Guidance for Design,
Installation and Operation of
     Soil Venting Systems
                   Working together for
                    a cleaner tomorrow
Wisconsin Department of Natural Resources
 Emergency and Remedial Response Section
             July 1993



             Prepared by:

Wisconsin Department of Natural Resources
Emergency and Remedial Response Section
            P.O. Box 7921
          Madison, WI  53707


Errata sheet for the Guidance for Design, Installation and Operation of Soil
Venting Systems, through February 7, 1994.

Additional information, changes, clarification and errata include the

   •  All wells, including air extraction and injection wells need to be
      abandoned after the project is complete.   This information is included
      on Page 2 under Wjs. Admin. Code NR 141   but was inadvertently left out
      of Subsection 5.4.


e«id«nc» for Soil Tratiaf Syttmt

                                   Table of Contents

      1 . 0   Introduction .  ......
      1.1   Purpose .....  ....."  ......  .....  •  •  ..... .    1
      1.2   Scope  of Soil  Venting and  Bioventing."  ...... . ..... •  • •    1
      1.3   Permitting,  DNR Regulations  and Related  Guidance ..... ' '  ' '    o
            1.3.1  LUST,  ERP and Superfund  Program Requirements, '  '.'.'.'.''    I
            1.3.2 Bureau of Air  Management.  ....                  .....    *
            1.3.3 Bureau of Wastewater.  ...    ''''••'*••  .....    2
            1.3.4 Department of  Industry, Labor  and  Human Relations.' .'  .'  .'  .'    4

     £*?  -Technical Considerations and Sfi-» Charart- .^^.^^                    ,
     2.1   Theory.  .... ......                   - **•*•  .......     3
     2.2   Site Characterization.  ....'.' .........  .......     5
           2.2.1 Contaminant Characterization       •••••,.... .....     8
           2.2.2 Geological Factors .......  .*.'.".'"' ........
            Horizontal Permeability.        .....  *  "  '   ,!!
            Stratification and Vertical          ' ......
                             Permeability.  ...
           2.2.3 Hydrogeologic Factors.   .  .         .............   J°
     2.3   Other Site-Specific Factors.   ......'.'.'.** ........
           Treatabilifry or Pilot Ta.'t.^C|   ....
     3.1   Laboratory Treatability Tests                   '  ........   12
     3.2   Pilot Tests ..........  .........  •  •  •  .....   12
           3.2.1 Purpose of a Pilot'lest.'  .*.'.'""-"""*;'"  ...... •  12
           3.2.2 Conducting a Pilot Test.   ...  ......  •••.....   12
           3.2.3 Analytical Monitoring Methods  for  Pilot Tests  '  ......   II
            Sites With  Petroleum Product     .......
                             Contamination.   .  .
            Sites With  Non-Petroleum'  ""*''""".'*'.•*
          3.2.4 Reporting  Results From  Pilot Tests   ':••••. ......  "
    3 . 3   Alternative to a Pilot  Test              .....  '  .......  16
                                      .......... .  •  .....  ...   18
    4.1   Well Placement and Air-Flow Modeling
                           . Achievable Air-Flow Ra^es, "and^ir^ission  "  '

    4.3   Well or Trench ' Des igA. ' ". \ [ [ \ [ [ ] ........ ......   24
          4.3.1 Vertical Extraction Wells.  . . ...... ........   27
          4.3.2 Horizontally Screened System DesigA. ' !    .........   ,n
          4.3.3 Gas Probes .....                       ' '  ...... ..JO
    4.4   Manifold and Instrumentation! ;;•'•••.••••*•••.••••.  31
    4.5   Water Trap ............      ...... ••-.....   31
    4.6   Blower (or Vacuum Extractor) Type and Size  *•*•••. .....   35
    4.7   Emission Control Devices.  .                  '      ....... " '
    4.8   Air Injection.   .......  ....... "  .....  "  *  ' .....   36
          4.8.1 Passive Vents .....  ...'."."  ......  ......  •   ,?
          4.8.2 Forced Injection .....  ...  .....    <;  .......   »o
          4.8.3 In Situ Air Sparging.  ..."!.".'!  .....  .......   H
    4.9   Other Design Considerations .....        «•••.......   jy
          4.9.1 Surface Seal ..........  •.•-««•.•......   jy
          4.9.2 Stagnation Zones.  ......'.I....'.  [  ,  ',  '  '  ' '  '   f?
          4.9.3 Vacuum- Enhanced Product Recovery.  .  .  .  .  .    .......   41
          4.9.4 Groundwater Extraction from Air -Extract ion 'wells;.'  .".'!*"   42
          4.9.5 Enhanced Biodegradation of Petroleum Compounds in
                SoilV ................  .......  ...:..    42

Guidance for Soli V«otin* Symttut                                                          Fag* ii

      4.10  Soil Venting System Design Report.   ......'	  43

      5.0   Operation of a Soil Venting System.  ..-....•....'	  46
      5.1   Overview.	  46
      5.2   As-Built Submittal	,.  ,	 .  43
      5.3   Reporting	.,	  49
      5.4   Case Close Out	  50

      6.0   References	  53


      Table  1-1      Guidance Documents Related to  Soil Venting	    3


      Figure 4-1    Vacuum at a Distance From a  Single
                     Air-Extract ion Well	   20,. 21
      Figure 4-2    Typical Air-Extraction Well  Design with
                     Above Grade Manifold	  28
      Figure 4-3    Wellhead Details with a  Buried Manifold	  33
      Figure 4-4    Combined Performance Curve for Three  Types of Blowers.   .  37
      Figure 4-5    Typical Air-Flow Patterns	   40

     Attachment 1
Guidance on air sampling and emission monitoring for LUST
soil and groundwater remediation projects with a synopsis of
air regulations.
     Acknowledgments.  In addition to many DNR employees, the following
     individuals also reviewed and commented on this document:

           Kelton Barr, C.P.G. - Geraghty & Miller, Inc.
           Chi-Yuan Fan, P.E. - USEPA Risk Reduction Engineering Laboratory.
           David Kill, P.E.  - Recovery Equipment Supply Inc.
           Michael C. Parley - Vapex Environmental Technologies, Inc.
           Tom R. Peargin, R.G. - Chevron Research and Technology Company.

     This document may not represent the views of all reviewers.  The DNR thanks
     the reviewers for donating their time and input.

     soil Vmtiac



















 Chlorinated polyvinyl chloride.  Material commonly used for

 Wisconsin Department of Natural Resources.

 Diesel Range Organics

 U.S. Environmental Protection Agency.

 Environmental Repair Program of the DNR.

 Emergency and Remedial Response Section of the DNR Bureau of
 Solid and Hazardous Waste Management.

 Flame lonization Detector.

 Granular Activated Carbon.

 Gas Chromatograph

 Gallons per minute.

 Gasoline Range Organics

 Ratio of horizontal  permeability to vertical permeability.

 Leaking Underground  Storage Tank Program of the DNR.

 Fhotoionization Detector.

 Polyvinyl Chloride.  Material commonly used for pipe, well
 casing,  and well  screens.

 Petroleum Volatile Organic Compounds.

 Standard Cubic  Feet per Minute.

 Total Petroleum Hydrocarbons.  As used in this document TPH
 refers to tests for gasoline range organics and diesel ranee
 organics.                                                 °

Volatile Organic Compound.


Guid«ne. lex Sell VmUag Syttmt

      1.0   Introduction.

      This  guidance  document is  intended to  aid environmental professionals  in
      designing soil venting systems for soil  contaminated with volatile  organic
      compounds (VOCs).  It  provides information to Department of Natural
      Resources (DNR)  staff  for  efficient and  consistent oversight and  review.

      This  document  should be read with  the  existing DNR Guidance for Conducting
      Environmental  Response Actions, specifically Chapter 7 (Site Investigation)
      and when  available,  Chapter 8  (Remedy  Selection).

      1.1  Purpose.                 .

      This  document  is a guide to using  soil venting as a  remediation technology.
      Soil  venting is a technology that  uses air  to extract volatile contaminants
      from  contaminated soils.  The  technology  is also known as soil vapor
      extraction, in situ volatilization, in situ vapor extraction, in situ air
      stripping, enhanced volatilization, in situ soil ventilation, and vacuum
      extraction.  The term bioventing has been applied to soil venting projects
     when biodegradation is  a significant part of the remediation process and/or
     biodegradation is enhanced with nutrient  addition.

     Soil venting is a multi-disciplinary process.  The designer should have a
     working knowledge of geology and basic engineering to design an optimal
     system.  A basic knowledge of chemistry is also necessary to develop a
     quality sampling and monitoring plan.

     This document  is intended as general guidance.   Because each site has
     unique characteristics, it may be necessary for system designers to deviate
     from the guidance.   The DNR acknowledges that systems will, deviate from
     this guidance when site-specific conditions warrant.   Vilheii deviations
     occur, designers should document these differences in their work plan to
     facilitate DNR review.   For additional information on the  DNR's permitting
     and regulatory requirements,  please refer to Subsection 1.3 in this

     This document discusses the basics of soil venting system  design.  Refer to
     the publications listed in Section 6 for more detailed discussions of soil
     venting systems.  A more complete list of articles is included in the
     reference  and the bibliography sections of the U.S. Environmental
     Protection Agency (EPA) Soil Vapor Extraction Technology, Reference
     Handbook (1991(a)).

     1.2   Scope of Soil Venting and Bioventing.

     Soil venting generally  works well with gasoline and some common solvents
     such as  trichloroethene and tetrachloroethene.  Remediating heavier
     hydrocarbons (jet fuel,  kerosene, and  diesel oil)  with  a soil venting
     system may be possible,  but the rate of remediation is  very slow compared
     to  more  volatile  compounds.   Enhanced biodegradation  takes place through
     oxygen delivery during  soil venting (Hinchee and Miller, 1990, Miller,
     1990).   Unusual site  conditions,  such  as  an inability to excavate, are
     necessary  to make soil  venting  technology the best alternative for the
     heavier  hydrocarbons.   Soil venting is  not appropriate  for  contaminants
     that do  not volatilize  or aerobically biodegrade.

     Soil venting may  be used with other cleanup  technologies, such as  steam
     stripping,  groundwater  extraction,  product recovery,  air sparging

  for Boil Vcatia* Symtmm                                                           Pag. 2

  (saturated zone) .and heated air injection  (unsaturated zone).

  Soil venting is an  effective technology to prevent vapor accumulation in
  buildings,  and soil is  also remediated in the process (Knieper, 1988).
  Using soil  venting  to remove vapors from a building can be considered an
  emergency or interim remedial measure.  In such cases, a pilot test is not
  necessary if the operator has received Bureau of Air Management approval.

  1.3   Permitting, DNR Regulations and Related Guidance.
  Refer to Table 1-1  for more  information on permitting and related guidance

  1.3.1 LUST,  ERF, and Superfund Program Requirements.

  Submittal Contents .  Recommended Leaking Underground Storage Tank (LUST) ,
  Environmental Repair Program  (ERP) and Superfund program submittal contents
  are listed  in Subsections 3.2.4, 4.10, 5.2, and 5.3.

 Wjs. Admin.  Code MR  141.  Air- extraction well designs and gas probes do not
 need DNR's preapproval under Chapter NR 141.   Designers must submit boring
  logs and well construction diagrams in accordance with NR 141.23 after well
  installation.  Designers must also abandon wells and gas probes in
 accordance with NR 141.25 after project completion.
 with DNR guidance on investigative wastes.

 1.3.2 Bureau of Air Management.
                        Designers should handle drill cuttings in accordance
 Wig.  Admin.  Code 406.  445.  and Aio,   Soil venting systems must comply with
 any state emissions standards.  Chapter NR 445,  Wisconsin Administrative
 Code, sets hazardous air emission standards for  atmospheric  pollution
 sources.  'Chapter 406  sets  requirements for air  permits  and  Chapter NR 419
 includes  additional requirements .  .Air emission  limits,  reporting, methods
 of monitoring,  and a summary of air  regulations  for petroleum sites are
 discussed in Attachment 1.   See Chapter NR 445 for a complete listing of
 compound- specific limits for other sites.   The total volatile organic
 compound  (VOC)  limit in NR  419.07  (4)  (b)  takes  precedence over the hourly
 limits for individual  compounds in Chapter NR 445.   Designers may need a
 permit from  the Bureau of Air Management prior to using  control or air
 treatment devices.   A  pilot test may be necessary to comply  with Bureau of
 Mr Management  requirements.

 Note:   If an air permit is  necessary,  the  application for the permit  should
 be  submitted early to  reduce  or prevent project  delays.   An  air permit
 takes  a minimum of two to three months after a COMPLETE  application is

 Form 4400-120 n   Designers must complete Form 4400-120 and receive DNR
 approval  prior  to operating a soil venting system at a LUST  site.  Data
 from a pilot test may  be necessary to  complete the  form.

 1.3.3  Bureau of Wastewater.

Water  Disposal .   Groundwater  pumped  from air-extraction wells and the
 accumulated water in a water  trap  must be  disposed  of in  accordance with
 state  and/or  local permits.   Local municipalities regulate discharges  to

Cuid«nc» £ot Sou Vmtlag Sritm*
                                       Table 1-1

                      Guidance  Documents  Related to Soil Venting
                                    Documents i
       Air Emissions
       Drilling,  Well
       and Abandonment
      Vapor Well
      Labeling and
      Color Coding


                   NR 406,
                   NR 419,
                   NR 445
                  NR  141
                  ILHR 10
                  DNR Rules
                  DNR Rules
                                   April 5,  1991
                                   Memo for  LUST
                                   None for  Other
 None Specific to
 Soil Venting
Guidance for
Treatment of
Groundwater and
Other Aqueous
Waste Streams
January 14, 1993
Program Letter
10, May 25, 19934
                                                  ERR Staff


3.2.3, 4.2,
4.7 and
1.3.1, 4.3
and 5.4
                    Staff or
                    Local POTW
                    ERR Section
              1.3.3, 4.5
              and 4.10
              1.3.1 and
                                 3.2.2, 4.4
                                 and 4.6
(1)   Guidance
(2)   Included
                     D°CUmentS refers to
                                                  documents other than this
                     as Attachment One.
                                    Jnteriffl Guidelines foe the

      Guidance titled Design Criteria for Process Equipment Buildings
      Associated with Environmental Remediation of UST/AST Sites
      «S !£ed £ Attf ^t Two to the Guidance on Design, Installation
      and Operation of Groundwater Extraction and Product-Recovery
      Systems.                                                   *

GuicUno for Soil VnUng Sy«t«M                  •

      sanitary sewers.  A Wisconsin Pollutant Discharge Elimination System
      (WPDES) permit is necessary for storm sewer or surface water discharge.
      See Guidance for Treatment Systems for Groundwater and Other Aqueous Waste
      Streams for a further discussion of permit requirements.

      1.3.4 Department of Industry, Labor and Human Relations.

      TLHR 10.  ILHR 10.41 covers color coding for flush mount well covers for
      groundwater monitoring wells and vapor wells.

      Electrical Safety.  See DILHR's Design Criteria for Process Equipment
      Buildings Associated with Environmental Remediation of VST/AST Sites, which
      is included as Attachment 2 to Guidance- on Design, Installation and
      Operation of Groundwater Extraction and Product Recovery Systems,

Cuidnc* tor Soil V«ntinj Sytt               .
                                                                                   Pag* 5
                      Cpnsideraflons and Site Chm-««.«-»rf
      2.1   Theory.
         an»«        dJSC^Ss1ion of the the<»7 and dynamics of soil venting.
     Jon ventin8   • *»*»**>&;*» encouraged to review polished literature on
     soil venting.   See Section 6  for a list of selected references.
     ll\\ ^lnSv, removesvVOCs  fro» "ils by creating an airstream through the
     soil that enhances the volatilization  of the VOCs and act-s  as a carrier

                  008-  S0il Venting alS° ^^  ~"bic ^ode-datio
     Actors? af follows :aCti°n/deStrUCti0n *" C°ntrolled ^  a T «f

                 Air-flow Rate.  The rate of air flow controls the advective
                 transport of the VOCs from the subsurface.   Soil permeability
                 is a major subsurface physical limitation associated with air-
                 flow rate.  Other important factors include  the number  of air-
                 extraction wells, extraction well placement, size and type of
                 blower, the amount of vacuum applied, and the depth  of  the
                 water, table.  Subsection 4.2 discusses air-flew rates to a
                 well.  Shan et al. (1992) and Baehr et al. (1989) discuss
                 .f^5£?\jf 1£ fl°W t0 an air-e*<=raction «ell.  Johnson et
                 al.  (1990) also discusses a method to estimate the air- flow
                 rate based on permeability that is useable for initial design
                 estimates .                                                 °

                 Air-flow  rates are less  critical to the biodegradation process
                 rJ!c  Y^^S Astern achieves  the most volatilization at high
                 rates of  air flow;  a bioventing system may operate at a much
                 slower air-flow rate,  possibly  as  much as  an order of magnitude
                 less  (see biodegradability below) .                       B'"-«iae
                «Sr?°  "T"^?1"    Th^ remediation rate in highly permeable
                soils  is  primarily controlled by the  rate of advection.

                If the unsaturated zone  is heterogeneous  (I.e.  fine-grained
                soils  mixed with coarse-grained  soils) , the extraction is
                dependent on the diffusion rate  of  the contJiminants  from the
                fine grained soil  matrix into the coarse -grained soil matrix.

                The extraction rate at sites  with fractured clay till or
                fractured consolidated deposits  is  also dependent on the
                diffusion rate because the VOCs  diffuse out of  the soil  or  rock
                matrix into the fractures, where advective  flow extracts the

                SoU Moisture.   The air- flow rate through soil may decrease if
                soil moisture occupies void spaces,  making  them unavailable to
                advective air flow.  High moisture in the capillary fringe zone
                reduces the effective porosity to air flow near the water
                table,  and may retard the extraction of the contaminants from
                the capillary fringe.   The highest levels of soil contamination
                at a site are often near or within the capillary fringe.   This
                occurs  because  the contaminants often collect at the top of the
                water table.  For these reasons,  the zone that is most

Ouidrac. for Soil Vwtiag Sy>t«M                                                       '    *•»• 6

                  difficult: to remediate (because of air flow patterns)  is also
                  the zone that often has the highest contamination.   Pumping
                  groundwater to drop the water table may expose more
                  contaminants to the air flow that were formerly submerged.   See
                  Subsection 4.9.4 and Guidance for Design,  Installation and
                  Operation of Groundwater Extraction and Product-Recovery
                  Systems for a further discussion of groundwater extraction.

