Guidance for Design,
Installation and Operation of Groundwater
Extraction and Product Recovery Systems
Working together for
a cleaner tomorrow
Wisconsin Department of Natural Resources:
Emergency and Remedial Response Program
August 1993
PUBL-SW183-93
Recycled/Recyclable
Printed on paper that contains
at least 50% recycled fiber
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Prepared by:
Wisconsin Department of Natural Resources
. Emergency and Remedial Response Section
P.O. Box 7921
Madison, WI 53707
PUBL-SW183-93
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Errata sheet for the Guidance for Design, Installation aiid Operation of
Groundwater Extraction, and Product' Recovery Systems, through February 7, 1994.
Additional information, changes, clarification and errata include the
following: ' .
• • Transmisivity is misspelled, it should be transmiss.ivity.
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Guidane* fcjr Orow»*f«t»r Extraction *nd Product Rteoviry Syitrai
Table of Contents
1.0 Introduction. i 1
1.1 Purpose. :. 1
1.2 Scope of Groundwater Extraction and Product Recovery Systems. . . 2
1.3 Permitting and Other Requirements 2
1.3.1 LUST, ERP, and Superfund Program Requirements 2
1.3.2 Water Supply Program Requirements. ... 4
1.3.3 Wastewater Program Requirements. 5
1.3.4 Department of Industry, Labor and Human Relations (DILHR) "
Requirements 5
1.3.5 Department of Transportation Requirements 5
1.4 Interim Remedial Measures. . 5
i
2.0 Site Characterization. ........... 6
2.1 Aquifer Characterization. . . ". 6
2.2 Geologic Characterization ........ 7
2.3 Extent of Contamination. . 8
2.4 Contaminant Chemistry. 9
2.5 Floating Product or DNAPL . 9
2.6 Other Site-Specific Characteristics. ...... 10
3.0 Aquifer Testing. H
3.1 Hydraulic Conductivity Estimates Based on Grain-Size Analysis. . 12
3.2 Bail-Down and Slug Tests 13
3.3 Pumping Tests , 14
4-J& Design andInstallation of a Groundwater Extraction System. ... 16
4.1 Capture Zone 16
4.2 Well or Trench Design. . 19
4.2.1 Drilled Wells 19
4.2.1.1 Drilling Method 19
4.2.1.2 Filter Pack, Screen, Casing, and
Well Development. ......... 20
4.2.2 Trench Systems 22
4.3 Pump Selection 23
4.3.1 Groundwater Extraction Pumps 23
4.3.2 Floating-Product and DNAPL Pumping Systems 24
4.3.3 Total-Fluids Pumps. . 25
4.4 Other Devices . 25
4.5 Groundwater Extraction System Design Report 27
5.0 Operation of a Groundwater Extraction System. 30
5.1 On-site Tests After Installation of the Extraction System. ... 30
5.2 As-Builts Submi'ttal 31
5.3 Groundwater Maps 31
5.4 Reporting. ! 32
5.5 Project Close Out 33
6.0 References 34
Tables.
Table 1-1 Guidance Documents Related .to
Groundwater Extraction Systems 3
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Guidance for Groundwatar Extraction and Product R«covary Syatams
Figures.
Pose ii
Figure A3-1
Attachments.
Attachment .1
Attachment 2
Attachment 3
Attachment 4
Plume Capture.
48
Waste Classification of Petroleum Products.
Design Criteria for Process Equipment Buildings Associated
with Environmental Remediation of UST/AST Sites.
Two-Dimensional Plume-Capture Calculations With Uniform
Horizontal Flow Under Static Conditions.
Two-Dimensional Plume-Capture Calculations With a
Horizontal Water Table Under Static Conditions.
Acknowledgments.
In addition to the many DNR employees who reviewed and commented on drafts
of this document, the following individuals also assisted the DNR with
reviews and comments:
C. W. Fetter, Ph.D., C.P.G. - University of Wisconsin, Oshkosh.
David L. Kill, P.E. - Recovery Equipment Supply Inc.
Steven L. Martin, C.P.G. - formerly with RMT Inc.
James P. Prieur, P.G., Paul Brookner, and Greg Kimball - Delta :
Environmental Consultants Inc.
Although each of the individuals contributed positively, this document may
not represent the views of all reviewers.
Thanks are extended to reviewers for the donation of their time and
invaluable input.
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Guidanc* for Groundwatar Extraction.and Product Racovaxy Systems
i
Acronyms. • *_
BOD5 Five-day biochemical oxygen demand.
Btu British thermal units.
DNAPL Dense Non Aqueous Phase Liquid. DNAPL refers to a non-soluble
or semi-soluble liquid with a specific gravity greater than one.
DNR Wisconsin Department of Natural Resources.
DOT Wisconsin Department of Transportation.
ERP Environmental Repair Program of the DNR (state response
program).
ERR Emergency and Remedial Response Program of the DNR.
.FID Flame lonization Detector.
GC Gas Chromatograph.
GPM Gallons Per Minute.
ILHR Wisconsin Administrative Code that is enacted by the Department
of Industry, Labor, and Human Relations has an ILHR prefix.
ILHR 10 refers to the rules on storage of flammable and
combustible liquids.
LUST Leaking Underground Storage Tank Program of the DNR.
NR Wisconsin Administrative Code that is enacted by the DNR has an
NR prefix.
PID Photoionization Detector.
POTW Publicly owned treatment works.
PVC Polyvinyl chloride. Material commonly used for pipe, well
casing, and well screens.
QA/QC Quality Assurance/Quality Control.
RCRA Resource Conservation and Recovery Act.
'WPDES Wisconsin Pollution Discharge Elimination System permit.
Page iii
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Guidance for Groundwatar Extraction and Product Recovery SystaffiS Page 1
1.0 Introduction.
This guidance document is intended to aid environmental professionals in
designing groundwater extraction and product-recovery systems for
remediating contaminated groundwater. It also 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 is a guide to-using groundwater extraction and product recovery as a
remediation technology. Groundwater extraction systems are systems that
pump contaminated groundwater from an aquifer on a long-term basis.
Groundwater extraction requires treatment and proper disposal of the pumped
groundwater. Groundwater that is treated on-site can be discharged to
surface water or groundwater under a Wisconsin Pollution Discharge
Elimination System (WPDES) permit. Treated groundwater (on-site or off-
site) may also be discharged to a publicly owned treatment works (POTW)
provided that prior approval is obtained from the POTW (See Guidance for
Treatment Systems for Groundwater and Other Aqueous Waste Streams).
Most of this guidance is specific to remediation of unconfined aquifers,
however, much of the guidance is also appropriate for confined aquifers.
The depth of the screened interval and the aquifer-testing methods may
differ from the guidance for capturing a plume in a confined aquifer or an
aquifer with a submerged plume. If enough piezometers are installed in a
confined aquifer to prepare a potentiometric surface map, that map should
be prepared in situations where this guidance discusses water-table maps.
An aquifer is defined in this document as any soil or rock unit that
contains water under saturated conditions. The classic definition of an
aquifer refers to soil or rock units that will produce economically
significant volumes of groundwater, and differs from the definition used in
this guidance. The term aquifer, as used in this document, can refer to a
unit that is overlain and/or underlain by a geologic unit that has
relatively higher permeability, and/or does not produce economically
significant volumes of water.
Product recovery refers to physically removing free product from the
aquifer by pumping. . In almost all cases, product recovery refers to
extracting floating-product from the aquifer. Recovery of sinking product
(dense non aqueous-phase liquid or DNAPL) by pumping is also considered
product recovery. .
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. When 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 document.
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Guidanca for Groundwatar Extraction and Product Racovazy Syatams , Page 2
1.2 Scope of Groundwater Extraction and Product Recovery Systems.
Primary goals for groundwater extraction systems are:
• To Contain Contamination to a Specific Zone. Dissolved
contaminants are prevented from migrating beyond the capture
zone by-pumping an aquifer at a sufficient rate from (a)
specific, location(s). .
