Manual A Software Guidance System Created for Vapor Extraction Applications A Practical Approach to tht Design, Operation, and Monitoring of In-Situ Soil Venting Systems Eoooomld Crur<4 >r Pnl C. Jokuo», Pk.D. SbcO Development WtJthoDo v Rexuch C«n*r About Thfc StMfc Go to Ftrsl C«rd Fteld TtStl V System Desica '(-—— —— J liVewtacPMsftk? T •^ Si* laveitfcttioa V ^ *•• Yipor f f TVettment Uatt_ ••• 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 For sale by the U.S. Government Printing Office Superintendent of Document*, Mail Stop: SSOP, Washington, DC 20402-9328 ------- ------- - H^rVentilate Users Manual Addendwn- Addendum for Microsoft Windows/Spinnaker PLUS Version 2.0 Summary Hyperventilate - the software guidance system created for vapor extraction applications is now available for IBM-compatible computers. In general, this new version (vi.O) appears and functions like the original Apple Macintosh HyperCard version. Due to differences in the computer platform and operating environment, however, there are some minor modifications. This addendum to the original users manual identifies those modifications. Hyperventilate v2.0is a product of collaboration between Shell Oil Company and U.S. EPA, and is still under evaluation. Should you encounter problems that you think are "bugs", please write to the author identifying the problem. Modifications • software platform The original Hyperventilate program was developed and operated under the Apple Macintosh HyperCard software environment, and initially there were no plans to develop an IBM-compatible version. Due to popular demand; however, the author relented and used the least painful method of adaption to the new platform. This was accomplished through the use of Spinnaker PLUS, a HyperCard-like program that can utilize pre-v2.0 HyperCard stacks and functions on both Macintosh and IBM-compatible platforms. The Microsoft Windows/Spinnaker PLUS version requires the user to have both Microsoft Windows and a "run-time" version of Spinnaker PLUS (Windows 3.0 version). Infor- mation on Spinnaker PLUS can be obtained from: Spinnaker Software 201 Broadway Cambridge, MA 02139 (617)494-1200 • stack names As listed on p4, of the original users manual, Hyperventilate for the Apple Macintosh consists of eight files. The Spinnaker PLUS version contains only seven files. The names are: HyperCard Version Name Soil Venting Stack Soil Venting Help Stack System Design Air Permeability Test Aquifer Characterization Compound list Update HypeVent f77.rl Spinnaker PLUS Versdon Name SVS. sta SVHS.sta SD.sta APT.sta AQ.sta CLU.sta HYPEVENT.exe none ------- installation all files must be copied into the PLUS directory on your hard disk. starting Hyperventilate v2.0b To startHyperVentilate v2.0b, open the Windows 'Tile Manager", navigate to within the PLUS directory, then open (double-click on) the tile SVS.sta. printing cards You may experience difficulties with some of the "Print" buttons in the program. Read your PLUS manual to overcome these difficulties. appearance of cards Generally, the cards appear as they are printed in the manual. Due to platform differences, however, some text will appear different This problem is unavoidable with Windows- based systems, as different users will have their computers configured with different screen fonts. tab keys Some cards utilize spreadsheets. In die HyperCard version the "tab" key is used to navigate through these tables. In the PLUS version the"tab"keyisnot active and you must use the "arrow" keys. speed Due to platform differences, the PLUS version does not operate as smoothly, or quickly, as the HyperCard version. The user will notice that with time the execution speed of the program will slow; therefore, it is recommended that you periodically exit from Windows and restart the system. On some machines, when Hyperventilate accesses the external compiled code HYPEVENTEXE after clicking on the "Generate Predictions" button on card 16 of the SVS.sta stack, there will be a long pause (as long as a few minutes) as PLUS Windows, andHYPER\T^^'£XEfightove^availablemeInory. Typicallycard 17 will eventually be displayed with a shaded rectangle along a portion of its lower base while this battle is occurring. Be patient and wait for the screen to blank out and display die message "HANG ON..." indicating that HYPEVENT.EXE is running. If you have limited memory (<4MG), or too many applications open, this message will not be displayed, and you will be returned to card 17 as if the program had run. The user needs to be aware that this may occur. ------- - Hyperventilate Adndum- Software Installation Procedure A discussion on how to load both Spinnaker PLUS and Hyperventilate * Loading Spinnaker PLUS * Creating the Spinnaker PLUS Icon and Opening Spinnaker PLUS • Loading Hyperventilate • Installing Spinnaker PLUS "Run-Time" Version with Hyperventilate These directions presume that the user has a working knowledge of Microsoft Windows. The operation of Spinnaker PLUS, and therefore the IBM-compatible version of Hyperventilate requires Microsoft Windows Version 3.0 or higher. If you arc using a version of Hyperventilate with a "run time" version of SpinnakerPLUS, skip to the "Loading Hyperventilate" instructions. Loading Spinnaker PLUS The Spinnaker PLUS package contains three 3.5-inch and three 5.25-inch diskettes from which to install the program. Use these steps to install the program: 1 . Enter Windows. 2. Double-click on the "Main" window icon (if this window is not already open). 3. Double-click on the "File Manager" icon; this will display the "Directory Tree" window. 4. Insert Disk 1 into the appropriate drive (A or B). 5. In the upper left corner of the "Directory Tree" window you will see symbols representing the drives on your system. Click on the drive (A or B) where you just inserted Disk 1. 6. A listing of the files on Disk 1 will appear, double click on the file "plssetup.exe". 7. Awindowcalled"SpinnakerPLUS Setup" will appear. Change the path of theinstallation from"C:NPLUS" to "C:\WINDOWS\PLUS" (Note: "C"is a standard drive specification; you should use the letter that designates where Windows is installed on your system). Click on "Continue." The program will start copying files from Disk 1 . Follow the rest of the instructions and prompts on the screen. 8. When the installation has been completed, exit the 'Tile Manager" and exit Windows. .. .l7?JtfJi?A-i r.ffflfACfl f, .w. • . ------- ~ Hyperventilate Users Manual Addendum- Creating the Spinnaker PLUS Icon and Opening Spinnaker PLUS 1. Re-enter Windows. (Note: exiting and re-entering Windows is a step recommended by the manufacturer of Spinnaker PLUS). 2. Close all windows so that the "Program Manager" window is the only one displayed on your screen. 3. At the bottom of the window, there will be program icons displayed for "Main," "Accessories," and others. Is there a program icon named "Windows Applications?" If yes, double-click on it and go to Step 4. If no, continue with Steps 3a-c to create one. 3a. dick on "File" and drag down to "New." A window called "New Program Object" will appear. 3b. Check to make sure "Program Group" is selected; click on "OK." A window called "Program Group Properties" will appear. 3c. The cursor will be located at the description field. Type in the words "Windows Applications" and click on "OK." An empty window will appear called "Windows Applications." 4. Withthiswindowopen,clickon"File"anddragdownto"New." Awindowcalled"New Program Object" will appear. 5. Check to make sure "Program Item" is selected; click on "OK." A window called "Program Item Properties" will appear. 6. Click on "Browse." A window called "Browse" will appear. 7. Under "Directories," double-click on "plus." 8. Under "File Name," double-click on the "plus.exe" file. This will bring you back to the "Program Item Properties" window. 9. Click on "Change Icon," click on the icon for "Plus," and click on "OK." 10. You will now be back at the "Program Item Properties" window. Click on "OK." 11. You will now be back to the "Windows Applications" window displaying your "Plus" icon. 12. Double-click on the "Plus" icon to run Spinnaker PLUS. Addendum 4 ------- Loading Hyperventilate The Hyperventilate package contains one 3.5-inch diskette from which to install the program. Theprogramcan be installed fromeitherthe DOS promptorfrom within Windows. The folio wing procedures are used for both types of installations (Note: For these installation procedures, the 3.5-inch drive from which you will be installing the program is assumed to be the B drive). DOS Installation 1. Insert the Hyperventilate disk into the appropriate drive. 2. From the C:N> prompt in DOS, type "COPY B:\*.* C:\WINDOWSPLUS". Windows Installation 1. Follows Steps 1 -5 of the "Loading Spinnaker Plus." 2. Click on the B:\folder icon so that it is highlighted and/or a dotted line appears around it 3. Ch"ckon"File"anddragdowntothe"Copy" command. The"Copy"windowwillappear. 4. The curser will be located at the "To" path. Type in "C:\WINDOWS\PLUS"; click on "OK." 5. When the installation is complete, exit from the "File Manager." Opening Hyperventilate 1. Enter Windows. 2. Double-click on the "Windows Applications" icon (if this window is not already open). 3. Double-click on the "Plus" icon. 4. Close the "Home" window. 5. Click on "File" and drag down to "Open." The window "Open Stack" will appear. 