                  Soil moisture is necessary for maximizing  biodegradation.  A
                  moderate level of soil moisture is necessary to maintain
                  viable, aerobic bioactivity.  Some practitioners propose that
                  soil moisture should be in the range of 40 to 60 percent of
                  field capacity, others propose that moisture should be between
                  50 to 75 percent of field capacity.  If soil moisture, drops
                  significantly below this range, the activity and even the
                  microbial population density can drop significantly.

                              The vacuum that is applied in  the subsurface lifts
                  the water table.   The effects of upwelling are greatest near
                  the extraction wells, where the vacuum levels are the highest.
                  If contaminants are submerged (below the water table) by
                  upwelling, the effectiveness of soil venting is reduced.

                  Stagnation Zones.   Subsurface structures and/or multiple air-
                  extraction wells can result in stagnation zones.  These; zones
                  are areas that have no or minimal air flow through the soil.
                  •The effectiveness of a soil venting system is minimal in these
                  zones.   Stagnation zones most often occur at locations in
                  between two or more air -extract ion wells that operate at a
                  relatively constant rate, but it can also occur if subsurface
                  structures block the air flow.  The reduced air -flow rate
                  through these zones reduces the contaminant extraction rate
                  from these zones.   These zones may also be zones of anaerobic
                  conditions (see biodegradability below) .

                  Vapor Pressure.  Vapor pressure is a critical factor in
                  assessing the ability of a soil venting system to volatilize
                  the contaminant in the soil.  Generally, the higher the vapor
                  pressure, the more likely a soil venting system will extract
                  the contaminant from the spil.  The vapor pressure of the
                  contaminants are highly temperature .dependent; higher
                  temperatures increase the vapor pressure and the rate of
                  volatilization.  A vapor pressure of 1.0 mm Hg at subsurface
                  conditions- is the cutoff for soil venting (Appendix B in the
                  USEPA Reference,  1991 (a)).

                  Henry's Law Constant and Solubility.  The rate that the
                  contaminants are released from the natural soil moisture (pore
                  water)  are dependent on the Henry's Law Constant for each
                  compound within the contaminant matrix.  The Henry's Law
                  Constant is the ratio of the concentration of a compound in air
                  to the concentration of the compound in water at equilibrium.
                  The Henry's Law Constant for a compound is a measure of the
                  rate that the compound will be released from the moist soil
                  into the soil air.  A low Henry's Law Constant indicates that
                  the compound at equilibrium in an air and water mixture is
                  largely held within the water phase.  It is, therefore, not
                  readily volatilized into the extracting air stream, resulting

Guldtace tee Sell ftntiac Sy«t«.

                  in a very slow rate of extraction.

                  Solubility in water is another factor in the extraction rate
                  for a specific compound.   A significant amount of a highly
                  soluble compound (acetone,  alcohols,  etc.)  dissolves in the
                  soil moisture,  retarding  the rate of  volatilization.  If the
                  soil venting system has a large enough air- flow rate to dry out
                  the soils,  then solubility is a less  critical factor.

                  fraoult's Law,   A mixture  of gasoline  and heavier hydrocarbon
                  compounds (such as  diesel or lubrication oil)  can be slow to
                  remediate,  because  the volatile compounds may be trapped in the
                  heavier,  relatively nonvolatile compound matrix.   In this case,
                  the effectiveness of a soil venting system  depends upon the
                  rate of molecular diffusion of the volatile compounds  out of
                  the nonvolatile hydrocarbon matrix.   Even a highly volatile
                  substance like  gasoline weathers  and  becomes much less volatile
                  as  the  highly volatile compounds  are  removed from the  mixture.

                  The extraction  rate  of the  less volatile  compounds is  often the
                  controlling factor  in  closing  out sites with soil  venting
                  systems.  Some  sites are not suitable for soil venting systems
                  because it may not be  technically feasible  for a system to meet
                  cleanup criteria for some compounds.  See Subsection 2.2.1 and
                  the above discussion of vapor pressure and Henry's Law
                  Constant.  The vapor pressure and the Henry's Law  Constant
                  should be assessed for unusual or unique mixtures  of
                  contaminants where soil venting has a limited history.  Bench
                  scale tests may also be useful in unusual conditions (EPA, 1991
                 Adsorption,  Adsorption of contaminants on the soil slows the
                 rate of extraction.  Soils that have a high surface area (fine-
                 grained soils) or high total organic carbon content have a much
                 greater ability to adsorb contaminants than soils with a small
                 surface area (coarse-grained soils).  Therefore,  coarse-grained
                 soils release contaminants at a faster rate thstn fine-grained
                 soils or soils with a high total-organic compound.

                 BjodeRradation,  Petroleum hydrocarbons biodegrade at a higher
                 rate under aerobic conditions than anaerobic conditions.  The
                 rate of biodegradation is generally controlled by four factors:
                 oxygen, food (the petroleum product) for the microbes,
                 moisture,  and nutrients.   The limiting factor under non-venting
                 conditions is usually oxygen.  A very slow air- flow rate is
                 usually sufficient to provide enough oxygen to the bacteria.
                 Aerobic biodegradation is not significantly inhibited until
                 oxygen levels drop below  5 percent.   When a soil  venting system
                 is  active,  the limiting factors generally will either be a lack
                 of. moisture or lack of nutrients .

                 It  is possible that portions of the  soil witMn a soil venting
                 regime are not frequently replenished by oxygen.   If this
                 occurs,  these zones will  be largely  stagnant and  only
                 anaerobically active with accumulating fermentation products ,
                 such as methane.   It is possible that anaerobic conditions
                 could exist in a  system,  even if there are high oxygen levels
                 in  the extracted  air.   This occurs because some of the

GuicUnc* for Soli V«ntin* Sy«t«M                   ,                                       *•»• 8

                  extracted air could have passed through "clean" soil'.

•  '                Generally the halogenated compounds biodegrade at a much slower
                  rate than petroleum fuels under aerobic conditions.

                  For specific details'on blodegradation, as part of a soil
                  venting system, please refer to Subsections 4.9.5 and 5.1.

      2.2   Site Characterization.

      The following is a summary of technology-specific aspects of a site
      characterization and should be used with Chapter 7 in the Guidance for
      Conducting Environmental Response Actions.

      Soil venting as a remediation technology depends on the flow of a fluid (in
      this case air) through the unsaturated soil.  For this reason,
      environmental professionals need to characterize the geological conditions
      of the site in sufficient detail so that they can design a soil venting
      system that is appropriate for the site conditions.  An inadequate site
      characterization may result in a venting system that has large stagnation
      zones, excessive groundwater extraction during times of high water table,
      significant short circuiting, or a system that will not work at all.

      The* following subsections identify the significant site characteristics
      that should be defined or estimated when considering a soil venting

      2.2.1 Contaminant Characterization.

      Characterize the site for contaminant types in order to prepare a
      monitoring plan that will comply with criteria set by the Bureau of Air .
      Management.  Characterizing the contaminants is also necessary to evaluate
      the feasibility of successfully remediating the site with a soil venting
      system.  Contaminant volatility should be • identified and characterized so
      designers can estimate the total mass of contaminants to evaluate the size,
      cost, and life of the project and to determine if there is a need for air
      emission controls.  Air standards are established by the Bureau of Air
      Management and are found in Subsection 1.3.2 and in Table 1-1.

      During the investigation, assess the components of the product lost and its
      degradation products.

            Example:  Halogenated solvents will often degrade to compounds that
            are more toxic than the original product that was released.
            Tetrachloroethane will transform to trichloroethane, then to
            dichloroethane, and finally to vinyl chloride, a known
            carcinogen (-Fetter, 1988).

      For emission estimates at sites with petroleum contamination, the two
      parameters that need to be assessed in soil are total benzene and total
      VOCs (see Attachment 1).  If a laboratory test is used to quantify the
      total VOCs for petroleum products, use an analytical test for TPH that* also
      quantifies compounds that are not identified in a normal VOC scan (propane,
      butane, pentane, etc.) .  Do not use a sum of benzene, toluene, ethylbenzene
      and xylene.  The Bureau of Air Management may require an air permit and
      needs to know what the potential contaminants at the site are and estimated
      quantities for each.

Guidance for Soil V«ntini Sy>t«M                                    !                       *„. 9

      An assessment of the vapor pressure and Henry's Law Constant for gasoline
      contamination is not necessary because of the large number of venting
      systems demonstrating that gasoline is readily removed from the subsurface.
      Gasoline is a mixture of more than 100 compounds.

      Some  compounds with less than six carbon atoms in  the molecule (C6)  have
      very  high vapor pressures and readily volatilize;  some heavier hydrocarbons
     .with  greater than nine carbon atoms per molecule (C9) volatilize very
      slowly.   Most of the highly volatile compounds are quickly extracted by a
      soil  venting system.   Rainwater,  et al.  (1988) demonstratisd in column
      studies  that when greater than 50 percent of the pentatie  is removed,  only
      10  percent  of the xylene is removed.   DiGiulio et  al.  (1990)  estimated that
      40  percent  of gasoline contamination may still remain when off gas
      concentrations have fallen to 1 percent of the initial concentration.   The
      lower volatility compounds in gasoline (>C9)  that  are less; readily
      extracted may prevent a soil  venting system from meeting  site-specific
      cleanup  standards that are based  on TPH.

      Soil  samples collected from soil  borings  should be field  screened for VOC
      measurements.   Field screening could consist.of headspa,ce analysis by PID
      or  FID;  headspace analysis by field GC; or headspace  analysis by the  Lab in
      a Bag Method (Robbins et al.  1989).

      2.2.2 Geological Factors.

      This  Subsection discusses  soil  description, horizontal permeability,
      stratification, vertical permeability, hydrogeology,  and  ether site-
      specific  considerations.                              '

     To design an effective  soil venting system, it is necessary to sufficiently
      characterize the  site geology to  evaluate  any preferred zones  of air flow
     An experienced scientist or engineer  should classify the borings in detail.

     To describe  the soil  column,  the  soil description should  include the

                 Approximate percentages of major, and minor grain-size
                 constituents.  Note: Terms such as  "and," "some,"  "little,"
                 "trace," etc. are acceptable if defined in percentages they
                 .represent;                                                    .

           •      Color and Munsell color;

                 Geologic origin;

                 Description of moisture content (dry, moist, wet);

                 Any visual presence of secondary permeability;

                 Voids or layering; .

                 Pertinent field observations such as odor;

                 Description and notation of any product smearing evidence.
                 Since depth of smearing is evidence of  past aquifer water-level
                 variations, note the depths carefully.

                 Any other pertinent observations.

Coldraca tor Soil Vatlas Sftttmf                                                          P*** 10     Horizontal Permeability.

      The horizontal permeability of the unsaturated zone is a key factor in
      designing a soil venting system,  and to some degree,  in estimating the life
      of the project.  The rate of contaminant extraction by volatilization and
      advection is proportional to the rate of air flow.   At a given operating
      vacuum, a soil venting system installed in a highly permeable soil will
      allow a high air-flow rate through the soil, whereas installation in a low-
      permeable soil will result in a lower achievable air-flow rate.

    «  There are two common ways to estimate what air flow is achievable from a
      soil venting system: a pilot test, or a permeability estimate of the soil.
      See Section 3.0 for pilot test information.     Stratification and Vertical Permeability.

      It is important to evaluate the presence of stratified soils at a site
      during the site characterization.  Stratified soils are soils that have
      been deposited in layers that are typically horizontal.  Stratification can
      channel the air flow through the relatively coarse-grained horizontal soil
      layers and restrict vertical flow through the relatively fine-grained
      horizontal layers.  The horizontal component of flow is increased relative
      to the vertical component, thus the horizontal zone of influence of an air-
      extraction well is increased.  Stratification at a site can easily be
      identified by an inspection of soil boring logs from the site.
      Stratification exhibits characteristics similar to a high Kh/Kv ratio on a
    .  macro scale.

      The Kh/Kv ratio is generally controlled by the natural depositional
      environment of the soils.  Horizontal channeling of the air flow patterns
      is caused by a high ratio of horizontal permeability (Kh) to vertical
      permeability (Kv).  Eolian silt deposits (loess) may have a Kh/Kv ratio of
      100 or more.  Glaciofluvial (or outwash) deposits commonly have a Kh/Kv
      ratio of 3 to 10.  Manmade fill typically has a Kh/Kv ratio near 1.  On a
      macro scale, glacial till may have a Kh/Kv ratio that is less than one due
      to vertical fracturing of the till.

      There are two ways to estimate the Kh/Kv ratio:  using pilot test data; and
      identifying the depositional environment and making assumptions for typical
      characteristics for different depositional environments.  The method
      proposed by Shan et al. (1992) can be used to estimate the Kh/Kv ratio from
      field pilot tests (Subsection 3.2).  The reference also includes figures
      that portray streamline flow patterns for different Kh/Kv ratios.

      System designers can evaluate the effects caused by stratification or the
      Kh/Kv ratio to adjust well placement to site-specific conditions as
      discussed in Subsection 4.1.

      The volatilization of VOCs from sites with stratified soils is often
      inhibited by poor air-flow rates  through the finer-grained soil layers.
      The diffusion rate of the VOCs from fine-grained layers into the coarser-
      grained layers controls the extraction rate, as the coarse grained layers
      act like short circuiting pathways for the advective air flow, and the air
      flow passes through the fine grained soils very slowly.

      2.2.3 Hydrogeologic Factors.

      Certain hydrpgeologic factors will affect  the design of a soil venting

Galdtaet tor Soil ttatiat 8r«t«u        '

      system.  The location of the screened portion of the air-extract ion wells
      is determined by the soil geology, surface conditions,  and the depth and
      seasonal fluctuation of the  water table.  The seasonable-high and the
      seasonal-low water table should be estimated during the remedial
      investigation.  Since investigations often span periods of only two-to-five
      months, it is generally necessary to estimate seasonal  variations.
      2.3   Other Site-Specific Factors.

      There are many other site-specific factors that affect  the design and
      performance of soil venting  systems.  A brief discussion of some factors
      include the following:

                  Surface Seal.  A surface seal, such as a pavement layer, is
                  often recommended in the literature.   A surface seal channels
                  air flow horizontally and restricts vertical air flow from the
                  ground surface near the extraction well(s).   Surface seals are
                  difficult to construct properly,  see Subsection 4.9.1.

                  Artificial  Conduits,   Backfilled trenches in soils can act as
                  short circuiting paths for the air flow.  Trenched sites with
                  relatively  impermeable native  soils are most affected because
                  the backfill in  the trench may be much more  permeable than the
                  natural soil.  Designers should indicate  utility trenches
                  (sewers,  water mains,  electricity lines,  etc.)  on maps with
                  soil venting system design plans.

                  Air-Flow Obstructions^  Building basements are  typical air-flow
                  obstructions which may change  the subsurface air flow patterns.
                  In these  cases,  designers should note  buildings with basements
                  in the reports,  especially if  the floor of a basement is near
                  or below  the capillary fringe.  Underground  storage  tanks are
                  also obstructions to  air flow  and designers  should also
                  indicate  their locations on maps  with  the soil  venting system

 Cuid«nc« for Soil Tcntlag 8rat

      3.0   Treatabllltv or Pilot Testing.

•  .    3.1   Laboratory Treatability Tests.
             **                                                               '• •
      Laboratory treatability tests are useful for sites with mixed wastes that
      have unusual characteristics..  Generally, because of past successes with
      common solvents and-highly volatile petroleum products on a national basis,
      these compounds do not warrant laboratory treatability studies for
      volatility.  See EPA Interim Guidance 1991(b) for guidance on treatability

      At sites with aerobic-degradable contaminants and substances that are toxic
      to microbes, such as leaded gasoline contamination or foundry sand,
      biodegradation treatability testing may be needed.  Other site-specific
      factors may also warrant biodegradation testing.

      3.2   Pilot Tests.

      A pilot test is preferred over a laboratory grain-size test to estimate the
      possible air-flow rate from a proposed soil venting system.  A pilot test
      is the only method that directly measures all pertinent site
      characteristics and geologic heterogeneities as an inherent part of the
      test procedure.

      A pilot test is a short-term test that typically is smaller in scale than a
      full-scale remediation system.  Generally, a pilot test at a LUST site or
      small ERP site is conducted for no longer than one day.  Some practitioners
      and the EPA may recommend long-term testing for certain situations, such as
      CERCLA treatability studies (EPA, 1991(b)).  NR 419.07 (3) exempts pilot
      tests of negative pressure venting systems from emission limits if the rate
      of air extraction does not exceed 100 scfm, and the test does not exceed
      eight hours at a site.  The pilot test is not exempt from notification and
      emission limits if it is conducted, longer than eight hours or exceeds 100

      3.2.1 Purpose of a Pilot Test.

      The purpose of a soil venting system pilot study is to determine design
      parameters prior to and for construction of a full-scale soil venting
      system.  For these purposes, a short-term pilot test with a small blower is
      usually sufficient.

      Key parameters include the following:

                  The air-flow rate that is achievable from a soil Venting system
                  extraction well configuration under a given vacuum rate.

           • •     The measurable vacuum at a .distance from the air-extraction
                  well  (zone of vacuum influence).

                  A quantitative estimate of the VOC emissions that initially
                  occurs with a soil venting system.

      3.2.2 Conducting a Pilot Test.
                                                       • .                •
      A pilot test should be conducted under conditions that are typical at the
      site.  For example, misleading pilot test results could occur if a pilot
      test  is conducted during or shortly after a rain storm.  The temporary

Baidtnet for Soil ftntlac feitm

      wetting front in the soil column created by infiltrated or pooled water may
      create a temporary surface seal to air flow.   In this example,  a temporary
      seal would suggest that the zone of influence is much greater than it
      really is.   Misleading results  could also occur if there is a significant
      ambient barometric pressure change during the test;  specifically,  if vacuum
      readings in distant gas probes  are taken for designing well placement.

      The following equipment is needed to conduct a pilot test:

                  Air -Extract ion Wells.   Designers  should install one to three
                  air-extraction wells at the site  for the pilot test.   Construct
                  these  wells according to the criteria for permanent full-scale
                  soil venting system use.   See Subsection 4 ..3 for construction

                  A water-table well  may be used if there  are no  air -extract ion
                  wells  constructed at the site for testing.   However, the
                  existing water-table wells should have a filter pack and
                  screen-slot size that  is appropriate for soil venting.   If  the
                  slot size and filter pack are too fine,  the vacuum  measured in
                  the extraction well  will be  too high and will' not reflect a
                  realistic vacuum for a given air- extraction rate.

