Guidance for Design,
Installation and Operation of
In Situ Air Sparging Systems
Working together for
a cleaner tomorrow
Wisconsin Department of Natural Resources
Emergency and Remedial Response Program
September 1993
PUBL-SW186-93
Recycled/Recyclable
Printed on paper that contains
at least 50% recycled'fiber
-------
Prepared by:
Wisconsin Department of Natural Resources
Emergency and Remedial Response Section
P.O. Box 7921
Madison, WI 53707
PUBL-SW186-93
-------
Guidanc* for In Situ Air Sparging Systems Fo8e
Table of Contents
1.0 Introduction. - 1
1.1 Purpose 1
1.2 Applicability o'f In Situ Air Sparging. 1
1.3 Permitting and Other Regulatory Requirements........... 2
1.3.1 LUST, ERP, and Superfund Program Requirements,, 4
1.3.2 Bureau of Water Supply 5
1.3.3 Bureau of Air Management 5
1.3.4 Department of Industry, Labor and Human Relations 5
2.0 Technical Considerations and Site Characterization. 6
2.1 Theory ...*..... 6
2.2 Site Characterization. 10
2.2.1 Contaminant Characterization 10
2.2.2 Geological Characterization.. 11
2.2.3 Hydrogeological Characterization. .............. 13
3.0 Treatabilitv or Pilot Testing. 14
3.1 Laboratory Treatability Tests 14
3.2 Pilot Tests 14
3.3 Pilot Test Reporting 1 17
4.0 Design and Installation of an Air Sparging System. ! 19
4.1 Well Placement 19
4.2 Well Design 20
4.2.1 Drilling Methods and Soil Descriptions. 20
4.2.2 Filter Pack 20
4.2.3 Seals 20
4.2.4 Well Screen and Casing 22
4.2.5 Wellhead 23
4.2.6 Development 23
4.3 Manifold, Valves, and Instrumentation 24
4.4 Air Compressor Selection 25
4.5 Other Devices 28
4.6 Monitoring Plan 28
4.7 Air Sparging System Design Report 29
5.0 Operating an Air Sparging System. 32
5.1 Overview 32
5.2 Start-up Testing 32
5.3 As-built Submittal 33
5.4 Progress Reporting. . . 34
"5.5 Project Close Out 35
6.0 References. 36
Tables
Table 1-1 Guidance Documents Related to Air Sparging Systems .... 3
Figures '
Figure 2-1 Groundwater Flow Patterns Caused by Density Changes ... 8
Figure 2-2 Air Flow Patterns. 12
Figure 4-1 Typical Sparging Well Design 21
-------
Guidance for In Situ Air Sparging Systems . age i
Attachments
Attachment 1 Policy on Air Sparging Wells for Groundwater Remediation
Acknowledgments
In addition to many DNR employees, the following individuals also reviewed
and commented on this document:
Gale K. Billings, C.P.G. - Billings and Associates, Inc.
Chi-Yuan Fan, P.E. - USEPA Risk Reduction Engineering Laboratory.
Michael C. -Marley- Vapex ^Environmental-.Technologies, .Inc;
This document may not represent the views of all reviewers. The Department
of Natural Resources extends thanks to reviewers for the donation of their
time and invaluable input.
-------
Guidanc* for In Situ Air Sparging Systems ase
Acronyms
CFM Cubic feet per minute
CPVC Chlorinated polyvinyl chloride. Material commonly used for pipe.
DNR Wisconsin Department of Natural Resources.
ERP Environmental Repair Program of the DNR.
ERR Emergency and Remedial Response Section of the DNR Bureau of Solid
and Hazardous Waste Management which includes ERP, Superfund, LUST,
Spills-and-Abandoned Containers.
LUST Leaking Underground Storage Tank Program of the DNR.
mm Millimeters.
MTBE Methyl tertiary butyl ether.
NR Wisconsin Administrative Code that is enacted by the DNR.
ppb Parts per billion
ppm Parts per million
psig Pounds per square inch gage pressure.
PVC Polyvinyl chloride. Material commonly used for pipe, well casing,
and well screens.
QA Quality assurance
S t >
QC Quality control
scfm Standard cubic feet per minute.
TPH Total petroleum hydrocarbons. As used in this guidance, TPH means
analytical tests such as GRO, DRO, and TRPH.
VOC Volatile organic compound.
-------
-------
Guidance for In Situ Air Sparging Systams I "se
1.0 Introduction.
This guidance document is intended to aid environmental professionals in
designing in situ air sparging systems to remediate contaminated
groundwater. It also provides information to Department of Natural
Resources (DNR) staff for efficient and consistent oversight and review.
This document should be used 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 is a guide to using in situ air sparging as a remediation technology.
In situ air sparging is a process in which a gaseous medium (commonly air)
is injected into groundwater through a system of wells. As the injected
air rises to the water table, it can strip volatile organifc compounds
(VOCs) from groundwater and the capillary fringe. The process also
oxygenates groundwater, enhancing the potential for biodegradation at sites
with contaminants that degrade aerobically.
The DNR developed this guidance for environmental professionals who
investigate contaminated sites and design remedial systems. Designing an
in situ air sparging system is a multi-disciplinary process; the designer
should have a working knowledge of geology, hydrogeology and basic
engineering to design an effective system.
The majority of this guidance is intended for smaller VOC contaminated
sites; however, some of the guidance is appropriate for larger sites.
Designers may need to deviate from the guidance in some circumstances
because each site has unique contaminants, access constraints, size,
hydrogeology, arid other characteristics.
If site-specific criteria pr conditions require a cost-effective system
design,that differs from this guidance, it is the responsibility of the
remediation system designer to propose an effective system to the DNR.
1.2 Applicability of In Situ Air Sparging. !
I
In situ air sparging is generally limited to the remediation of
contaminated groundwater in shallow portions of unconf ined aqiuif ers.
Marley (1991 and 1992), Ardito (1990) and Brown (1992) discuss site-
specific applications of this technology.
Generally, air sparging works best in shallow water table aquifers;
however, air sparging may also be an appropriate choice fpr deep aquifer
contamination in rare cases.
Air sparging is not appropriate for sites with groundwater contaminants
that cannot be remediated by air stripping or degraded aerobically. For
example, air sparging may not be appropriate for some LUST sites with very
high concentrations of methyl tertiary butyl ether (MTBE).
In some situations, other remediation technologies may be !more effective
than in situ air sparging. Johnson, et al. (1992) demonstrated in a large-
scale laboratory demonstration project that using groundwater extraction to
lower the water table for soil venting is more effective than in situ air
sparging. There are sites where the cost of pumping to lower the water
-------
Guldaneo tor In Situ Air Sparging Systems Page 2
table is impractical; in these situations, in situ air sparging may be an
appropriate choice.
In most cases, air sparging is used in conjunction with a soil venting
system (See Guidance on Design, Installation and Operation of Soil Venting
Systems'). If soil vapor extraction is not used, the system must meet, the
criteria discussed in Subsection 1.3.1 of this guidance. An air sparging
system may also be used in conjunction with a conventional groundwater pump
and treat system (See Guidance on Design, Installation and Operation of
Groundwater Extraction and Product Recovery Systems') . In situ air sparging
has been used to remediate groundwater at some Leaking Underground Storage
Tank (LUST) sites without using groundwater extraction.
Air sparging should only be used at sites with appropriate geologic
conditions. Any layers of fine-grained materials or any other geologic
heterogeneities that may limit vertical migration of air to the water table
surface will limit the ability of air sparging to work efficiently.
The following are examples of situations where this guidance may not be
completely appropriate:
A site with 10 air sparging wells is likely to need continuous
split spoon sampling in the majority of the wells for
verification that the geologic characterization is accurate;
but a site with more than 100 wells clearly does not need to
have the majority of the wells sampled.-
A very small site with a highly permeable (>1 E-2 cm/sec),
relatively isotropic aquifer that will vise air emission
controls on the soil venting system may not need the level of
detail proposed for pilot testing. At such a site, air flow is
restricted primarily by the pressure necessary to depress the
water column within the sparging wells. In this case, pressure
requirements of the system may be estimated based on static
water levels. An additional estimate of the pressure
requirements to counteract pipe friction, change in head due to
upwelling, and the pressure necessary for air entry into the
aquifer is also needed. Since an air emission control system
is proposed, pilot testing is not necessary to quantify an
emission estimate.
Wells smaller than those recommended by the guidance may be
used at a site with a very large system that has sufficient
groundwater monitoring wells. At these sites, the cost of more
than 50 wells all 2 inches in diameter with threaded access
caps on the wellheads may be excessive.
Although this guidance specifically refers to injecting air into
groundwater, there may be times when injecting ozone, oxygen, ammonia,,
nitrogen, or possibly other gaseous substances are appropriate. The use of
substances other than air, oxygen or ozone requires approvals from the DNR
Water Supply program and should be justified in a workplan.
1.3 Permitting and Other Regulatory Requirements.
Refer to Table 1-1 for more information on permitting and related guidance
documents.