6. Either double-click on the "SVS.STA" file or click on "SVS.STA" and then click on "Open." The user is now in Hyperventilate. ------- - Hyperventilate Users Mamuil Addenditm- Ihstalling Spinnaker PLUS "Run-Time" Version with Hyperventilate 1. Create a subdirectory on the hard disk for Hyperventilate and Spinnaker PLUS "Run Time." For example, from the C:\> prompt, type "MD WINDOWSNPLUS". 2. Copy all die files from both the Spinnaker PLUS "Run Time" diskette and the Hyperventilate diskette to the subdirectory. For example, from the C:\> prompt, type "COPY B:*.* C:\WINDOWS\PLUS". 3. Follow directions in "Creating the Spinnaker PLUS Icon and Opening Spinnaker PLUS" with die following exception: substitute "plusrtexe" for "plus.exe" in Step 8. 4. Follow directions for "Opening Hyperventilate" to run die program. .Addendum.^.. ------- - Hyperventilate Users Manual • Disclaimer The Hyperventilate software package was completed under a Federal Technology Transfer Act Cooperative Research and Development Agreement between EPA and Shell CHI 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 isrecognized as an effective remediation alternative for many underground storage tank sites. Hyperventilate is based on the document titled, "A Practical Approach to die 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. EPAwillnotprovideinstatlationservicesortechnicalsupportinconnectionwiththeHyperVen^ 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. ------- - 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 Room EC-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. ------- -Hyperventilate Users Manual - 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, HX, 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. ------- ------- - 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 Hyper Ventilate - General Features of Cards - Sample Problem Exercise - Navigating Through Hyperventilate - Is Venting Appropriate? - Field Permeability Test -System Design References i ii 2 4 4 4 5 5 7 8 8 12 22 26 35 36 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 of In Situ Soil Venting Systems ------- -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. ------- -Hyperventilate Users Manual - Pressure Gauge Vapor Flow Air Bleed Line I Vacuum f Pump Flow Meter Vapor Well Vapor Treatment Unit Flow Meter Contaminated Soil Vapor Flow Groundwater Table flume Figure 1. Schematic of a typical vapor extraction operation. ------- - Hyperventilate UsersManual- 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 Hyper Ventilate 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 ------- - 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 them 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 "tf" 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 a 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 comer, 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. ------- - Hyperventilate Users Manual - Buttons XI A Practical Approach to the Design, Operation, and Monitoring of In-Situ Soil Venting Systems wsioa 1.01 «19«1 AH Rifttt fiwtmi Economics t HyjuCwi Buck Cnttti >y: PavlC. Johnson, Ph-D. Amy J. Strttntm Shell Development WwthoDo v R«j«»reh Center About This Stack Go to First Card 4 SyMMnMontorinc ^ Field Tests System Design 4 Sit Investigation -f About Soil Venting Is Venting Feasible? Vapor FlDV \ 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 10 rust card in Venting Stack Goe next cam Oo t> Help card text field (Calculate) Perform »C«Jculatkm When curious, dick on Symbols, or Fields Fields may contain information, or they may be a place for you to input numbers. Scrolling Field: dick on tiro vs to move *xt up or do va Bond Data Field: When you see MI I-beam conor tppeu in a boxed field, click the mouse in The box «> set Hie cursor. Then you m»y enter dtte.. A bunon vlll ten usu»Dy be pushed to perform en ection or cekuktion. Click on the wrovs , or move the box up or dovn vlthihe mouse. In this *n*. TOU can Try this example: Enter Number in Box I 11 inches (Click for calculation) 2.54 centimeters Figure 3. Card HI of the "Soil Venting Help Stack" stack. ------- -Hyperventilate UsersMamal- 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) Airow 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). ^^^^^^^^m^^^^^^^^^^^^^*^^^^^*mt^^^^^^^^^^^^m^*mmm^^^^^^^^^^^^^f^^^m In-Situ Soil Venting System Design Process Ton ran click on «ny block in ftis di*cnm * get more information about (hut pwticukr >*p. Or jou era begin »t the start of die pieces* by ctjckine °n either the "LetX or Spill Discovered" box, or fee urov M the bonom of (his card. (Let* or Spffl Discovered} "Clean- Sits Figure 4. Card 3 of the "Soil Venting Stack" stack. V ------- •Hyperventilate Users Manual - Number of Venting Wells... The procedure forestimatinc fee required number of extraction vclb is similar to the process used previously to determine if venting Is appropriate at a given site. As illustrated at the right, vt vill estimate single vertical veil flovrates, calculate the minimum vapor flov required, determine fee anal extent of influence, and then factor in any site-specific limitations. This information tten determines the necessuy number of extraction veDs. Jost proceed «foDo v the steps dictated on [ tie foDovinj cards—> Flovrate Eattmatlon Maximum Removal Rate Volume Requirement Slw- Specific Limiwions Area of Influence Requirement Figure 5. Card SD1 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: Tit'e 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). ------- Step 3: 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 title card of the "Soil Venting Stack" (Figure 2). Step 4: Location: Tide 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 (8t hold button dovn) to see costs associated vith that item. ft Figure 6. Card 27 of the "Soil Venting Stack" stack. ------- -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 night be applied to remediate a given site. The organization and logic of this stack follovs the paper: *A Practical Approach to the Design, Operation, and Monitoring of In-Situ Soil Venting Systems* Uy: P. C. Jobason, C. C. Stuley, M, W. Kemllovskl, J. D. ColHuit, & D. L. Byes* published in Ground Water Monitoring Reviev, Spring 1990, p. 159-178 If M tikis toiat yom to aot feel comforatla witk ttt* vst of Qt» tanois, click oic« on '?• for note iifo on the neckamics of tkis slack... 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 should feel comfortable navigating around in Hyperventilate. 10 ------- r About Soil Veatiag... Soil Venting (a.k.a. "in-situ soil venting", "vacuum extraction", & "in-situ vapor extraction") is rapidly becoming one of the most practiced soil remediation processes for permeable soils contaminated vith relatively volatile hydrocarbons. The underlying phenomena that influence the success of any soil venting operation are easily understood. By applying a vacuum Vepor Treatment Unit Vacuum B lover Figure 8. Card 2 of the "Soil Venting Stack" stack. Help: About Soil Venting More information about sofl venting cut be found in the foDo Vine articles: M. C. Mtrky and O. I. Hoeg, Induced Soil Venting for (be RecoveryfRes*>r»tion of Gasoline Hydrocarbons in tbe Vados* Zone, NWWA/API Conference on Petroleum Hydrocarbons and Organic Chemicals in Orotindvewr, Houston, TX, 1984. P. C. Johnson, M. W Kembfcvstt, and J. D. Colftart, Practical Screening Models for Sofl Venting Applications, NWWA/API Conference on Petroleum Hydrocarbons and Organic Chemicals in Groundvurr, Houston, TX, 1988. N. J. HuttJer, B. E. Mtnphy, tad J. S. Oierte, S*» of Technology Reviev: Sofl Vapor Extraction Sysfcms, U.S.H.P.A, CR-814319-OM, 1988. D. J. Wilson, A. N. Claike, and J. H. Claike, Sofl Clean-tip byin-Jttu Aeration.!. Mathematical Modelling, Sep. Science Tech., 23:991-1037,1988. H2 Return [Print References] Figure 9. Card H2 of the "Soil Venting Help Stack" stack. 11 ------- - Hyperventilate Users Manual - V.3.2 Sample Problem Exercise • Is Venting Appropriate? In fV.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. North South 10' 20 _ § j 30, 50 — 60—I • M» « • H • .m* * * •1 • ^^p> • -0.3 1 •0.2- - j "0.02 -0.0 .0.0 I *OT - I -0.0 • 1.7 1 -24 i ,73 l L9.5 ' k V Tank Sandy V Backfill Clay V ------- -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). IB Venting Appropriate? Read This i FlOVIMB 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. ------- - Hyperventilate Users Manual- Flowrate Estimation: O Medium Sand ® Fine Sand OSiltySand O Clayey Silts O Input Your Ovn Permeability Range Permeability Range (darcy) 1) Choott Sou Type, or Optional- Enter your 2) Enter W«n Rid to (in) 3) Enter Rtdtw of Influent* (fO *, Intern! Thickness*1 4) Optional - Enter your ova v»U vacuum (406* - max) 5) Click button t> eilcuk* Predicted Plovnte Ranees I 1 I toT 10 I Veil Radius Radius of Influence in ft Interval Thickness* I 66 Ift [ —>Calculate Flovrate Ranges*— ] * tUcloui of >cnu«i iattrvil, or Predicted Flovrate Ranges WeU Vacuum P. (torijO) Fk)Vi»te (SCFM) .1.0. 20 Q.33 1.30 Figure 12. Card 8 of the "Soil Venting Slack" 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. ------- -HyperventilateUsers[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 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 •iiftYHovDo I M««su» » Distribution?] Figure 13. Card 10 of the "Soil Venting Stack" stack. Help: Compound List | Viev Only Mode | * Compound Name Mass Fraction Molecular Weight (c) Vapor 1 2 3 4 5 6 7 8 9 10 propane isobutane o-butane trans-2-butene cis-2-butene 3-methyl-l-butene isopentane 1-pentene 2-methyl-l-butene 2-melhyl- 1, 3-butadiene 0.00 0.00 0 0 0 0 0.0069 0.0005 0.0008 0.0000 44.1 58.1 58.1 56.1 56.1 70.1 72.2 70.1 70.1 68.1 8. 