, To Extract Dissolved-Phase Contamination. Some of the
dissolved contamination is physically removed from the aquifer.
• To Create a Cone of Depression for Product Recovery. In some
cases, 'groundwater extraction is used to create a cone of
depression to draw non-aqueous phase liquids toward the
recovery well. .
• To Lower the Water Table for Soil'Venting. In some cases,
groundwater extraction may be used to lower the water table to
dewater the smeared zone, which enables soil venting to
remediate highly contaminated soil.
Soil venting and vacuum-enhanced product recovery are remediation
technologies that are commonly used in conjunction with groundwater
, extraction. Vacuum-enhanced product recovery uses product recovery with
groundwater extraction and soil venting technologies in the same well(s) rtor
increase the rate of product extraction and to reduce the drawdown. See,
Guidance for Design, Installation and Operation of Soil Venting Systems for >
more detailed information about soil venting systems. Applying a vacuum to
a groundwater extraction well(s) can also increase the rate of groundwater
extraction from the well(s) at sites that have a low-yielding well(s).
DNR may require aquifer-restoration techniques other than groundwater
extraction if operation of a groundwater extraction system lowers the water
table enough to damage a wetland or marsh.
1.3 Permitting and Other Requirements.
Refer to Table 1-1 for more information on DNR rules, guidance documents
• and agency contacts related to groundwater extraction system design.
1.3.1 LUST, ERP, and Superfund Program Requirements.
gubmittal Contents. Recommended Leaking Underground Storage Tank (LUST),
Environmental Repair Program (ERP) and Superfund program submittal contents
are listed in Subsections 4.5, 5.2 and 5.4. •
Wis. Admin. Code NR 141. This code requires preapproval for all
groundwater extraction/product recovery wells. Designers must submit an
application to the Superfund, ERP, or LUST programs to install a
groundwater extraction/product recovery well, which may be part of the work
plan for the site. The application must include the information in
Subsection 4.2. The same preapproval requirement applies to aquifer test
wells (Subsection 3.3). Forms 4400-122 (Soil Boring Log), 4400-113A
(Monitoring Well Construction), and 4400-113B (Monitoring Well Development)
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Guidance for Groundwatar Extraction and Product Recovery Syitl
;..,^:-: Table J.rl
Guidance Documents Related to Groundwater Extraction
and Product Recovery
Topic
High Capacity
Well Permits
Drilling, Well
Construction,
and Abandonment
Groundwater
Treatment and
Disposal
Investigative
Wastes
Free Product
Disposal
Free Product
Transportation
Off Site
Electrical and
Building
Safety
Pertinent
Rules
NR 112
NR 141
and
NR 112
Various
DNR Rules
Various
DNR Rules
Various
DNR Rules
Various
DOT Rules
Various
DILHR
Rules
Guidance
Documents!
None
None - •••#
Guidance for
Treatment
Systems2
January 14, 1993
Memo3
January 3, 1992
Memo*
None
DILHR UST/AST
Program Letter
10, May 25, 19935
Agency
Contact:
DNR Water
Supply
Staff
DNR
District
ERR Staff
District
ERR and/or
Wastewa.ter
Staff
DNR
District
ERR Staff .
DNR ERR or
Hazardous
Waste Staff
DOT Staff
DILHR Staff
and/or
Local
Building
Inspectors
Reference
Section
Subsection
1.3.2
Subsections
1.3.1, 3.3
and 4.2.1.2
Subsections
1.1, 1.3.3,
2.4, 3.0
and 5.4
Subsections
1.3.1 and
3.0
Subsection
2.5
Subsections
1.3.5 and
2.5
Subsections
1.3.4, 2.5,
4.3.1 and
4.4
Notes:
(1) Guidance Documents refers to guidance documents other than this
document.
(2) Guidance entitled Guidance for Treatment Systems for Groundwater
and Other Aqueous Waste Streams
(3) Guidance entitled General Interim Guidelines for the Management of
Investigative Waste.
(4) Guidance entitled Waste Classification of Petroleum Products,
included as Attachment One.
(5) Guidance entitled Design Criteria for Process Equipment Buildings
Associated with Environmental Remediation of UST/AST Sites,
included as Attachment 2. -
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Guldanc* for Groundwatar Extraction and Product Recovery Systems ~ Page
»
must be completed and submitted In accordance with Chapter1 NR 141 after
well construction is completed. Any well that is no longer in use must be
abandoned in accordance with Chapter NR 141, and documentation must be
submitted to the DNR on Form 3300-SB.
Investigative Wastes. Drill buttings should be handled in accordance with
DNR guidance on investigative wastes. This guidance is available upon
request.
Product Disposal... Product disposal is dependant on the final use and/or
, disposal option for the product. Petroleum-product disposal and/or . ;
recycling is discussed in Attachment 1. DNR will assess regulatory
requirements for recovered non-petroleum products on a case-by-case basis..
Federal Free-Product Requirements. 40 CFR 280.64 requires responsible -
parties at LUST sites to conduct free-product removal in a manner that
minimizes the spread of contamination into previously uncontaminated zones
by using recovery and disposal techniques appropriate to the hydrogeologic
conditions at the site. In addition, the responsible parties must properly
treat, discharge or dispose of recovery by-products in compliance with
applicable local, state, and federal regulations. This involves preparing
and submitting a free-product removal report within 45 days after
confirming a discharge to the DNR. The report should include the following
information:
• The name of the person(s) responsible for implementing the
free-product removal measures;
The estimated quantity, type, and thickness of free product
observed or measured in wells, bore holes and excavations;
• The type of free-product recovery system used;
• The location of any possible discharge from a free-product
recovery system Con-site or off-site) during the recovery
operation;
The type of treatment applied, and the effluent quality
expected from any discharge;
• The steps that have been taken to obtain necessary permits for
any discharge; and
• The chosen disposal/recycling option for the recovered free
product.
1.3.2 Water Supply"Program Requirements.
NR 112 and High Capacity Well Systems. Chapter NR 112 requires the Bureau
of Water Supply's preapproval for high-capacity well systems. A high-
capacity well system is an extraction system that produces over 70 gallons
per minute (gpm) of groundwater. A system of wells at one site that
produces a total of 70 gpm or more is considered 'a high-capacity system,
even if each well pumps less than 70 gpm. A separate application submitted
to the Bureau of Water Supply is required for high-capacity well systems.
See Chapter NR 112 for a list of required information in an application for
a high-capacity well system.
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Guidance for GroundwatM Extraction and Product Recovery Sy»t«ns - ' page 5
1.3.3 Wastewater Program Requirements.
Groundwater treatment and water disposal are addressed in the Guidance for
Treatment Systems for Groundwater and Other Aqueous W&ste. Streams.
1.3.4 Department of .Industry, Labor and Human Relations (DILHR)
Requirements..
ILHR 10. Designers -must follow DILHR codes pertaining to storage tanks for
recovered product, electrical safety and building safety. See Attachment 2
. .for more information on DILHR's requirements.
1.3.5 Department of Transportation Requirements.
Shipping Free Product. The Department of Transportation (DOT) requirements
for off-site transport of recovered product are based, in part, on results
of flash-point tests.
1.4 Interim Remedial Measures.
Interim remedial measures may be appropriate at certain sites. When
appropriate, the DNR encourages responsible parties to implement interim
remedies as soon as adequate information is available to design, construct
and operate a remediation system. This is especially necessary for free-
product removal and source containment/control. The following are examples
of situations where interim measures may be warranted.
A groundwater extraction system is installed in the source area
as an interim measure prior to fully completing the groundwater
investigation. This type of measure is most common when
attempting to hydraulically contain and capture a dissolved-
phase plume with high contaminant levels that: is moving quickly
away from the source area.
Floating product is hydraulically contained and captured.
• Hydraulic containment is needed to prevent dissolved-phase
plume migration towards a receptor, such as & municipal well,
or a sensitive natural resource, such as a! trout stream.
Interim measures require the same preapprovals and permits as final
remedies (See Subsection 1.3).