-------
Guidance for In Situ Air Sparging Systems
Page 3
Guidance Document
Topic Pertinent
Coupling System
with a Soil
Venting System
Air Emissions
Drilling, Well
Construction,
and Abandonment
Well Labeling
and Color
Coding
Injection Wells
Investigative
Wastes
Electrical
Safety
None
NR 406,
419 and
445
NR 141
ILHR 10
NR 112
Various
DNR Rules
Various
DILHR
Rules
Table 1-1
:s Related to In Sit
Guidance
Documents^
None
None
None
None
August 14, 1991
Memo2
January 14, 1993
Memo 3
DILHR UST/AST
Program Letter
10; May 25, 1993<,
u Air Sparging
Agency Reference
Contact Section
DNR
District
,.ERR...Staff
DNR Air
Management
Staff
DNR i
District
ERR Staff
DILHR
Injection
Well
Coordinator
in Water
Supply
DNR
District
ERR Section
DILHR Staff
and/or
Local
Building
Inspectors
Subsection
1.3.1
Subsection
1.3.3
Subsections
1.3.1 and
4.2
Subsection
1.3.4
Subsection
1.3.2 and
4.5
X.^.JL
Subsections
1.3.4 and
4.4
Notes :
(1) Guidance Documents refers to guidance documents other than this
document.
(2) Guidance attached as Attachment 1.
(3) Guidance titled General Interim Guidelines for the Management of
Investigative Waste.
(4) Guidance titled Design Criteria for Process Equipment Buildings
Associated with Environmental Remediation of UST/AST Sites,
included as Attachment Two to the Guidance on Design, Installation
and Operation of Groundwater Extraction and Product Recovery
Sys tems .
-------
Guidance for In Situ Air Sparging Systems Pa8e *
1.3.1 LUST, ERP, and Superfund Program Requirements.
Submittal Contents, Recommended LUST, ERP and Superfund program submittal
contents are listed in Subsections 3.3, 4.7, 5.3, and 5.4.
Soil Venting Systems and Vapor Phase Transport. A soil venting system used
in conjunction with an air sparging system is necessary to limit/prevent
vapor phase migration when ANY of the following conditions exist at a site:
The air sparging wells are in an area that has contaminated,
unsaturated soil. It is impossible to estimate the emissions
from an air sparging system that is not used in conjunction
-with a-.vapor-:extraction--system_in.-contaminated .soil. Soil
samples from soil borings should be collected to confirm that
the unsaturated soil is uncontaminated if a soil venting system
is not planned.
Any buildings or other structures within 100 feet of any air
sparging well that may accumulate vapors.
More than 50 percent of the ground surface is paved within 50
feet of any air sparging well. Pavement may cause lateral
vappr phase migration of VOCs.
Clay or silt layers are present in the unsaturated zone that
may cause lateral vapor phase migration of the VOCs.
There is a potential for any free floating product at the site.
Upwelling could spread the free product to "clean" areas.
There is evidence that air emissions could exceed air
standards.
On a site-specific basis due\to other factors, the DNR may ^
require a soil venting system to be used in conjunction with an
air sparging system.
When a soil venting system is installed, the soil venting system should
extract at least four times as much air as injected by the air sparging
system, unless other means are used to demonstrate that all injected air is
captured and there is no vapor phase migration. The soil venting system's
zone of influence should cover the entire area covered by the air sparging
wells to assure that all emissions are captured and quantified. If any
'structures are located near the sparging wells, gas probes should be used
to assess subsurface pressure and vapors (See Subsection 5.2).
If a soil venting system is not proposed, a minimum of two gas probes
should be used to evaluate the presence of subsurface vapors and pressure.
Water table observation wells that are located within the system's zone of
influence may be used as substitutes for gas probes.
Wis. Admin. Code NR 141. Well design details are site specific. Because
some wells at a site may be used for groundwater sampling, they must be
developed to NR 141 standards. Consultants should submit boring logs and
well-construction diagrams after well installation, in accordance with
NR 141. If the wells are used for collecting groundwater samples or
preparing a piezometric surface map, they must be surveyed to NR 141
requirements. Well abandonment procedures in NR 141 are applicable.
-------
Guidance for In Situ Air Sparging Systems PaSe 5
Investigative Wastes. Drill cuttings should be handled iri accordance with
DNR guidance on investigative wastes.
1.3.2 Bureau of Water Supply.
Injection Well Issues. Because air sparging uses injection wells, it is
regulated by the DNR Bureau of Water Supply under Section NR 112.05 of the
Wis. Admin. Code. The LUST program has the authority to approve air
sparging systems on behalf of the Bureau of Water Supply if air, oxygen or
ozone and no other substances that may adversely impact water quality
are injected into the groundwater (See Attachment 1). The Bureau of Water
Supply must approve projects if nitrogen or other gases are injected into
..: groundwater; -;or-if :-compressors_.that ..are.not-. oi.-l-~Less-.~are.used. -:A-.separate
approval from the Bureau of Water Supply may also be needed for ERP and
Superfund program sites.
1.3.3 Bureau of Air Management.
Wis. Admin. Codes 406. 445. and 419. The DNR Bureau of Air Management
regulates air emissions from remediation sites. All air sparging systems
need preapproval from the Bureau of Air Management prior to installation.
If a soil venting system is also used at a site, the emissjions from an air
sparging system are drawn into the soil venting system which allows the
operator to sample and quantify the emissions.
See Attachment 1 of the Guidance on Design, Installation and Operation of
Soil Venting Systems for air emission limits at LUST sites. Chapters
NR 419 and 445 contain a complete listing of compound-specific limits for
other sites. The lower of the total VOC limits in NR 419.07 and the limits
for individual compounds in NR 445 apply to non-LUST sites.
If a soil venting system is not proposed for a site, designers should
estimate the atr emission rate for contaminants that 'will be released into
the atmosphere through the ground surface.
1.3.4 Department of Industry, Labor and Human Relations.
ILHR 10. Designers must follow the Department of Industry, Labor and Human
Relations' (DILHR) rules related to flammable and combustible liquids,
electrical safety and building safety. See Attachment 2 to the Guidance
for Design, Installation and Operation of Groundwater Extraction and
Product Recovery Systems for a discussion of DILHR's rules.
'ILHR 10.41 covers color coding for flush mount well covers of groundwater
monitoring wells and vapor wells. For purposes of ILHR 10, an air sparging
well is considered a groundwater well.
-------
Guldanc* for In Situ Air Sparging Systems P°8e
2.Q Technical Considerations and Site Characterization.
2.1 Theory.
Injecting compressed air into an aquifer accomplishes two goals:
Air Stripping, As the air rises to the surface of the water
table, VOCs are stripped from the contaminated groundwater.
Oxygenation. The groundwater is oxygenated, which enhances
biodegradation of aerobically degradable organic compounds.
Pumping air into the, aquifer -causes the .-following to .occur:
Vapor Phase Migration. The injected air creates a slight
positive pressure in the unsaturated zone near the air sparging
wells. If no soil venting system is used, vapor phase
migration of VOCs may occur. If a soil venting system is used,
it should be designed to capture the vapors.
Changes in Aquifer Characteristics. The effective porosity to
water flow is reduced when there is a mixture of liquid and gas
phases in the aquifer, reducing the hydraulic conductivity.
Air sparging technology is fairly new and the dynamics are not yet well
understood. Other potential effects of air sparging that have not been
fully evaluated through research include the following:
Air Flow Dynamics. It is not yet clear if the air moves
through the aquifer as a large number of very small bubbles, or
if the air flows through preferred (finger-like) flow channels
in natural soils. For a given volume of air, channeling
reduces the air contact surface area to groundwater and aquifer
material, which reduces the mass transfer of VOCs and oxygen.
The distribution of the channels, and the subsequent mass
transfer limitations of VOCs and oxygen, dominate the
effectiveness of the process. Marley (1992) briefly discusses
this effect.
Ahlfeld (1993) indicates that the density and viscosity
differences between air and water and the capillary resistance
produced by the surface tension at the air/water interface
within the soil pores govern whether or not bubbles or channels
form. Various sizes of glass beads were used in laboratory
experiments to evaluate the air flow dynamics. In the lab, it
was visually determined that a grain size of 0.75 millimeters
(mm) or less resulted in channelized flow, however, grain sizes
greater than 4 mm resulted in bubble flow. In between 0.75 and
4 mm grain size, there was a transition between bubbles and
channeling. Ahlfeld (1993) further indicates that very small
heterogeneities can control the air flow dynamics in a medium
that otherwise appears to be homogenous.
If there are stratified soils present at a site, the air is
likely to flow through high-permeable strata in an
unpredictable manner. Ahlfeld (1993) suggests that strata of
differing permeabilities produces air flow patterns that are
strongly controlled by the contrast in permeability, the
-------
Guidance for In Situ Air Sparging Systems ' Pas° 7
geometry, and the size of the strata. Ahlfeld (1993) further
proposes that the injected air will not reach soil immediately
above a low permeability zone because the low permeability soil
will be a barrier to air flow. In this case, that soil is not
readily remediated by the system.
If there are stratified soils, it is also possible that high
levels of contaminants could be forced into clean areas outside
the soil venting system's zone of influence.
Convection Currents. Convection currents form and circulate
the groundwater near the wells (Wehrle, 1990)., The convection
currents are..formed because ,ther..bulk.density .of . the .air bubble
and water mixture near the well(s) is less dense than the
groundwater that is farther away from the well(s). This
creates groundwater upwelling near the air sparging well(s),
which continuously provides a mechanism for circulating water
from other areas to the area of the air sparging well(s). See
Figure 2-1.
It is likely that groundwater convection currents are strongest
when air flow is in the form of small bubbles. In this case,
the gas phase and liquid phase move through similar flow
pathways. If the air flows in channels, the air and liquid
phase are likely to take different flow pathways which reduces
or eliminates the formation of convection currents.
The convection currents are likely to be strongest when the
site's conditions are nearly isotropic. Stratification will
reduce the ability of the system to create convection currents.
Significant stratification may cause air pockets to develop in
the aquifer and may completely prevent the formation of
convection'currents.