04673 K> 2.75865 n 1.97431 if 1.84196 Ii! 1.67019 II 0.88399 11 0.73146 11 0.64989 m 0.62093 if 0.60914 K> I 0.99628 Sum of Mass Fwctons (ihoxild b« .1) Hov Do I Mewuie a Dlstribution?^« Rttum te Vapor Cone. Estimation Card Figure 14. Card H16 of the "Soil Venting Help Stack" stack. 15 ------- -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 ------- -Hyperventilate Users Manual - Maximum Remo val Rate Estimate* select your unit preference beta v OUcg/m Ho*: These are "maximum removal rates", and should only be used as screening estimates to determine if venting is even feasible at a given site. Continue on to the next card to assess if These rales an acceptable... Temperature (*C) Soil Type Sofl Permeability Range (darcy) Well Radius (in) Radius of Influence (ft) Contaminant Type Permeable Zone Thickness (ft) Pv - Well Plovrate Estimates Max. Removal Rate Estimates Vacuum [SCFM] [»'*J (inHjO) (single veil) (single veil) ™.5.._. ...IQ .. 20 40 120 200 .... 0,66 .... } 30_ 2.54 ....JLZ..L.... ... 6,83 1007 to to to to to to to ....112... 6.5$, 13...Q2._ 25.38 68.27™ 100.66 6 . .....12 25 52 ._.....&0_ 178_ 364 to to to to to to to ....._.6.2 __12L_ 2.5J 517 7.o,9_ 1778 3636 Figure 15. Card 12 of the "Soil Venting Stack" stack. I* Soil Veatiog 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 ®kg Estimated Spill Massl 4000] Q ib (2J Enter Desired i—Tgj Remediation Time ' vAx ^ ->Press to get Rates<- J Single Vertical Well Results days Desired Removal Rate: Gauge Vacuum (in H20): Min Flovrate @ 200 in H2O Max Ftovrate @ 200 inH2O Max. Est Removal Rate: (lover estimate) • per veil j^ (upper estimate) - per veil [~ 200 ID. 07 100.66 (inHZOJ [SCFM] [SCFM) 164.892 IfcMJ Figure 16. Card 13 of the "Soil Venting Stack" stack. 17 ------- - HyperVentUate 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 Figure 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. ------- - Hyperventilate Users Manual - Model Predict/oat To the rightist summary of the data you havt input Ifyouvishto change a»y of the tafo, then click on the parameter name, and redo the calculations on the cud you vill be taken to. Press the blinking 'Return' button to come back The model returns output that tllovs you lo deterniine iwidual unounts of compounds falling vithin 5 boOinc point IUICM. Type in your OVA nnces, or choose the default values. lllHI Son Type Sofl PenwibflHy Rant e (daicy) Well Radius (in) Radius of InOoence (ft) Comuoinut Type Penneable Zone Thickness (ft) [ —> get Default BP Ranges <— .*!.. Boilinsf Point Ranee -=5DL ..11.1...... Jo, 144 tp ?0 £.. ...IQ.......UOJ.JIU..C £. c H4 250 Generate Predictions til me more about BP runes. Figure 17. Card 16 of the "Soil Venting Stack" stack. —> Import Oata<— ^ S«nmttd Vapor 0.20S3H*03 FIRST PRESS TOE IMPORT n ATA R T TTIt iM I These an the results for the contaminant type that you have QtfM(O) L-airt f-residual .00 .24 .57 .98 1.49 2.11 2.87 381 Vapor Cone. [» Initial] 100.000 75.062 58.631 48.078 39.390 31.941 25.916 21 ISO Residual Level [98 Initial] 100.000 95.000 90.022 65.034 60.034 75.035 70.035 65037 £ Mia Yalnn* ID Benum ImlflAl t>»*M«uil 1 ijii Temperature (*C): ry Contaminant Type: BP«1 Residual [96 total] .690 .123 .000 .000 .000 .000 .000 .000 BP*2 Residual [96 total] 11.650 9.263 6.755 4.512 2.632 1.222 .385 068 BP*3 Residual [96 total] 24.010 23.982 23.474 22.403 20.771 18.503 15.556 12.053 128 48 |L~^ l- If 0.10 | MJM!,,!! 18 | Weatheiei Gasolla* BP*4 Residual [96 total] 22.140 23.000 23.820 24.577 25.246 25.766 26.031 25.919 BPttS Residual [96 total] 41.510 43.632 45.950 48.509 51.350 54.509 58.028 61.959^ ^> 'B ?£ m m IHUl h«j 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 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 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: Card 18 of the "Soil Venting Stack" stack. Action: Click on the right-pointing arrow button to advance to can! 19. Result: 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. I^^^^^^^^M^MW^^^^^H^^^BM^^^^^^^^HMWiV^^^^^^B^^MP^^^^H^^^^M^^^^^^B 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 [*C]: ConttainBAtTyp*: ^_ Soil Type: [^ Well Radius [in]: Eat. Radius of Influence [ft]: Penmetble Zone Thickness [ft]: Flown* per Well (120" Vtc) [SCFMJ ZTovn* per Well (120" Vtc) [SCFM] Min. VoL of Air [Uf-iesidukl]: Estimated SpflJ Mtsj: Desired RemediatJon Time [dtyi]: 18 Wmtk«ra< GuolfB* 6.6 6.83 68.27 128.48 4000 180 OB Tour Inpwt Parameters Figure 19. Card 18 of the "Soil Venting Stack" stack. 21 ------- - Hyperventilate Users 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 API 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 AP3 of the "Air Permeability Test" stack. Step 3: Location: Card AP3 of the "Air Permeability Test" stack. ------- -Hyperventilate[Users Manual - Action: Step 4: Step 5: Result: Location: Action: Result: Location: Action: Result: 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 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. Card APS of the "Air Permeability Test" stack. Click on the "Return" button to return to card API of the "Air Permeability Test" stack. Then click on the "Data Analysis" button. You are now at card APS of the "Air Permeability Test" stack. Card APS of the "Air Permeability Test" stack. Read the text, then step through cards AP6 and AP7, until you reach card APS of the "Air Permeability Test" stack. You are now at card APS of the "Air Permeability Test" stack. Air Permeability Test - Instructions 1) 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 i™, to seal annular borehole region). [ shov me sample data FOR Volwne EstiiMtioa: Enter 1) Soil Layer Thickness {ft]: 2) Estimated Radius of Influence [ft]: 3} Air Perm. Tesi Flovrue {CFM J: 6.6 50 15 ( -> Calculate < Pore Volume: Time to Extract a Pore Volume: APS Figure 21. Card APS of the "Air Permeability Test" stack. 23 ------- -Hyperventilate Users Manual - Step 6: Location: Action: Card AP8 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 Gauge Vacuum [mini fin H?O1 9 0.1 11 0.2 15 0.2 23 0.4 30 0.7 40 1.3 100 2.8 flowrate screened interval thickness Time fmin] 4 7 9 12 16 24 30 39 52 77 99 110 121 141 = 15 = 6.6 Gauge Vacuum [in H?O1 1.2 3.0 4.3 5.5 6.9 9.9 11 13 16 20 21 23 24.5 25.5 SCFM 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 "~>Calculate<~" 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. 24 ------- -Hyperventilate Users Manual - Air Permeability Tett - Data Analysis (cont.) Eater radial 2) distances of monitoring poino Enter measured —< 2) times and gauge vacuums ^3) Enter (optional): a)ftovra* L 15 1(SCFM) b) screened interval thickness 6.6 I (ft) 53 (min) (inH20) r= j 32.4 |(0) (nun) (in H20) 9 11 15 23 30 40 100 O.I 0.2 0.2 0.4 0.7 1.3 2.8 o " , 4 7 9 12 16 24 30 39 52 7V 1.2 3 4.3 5.5 6.9 9.9 11 13 16 20 -6 J & is .. <> Figure 22. Card APS of the "Air Permeability Test" stack. Air Permeability Test - Data Analysis (cont.) On the previous Card (AP8), the da» you input vere fit to the Approximate expression given on Card AP6. It v*s analyzed using both methods described on card AP7, if you input values for the extraction veB ftovrate (Q) and the stratum thickness (in). Belov each column of data, the tvo calculated permeability values aic denoted by: darcy(A) - refers to calculation method 1 (see Card AP7) - refers to calculation method 2 (see Card AP7) During the regression analyses, the data expressed w pairsof points (ln(t),P') are fit to a tine The "correlation coefficient", r, is a measure of hov veil the date conform to the theoretical curve. As i-->l, the data points all fall on the theoretical curve. At the right are given the correlation coefficient values for the three data sets For more info on the meaning of r, consult any introductory Statistics book. Correlation Coef. (r) data set tl |0.941158 | data set t2 I 0.98602 data set 13 I NoDat* Figure 23. Card AP9 of the "Air Permeability Test" stack. V ------- - Hyperventilate Users Manual - System Design Slulr/* T««ffl» riUf fa* O«>*------- -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 ID provide a generic recipe for vacuum extraction system design; instead v» suggest the lollo vine •» » structured thought process. As you shall see, even in a structured thought process, intuition tnd experience play importat roles. Then la no substitute for a food fundamental understanding of vapor flov processes, transport phenomena, tad groundvater flov! O Number of Extraction Wells OWell Location O Veil Construction O Surf ace Seals O Groundvater Pumping System O Vapor Treatment * 33* Figure 25. Card 24 of the "Soil Venting Stack" stack. Number of Venting Wellt . . . The procedure for estimating the required number of extraction veils to stanfltr tt the venting a appropriate at a given st*. As fllustt»fcd at ft* right, v» vill eitlmaie single vertical veil flovrates, calculate the minimum vapor flov required, determine ine anal enent of influence, and then factor in any site-specific limitations. This information then determines the necessary number of extraction veils. Jut proceed to folio v the steps dictated on the foDoving cards — > FJovrate Estimation Maximum Removal Rate Minimum Volume Requirement Site- Specific Limitations Ana of Influence Reauinment N\_ Hunter (i . °' A-^ Sxtnctlom sy Wells 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 subsurface interval (ft BGS) description of contaminant radial extent of contamination (ft) interval thickness (ft) average contaminant concentration Medium Sand 10-30 gasoline 20 20 100 Soil Zone Clavev 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 H2O) WeU 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. . . (soilstiaticraphy fc containinant characteristics) Please enter the required information for etch distinct soil layer, click on (he "Upde* " button, and then proceed to the neit cud (i.e. cUck on rijht irrov at bottom). f the »b kev can be used to me ve betveen cells) Select the totrt mas tinit* that you prefer C Clear All Entries J OPb] Description of SoU Unit J. JLltaL 4 DepthBOS* 30 «L A ... _»,. _»., 3SL .