                  It is  important to  choose a well  with known construction
                  details if  a water-table  well  is  used, because water-table
                  wells  typically have less  than 5  feet of screen  exposed  to  the
                  unsaturated zone.  It  is  also  important  to  operate  the pilot
                  test in a manner that  does not significantly  lift the water
                  table  during the test.  Lifting the water table by  the vacuum
                 more than half way up  5  feet of unsaturated screen  greatly
                  limits the use of the  data for estimating achievable air flow
                 per foot of well screen.  It is highly recommended that the
                 consultant use a small -diameter pump to lower the groundwater
                 to assure accurate pilot test data.  See Subsection 4.9.3 for a
                 discussion of matching drawdown to the applied vacuum.

                 Portable Blower (or Vacuum Extractor^ .  A small blower should
                 be used to pull air from the air -extraction well(s) during the
                 pilot test.  The blower can be almost any size.  Since pilot
                 tests are exempt from the air emission limits - provided the
                 test  is conducted at less than 100 scfm - a large blower may
                 not be useful in high-permeable soils.  Blowers should be
                 equipped with a discharge stack.  A muffler (or silencer) on
                 the exhaust and a dilution (or bleed) valve on the blower inlet
                 are also recommended.  Designers should use blowers with an
                 explosion-proof motor and switch.  In most eases, regenerative
                 blowers are used for pilot tests, however, a high vacuum blower
                 may be necessary at sites with low-permeable soils.
                 Extraction Well Sample Port and Instrumep^atf-f «ni   The basic
                 instrumentation needed on a pilot test is an air -flow meter,
                 vacuum gauge,  and thermometer.   See Subsection 4.4 for a
                 further discussion of instrumentation.  A sjample  port is also
                 needed to collect .air samples .   It may be most convenient to
                 install all instrumentation and the sample port on a single
                 temporarily- ins tailed pipe between the blower and the
                 extraction well.  A section of  2 -inch diameter or smaller pipe
                .is  recommended for  this purpose if an averaging pitot tube or

CuidUmc* for Soil V«ntln* Systw*                                   •                       **«• 1*

                  regular pitot tube is used.   See Subsection 4.4 for a
                  discussion of sizing a pipe  to a pitot tube..

                  Note:  The temperature of the air stream at the wellhead may be
                  a qualitative indication of  the residence time of the air in
                  the subsurface.•  If a pilot  test is conducted in mid-summer and
                  the extracted air is significantly warmer than the natural
                  grouridwater temperature, the air has a low residence time in
                  the soil.  The converse is also true -- unusually cold wellhead
                  temperatures in winter also  indicates a low residence time.

                  Sample Collection Equipment  or Instruments.  See Attachment 1
                  for a discussion of typical  sampling equipment.  Attachment 1
                  is designed for petroleum sites.  However,  field instruments,
                  portable gas chromatographs, and carbon'tubes (or other
                  adsorptive media) are useable at other sites.  The equipment
                  used must be appropriate for the site contaminants.  See
                  Subsection 3.2.3 for a further discussion of equipment

                  A combustible gas meter may  be needed at sites with ignitable
                  contaminants to ensure that  the off gas measured at the stack
                  is below the lower explosive limit.

                  Zone of Influence Instrumentation.  The vacuum in the soil at a
                  distance from the air-extraction well can be measured at
                  existing water-table wells,  other air-extraction wells, or with
                  temporary gas probes that are normally used for soil gas
                  surveys.  Some designers also install permanent gas probes as
                  discussed in Subsection 4.3.3.  Since water-table monitoring
                  wells generally have less than 5 feet of exposed screen above
                  the water table, measuring the vacuum in water-table wells
                  provides a vacuum reading that is essentially measured at the
                  warer table, provided that the well casing couplings are air
                  tight.  Air-extraction wells generally have longer screens and
                  measure an average vacuum over the entire screened interval.
                  Because there are significant vertical pressure gradients under
                  active venting, it is IMPORTANT to use vacuum monitoring points
                  that are equal in depth (or as close as possible), unless a
                  three-dimensional model is used that corrects vertical

                  To measure the vacuum in a well, fit an air-tight cap with a
                  hose barb to the well and use an. inclined manometer, vertical
                  manometer, or magnehelic gauge.  Vacuum measurements should be
                  to two digits of accuracy (e.g., 0.01 to 0.99, 1.0 to 9.9, and
                  10 to 99).  If the vacuum is very low, use an inclined
                  manometer or other device that can accurately measure to 0.01
                  inch of water column.  Vacuum measurements should be taken
                  after the vacuum in the subsurface has stabilized.  A minimum
                  of two measurements, at different times, at each data point
                  should be taken to assure that the vacuum has stabilized.
                  Generally, in coarse-grained soils the vacuum measurements are
                  reasonably stable after a half hour.  Subsection 4.1 describes .
                  how to use this data to evaluate well placement. . Note: If
                  designers use manometers instead of magnehelic gauges, they are
                  available with oil instead of water.  This may be an advantage
                  in'freezing weather.  Oil manometers are calibrated to the  .

Outamci tar Soil Vmtiag Sr»tm*                                    i                      „
                                                                                  rag* IS
                  density of the oil and cannot be used with water.   Some air-
                  flow modeling methods require barometric  pressure  monitoring
                  during the pilot test to  correct for  atmospheric pressure

      Some  sites  are  sufficiently, .simple so three -dimensional vacuum measurements
      are not needed,  but sites with complex stratified soil may need three-
      dimensional vacuum measurements to fully  understand th« air flow patterns
      Probes that are  normally  used for soil -gas surveys can be used instead  of'
      wells to measure the vacuum at specific discreet  depth intervals.

      If multiple air-extraction wells  are  available for testing, test each well
      by extracting air from it during  the  pilot test.   Test wells that are most
      likely to be used in a full-scale system.  If the  vacuum stabilizes at  a
      distance from the well in a reasonable period of time, multiple  air-
      extraction  well  tests  can be used for zone of influence measurements    If
      it takes more than  two hours for  an air-extraction well to stabilize  only
      a few wells  can be  tested during  the  eight hour air emission exemption

      If .the air-extraction well is screened into the water  table,  measure  the
     depth to the water table  -- both before and IMMEDIATELY after the pilot
     te^*TJ^en  if the Wel1 is B0t screened into the water table,  inspect the
     well IMMEDIATELY after the pilot test for water accumulation in the bottom

            ttow during £%£? *" ""* tO — — «" «*— *•** available
     Some consultants operate the pilot test at two or more air-flow rates
     during the pilot test to gather information for air modeling.   The method
     proposed by Clarke et al. (1993) and Wilson et al. (1992)  - to scale up
     from a pilot test to a full-scale system - requires flow and vacuum
     measurements at three or more different flow rates.  Note:  If the method
     r™! d %l      /* al- (1"3) ^ WilS°n 6t al- (1992>  :Ls used'  ^e DNR
     recommends flow and vacuum measurements at four or more different flow
    3.2.3 Analytical Monitoring Methods  for Pilot Tests.

    Use the  same  analytical methods  during the pilot  test  a» would be used in a
    full-scale remediation.   Frequency of sampling is not  specified for a  pilot
    test  but a minimum of two  gas samples should be  collected for analysis
    If a field portable instrument is  used,  take  samples every half hour or
    every hour.                                              J

    Do not take the  first  sample until after approximately 100 to  300 cubic
    feet of air has  been evacuated from  the  soils  adjacent to tiie well air-
    extraction well.  This initial purge of  air is needed  to thoroughly
    evacuate the air that  has been in  and near the air -extraction well and
    filter pack.  If 100 cubic  feet was  not  produced within 30 minutes because
    of low permeable soils, sampling after 30 minutes is acceptable.     Sites With Petroleum Product Contamination.

    During the pilot test, assess both total VOCs  and benzene (see
    Attachment 1).

Ould«nc» *or Boil V«ttn» Symttmt                                     •                     *"** 16     Sites With Non-Petroleum Contamination.

      Assess the known and suspected contaminants and any biodegradation products
      of the'contaminants during the pilot test.  Any other non-natural gases or
      vapors that may be in the subsurface from on-site and possible off-site
      sources should also be assessed.

            Example: There is a tetrachloroethene loss at a manufacturing
         .   facility, and there is an UST containing gasoline 200 feet from the
            tetrachloroethene spill site.  Even though there is no known gasoline
            loss, the pilot test at the tetrachloroethene spill site should also
            test for benzene and/or petroleum hydrocarbons in this case because
            vapor phase migration may occur over significant distances (Mendoza
            and McAlary, 1990).  Besides gasoline constituents and
            tetrachloroethene, samples should be analyzed for trichloroethene,
            1,2-dichloroethene, and vinyl chloride because these compounds are
            degradation products of tetrachloroethene and are expected to be

      3.2.4 .Reporting Results From Pilot Tests.

      The results of a pilot test can be included in the site investigation
      report, the design report or as a separate report.  The report from a pilot
      test should include the following:
                  A description of the test and final conclusions.  The text
                  should include dates, weather (ambient temperature, wind,
                  etc.), and any other pertinent field observations from the
                  pilot test.  The barometric pressure and whether climbing or
                  falling may also be listed.
                  A site map drawn to scale  (horizontal accuracy to +/- one
                  foot).  The map should indicate:

                  —     Locations of air-extraction wells and vacuum measuring

                  —     Suspected and/or known source location(s)  (if differing
                        contaminants types are present ait a site,  the locations
                        should identify the  contaminant types);

                  —     zone of soil contamination (if three-dimensional  data is
                        available; multiple  maps may be used);

                  —     Paved  areas, buildings, and structures  that may act  as a
                        surface seal or an infiltration barrier;

                  —     Buried utility  trenches that, may act as zones of  higher

                  -     Scale,  north arrow,  title  block, site name, key. or
                        legend, and date(s)  of pilot test;

                  —     Any other pertinent  site  information that  may affect a

Cuidmc* /or Soil Vatinf Syttmu
                        permanent: soil venting system on the site,  such as
                        overhead power lines (they may conflict with future
                        drilling activities).

                  A graph representing subsurface vacuum at a distance from the
                  extraction well.,is recommended if there ar« three or more data
                  points in addition to the air-extraction well,.  The distance
                  scale should be on the horizontal axis and th« vacuum should be
                  plotted on the vertical  axis.   The graph may be plotted on
                  normal graph paper or on semilog paper with the vacuum on the
                  log  scale.   Note:   The DNR recommends  semilog graphs for this
                  purpose.   The  graph should identify which elata points were
                  used.   A line  or curve predicting the  vacuvun at a distance from
                  the  air-extraction well  should be drawn on thts  graph.   The line
                  or curve may or may not  intersect the  air-extraction well due
                  to partial penetration effects and possible: extraction well
                  inefficiency.   Note:   If the screened  intervals between
                  different monitoring points vary significantly, the graph may
                  not  provide a  smooth curve because there  are significant
                  vertical  pressure  gradients under active  extraction.

                  A water-table map  of the  site  for the  day of the pilot  test.

                 A cross section showing screened intervals,  geological-units
                  contour lines of vacuum readings,  and vacuum measuring points.

                  If sufficient data points are available,  a map of measured
                 vacuums and contours of the vacuum in the soil during the pilot
                 test may be included.  This map  is  only recommended if the
                 full-scale remediation system will use a  single air-extraction
                 Tabulated flow rates,  vacuum distribution, soil gas
                 temperatures, times of readings, ambient barometric pressure
                 (if taken), and the ambient temperature.

                 Water levels in all wells.
                 A complete description of the field equipment and field
                 procedures that were used.

                 Sampling methods and procedures.
                 Analytical methods,  analytical  results,  and lab reports.   The
                 analytical results should be quantified  in uiasi; per volume
                 units,  such as  pounds per cubic foot or  milligrams per cubic
                 meter of contaminants in air.

                 Boring  logs and well-construction' diagrams for air-extraction
                 wells.   If groundwater monitoring wells  are used for measuring
                 vacuum,  the screened interval of  the monitoring wells.should be
                 listed  in a table and/or the well construction diagrams should
                 be included in  an appendix.  Any  vacuum  measuring points  that
                 are in  fill should be identified  as  such.

Guid«nc» for Soil Vantins Sftttmrn                                          •                ***• 18
                  Engineering calculations.   Clearly state all assumptions.
                  Legible, hand written calculations are acceptable.   Include the
                  initials or name of the author and the person who performed a
                  quality- control check of the calculations.   List references for
                  any formulas that were used.
      5                           s
                  Any other pertinent field data.

      Some pilot test reports also include a conceptual or detailed design of a
      full-scale soil venting system.  If a pilot test report includes a detailed
      design,  see Subsection 4.10 for recommended submittal contents.

      3.3   Alternative to a Pilot Test.

      Another way to estimate the air flow available from a soil venting system
      is by estimating the permeability of the soil based on a grain-size
      analysis.  This method should only be used if all of the following
      conditions exist:

            •      The unsaturated zone of the site is a single relatively
                  homogenous geologic unit.

            •      The volume of contaminated soil is very small.

            •      The total mass of contamination is relatively small.

            •  '    The Bureau of Air Management approves of the soil remediation
                  without conducting a pilot test.

      The best reason for using this -method is the low cost of a grain-size
      analysis relative to a pilot test.  The following are disadvantages of
      using this method:

            •      The effects of geologic heterogeneities are exaggerated by
                  using only a small sample(s) to characterize a site.  Sampling
                  location selection can inadvertently bias the results.

            •      Layered geologic conditions cannot be evaluated by  using a
                  grain- size analysis to estimate intrinsic permeability because
                  of the variations in permeability.

            •      Air emissions cannot be estimated.

            •      The calculated permeability assumes dry soil.  If there is
                  significant .soil moisture, the permeability to air  flow could
                  be less than estimated.

      To calculate the air flow available by the grain- size analysis  method,
      first estimate the hydraulic conductivity by using a mathematical analysis
      of the grain, size (Shepherd, (1989)., Hasch and Denny, 1966 or by the Hazen
      method in Freeze arid Cherry, (1979) and Fetter (1988)).  Note:   The Hazen
      Method is only valid when. 0.1 < Dio <  3.0 mm.  Then calculate the  intrinsic
      permeability of the soil from the hydraulic conductivity.  Note:  At 15
      degrees  Celsius, the conversion factor is approximately 1 darcy -8.5 E-4
      cm/sec based on data from Fetter (1988), page 84.  Finally, estimate the
      air -extract ion rate (Johnson et al. , 1990, see figures 4 and 5) per unit
      length of extraction-well screen.

Guidtne* for Soil Vtatiat Syntmu                                                          p • 19
            Design and Installation of a Soil Venting System.

      The soil venting system components are described in this  section,  beginning
      with a Discussion of well placement.  .The  discussion of design parameters
      then follows the same route as the flow of air:  from well design,  to
      manifold,  to water trap,  and the blower (or vacuum extractor).   Subsections
      4.7 through 4.9  discuss other equipment that may or may not be used at a
      site.   This Section concludes with a discussion of the  information that
      should be  submitted to the DNR.

      4.1   Well Placement and Air- Flow Modeling.

      The key design variables  with soil venting are  the number of air -extract ion
      wells  and  the flow rate from each well.  There  is  no equation  to determine
      these  parameters.   In the literature, well spacing generally ranges  from 20
      to  50  feet.                               .

     A capture  zone for a well can be mathematically determined for  groundwater
     plume  capture (given the  gradient, extent  of contamination, pumping  rate
     and aquifer transmisivity) .  Soil venting  systems  do not have a single
     mathematical solution to use for determining well placement.  Some
     mathematical models  exist  that are excellent tools for estimating well
     spacing, however,  the users of these models should be sufficiently skilled
     to know if and when model assumptions are valid.

     Some system designers use a model that estimates the number of pore volumes
     that are needed to clean up a site.  An air-flow rate that is based on pore
     volumes is then selected.  If a method based on pore volumes is proposed
     the volume of air that enters the well(s) through the ground surface nea^
     the well should be assessed using a method that evaluates  three-dimensional
     air flow, such as the method described by Shan et al  (1992)  or by a
     similar method.   Other models are complex two-  or three-dimensional models
     of air flow patterns.  Some models use pilot test data to  determine site-
     specific parameters, such as Kh/Kv ratio, intrinsic permeability, etc
     Some of the mathematical models (both analytical and computer)  used for
     modeling air flow through soil are based on horizontal flow only and do not
     take into account vertical recharge through the ground surface.  Models
     that use limited assumptions, such as horizontal and not vertical air flow
     are  good tools for rough estimates, but are not useful for determining an '
     exact distance for well spacing.   Designers should assess  the key
     assumptions in an air-flow model prior  to its use-.   Professional judgement
     is necessary in  interpreting model results.

     The  DNR does not  endorse any models and does not require* air modeling for
     the  system  design.   If a model is used,  include  the key  assumptions and
     results of  the model in an appendix to  the  design report:.