The convection currents may also cause significant lateral
transport of the groundwater, possibly forcing contaminated
groundwater into previously uncontaminated locations. In some
situations such as submerged plumes or small, highly
concentrated plumes the migration of contaminants away from .
the sparging points into "clean" areas is a significant
concern. Groundwater extraction may be necessary in some
situations to provide hydraulic containment of the convection
currents.
Upwelling. Water table upwelling occurs due to the added
pressure and volume of air that is applied to the saturated
zone. Current literature indicates that upwelling is usually
less than a foot. The amount of upwelling is dependant on
injection pressure and soil properties.
Some practitioners propose that upwelling remains as long as
air is injected, however, other practitioners propose that
initial upwelling is transient and dissipates. Current
theories include the following proposals:
Air transport will probably be in the form of bubbles at
sites where upwelling remains during air injection. In
this case, the upwelling is due to the non-equilibrium
-------
Guidanca £ot In Situ Air Sparging Systems
Page 8
Figure 2-1
Ground water flow patterns caused by density changes
Air-sparging-well
Water table
Convection current
Note: not to scale, for conceptual discussion purposes only
-------
Guidance for In Situ Air Sparging Systems .. Pa8e 9
condition caused by lighter bulk density of the air-water
mixture near the air injection point.
Air transport will probably be in the form of channels if
upwelling is transient and dissipates within a day (or
less) after air injection is started. In this case,
upwelling is initially caused by the formation of air
channels as the air displaces the groundwater. With
time, the water level will drop to static levels as the
water table attempts to reach an equilibrium level.
Martinson and Linck (1993) present data from multiple
.jmonitoring .-wells ..at-..a specif ic_.site._.( See -Figure .8 .-.in-i-Martinson
and Linck's paper). At this example site, approximately 50
percent of the initial upwelling dissipated within one hour
after startup, approximately 75 percent of the initial
upwelling dissipated in two hours, and approximately 90 to 95
percent of the initial upwelling dissipated in a day. After a
number of days of system operation approximately 5 percent of
the initial upwelling remained. In this example, most of the
upwelling effects are probably caused by initial air
displacement effects as air channels form. Because some
upwelling is permanent (remains as long as the system is
operating), it is also likely that some of the upwelling is
caused by density effects. Because upwelling in this case is
neither completely permanent or transient, it is likely that
both air channeling and convection currents exist: at this
particular site.
Aquifer Clogging and Redox Conditions. Iron a.t high
concentrations may precipitate into the aquifer, reducing
porosity and permeability. Other metals may also precipitate
within the aquifer, due to the change in redox conditions.
There is no good guideline for a maximum iron concentration; it
is likely that dissolved iron concentrations higher than 10
mg/L could cause precipitation problems. However, this
guideline may change with more project experiences.
Increasing the dissolved oxygen level in the groundwater may
mobilize some metals, including cadmium. Using geochemical
models such as MINTEQA2, may help designers estimate the
potential for precipitating or dissolving metals.
Gas phase clogging may occur in some geologic 'situations
because air pockets can be trapped in the interstitial void
spaces within the aquifer. This is most likely to occur in
stratified soils where silt and clay layers trap the gas phase.
Sites that are contaminated with aerobically degradable
compounds generally have low-dissolved oxygen in the
groundwater because the oxygen has been used up by biological
activity. Therefore, oxygen in the trapped ailr pockets can
dissolve into the groundwater. Inert nitrogen is left (which
does not readily dissolve), reducing the effective porosity to
groundwater flow and lowering effective water permeability.
Biofouling may occur if a biomass forms in the void spaces
within the aquifer.
-------
Guidance lor In Situ Air Sparging Systems Page 10
If oxygen is used instead of (or as a supplement to) air
injection, significant redox changes will occur which increases
the risk of aquifer clogging relative to air injection.
. Temperature Requirements. Both volatilization and
biodegradation are enhanced with higher temperatures. It has
not been determined if adding heat to the injected air is cost-
effective. Some heat is added to the air because the air is
compressed (ideal gas laws).
Air that is below the natural groundwater temperature should
not be injected. Note: Although heat is added in the
;-_-compress ion -.process,.. .the..~.;temperature-may_
-------
Guidance for In Situ Air Sparging Systems P"8e 11
regulated compounds that may be present at the site to assess in situ
treatability.
Free Product. If there is any measurable floating product (measurable
thickness greater than a film) within the sparging zone, the free product
should be removed using groundwater extraction and product recovery prior
to operating an air sparging system. Otherwise, groundwater upwelling near
the sparging wells may cause free product to migrate to formerly
uncontaminated areas. The DNR will only allow sparging within a zone of
free product in rare situations, and only if there is a groundwater
extraction and product recovery system also in use.
If: an air .sparging.system-is ^proposed .at. a. site ^with.-a-r-smal-l:-volume of free
product (too small to recover by pumping), the system designer should
describe the measures that will be taken to prevent free product migration
away from the sparging system in the work plan. In this case, a soil
venting system is also necessary because of the high quantity of
contaminants. It is also likely that air emission control and permitting
will be needed on the soil venting system.
Oxygen Levels. When the contaminants at the site are aerobically
biodegradable, testing for dissolved oxygen should be conducted to
determine a baseline of dissolved oxygen levels prior the air sparging
system start-up. The DNR recommends that consultants conduct: at least two
rounds of dissolved oxygen sampling in all monitoring and possibly some
sparging wells at the site.
2.2.2 Geological Characterization.
Geologic Characterization. Air sparging depends on the ability of injected
air to strip VOCs from the groundwater and rise to the water table where it
exits the saturated zone. ANY LAYERS OF FINE-GRAINED MATERIALS OR ANY
OTHER GEOLOGIC HETEROGENEITIES THAT MAY LIMIT VERTICAL MIGRATION OF AIR TO
THE WATER TABLE SURFACE WILL ADVERSELY AFFECT THE ABILITY OF AIR SPARGING
TO WORK EFFICIENTLY (See Figure 2-2).
Note: In Figure 2-2, the air flow patterns in the saturated zone are
assumed to curve outward from the well in the isotropic example
because of groundwater convection patterns shown in Figure 2-1.
A deep boring(s) is needed prior to designing an air sparging system to
assess the geologic conditions in the depth interval between the water
table and the base of the sparging well screen. This boring could be
'drilled during the site investigation.
A hydrogeologist as defined in NR 500.03 (64) or NR 600.03 (98) should
classify the borings in detail. A soil description should include the
following:
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,
-------
Guidanc* ,£or In Situ Air Sparging Sy«t«m»
Page 12
Figure 2-2.
Air flow patterns
r Land surface
Air sparging and soil venting under isotropic conditions
Air sparging and soil venting under heterogeneous conditions
Note: not to scale, for conceptual discussion purposes only
-------
Guidance for In Situ Air Sparging Systems Pa8e 13
Geologic origin,
Description of moisture content (dry, moist, wet),
Any visual presence of secondary permeability,
Voids or layering,
Pertinent field observations such as odor,
A description of any evidence of product smearing. Since depth
of smearing is evidence of past aquifer. water level variations,
.note the-depths-carefully.
Sparging system designs for sites with any stratification should include a
detailed description of how the design is tailored to the site's geological
conditions.
Average Grain Size. The soil below the water table should be characterized
for grain size by sieve analysis for filter pack and screen slot size
design (See Subsections 4.2.2 and 4.2.4).
2.2.3 Hydrogeological Characterization.
Primary Permeability. High horizontal permeability is necessary to allow
air to be inj ected into the aquifer at an effective rate. The vertical
permeability must be high enough to allow the air to rise through the
aquifer and exit at the water table. Subsection 4.4 discusses air flow
rate per sparging point in more detail.
Secondary Permeability. If a significant portion of the air flows through
fractures or channels, then only some of the contaminated soil or water
will be in contact with the air stream. In this case, the effectiveness of
air sparging is reduced and it will take longer to clean up the
contamination. This is likely to occur in glacial till and fractured
consolidated deposits, and to a lesser degree in other soil types.
Depth to the Water Table and Time Varying Conditions. Designers should
estimate the depth to water table under all seasonal conditions. This
information is necessary to design wells and to select air compressors.
Subsections 4.2.2, 4.2.4, and 4.4 discuss the importance of depth to the
water table.
'Groundwater Migration. The natural rate of groundwater migration past the
air sparging wells is a very important parameter. Air sparging is a
groundwater remediation technology, thus the groundwater regime should be
accurately understood. Designers should conduct aquifer testing on a
number of monitoring wells at the site. The wells used for stir sparging
may only be used for bail down or slug tests if the filter pack is
sufficiently coarse. Because the recommended filter pack ;si2;e for air
sparging wells is equal to or finer than the native soils (See subsection
4.2.2), bail down/slug test results from sparging wells may exhibit
artificially low results. Bail down/slug tests and step drawdown tests are
discussed in Section 3.0 of Guidance on Design, Installation and Operation
of Groundwater Extraction and Product Recovery Systems.
-------
Guidance for In Situ Mr Sparging Systems "8e
3.Q Treatabilitv or Pilot Testing.
3.1 Laboratory Treatabllity Tests.
There are no applicable laboratory treatability tests for air sparging. If
biodegradation is a key part of the remediation process at a site,
degradability tests should be used to assess the need for supplementary
nutrients or estimating the rate of decay. Most LUST sites do not warrant
any laboratory biodegradation studies because most petroleum-based
hydrocarbons are easily degraded aerobically.
3.2 Pilot Tests.
A pilot test is conducted for two purposes: engineering design and
estimating emissions from a soil venting system (if used).