*... to SB- Description of Contamination Contaminant Distribution ntiu [A] JO. 20 [ftl JO. —JUKU- 1000 CeJe. To«l Mess DC] J2IL2. 0.0 •Maw Grauf Bwfut Figure 27. Card SD2 of the "System Design" stack. Design Input Parameters... Please envr the nguixed infoimation for eech distinct soil layer, and then proceed to the next card. No*: - click on an; (able headinc to tet more info - use tab key to move betveen cells O MtUva, Su* On&i'oi O Billy Bui Extraction Wefl Construction • Ewtr or ckMf• (nm Ust «t to) rjgil Figure 28. Card SD3 of the "System Design" stack. V ------- - 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). Step 8: 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 Rangeso-" 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. ------- -HyperventilateUsersManual- Critical Volume Calculation... typically observed In venting operations. The results an plotted in this vay t> emphasize that Ac degree of remediation that can be achieved by venting depends mainly on the volume of vapor extracted divided by the initial mail of residual hydrocarbon. For the example pictured at the right, approximately 100 liters of air must be vitbdravn from the subsurface In order to remove about 90O of a single gram QC/QC(UO) 1 % Removed 100 Return to Design Weathered Gasoline T-20*C 10% moisture content C(t=0)« 222 mgrt Figure 29. Card SD5 of the "System Design" stack. Critical Volume Predictions... Simply enter the temperature at the right, and then specify the composition of your contaminant. If you are unsure about this, elicit on the "About Composition..." button located at the low right The model returns output that alia vs you to determine residual amount! of compounds falling; vithin 5 boiling point ranges. Type in your ovn ranges, or choose the default values. tell me more about BP ranges. Contaminant Composition (choose one) J~ 1 L_ ;> Enter Distribution D "Fresh" Gasoline i) "Weathered" Gasoline ( Viev Distributions J ( ~> get Default BP Ranges <— ) .M!i.ngP.oint.Bange....»3.. M!.i.Gg.P.oint.RaBge..*4. Boilinp Point Ranfe ------- - Hyperventilate Users Manual - Step 10: Location: Action: Result: Step 1 1 : Location: Action: Result: Step 12: Step 13: Step 14: Location: Action: Result: Location: Action: Result: Location: Action: Result: Card SD7 of the "System Design" stack. Read the instructions, then click on the "-->Import Data<~" button. Your screen should look like Figure 3 1 . 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. Card SD7 of the "System Design" stack. Click on the "Return to System Design" button 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**11 column for the medium sand soil unit. Card SD3 of the "System Design" stack. 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 Card SD3 should now resemble Figure 28. Card SD3 of the "System Design" stack. Click on the right-pointing arrow at the bottom of the page to advance to Card SD4 of the "System Design" stack. Card SD4 of the "System Design" stack should appear on your screen. Card SD4 of the "System Design" stack. 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. 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. ------- 'Hyperventilate Users Manual - To read about these, click on the "Number of Wells" column heading. Your card SD4 should resemble Figure 32. // is importani 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 1,P.T. Kostecki and E. J. Calabrese, editors, Lewis Publishers, p.253 - 281, 1991. 33 ------- - Hyperventilate Users Manual - —> Import Data <--J Saturated Taper n 0' rm»/r i In*'L1 FIRST PRESS THE IMPORT DATA BUTTON! These are the results for the contaminant type that you have L-ato g-iesidual .00 .24 .57 .98 1.49 2.11 2.87 3.81 Vapor Cone. I» Initial] 100.000 75.062 58.631 48.078 39.390 31.941 25.916 ^1.150 Residual Lewi [* Initial] 100.000 95.000 90.022 85.034 80.034 75.035 70.035 65.037 £ Min Volwott to 1 ^ >90» of Initial IJji Temperatui$ Contamlnai BPI1 Residual [96 total) .690 .123 .000 .000 .000 .000 .000 .000 BP*2 Residual [96 total] 11.650 9.263 6.755 4.512 2.632 1.222 .385 .068 EtolDDV* Resliwl e(*O: « Type: BPI3 Residual [SB total] 24.010 23.982 23.474 22.403 20.771 18.503 15.556 12.053 128.48 | JrJShlSi 18 | Wettheiet Gasoline BP»4 Residual [96 total] 22.140 23.000 23.820 24.577 25.248 25.766 26.031 25.919 BPtS Residual 41.510 O 43.632 ~ 45.950 fl 48.509 I! 51.350 | 54.509 56.028 || 61.959 O Return to System Design Figure 31. Card SD7 of the "System Design" stack. Design Input Parameter*.. Pleasa enter (1) the desired time period for remediation, (2) the design gauge vacuum, and then (3) click the "update" button. No*: - click on any table heading to get more info - we tab key to move berveen cells Minimum Number of Wells Description of Soil Unit Tune for Clean-up Mays| Design Vacuum ------- - Hyperventilate Users Manual - References Hutzler, N. J,, Murphy, B. E., 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. D., 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 Huh, 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. Sci. Health, A17(l), 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. ------- ------- - Hyperventilate Users Manual - Appendix A: "Soil Venting Stack" stack cards. ------- 'Soil Venting Stack" Cards A1 p I A Practical A t»tb* Uooitoruc of lB-Sita Soil V« m»IJI •mi AaH0uai DdoaCMia •1C. JU A»TJ. i tf n.o. M«l1M>«tak ff OttoOMClf* I«Tn •*T Tbi» HypaOrt Stact v» u «*d to halp guuto mnu unmulit icantott through tt» ttttvte frocM Mcavjary to doada if ant bov (oil wntug migM 1» appliad IP ra foUowitbapana i »gT»i «» Tl» orgunboo and lope ef UMJ rack ckto •i UoKtoruc of I»-Sit» Soil Votuf C. C. >h»by, M. W. Lnumtt. J. D. Cdtel. * D. L. *) nd Wnv UaBitoni«Rnwv, Spring 1990, p. 159-178 Soti Vtnhag (».»«. 'u wring*, •^icuantanetwo*, Ic in-ntu Tipef mutUmi") n npdl; taconiag «o> rf Ot mod f« pnmiil* Kib taflunot Iha weeaa) ef anf toil ivtiag ofMnboci •• MBly uudaritoid. By^^7ii«iiKui ID tl» follow* canto v» vflt wun U* • latk or 9ill l» tan ilaeomd, No» wt vill Off Ormifb » l»gdl to ( art dupUp da flovdvt tte if tto uferttBthn«btpncm. Clickint viUu B7 [IDCMI box viD Mfei f»u to tW «q»ct «f ttt ttougU Soil Venting System Design Process Invwtifilioa • nil im»Higaii)u n conducud to BOOB Of Mil VBd * ............ * ........... ' ...... Tte mttct on pntrtial human and rawMan. and it conductad in a nlatnalrihoitpriodor, on* •qlon Ite (*Mtaiit7 of «D traM Otnammtioo («*, q«d, fnittiBf pnttan ta wtrtfatad. m ttao 0» fin! Soil Vwung it mod liWy to bt HBOMBM vtaB foilt «• mtdjmA t QlD-SituBtortinJalioo O^ftiMififrtii^rttiliKmi OSolw* ExtndiaaSoil Voting M ite pou* «• vill prooMd Urougb a 0*104*. proc«i to (tacidt if Mil At telonltM I ------- 'Soil Venting Stack* Cards A2 O top* Y«* O»o Pwmdility Rang* Til inrtilitj lti»t« I I Itol Ifl I Vdl Radn I 2 I in Ratal of laftam I 40 lit I 6.6 in rate oecw* vbmmr Om npon ronowl by anting w ' or in tqvilitniaa vilh (be IntheraacardyouviUutuBMa of JOW O tfai uMnctMtt in tte i^frv krfl oocnr of th0 uul cvd. Vapor CMMHUMMM 1 Typ« in Tonponhn (*C) (tit ) Calculation 20 J Click to EiMr Contortion of Coolan»nM* O Enter Diitnbuaon ! or O 'FrBh' Gasoline Cboon one of tht Drfwlt DirtnbUiOM ® • Wnttond" Gawlme T) Click to Vwv DiUhbuboB, (optiond) T) Click to Parfonn CalniMxM C VJOT Dutnbuuopi 3 O P«fonn CalcublKW Remov*! R*te Estintmtes Tht nmowi rate occm vl Ua Kport ronowd by wntmg or in equilibnun nth U» Th> 'RonMil Rate' if amply OB prodict of )!• flovnto tim« te npor caocartntooo. R«to Vipor z V»por ConcntratioB Flovrat* ean mf 5 10 20 •4 60 120 2on 0.33 0.66 1.30 ?-5L J.71 6. S3 1007 to to to to In to to 3.32 6.S9 >3.tt? 2S.3S 37.09 6127 10066 6 12 25 52 SO 17S 3M 121 2SI 517 799 1778 3636 At Ihu potnt, you coopv* the with you- diond ran»*il rate. If OB do« not (End yo«r dwnd iwoml rate, ttm soil wring » ootltMy to OBM TOtr andi, Dndi UMJIV rwlifttc. Imhaanitanb. T»villr«ru» CD Enter Ownd Remediation Tins O «««t • Uf*tRW»<— Sugte Venial taHZO): pan 9200 _UJ IOt.66 MM) |hK20; |1CFH| [: «^->-»-*«» rjfrr Ml MM) W) oriy• • Ibiteaf, ad **^*|M te raRmd if ^cfting is TypioUy doing toil untinft tbtz (vbntetottl *por fiovrate • W of not1 [QC(tXQC(UQ)],«bilttni *..-j|'--_ TJlllI ,—I*. — UUffUBUUM "UUI II tott votinte of i .1 .01 .001 .0001 ------- •Soil Venting Stack' Cards A3 Is Veatiaf Appropriate* IK Wa (120- Y«J [tCPM] NotolW MM.Tci*A*(m-wil.lt of wtUf if Clidt on (to tah» to OB rij* to System Design System Desifa... ------- "Soil Venting Stack* Cards A4 System Dcsira... Economics... System SJbat Down •Click' OB 107 item telov (t hold button don) to M cocte vitk that item. TrgKiotl clMD-up Ineti HOOK - J250K for tta wting on •idnbmdootbBiftumM pomtiil iapKt flat «7 randtal m»y bm on «r clMo-up tiini, ptrmiaing Kd tfci typt of O £>lncti«B V«U V ^or C O EHr«tioa V«U Vtpor Compontto* *too to ralKMi to nf*tr Tte tvo mjor COM •• Titb Uv OSoil Borin* EMa Acknowledgements. ------- ------- r 'Hyperventilate Users Manual - Appendix B: "Soil Venting Help Stack" stack cards. ------- •Soil Venting Help Slack' Cards B1 Help: Stack Information Buttons Biraom have been placed in each curd. Clicking on any button will perform in action. tuA ac When curiaiu, click an Symbol*, Picmet or Tea. Fields Field! my contain information, or they my be i place for yon to input nimben. Scrolling Fi«M: Help: About Soil Venting Un» afonpuo. Awl (oil wumi OB te rood t> *» followiit Orp V Onmtwua. tfaUM, TX. I Or|>Ke N.I.Itaotot. B.E. Mun*».l»U S OMB. SUB orTuhDotoiy SCVBW: Soil Vapor Eincioe I SyiMHl. UJB^jk, CRJU319-01-1. 