     The  zone of influence is the area from which an  extraction well can
     effectively draw  air.  Figure 4-1 is based  on the mathematical  formulas  in
     Shan et al.  (1992);  it simulates  the vacuum that would be measured  in
    water-table wells at different distances  from a  single air-extraction well
     There are four different graphs simulating  Kh/Kv ratios of  0.67,  1, 3  and
     10.  As  demonstrated in Figure  4-1 there  is no clear cut "radius" of  '   -
     influence;  the effectiveness  gradually decreases with distsmce    In theory
    the vacuum  extends  significant  distances beyond  the point «4iere  it- can be
    measured by field measuring devices.  Even  though in theory there is  a
    vacuum at these great distances,  in reality, the vacuum is  so low that
    there is  induced air movement through  the sell.   The

GulcUnc* tor Soil V«ntin* Syibaa*
                                                                                   P««» 20
       Figure 4-1
       Vacuum at a distance from a single extraction well


                                Vacuum With On* Air Extraction Wall
r 100-:
60 :
0.6 :
0.4 :
0.1 ".
0.06 :



.001 •


V :
\. 1
\ I
N. . • :
: N. j
' 20.0 Depth to Woter Table (feet) x. ]
20.0 Depth to Base of Screen (feat) x.
12.5 Depth to TOD of Screen (feet) \
: 17.5 Depth of Predicted Vacuum (feet) \
; 7.5 Length of Screen (feet) N.
50.0 Air Flow Rate (scfm) xss^
0.67 kh/kv (or kx/kz) Ratio >v
' 1.00E+01 Horizontal Permeability (Darcies) ^
1.5QE+01 Vertical Permeability (Darcies) i i i i

D -20 40 60 80 100
       Figure 4-1A
                                  Distance From Air Extraction Well
                                 Vacuum With One Air Extraction Well


[-100 j
60 :
0.6 :
0.1 .
J.04 ]



•\ . j
>. :
• ^\ •
• 20.0 Depth to Water Table (feet) ^ — '
: 20.0 Depth to Base of Screen (feet) ^s.
12.5 Depth to Too of Screen (feet) \
: 17.5 Depth of Predicted Vacuum (feet) \.
• 7.5 Length of Screen (feet) , ..
• 50.0 Air Flow Rate (scfm) \.
1.00 kh/kv (or kx/kz) Ratio ^s.
1.00E+01 Horizontal Permeability (Darcies) \
1.0QE+01 -Vertical Permeability (Darcies) i i i i

0 20 40 60 80 100
       Figure 4-1B
Distance From Air Extraction Well

Guidance tax Soil Tooting Sy>tea>
                                                                                              Face 21
       Rgure 4-1 continued



                                    Vacuum With One Air Extraction Well
      Figure 4-1C


— HJ-
0.6 :
0 i
0.06 :
'• ' . '
v - i
: "\^^ .
; ^"^^^^ j
. ^J
20.0 Depth to Water Table (feet)
20.0 Depth to Base of Screen (feet)
12.5 Depth to Top of Screen (feet)
17.5 Depth of Predicted Vacuum (feet) :
7.5 Length of Screen (feet) :
50.0 Air Flow Rate (sefm) :
3.00 kh/kv (or kx/kz) Ratio
1.00E+01 Horizontal Permeability (Darcies)
3.33E+00 Vertical Permeability (Darcies) i ,
0 20 40 60 80 10

                                     Distance From Air Extraction Well
                                   Vacuum With One Air Extraction Well
60 :
— 1-9-
0.6 :
0.06 :
0.04 :
p Q\


"^^^-^ •
• ^"^~~^^-^ ' : "
• — — -^^J

20.0 Depth to Water Table (feet) '
20.0 Depth to Base of Screen (feet)
12.5 Depth to Top of Screen '(feet)
17.5 Depth of Predicted Vacuum (feet) :
7.5 Length of Screen (feet) :
50.0 Air Flow Rate (scfm) -
10.00 kh/kv (or kx/kz) Ratio
1.00E+01 Horizontal Permeability (Darcies')
1.0QE+00 Vertical Permeability (Darcies) , , , ,

                                 20           40           60

                                    Distance From Air Extraction Well
           . 100
      Figure 4-1D

Guidance for Soil V«otin* Sytttm*               >                                          p«g« 22

      numerical example below is based.on the graph in Figure 4-IB where the
      Kh/Kv ratio is one.

                  Example:  The stabilized (steady state)  vacuum and the distances
                  from the  vacuum measuring points to a single air-extraction
                  well in a uniform sand are as follows:

                              Measuring Point      Vacuum      Distance
                                                (Inches of      (feet)
                                              Water Column)

                                    W-l             54           NA
                                    MW-2              5.2         10
                                    Mtf-1              1.6         20
                                  .  MW-5              0.25        40
                                    MW-4              0.10        50

                  In this case,  the  vacuum decreases by 3.6  inches of water
                  column from 10 feet  to 20 feet,  and it  decreases by 0.15 inches
                  of water  column from 40 to 50 feet.   Assuming that the rate of
                  horizontal air flow  is directly proportional to  the horizontal
                  difference in pressure head,  the air velocity through the soil
                  at 40 to  50 feet from  the air-extraction well is only 4.2
                  percent of the velocity at 10 to 20 feet (0.15 / 3.6  - 0.042 or
                  4.2 percent).

                  As the air velocity  through soil decreases  at greater distances
                  from  the  well,  the system's ability to  volatilize and remove
                  VOCs  by advection  is reduced at a distance.   In  this  example,
                  the effectiveness  of the system is only marginal at distances
                  beyond 50 feet even  though there is measurable vacuum to 75
                  feet  and  immeasurable  vacuum beyond.

                  Since there is a significant vertical pressure gradient,  it is
                 VERY  IMPORTANT that  all vacuum measuring points  are equivalent
                  in depth  when using  vacuum versus  distance  data  to evaluate
                 well  spacing,  unless a three-dimensional model is used that
                  corrects  for vertical  gradient.

     Use professional judgement to  estimate the well  spacing that is needed in
     each specific  situation.   Take the following items  into account when
   . assessing optimal well .placement:

                 Some areas  of  a site usually have  much higher levels  of soil
                 contamination  than others.   It may be appropriate to  use  a
                 closer well spacing  in these  areas to increase the  rate of
                 remediation.                       -                                •

           •     Generally,  there is  a  tradeoff between time,  efficiency,  and
                 cost.  Closer well spacing speeds  the cleanup, but  increases
                 costs for wells, analytical testing and blower capacity.   If
                 the total cost  of wells  is  significant, a longer  cleanup  time
                 with fewer wells,  spaced farther apart may be more  appropriate.

                 Relatively close well  spacing is needed  in  low permeable  soil
                 because the rate of  air  flow  from  each well  is very low,  and
                 therefore the rate of  contaminant  extraction on a pounds-per-
                 time basis is also very  slow per well.  In high permeable soil,

Gaidtaem for Sell tontine Sy«t«M                        •                                  p.g. 23

                  wells can be placed farther apart because higher air flow per
                  well can result in a greater rate of contaminant extraction per

                  If the Kh/Kv ratio is very high due to the depositional
                  environment of the soil,  or if there is a high quality surface
                  seal, the air-flow pattern will have a preferred horizontal
                  orientation.   In this case, wells can be placed farther apart
                  because there is less vertical recharge near the air-extraction
                  wells. '

                  In a heterogenous,  mixed  lithology site,  the «one of influence
                  in the more permeable layers is  augmented by overlying layers
                  of silts and  clays,  which allows increased well spacing.   The
                  silts and clays,  however,  take longer to clean up because
                  extracting contaminants from these soils is limited by the rate
                  of diffusion.

                  At sites with a very shallow water table,  a significant
                  proportion of the air that enters the air-extraction well(s)  is
                  from.the ground  surface near the well.   In these cases,
                  relatively close  well spacing may be  necessary.

                  To remediate  contaminants  that have a low vapor pressure
                  through  volatilization, relatively rapid air-flow rates through
                  the soil are necessary.  In this .case,  relatively close well
                  spacing  may be appropriate.   Enhancing biodegradation, however
                  does not usually  require a high  air-flow rate.

                 At sites  where geologic conditions at depth are  sufficiently
                 uniform,  a  single set of wells at  the  same depth may be
                 sufficient.  Sites that are  significantly stratified or that
                 have other  geologic heterogeneities in the site soils may have
                 a very high rate of contaminant removal initially, but the
                 removal rate will decline rapidly after the coarse-grained
                 layers are  remediated.  Late  in a project the rate of
                 extraction  is controlled by  the rate of VOC diffusion out of
                 the.fine-grained soils.  At a site with these conditions,
                 tailor the design for the natural geologic conditions.

                       Example:  A site has two distinct, fairly thick geologic
                       units, a sand and gravel unit and a sllty sand unit.
                       Remediation of the silty sand unit is expected to be much
                       slower than the sand and gravel unit.  lin this case,
                       fewer extraction wells screened in the sand and gravel,
                       and more extraction wells screened in the silty sand may
                       maximize the remediation rate of the silty sand.  Air-
                       injection wells (Subsection 4.8) may also be needed in
                       complex geological conditions.

     The spacing of air-extraction wells in a full-scale soil venting system is
     determined by the desired air-flow rate through the impacted soil and the
     desired rate of cleanup.  Use professional judgement to weigh the costs
     against the cleanup time when determining well placement.  A higher air-
     flow rate is needed for an increased rate of volatilization and advection.
     The air-flow rate is less  important if diffusion and biodegradation are
     controlling factors in the remediation rate.

Ouid«no» for Soil Vntlns Symttm*                                 .                         *•»• 2*
      Buscheck and Peargin (1991) suggest that the design radius of vacuum
      influence at a gasoline"contaminated site be at the distance where the
      vacuum .in the soil is 1 to 0.1 percent of the measured extraction well
      vacuum."  According to the Buscheck and Feargin method applied to the
      numerical .example above,  the well spacing (which is twice the design radius
      of vacuum influence) should.-range from 20 to 65 feet.

      Generally, the well spacing should range from 20 to 50 feet..  If proposed
      well spacing is closer than 20 feet or farther than 50 feet, and the
      Buscheck and Feargin (1991) method is not used, the spacing selected should
    •  be justified in the workplan submitted for the site.

      4.2   Air Permeability, Achievable Air-Flow Rates,  and Air-Emission Limits.

     •Use the vacuum and air-flow rate measured from the air-extraction well
      during the pilot test to estimate the vacuum and air-flow rate that are
      achievable in a full-scale soil venting system design.

      If pilot test results from multiple geologic strata are evaluated, it may
      be appropriate to evaluate the achievable air-flow rate per foot of screen
      and/or the intrinsic permeability of each geologic unit.  If all the wells
      in a final system design have equal screen lengths in the same lithologic
      materials, the flow rate per well can be used instead of calculating the
      flow per foot of screen.

      In most cases, if the vacuum is loss than about 40 inches of water column
      (one-tenth of an atmosphere), designers can assume that the rate of air
      flow to vacuum is linear.  Note:  This assumption is invalid because air is
      compressible, but the method is useful for estimating air flow under low
      vacuum conditions.

            Example:  If the pilot test indicates that 72 scfm is -achievable from
            a well under 9 inches of water column vacuum, the system is designed
            to have 14 inches of water column at the well head.  The flow rate
            would be:

            72 scfm *   Q  — approximately 112 scfm

      Where the vacuum is greater than about 40' inches of water column, the rate
      of air flow to vacuum is not directly proportional because air is a
      compressible fluid.  In this case, adjust the required vacuum to account
      for the compressibility of air.  A multiplier that approximates the
      compressibility of air is appropriate.

            Example:  A pilot test indicates that 40 scfm are achievable under 3
            inches of Hg.  Note:  1 inch of Hg - 13.55 inches of water column.
            The full-scale system is intended to provide 100 scfm from each air-
            extraction well.

            3 Inches Hg *  ,„  S<1 m  — 7.5 inches Hg uncorrected for compression
                      °    40 sctm

            Assume that atmospheric pressure is 29.92 inches Hg.

Guldtnci tot Sail Vtotlog Syttmu

            7.5 Inches Hg *   *9'*2 '3 inehas gf
                        *    29.92-7.5 inches Hg    y'u
            In this example,  9 inches of mercury vacuum is  necessary to achieve
            100 scfm per well.   This empirically-derived approximation is not
            very accurate at  vacuums above 10 inches  of Hg, but it is generally
            usable in the vacuum range of most soil venting ssystems.   A better,
            more complicated  correction factor that compensates for the laminar
            to turbulent flow transition is described in Clarke et al.  (1993) and
            in Wilson et al.  (1992).   If the system is very large  and/or will run
            at high vacuums,  use the correction method described by Wilson
            instead of the simplistic method described in the example above.

            The above correction factors assume that  there  is no water-table
            upwelling.   If there is  significant upwelling,  the  screen length  in
            the unsaturated zone changes,  and ,the estimate  is not  correct.

     If  the pilot test uses  a 2-inch well and the full-scale system  uses a 4-
     inch well,  approximately 15 percent more  air flow will be extracted at  the
     same vacuum because  of  the larger  well  (Johnson et  al., 1990).

     The above means  of estimating  the  achievable air-flow rate in a full-scale
     soil venting system  assumes that the soil  intrinsic permeability and the
     exposed  length of screen remains the same  over  time.  There  are a number of
     reasons  that the  air-flow  rates  in soil venting systems change with time
     including the  following:

                  Seasonal water-table fluctuations and Vacuum  induced water-
                  table fluctuations change the amount of well  screen available
                  for air flow.

                 Clay and silt  soil types may dry out and crack while operating
                 a soil venting system,  increasing air flow through secondary

                 The effective porosity  (to air flow) of the soil and thus air
                 permeability can increase as moisture is reduced in the soil by
                 the drying effects of the air flow.

                 The air permeability of the unsaturated zonis changes with
                 infiltration events because of fluctuating effective porosity
                 to air, changing the air flow to the well(A).   A paved ground
                 surface can minimize this effect.

     Pilot  test data should be used because it is the best data available for
     designing a soil venting system, even though it  may not provide 100 percent
     accurate  results.

     Determine a total desired air-flow rate for the  site using the total
     available well-screen length from all wells and  the rate of air flow per
     linear foot of screen.  If all wells in a final  system design have equal
     screen lengths in the same lithologic materials, the flow  rate per well  can
     be used instead of calculating the flow per foot of screen,.  In general,
     the  total flow rate will be between 50 and 500 scfm for  most petroleum
     sites.  Sites that have  a larger area than typical petroleum sites may have
     higher total flow rates.  Some sites that have contamination in a very
     limited area (diameter of 50 feet or less) may only require one air-

Ould*nc« for Soil Venting Syfttm*                            .                              P«M 26

      extraction well and less than 50 scfm.

      To evaluate whether or not the vacuum will be too high,  which may create an
      unacceptable amount of upwelling,  designers should determine the design
      vacuum and air-flow rates.  It is possible that  the vacuum will lift the
      water table above the zone with the highest level of contamination.   In
      this  case,  the high vacuum is counterproductive  because  the contamination
      is submerged below the cleansing effects of the  air flow.   A, lower vacuum
      and corresponding lower air-flow rate is more productive over time,  unless
      the groundwater table is lowered by pumping.   Pumping groundwater is
      discussed in Subsection 4.9.4.

      The rate of contaminant extraction will decline  with time during a full-
      scale site remediation.  The anticipated contaminant removal rate at start-
      up is similar to the pilot test results.  If the air-extraction wells are
      not installed in the highest soil contamination  zone,  the contamination
      extraction rates may actually climb for the first few days after full-scale
      start-up as contaminants are drawn towards the well(s).   Otherwise,  the
      pilot test results may provide the highest achieved contamination
      extraction rates.  For engineering design purposes,  apply a safety factor
      of 1.5 to the highest.levels of contaminants  in  the air  during the pilot
    .  test  to predict the highest levels of contaminants from  a full-scale

      Compare the maximum air emissions  at start-up to the total desired air-flow
      rate  using the emission limits and the  achievable air-flow rate calculated
      from  the pilot test data (with safety factor).   It is possible that  air
      emission control will be needed; no emission control is  necessary or;  the
      initial flow rate from the system needs to be limited using a timer  or a
      dilution valve.   Air emission control devices are discussed in greater
      detail in Subsection 4.7.

      The air emission limits in Wisconsin are based on the total mass of
      contaminants emitted during a period of time. If no emission control is
      anticipated,  the contaminant extraction limits are the limiting factor
      during start-up.  The limits for petroleum sites are discussed in
      Attachment 1.   System designers can estimate  the maximum air-flow rate at
      start-up by dividing the total emission limit by .the concentration measured
      during the pilot test.   '     '

            Example: A LUST site pilot test indicates  that total VOCs are
            1.0 E-3  pounds per cubic foot and benzene  is 1.0 E-6 pounds per cubic
            foot.  Assume that the total VOCs are limited to 5.7 pounds per hour
            and benzene is limited to 300 pounds per year.  The  maximum air-flow
            rate  for total VOCs is then estimated to be:

               5.7 pounds per hr      e ^nn   .   .   .    ^.  *   „     t_
            1 E-3 pounds per foot?  ' " 5'700  standard  cubic feet Per hour

            5,700 standard feet3 per hr   «c   *
                 ..f.   .          , *        <• 95 scxm
                 60  minutes per hr

            Applying a safety factor of 1.5,  the maximum becomes:

            95 scfm
                     - 63  scfm

Gatdtnci tar Soil Vmtiag Bfttim*                                                  '        $M. 2?

            A similar calculation for benzene is:

             -	300 pounds per yr
             1.0 £-6 pounds per foot3   " 30°'°°°'°°° standar^ cubic feet per year

             300,000,000 standard feet3  per yr
                 525,600 minutes per year      "     s ffl

            Applying a safety factor of 1.5,  the maximum  becomes:

             570 scfm
                     -380  scfm
            In this  example  the limiting  factor  is  total VOC«.  The  designer
            (based on past experience) anticipates  that the «ystem will have a
            contaminant extraction rate at about one-third of the  maximum after
            two months.  Therefore, the designer selects a blower  much bigger
            than 63  scfm.  The flow rate  at start-up  is limited to approximately
            63 scfm  by using a dilution valve  (Subsection 4.A).-  If  approximately
            two or three months of sampling indicates that a hijjher  air-flow rate
            can be used while complying with the air  rules, the system operator
            increases the flow rate by adjusting the.dilution valve  to increase
            the contaminant  extraction rate.

            Note:  Upon start-up, a dilution valve may be used t:o  control  total
            VOC emissions, but not to control benzene emissions,

     4.3    Well or  Trench Design.

     Vertical  air-extraction wells at most sites are used to extract  air  from
     the soil.  In  rare cases, a horizontal air-extraction system is warranted
     over vertical  wells.   Conceptually, a trenched  system is preferred if  the
     groundwater  table is very shallow (less than about 10 feet)  or if the  soil
     contamination  is very  shallow.  Figure 4-2 shows a typical well design.

     4.3.1 Vertical Extraction Wells.

     The extraction wells should be constructed using 4.25-inch or larger
     inside-diameter, hollow-stem augers.  Any drilling methods; (other than
     hollow-stem auger), such as mud or clear-water direct rotary, should not be
     used if the method creates an excessive filter cake buildup on the bore-
     hole wall.  Refer to Subsection 1.3.1 for a discussion of regulatory
     requirements on well construction.

     The pipe and screen should be flush threaded schedule 40 EVC or CPVC.
     Steel or other materials may also be used.   The recommended diameter of the
     screen and casing is 4 inches.  Two-inch, 2.5-inch,  and 3-inch diameter
     screen and casing are also used on some systems.

     The advantages of 4-inch diameter over 2-inch are:
                 The flow rate at a given vacuum is higher with  a larger well
                 (Johnson et al., 1990).   Doubling the well diameter increases
                 the air-flow rate by 15 percent.   Two-inch diameter wells are
                 more restrictive to air flow.