The equipment for an air sparging pilot test generally includes the
following:
Air Compressor. The air compressor can be any type of air
compressor listed in Subsection 4.4. The compressor should be
large enough to inject sufficient pressure and flow to at least
one well and possibly multiple wells simultaneously. An
appropriate range for minimum capacity is approximately 3 to 10
scfm and 6 to 20 psig per well. Designers should avoid using
high-pressure compressors that may pneumatically fracture the
aquifer.
Manual Pressure Relief Valve. A manual pressure relief valve
should be installed at the blower outlet to manually relieve
air pressure to control pressure and flow rate. Using a
throttle valve may be used instead of a manual pressure relief
valve on compressors that are equipped with a receiver and
automatic high-pressure shut-off switch.
. Pressure Gauge. The pressure gauge may be calibrated in inches
of water column or in psig. It should be installed on the pipe
between the air compressor and the air sparging well. Two
digits of accuracy is recommended.
Flow Meter. The flow meter measures the rate of air injection.
It may be a heated wire anemometer or a rotameter; other
devices are also acceptable. In general, pitot tubes do not
provide accurate quantification of the air flow rate below an
air velocity of 1,000 feet per minute. If designers use a
pitot tube, they should install it on a pipe with a small
enough diameter that provides sufficient air velocity for
accurate results.
Some flow meters may not provide accurate quantification of air
flow when the air is compressed and heated (by compression);
correction factors may be needed. Designers should consider
pressure and temperature when evaluating the ability of the air
flow meter to provide accurate results prior to use. Since the
air is compressed, the flow rate should be corrected to
standard temperature/pressure conditions (scfm, not cfm). Two
digits of accuracy is recommended.
-------
Guidance for In Situ Air Sparging Systems *8e
Thermometer. The thermometer verifies that the additional heat
from compressing the air does not damage the test equipment or
well. If the temperature rises above 140 degrees fahrenheit,
PVC may become too weak to hold the pressure. Temperature
measurements may also be necessary for a correction factor to
the flow meter measurements.
Air Sparging Well(s). See Subsection 4.2 for a discussion of
well design. The air sparging well(s) that are tested should
be in an area of high groundwater contamination to provide a
realistic estimate of emissions from the soil venting system.
If the well(s) tested are not in the highest areas of
. .-contamiTiation,_designers--should-estimateLand--use...aiCorrection
factor based on groundwater sample results when estimating
emissions that occur at start-up of the full-scale system.
Automatic Pressure Relief Valve (Optional). An automatic
pressure relief valve may be installed along with the manual
pressure relief valve to assure that improper use: of the manual
valve does not inadvertently over-pressurize the system. If
the system is over-pressurized, test equipment may become
damaged and/or the aquifer could become pneumatically
fractured. See Subsection 4.4 for a discussion of maximum
pressure.
Pilot tests.provide design data for full-scale implementation. The quality
of the data for that purpose varies from site to site. Design data
examples include the following:
Test results from a simple site with wells installed less than
15 feet below the water table in highly permeable isotropic
conditions are likely to^provide excellent design data that is
otherwise unobtainable.
Data that is obtained at a site with relatively Impermeable
soils (<1 E-4 cm/sec) is likely to have air flow channeling.
When high air pressures are necessary at sites: with low-
permeable soil, it is likely that each well at: a site will
behave differently. In these situations, a pilot test from a
single well or only a few wells at the site may not represent
the whole site. In these situations, after system start-up,,it
may be necessary to fine-tune the system to achieve a
sufficient flow rate in every well.
To conduct a pilot test, system operators should increase air pressure
slowly with the manual pressure relief valve. Pressure and flow readings
should be taken at four (or more) different times at each valve setting to
evaluate whether or not the pressure and flow rates have stabilized.
Operators should take measurements using at least three different valve
settings. In all cases, excessive pressures should not be used. See
Subsection 4.4 for example calculations for determining maximum pressure.
Stabilized pressure and flow data should be plotted on a graph that
indicates the flow and pressure requirements for the well.
Note: Designers should not use early data if it does not correlate
consistently with later data because early data may not have been from
stabilized readings.
-------
Goldono for In Situ Air Sparging Systems *se
If designers install or anticipate installing a soil venting system, they
should conduct both a pilot test for air sparging and soil venting to
estimate emissions upon start-up of a full-scale combined system.
Designers should conduct the soil venting pilot test for a minimum of one
hour (preferably more) prior to air sparging to establish a baseline of
vapor extraction capability and emissions without sparging. The system
should then be operated for a minimum of three hours (preferably much
longer) with the air sparging well or air sparging system activated.
Using the baseline level of air emissions (under air extraction only) and a
stabilized emission rate with air injection, designers should calculate
contaminant extraction levels that are attributable to sparging on a
contaminant-mass-per-air-.volume-basis .at--start-.up.
Example: To estimate the emissions upon startup, use pilot
test data.
Assumptions:
All injected air is withdrawn by the air extraction
system under stabilized conditions.
1 E-4 pounds of contaminants per cubic foot of air are
extracted under vapor extraction at 65 scfm without air
injection.
5 E-4 pounds of contaminants per cubic foot of air are
extracted at 65 scfm extraction rate and 5 scfm injection
rate.
The air sparging well is located in the most heavily
contaminated part of the plume (if it is not, apply a
correction factor based on groundwater sample results).
Vapor extraction (extraction only) baseline emissions.
i
1 E-4 lbs/ft3 * 65 scfm * 60 min/hr - 0.39 Ibs/hr extraction
rate.
Emissions from vapor extraction and sparging (extraction and
inj ection).
5 E-4 lbs/ft3 * 65 scfm * 60 min/hr -1.95 Ibs/hr extraction
rate.
1.95 Ibs/hr - 0.39 Ibs/hr - 1.56 Ibs/hr increase attributed to
air injection.
1.56 Ibs/hr Q^ jbs/hr increase per scfm of injected air
5 scfm
Note: Due to the unpredictable nature of air flow patterns and
site-specific heterogeneities, the pounds per hour increase per
scfm may be no more accurate than an order of magnitude.
However, because better data is not available, it should be
calculated and used for emission estimates.
If site conditions are conducive to estimating a zone of influence
(described further in Subsection 4.1), designers should evaluate the zone
of influence during the pilot test. It is unlikely that a single day test
will provide accurate determination of the zone of influence, but the
-------
Guidance for In Situ Air Sparging Sy«t«ns Pase
following qualitative data may be obtainable:
Measuring upwelling in wells at the site. If upwelling is
measured,'periodic measurements should be taken in multiple
monitoring wells to evaluate upwelling effects: over time.
Plotting a graph with upwelling effects over time may provide
information on whether or not convection currents are likely to
exist under active air sparging at the site.
Measuring subsurface gas phase contaminant concentration
changes in gas probes or water table wells.
If a soil vent ing : system is.not-used.during..the_test,. .changes in .subsurface
gas concentrations in temporary soil gas probes or water table observation
wells may provide excellent zone of influence data. Because the measurable
effects of a short-term test are dependant on the rapid transport of air
through the aquifer and unsaturated zone, short-term tests; may be
unreliable at relatively impermeable sites. However, short-term tests may
provide good quality data at high-permeable sites.
3.3 Pilot Test Reporting.
The reporting of a pilot test may be a separate report, combined with an
investigation report, or included with the design report. Designers should
include the following information in a pilot test report:
Discussion.
General discussion describing the test and a discussion of the
hydrogeological conditions at the site.
Design of the sparging wells. List the screen length and
diameter, slot size, depths and specification of the filter
pack and seals, bore hole diameter, and the drilling method.
A discussion of the air flow rates that were injected and
extracted during the test and how the contaminant
concentrations in the soil venting system (if installed)
changed with differing air injection rates. Also include the
ratio of extracted to injected air flow rates.
If a zone of influence is estimated, discuss how the estimate
was determined and provide a discussion of the field data that
was used to make the estimate.
Include conclusions reached for design (See Section 4), well
placement and spacing, number of wells, pressure and air flow
requirements for the air compressor, and any pther pertinent
details.
Any other observations.
Figures.
A graph indicating the pressure and air flow characteristics of
the air sparging well(s) that was tested.
If upwelling in monitoring wells is measured,! the designer
-------
Guld&ne* for In Situ Air Sparging Systems
Pa8e 18
should include a. graph indicating upwelling (y axis) versus
time (x axis). Data from multiple wells can be included in a
single graph.
Geologic cross section(s).
A map of the site drawn to scale, including:
locations of existing sparging wells,
locations of existing air extraction wells, if a soil
venting system is used,
suspected and/or known source location(s) (if differing
contaminant types are present at a site, identify the
contaminant type at each source location),
zone of soil contamination,
zone of groundwater contamination,
scale, north arrow, title block, site name, and key or
legend,
any other pertinent site information.
A water table map for the day of the pilot test.
An iso-concentration map with groundwater dissolved oxygen
levels (if the contaminants are aerobically degradable);
Tables.
Water levels/elevations and dates of measurements in monitoring
wells.
Field data, including times of readings, air flow rates,
injected air temperature, and injected air pressure.
App.endi.ees.
Complete discussion of field procedures for the test.
Boring log and construction diagram for sparging well(s).
Calculations determining the hydraulic conductivity and natural
groundwater migration rate.
Laboratory reports, if applicable.
In addition, designers should include the information listed in Section 3.0
of the Guidance on Design, Installation and Operation of Soil Venting
Systems if a soil venting system is installed or planned for the site.
Additional information may also be necessary on a site specific basis.
-------
Page 19
Guidance for In Situ Air Sparging Systems
4.0 nestpn and Installation of an Air Sparring System.