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Guidanc« for Groundwatar Extraction and Product Racovary Syatams page
2.0 Site Characterization.
The following subsections outline site characterization information that is
necessary to prepare a remedial design for the system. In many cases,
remedial system design (Section 4) can be started before the site
characterization is complete. It may be possible to evaluate treatment
devices, well design, disposal options, etc. prior to fully completing the
site investigation. -Because additional plume migration may occur, the
validity of the site investigation report decreases with time after its
completion. ' '
2.1 Aquifer .Characterization.
Important site aquifer characteristics include the following:
Hydraulic Conductivitv. The horizontal hydraulic conductivity
is used to estimate the natural migration rate and the
groundwater extraction well(s) pumping rate. See Section 3 for
a discussion of aquifer testing and Subsection 4.1 for a
discussion of plume-capture calculations.
Aquifer Thickness and Depth. The aquifer thickness is needed.
to determine transmisivity from the hydraulic conductivity
estimate for plume capture (Subsection 4.1). The plume depth
within the aquifer is also needed to establish the screened
interval when designing a groundwater extraction well or trench
system (Subsection 4.2). A boring should be drilled to verify
the hydrogeologic conditions in the screened interval prior to
installing an extraction well.
At small sites with very thick aquifers (over 50 feet of
saturated thickness), a boring does not need to extend to the
base of the aquifer IF a piezometer indicates that the plume
does not extend to the base of the aquifer. Subsection 4.1
discusses estimating an effective aquifer thickness for plume
capture in thick aquifers.
If a deep boring is drilled through a highly-contaminated zone,
drilling techniques may have to be modified to limit the
potential contaminant movement into previously clean zones.
Temporary well casings or other preventative measures may be
necessary in some situations.
Transmisivity. The following information is used to determine
plume-capture: the saturated-aquifer thickness (or effective
thickness, if appropriate) multiplied by the horizontal
hydraulic conductivity equals transmisivity. See Subsection
• 4.1 for more information.
Natural Horizontal Groundwater Flow Direction and Gradient.
The direction of groundwater flow and hydraulic gradient are
necessary for plume-capture calculations (See Subsection 4.1).
If there is a potential for time-varying natural groundwater
flow directions, the plume-capture calculations can provide
misleading results. It is advisable to prepare a minimum of
three water-table maps of the site with a minimum of one month
(preferably two months) between.each set of readings to verify
the natural direction of groundwater flow. If there is a
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Guid«nc« for 6roundw«t«r Extraction and Product Rtcovtsy Sy»t«M =„, 7
potential for significant plume migration, it: may be better to
quickly address contamination problems instead of waiting to
accumulate water-table data. It is recommended that designers
evaluate of the advantages of, collecting more data versus the
advantage of rapidly capturing the plume to avoid significant
migration.
The direction of groundwater flow is typically the same as the
downgradient slope of the water table, however, the groundwater
flow may vary in anisotropic conditions. If iso-concentration
.. maps suggest that the migration direction is not directly
downgradient, the remediation system designer should consider
the potential for future migration to differ from the
groundwater gradient.
Water-Table Fluctuations. Fluctuations of the water table are
evaluated to determine the screened interval of wells and
trenches. This is important at sites with floating product, so
that the floating product can enter the well screen. It is
also important at other sites to ensure that the wells are
installed deep enough to provide the capacity needed for plume
capture under a seasonal-low water table.
Storage Coefficient or Specific Yield. The storage coefficient
or.specific yield is calculated and reported if pumping tests
are performed (Section 3).
Grain-Size Distribution. The well-screen slot-size is
determined by the grain size of the filter pack, which is
determined by the grain size of the formation adjacent to the
screen. A boring should be drilled to obtain the grain-size
sample(s) to determine the groundwater extraction-well screen-
slot size. If it is apparent during the investigation that
. groundwater extraction is needed, a deep boring should be part
of the site investigation. Subsection 4.2.1.2 discusses sizing
the filter pack and slot .size.
2.2 Geologic Characterization.
A geologic characterization assesses the interaction of aquifers and
aquitards that may be present at a site. The important site geology
characteristics are as follows:
Geologic Unit Below the Aquifer. The importance of
characterizing the unit below the aquifer varies greatly from
site to site. Guidelines to follow include:
It is necessary to assess the vertical component of the
hydraulic gradient with a well nest that includes at least one
piezometer if there is the potential for vertical migration to
lower geologic units
If the contaminant plume does not reach the base of the
aquifer, the underlying unit is relatively unimportant and may
be estimated for depth only. In this case,, the "clean" water
under the plume should be characterized with at least one
piezometer.
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Guidcnci for Groundwatir Extraction and Product Recovery Systems • Page 8
If the contamination extends to the base of the aquifer, *-.
designers should assess the ability of the underlying unit to
restrict the movement of the contamination (less-permeable
unit) or its ability to transmit contaminants (more-permeable
unit). Characteristics of underlying hydrogeologic units to
assess include:
— hydraulic conductivity (vertical if less-permeable, or
• both vertical and horizontal if high-permeable);
— secondary permeability; and
— vertical gradients. .
If there is a potential for DNAPL at the site, designers should
accurately define and characterize the depth of the. aquifer .
base. A large volume of DNAPL may flow in a direction •
different than the groundwater flow if the surface of the • :
confining layer slopes in a different direction than the • ,
groundwater gradient. Therefore, the topography of the
confining layer surface should be determined.
' " i
• Geologic Unit Above the Aquifer. If the aquifer is confined,
the overlying confining layer should be characterized for , :
vertical hydraulic conductivity and the gradient across the , ?
unit.
: .fro.!!.. Des crip tion^ A hydrogeologist that meets the definition
in NR 500.03 (64) (or NR 600.03 (98)) should prepare the boring
logs. Soil description should include the following
information:
— Approximate percentages of major and minor grain-size
constituents. Note: Terms such as "and," "some,"
"little,"."trace," etc. are acceptable if percentages
they represent are defined;
— Color and Munsell Color;
— Geologic origin;
— Description of moisture content (e.g., 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. Hydrogeologists should note the depths
carefully because depth of smearing is evidence of past-
aquifer water-level variations.
2.3 Extent of Contamination.
A definition of the areal and vertical extent of contamination is necessary
for plume-capture calculations (See Subsection 4.1). The vertical extent
is also necessary for well design (See Subsection 4.2).
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Guidance for Groundwatar Extraction and Product Racovary Syatams Pag, 9
Soil samples collected from soil borings should be field screened for VOC
measurements at sites where VOC contamination is suspected. Field
screening may consist of the following:
Headspace analysis using::
I
Photoionization (PID);
• Flame ionization detector (FID);
Field gas chromatpgraph (GC); or
Lab in a Bag Method (Robbins, 1989). -
Other pertinent field observations such as odor should be included in the
site investigation report, and any evidence of product smearing should be
noted and described (product smearing means a free-phase product coating on
soil particles).
2.4 Contaminant Chemistry. f
Treatment and/or disposal systems must be designed for the extraction rate
and types and 'concentrations of the site contaminants. See" the Guidance
for Treatment Systems for Groundwater and Other Aqueous Waste Streams for a
detailed discussion of groundwater treatment.
Seals, bearings, pitless adaptor/units, and motor leads in pumps designed
, for clean water use are often not compatible with contaminants, so special
pumps may be required. Designers should assess well materials and
equipment for contaminant compatibility before using them in the extraction
system.
2.5 Floating Product or DNAPL.
If a floating, recoverable product layer is present at a site, designers
must insure that the well-screen interval intersects the product layer
under static conditions and all potential-pumping levels (see
Subsection 4.2). .
In some cases, only a small volume of floating product is present at a
site. In this case, the designer should evaluate whether or not product
recovery by pumping is necessary, or if other means (such as evaporation by
soil venting) can efficiently extract the product.. There are several ways
to estimate the volume of floating product (Hughes 1988, Testa 1989, and
Farr, 1990). Kemblowski (1990) also discusses fluctuating product
thickness that is caused by fluctuating water tables. If the volume of
product is too small to warrant extraction using product recovery
techniques, an estimate of the product volume should accompany a
justification in the work plan, along with the alternative approach for
removing the free product.