Oold«ac» for Soil Vntint Syst
                                                                   Ff«« 28
      Figure 4-2
      Typical air extraction well design with above grade manifold
Sample port
Flow meter  Vacuum
*^o   Q' o ^Thermometer
                       Surface seal

                       8 to 10 inch boring
                       2 to 4 inch diameter well casing

                       Cement or bentonite/cement grout
                        Bentonite seal

                        Fine filter pack

                        Well screen

                        Coarse filter pack
                        Bottom plug
      Seasonal low water table

Guidtnm tee Sail tontine Sy«t«ms                                                          PM> 29

                  Little water is lifted up the well,  if the  up-hole air velocity
                  flow is limited to 1,000 feet per minute or less.   This reduces
                  water production and accumulation.   In many cases,  a water trap
                  (Subsection 4.5)  is not needed on a  soil venting system if the
                  up-hole velocity is minimized.  A 2-inch diameter,  schedule 40
                  well casing will only deliver 23  scfm if the up-hole velocity
                  (at atmospheric pressure)  is  1,000 feet per minute.   A 4-inch
                  diameter,  schedule 40 well will produce 88  scfm at 1,000 feet-
                  per-minute of up-hole velocity.

                  Packers may be  used to seal off portions of a screen that
                  intersect  relatively clean soils.  There are packers and
                  similar devices available  off the  shelf for insertion in a 4-
                  inch diameter pipe.

                  If  there is  a sufficient water  accumulation to block off a
                  significant  portion of the screen, it may be necessary to  pump
                  groundwater  from  the well.  A greater variety of pumping
                  equipment  is  available  that can be used inside 4-inch wells
                  rather  than  2-inch wells.

     If the diameter  is  less  than  2 inches or greater than 4  inches,  the
     diameter should be justified  in the work plan submitted  for  the  site.

     The Screen.length is a function of the water-table depth and the
     contamination zone.  In isotropic soil conditions, set the base of the
     screen at the seasonal-low water table.  Set the top of the screen at a
     depth that will channel most or all of the air flow through the
     contaminated soil and limit short circuiting of relatively clean air from
     the ground surface.  At some sites with unusual or complex geological
     conditions, it may be appropriate to nest wells.   In this case, set the
     well-screen depth for each well for the specific  purpose of that well (such
     effects)"8 SCreetlS itl differinS geologic strata to reduce short circuiting

     At  petroleum sites, the soil near the capillary fringe may have the highest
     levels of soil contamination because contaminants often  collect at the top
     of  the water table.  The air-flow rate through the soil  is  reduced near the
     capillary fringe because of reduced effective  porosity for  air flow   By
     screening the wells near the water table,  the  rate of contaminant
     extraction in these cases is maximized.  This  channels more  air flow past
     the high contamination zone.  This may be an appropriate a.ction at this
     type of site to  reduce  the air flow through the upper, relatively clean
     soils.                                                          •

     It  is permissible to install additional screen length below  the water table
     to  place a groundwater  extraction pump.  With  a pump that has sufficient
     capacity,  this form of  pump  placement allows the  system  operator to dewater
     the entire screen,  if necessary.   See Subsection  4.9.3 and 4.9.4 for a
     discussion of groundwater extraction and  free-product recovery.   Designers
     should place  a plug at  the base of the well screen in accordance with
     NR  141.

     The filter pack  should  be sized for the formation.   Since air-extraction
     wells are  not developed,  a filter pack that is  coarser than  a typical well
     used for groundwater extraction,  is usually acceptable.   Size the screen-
     slot size  for the filter pack.   Generally,  a slotted pipe provides

0uid«nc» tor Soil V«ntln» Sytttmm                                                              30.

      sufficient open area per linear foot of screen.  The  filter pack and well •
      screen-slot size at and below the seasonal-high water table should be
      determined based on groundwater extraction criteria.   Please  refer to  the
      Guidance for Design, Installation and Operation of Groundwater Extraction
      and Product-Recovery Systems for groundwater extraction well  design.

      The top of the filter pack should be a short distance above the top  of the
      screen; generally 1 to 2 feet is appropriate.  If  a coarse-gravel  pack is
      used,  a fine-filter pack that is 6 to 12 inches in height can be placed
      above the coarse-gravel pack to limit the potential for grout or bentonite
      entering the well screen.

      A bentonite seal is often used to prevent grout from  entering the  screened
      interval.  In air-extraction wells,  limit the bentonite seal  to a  short
      thickness of 6 to 12 inches because bentonite can  dry out in  the
      unsaturated zone.  This may allow air to short circuit through the annular

      Cement grout or bentonite/cement grout in the annular space above  the
      bentonite seal should be vised.  The grout seals the annular space  up to the
      ground surface or to the manifold, if a buried manifold is used.   If the
      grout is poured instead of tremied into place, use care to avoid displacing
      or damaging the bentonite seal and upper-most portion of  the  filter-pack.

      A tee fitting and not an elbow to connect the air-extraction  well  to the
      manifold should be used.  Using a tee fitting allows  for  the  attachment of
      a threaded cap to the top.  The threaded cap provides access  to the
      interior of the well to take water-level measurements or  to install  pumps
      or packers.                          •                '                            .

      If the manifold is buried, the surface seal should be constructed  in a
      manner similar to that described in Chapter NR 141.  An air and water-proof
      manhole cover should also be used.  Other fittings (valves, etc.)  discussed
      in Subsection 4.4 can also be installed under the  manhole cover(s).

      4.3.2 Horizontally Screened System Design.

      Horizontally-screened systems are sometimes used at sites where groundwater
      tables are shallow or where contamination is limited  to shallow portions of
      the soil column.  A significant amount of care is  necessary when designing
      and installing an efficient horizontally-screened  soil venting system.

      Short circuiting of air .flow through the backfill  above the screen or
      perforated pipe is a common problem.  Mixing a small  amount of bentonite
      into the spoils prior to back filling may reduce the  permeability  and  short
      circuiting problems.

      A thorough hydrogeologic knowledge of the site is  essential to design  a
      trench for an air-extraction system.  Because vacuum  induced  water-table
      upwelling and/or seasonal variations in the water  table can flood  the  air
      inlets in the perforated pipe or screen, the screen or perforated  pipe
      needs to be installed high enough to prevent flooding.

      Generally, a horizontal system is installed with a backhoe.   Dig the trench
      and install a PVC-perforated pipe or screen in a pea  gravel backfill.
      Place the spoils that were removed during trenching over  the  gravel.
      Placing plastic sheeting above the gravel and below the backfilled spoils
      reduces vertical short circuiting of air through the  trench backfill.

Cuid«nc» tot Soil Vratlof                                                                 ,
                                                                                  P«*» 31

      Compact the spoils as much as possible to reduce  the vertical  permeability
      f J! ^T10!^18 ?0t, Safe C° enter>  comPact tl»e spoils by tamping the soil
      with the backhoe bucket in very thin lifts.

      If pavement is placed over the trench)  plastic sheeting  should be installed
      under any gravel subgrade that is placed  below the pavement.   This will
      limit vertical recharge from the subgrade to the  backfill.

      Installing  a trench that is very long may increase the occurrence of  short
      circuiting.  Since the  construction  of  a  trench may cause  a short
      °  T1^,1?8  "^ f°r  air fl°W'  the lonSer the trench, the  greater the
     probability of inadvertently constructing a short circuit  route in the
      trench.                    •

     Handle excess spoils  that  are not placed back in  the excavation in
     accordance with  the DNR guidance on  investigative wastes or solid and
     hazardous waste  regulations  dependant on the volume of contaminated soil.

     4.3.3 Gas Probes.

     Permanent gas probes are vapor wells that are installed to assess
     vacuum/pressure and subsurface vapor concentrations of VOCs and/or
     biodegradation products.  Temporary gas probes,  such as those used for soil
     gas surveys are also acceptable.  The construction details;, materials
      i^T' etC'  a"not sPecifi«d in Chapter NR 141.   However,  gas probes
     should have an annular seal and a surface seal  constructed to Chapter  NR
     141 standards to prevent the gas probe from acting as  a conduit for

                  an^°f a Sh°rt CirCUit route for air  flow-   I* * g«  Probe is
                  0f1b*1T ^ seasonal-hiSh wat« table, then the pVobe is a
                              S ^ C0nstruct the  •" P«*'e  to Chapter NR 141
     Purging a minimum of 3 to 5 volumes  (of air)  is  appropriate when taking
     samples for field instruments  or laboratory analysis.

                      1 £°r " dUCUSSl'"1  °£ *>-*« «as probes  tn predicted

    4.4   Manifold and Instrumentation.

    The manifold in soil venting systems is either installed above grade or it
    is buried.  When  the area is used for  activities that will not allow the
    use of above-ground manifolds  (parking lots, driveways , dispenser islands,
     JC>)> Jhe"anlfold should be buried.   Above-ground manifolds are suitable
    when uninhibited  access  does not have  to be maintained at a site.

    If contaminant migration is minimal AND if the DNR project manager
    approves, some systems may operate only during the warmer portions of the
    year.  In cases where the  project must  operate all year, the manifold
    should be winterized (or capable of being winterized) at a later date
    Generally, an above -ground manifold can be winterized with self regulating
    heat tape and/or pipe insulation at any time.   Above-ground systems
    therefore, are not usually winterized until it is necessary.   Buried
    manifolds are not easily winterized,  so these systems are usually insulated
    or installed near or below the frost level.  If the manJLfold is winterized
    at a later date with heat tape, use CPVC pipe instead of PVC pipe to
    provide higher strength in high temperatures.

Ould*nc« for Soil Vntinc Sy«t««s                                                          P«S« 32

      Generally, .manifolds should be constructed with 4-inch pipe.   Systems have
      been installed with manifolds as large as 24 inches in diameter,  but these
      large systems have centrifugal blowers that require a low manifold vacuum.
      The designer should evaluate pipe friction in the system to ascertain that
      the manifold will conduct the desired air-flow rate under either of the
      following conditions:

                  If a 2-inch manifold pipe is used,  the  air-flow rate is over 50
                  scfm and any piping run is longer than  50 feet.

            •      If a 4-inch manifold pipe is used,  the  air-flow rate is over
                  300 scfm and any piping run is longer than 50 feet.

      The manifold may accumulate condensation if the air velocity is  lower than
      a  few thousand feet per minute.  One method to avoid a condensation buildup
      is to slope the manifold towards the air-extraction wells where  it can
      drain.  Another satisfactory method with buried manifolds is. to  use a
      relatively small-diameter vertical pipe where the direction changes from
      horizontal to vertical, allowing the airstream to carry condensation up
      towards  a water trap..  This method is satisfactory  if the air flow in this
      smaller pipe has an up-hole air velocity of 3,000 feet per minute or more.
      A  less satisfactory method is to maintain a high air velocity on the entire
      manifold by using a small-diameter pipe.   This alternative is less
      satisfactory because pipe friction may be excessive,  resulting in added
      requirements for blower capacity and excessive electrical costs.

      Designers should configure the manifold and place valves in such a way to
      allow control and sample collection at each well.  Above-ground  systems may
      have the sample ports and instrumentation for each  well near the well
      itself.   The sample ports and instrumentation on buried manifold systems
      may be located near the blower system where the manifold pipe exits the
      ground.   Figure 4-3 shows two different options for instrumentation
      locations on a buried manifold.  The option that places the instrumentation
      nearest  the well generally provides the best vacuum and temperature
      information for the well, but is more likely to freeze up in winter on low
      flow systems and systems with a shallow water table.

      Construct the manifold with glued fittings,  since slip fit joints may fail
      with time.   It is recommended that a steel wire or  similar material is
      installed in the trench with buried manifolds that  have plastic  pipe to
      find the trench later with a metal detector.   Note:   This is unnecessary at
      sites with reinforced concrete pavement,  since the  metal detector will only
      "see" the rebar.

      Install  a flowmeter, a vacuum gauge or manometer, a thermometer,  and valve
      at locations where samples are collected.  These devices are described as
      follows:                                                 •

            •      Valves.  Each well should be installed  in a manner that allows
                  the well to be isolated from the rest of the system.   PVC ball
                  valves or gate valves are generally used to isolate  each well:
                  If the flow rate through the pipe is expected to be  over 100
                  scfm, the valve should not be smaller in diameter than the
                  manifold pipe.  In lower-flow systems,  the valve may be smaller
                  to reduce costs.

                  A dilution or bleed valve is also needed on the manifold
                  immediately before the air enters the air filter or  blower (if

Gaidanet tat Soil Italia* Sr«t«M

    Figure 4-3
    Wellhead details with buried manifold

  Ground surface     Air and waterproof
       /          /well cover
                                                                     P««« 33
                          Steel wire
                         Manifold pipe
                    Air extraction well
                                                              n O O
                                           Frost level
                                           or below

                Sample port and
                                              Instrumentation located
                                              near blower

                    Air and waterproof
                    well covers
                  Sample port and
                                             Ground surface
Frost level
or below
                                                       at wellheads
                                                         Steel wire
                                      Manifold pipe

Guidinc* for Soil Voting Sy«t«««                       •                                   P«c« 34

                  no filter is used).   The dilution valve allows atmospheric air
                  into the blower,  when opened,  and relieves vacuum to reduce
                  overall air-extraction rates from the wells.   Do not install
                  the dilution valve between the wells and the  sample ports,
                  because the sample results would not represent extracted air
                  concentrations. ..A dilution valve is more energy efficient than
                  a throttle valve  that restricts air flow because blowers
                  require the least amount of electrical power  when.the pressure
                  differential across the blower is relatively  low.  In addition
                  to a dilution valve,  install an automatic pressure relief valve
                  if the blower may overheat under a blocked flow condition.  A
                  silencer on the inlet to the dilution valve may be needed in
                  some cases.  If the dilution valve is opened  to the atmosphere,
                  an air filter on  the blower is needed, even if it is a
                  centrifugal blower.

                  An alternative to installing the dilution valve that opens to
                  atmosphere is to  install a bypass valve to draw air from the
                  blower exhaust.   This allows air to circulate from the exhaust
                  back to the blower inlet.   This alternative does not need a
           •   ,    silencer on the intake which lowers equipment costs.  A bypass
                  valve,  however, does  not allow the system operator to dilute
                  the airstream at  the  stack to  reduce the concentration to below
                  the lower explosive  limit.

                  Sample Port.   The sample port  design is specific to the sample
                  container and the field procedure for collecting samples.   It
                  may have a septa  fitting for direct syringe insertion,  or it
                  may be as simple  as  a hose barb for a piece of plastic tubing.
                  The sample .ports  may  have to be fabricated for the specific
                  sampling devices.

                  Flow Meter.   Averaging pitot tubes or regular pitot tubes  are
                  generally used to measure air  flow.   Pitot tube manufacturers
                  specify that a number of transverse readings  are collected at
                  different points  within the air stream when pitot tubes are
                  used.   Averaging  pitot tubes are designed to  only require  a
                  single reading.   In general, manufacturers recommend 10 or more
                  straight unobstructed pipe diameters upstream and five or  more
                  diameters downstream  of the pitot tube or averaging pitot  tube.
                  (Example:   A pitot tube on a 2-inch pipe requires 20 straight
                 'unobstructed inches upstream of the. pitot tube and 10 inches
                  downstream.)   A minimum of approximately 1,000 feet per minute
                  of air velocity is needed to get accurate readings,  therefore,
                  the pipe diameter may need to be reduced at the location within
                  the manifold where the flowmeter is installed.

                  Orifice plate meters  are also acceptable if they are installed
                  in accordance with manufacturers specifications.

                  Hot wire anemometers  are also used in soil venting systems,  but
                  may be  inaccurate if  there are  liquid water droplets in the air
                  stream.   These devices must be  classified as  "intrinsically-
                  safe* when working with ignitable contaminants.

                  For a  discussion  of flow meters,  see Ginesi and Grebe (1987).

           •      Vacuum.  Measure  the  vacuum with a manometer,  a magnehelic,  or

Ouldtnet tar Soil Vatlac SjriUtt                                                          p-s- 35

                  a vacuum gauge.   Most soil venting systems operate at a low
                  enough vacuum that the measurements are read in inches of water
                  column.  Higher  vacuum units may use inches of mercury as
                  vacuum measurement units..  Note:   1 inch of Hg - 13.55 inches
                  of water column.  Vacuum gauges should be to two digits of

                  Temperature,   The temperature is  usually read with a bimetal
                  dial-type  thermometer that is installed through a hole in the
                  manifold pipe.

                  Relative Humidity or  Dew Point   Relative humidity or dew point
                 .measurements  are not  required,  but may be beneficial when
                  evaluating moisture content for biodegradatioin or carbon
                  filters.   Use &  wet bulb thermometer or digital meter to
                  measure relative humidity or dew  point.

     4.5   Water  Trap.                                            "

     A water trap (also  called a  separator tank or demister) may be necessary
     In general,  a water trap  should be included in the  design  if the  up-hole
     air velocity in the air-extraction wells  is greater  than 1,000 feet  per
     minute or if a rotary  lobe blower is  used: situ air  sparging  (see
     Guidance on Design, Installation and  Operation of In Situ Air Sparzine
     Systems) is  used, a water trap should be  included because the sparEine
     process can  cause water to enter the  air-extraction wells.

     Water trap configurations include the following:

                 A vertical pipe,  cap,  and tee in a manifold that is capable of
                 holding less than 5 gallons;

                 A large tank in line with the manifold;

                 An engineered trap that uses a cyclone action to separate the
                 water droplets from the air stream.
     It  is  necessary to address the water that accumulates in water traps   If a
     groundwater extraction system is also used at the site, the accumulated
     water  can be added to the pumped groundwater that is treated and/or
     disposed of.   If no groundwater extraction system is used at the site  it
     is necessary to arrange for proper disposal of the water.

     4.6    Blower (or Vacuum Extractor) Type and Size.
     The following are three common types  of blowers for soil venting systems:

                 Centrifugal.   Centrifugal blowers  perform best in high flow,
                 low vacuum  applications.   Advantages of centrifugal blowers'
                 include  low equipment  cost,  low electrical costs,  and minimal
                maintenance requirements.   The main disadvantage is that  they
                cannot develop a  high  vacuum.   These units nre  only usable  in
                sand and gravel environments or in .trenched systems that  have a
                very high length  of perforated pipe.  Due to the small vacuum
                they develop,  long manifold systems  may  need large-diameter
                manifold piping to reduce pipe friction.

                Regenerative,  Regenerative  blowers  develop hijjher vacuums  than

 lor Soil V«ntln« Symttmt                                        ,                   *««• 36
            centrifugal blowers  (up to 8 inches of mercury) .  These are the
            most common blowers  for smaller sand and gravel sites.

       •""    Rotary Lobe.  The rotary lobe blowers are capable of producing
            very high vacuums (up to 15 inches of mercury is not uncommon) ,
            which is the primary advantage of this blower type.
            Disadvantages include higher cost, high electrical demands,
            high noise levels, and frequent maintenance requirements.  Soil
            venting systems in silt or clay soils require the rotary lobe's
            high -vacuums .                           '        •

Figure 4-4 shows performance curves for these three blower types.  Each
curve  on the figure is for comparison purposes only; larger and smaller
models are available for each blower type.  It is apparent that the rotary
lobe units have a very high vacuum capability and are the best choice for
sites  that need a high vacuum.   It is also readily apparent that a
centrifugal unit is the best choice for sites that have high-flow rates
that are achievable with a low vacuum.  Regenerative blowers have
characteristics between the rotary lobe and centrifugal units.