An in situ air sparging system consists of a number of components which are
described in this section, beginning with a discussion of well placement
and design The discussion of design parameters includes well design,
manifolds and blowers. Subsection 4.5 discusses other equipment that^may
or may not be used at sites, and the section concludes with a discussion of
the information that should be submitted to the DNR.
4.1 Well Placement.
The air sparging well's zone of influence may be estimated by measuring one
or-more-of the following:
the change in water table elevation (upwelling);
the use of gas tracers;
measuring the change in dissolved oxygen (saturated zone);
oxygen levels (unsaturated zone); and
measuring the change in contaminant concentrations (saturated
and/or unsaturated zone).
Note: The use of any tracers requires prior approval from the
Bureau of Water Supply.
It is permissible to select a well placement configuration without
scientifically determining a zone of influence at the site, provided that a
relatively close well spacing is used. The department ddes not recommend a
specific method to determine a zone of influence. Well spacing of 12 to 50
feet has generally been used, according to the literature. If well spacing
is closer than 15 feet or farther than 30 feet, designers should include a
justification in the work plan. Some designers use a grid pattern of
sparging wells in the source area and other designers use a line of wells
oriented perpendicular to the direction of groundwater flow., Some
designers have .used the same number of air sparging wells as air extraction
wells in the soil venting system (if installed) and other designers use a
significantly larger number of sparging wells than air extraction wells.
Under active air sparging, the lateral distribution of contaminants in the
-saturated zone may increase due to the convection currents discussed above
'in Subsection 2.1. Therefore, additional groundwater monitoring wells and
air sparging wells may be necessary near the perimeter of the contaminated
zone. If air sparging wells extend to the perimeter of the plume,
groundwater extraction may not be necessary at some sites. If air sparging
is only used in part of the plume, groundwater extraction will probably be
necessary to capture any lateral migration that results from convection
currents. .
The system designer should use their professional judgement to space wells
in a pattern that will effectively decontaminate the aquifer and capillary
fringe at the site.
-------
Guidance for In Situ Air Sparging Systems Pttse 20
4.2 Well Design.
Figure 4-1 portrays a typical air sparging well design.
4.2.1 Drilling Methods and Soil Descriptions.
A hollow stem auger is the preferred drilling method, and the auger should
be 4.25-inch inside diameter (or larger) for 2-inch diameter wells. The
wells should be 2-inch diameter or larger so that conventional well
development equipment can be used. Designers should justify using drilling
methods other than hollow stem auger on a site-by-site basis in the work
plan.
Continuous sampling by split spoon is recommended to characterize/verify
the geologic conditions because the geological conditions must allow the
air to rise to the water table. It is highly recommended that a
hydrogeologist collect samples from above the seasonal, high water table to
the base of the screened interval from a sufficient number of wells to
verify the geologic characterization. A hydrogeologist as defined in
NR 500.03 (64) or NR 600.03 (98) should describe the soil in detail. See
Subsection 2.2.2 for soil description information.
4.2.2 Filter Pack.
Designers should select the filter pack for the well based on the average
grain size of the geologic materials below the water table. Samples for
grain size analysis should be tested prior to designing an air sparging
system. A sieve analysis is usually sufficient for filter pack design (a
hydrometer test,is usually not needed).
The average grain size of the filter pack should be as close to the native
soils as practical. Coarser materials should not be used for the filter
pack, however, slightly finer-grained material may be used. If the filter
pack's average grain size is larger than the native geologic materials, the
filter pack may be more permeable than the native soil. While a highly
permeable filter pack is an advantage in constructing wells for other uses
(monitoring or extraction), a filter pack that has a significantly higher
permeability than the surrounding formation will be a conduit for upward
short circuiting of air in the depth interval between the bentonite seal
and the top of the well screen. This reduces the lateral movement of air
into the aquifer. If the filter pack is significantly smaller than the
native soils, too much restriction to air flow results. Natural filter
packs may be used in caving formations provided that the native materials
'do not have significant levels of fines that may accumulate within the well
screens.
The filter pack should extend from the base of the well screen to a minimum
of 1 to 2 feet above the screen.
4.2.3 Seals.
A bentonite seal that is 0.5 to 2 feet thick should be placed above the
filter' pack. The annular space seal (above the bentonite seal) should be
constructed with either bentonite cement grout or bentonite. A tremie
should be used to place grout when installing a seal below the water table.
The surface seal should be constructed in a manner that complies with
NR 141.
-------
Guidanco for In.Situ Air Sparging Syst«na
F«s« 22
Figure 4-1
Typical air sparging well design
Air and waterproof
well covers
Access
cap
Surface
seal
Ground ssurface
.Temporary port for flow
meter and thermometer
Check valve
Y
Pressure \
gauge Throttle
valve
8 to 10 inch diameter bore hole
Grout or bentonite
Well casing
Bentonite seal, 0.5 to 2 feet
Filterpack extends one or more feet
above screen
Well screen 2 to 5 feet long
-------
Guidance for In Situ Air Sparging Sy«t«ms Pase 22
Designers should use a. flush mount protective cover over the well, as
described in NR 141 if the manifold is buried. If so, other fittings
discussed in Subsections 4.2.5 and 4.3 can be installed under the manhole
cover(s). If there is not enough physical space for these fittings under
an NR 141-approved cover, a different air- and water-tight manhole can also
be used.
4.2.4 Well Screen and Casing.
Air sparging transfers air through the well screen to the filter pack and
then to the contaminated zone within the aquifer. Since the majority of
the air flows out of the well screen near the top of the screen,.designers
,- should-.set- the.-:top .oft the-.well.-screen. at .-the^base .of -the .-contaminated
groundwater plume under seasonal low conditions. At a minimum, the top of
the screen should be set 5 feet below the seasonal low static water table.
If different criteria are proposed for setting the screen depth, designers
should include a justification in the workplan.
The pressure that is needed to inject air into the aquifer is higher than
the pressure that-is required to depress the static water level to the top
of the screen. Since a number of wells are manifolded together on a common
header, all wells on a manifold are essentially operated at an equal
pressure. If the top of a well screen in one well within a system is
installed closer to the water table than the other wells, most and possibly
all of the air will pass through this shallower well. This happens because
less pressure is needed to inject air to the top of the screen in that
well. Designers may use throttle or solenoid valves to equalize air flow
to the wells, as an alternative.
At sites where groundwater will not be extracted, it is recommended that
designers estimate the exact depth at which each well will be installed by:
drawing an accurate water table map;
surveying the elevations of proposed air sparging well
locations; and
calculating the estimated depth of the water table for each
well to determine the screened interval.
If groundwater is extracted, a cone of depression significantly changes the
shape of the water table. Other devices such as solenoid valves (See
Subsection 4.3) may be needed to compensate for varying screen depths
"caused by the drawdown.
Sites with seasonal variations in groundwater flow direction may also
adversely impact the system design.
Example: A system that is designed for a site with natural
groundwater flow toward the southwest. This site has higher water
levels on the northeastern side of the site than the southwestern
portion of the site. Later, the gradient shifts to a natural
groundwater flow direction towards the southeast. The higher
groundwater elevation will then be located in the northwest portion
of the site.
In this situation, the increase in groundwater elevation on the
western side of the site increases the pressure requirements in air
-------
Guidance for In Situ Air Sparging Systems , Pa»e 23
sparging wells on the western part of the site relative to the
eastern part of the site. If all wells are on a single common
manifold, then the western wells will not inject as much air as the
eastern wells.
In this case, the western side of the site receives less air (or
possibly no air) from the air sparging wells, reducing overall system
effectiveness. The use of throttle valves or solenoid valves may
alleviate this situation (See Subsection 4.3).
The slot size should be appropriate to the filter pack size; filter pack
sizing is discussed in Subsection 4.2.2. Since air readily passes through
well.:screens, ..a. small ..slot. size. usually~is_ sufficient-.- and -underestimating
the slot size (by a small margin) relative to the filter pack is
usually acceptable.
A relatively short length of screen for a well, such as 2 to 5 feet is
sufficient; some designers have proposed a 1-foot screen length. The well
screen typically is a slotted pipe constructed of PVC or CPVC. Generally,
the screen is flush threaded with schedule 40 or 80 pipe. A bottom plug is
necessary. Designers should not use glued couplings and bottom plugs
because they may adversely affect any groundwater samples from the wells.
In most cases, designers should use 2-inch well materials., If designers
plan to use packers in the well at a later date to physically block off
portions of a screen, other screen diameters (such as 4-inch) may also be
used. In general, the screen diameter should not be smaller than 2 inches,
because it is difficult to develop smaller diameter wells. The well casing
and pipe schedule should be constructed of the same materials as the well
screen. Drillers should install "0" rings or other seals and wrench all
threaded casing joints tight to limit air leakage from the jcdnts.
During well installation, the depth from the top of casing or,standpipe
tp the top of the screened interval should be measured to 0.1 foot of
accuracy.
4.2.5 Wellhead.
Designers should connect the wellhead to the manifold with a tee, which
allows a threaded top cap to be attached. This configuration allows access
to the well for bailers or water level measuring probes.
During the system installation, if the length of the well casing (or
'standpipe) is changed while connecting the well to the manifold, the change
in elevation at the top of each well should be measured to 0.1 foot.
Designers should adjust the well construction records to reflect any
changes in the elevation at the top of the casing. The original casing
measurement for each well is discussed in-Subsection 4.2.4.
Wells should be surveyed to determine elevation if they are used for
collecting groundwater samples or preparing a pie'zometric surface map
(otherwise surveying for elevation is not necessary).
4.2.6 Development.
All wells should be developed to NR 141 standards to minimize fines that
may accumulate in the screen. Water produced by well development should be
handled in accordance with the DNR guidance on investigative wastes.