1«M. | D.I. Wilaoa. A. N. OKto. «d J. H.d«*». Soil r>M->p by ffl*tu Acnao^ I ISM, Help: In-Situ Soil Venting System Design Process Help: Preliminary Site Investigation Thi* if the deciiion prooeM iha one nuut follow to: I) decide if toil vetoing it tpplioble it a given cite & Z) design in effective toil venting iyttem ll ii tn tbridged vention of Rfure 2 in M Practical Approach to tte Duif*. Opmtiat, A Mont/WMf ofln-Siut Soil V,HIM, Syntmt". by P. C. Johnon. C. C Stanley. M. W. Kcmbtowiki, 1. D. Colthvt, Kid D. L Bycn. Mow infonniiion about rile invcmimoon and rcmedution can be found in the following nuclei: API Publication 1C28 "A Guide to the Aseunxnt and Remediation of Underground Petroleum American Petroleum Innitulc, 1230 L Street Nonhwen, Waihington DC, 20005 Help: Thermal Desorption Pntm Dtteriptiea in i thermal dexirptii proccaa, aoik conuuninaicd with voUnlc/iemi-voUUJe orfanic* ire heated, and the volatilized contaminUM are nripped with air, •team, or combuation producu (burner flue (ate*) at relatively nodeat tonptnmn* comparad wiih incinentica (200-500'C > 1000-1200'CX Ihedcaortaed organic oonuunuumu are Help: Incineration FnctH Dticriflio* Incinenuon, or the thermal douwcuon of waoea, it a complete dcatruction technology that can be uaed to treat aoila contaminated with a wide range of hazardous organic •ea. Contaminated aoila. tludgea, or liquid waitca are added to a high-Umpenturc combuition (rotary kiln, fixed hearth, multiple heanh. nuidixed bed, liquid Pncfti Dtterifdam Compoatrat a an above-ground soil mmatonent lechniqiie in which amended toil, containing organic waittt, it placed in large pile* and aerated. The tendon enhances microbial dejradation by providing oxygen to Hie toil/wane. Wife time, the deoompofed wane i§ reduced in weight and volume, and Ite proceaa produce, a ttabifoed. enriched. humu»-like maurial. Pratfii Dncripllau "Landfmrming" icfen to the practice of tprcading organic over an are* of land, then relying on natural microbial action to degrade the wine. It in widely accepted and con-effective practice for Ihe treatment of petroleum hydrocarbon*, chlorinated compound!, and peadcidea. Inthu procew aoil-uMciated roieroorganiBn§ (bacteria and ------- •Soil Venting Help Stack* Cards B2 Help: In-Situ Biostimulation Help: Solidification / Stabilization Dttcrtfttfm Pnattt DttcrifUf* Treatment of groundwter Hid toil comanunaiion below the water able ("utiiriied zone") by in-«ini bioctimulaiian involve, flic addition of nutrienn and/or O2 (uwally ai H2O2 or liquid O2) 10 m aquifer in order to enhance the degradation of the hydrocarboni by indigenoua uil microbe*. The nutriena mi oxygenate added above (mind to Stabilisation and | ir Em] UK Taa eqaMioa totow • ia> Help: Unit Conversion (k and K) I > am nlae tf kydnuMe andxb>riiy m fenaMUiir n be cnvuvd DCaoOKaaaalcaiai O cmk O ftM • on1 O darcy Compwud Nimt uobuiane n-buune truw-2-bulene cia-2-bulene 3-methyl-1-buune 1-pcniene 2-meihyl-l.buUnc 2-methyl- IJ-buladiene Man MaUcalar Prm.r< Fr.di.. Wri.lt (.) 0.00 0.00 0 0 0 0 0.0069 0.0005 0.0001 1.0000 .1 5..1 58.1 56.1 56.1 70.1 72.2 70.1 70.1 68.1 0.94 0.7S 0.7 047 04S ------- 'Soil Venting Help Stack" Cards B3 Summary Card: Site Characterization Compound List Default Data Acomplete tile tttrumemmuat determine tie following: Svburracc Characterbliei Caatamin*M Dcltaeatloa • enmiofri Help: Data for Fortran Program Help: How Do I Measure a Distribution? Ml* V*cr » Compound Na MdtoilirCQ W«H. 01 («-) (AOD) SohiMlitr Du. 9T» CodT 20-C cu-2-bbBB» 3-oxrtyl-l ITt-l t^JBW-1. 44.1 St.l 51.1 56.1 56.1 70.1 72.2 70.1 70.1 «l.l »J i.n 2.11 1.J7 1.7J 0.96 0.71 0.7 0*7 OJ55 62 »9 61 430 430 130 4« 141 113 6*2 73 537 946 20* 204 701 l«3 710 52) 323 0.00 OJM> 0 0 0 0 O.OOW 0.0009 O.OOM o.oo«o Help: Calculate a Distribution Help: About Calculation In dm eniimtion of equilibrium (•Hinted) vipor conocmnlioni. we mume ttut the conuminim coocenmtiom in fral enough (>200 m|At TTH) flat it U dilthbuled between vipor, locfeed. ditiolved-in-ioil- moimre, A fiee-phuct. In thii cue, the oqutlion u the right •pjttia Oook for -JUouH'i UW * Ae Idoil Gw LJW-in my IpUiiMxiynuiuoi tcxioook fof RferenoEt). We do correct for • nal v^gr nManm Help: 6a) Dilution Effects [Bypassing] Help: 6b) Liquid Layers SM< View Vi*w Tbefnure ibove depicuihe cue where ume npan "liypMi* taum of conmiintion. nd flmdbre the npon removed from the unction well npretem t mixture of the vcpon obninod from both contmintted md elan vipor nowpMhi. One am roughly judge the tmounl of byp«nn» by the weU placement, fcncning, md conuunirmu diflhbutioa Genenlly, otnerved la Figure fib, rapor flowi pnllel to, but not through, the tone of iorutr^trieugn^icmtiniwtnniterreiiiunceiiviDorphuc diffuriaa. ThU would be the cue for • Uyer of liquid hydrocarbon rening on top of m irrfxnnemble Brali or the witer table. ThU problem wu studied by lohntan «t «109M. NWWVAP1 Pcmtoim Hydroorbont Conference) for ------- "Soil Venting Help Stack" Cards H25 B4 Help: 6c) Low Permeability Lenses Help: 6c) Low Permeability Lenses - Equations i HI In the situation depicted above, vipor flow I put, rather than through the contaminated toil zone, nich as might be the cue for • contaminated clay lent surrounded by sandy aoili. In this case vapor diffusion through the clay to the flowing vapor limit* the removal rale (the removal rale actually become* Lars Da • Calculation c l=j/d| Undine of •oricd-oW UK \m\ o • pmu [•) cudndnl MM) i* a) |BS/kfj UDC Id] Derivations for that equations arc given in Johnson, « al - "A Practical Approach u the Design, Operation and Monitoring of In Situ Soil Venting System** • 1990. These Equations are valid for single-component Help: Default Boiling Point Ranges Help: Boundary Layer Equations The Fonnn program HYPEVENT will report residual levels of compounds filling between user specified boiling point ranges. The default values have been chosen so that residual levels of compounds with boiling points between the following compounds are grouped together: Propane • Isopemane (-50 to 28 C) bopenunc - Benzene (21 to 80 C) Benzene - Toluene (80 - 111 C) Toluene- Xylenes(111 - 144C) Xylenes - Methylnapihalene (144-250 C) The equation above estimates the removal rale from a layer of liquid product by a •ingle well, baaed on a Boundary Layer Theory approach to the problem. It it not directly applicable to mixtures, because it aaaaaaaaaaaaaaavaal left Do • Calculation 1» - P,)] R«t * fHinmnrt rnacvd rue T| * efficMicy lelim* ti p* * «*Toc«** BDil verpor (haTuHoa eocffiocBt toa^/kj jt s vucoHCy at ui j» IJ, i ]0-4 f/bB-« ^ « ami penneibilicy BO vtipor flow |c»2j Rj > ndtu* tf nnuEBDB of ycBhnf weU [em) 1^. => voui&f iMdl ndta* [cm| PAM > kbMttt.* atobamt pcwtoc - 1 X)l« x 106 t/an-*a P, "itadufcpreMP B,-cr the nearest minute should be sufficient- Samplc devices are Rolen watches, hour glasses, sun dials, and timers. ------- •Soil Venting Help Stack' Cards 85 Vapor Flow Rates... Pressure/Vacuum Readings. Vipor flow rates from each extraction well «nd into any injection wellt should be monitored. Sample meuurint devices include pilot tubet, oriface plates and rotameters. It ii important to hive calibrated these device* at the field operating prcaauroi and temperatures n Pla» Pressuref/Vacuums ihoukl be manured at each extraction and injection well. In addition, subsurface pressure distributions (measured with loae tone inullaiioni) are uaeful for deia mining the zone of influence and vapor flow patha. Typical preuure/vacuum measuring devieea include manometer! and differential prcaaurc (augea. Vapor Concentrations & Composition... Temperature... The vapor concentration and coR^Maition liutii each extraction well ahould be analyzed pehodicatly. This data ia multiplied by the extraction well flowrate u> calculate the removal rate (i.e. Ib/day). and cumulative amount of cotvaTunant removed. By itself, vapor concentration dan doe» not give a complete picture of the system* performance. Dcucam The aoil and ambi 4, 4, nt lemptratiirea can have a significant effect on the performance of aoil venting system*. The aoil temperature affectt the contaminant vapor concentration!, while the ambient temperature controli whether or not condensation. or even freezing will be aigiuficani. Por future reference, therefore, it ii aseJul to record the ambient and aoil temperatures. Water Table Soil Gas Concentration & Composition... Whenever the contaminated lone lie» near the groundwater table (within 3 to 5 ft), it ia important to monitor the water table level tt> ensure that contaminated soil! remain fnpiTifd to vapor flow. Measuring the water table level during venting ia not a trivial talk becaiue the monitoring well muat remain scaled. Uncapping the well releaaea the vacuum and any effect that it hat on the water table level. WuehaBWan Theac ahould be measured periodically at different radial distance* from the vapor extraction weUXi). Data from aoil gaa sampling ii valuable for three