Other  blower types, such as liquid ring, may also be used when conditions

The type and size of the blower  determines the 'electrical requirements.
Some of the rotary lobe units are large enough to require three-phase

A discharge muffler should be used to reduce noise for larger soil venting
systems, especially systems that use rotary lobe blowers.

Size the circuit breaker for the motor to trip the circuit breaker if the
rotor  is locked.  The motor and  all controls should be explosion-proof if
there  is ANY POSSIBILITY of igniting the contaminants.  Sensors should be
intrinsically-safe and controllers need to be in explosion-proof enclosures
or located in non-hazardous locations.

Rotary lobe blowers and other blower types that have close tolerance
clearances should be equipped with a particulate air filter.  Regenerative
blowers may also need an air filter.  A centrifugal blower is usually best
used without an air filter because the filter restricts air flow.

It is  recommended that the discharge stack be constructed with CPVC or
other  materials that retain strength at high temperatures on the higher
vacuum systems.  The higher discharge temperatures on the high vacuum
systems may weaken FVC.  Host blower manufacturers include methods for
estimating the discharge temperature from the blower.  If the discharge
temperature reaches approximately 140 degrees 'fahrenheit (or higher) , PVC
may become too weak.  In general, FVC is acceptable on all centrifugal
blower systems.  A drain at the  base of the stack is useful to drain any
accumulated moisture.

4.7    Emission Control Devices.
If emissions exceed the table value of any contaminants listed in Table 3
of Chapter NR 445, then 95 percent contaminant removal or destruction
capability is required.  Sources requiring air treatment devices that
exceed table values in Table 3 need DNR Bureau of Air Management permits.
The following are three types of air treatment devices for controlling

ftiidaoc* for Soil Vmtlai Syittmt
                                                                  P«8« 37
       Figure 4-4
       Performance curves for three types of blowers
                                          Rotary lobe blower

                                          Regenerative blower
                                    "" "~ Centrifugal blower
                                     160    200
                                Airflow - SCFM
240   280
     Centrifugal blower type shown is a New York model 2004A at 3500 rpm
     Regenerative blower type shown is a Rotron model DR707
     Rotary lobe blower type shown is a M-D Pneumatics model 3204 at 3000 rpm
      nmcoh« °es* nc* endorse tnese b'ower manufacturers; performance
     curves shown for discussion purposes only

GolcUnc* for Soil Viotinc Sytttmf                    •                                      ?•»• 38

      emissions from petroleum projects:

                  Incineration.   Incineration is most cost-effective with high
                  contaminant levels because the contaminants  provide a
                  significant amount of fuel for the incineration process.

                  Catalytic Destruction.   Catalytic units  generally are used with
                  high contaminant levels,  but lower contaminant levels compared
                  to the incineration units.   If the contaminant level is too
                  high,  the catalyst becomes too hot and burns out.   Pilot test
                  data is necessary to assess if it is appropriate to use
                  catalytic destruction units.

            •      Granular Activated Carbon (GAG).   GAG units  are not used
                  frequently in Wisconsin compared  to other states.   At the
                  levels where GAG is most cost effective,  the emission limits in
                  Wisconsin generally allow a direct discharge.   If.carbon
                  filters are used,  a device to dehumidify the air may be needed.

      Other treatment devices,  such as bio-filters  or internal combustion engines
      may also  be acceptable to  the DNR on a site-specific basis.  This should be
      discussed with the DNR project manager before purchasing and installing.

      Greater blower-pressure capacity is needed with off-gas  control systems
      because of the flow restriction within the system.   Manufacturers of off-
      gas control equipment may  provide pressure and flow  requirements for

      4.8  Air Injection.       '      ' .

      Some  projects use  air injection to  direct air flow through a specific part
      of  the contaminated soils.   It is usually used to help create  more flow
      near  the  capillary fringe, which is often the hardest part of  the soil
      column to remediate.

      In  general,  do not use air injection if the injected air temperature  is
      lower than the normal groundwater temperature.   The  colder air reduces the
     volatility of the  contaminants and  also reduces the biodegradation rate.

     4.8.1 Passive Vents.                                            .

     Some  projects use  passive  air injection to help direct air flow through
     contaminated zones.   Passive air vents  are venting wells that  inject  air
     under atmospheric  pressure without  using a blower.  The  driving -force is
     the induced vacuum in the -subsurface  that* is  created by  the  soil venting
     system.   Only a small percent of the  air that is extracted from a soil
     venting system is  from passive injection.   Air-flow rates  in passive
     injection wells typically  cannot be accurately quantified because of  the
     low rate  of air flow into  the well.   The wells can be constructed for the
     purpose of air .injection,  uncapped  water-table monitoring wells,  or air-
     extraction wells that are  valved off  of the manifold and open  to the

     Generally, passive injection is not very effective.   However,  converting
     existing  wells to  passive  injection may be appropriate if useable wells
     already exist at the  site.   •                                                   .

Gaidtnci tor Soil Vtettiac Syfttmt                                                          Pmg. 39

      4.8.2 Forced Injection.                               !   •

      In some cases,  clean (contaminant-free)  air is injected into the soil
      through a series of wells or trenches..   Designers should justify the use of
      forced injection in the workplan on a site-specific basis, -i

      To assure that  the injected air is extracted by the extraction system,  the
      injection rate  should be no more than one quarter of the extraction rate.
      If the proposed ratio of.injection to extraction is greater  than 0.25
      provide justification in the work plan.    Air injection wells must inject
      air at very low air-flow rates  if they are within the izone of
      contamination.   Otherwise,  they may force contamination outward to
      uncontaminated  areas or through the ground surface.   If air  injection is
      proposed within the zone of contamination,  air modeling is needed to
      evaluate flow paths.

      Air that is oxygen deficient should not be injected at sites with
      aerobically degradable contaminants because it could slow the
      biodegradation  rate.

      To  assure that  there  is  no  positive pressure  in the  subsurface  near
    •  basements or other structures where vapors  may collect,,  gas  probes  may be
      needed with air injection on a  site-specific basis.

      It  is  possible  to  heat air  to increase the volatility  of the  contaminants
      If heat  is  added,  the  temperature must be low  enough so  that  it does not
      disinfect the soils, which  adversely affects natural biLodugradation.

     4.8.3  In  Situ Air  Sparging.

     Air sparging is a  form of forced air injection into the saturated zone   If
     air sparging is used,  include a water trap in  the design of the soil
     venting system.   The sparging process may cause excessive amounts of water
     to enter the air-extraction wells.  See Guidance on Design,  Installation
     and Operation of In Situ Air Sparging Systems for a detailed discussion of
     air sparging.

     4.9   Other Design Considerations.

     4.9.1  Surface Seal.

     A surface seal,  such as a pavement layer,, is often recommended in the
     literature.  A surface seal directs air now horizontally and restricts
     vertical air flow from the ground surface near the extraction well(s)
     Sites  that are highly stratified, or sites that have a high Kh/Kv ratio do
     not need surface seals because the natural geologic conditions force the
     air-flow patterns horizontally.   Sites without a high Kh/Kv ratio or
     stratification may benefit from a surface seal.  Figure 4-5 indicates air-
     flow patterns with a quality surface seal, a poorly constructed surface
     seal and no surface seal.

     If  surface seals are used,  it is important to construct them  properly.
    There  is usually a gravel subgrade below  pavement.  Significant quantities
    of  air can flow  horizontally through a highly permeable subgrade toward the
    extraction well(s), even though  the subgrade is less than a foot thick.
    The propensity of the subgrade to act as  a short circuiting route is
    directly proportional to the ratio of horizontal permeability of the
    subgrade  to the  vertical permeability of  the underlying soils.

Guidmc* tor Soli Vontiag Synttmm
                                                                                  P«S« 40
      Figure 4-5
      Typical air flow patterns
                                                                      Ground surface

                                                                              . •(*•
   Isotropic conditions
Stagnation zone

    Stagnation zone

    isotropic conditions with perfect surface seal

                                         /• Stagnation zone ,1"
    Isotropic conditions with gravel subgrade under surface seal

             •          \                     .       .     .    \
    Heterogeneous conditions
   Stagnation zone
    Note: Not to scale, for conceptual discussion purposes only
          Flow is three dimensional. Recharge also occurs in the dimension
          perpendicular to the drawing.

Guidaas* tor Sou Vmtiaf Syittas
                                                                                  P«8» 41

      Surface seal modeling is  described by Krishnawa et a]   ri988^   Tn t-Ko

      S^TISIS'  S^  »***«£ tJSSJ*i.££i fl^d

      suSacf 'sea?          n  *    recharS* that occurs with  . very high quality
 finer eralne^ T? '"P61^ inf a11 a *»"* surface seal,  especially in
 firSiS   ?  s^ls«  Because of the potential for horizontal short
 circuiting immediately below the seal.

 4.9.2 Stagnation Zones.

 Stagnation zones are  areas  that have little or no air flow because two  or

      WS   6  UUi    ^
                                    in diffe"»t directions

                                                                            of a
     a1modi~i0n Wil1 Sene?ally occur a<= Blower rates in .stagnation zones than
     at other areas of a site due to the low velocity of air flow through these
     soils.   Because stagnation zones are created by the location of onf air!
                  11 riativt                                   "
                                                      Systeils with
wes   mcint
f^i™    C   i?   ^     operation requires periodic changes in flow rates
from each well   Designers should change flow rates from different wells

                                                                 eren  wells
    As discussed in Subsection 2.1, stagnation zones can also be anaerobic
    zones where aerobic biodegradation is slowed due to Umited oxygen

    4.9.3 Vacuum- Enhanced Product Recovery.

          Lrer   y £"***•"* '  ™* <*"*»<* for Design,  iHstallatlo^d
    Operation of Groundwater Extraction and Product -Uecoverr Systems provides a
                                    aPFlied t0 ** ""very well  should not be
                                   is created by
          Example:  Assume that the  submerged portion of th«s roe'ovaxy well is

          iStET? t-H     I1?"? C? 8roundwater flow» «* the unsaturLed screen
          portion of the well  is 100 percent  efficient to air flow.  A 10 gpm
          pumping test indicates that the specific capacity of the recovery

          well is 12 gpm per foot of drawdown.  The hydraulic conductivity
          determined from  the  pumping test is used to calculates the capture

          zone.  It is determined that 50 gpm is required to capture the plume

Ooidmoa *or Soil V«ctin* Sy*tma                                                          **•• *2

            The predicted drawdown at start-up of the recovery system is:

            ^-L	50 SPm	-5	» 4.17 feet or 50 Inches of water column
             12 gpm per ft of drawdown

            Therefore, the maximum vacuum that should be applied to the well is
            50 inches of water column.

            If the specific capacity is unknown,  it can be estimated.  See
            Attachment 3 to the Guidance on Design, Installation and Operation of
            Groimdwater Extraction and Product-Recovery Systems for estimating

      Volatilization of liquid product will take place because vacuum-enhanced
      product recovery passes the air flow through a well that has liquid phase
      product in it.  This raises the possibility that the air emissions may be
      quite high, possibly exceeding air emission limits.  Designers should
      evaluate the cost efficiency on a site-by-site basis to compare the costs
      of air emission control with the advantages of vacuum-enhanced product

      Also see Subsection 4.9.4 in the Guidance on Design, Installation and
      Operation of Groundwater Extraction and Product-Recovery Systems for a
      discussion of well design.

      4.9.4 Groundwater Extraction from Air-Extraction Wells.

      In some situations, air-extraction wells may also be used for groundwater
      extraction.  In most cases, air-extraction wells are used for groundwater
      extraction because they are in a convenient location and drilling costs are
      reduced by using one well for two purposes.  In other cases, the vacuum is
      used to increase the yield of the well.  Occasionally, the water is pumped
      out of the well to counteract the effects of upwelling, and to lower the
      groundwater table to expose this smeared zone to air flow (Johnson, et al.,

      If a well serves these two purposes  (groundwater and air extraction), it
      must be designed for both purposes.  Construct the lower portion of the
      well that is used for groundwater extraction with a well screen and filter
      pack sized for groundwater extraction.  If the slot size or filter pack is
      too large, the well may pump sand.   See Guidance for Design, Installation
      and Operation of Groundwater Extraction and Product-Recovery Systems.

      If the formation is highly permeable, enormous quantities of groundwater
      have to be extracted to significantly lower  the water table.   If the
      primary purpose of groundwater  extraction is to lower the water table to
      expose contaminated soil to the air  flow (and not to extract dissolved
      phase contaminants), it may not be cost-effective to pump and  treat
      groundwater  at  some sites.  In  this  situation,  in situ  air sparging or
      other techniques may be preferable.  See Guidance on Design, Installation
      and Operation of In Situ Air Sparging Systems.

      4.9.5 Enhanced Biodegradation of Petroleum  Compounds  in Soil.

      Petroleum based contaminants readily biodegrade during  operation o'f a soil
      venting  system.   Biodegradation for  petroleum projects  is  an important part
      of the remediation process because a significant quantity of the

GuiOtnet tot Sell Vmtiac SystM*

      contaminants are destroyed by natural bacteria (Hinchee and Miller,  1990
      and Miller,  1990).  Generally, the degradation rate is much faster under
      aerobic^ conditions than anaerobic conditions.   The level of oxygen is
      usually the  limiting factor under static conditions,   The venting system
      provides oxygen when.using active venting,  and moisture or nutrient  supply
      become  the limiting factors,

      To  quantify  biodegradation rates  based on oxygen or carbon dioxide
      emissions, it is necessary to measure background oxygen and/or  carbon
      dioxide  in the soil.   Ideally,  the background  measuring point is  one or
      more upgradient water-table well(s),  and/or gas probe(«)  that are located
      in  an uncontaminated part  of the  site which is/are not us«d for air
      extraction.   Measuring the ambient background  levels of o:cygen  and/or
      carbon dioxide .in the  soils is  necessary whenever oxyg«n or carbon dioxide
      samples  are  collected  because the  ambient levels may change seasonally
      (Wood et. «!..  1993; Solomon and Cerling, 1987).   The  change in the  carbon
      dioxide  or oxygen levels,  relative  to background,  is the value  to use when
      quantifying biodegradation rate.  Attachment 1  includes! a  sample  method  to
      quantify the biodegradation rate based on carbon dioxide.

     The advantage  to using carbon dioxide measurements  to measure
     biodegradation is  that carbon dioxide can be quantified with a high  level
     of precision at very low levels;  It  is difficult  to precisely measure a
     very small oxygen  deficiency.  Two disadvantages to measuring
     biodegradation with carbon dioxide are that carbonates in the soil can
     dissociate or precipitate, and carbonic acid can form which reduces the
     accuracy of the estimate.  Generally, the literature indicates that
     practitioners prefer to use oxygen to quantify biodegradation,  instead of
     (or in addition) to carbon dioxide because oxygen is less affected by the
     soil geochemical properties.

     Also,  see Subsection 5.1 for a discussion of oxygen breakthrough.

     4.10  Soil Venting System Design Report.

     In  some  cases, the design of a soil venting system is included in a
     comprehensive report with the results of a pilot test.  In other  cases, the
     design is submitted separately.  A report that  includes the design of a
     soil venting  system should include the following:
Pas* 43
                A discussion of the system design and a description of
                capabilities for remediating the soil at the  site.   Include a
                brief discussion of the geological conditions at the site.

                Describe  the logic  used to determine  well placement and

                Details of  the  air-extraction well design include the screen
                length and  diameter, slot  size,  depths  and specification of the
                filter pack and seals,  and the drilling method,.  If multiple
                well  depths are needed,  discuss  the logic for determining, well-
                .screen depths.
                Justify a horizontally-trenched  system  if it:  is proposed in the
                design report.

GultUoca for Boil Vntias Sytttmt                                                          p*** **

            •     Details of the manifold design including pipe type,  diameter,
                  and a description of instrumentation for measuring flow and
                  vacuum.  Indicate the depth of the manifold,  if-it is buried.
                  Blower specifications including total anticipated air-flow
                  rate, vacuum levels, type and size of blower.

                  Discuss the Wisconsin air emission limits,  anticipated flow
                  rates, pilot test results, and the possible need for air
                  emission control devices.  If air emission control is proposed,
                  discuss the type of system and the status of any air permitting
                  requirements.  The discussion should include an estimate of
                  total VOCs in the unsaturated zone.

            •     Discuss options for water disposal, if a water trap is

                  The height of the stack.

                  Monitoring plan.

                  —     Non-petroleum sites.  There are no specific requirements
                        for non-petroleum sites.  The designer should propose a
                        monitoring plan in the workplan,.  In most cases,
                        reporting frequency and sampling frequency will be the
                        same as the one in Attachment 1.  Sampling parameters,
                        methods, etc. are determined on a site-specific basis.

                  —     Petroleum sites.  Attachment 1 is a generic plan for
               '         petroleum sites.  The designer should prepare a site-
                        specific plan based on Attachment 1.   Deviations from
                        Attachment 1 should be identified and justified.  If a
                        photoionization detector is used, see Robbins et al,
                  A map of proposed well locations drawn to scale. The map should
                  include the following:

                  —     locations of proposed and existing air-extraction wells;

                  —     locations of the manifold, instrumentation, and sample

                  —     location of blower and other equipment;

                  —•    suspected and/or known source location(s)  (if differing
                        contaminant types are present at a site, the locations
                        should identify the contaminant type);

                  —     extent of soil contamination;

                  —     paved areas, buildings, and structures that may act as a
                        surface seal or an infiltration barrier;

                  —     buried utility trenches that may act as zones of higher

Guidance for Soil Venting Syst«u                                       •                    p.,. 45

                  -     scale, north arrow, title block, site name, and key or
                        legend; and

                  —     any other information.

                  A current water-table map and a table of water levels.
                  Indicate the date of water-level measurements on the map.

                  A process flow diagram indicating piping network,
                  instrumentation and key components.
                  Engineering calculations for determining the well spacing and
                  zone o.f influence measurements from the pilot test, if any.
                  Clearly state any assumptions.  Hand written (if legible)
                  calculations are acceptable.  Include the initials or name of
                  the author and the quality control-checker.  Include references
                  for any formulas used.

                  If an air-flow model is used,  include the results of the model
                  and any assumptions that the model uses.