-------
Guidano* for In Situ Air Sparging Systems *«S« 24
4.3 Manifold, Valves, and Instrumentation.
The manifold is typically buried underground; however, if land use and
traffic patterns allow, the manifold may be installed above ground. If the
manifold is buried, it may be installed at or below the frost level, or it
may be installed just below the ground surface. If it is within the frost
zone, it may need to be protected from frost with insulation and/or heat
tape.
The manifold can be 2-inch diameter or larger and constructed of steel, PVC
or CPVC. Other diameters and materials' are also acceptable. Designers
should not use PVC if heat tape is used; instead, they should use CPVC or
other materials. -PVC-or'CPVC may-.not withstand. ,the.-pressure.=at. elevated
temperatures. See Subsection 4.4 for a discussion of the temperature
increase in compressed air.
Unglued slip-fit fittings should not be used because the pressure may cause
the fittings to loosen. See Subsection 5.2 for a discussion about
volatiles in glues that may be used on glued fittings.
)
If a buried manifold constructed of plastic pipe is used, designers should
install a steel wire or some other material that can be detected by a metal
detector above the manifold piping. This provides a means of determining
the exact location of the manifold with a metal detector. Note: This is
unnecessary at sites where reinforced concrete is used, since the metal
detector will only detect the rebar.
Marley (1992) recommends that designers install a check valve between each
well and the manifold. This prevents the temporary high pressure in the
screened interval of the aquifer from forcing air and water back into the
manifold system from the well after the system is shut off.
Designers should install an adjustable throttle valve for each well. This
allows the well to be isolated from the system, or to be adjusted for air
flow rate. If the manifold is below grade and flush mount well covers are
used, the valve between the manifold and the well can be located inside the
well covers.
It may be necessary to throttle air flow rates to different wells for
optimal operation. However, throttling air flow increases the requirements
for blower capacity and restricting flow increases electrical requirements.
Since throttling air flow to optimize system performance is inefficient
from an energy and equipment standpoint the system should be designed
precisely and only using throttling for system optimization. It is not
appropriate to use throttling to compensate for an inadequate system
design.
A port that can be used to temporarily attach a flow meter for each well is
recommended. See Subsection 3.2 for a discussion of flow meters and
Subsection 4.4 for a discussion of flow rates. If designers plan to adjust
air flow to each well with the throttle valve, a means to temporarily
attach a flow meter is absolutely necessary. Otherwise, it is impossible
to know how to set the valve. If a flow meter is temporarily attached, it
should not significantly change the air flow characteristics. For example:
rotameters have significant flow restriction and should not be used
temporarily on a permanent system; however, they may work well in pilot
testing because they are used during the entire test.
-------
Guidance for In Situ Air Sparging Systems ae"
Designers should install a port that allows temporary attachment of a
pressure gauge and thermometer to the well, well cap, or manifold near each
well to monitor the air injection pressure and air temperature at the well.
If a check valve is not installed on each well, designers should locate a
single check valve between the manifold and the flow instrumentation
described in the next paragraph.
A permanent pressure gauge, thermometer, and flow meter should be installed
between the manifold system and the manual pressure relief valve (described
in the next paragraph) to measure total system flow, temperature, and
pressure. Designers should follow manufacturers recommendations for length
of-unobstructed-flow both- upstream .-and .-downstream .of .the .flow, meter.
A manual pressure relief valve should be installed immediately after the
air compressor outlet. This valve exhausts excess air from the manifold to
either the atmosphere or the air compressor air inlet. A silencer may be
needed if the valve exhausts to the atmosphere, but an exhaust silencer is
unnecessary if the outlet is plumbed into the blower inlet.
An automatic pressure relief valve may be installed to prevent excessive
pressure from damaging the manifold or fracturing the. aquifer in the event
of a system blockage (See Subsection 4.4).
Solenoid valves may be used on the wells to individually activate and
deactivate different wells. When using solenoid valves, each well (or part
of the well system) receives all of the air produced by the air compressor
system for the period of time that the solenoid valve is open to that
well(s). Thus, when operating only a single well or only a few wells -
at a time, solenoid valves reduce the possibility that a s!ingle well in the
system will transmit an unusually large or small amount of air. If
solenoid valves are used, the AVERAGE air flow rate over time should be
within the 0.5 to 20 scfm range that is recommended in Subsection 4.4. See
Subsection 4.5 for a discussion of control panels.
I
If solenoid valves or timers are used, cycling the wells may cause surging
in the wells, similar to surging during well development. Surging may
cause silt to buildup in the wells, requiring periodic jetting of the wells
to remove the fines. Buildup of fines in the wells may be reduced by
placing a check valve on each well to reduce backflow.
Solenoid and check valves may significantly restrict air flow. The
pressure drop across solenoid and check valves (if used) should be
'evaluated as part of the design.
4.4 Air Compressor Selection.
There is no database or calculations to determine the air requirements for
air sparging to remediate a site. The average air flow rate should be in
the range of 0.5 to 20 scfm per well. If an average air flow rate proposal
is outside of this range, the proposed flow rate should be justified in the
work plan: Marley (1992) indicates that typical air flow rates are 3 to 10
scfm per sparge point.
Designers should avoid excessive pressures that could cause equipment'
failures and/or the creation of secondary permeability in the aquifer (See
Subsection 2.1). There may be situations where pneumatic fracturing is
desired, but HIGH PRESSURE TECHNIQUES THAT MAY FRACTURE THE AQUIFER SHOULD
-------
Page 26
Guidanc* for In Situ Air Sparging Systems
NOT BE USED WITHOUT JUSTIFICATION IN THE WORK PLAN AND PRIOR APPROVAL FROM
THE DEPARTMENT.
Example: To estimate the maximum pressure that can safely be
used without creating secondary permeability, assume that the
pressure must not exceed the weight of the soil column above
the screen.
Assumptions:
soil particle density of 2.7,
- water table depth at 18 feet,
.:-spargiTig.-system--screened^interval-from .30 to 35 feet, and
- , porosity of 30 percent or 0.3.
To estimate the overlying pressure exerted by the weight of the
soil- column:
.3
Weight of soil - 30 ft * 2.7 * (1-0.3) * 62.4 Ibs/ft
- 3,538 pounds per ft2
Weight of water - (30-18) ft * 0.3 * 62.4
- 224 pounds per ft2
Total - 3,538 + 224 - 3,762 Ibs/ft2
- 26 psig at 30 feet of depth (the top of screen).
In this case, injection pressures higher than 26 psi could
cause secondary permeability channels to develop. This example
is based on simplistic assumptions and designers should
evaluate additional geotechnical information if it is
available.
Using pilot test data, designers should calculate the pressure that is
necessary to achieve the desired flow rate under both seasonal high and low
water table conditions. Professional judgement is necessary to determine
the design pressure and flow rates per sparging point. If an air flow rate
of 0.5 scfm cannot be maintained at the maximum pressure, the soil
permeability may be too low and in situ air sparging may not be appropriate
.for the site.
The air compressor needs to produce sufficient pressure to depress the
water level in all wells below the top of the screen. The.pressure needed
to counteract the static water level in the wells can be significant during
seasons of high water levels. During seasons of low water levels - when
the top of the screen is closer to the water table - the pressure is much
lower and the air compressor can inject much more air to the system. The
air compressor should not be capable of injecting too much air flow
relative to the soil venting system flow rate (See Subsection 1.2.1).
Since ambient air is used in an air sparging system, non-explosion^proof
equipment may be used if the air compressor and associated wiring is in a
safe location. Explosion-proof equipment may be used as a safety
precaution. It is the responsibility of the system designer to verify the
safety of non-explosion proof equipment. Local electrical inspectors may
-------
Guidance for In Situ Air Sparging Systems P*8e
also require explosion-proof equipment on a site-specific basis.
System designers should only use air compressors that are rated for
continuous duty. Common air compressor types include:
Reciprocating Air Compressors. Reciprocating air compressors
should only be used when high pressure is required and a low-
flow rate is acceptable. Only oil-less air compressors are
acceptable because of the potential to inject oils into the
aquifer if a seal (piston ring) fails. Since these air
compressors may produce, sufficient pressure to burst PVC and
CPVC pipe and fittings, designers should install an automatic
pressure -relief valve on the -air,compressor-outlet.
Rotary Lobe Blowers. Rotary lobe blowers are positive pressure
blowers capable of pressurizing air up to 15 pounds per square
inch. Blowers may have an oil-filled gear case, but may not
use any other lubricants or fluids that could enter the air
stream and reach the groundwater.
. Regenerative Blowers. Regenerative blowers are relatively
simple and maintenance free compared to the other blowers.
Because of their low pressure capability, regesnerative blowers
can only be used at sites that can be operated at relatively
low pressures. In most cases, it is likely that a multi-stage
blower will be needed for higher pressure capability.
Designers may use other compressor types, such as a rotary screw
compressor. If designers use an alternative compressor that could inject
oil, a filter must be used to remove the oil. Designers need preapproval
from the DNR Bureau of Water Supply when using alternative compressors.
Designers should install an air filter that prevents particulate matter
from damaging the air compressor. A silencer on the air inlet may also be
desired.
The air inlet should be installed in a contaminant free environment. The
air inlet should be located outside of the building if the air compressor
is installed inside of a building that may have airborne contaminants
such as a service garage. If the air inlet is located near the stack of a
soil venting system, designers should use a minimum of 10 feet of vertical
separation. If ambient outside air is used, the system should only be
operated when the injected air temperature (measured at the wellhead) is
'equal to or greater than the natural groundwater temperature.