reasons: (1) by comparing extraction well concemrauona with aoil gas ooneentrationa, it is possible to catimaie the fraction of vapor that ia flowing through the contaminated ic (i.e. the 'efficiency'' of Cumulative Amount Removed. Extraction Well Vapor Concentration. CUMULATIVE AMOUNT REMOVED it determined by integrating the measured removal rates (flowrate x | concentration) wWt time. While this value indicates how much contaminant ha* been removed, it • | usually not very useful tar determining when to lake confirmation borings unless the original spill mass ia known very accurately, la most cases that CW6) Tua>(daya) EXTRACTION WELL VAPOR CONCENTRATION the vapor concemraiiona are good indication! of how effectively the venting rynem is working, but in vapor extraction well concentrations are not strong evidence that aoil concentration! may also be due to other phenomena such aa water table level increases, mass transfer resistance (mart) ------- •Soil Venting Help Stack" Cards B6 Extraction Weil Vapor Composition... Soil Gas Data... EXTRACTION WELL VAPOR COMPOSITION when combined with vipof concentration* Out dm fivei more in»i|htinu>theeffeaivGneMofihc •yaem. If the local vtpor change in campotition. it» probably due to increaaed raw transfer micanrr (wafer able ipwellinj. drying-out of low penncability lonta, etc.), and ii net SOU. GAS DATA Ihif d*u ii the mo* meful becniie it yiddi infonmlion about the midual oompocilioa nd enatt of Soil Gu Monilorlng IniUlUtlan KctulU Vq am (•*« Vipof ooncsimtMM mi notf in ftnenJ, be luod ID dcurmine the rartkul lord, euept in the limit of | v«9 lowrakkwl kwli (when propooiocul to »oil rc«------- ------- -Hyperventilate Users Manual- Appendix C: "Air Permeability Test" stack cards. ------- •Air Permeability Stack' Cards C1 Air Permeability Tests... The purpoee of in air permeability lot if to obtain lite-cpecific data thai will be Calculate <- ] Air Permeability Test - Sample Data Pictured at the rifht are the MU vacumu nMawBDBnti from an air penneability inanity TV cpecific opentini in *A Practical Approach u> te DenfA Operation, and Momtoriai of In Situ Soil Vom*t| Synem", by P. C Air PermeaMlity Test * Data Analyrfs The expecttd decnaie in labeurface preacure (incrmae in |au|e vacuum) P if predicted by: <«»MfMi«iltl**0|«>*n*aB«a> Air Permeability Test - Data Analysis (cont.) For (r* C|iH k P** t) < 0.1, the |overniii| equation cm be approximated by the exfroaiaa: TUf Equation praScif that a plot of P* -vt- ln(t) ihould be a Mrai|ht line wiQi slope A and y-imeraept B equal to: Air Permeability Test - Data Analysis (cont.) The permeability, k. can dm be calculated by on* of two mothodc ft-. The fim if applicable when both Qtflowraic) and n> (well acre ^•^ known accurately. The caJcnlamd tlope A U uaed: © The Kcond appmeh if uaed whenever Q or m am not known wiA confidence. Jn thif caw, both the tlopc, A. and Wercept, B, m uaed: Air Permeability Test - Data Analysis (cont.) ------- •Air Permeability Stack" Cards C2 Mr Permeability Test - Data Analysis (cont.) 1» ^ JUIIIM. rmi Cfilt). te Hit 1 in i M«. II nil •hail njij >irt •>mli i i lii m tin muiimm inpnajw i«m i« mil nrt. if mil ni|iiil » ijim fw TW KncCMAIT) ------- ------- - Hyperventilate Users Manual - Appendix D: "Aquifer Characterization" stack cards. ------- •Aquifer Characterization" Stack Cards D1 Aquifer Characterization: To achieve efficient «««*«. the to expand ID air flow, ttaerafon, in moat caaea where the reaidual toil conlaminatian liet clow to, or below, the Mined nil lilili). ii milll ••Mill In Aquifer Characterization: Shu* mo* vantiai fjMam are tamltod •bow "phreaUc aquifere" (iquitei with MrfWii), ID* two prinvy njuif• pmmno* needed for oetign K • HyilTBIIllIT OOBOuOUVIly S • •fltoiv* porouty {or fpedrw yield) Itofim tedion of ihe fundvncnul Aquifer Characterization: Th«« penmeun (K and S) cen be eclkMUd uinf Iht nnlu of e modwd (rouadwaier pump ten with i comua punrii« nu. The mutu tra UMD oampend igiiact nandord type eurvei* for ^wafic aquifer titmiiam (i.e. leaky, unconfined aquifers, stt). pump MM*, md data analyst*. " bunon below far more alfeiraatioa on ftuf Ml*, bill taata. Aquifer Characterization - References ). Bev. -Hyonulici of OnoadwaW. McGnw-Hilt. 1979. ISBN CMTT-OW170-9. p.4«3.490. R. A. fnei* and I. A. Cherry. "Groundw.ier-, Premiee-Hall. 1979. ISBN 0-13-MS312-*. p. «9 - Ml ------- - Hyperventilate Users Manual - Appendix E: "System Design" stack cards. ------- 'System Design* Stack Cards E1 Number of Venting Well* ml oBMm tar ««* *ttaa ml try*, dkk cm die TptaB* tana, mt tat pnncd •> te Mil end (it. dick » n|M H fvllB^ C Cl«ir All EHrin J prom mat pcvioojty ID iaamam t vaumj at ^^tafoat it • ftWB «•. A> lUmmanl ic <• li^tt, »• oil ingle MTBMI »«U downrt, rolfnlut V.DOJ flew mpn* fee ml UMU of isflaoBO. fetor 11 ray iK-ipcafictuxu Design Input (DfediucdBmcpcralfor ten 0) dick ibe "upd**' Maumim Nmber of Welli Volume Predictions.., Critical Volume Calculation... O Enur Oinribuiian Q -Frah" Gasoline ® "Wottwrcd' Gisolme If »« « mom ikav itaw. die* • fe 'About bana tocttd u Ibe law ri|bL -> Stt DcfuH BP R»|« nwml mm. wMb to 100 200 Q«An(t»0) (1/j) Generate Crtdlctlon« Removal Efficiency... Tta nibivfiB • difficult to ) S.UrmUJ Vapor Mi* V.l.m. to Kcmo*« >*** «T Uilicl Rt.id««l I Ttcv me 4« MttlBfor Ac me atamet m "A Pnoial Appraxt» die DB^K. OJWMOB, ud Moniwmj of Ii Sim Soil Low Permobiliiy Laim Ground W»tcr Upoclling R«mm to Symm IX»igi ------- •System Design* Slack Cards E2 Help: Well Parameters Help: Minimum Number of Wells No. tar rf Wen." * akvbM >> to n» •WtU Rjdin.-. kpunliiilkiterasiMaflkt i*>lisafSl»ilta*jarasiMaflk*MU I *-— *-** >— -*-| H-| —--•:- , mpierirf •• p. •niii. *• <» «oii fen-Mi. —I liaaniltflh* ~| T tap— —. J 1 Tta •roica'aa •«». »>•» fle gage |IIM«M» im Tte Contaminant Composition Vkw Compoand Num Wtiakt (t) 1 2 3 4 S 6 7 S 9 10 propane isobutane n-butane tnns-2-butene cj**2"butcne 3 -methyl- 1-buiene mpoicuic l-pentene 2-methyl- 1 -buteoe 2-methyl- 1 >buudieoe 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.00000 44.1 51.1 SS.1 56.1 56.1 70.1 72.2 70.1 70.1 61. 1 8.5 O 2.93 111 | 1.97 li 1.79 1 0.96 * 0.7S 1 0.7 t 0.67 ! 0.65 O • lomof Mi«fW*oa> How Do I Measure a Distribution? Determining the exact composition of complex mixtures (such as gasoline) requires specialized analytical techniques. For the purpose of estimating the response to venting, however, an approximaie composition can be used with very food results. To determine an approximate distribution, one must analyze the mixture by gas chromaiofraphic analyses. Prior u> the analyses, choose about 6-10 marker compounds whose properties are well known. Calculate a Distribution taftlKlOCnMrV* K4m4lpMB»»iM> • Bill fc.TAfao.ih.oist. Tsca. Click CMcaUat. OjOO OM 0.00 1111 t>M OM OM OM OM 0.00 0.00000 1.00000 0.00000 0.00000 0.00000 0.00000 0.00000 0.00000 Well Location To be able to fuccestflilry locale extraction wells, pauivc well*, and nir&oc seal* one must have * good understanding of vapor flow behavior. Wells location* should be chosen to maximize vapor flow through the contaminated zone, while mintmizint vapor flow through other tone*. If one mil is sufficient, il should almost always be placed in the geometric center of the Return to Design Well Construction Surface Seals Welk should be screened only through the zone of contamination, unless the permeability to vapor flow is so low that removal rate* would be greater if flow were induced in an adjacent soil layer. Removal rate estimates for various mass-transfer limited scenario* are discussed elsewhere in this stack. Based on predictive equations, the flowrace is nprrtal to mmtssf by 15* when the exttmction well PVCPtpe Surface seals, such s* polymer-based linen and asphalt, concrete, or clay caps, are sometime* used to control the vapor flow pains. Figure 12 Ulusttmies the effect thai a surface seal will have on vapor flow panerns. For shallow treatment zones (<5 m) the surface seal will have a significsni effect on the vapor flow paths, and seals can be added or removed u achieve me desired vapor flowpath. For tl'OpCB'MllHIlfalX ------- -System Design' Stack Cards E3 Bp««l»( (*»»-*>) of tta Cranadwaur Ubto wiU ootw S^apor Treatment Systems CttraXly UMK I four nun pnwem mifcbte ------- Hyperventilate Users Manual- Appendix F: "Compound List Update" stack cards. ------- "Compound List Update* Stack Cards F1 Compound List Update Thit card it provided at • utility to let you add, or deklc compound! from Die Compound Lid Data BMC Ihit th* program utet. You may not deloe or change the propeniea of the bate 62 compound*, tince ihete are needed for the two deftuh fatoline cue calculation (i.e. the "Frah" and "Weathered" gatolinet). If you wish to change any of ihc properbe* of the added chemical!. Tint delete them, then reinsert them into the Compound lift Du* Bate. Follow the direction below: T} Qaafc OK of Ac foOowil«: ®ia»rl clumul QttltU ekciniul [T) Iqw «e pnacwi u *K nabi r» or \em) CWmieal ___ M«l*t»iar Wciiht (j/mot.) Viper Preunre *}2*C [•in-1 Boiliaa Pool «>1 aim 1C] Expound NOODOB Not A«n|icdl ------- - Hyperventilate Users 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, C.C. Stanley, M.W. Kemblowski, D.L. Byers, andJ.D. Colthan 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 trivia!. 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 al. 