                  Engineering calculations predicting the total air-flow rate.
                  Include the performance curve  that is provided by the
                  manufacturer of the blower.  Note the manufacturer and model of
                  the blower.   Note the rpm of the blower if it is belt driven.

                  A description of sampling procedures and analytical methods.

                  Form 4400-120 for LUST  sites.

Guid«nc« for Soil V«ntln« Sy*t«u                                                          FmR* *6

      5.Q   Operation of a Soil Venting^System.

      5.1   Overview.

      Operation of a soil venting system requires ongoing monitoring and system
      adjustment to maximize performance.

      Immediately after start-up, VOCs associated with the glue from the manifold
      are discharged from the system.  Samples for compound-specific testing
      should not be collected until at least one or two hours after start-up to
      allow the VOCs from the glue to be discharged from the system.

      For safety purposes, air should not be discharged from the stack at or
      above the lower explosive limit.  The use of a dilution valve may be
    •  necessary at some sites during the pilot test or vtpon start-up.

      Immediately after start-up of a soil venting system, a large mass of VOCs
      are rapidly removed because the concentration of VOCs in the extracted air
      is very high.  During this.initial phase,  air-flow advection through the
      coarse-grained soils rapidly extracts VOCs from coarse-grained soil.  If
      there is a significant amount of stratification or other geologic
      heterogeneities in the site soils, the extraction rate will rapidly decline
      to a non-zero asymptotic rate of extraction.  Buscheck and Peargin (1991)
      and Johnson et al. (1990) have an excellent discussion about the reduced
      extraction rate over time.

      Small fluctuations in the extraction rate are normal with soil venting

      A slow contaminant-extract ion rate may occur even if soil sample results
      indicate there is a significant amount of contaminants remaining in the
      soil.  The slow extraction rate can be due to a number of factors:

            •     Fine-grained soil units or layers readily retain significant
                  quantities (relative to coarser-grained units) of contaminants.
                  Clay soils will commonly retain contaminants at concentrations
                  that are orders of magnitude higher than the coarser-grained

                  The fine-grained soil layers in stratified soils are generally
                  parallel to the direction of the air flow.  Therefore, the
                  pressure gradient induced by the vacuum does not force the air
                  flow  (and VOCs) through the fine-grained soil layers.  Instead,
                  the air flow is around the fine grained layers.  In many cases,
                  the VOCs diffuse very slowly out of the fine-grained soils into'
                  the coarser layers for advective transport to the extraction

            •     Even  if the geology is largely homogenous, the distribution of
                  the most highly contaminated soil in the unsaturated zone is
                  typically near the water table.  The extraction of VOCs is
                  slowed in the most highly contaminated soil because the air-
                •  flow  rate is relatively slow near the capillary fringe due to
                  the reduced effective porosity to air flow.
                  Remaining contaminants are relatively non-volatile.  See
                  Subsection 2.1 for a discussion of vapor pressure and Raoult's

Guldmet tar Soil Vntiat Syt

      The following are reasons that extraction rates can increase significantly:

                  A new loss of product.

                  Higher air temperature  raises the  volatility of contaminants.
                  If there is a high air-flow rate and a low air residence time
                  in the soil,  the ambient temperature in the warmer months can
                  increase the volatilization rate.   Use temperature trends over
                  time  at the wellheads to assess this effect.

                  Water-table fluctuations can expose additional contamination
                  that  was previously, submerged.

     After the system  has operated for a few months to a few years, the
     emissions fall to A very low level,  relative to initial concentrations.  At
     this point,  significant contaminant reduction  at petroleum sites is  due  to
     biodegradation.   In these cases, the soil venting systems  provide oxygen to
     the bacteria.  Aerobic  biodegradation is not significantly inhibited until
     oxygen levels  have  dropped below 5  percent.  See Attachment 1  fot a  sample
     method for determining  the biodegradation rate based on carbon dioxide.

     It is possible that oxygen deficiency in stagnation zones  could exist  even
     if extracted air  is  quite low in carbon dioxide  and high in oxygen because
     of dilution.   If most of  the  air passes through  relatively  clean soil and
     only a small amount of  the extracted air passes  through biologically active
     contaminated zones,  there could be  oxygen deficient parts of the site that
     go undetected because of  oxygen breakthrough.   Therefore, at larger sites
     that have the potential for oxygen breakthrough,  it may be prudent to
     install gas probes near predicted stagnation zone locations to assess
     oxygen and carbon dioxide.  Gas probes in those locations way also be
     useful for assessing contaminant concentrations or methane.

     On a site-specific basis,  if significant biodegradation ralres are necessary
     to complete the cleanup (for a site with significant levels of aerobically
     biodegradable, but relatively non-volatile compounds),  an evaluation of
     methane may also be needed to assess the presence of anaerobic zones.

     Biodegradation requires a high moisture content in the  soil.  During colder
     months  the atmospheric dew point is likely to be lower  than the soil
     temperature.   In this case air that is drawn through the ground can remove
     significant amounts of moisture from the soil.   When the atmospheric dew
     point is  higher than the soil temperature (which occurs occasionally during
     the  summer months) drying the soil with an excessive air-flow rate  is less

     Because biodegradation requires a  fairly high moisture  content, it  is
    •possible  that using a slower air-extraction rate late in a project  is more
     productive  than a  high rate of air flow.   A high air-flow rate  may  remove
     too much  moisture  and inhibit bacteriological activity.   Opening  the
     dilution  valve to  reduce the flow  rate may be necessary to reduce the
     drying effects of  the air flow. Another option is to use  a timer to
     operate the system for only a few hours  per day.  If the blower is very
     large, it may be practical to purchase and install a smaller blower because
     of reduced electrical demand and/or  reduced maintenance  costs.
     Stagnation zones that develop between the air-extraction wells  in multi-
    well systems  inhibit the ability of  a soil venting system to operate
    efficiently throughout the entire site.   Changing the flow rates from

GuitUnc. for Soil V«otin* SystoM                           '                               *•*• 48

      different wells on a periodic basis improves overall system performance.

      Some consultants use temporary or permanent gas probes to evaluate air
      quality"within the subsurface at points other than the extraction wells.
      Water-table wells can also be used for air sample collection.   If the trend
      of air samples from the probe(s) over time indicate that high levels of
      VOCs and/or biodegradation products (carbon dioxide or methane) are
      remaining, it is a clear indication that the part of the site where the
      probe(s)  is/are located is not being cleaned up.  Either the probe(s)
      is/are located in or near a stagnation zone, or something else is not
      working correctly.

      Some operators cycle soil venting systems by operating the system
      intermittently.  In the literature, there is no clear advantage or
      disadvantage to cycling soil venting systems.  If the consultant chooses  to
      cycle the1 system, the sampling plan should acknowledge that cycling causes
      inconsistent contaminant-extraction rates over time.  Increased sampling
      frequency may be necessary to accurately evaluate the extraction rate.

      5.2   As-Built Submittal.

      After a soil venting system is constructed, the "as-built" information
      should be included in a report.  Since most of the information is in a
      design report, a separate submittal is not always necessary.  The "as-
      built" information can be included in the first progress report after
      start-up.  The "as-built" submittal should include the following:

                  Any deviations from the specifications in the design report.

            •     A map of actual-well locations .drawn to scale. The map should
                  include the following:

                  —     locations of existing airrextraction wells;

                  —     the manifold, instrumentation, and sample port .locations;

                  —     location of blower and other equipment;

                  —     suspected and/or known source location(s) (if differing
                        contaminant types are present at a site, the contaminant
                        types should be identified per location);

                  —     zone of soil contamination;

                  —     paved areas, buildings, and structures that may act as  a
                        surface seal or an infiltration barrier;

                  —     buried utility trenches that may act as zones of higher

                  —     scale, north arrow, title block, site name,  and key or
                        legend; and

                  —     any other pertinent site information.
            •     A table with the air-flow rate, vacuum levels, and temperature
                  at all sampling locations at start-up.

Guidance for Soil Vratin* Systn*                                                          ¥•&»

                  A table of water levels in all wells.

                  Air-extraction well construction diagrams.

                  Boring logs and any other documentation required by Chapter NR
                  141.   .  .       ,

                  Any other pertinent information.

      5.3   Reporting.

      The reporting frequency for most sites are as follows:

                  Petroleum sites.  As described in Attachment 1.  The DNR
                  project manager may specify a different reporting schedule.

            •      Non petroleum sites.  The reporting frequency will be
                  established on a site-specific basis by the DNR project

      Progress reports should be sequentially numbered starting with the first
      report after the remediation system start-up.  In  general,, the progress
      reports  do not need to be detailed documents.  In  most cases, only one or
      two pages of text in a letter format with supporting tables and figures is

      The progress reports should include the following  information:

                  A brief discussion of the progress of  the remediation system

                  —     Contaminant extraction totals to date in pounds or
                        gallons of contaminant(s) removed.

                  —     System operation details; periods of shvit down, equipment
                        malfunctions,  etc.

                  —     Overall evaluation of the system effectiveness.

                  —     Recommendations for future activities,  if appropriate.

                  Graphs that include data through the life of the project are
                  very useful to evaluate•trends.  Graphs may include:

                  —     Total contaminant removal graph  with time on the
                        horizontal axis and cumulative contaminant removal on the
                        vertical axis.  The consultant may provide a graph with
                        this information on a per well basis foi: smaller systems
                        (four wells or less),  but a graph on a per well basis
                        typically is not required unless requested by the DNR.

                  —     Contaminant level time graph, with time on the horizontal
                        axis and mass per volume values  on the vertical axis.  A
                        graph on a per well basis is recommended for smaller
                        systems,  but typically is not required for larger
                        systems..                              i

            •      Tables that include data throughout the project are useful to

OuicUnc. fox Soil Vantlas Sy«t«««                                                          Fag* SO

                  establish trends.   Include the following tables:

                  —     Field data and flow-rate measurements.

                  —     Contaminant levels and extraction rates at  each sampling
                        point.  (This table can be combined with the field data
                        table- if space allows).

                  —    -Table of water levels and product levels or thicknesses.

            •      If analytical available from & laboratory, include the
                  lab reports.

            •      A discussion of sampling procedures,  analytical procedures,
                  etc. is not required, but include a reference to  the report
                  that lists the procedures.

            •      Any other pertinent information or data.

      5.4   Case Close Out.

      When to Consider a Site for the Close Out Process.   The volatilization rate
      on a pounds-per-day basis needs to be calculated prior to sampling before
      terminating operation of a soil venting system.   If the contaminants are
      aerobically biodegradable, the sum of the current rate of both
      volatilization and biodegradation — on a pound-per-day basis  — should be
      included in the mass removal calculation.  It is premature to consider the
      site for case close out if the mass-removal rate is significant,  relative
      to the remaining contamination mass.

      Methods  For Determining the Biodegradation Rate.   To determine the
      biodegradation rate, the DNR recommends the methods discussed in the
      April 5, 1991 guidance on air monitoring for LUST sites,  or other
      scientifically-valid methods,  such as a soil respiration  test.  Background
      carbon dioxide levels, oxygen levels, or both are necessary to evaluate the
      biodegradation rate.  High carbon dioxide levels do not always mean a high
      biodegradation rate.

      Site-Specific DataNecessary to Consider Terminating Operation of a Soil
      Venting System.  The DNR will evaluate soil venting system termination on
      the basis of confirmation borings.  Soil samples need to  be analyzed for
      the appropriate contaminants,  as follows: .

            •      For petroleum contaminated sites, soil samples for PVOCs and
                  GRO and/or DRO need to be collected as appropriate for the

            •      For non-petroleum contaminated sites and sites that have a
                  mixture of petroleum and non-petroleum contamination, the
                  system operator must use sampling protocols that  are
                  appropriate for the site. .The -system operator should consult
                  the DNR project manager to determine appropriate  laboratory

      Number of Soil Borings Per Site.  The number of soil borings  will-vary from
      site to  site.  Generally, two soil borings are the minimum number to
      determine a soil venting system operation termination. For larger, more
      complex sites, approximately one spil boring for every three.air-extraction

Guiifae* for Soil Vuntlat 8]rat
 for Soil V«otirn &y*ttm*
                                                                                Fag* 52
contact the  appropriate Emergency and Remedial Response Unit Leader in  the
district .where the site is located.

Gaidaiet for Soil tontlng Syttttu                                         •                 r  • ss

      6.0   References .

      Baehr,  A.L. ,  Hoag, G.E.,  and Marley,  M.C.   1989.   Removing Volatile
      Contaminants  from  the Unsaturated Zone by  Inducing Advective  Air-Phase
      Transport.  Journal of Contaminant- Hydrology,  4:1-26.
                                 **                        .   i
      Buscheck, T.E.  and Peargin T.R. ,  1991.   Summary of a Nation-Wide Vapor
      Extraction System  Performance Study.   Proceedings  of Petroleum Hydrocarbons
      and Organic Chemicals in  Ground Water:   Prevention, Detection, and
      Restoration.  November, 1991.  NWWA.   Pages 205 to 219,,

      Clarke, A.N. . Megehee, M.M. and Wilson,  D.J.,  1993.  Soil  Clean  Up by  In-
      Situ Aeration.  XII.   Effect  of Departures from Darcy'jj Law on Soil Vapor
           ti°n'  Sepaeation Science and Technology.  Volume 28.   Pages 1671 to
     DiGiulio D.C., Cho J.S., Dupont R.R. , and Kemblowski M.W.  1990
     Conducting field Tests for Evaluation of Soil Vacuum Extraction
     Application.  Proceedings of the Fourth National Outdoor Action Conference
     on_ Aquifer Restoration, Groundvater Monitoring, and Geophysical Methods.
     « W \nA *  ftfly ( 1 7 9 U ,                                      '
     EPA.  1991(a) .  Soil Vapor Extraction Technology, Reference Handbook
     February, 1991.  EPA/540/2-91/003.

           1991-  Guide for Conducting Treatability Studies Under CERCLA-
             °      aCti°n'  Interim Guidance.  September 1991.  EPA/540/2-'
     IeSfrv,C'W'  1988" APPlied Bydrogeology, Second Edition.   Merrill
     Publishing Company.  Columbus, Ohio.

     Freeze R.A.  and J.A. Cherry.  1979.   Groundvater.  Prentice Hall
     Englewood Cliffs,  NJ.                                            '

     Ginesi  D   and Grebe,  G. ,  1987.   Flowmeters a Performance Review.
     Chemical Engineering, June  22, 1887.  Pages 102 to 118.

     Hinchee,  R.E.  and  R.N.  Miller, Bioventing for In Situ Treatment of
     Hydrocarbon  Contamination.   Hazardous Materials Control, Vol.  3,  Number 5
     Sept/Oct 1990,  Pages 30 to  34.

     Johnson,  P.C.,  M.W.  Kemblowski, and  J.D.  Colthart.  1990,, Quantitative
     Analysis  for the Cleanup of Hydrocarbon Contaminated Soils by  In Situ
     Venting.  Groundvater,  Volume  28,  Number  3,  May- June 1990,  Pages  413 to
     *frfc«r »                   .           "                         • ,

     Johnson,  P.C.,  M.W.  Kemblowski, and  J.D.  Colthart.  1988.! Practical
     Screening. Models for Soil Venting  Application.  Proceedings of Petroleum
     Hydrocarbons, and Organic Chemicals in Ground Water:  Prevention, Detection
     and Restoration.  November,  1988.  NWWA.  Pages 521  to 346,,

    Johnson, R.L.,  Bagby, W. , Matthew, P..  and Chien, C.T.  1992.  Experimental
     Examination of  Integrated Soil Vapor Extraction Techniques.  Proceedings of
    Petroleum Hydrocarbons and Organic Chemicals in Ground Water: Prevention
    Detection, and Restoration.  November,  1992.  NGWA.  Pages  441 to 452.

    Knieper, L.H. Pollution Engineering.  August, 1988.  Page 56.

Guid*Bca tor Soil V«atin* Sy«t««m                                                          Fae* 5*

      Krishnayya, A.V.,  M.J.  O'Connor,. J.G.  Agar,  and R.D. King.   1988. Vapor
      Extraction Systems,  Factors Affecting  Their  Design and Performance.
      Proceedings of Petroleum Hydrocarbons  and Organic Chemicals in Ground
      Water: 'Prevention, Detection,  and Restoration.  November,  1988.  NWWA.
      Pages 547 to 569.  •
      Masch, F.D. and K.J. Denny.  1966.  Grain Size  Distribution and its  effect
      on the permeability  of unconsolidated  sand.   Water Resources Research.
      Volume 2, Number 4,  pages 665 to 677.

      Mendoza,  C.A. and  McAlary, T.A., 1990..  Modeling  of Ground-Water
      Contamination Caused by Organic  Solvent Vapors.  Groundwater, Volume 28,
      Number 2, March-April 1990.  Pages 199 to 206.

      Miller, R.N., 1990.   A Field Scale Investigation  of Enhanced Petroleum
      Hydrocarbon Biodegradation in the Vadose Zone Combining Soil Venting and an
      Oxygen Source with Moisture and  Nutrient Addition.  Ph.D.  thesis,  Civil  and
      Environmental Engineering Department,  Utah State  University, Logan Utah.

      Rainwater, K., Claborn, B.J.,  Parker,  H.W.,  Wilkerson, D.,  and Zaman, M.R.
      Large-Scale Laboratory Experiments for Forced Air Volatilization of
      Hydrocarbon Liquids  in Soil.  Proceedings of Petroleum Hydrocarbons  and
      Organic Chemicals  in Ground Water: Prevention,  Detection,  and Restoration.
      November, 1988. ' NWWA.   Pages 501 to 512.

      Robbins,  G.A., Bristol, R.D., and Roe, V.D.   1989.  A field Screening
      Method for Gasoline  Contamination Using a Polyethylene Bag Sampling  System.
      Ground Water Monitoring Review.   Fall, 1989. Pages 87 to  97.

      Robbins,  G.A., Deyo, E.G., Temple, M.R., Stuart,  J.D., and  Lacy,  M.J.,
      1990.  Soil-Gas Surveying for Subsurface Gasoline Contamination Using Total
      Organic Vapor Detection Instruments.  Ground Water Monitoring Review.
      Summer, 1990.  Pages 122 to 131.

      Shan, C., Falta, W.,. and Javendel, I., 1992. Analytical Solutions for
      Steady State Gas Flow to a Soil  Vapor Extraction Well.  Water Resources
      Research, Volume 28, Number 4, pages 1105 to 1120.

      Shepherd, R.G.  1989.  Correlations of Permeability and Grain Size.   Ground
      Water.  Volume 27, Number 5, Pages 633 to 638.