As part of the design, the system designer should calculate the air
compressor exhaust temperature based on manufacturer's data. CPVC, steel
or other materials should be used instead of PVC manifold materials if the
blower exhaust temperature is higher than 140 degrees fahrenheit. If ,the
blower exhaust temperature is higher than 200 degrees fahrenheit, either a
heat exchanger or pipe materials other than CPVC may be necessary. If
pressures higher than 15 psig are anticipated, evaluate manifold materials
for strength at anticipated operational temperatures and pressures.
If the compressor has a receiver (air tank), an automatic water trap is
also recommended to drain condensate from the receiver. Note: Condensate
from a "clean" air tank is not considered an investigative waste.
-------
Guidance £or In Situ Air Sparging Systems Pa«e 28
4.5 Other Devices.
The DNR Bureau of Water Supply needs to approve any other devices,
including heaters, that have any potential to introduce contaminants into
the injected air stream. Other devices that may be used include the
following:
Control Panels^ Solenoid valves, if used, are controlled by a panel with a
timing device (See Subsection 4.3) to sequence, each valve for a period of
minutes.
Thermal or Pressure Sensor. A sensor located at the blower exhaust may be
used -for automatic--shutdown .:if-the-pressure-. and/or-; temperature -exceeds
design criteria.
Timers. A timer may be needed to limit initial air emissions (See
Subsection 5.1).
Heaters,, Heaters may be used in some situations to warm the injected air.
Heaters that may inject air that is deficient in oxygen should not be used
at sites with aerobically degradable contaminants. In most cases, the heat
added during compression should add enough heat to maintain the temperature
above the natural groundwater temperature, however, systems that operate at
low pressure in winter may require additional heat. Also, additional heat
may be necessary in winter if long piping runs are exposed to subfreezing
temperatures.
Oxvgen Generators. Some sites may use oxygen injection instead of or in
addition to air injection. Oxygen generators must receive prior approval
from the Bureau of Water Supply. Levels of oxygen should not be excessive :
at sites where the change in groundwater redox conditions could be
detrimental, such as sites with high levels of dissolved iron.
Pure oxygen is a highly reactive substance. If pure oxygen or elevated
levels of oxygen (relative to atmospheric oxygen concentration) are used,
ALL MECHANICAL COMPONENTS THAT ARE IN DIRECT CONTACT WITH THE OXYGEN SHOULD
BE APPROVED BY THE MANUFACTURER FOR USE IN PRESSURIZED OXYGEN-RICH
ENVIRONMENTS. Components that are not designed for use in pure oxygen may
cause a fire and/or catastrophic failures of pressurized lines, pressure
vessels, valves, and fittings.
4.6 Monitoring Plan.
'System operators should monitor two or more groundwater monitoring wells
downgradient from the farthest downgradient air sparging well on a regular
basis for the parameters appropriate to the contamination at the site. If
the contaminants aerobically degrade, it is also appropriate to monitor
dissolved oxygen in those monitoring wells.
During startup, samples need to be collected from groundwater monitoring
wells to determine if there are any changes in the groundwater flow
patterns that are caused by convection currents. This includes monitoring
side and upgradient wells to determine if contamination is forced outside
the zone of influence. If after three months, contaminant migration
outside the zone of influence does not exist, sampling frequency in side
and upgradient wells may be reduced or eliminated at most sites.
The DNR project manager may require additional monitoring points,
-------
Guidance for In Situ Air Sparging Syst«ns - , Fage
frequency, and parameters.
If a soil venting system is also installed, refer to the Guidance on
Design, Installation and Operation of Soil Venting Systems for monitoring
requirements for the soil venting system.
4.7 Air Sparging System Design Report.
An air sparging system design may be included in a comprehensive report
with the results of an investigation, or it may be submitted separately.
The design report of a sparging system should include the following:
Discussi'on.
Briefly discuss the geologic and hydrogeologic conditions at
the site and an include an estimate of the natural migration
rate of the groundwater. If any stratification is present at
the site, include, a detailed discussion of how the air flow
patterns are affected,
Discuss the anticipated changes of the groundwater flow
patterns that may be caused by convection currents and ways the
system design will limit/prevent migration of contaminants
outside of the zone of influence.
Include a general description of the system: number of wells,
air flow rate and pressure requirements, etc.
Describe the reasoning used to establish well spacing and the
well pattern (grid or line).
Include results of any pilot tests that were conducted.
Discuss the air flow rates that were injected and extracted
during the pilot test and how the contaminant concentrations in
the unsaturated zone changed with differing air injection
rates.
Include a proposed monitoring plan for monitoring wells,
including sampling frequency and parameters. If the wells have
not yet been installed, discuss the proposed locations of the
wells.
Include a design of the sparging wells. Provide details on the
following:
screen length and diameter;
slot size;
depths and specification of the filter pack and seals;
depth of the screens relative to the water table;
bore hole diameter; and
the drilling method.
Include a manifold design with the following information:
- pipe type;
diameter;
location of valves;
a description of instrumentation for measuring air flow
-------
Guidance for In Situ Air Sparging Systems
Page 30
Figures.
Tables.
rate, vacuum and temperature; and
the depth of the manifold, if buried.
Include air compressor specifications with total anticipated
air flow rate and pressure levels. Also discuss the ratio of
extracted air to injected air if a soil venting system is
installed/proposed for the site.
Include details of any other remediation systems that are
planned for the site.
If free product exists at the site, designers should describe
what measuresthey will take-to avoid-pushing free product into
other areas by upwelling.
If a soil venting system is not proposed for the site, include
a justification and address all of the constraints outlined in
Subsection 1.3.1 of this guidance.
Include a map of proposed air sparging well locations drawn to
scale. The map should include the following:
locations of proposed and existing sparging wells;
the manifold location;
location of air compressor and other equipment;
location of the air inlet to the air compressor;
suspected and/or known source location(s) (if differing
contaminant types are present at a site, identify the
contaminant types for each source area);
zone of soil contamination;
zone of groundwater contamination;
scale, north arrow, title block, site name, and key or
legend; and
any other pertinent site information.
A current water table map.
Geologic cross section(s).
A map indicating the proposed monitoring locations for
determining sparging effectiveness. (This map can be combined
with the water table map into one figure.)
Process flow diagram indicating the piping layout,
instrumentation and other key components.
Table of water levels/elevations in monitoring wells.
Table of anticipated air sparging well screen depths and static
water levels.
Appendices,
Calculations for determining the well placement, if any.
-------
Guidance for In Situ Air Sparging Systems '. Fase 31
Designers should include engineering calculations used to
select the air compressor. Include the manufacturer and model
of the air compressor, the performance curve that: is provided
from the manufacturer, total anticipated air flow rate,
pressure levels, anticipated air compressor exhaust
temperature, and type and size of air compressor. If the air
compressor is belt driven, the rpm of the blower should be
listed if that data is used for calculating the flow rate. If
a pilot test was performed, include the graph indicating the
flow and pressure relationships observed during the pilot test.
Grain size analysis of the soils.
Calculations determining the hydraulic conductivity and natural
groundwater migration rate.
Detailed field procedures for monitoring dissolved oxygen (if
measured).
All information listed in Subsection 4.10 in the Guidance on Design,
Installation and Operation of Soil Venting Systems should also be included
if a soil venting system is installed or planned for the site. Additional
information may also be necessary on a site-specific basis.
-------
Page 32
Guidance for In Situ Air Sparging Systems
5.0 Operating an Air Sparging System.
5.1 Overview.
Operation of an air sparging system requires ongoing monitoring and system
adjustment to maximize performance. Efficient and successful operation of
the system requires a continuous effort to ensure the system operates
efficiently. It is the responsibility of the consultant to operate the
system in an effective manner.
If consultants find a more efficient/ effective method to operate the
system, they should evaluate any changes to the system on an economic
basis. If-a -system is-not-operated properly, -a-contaminated -groundwater
plume may migrate from the site.
If the emissions from the combined vapor extraction and sparging system are
initially expected to exceed allowable air standards, operators may need to
cycle the sparging system (but not the negative pressure vapor extraction
system) by operating it for a few minutes each hour on a timing device.
Refer to the discussion of cycling and potential silt buildup in the wells
in Subsection 4.3. Subsection 3.2 contains information on how to calculate
the expected emissions increase, which is attributable to air injection
upon start-up. After emissions drop, the sparging system may be operated
continuously.
An alternative to cycling the sparging system is to control air emissions
on the soil venting system with a treatment device.
During the first few months of operation, it is necessary to monitor the
upgradient, side-gradient, and downgradient monitoring wells to verify that
convection currents are not causing lateral migration of contaminants
outside the zone of influence.
Operators should use downgradient groundwater monitoring to verify the
system's effectiveness. If downgradient monitoring indicates that a system
is not working, the designer should assess the system and plan to correct
any problems. The department may require additional modifications.
5.2 Start-up Testing.
Prior to start-up, volatiles should be purged from the manifold system if
any chemical adhesives were used in constructing the system. To purge all
volatiles from the system prior to injecting air into the aquifer,
'operators should run the air compressor for a minimum of 10 minutes and
up to two hours with all well valves open and all well caps and covers
removed. All air exhaust from the manifold system will then exhaust from
the wellheads and will not be injected into the aquifer. After the initial
purge is complete, operators should replace the caps and well covers.
After an air sparging system is constructed, operators should conduct on-
site testing of the system using the following guidelines:
If solenoid valves are not used to equalize flow to each well,
operators should evaluate each well for flow and pressure
characteristics by using a flow meter at each well. Throttle
valves should then be used to equalize flow to each well.