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 and 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 she 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/hydrogeological 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 Extraction Well Vapor Flow Contaminated Soil Vapor Flow Free-Liquid Hydrocarbon Groundwater Table Sotubk Plume Figtm 1. "Basic" in situ soil-venting system. Process Output Syaetn Shut-On FffHre 2. In stta soil-venting system design process. ------- ble 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 0.0 T(°C) b 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 (he., 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) where: Ces, = estimate of contaminant vapor concentration [mg/L] Xj = mole fraction of component i in liquid-phase residual (Xj = 1 for single compound) Pi" = pure component vapor pressure at tempera- ture T [atm] MW,J = molecular weight of component i [mg/mole] R = gas constant = 0.0821 l-atm/tnole-0K T - absolute temperature of residual [°K]. Table 1 presents data for some chemicals and mix- TABLE 1 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 tetraethyllead gasoline1 weathered gasoline2 Mw ------- tures 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 residual concentration (but still depend on composition), and Equation 1 is applicable (Johnson et ai. 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 will decline with time due to changes in composi- tion, residual levels, or increased diffusionat resistances. These topics will be discussed in more detail. Under Ideal Vapor Flow Conditions ~. ) - conctnmoon in medune-equviknl pom (wl/vol.) unio *•" Ffeu* 4. !• sft» rat*) i nte tad vtpor concentration. complete the cleanup within eight months, then Raccepu- We = 6.3 kg/d. Based on Figure 4, therefore, Cen would have to average >1.5 mg/L (2400 ppmou) for Q=2800 l/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. listica lly What Range of Vapor How Rates Can Re 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 /s], can be used for this purpose: k [l-(PA,m/Pw)2] (5) where: k « u, = Pw = pA------- This equation is derived from the simplistic steady- s :ate 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" Rt. Values ranging from 9m (30 ft) to 30m (100 ft) are reported in the literature (Hutzler et al. 1988) for a variety of soil conditions, but fortun- ately Equation 5 is not sensitive to large changes in Rj. for estimation purposes, therefore, a value of Rt=12m (40 ft) can be used without a significant loss of accuracy. Typical vacuum well pressures range from 0.95 - 0.90 atm (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/PAtm) for a 5.1cm radius (4-in diameter) extrac- tion well, and a wide range of soil permeabilities and applied vacuums. Here H denotes the thickness of the screened interval, which is often chosen to be equal to the thickness of the zone of soil contamination (this minimizes removing and treating any excess "clean" air). For other conditions the Q*/H values in Figure 5 can be multiplied by the following factors: Rw a 5.1cm (2 in) R, = 7.6m (25 ft) - multiply Q*/H by 1.09 Rw = 5.1cm (2 in) R, = 23m (75 ft) - multiply Q*/H by 0.90 Rw * 7.6cm (3 in) R, - 12m (40 ft) - multiply Q*/H by 1.08 Rw = 10cm (4 in) R, = 12m (40 ft) - multiply Q*/H by 1.15 Rw = 10cm (4 in) R, = 7.6m (25 ft) - multiply Q*/H by 1.27 As indicated by the preceding multipliers given, changing the radius of influence from 12m (40 ft) to 23 m (75 ft) only decreases the predicted flow rate by 10 percent. The largest uncertainty in flow rate calcula- i ions will be due to the air permeability value k, which can vary by one to three orders of magnitude across a site and can realistically only be estimated from boring log data within an order of magnitude. It is prudent, therefore, to choose a range of k values during this phase of the decision process. For example, if boring logs indicate fine sandy soils are present, then flow rates should be calculated for k values in the range of 0.1ntaminant vapors. For this "best" case the estimated removal rate is given by Equation 2: noo (m vm-min) Vapor Flowme (scfm/ft) .0001 - o.ot i 0.001! .i i 10 too ton Soil Permeabilty (dajcy) vacuum uprated a equivalent water column heiihu Figure 5. Predicted steady-state flow rates (per unit well screen thickness) for a range of soil permeabilities and applied vapor flow / SMfeVKW b) liquid e c) Figure 6. Scenarios for removal rate estimates. R«, = Ccsl 0 (2) Changes in- Cest are still being neglected with time due to composition changes. Other less optimal condi- tions are often encountered in practice and it is useful to be able to quantify how much lower the removal rate will be from the value predicted by Equation 2. We will consider the three cases illustrated in Figures 6a, b, and c. ------- 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^Ml-'WQCes, (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: Cesl JM (eDu/k)"2 (ln(RI/Rw)/(PAlm - PJ]"2 where: T) = efficiency relative to maximum removal rate D = effective soil-vapor diffusion coeffici- ent [cnvVs] p. = viscosity of air = 1.8 x 10* g/cm-s k = soil permeability to vapor flow [cmz] H = thickness of screened interval [cm] R{ = radius of influence of venting well [cm] Rw - venting well radius [cm] PAIID = absolute ambient pressure = 1.016 x 10* g/cm-sj Pw = absolute pressure at the venting well (g/cm-s2] R! < r < R2 = defines region in which contamina- tion is present. Note that the efficiency T\ is inversely proportional to the screened interval thickness H because a larger interval will, in this geometry, pull 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 €?: D = D° where eA and eA are related by: (8) (9) Here pb and 6M are the soil bulk density [g/cma] 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=0.90 atm (0.91 x 10* g/cm-s1), and the contamination extends from the region Rt = Rw = 5.1cm to R2 = 9m (30 ft). The well is screened over a 3m (10 ft) interval. Assuming that: Pb = 1.6 g/cm5 6M = 0.10 D" » 0.087 cm'/s eT = 0.30 RI = 12 m then the venting efficiency relative to the maximum removal rate (Equation 2), calculated from Equations 7 through 9 is: •n = 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 clay 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 tow permeability will exist with a thickness 5. An estimate of the removal rate R«, from a contaminated zone extending from R] to R2 is: = IE (10) where D is the effective porous media vapor diffusion coefficient (as calculated previously from Equations 8 and 9) and Ces, is the estimated equilibrium vapor con- centration (Equation 1). With time 8(t) will grow larger. In the case of a single component system the dry zone thickness can be calculated from the mass balance: (H) where C, 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: (12) As an example, consider the case where benzene (Q, = 3.19 x 10* 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), pt = 1.6 g/cms, D° = 0.087 cmVs, and eT = eA = 0.30. Figure 7 presents the predicted removal rates and "dry" zone thickness 8(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 rat ;s 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 rerioved 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 Hcag (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, bu: 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 foi 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 (kg/d) 100. 10 i benzene (20 C) R, »S.l cm R2»900cm 200 "Dry" Zone Thickness 6 (cm) 100 0 100 200 300 400 500 Time (d) Figure 7. Estimated maximum removal rates for a venting operation Untiled by diffusion. a) % removed .0001 100 200 Qi/m(t=0) (I/g) b) QC/QC(t=0) .01 .001 .0001 Weathered Gasoline T-20°C 10% moisture content dinted front 4.ph>K » C0=0) = 270 mgfl Approximate Composition 100 80 % removed "60 •40 20 300 0 100 200 Qt/m(l=0) (1/g) 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 rale 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 isobutane ii-butane trans-2-butene cis-2-butene 3-methyi-l-butene isopentane 1-pentene 2-methyl-l-butene 2-methyl-t,3-buladiene iwpentane trans-2-pentene 2-methyl-2-butene 2-methyl- 1 ,2-butadiene 3,3-dimethyI-l -buiene cyclopentane 3-methyl-l-pentene 2,3-dimethylbutane 2-methylpentane 3-methylpentane n-hexane methylcyclopentane 2.2-dimethylpentane benzene cyclohexane 2.3-dimethylpentane 3-methylhexane 3-ethylpentane n-heptane 2,2,4- 1 rime thy 1 pe n t a ne methylcyclohexane 2,2-dimethylhexane toluene 2,3,4- trimethylpentane 3-me thy (heptane 2-methylheptane n-octane 2,4,4-trimethylhexane 2,2-dimethylheptane e thy (benzene p-xylene m-xytene 3,3,4-trimeihylhexane o-xy!ene 2,2,4- trimethylheptane n-noname 3,3,5-trimethylheptane n-propylbenzene 2,3,4-trimelhylheptane 1,3,5-trimethylbenzene 1 ,2-4-(rimeihylbenzene n-decane methylpropylbenzene di methy le thy (benzene n-undecane 1 ,2,4,5-tetramethylbenzene 1 ,23,4-tetramethylbenzene 1 ,2,4-trimethyl-5-ethylbenzene n-dodecane napthalene n-hexylbenzene meihylnapthalene Total (Mass Fractions) off Fresh and Weathered Gasolines Mw (8> 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 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 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 0.0343 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 mode]. The necessary minimum average vapor flow rate 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 Off-Silt Passive Air Injection Well or Perimeter Gnxmdwtier Moniiorirtf Well b) Wiier Table Upwellinj Caused by Vicinal) Figure 9. (i) Use of passive vapor wells to prevent migration of off-rite 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 ------- Preuurc V«po» Rownwtcr Pressure