Designers should carefully choose equipment if ignitable floating product
is present at a site. Intrinsically-safe or explosion-proof equipment is
typically required when ignitable contaminants are present. See
Attachment 2 for more information on equipment selection.
The British Thermal Unit (BTU) content of the recovered petroleum product
may be needed to assess petroleum product-disposal options. BTU content
may affect the ability to-recycle the product as a fuel because too low a
BTU content may make it too costly to recycle the product for fuel usage..
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Guidance tor Groundwater Extraction and Product Recovery Systems page 10
Flash point is used to characterize the product for shipping the recovered
product off-site in accordance with DOT regulations. . ' *-.
2.6 Other Site-Specific Characteristics.
Other site characteristics that should be included in hydrogeologic
investigations include, but are not limited .to, the following:
Presence of nearby wetlands or surface water bodies;
• A fractured-aquifer matrix;
Structures that affect groundwater and/or floating product or
DNAPL-flow;
• High-capacity wells that influence natural-flow patterns; and
• Other wells which might be impacted. ' I •
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Guidance for Groundwat.r Extraction and Product Rtcovary Systtms " f u
3.0 Aouifer Testingr
Aquifer testing is necessary to estimate the hydraulic conductivity or
transmisivity for plume capture calculations; In some cases, the hydraulic
conductivity tests .conducted during the site investigation provide
sufficient data for remedial design. In other cases, a pumping test prior
to remedial design-may be necessary to accurately estimate the rate of
groundwater pumping that is needed to capture the plume.
In some situations, aquifer testing techniques such as a slug tests bail-
. down tests, and grain-size methods provide sufficiently accurate hydraulic
conductivity estimates. However, these techniques may not be sufficiently
accurate for design purposes.
The following is aJList of aquifer tests in decreasing order of accuracy:
Long duration (multi-day) constant rate pumping tests;
Short duration (less than eight hours) step drawdown tests;
Bail-down and slug tests; or
Permeability calculations based on grain-size analysis.
Some suggested guidelines when testing aquifers include the following:
A plume in sand or gravel that is hundreds of feet long and
over 100 feet wide is a major groundwater extraction project;
therefore, a pumping test is probably necessary.
In silt and clay soils, a likely pumping rate is several gpm or
less. A bail-down test from each well generally provides
sufficient data for evaluating design, treatment, and/or
disposal options. Although a pumping test more clearly defines
an aquifer, it may be more cost effective to oversize the
groundwater extraction/treatment system and delay a pumping
test until after the system installation, provided that it is
relatively inexpensive to oversize the groundwater treatment
system.
A pumping test is probably needed prior to designing
groundwater extraction systems that are likely to produce more
than 50 gpm, but is probably, not necessary for systems that are
likely to operate at less than 5 gpm. If the system is likely
to produce in between 5 and 50 GPM, designers should assess
site-specific factors such as water disposal options, treatment
needs, etc. to determine what level of accuracy is needed for
an aquifer test.
A careful evaluation of the costs and benefits of a pumping test may be
warranted. If a pumping test is not proposed at a site, the hydrogeologist
should include an evaluation of the aquifer-testing data quality in the
report to justify the exclusion of a pumping test.
If a number of aquifer-testing results are available, the geometric mean of
the results should be used to. calculate the average hydraulic conductivity
(Domenico and Schwartz, 1990; page 67). If multiple hydrogeologic units
are present, designers should calculate the geometric mean for each
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GuidEDC* for Grcrundwat«r Extraction and Product Recovery Systwns Page 12
hydrogeologic unit, not a single, overall site average. If some results
have a higher degree of certainty, designers should NOT use the results
that are less certain in the calculation.
Example: If both pumping test results and Hazen method results are
available, the Hazen method results should not be used when
'calculating the geometric mean due to the higher level of
uncertainty.
The groundwater discharged during an aquifer test or well development
, .should be sampled and chemically analyzed for contaminants and other
parameters that may affect the treatment system and/or disposal options
(See Guidance for treatment Systems for Groundwater and Other Aqueous Waste
Streams for more information).
Water that is produced as part of aquifer testing must be handled in
accordance with DNR rules applicable to investigative wastes. Portable,
low-volume air strippers or carbon filters may be used as treatment for
water that is produced by pumping tests. Preapproval is necessary by the
Wastewater program if discharging to a storm sewer or surface water body.
In some cases, a POTW will accept untreated pumping test water without
4 significant costs. The POTW will probably require test results from the
well prior to approving the discharge. It may require parameters in
addition to LUST, ERP, or Superfund program requirements, such as BOD5 or ,- •
suspended solids. The local POTW should be contacted to determine -. '
necessary analytical requirements.
Designers should evaluate the means and costs of water disposal when
determining which aquifer characterization method to use.
3.1 Hydraulic Conductivity Estimates Based on Grain-Size Analysis.
A mathematical determination of the hydraulic conductivity based on the
grain size is rarely appropriate for designing a groundwater extraction
system. A grain-size test may be used in unconsolidated material to
corroborate other tests. The reasons for poor performance of this test
include the following:
There are a number of methods available (Shepherd, 1989, Masch
and-Denny, 1966, .Hazen method described in Freeze and Cherry,
1979 and Fetter, 1988), but no single test is proven to be best
under all conditions.
• Most methods are only applicable to sand. Note: The Hazen
Method is only valid for a grain size of 0.1 < D10 < 3.0 mm, the •
Masch and Denny, method is limited to samples of unconsolidated
sand. • ,
The samples that are collected for grain-size analysis are from
very small discrete locations. Often, only one to three
samples are tested; therefore, only a few discrete parts of the
site are used to estimate the overall site hydraulic
conductivity and transmisivity.
• Some methods disregard soil density, porosity, grain roundness,
etc.
Only groundwater flow through primary porosity in soil is
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Guid«nc« for Groundwattr Extraction and Product Racovary Syitami
evaluated in a grain-size test, if there is flow-through
secondary porosity - such as fractures in till - the
conventional tests are invalid.
The tests are not appropriate for bedrock.
3.2 Bail-Down and Slug Tests.
Bail-down (water-table wells and piezometers) or slug tests (piezometers)
provide better hydraulic conductivity estimates than grain-size-analyses.
Note: For purposes of this document, a bail-down test is a test that.
instantaneously extracts or withdraws a volume of water or a slug
from the well, and a slug test is a test that instantaneously injects
a solid slug" into the well.
Slug tests are conducted in piezometers AND ONLY IN PIEZOMETERS. A
slug test in a water-table well will force water into the unsaturated
filter pack and possibly the unsaturated native soils, increasing the
length of submerged screen. Changing the .length of the submerged
screen during the test, makes the test invalid (Bouwer, 1989).
Most general hydrogeology texts describe these tests and provide a number
of references. Selected references include Cooper, et. al. (1967), Bouwer
and Rice (1976), and Bouwer (1989); there also are many other articles on
these tests in various publications.
Bail-down or slug tests may not provide the most accurate results for the
following reasons:
Only the part of the aquifer immediately adjacent to the filter
pack and screen is evaluated.
When testing water-table wells, only the uppermost part of the
aquifer is tested. More representative results are obtained
from wells which reflect an overall average of the aquifer.
If tests are conducted using piezometers, they only test a very
small part of the aquifer in the vertical dimisnsion because
piezometer screens are usually only 5 feet long and the sand
pack is 7 to 8 feet long.
If there is flow in secondary porosity channels, the wells may
not intersect the channels or fractures and would only evaluate
the primary permeability. If a fracture is intersected by the
well, the interpretation could also be inaccurate because'the
assumptions in the conventional methods are violated (Karasaki
1988). '
If the wells are not adequately developed, they will not yield
meaningful results. Smearing of the bore hole during drilling
will cause the well to reflect an artificially low
permeability.