      •Solomon,  D.K. and Cerling, T.E., 1987.  The Annual Carbon Dioxide Cycle  in
      a Montane Soil:  Observations, Modeling, and Implications for Weathering.
      Water Resources Research, Volume 23, Number 12, pages 2257 to 2265.

      Wilson, D.J, Clarke, A.N, and Megehee, M.M., 1992.  Darcy's Law Limited in
      Soil Venting Test.  Environmental Protection, November, 1992, pages  26 to
      28 and 54.

      Wood, B.D., Keller,  C.K., and Johnstone, D.L.,  1993.  In Situ Measurement
      of Microbial Activity and Controls on Microbial C02 Production in the
      Unsaturated Zone.   Water Resources Research, Volume 29, Number 3, pages  647
      to 659.

      Wisconsin Administrative Code NR  141,  Groundwater Monitoring Well-

Guidanc* for Soil Vratin* Sjr«t«a»                                     r                      pM. 55

      Wisconsin Administrative Code NR 419, Control of Organic Compound

      Wisconsin Administrative Code NR 445, .Control of Hazardous Pollutants.

      Wisconsin DNR - Guidance on. Design, Installation and Operation of In  Situ
      Air Sparging Systems.

      Wisconsin DNR - Guidance on Design, Installation and Operation of
      Groundwater Extraction and Product-Recovery Systems.

      Wisconsin DNR - Guidance, for Treatment Systems for Groundwater and Other
      Aqueous  Waste Streams for a further discussion of permit requirements.


     Attachment 1
Guidance on Air Sampling


                                                                     State of Wisconsin
     DATE:       April 5, 1991                                     File Code:  444Q

     TO:         District AM staff
                 District and Central Office LUST staff
     FROM:       Dan Johnston  AM
                 George Mickelson \SW/3
     SUBJECT:    Guidance on air sampling and emission monitoring for LUST soil and
                 ground water remediation projects with  a  synopsis of air
     This memo is intended to (1)  assist district staff in understanding air

     SST JST±1S ^L!!!!^_!? 'Oil "d •»«- -t- remediation
'                           8amn                           stu
                                                         y88 *an  « ^ stu
     LUST remedial technologies  that produce air emissions. Existing and new
     projects are subject  to the regulations set forth in sec. KR 419.07  wis  Adm
     Code,  some of the regulations in NR 419.07 are summarized below?
        ho          frequen=y and method» of monitoring described here are intended
        be used for  new  soil venting systems and new ground water air stripping
            '  Se°~    419'07' WiE- Adm- C°de' 8et8 f°rth re^ir^ents f or ?£ *
       eth         ««» «» «»"*ions from negative presnur* venting systems.
    onlv   £h   frequency and methods of Campling discussed in this memo are a guide
    only,  the air management staff or the LUST hydrogeologiat has the authoritv to
    specify additional  samples based on site conditions.               authority to

    Means  and methods of monitoring other remedial systems a± H site (landf armed
    soil,  etc.) are not discussed here, means and methods for monitoring theS
    systems are approved by the air management staff on a site by site basis?
    Is^nof a~X^^              »"                       P      • t- -mo
    Since existing remedial systems that are in place and have  an established
    monitoring plan may not use the same analytical methods  or  frequency described
    here, it is up to the district staff to determine on a site specific basis if
    monitoring modifications for existing projects should be made.

    The frequency and type of monitoring described here  is expected to be
    sufficient for the vast majority of LUST sites.   Air monitoring for soil and
    ground water systems is conducted for two purposes,  (1,  compliance with air
    management rules, and (2) for measuring progress and performance of the
    remediation system.  For compliance with air regulations, the air management
    ?«f iTrn?:01?^ different "Coring P^n,  for performance monitoring, the
    district LUST staff may also specify a different monitoring plan. .

Except: for requirements set forth in the rule, sites that may not be
applicable to the monitoring methods and frequency described here include the
Nonfuel wastes, such as halogenated solvents.
have different emission limits that need to be
specific basis.
                                                           These materials
                                                           assessed on a site
            A large remediation system that is operating near the benzene
            emission limit may require more frequent stack sampling for
            compliance purposes.

            A soil venting system with 4 or more wells may not need the
            frequency of wellhead samples described here, less frequent
            wellhead sampling may be appropriate.

            Less frequent sampling may be appropriate for very small systems
            that are well below the emission limits.

A synopsis of pertinent air regulations is as follows:

            The maximum amount of benzene that can be emitted per year is 300
            pounds without a permit and without installing lowest achievable
            emission technology.  There is no hourly or daily limit [NR 445.04
            (3) (a) and NR 445.04 Table 3, Group A] .

            If a treatment system for benzene is used, the system requires no
            less than 95% destruction of benzene to comply with the "Lowest
            achievable emission rate limit" [NR 445.04 (3) (a)].

            The maximum amount of VOCs that can be emitted to the ambient air
            is 9 pounds per hour of total VOCs [NR 419.07 (4) (b)].

            The maximum amount of VOCs that can be emitted per hour without an
            air pollution control permit is 5.7 pounds total VOCs.

            If the remediation will be completed within 3 months (after
            startup) and if the total VOC emission is greater than 5.7 pounds
            per hour, a permit is not needed [NR 406.04 (1) (m) ] .  But the
            system shall not emit more than 9 pounds of total VOCs per hour.

          *  Frequency of -testing for organic compounds shall be once each day
            for the first 3 days of operation, weekly for the next three
            weeks, and monthly thereafter. The benzene emissions shall be
            tested once during the first 3 days of operation, once during the
            third week of operation, and once every six months thereafter. [NR
            419.07(6)].   "•

     ' .     The method of testing for total VOC or benzene emissions shall be
            approved by Air Management in advance of the tests.

      .     Pilot tests for soil venting systems are exempt from permit
            requirements [NR 406.04 (1) (m) 3], notification requirements, and
            hourly emission limits [NR 419.07 (3)  (a) 4], provided, that the
            pilot test is conducted for a maximum of 8 hours and the total  .

            flow rate is a maximum of 100 standard cubic feet per minute.
            Tests of longer duration or higher flow rates are not exempt.
       *                          *        "
            Form 4400-120 (Application to treat or dispose! of petroleum
            contaminated soil) is required for soil remediation systems, even
            if no air management permit is necessary.  This form is not
            required for ground water remediation systems, such as air
            strippers, but ground water remediation systems are required to
            file an application form with the Bureau of Air Management.

            The following sources are exempt from total VCiC limits, and
            reporting requirements (for VOCs); treatment of potable water
            supplies, crop irrigation systems, remedial actions under CERCLA,
            and permitted sewage treatment plants [NR 419.07 (3)].
            Applicability of the rules to these projects should be verified
            with the air management staff on a site by site basis.  These
            projects are still required to comply with the benzene limitations
            listed above and hazardous air rules in NR 445.

Some answers to frequently asked questions about the rules are as follows:

            For determining compliance with Chapters NR 406.04(1)(m) and NR
            419.07 of the air regulations, the sum of total emissions for all
            remedial activities at a site are calculated.  In a case where
            there is; a soil venting system, an air stripper, and/or
            landfarmed soils, the emissions from all remediation sources are
            summed for determining compliance with air regulations.  If some
            emission points are on site (a soil venting system) and some off
            site (soil disposal in landfills), the only sources to sum for a
            site are on site sources.

            Sources at a site that are not associated with soil and ground
            water remediation activities are not included in the sum of all
            sources mentioned above.

            Two parameters are needed for measuring compliance with air rules,
            benzene and total VOCs.  BETX analysis is not needed for air
            management analysis, however it may be required for a wastewater
            discharge permit.  The analytical requirementa for determining
            compliance with air management rules do not exempt sampling for
            compliance with other rules.

            When VOCs are the only air pollutants emitted from the source,
            then no air permit is required if total VOC emission is under 5.7
            pounds per hour and total benzene emission is less than 300 pounds
            per year.                       .

      . ,    If total VOC emission is above 5.7 pounds per hour during any
            single monitoring event, an air permit is required, unless the
            remediation is completed within 3 months of startup.

            If an air treatment system is in'use on a remediation system and
            if the treatment system is not needed for compliance with air
            regulations, the emission control system can be removed upon
            approval from the air management staff.

            If there is no air permit required, the air management staff still
            need to preapprove the remediation except for those sources listed
            in MR 419.07 (3) (a).  These sources include; treatment of potable
            water supplies, crop irrigation systems, remedial actions under
            CERCLA, and permitted sewage treatment plants.

            The district LUST staff may need to preapprove -the remediation.
            Air management must preapprove all soil and'water remediation
            projects. The consultant should verify the need for preapproval of
            a remediation workplan on a site by site basis with the district
            LUST staff.

            For purposes of calculating benzene emission, the year starts when
            the first air emitting device at the site starts operation.

The parameters, recommended sampling locations, and recommended methods
include the following:


            Ground water treatment units generally are sampled at the influent
            and effluent on a regular basis for BTKX to comply with the
            wastewater discharge permit.  Calculate the benzene emission by
            subtracting the effluent benzene from the influent benzene values,
            multiply by the ground water mass flow rate.

            For soil venting systems, samples are to be collected at the point
            of emission (stack).  If there is only'one air extraction well,
            the benzene sample, may be collected at the extraction well instead
            of the stack.  A single sample can be collected or up to three
            consecutive hourly samples can be collected and averaged.  Benz«n«
            is measured by either; a carbon adsorption tube or a tenex tub*
            that is analyzed by a laboratory, or a portable gas chromatograph
            (field GC), or another method approved by the air management
            staff.  Procedures are discussed below under total VOCs.

            Total VOCs.

            No specific methods of sampling total VOCs from ground water
            treatment units are specified for all projects.  It is possible
            that total VOC samples will not be required by the air management
            staff on smaller (less than 35 gallons per minute) air stripping
            units.  This is because the smaller units are unlikely to exceed
            the 9.0 pound hourly limit.

            -     Calculations for the maximum total VOCs at. 35 gallons per
                  minute are as follows:

                        35 gallons / minute * 8.34 pounds / gallon * 60
                        •minutes / hour .« .12510 pounds per hour of ground

                        9 pounds total VOCs / 12510 pounds water «- 0.000508 or
                        roughly 500 parts per million by weight(ppm).

       Since very few projects have a concentration of total
       petroleum hydrocarbons (TPH) as high as 500 ppm during an
       active ground water extraction project, samples for total
       VOCs generally are not required on smaller (less than 35
       gpm) air stripping units.

       Systems larger than 35 gpm may need :j rounds of both
       influent and effluent ground water TPH samples early in the
       project to ascertain that the 9 pound per hour limits are
       not exceeded.  If sample results indicate that the 9 pound
       per hour limit is being exceeded,  th« air management staff
       probably will have an increased future involvement in the
       project.   An alternative to sampling ground water is to
       sample the air stream according to the methods described for
       soil venting systems.   The disadvantage of sampling the air
       stream is the requirement for an accurate air flow
       measurement  to quantify a mass per time value.

 For  soil  venting 'systems, the total VOC  samples are to  be
 collected at  the emission point (stack)  for  compliance  purposes
 and  at each air extraction well for measuring system performance
 If there  is only one air extraction well, only I singX sample
 needs  to  be collected.  When  sampling  for air compliance purposes,
 a single  sample can be collected, or up to three consecutive
 hourly samples  can  be collected and averaged.  Methods to use to
 measure total VOCs  include; a laboratory analysis of a carbon^
 adsorption  tube, a  field 6 C, a  flame ionization detector  (FID),
 or a photoionization detector (PID), or another method approved by
the air management  staff.  Each of these methods has different
procedural  requirements, these are as follows:

      Laboratory analysis of a carbon adsorption tube or tenex
      tube.  NO procedures are specified, describe method of
      sampling and analysis in workplan.

      Field GC.   A description of the devic«, Jinalytical
      procedure, and a description of the standard should be

      flame out is experienced, a dilution device OK a serial
      dilution method of analysis described by Robbins (Ground
      Water Monitoring Review, Fall 1990, Page 110 to 117) should
      be used.  Assume a molecular weight of 95 grams/mole when
      converting' from parts per million to a mass per volume
      (pounds per cubic foot or grams per cubic meter).

-     PIDs.  Only PIDs with a lamp with a 11.7 eV ionization
      potential may be used.  10.2 eV and 10.6 eV lamps do not
      detect all the compounds that are in gasoline.  PIDs should
      be calibrated to a standard recommended by the instrument
     • manufacturer. PID readings are adversely affected by carbon
      dioxide'in the air sample and they do not provide a linear
      result with increasing concentrations of VOCs in air,
      therefore, a serial dilution method is required (referenced
      above under FIDs).  The dilution method must be with ZERO
      grade air, or air with no moisture. Otherwise changes in the
      relative humidity of the ambient air will make correlation
      with one -sampling day to another impossible.  The dilution
      must be done until the results from three dilutions plot
      linearly and the final concentration is less than 125ppm.
      Assume a molecular weight of 95 grams/mole when converting
      from parts per million to a mass per volume.

-     Other methods.  If another method is proposed by a
      consultant, the specific field and analytical procedures
      need approval from both the air management staff (for
      compliance purposes) and the district LUST staff (for
      performance purposes).

Carbon dioxide fsoil venting svstema onlv>.  Carbon dioxide is
only for measuring the rate of biodegradation, this parameter is
not measured for compliance with air management rules.  The sample
points are each air extraction well and a background well.
Ideally the background well is an upgradient water table well that
is located in an uncontaminated part of the aquifer and is not
used for 'air extraction.  The background well is strictly a
background location for measuring ambient levels of carbon dioxide
in the soils.  Carbon dioxide can be measured by any convenient
means available (including Drager Tubes or similar devices).  The
work plan should describe the sampling devices and the procedure
for sampling the background well.  Purging a minimum of 3 to 5
well volumes (of air) from the background well is appropriate
prior to sampling.

A quantification of bioremediation rate is not required.  If the
consultant desires to quantify the rate of biodegradation, a
sample procedure is as follow:

      Assume that all excess CO2 above background its generated by
      biodegradation.  In this case, elevated CO2 means the
      difference between the background CO2 level and the wellhead
      CO2 level..  This also assumes that no carbon remains in the
      soil as part of a biomass.

                  Assume that all gasoline is methylcyclohexane  (C7H14), this
                  compound has a molecular weight  (98.2) that is similar to
                  unweathered gasoline  (approximately 95).   (Note: If site
                  specific product chemistry information is available, use
                  site specific data.)

                  For purposes of the following example, assume that the
                  elevated level.of carbon dioxide level is one percent.  At
                  1% CO2, one cubic foot of air contains:

                        0.01 * (1 ft*3) * (28.3 l/ft*3) /  (22.4 I/mole) -
                        0.0126 moles  CO2.

                  Since there are 7 moles of carbon dioxide generated from
                  every mole of gasoline (assuming methylcyclohexane or
                  C7H14), for every cubic foot of air that has CO2 elevated by
                  1%, one cubic foot  represents:

                        (0.0126 moles CO2) / (7 moles of CO2 per mole of
                        gasoline) « 0.0018 moles of gasoline

                  The weight of 0.0018 moles of gasoline is:

                        (0.0018 moles) * (98.2 grams/mole) * (0.0022
                        pounds/gram)  «= 0.00039 pounds of gasoline.

                  Therefore, for every standard cubic foot of air that has CO2
                  elevated by 1%, 0.00039 pounds of gasoline is destroyed by
                  biodegradation.  5% CO2 elevation would represent

                        (5) * (0.00039 pounds of gasoline at 1%) « 0.00195
                        pounds of gasoline per cubic foot of air.

            Other measurements (soil  venting systems onlvl.  Other operational
            measurements that should  be determined at each sampling point
            during each sampling event include; the air flow rate in cubic
            feet per minute, the temperature, and the vacuum.  Air flow rate
           . can be measured with an averaging pitot tube, a pitot tube or an
           . anemometer.  Vacuum can be measured with a manometer or a
            magnehelic.  Temperature  is measured by any convenient means
            available.  Relative humidity can be measured as a option, but is
            not required.

Monitoring frequency is specified for soil, venting systems in the regulations
but frequency for other types of remediations is not specified in the
regulations.  Recommended sampling frequency for all systems is as follows:

           .Ground water treatment systems generally have a sampling frequency
            specified in the waste water discharge permit.  For this reason,
            sampling frequency for air management purposes generally will be
            as specified in the waste water discharge permit or monthly,
            whichever is more frequent.


            A typical soil venting system could have the following monitoring
            frequency, unless otherwise specified by the air management or
        f    IMST staff.

            -     For benzene, one test during startup (one test anytime
                  during the'first 3 days), one test during the third week,
                  and one test every 6 months thereafter.  If the consultant
                  prefers more frequent monitoring for benzene, this should
                  not be discouraged.

            -   '  For VOCs, test daily for the first 3 days, weekly for the
                  next 3 weeks, and monthly thereafter.  If analytical costs
                  are significant, wellhead (but not stack) samples can be
                  collected on a reduced frequency (such as quarterly) on
                  larger systems, if approved by the district LUST staff.
                  Only air management staff can approve reduced sampling
                  frequency on the stack.

            -     Carbon dioxide is tested quarterly after one quarter.

            -     Flow rate, vacuum, and temperature are measured every time
                  that other samples are taken.

Air management staff may allow air emissions testing to be discontinued (upon
written approval) if past sampling indicates that the remediation system(s)
are emitting contaminants at rates significantly below air management
regulations.  In this case, district Lust staff may reduce sampling frequency
to a quarterly basis for total VOCs and discontinue sampling for benzene.

If changes to a remediation system are to be made after the first month that
may raise emissions by more than 50%, the monitoring frequency for total VOCs
should be weekly for 3 weeks and monthly thereafter.  Changes that can be
expected to increase emissions from a soil venting, system include (but are not
limited to) the following; adding extraction wells, increasing air flow rate
by more than 50% by; adjusting a bleed or dilution valve, or by increasing
blower capacity. Changes that can be expected to increase emissions from air
strippers include (but are not limited to) increasing the water flow rate,
adding additional extraction wells, or reducing residence time in sparge

Reporting. The recommended reporting frequency is monthly for the first 3
months and quarterly thereafter.  During the first month of operation the
emission reports are to be submitted as soon as possible to the air management
staff.  All other reports are submitted to both the air management staff and
the district LUST staff.  Since the air management staff is only concerned
with air emissions and not other details associated with the. site remediation,
a separate report for air management may be appropriate that only describes
details pertinent to air emissions.  -If the same report is submitted to both
air management .and LUST staff, it is recommended that the consultants discuss
pertinent air issues in the beginning of the report.             .