Swiping Probes Fipre 10. Air-pernMtMltty lest 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: (13) For (r2 eji/4kPAUnt)<0.1 Equation 13 can be approxi- mated by: P' = Here P' 4jon(k/u) -0.5772 - In Alm (14) = "gauge" pressure measured at distance r and time t = stratum thickness = radial distance from vapor extraction well = soil permeability to air flow = viscosity of air = 1.8 x 10^ g/cm-s = air-filled soil void fraction = time = volumetric vapor flow rate from extraction well = ambient atmospheric pressure = 1.0 atm = 1.013 x 10» g/cm-s2. Equation 14 predicts a plot of p'-vs- In(t) should be a straight line with slope A and y-intercept B equal to: m r k ix e t Q A = B = 4*m(k/u) Q 4nm(k/iO -0.5772 - In Aim (15) 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: 4Aiun The second approach must be used whenever Q or m is not known. In this case the values A and B are both used: + 0.5772) (17) 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 rp for one pore volume to be removed is: TP = Vp/Q = €A irR2 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 mj /min (20 ft3 /mm). Then Tp=475 m V0.57 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 = 4irT S(r,t)/W(u) (19) where: W(u) is the well function (Bear 1979) of u = Sr2/ ------- 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 weils 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 Res, 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 Nwens required to achieve the acceptable removal rate is: - Raeceptable/Resl (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 soil zone. If our spill mass is 1500kg (=500 gal), then a mini- mum of 1.5 x 10" 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 m3 /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 residual soil contamina- tion are removed from the entire zone of contamination Nmin- This is simply equal to the ratio of the area of contamination Acon,.™,,^,,,,, to the area of influence of a single venting well irR]2: Acontl (21) This requires an estimate of RI, which defines the zone in which vapor flow is induced. In general, RI 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). P. [! + ------- a) welh I) b) viporflcw . line* injection well 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 welt with time). A passive well is simply a well that is open to the atmosphere; in many cases ground water monitoring welts 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 lie 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- "opra" mil tuifice b> impermeable K»l Fignie 12. Effect of surface seal on vapor flow path. cement cip S) Figure 13. (a) Extraction well construction, and (b) air-tight groMd water level meawuiag system. terns. For shallow treatment zones (------- 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 unhs: 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 ppmv. More con- centrated vapors can cause catalyst bed temperature excursions and meltdown. • Carbon beds: Carbon can be used to 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 welts: 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: • Soil-gas vapor concentrations and compositions: These should be measured periodically at different radial distances from the extraction well. Figure 14 ------- 1/8" OD Teflon Tubinf Ground Surface Box ConMiimif Vipor Sunpliiii Pom AThomooaupia Jang 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 4>=Cex,r«,jon weii/Cjoi, g». 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 confir- mation borings unless the original spill mass is known accurately. In most cases 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 zone; 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 CVCOa 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 t>r 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 wells 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. 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) and 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. JO- J. 1 i-- 1 w- Vapor ? — * » =« \ WWiM SMHliH mo_ \ J *«" •"r v. r , (Kkllll \ * \ Fine to CtmStM Silly CUjr * Otyey Silt Medium Swd • 03 / Ml .« ' WT7 •151 J»7 Dill 1.1 ' MaiifoM a.X' °w?Si2r* t A . D j .u , 214 . •1 ant • • 0)1 •0.1' •M . 1-J 1J »f HB-17 SuUcOmnd wwrlttk KB 7HB-5 HB25 IV.pt. HB3 HB-21 ««»«yWdll Rtcovnj Wdl] Figure 15. Initial tout hydrocartwn 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 b 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: Ceit = 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 R(K!eept.bie- Assum- ing M\$pm = 4000kg and T = 180 d, then: R.ccept.We = 22 kg/d Using Equation 2, Ceit = 240 mg/L, and Q = 28001/ min (100 cfm): Re« = 970 kg/d which is greater than R»cccpl.bie- • 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 m3/m-min Rw = 5.1cm, RI = 12m 0.43 < Q < 43 ftVft-min Rw = 2.0 in, R, = 40 ft. The thickness of this zone and probable screen thick- ness of an extraction well is about 2m (6.6 ft). The total flow rate per well through this zone is estimated to be 0.08l«.m) 0 HB-14D(t=9.8cn) + HB-IO (r*7.6m) n1^ a -^ D -f^o0 f .*v° dP H f + + a ° ^s*0 ° T O t x * 1 10 *o £*° A k A A 100 1000 Time (min) FIfwe 16. Air permeability test results: (a) vapor extraction lest; (b) air injection test [In HjO] denote vacuums expressed a* equivalent water column heights. determine the permeability to vapor flow. The k values ranged from 2 to 280 darcys, with the median being ~8 darcys. System Design • Number of vapor extraction wells: Based on the 8 darcys permeability, and assuming a 15cm diameter (6 in) venting well, a 2m screened section, Pw = 0-90 atm (41 in H2O vacuum) and R|=12m, then Equation 5 predicts: Q = 0.7 mVmin = 25 cfm Based on the preceding discussion, a minimum aver- age flow rate of 1.5 mj/min is needed to reduce the residual to 1000 ppm in six months. The number of wells required is then 1.5/0.7 = 2, assuming that 100 percent of the vapor flows through contaminated soils. It is not likely that this will occur, and a more conservative esti- mate of 50 percent vapor flowing through contaminated soils would require that twice as many wells (four) be installed. A single vapor extraction well (HB-25) was installed in this soil layer with the knowledge that more wells were likely to be required. Its location and screened interval are shown in Figure 15. Other wells were installed in the day layer and upper sandy zone, but in this paper only results from treatment of the lower contaminated ------- isone 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 IS. {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 idjacent to the aquifer. The vapor flow rate from HB- 25 and vapor concentrations were measured frequently, ind the vapor composition was determined by GC-F1D analysis. In addition, the water level in the ground water monitoring wells was measured with the system pictured n 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 aim (20 in H2O vacuum), and :he flow rate was initially 12 scfm. It gradually decreased :o 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 How. 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 i he total concentration of known and unknown com- ]x>unds 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 Ihere 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 = :i 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 HB-25 100 Vacuum (in HO) M 120 100 80 to 40 0. 4 1? — •-- HMK \' "''",.' i * • **, /'' V i' ^ '15 10 •5 Ftowraie (SCFM) 20 40 60 10 100 120 Time (d) E vMaynu ttpmwt u equivalent wuer eohnui height* b) 0 20 40 60 80 100 120 Time (d) Figure 17. Soil-venting retails: (*) vacuum/flow rate data, (b) concentration/composition data. a) Removal « Rale (kg/d) so 400 200 too Cumulative Recovered (gal) 20 40 60 *0 100 120 Time (d) b) ftH.O 2 0.3- 0.0 I 10 Time (min) (ft HO) denote vtcuums expressed is equivalent water column heights Figure 18. 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 upweiling *as monitored. Figure 18b presents the results. Note that the water table rise paralleled the vacuum increase, although the water table did not 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 4> 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 residual 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, 1.0 0.8 C(t)/C(t=0) 0.6 CftVC(l=«) predicted C(lVC(l=0) measured weathered gasoline m(t=0)-4000kg 0.4 0.2 0123456789 10 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 of NWWA/AP1 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/API 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. 1988. 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 (Westhollotv 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 environmental risk ------- assessments. Curtis C. Stanley received Ms degree in geology with an engineering minor from North Carolina State Uni- versity in 1979, He is currently a senior hydrogeologist for Shell Oil 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 ami 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 Shtil Development Co. (Westhollow Research Center, Houston, TX 77082) where he has worked since 1985. He obtained his M.S. degree in civil engineering from tht Technical University of Warsaw, Poland, in 1973 andhisPh.D. 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 Mtxico 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 t'he 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. ------- ------- SOFTWARE held by Library Database Coordinator, piease inquire at Circulation Desk ------- -------