Note: Because wells that are not developed to Chapter
NR 141 standards typically do not provide accurate
hydraulic conductivity estimates with slug or bail-down
tests, these wells should be redeveloped prior to aquifer
Page 13
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Guidanca for Groundwatar Extraction and Product Racovary Systams Page
testing. . •
High-permeable aquifers often yield artificially low estimates
with slug/bail-down tests because the .injection/extraction rate
relative to the rate of the induced inflow/outflow from the
aquifer is not instantaneous.
If the filter pack is less permeable than the native soil, the
calculated hydraulic conductivity is artificially low because
the test measures the hydraulic conductivity of the filter
pack. Chapter NR 141 specifies the size of the filter pack and
slot size in monitoring wells. A screen slot size that is too
small can also limit the groundwater flow into a well lowering
the hydraulic conductivity estimate in high-permeable aquifers.
3.3 Pumping Tests. "
A pumping test extracts groundwater at a constant rate for a number of
hours, and a step drawdown test varies the pumping rate over time. These
tests are used to calculate the aquifer transmisivity and specific yield or
storage coefficient. Most general hydrogeology texts cover the basics of
pumping tests; Kruseman and de Ridder (1990) is an excellent reference.
In some cases, an additional monitoring well or aquifer-test well is
necessary to perform a pumping test. A pumping test can be performed in an
aquifer-test well constructed for the pumping test, a groundwater
extraction well, or an oversized (4-inch) monitoring well. An aquifer-test
well should be evaluated for entrance velocity (Subsection 4.2.1.2) prior
to installing the well. A wire wrapped screen may be necessary in high-
permeable aquifers to reduce entrance velocity. In this case incrustation
due to- a high entrance velocity is not an issue because of limited pumping
duration, but flow restriction through too small a slot size could occur.
A longer well screen than normally used for a monitoring well may also be
necessary to achieve the desired drawdown and flow rate during the pumping
test. If the aquifer-test well is upgradient of the source and within the
same geologic.unit, it-may produce clean water. Disposing of clean water
from a pumping test is much easier than contaminated water. This may be a
factor when planning the duration and pumping rate for a test. Aquifer-
• test wells require preapproval under NR 141.
General considerations for pumping tests include the following:
A method that accounts for partial penetration and/or
unconfine'd conditions is appropriate in most aquifer-
decontamination projects. During a pumping test, the
groundwater below a partially penetrating extraction well is
•relatively stagnant and does not "flow" during the test,
therefore, this portion of the aquifer is not "tested" during
the pumping test. Methods that assume a fully penetrating well
could result in a transmisivity estimate that is artificially
low.
Driscoll (1986) indicates that partial penetration effects are
minimized at a distance (from the extraction well) that is
twice the aquifer thickness. Therefore, methods based on fully
penetrating wells (including the Jacob straight line method)
can be used on data from monitoring wells that are a
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Guidance for Groundwater Extraction and Product Recovery Systems p4Re
significant distance from the extraction well. If the Jacob
straight line method is used, the calculated u value should be
less than 0.05 (Driscoll, 1986).
'• f v" •, " „''.'."-' '; -
N. Boulton and S. Neuman have each published a number of
articles about aquifer testing in unconfined conditions.
Fetter (1988) lists a number of references related to aquifer
testing (pages 209 to 212) including most of those by Boulton
and Neuman.
. The clas'sic pumping test for a water-tables aquifer is a 72-hour
test. Confined aquifers may need a 24-hoiir test. At some
small .sites, a low-capacity test (less than 10 gpm) for a.
shorter period of time (8 to 24 hours) may be sufficient.
The length of the pumping test may need to be modified if the
hydrogeologist conducting the pumping test: determines that a
different length of time for the test is tiecessary, based on
initial test data. If early test data suggests that the
drawdown in an unconfined aquifer has stabilized, the pumping
test should continue long enough to ascertain that a delayed
yield or slow drainage effect is not influencing the
interpretation.
Water-level measurements should be collected at all available
measuring points. Even distant points that are outside the
radius of influence provide data on background water-level
fluctuations during the test.
Note: Hydrogeologists should collect water and product
level measurements in wells with floating product.
However, wells with floating product: should not be used
for pumping test evaluation, unless ;there is a shortage
of wells at the site. Because the dynamics of multi-
phase fluid flow into and out of a well with floating
product may introduce error, these monitoring wells may
provide misleading results. If wells with floating
product are used, the density of the product should be
estimated to calculate the equivalent head in the well.
In all cases, recovery data for a pumping test is collected and
evaluated, especially at the groundwater extraction.well.
Casing storage can influence early drawdown ciata in large-
.diameter wells that are installed in relatively impermeable
aquifer's. See Kruseman and de Ridder (1990) and/or Driscoll
(1986).
In some cases, a short step-drawdown test is a viable alternative to a
full-scale pumping test. Small-diameter electric submersible pumps that
fit in 2-inch wells that can be used for step-drawdown tests are available.
If a 4-inch monitoring well is used at the site, a higher capacity step-
drawdown test can be conducted.
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Guidance for Groundw«t»r Extraction and Product Recovery Sy»t«ms Peso 16 -
.1 * •
4.0 Design and Installation of a Groundwater Extraction,System.
i
Groundwater extraction and product-recovery systems may consist of a single
well, include multiple low-capacity wells, or use a trench system. It may
be appropriate to install a groundwater extraction or extraction/product-
recovery well in the source area to minimize free-product migration, as
well as install a groundwater extraction well further downgradient to
capture dissolved-phase contaminants. No specific extraction system design
is appropriate for all conditions; a system should be tailored to meet
site-specific conditions and contaminants. .
4.1 Capture Zone. '.'•••'
' «i
Groundwater extraction systems are designed to contain and remove4 .
contaminated groundwater from the aquifer. The size of the plume which .the
extraction system will be designed to extract varies from site to site
depending upon factors such as aquifer conditions, degree of contamination,
distribution of contamination, and the location of receptors. A .
groundwater extraction system may operate as a form of source control, or
as aquifer restoration, or for both purposes. If free product is present
at a site, the system may consist of two recovery wells; one for free-
product recovery in the source area, and one downgradient to capture a
dissolved plume.
A larger capture zone, over and above the zone of contamination, is
sometimes warranted if there is a low level of confidence in the
distribution of contamination or the aquifer-testing results.
Some sites have primarily radial migration away from the source, other
sites have a lineal plume extending from the source. -The methods of
evaluating capture vary depending on the plume configuration. In general,
most remediation systems at smaller sites can be modeled if one of these
two plume configurations match the following descriptions:
Sites With High Hydraulic Conductivity and High Natural
Groundwater Migration. These sites typically consist of a
long, narrow plume that extends downgradient from the source
area. Contaminant transport at these sites is primarily
controlled by advection. Diffusion and dispersion are only
minor transport processes. Capture zones are calculated based
on three parameters: pumping rate, natural gradient, and
transmisivity.
Dispersion allows contaminants to travel along routes other
than streamlines. The capture zone should be designed to
' capture a larger area than the known zone of contamination.
The width of the extraction system's capture zone should be 15
to 25 percent (or more) wider in high-permeable aquifers and 30
to 50 percent (or more) wider in moderate to low-permeable
aquifers.
The following two methods, analytical and mathematical, are
used to determine the capture zone:
— Analytical. A very simple two-dimensional model that is
appropriate for simple sites with a single extraction
well is described by Todd (1980, pages 121 to 123). An
example of this method is included in Attachment 3.
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fiui(f«nca tor firoundwafcar Extraction and Product Recovery Systems i Page 17
Another method is described in Javandel and Tsang (1986),
and in Fetter (1993). Several hydrogeology texts, such
as Domenico and Schwartz (1990), also describe similar
mathematical solutions for the capture zone. Other
analytical methods for more complicated, site conditions
using advanced mathematics are presented by Strack
(1989). Grubb (1993) applies the same mathematical
principles that are used by Strack for simple site
conditions. Both Strack and Grubb provide methods for :
confined and unconfined aquifers.