Upon start-up, an air sparging system can produce significant
-------
Guidance for In Situ Air Sparging Systems ase
volatilization of VOCs. The department highly recommends using
field instruments at start-up to evaluate air emissions from
the soil venting system.
If there is any bubbling in piezometers at the- site, operators
should install air-tight caps on these wells. If these wells
are uncapped, they could be a conduit for air flow to short
circuit through the well instead of through the contaminated
aquifer.
Take total pressure and flow measurements after the system
stabilizes and measure the pressure or vacuum at gas probes and
. water, table wells -to-;evaluate_different rparts :.of .-.the .site -for
subsurface air pressure/vacuum.
SYSTEM OPERATORS SHOULD REEVALUATE CONTINUED OPERATION OF THE
SPARGING SYSTEM FOR SAFETY REASONS IF ANY POSITIVE SUBSURFACE
AIR PRESSURE READINGS AND/OR HIGH LEVELS OF VAPOR PHASE
CONTAMINANTS ARE MEASURED IN GAS PROBES ADJACENT TO BUILDINGS
OR OTHER STRUCTURES THAT MAY ACCUMULATE DANGEROUS VAPORS.
OPERATORS SHOULD DISCONTINUE OPERATION OF THE AIR SPARGING
SYSTEM IF CONDITIONS ARE UNSAFE. It may be necessary to turn
off selected sparging wells to reduce subsurface pressure in
some cases.
If some of the wells require more air pressure than the operating pressure
provided by the air compressor and therefore do not transmit any air
operators should evaluate replacing the wells or repairing the system.
5.3 As-built Submittal.
After completing the on-site tests described above, operators should
include the system as-built information in a report. Because most of the
information is included in the design report, a separate submittal.is
usually not necessary. In most cases, the as-built information can be
included in the first progress report after start-up (See Subsection 5.4).
The as-built submittal should 'include the following information:
Results of on site testing to verify that each well transmits
approximately the same amount of air.
Any deviations from the specifications in the design report.
A map of actual well locations drawn to scale, including:
locations of existing sparging wells;
the manifold, instrumentation, and sample port locations;
location of air compressor and other equipment;
suspected and/or known source location(s) (if differing
contaminant types are present at a site, identify the
contaminant type at each location); ,
zone of soil contamination;
zone of groundwater contamination;
scale, north arrow, title block, site name, and key or
legend; and
any other pertinent site information.
Table of air sparging well screen depths and static water
-------
Guidance for In Situ Air Sparging Systtms Page 34
levels prior to start-up.
Well construction diagrams.
Boring logs and any other information required by NR 141.
Any other pertinent information.
5.4 Progress Reporting.
Consultants should sequentially number progress reports, starting with the
first report after the remediation system start-up. In most cases, it is
sufficient to .include-only one or .two -pages .of text ...in -a._letter. format with
supplementary tables, graphs and a site map. The progress reports should
include the following information:
A brief discussion of the remediation system's progress that
includes the following information:
Contaminant extraction total to date in pounds or gallons
of contaminant removed;
System operational details, periods of shut down,
equipment malfunctions, etc.;
Overall evaluation of the effectiveness of the system;
Changes and those effects on the sparging system, if the
water table elevation has changed significantly from the
position that the system was originally designed; and
Recommendations and justifications for future activities,
if appropriate.
* A site map that indicates the location of wells, etc. The well
location map from the as-built submittal is sufficient.
A water table map from the most recent round of water levels.
This map can be combined with the above-mentioned site map.
* Tables that include data throughout the project are useful to
establish trends. Tables should include the following
information:
Field data and flow rate measurements;
Water levels/elevations.
Analytical data summarized from laboratory reports.
Laboratory reports.
A discussion of sampling procedures, analytical procedures,
etc. is not required, but a reference to the report that lists
the procedures should be included.
If a soil venting system is operational, the information
included in Subsection 5.3 in the Guidance on Design,
Installation and Operation of Soil Venting Systems.
Any other pertinent information or data.
Operators should submit progress reports each month for the first three
months of the system's operation and quarterly thereafter, unless otherwise
-------
Guidano* for In Situ Air Sparging Systems pase
instructed by the department. The DNR project manager has the authority to
add additional monitoring and submittal requirements to the above list
based upon specific site conditions.
5.5 Project Close Out.
Consultants should follow the procedures in Chapter 10 of the Guidance for
Conducting Environmental Response Actions when closing out a site. Note:
At the time this Guidance was prepared, Chapter 10 was not yet complete.
After gaining approval to close out a site, all wells should be abandoned
within 60 days (after they are no longer used), according to NR 141. If a
sparging :well is used, for .groundwater.-sampling as .part of >long-term
monitoring, that well is considered to be in use and does not require
abandonment until long-term monitoring is concluded.
-------
Page 36
Guidance for In Situ Mr Sparging Systems
6.0 References.
Ahlfeld, D.P. 1993. Abstract for a. paper titled "Fluid Flow Mechanisms
that Govern Air Sparging Effectiveness." Abstract printed in Ground Water
Volume 31, Number 5, pages 829 to 830. Paper to be delivered at the
Conference titled Chlorinated Volatile Organic Compounds in Ground Water,
October 17-20, 1993. National Ground Water Association (NWWA).
Ardito, C.P. and Billings, J.F., Alternative Remediation Strategies: The
Subsurface Volatilization and Ventilation System. Proceedings of the
Petroleum Hydrocarbons and Organic Chemicals in Groundwater: Prevention,
Detection, and Restoration, NWWA, pp 281 to 296.
Brown, R.A. and Jasiulewicz, F. 1992.. Air Sparging: A New Model for
Remediation. Pollution Engineering. July 1, 1992, pp 52 to 55.
Fetter, C.W. 1988. Applied Hydrogeology. Merrill Publishing Company,
Columbus, Ohio.
Freeze, R.A. and Cherry, J.A. 1979. Groundwater. Prentice Hall Inc.,
Englewood Cliffs, NJ.
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.
Marley, M.C. 1991. Air Sparging in Conjunction with Vapor Extraction for
Source Removal at VOC Spill Sites. Paper presented at the Fifth National
Outdoor Action Conference, NWWA, May 13-16, 1991.
Marley, M.C., Hazebrouck, D.J., and Walsh, M.T. 1992. The Application of
Air Sparging as an Innovative Soils and Groundwater Remediation Technology.
Groundwater Monitoring Review. Spring, 1992, pp 137 to 145.
Martinson, M. M. and Linck, J.A. 1993. Field Pilot-Testing for Air
Sparging of Hydrocarbon-Contaminated Ground Water. Proceedings of the
Sixteenth International Madison Waste Conference. University of Wisconsin-
Madison. In press at this time.
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.
Nyer, E.K. 1985. Groundwater Treatment Technology. Van Nostrand Reinhold
Company, New York, New York.
Wehrle K. In-Situ Cleaning of CHC Contaminated Sites: Model-Scale
Experiments using the Air Injection (In-Situ Stripping) Method in Granular
Soils. Contaminated Soil'90, pages 1061 to 1062.
Wisconsin Administrative Code NR 141, Groundwater Monitoring Well
Requirements.
Wisconsin Administrative Code NR 419, Control of Organic Compound
Emissions.
-------
Guidance for In Situ Air Sparging Systems | Pa8e
Wisconsin Administrative Code NR 445, Control of Hazardous Pollutants.
Wisconsin DNR - Guidance on Design, Installation and Operation of Soil
Venting Systems.
Wisconsin DNR - Guidance on Design, Installation and Operation of Ground
Water Extraction and Product Recovery Systems.
-------
-------
Attachment 1
Policy Memo on Air Sparging Wells for Groundwater Remediation
-------
-------
State of Wisconsin
^KRESPONDENCE/MEMORANDUM
DATE: August 14, 1991 FILE REF: 4440
' TO: District LUST Staff
FROM: Robert Krill,
Paul Didier, :
SUBJECT: Policy on Air Sparging Wells for Ground Water Remediation.
Air -sparging ..wells ..are..used .to. inj.ect..compressed..air JLn.toa...«hallow..part ..of .the
aquifer. The purpose of using compressed air injected into wells is to air strip
VOCs from the ground water and oxygenate the water which will promote
biodegradation of aerobically biodegradable compounds. A summary of pertinent
regulations is as follows:
Section NR 112.05 administrative code - -addresses injection wells.
.... underground placement of any substance as defined in s. 160.01
(8), Stats., is prohibited.
Section 160.01(8) Wi statutes - defines substances to include ....
any solid, liquid, ... or gaseous material ..... (that) may
decrease the quality of groundwater.
Since the air sparging wells are intended to improve ground water quality and
will only be used to inject air in ground water that has already been impacted
by contamination, they are considered beneficial.
"v '
To assure that the air sparging system does not introduce any "substances" into
the ground water, an oil-less air compressor, oil-less rotary lobe blower, or
oil-less regenerative blower"must be used." (Note: Rotary lobe blowers that use
lubricants in a gear case are acceptable.) If any other blowers are proposed
for use, consultation with the Bureau of Water Supply is always necessary.
If an air pump is used that meets the above criteria, and if the air pump inlet
is in an area free of atmospheric'contaminants, and if no other devices are
present that may contaminate the injected air stream, approval from Water Supply
is not necessary.
The Bureau of Water Supply reports injection wells to the EPA, for this reason
Rich Roth must be copied on approval letters (including old. projects that are
already approved) for air sparging projects, his address is?
Richard Roth
Bureau of Water Supply, WS/2
P.O. Box 7921
Madison, WI 53703
The Bureau of Water Supply will allow the LUST program to approve air sparging
projects on their behalf in accordance with the above requirements.
-------
------- |