If there are known seasonal fluctuations in the
groundwater gradient, the capture zone should be •
calculated under all known groundwater gradients to
-verify that contaminant capture will occur.
— Computer. This method is appropriate for sites with
multiple extraction wells, an extraction trench, or with
sites that experience significant changes in groundwater-
flow patterns due to seasonal effects or natural
infiltration effects. There are many two-dimensional
modeling programs available that can quickly and
inexpensively evaluate groundwater flow to extraction
well(s). At more complex sites, three-dimensional models
may be needed, however, cost will often preclude their
use at simple or small sites. The extraction system
should be modeled under differing natural gradients to
assure that the extraction well(s) is in the optimal
location and has a sufficient pumping rate -under all
seasonal effects.
Note: The CNR does not endorse or approve
groundwater modeling programs. It is the
responsibility of the remediation.system designer
to use a model that will provide correct and
meaningful results. The designer is expected to
provide sufficient documentation for DNR model
review.
Sites With Low Hydraulic Conductivity and Minimal. Natural
Groundwater Migration. If the site has very low-permeable
soils, it is likely that contaminants have migrated radially
away from the source primarily due to diffusion and not
advection. A centralized extraction system in the source area
may be, used if contaminants have migrated a short distance or
mostly radially away from the source area.!
In these cases, the remediation system designer needs to design
a system with a cone of depression that establishes an inward
gradient at the perimeter of the contamination zone. The DNR
does not specify a minimum inward gradient; however, a minimum
inward gradient of 0.01, or more, is recommended. The system
may be designed based on computer modeling (see computer
information above) or by an analytical method. An analytical
example of this method based on Todd (1980) is included in
Attachment 4. Other analytical solutions are also acceptable.
At large sites with low anticipated pumping rates,-the designer
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Guidance for Groundwatar Extraction and Product Recovery Systems Page 18
should consider calculating the time of travel from the
perimeter of contamination to the extraction points. This
estimate is a measure of the time that is necessary to extract
one pore volume from the limits of contamination. If a long
period of time is necessary to extract one pore volume, then it
is likely that groundwater restoration will take a long time.
The modeling methods"1 above are typically based on two-dimensional capture
zone calculations. Because the methods are two-dimensional, the estimated
pumping rate can be overestimated in very thick aquifers if the total
. aquifer thickness is used in the calculations, and water is only extracted
from the upper portion of the aquifer. When calculating the extraction
rate from a partially-penetrating well in an aquifer that is very thick
relative to plume depth, it may be appropriate to assume an "effective"
aquifer thickness that is less than the full thickness.
In the case of. a partially penetrating groundwater extraction well
installed at the water table, designers can assume an effective aquifer
thickness that-is the sum of one-half of the plume-capture zone width, plus
the screen length. Partially penetrating groundwater extraction wells
screened below the water table (confined aquifers and submerged plumes in
unconfined aquifers) may have an assumed effective-aquifer thickness that
is equal to the capture zone width plus the screen length. This method of
estimating an effective-aquifer thickness is not absolutely correct in ., :
mathematical terms, but it should provide reasonable results, assuming • •;
isotropic conditions. This approach is based on simplistic assumptions;
other scientifically valid methods based on known site-specific conditions
may also be used.
After the flow rate is determined, the designer should predict the drawdown
in the well to determine if it is reasonable. If the well is a partially
penetrating well, a correction for partial penetration should also be made.
Attachment 4 includes sample calculations for drawdown and partial
penetration. Also, see the discussion of maximum drawdown recommendations
for extraction wells in Subsection 4.2.
If a single well does' not deliver the capacity that is necessary for plume
> capture, designers should consider other alternatives to assure that the
extraction system will deliver the desired capacity. There are a number of
.options that can be used in those situations, including:
Multiple extraction wells can be, used with reduced-flow rates
on a per well basis, which reduces drawdown in each well. When
multiple wells are used, superposition can be used to estimate
the drawdown in each well.
• A trench system may be used instead of a well.
• The length of the screen can be increased. The system designer '
should carefully consider the costs associated with pumping,
treating, and disposing of clean water that is pumped from
under the plume if this option is considered. This option may
seem cost-effective because it moves more water at a minimal
cost, initially. BUT, in some cases; the treatment and
disposal costs for pumping clean water for many years make this
a'high-cost option.
The modeling methods described above are only applicable to flow-through
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OaiAtnct tor Groundwttr attraction and Product Rtcov«ry Systnu faee 19
primary porosity. If flow-through secondary porosity (fractured flow)
affects contaminant migration, the consulting hydrogeologist should propose
an alternate means of locating groundwater extraction systems based on the
apparent direction of contaminant flow and distribution.
After installation and start-up of the groundwater extraction system,
designers should periodically prepare water-table maps that depict the
capture zone. See Subsection 5.3 for more information on groundwater maps.
4.2 Well or Trench Design.
A groundwater extraction system in high-permeable soils typically consists
of a drilled well(s), and a groundwater extraction system in low-permeable
soils typically consists of a trench system(s). There are no specific
conditions that determine the use of a trench instead of a well. If the
desired groundwater extraction rate cannot be achieved with less than about
10 feet of drawdown in a water-table well, a single well is insufficient
and a trench or multiple wells are needed. If floating product is present,
the drawdown should be limited to no more than 5 to 6 feet to limit product
smearing on soils. There is no recommended maximum drawdown in wells that
are installed in confined aquifers or that pump from submerged plumes.
Generally, at least 5 feet of screen should be in the aquifer under pumping
conditions.
Note: Product smearing occurs when the soil particles are coated with
free product and the interstitial void spaces between the particles
are partially filled with free product.
A trench system may be difficult or impossible to install if the trench
does not stay open long enough for pipe installation and backfilling, and
installing a very deep trench may be impractical. If a single well is
insufficient and a trench system cannot be installed, multiple low-capacity
wells may be necessary. .
4.2.1 Drilled Wells.
If the groundwater extraction well is screened (or open hole in bedrock) in
a confined unit, the well should be designed to prevent contaminants from
flowing upward.through the annular space to uncontaminated zones. In some
cases, a temporary (or permanent) casing that seals off upper, "clean,"
high-permeable zones during drilling is necessary. This may preclude the
use of some drilling methods (hollow-stem auger and bucket auger) at some
confined-aquifer sites.
4.2.1.1 Drilling Method. •
There are many site factors that determine the method of drilling. The
system designer should use a method that results in proper construction of
an efficient extraction system. Driscoll (1986) is an excellent reference
for drilling methods. For shallow, large-diameter wells in low-hydraulic
conductivity environments, a large bore hole may be needed. The following
is a brief summary of the commonly used drilling methods:
Cable Tool. Cable drilling offers great flexibility. The well
can be installed with a natural-filter pack when the casing-
pullback method is used, or with an artificial-filter pack when
, a large-diameter temporary casing is used. Because .there is
minimal smearing (relative to hollow-stem augers) and no filter
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Guidance for Groundwater Extraction and Product Recovery Systems Fags 20
•*
cake against the bore-hole wall, well development time is
reduced. The disadvantage of cable drilling is the large
amount of time it takes to install a well.
.Note: Many cable drillers use arc welding and a cutting
torch. Drillers should be warned of any ignitable
contaminants or the presence of a floating-product layer.
If these conditions exist, the driller should use a
threaded and coupled pipe.
• Hollow--Stem Auger. In some low-flow applications, a 6.25-inch
inside-diameter hollow-stem auger can be used to install a 4-
inch well constructed of polyvinyl chloride (PVC). Some
drilling contractors have 10.25- or 12.25-inch inside-diameter
hollow-stem augers that can be used for larger wells.
Advantages include speed and the ability to collect split-spoon
samples and conduct field headspace tests.
The disadvantage of the method is that large-diameter augers -.'
can only penetrate limited depths. There can be considerable
smearing of the bore-hole wall in stratified formations,
especially if those formations are loose or soft (as exhibited NN
by low-blow count N values) because the finer-grained soil .;
cuttings may be pressed into the coarser-grained layers. The , >
smearing effect is less critical in clean outwash deposits. .In -M^^'
most cases, flush threads should be used for screen and casing.^7
Mud and Clear-Water Rotary.' Mud rotary is a common method for
drilling water-supply wells. Drilling mud should not be added
if the hole stays open with clear water. Wells drilled with
this method need significant development to remove the filter
cake from the bore-hole wall especially in high-permeable
formations. The main advantages of this method are speed and
the availability of drilling rigs.
Bucket Auger. When drilling in fine-grained soils that stay
open, a large-diameter well can be installed by using a'bucket
auger. The bucket auger is a good choice if the design bore-
hole diameter exceeds a couple of feet and the well is fairly
deep. If the hole will not stay open, a bucket auger is not a
good choice.
Other methods, such as air rotary or rotasonic, may be appropriate in
unique situations such as in bedrock. In all cases, drill cuttings must be
• handled in accordance with the DNR rules' that are applicable to
investigative wastes.
4.2.1.2 Filter Pack, Screen, Casing, and Well Development.
Filter Pack and Well Screen. If-designers use a filter pack, it should be
appropriately sized to the native soils. An artificial-filter pack extends
a minimum of 2 feet above the top of the screen. If a long screen in a
loose formation is used, the filter pack should extend a minimum of 5 feet
above the top of the screen because a large amount of filter pack and
native soil can be removed from the bore hole during development. If
sufficient materials are removed, the filter pack and annular space seal
can collapse to the top of the screen.
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Guidtnct. for GrounoV«t«r Extraction and Product Recovery Systems Page 21
The well screen may be constructed of PVC, low-carbon steel, galvanized
steel, or stainless steel. 'In unusual-site conditions, other materials may
be appropriate. The remediation .system designer should consider the
duration, of the project when selecting s'creen material. The screen
manufacturer may provide advice on material characteristics to limit or
prevent corrosion,;incrustation and contaminant compatibility. Non-
reactive materials need to be used in extraction well design. In unusual
cases, such as very deep wells, the physical strength of the screen should
also be evaluated in consultation with the screen manufacturer.
The slot size of the screen should be sized to the filter pack (or natural
pack if used). See Chapter NR 112 for a discussion of filter pack and
screen specifications. If a natural-filter pack is used, refer to page 435
in Driscoll (1986) for a discussion of screen-slot size. A well with a
screen that has slots that are too large and/or a filter pack that is too
coarse may pump sand. If stratified conditions exist, & relatively fine-
grained layer should be used for selecting the filter pack and the well
screen-slot size. On-site screen manufacturing, such as torch cut slots
and drilled perforations, and on-site slotting by saw cutting are not
acceptable.
The screen diameter is usually a function of the type of pump(s)
(Subsection 4.3), sensors (Subsection 4.4, Control Panel) and possibly a
shroud (Subsection 4.4) that are installed in the well. Only in rare cases
is a screen diameter controlled by factors other than the pumping equipment
dimensions.
If there is a possibility that a floating product or DNAPL recovery pump
installation may be needed in the well, the well-screen diameter should be
sufficient for a two-pump system (Subsection 4.3). In some cases, a
recoverable floating-product layer forms after pumping begins, even though
it did not appear during the investigation. If there are unusually high
dissolved-contaminant concentrations, the designer should use a well with a
sufficient diameter to also hold a product recovery pump, .in case it is
later determined that a product pump is needed.
If floating-product recovery is initially planned, or there is evidence
that floating product may be drawn into the well, the top of the screen
should be above the seasonal-high static water table. If recoverable
floating product is unlikely to be present, the top of the screen should be
set at or above the top of the plume.
The base of the screen should be set so that the entire length of the
screen extends, through the entire contamination zone. In general, it is a
good practice to maintain at least 5 feet of well screen within the aquifer
under pumping conditions. In some cases, the base of the screen is set
slightly below the plume to maintain at least 5 feet of screen below the
pumping level.
If multiple high-permeable zones are present and contaminated, THE SCREEN
MUST NOT CROSS CONNECT HIGH-PERMEABLE ZONES THAT ARE SEPARATED BY LOW-
PERMEABLE ZONES. In these cases, designers should use separate wells for
each high-permeable zone because a single well in this situation would be
an artificial conduit to vertical-contaminant: flow during periods when the
well is not pumped.
Screen incrustation can occur if the entrance velocity is greater than 0.1
feet per second (Driscoll, 1986). Driscoll (1986) contains example
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Guidance for Groundw»t«r Extraction and Product R«cov«ry Systwns Page 22
calculations for determining entrance velocity. Most well-screen
manufacturers will provide the open area per lineal foot of screen for the
calculations. Designers should use the estimated length of screen under
static, seasonal-low water-table conditions, minus the anticipated
drawdown, when estimating the length of screen for calculations. If the
design calculations indicate that entrance velocity is greater than 0.1
feet per second, other screen types or larger-diameter well(s) may be used.
If the calculated entrance velocity is significantly above 0.1 feet per
second, the well may not produce the desired extraction rate. Attachment 4
discusses estimating drawdown.
A bottom plate must be used on all well screens. If it is possible to -
recover any DNAFL, the base of the screened portion of the well should be.
designed so that as much DNAPL is recovered as possible.
•
Bedrock Wells. Well installation with open hole is acceptable if the
extraction well is in bedrock, instead of constructing the well with a
filter pack and screen. An open hole should not cross connect high-
permeable zones separated by a low-permeable zone(s).
Casing. The casing may be PVC (when PVC screens are used) or steel pipe.
In some rare cases with unusual-site conditions, stainless steel casing or
other materials may be used. If the well casing is less than 8 inches in
diameter, the casing should be schedule 40. If the well diameter is equal
to or greater than 8 inches, see Chapter NR 112 for casing wall thickness
specifications. If unusual conditions warrant using stainless steel .
casing, the-DNR project manager may allow a thinner wall thickness.
Development. After the well is completed, the well should be developed.
Driscoll (1986) provides an excellent discussion of well development
methods. Development over and above Chapter NR 141 requirements is
encouraged to provide an efficient extraction well.
Any grout in the annular seal should be allowed to set for a minimum of 12
hours prior to well development. Also, significant quantities of water and
fines can be produced by some development methods. The system designer
should plan for disposal of development water before installing the
well(s). .
• 4.2.2 Trench Systems.
Trench systems are only used to install groundwater extraction systems if
the water table is very shallow and the soil has low permeability. They
are typically installed by a backhoe. The purpose of the trench is to •'
create a high-permeable channel through the native soil to extract more
. groundwater than a well. The saturated zone of the trench should be
backfilled with a high-permeable material, such as coarse sand or gravel.
If the trench is very long, a perforated pipe or well screen should be
installed horizontally in the base of the trench to conduct water ,to an
extraction well or sump.
The unsaturated zone of the trench should be backfilled with the spoils
that were originally excavated from the trench. In some cases, a geo-
textile can be installed above the coarse gravel and below the backfill.
If floating product is present, the high-permeable material should extend
one or more feet above the seasonal high water table to.assure that the
floating product will not rise into the native fine-grained backfill.
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Guid«nc« for Groundw«t«r Extraction «nd Product Rteovtry Syatwas
Designers should install a well or sump - while backfilling the trench - in
the high-permeable backfill material in the trench. The well should be
installed as plumb as possible. Often, the well screen and casing are
assembled prior to placement in the excavation, then the screen/casing
assembly is hung by the backhoe into the excavation. Lastly, rope is used
to support the top of the screen/casing assembly in the vertical position
during backfilling. •
Note: Screen and casing specifications for the well or sump are the
same as those described above in Subsection 4.2.1.2.
A backhoe can be used to install a groundwater extraction well at sites
with low permeability and a high-water table. The well can be installed in
a former buried storage tank excavation, if appropriate. In this case,
well construction is -similar to a trench system.
!
4.3 Pump Selection.
4.3.1 Groundwater Extraction Pumps.
Electric submersible pumps are the groundwater extraction pumps usually
used at contaminated sites. In lower flow-rate applications, alternative
pumps such as pneumatic pumps are also used.
Pump materials should be compatible with the contaminants present at the
site. The pumps should be constructed of stainless steel, and the motor
leads, seals, and bearings should be made of materials that are compatible
with the site contaminants.
In general, submersible pumps do not have to be explosion-proof because the
pump motor is below the intake of the pump (therefore the pump motor is
always submerged and is isolated from the contaminant vapors) . Electrical
sump pumps that have a motor above the 'pump inlet should be explosion-
proof; see Attachment 2 for more information.
i • •
Designers should select the pump based on the desired pumping rate and the
hydraulic head. Calculation of the total head is the total of:
the elevation to which the water is pumped^ minus the pumping
elevation;
the total head loss due to pipe friction; and
heac loss from all other fittings and devices such as flow
meters, valves and possibly the treatment system.
The pump should be s'elected based on performance curves provided by pump
- . manufacturers. . . .
• * i
If a pump that has excess capacity is used, a throttle valve may be added
to the line near the treatment system to artificially create more head. If
a throttle valve is used, care is heeded to avoid burning out the pump by
creating too much restriction to groundwater flow. A pressure gauge marked
with the maximum pressure (from manufacturers data minus elevation head)
may also be installed in the line near the throttle valve to prevent
accidental damage to the pump. Restricting flow in this manner is not
recommended for long-term operation; it is only appropriate for temporary
operational needs. Other devices to prevent over pumping are discussed in
Subsection 4.4 under control panels. • - .
23
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Guidance for Groundwatcr Extraction and Product R«cov«ry Syituns paBe 24
t - ' *
Electrical connections to the pumps must be designed to specifications that
are acceptable to the local electrical inspector. The wire insulation to
the pump motor should be compatible with the site contaminants. If the
contaminants are ignitable, the local electrical inspector may require an
explosion-proof junction box mounted on the outside of the well casing.
Compressed air lines that are used for pneumatic pumps can freeze up in
. cold weather, and they should be protected from subfreezing conditions if
practical. An automatic water trap should be installed on the air line to
assure that any water that condenses in compressed air lines does not enter
, the pump or the pump controller. If the air compressor has a receiver (air
tank), installing an automatic water trap is recommended to drain
condensate from the receiver. . .
A.3.2 Floating-Product and DNAPL Pumping Systems.
Floating-product and DNAPL recovery pumps are designed or controlled to
only pump free product, and the pumps may be electric or pneumatic. The
selection of a pumping system is based on the following information:
Range of Water-Table Fluctuations (Excluding DNAPL Pumps'). If
the water table fluctuates more than 0.5 feet per week on a
regular basis, the pump should be able to operate under
changing water-table conditions. Designers should use pumps
that have a float mechanism that automatically adjusts to
changing water levels, or that use a filter that allows product
(but not water) to flow into the pump inlet. Pumps that depend
on a preset elevation of product are often set at the wrong
elevation.
• Frequency of Maintenance/Inspection. Pumping systems that
require frequent maintenance or frequent elevation changes are
very expensive in the long-term because of the extra site
visits that are required.
Potential for Failure. The pumping or DNAPL system should be
operated independently of the groundwater extraction pumping
system. This ensures that groundwater extraction continues and
plume capture and containment is maintained if there is an
equipment failure..
Note: A single control panel for both systems is
acceptable.
Characteristics of Failure. Some pump systems can cause
catastrophic failures in other associated equipment. For
example; a pneumatic pump or control unit failure can cause
over-pressurization and other equipment failure. If designers
use pneumatic pumps, it is very important that the product tank
is properly vented and the air compressor has a reliable
pressure regulator.
• Volume of Product to Pump. In almost all cases, a low-capacity
product pump is sufficient. For example, at only 0.1 gpm the
pump can still recover over 4,000 gallons per month.
• DNAPL. In the rare case where DNAPL is recoverable, or
anticipated to be recoverable, the pump should be designed for
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Guidance for Groundw«t«r Extraction «nd Product R»cov«ry Systwu i
DNAPL recovery. These pumps have an inlet at the base of the
pump so that accumulating DNAPL in the basse of the screen or
sump can be removed. •
The following are the three main types 6f floating-product pumping systems:
Floating Pump or Pump With Floating Inlet, These pumps
automatically adjust to water-table fluctuations and pump down
to a product layer of less than 0.05 feet.
25
Preset Pump Elevation With Hvdrophobic fllt-py, These pumps
allow product (but not water) to flow into the pump mechanism.
These pumps are often designed to pump down to a thin product
film within a fairly short vertical range.
££. et Pump Elevation With Electric Sensors or Density
Cor. -rolled Valves That Only Allow the Pump fo Pump Product:,
These pumps must be set at the elevation of the product layer
to operate properly. In some cases, a conventional groundwater
submersible pump can be used with electric sensors that turn
the pump on or off if the product layer builds up to a fairly
thick layer above and below the pump inlet.
There are also other types of floating-product pumping systems, including
combinations of the above-mentioned system.
4.3.3 Total -Fluids Pumps.
Some sites with very low permeability often use a single total-fluids pump.
A total -fluids pump pumps all fluids from the well, floating product,
water, and/or DNAPL. The pumped liquid should be discharged to an above-
ground product separator (See Subsection 4.4). Pneumatic pumps are often
used in low-capacity applications because they can safely run dry without
danger of burning out or damage from running dry.
When designing a total-fluids pumping system, designers should consider the
pump's potential for freezing. See the discussion of pitless adapters in
Subsection 4.4.
4.4 Other Devices.
In some cases, other devices are also part of the groumdwater extraction
system. A summary of these components includes the following:
Pitless Adaptor. Groundwater extraction systems should use a pitless
adaptor or a pitless unit to transfer groundwater from the well to buried
piping outside of the well casing to avoid freezing (See IDriscoll, 1986;
page 626). As a result, the water does not pass through any piping at or
above the 'frost level. The pitless adaptor/unit allows the submersible
pump to be - -moved from the well without significant plumbing difficulties.
The pitless adaptor/unit should be designed to allow access for taking
water-level measurements. Some pitless adapters have very small holes that
severely limit the diameter of the water-level indicator that can pass
through the holes. In larger-diameter wells, pitless units are available
that do not block access for product recovery pumps. Access intp the well,
past the pitless adaptor/unit, should be verified in the design.
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Guidanc* for Groundw«t«r Extraction mad Product R«cov«ry Sy»t«mo • Pace 26
A pitless adaptor/unit may be used for the groundwater pump in a two-pump
system, but not for the product pump. Because depth -adjustability for a
product pump is important to the project success, the hoses for pumped
product should extend out the top of the well. In addition, designers
should use a support cable that allows simplified depth adjustability of.
the product pump.• A pitless adaptor usually is not needed for the product
pump since most floating products (or DNAPL) do not readily freeze.
Note: The seals in pitless adapters and pitless units should be
compatible with the contaminants.
Pitless adapters and pitless units may be used for total-fluids
applications if a,single pump is used for a water and product mixture.
Well Cover. Well covers are commercially available with padlock hasps,
both with and without a connection to the electrical conduit for
submersible pumps. .The well cap should be lockable, however, when product
recovery wells are installed, a small lockable enclosure may be installed
over the well as a substitute for a locking well cap. This enclosure
houses the electrical connections to the pump(s), winches for raising and
lowering the pump(s), and any hoses to convey pumped product. If the wells
are part of a high-capacity system, see NR 112 for additional Bureau of ;:V
Water Supply requirements for well-cover designs.
Shroud. A shroud is a sleeve around the motor of a submersible pump that
forces water past the motor to cool.it. It is primarily used if the.pump
is installed very close to the base of the screen.
Manifold. The manifold consists of the piping system that is used to move
the pumped liquids to the tanks and/or treatment system. It may be above
ground, but in most cases it is buried. These manifold lines need to be
constructed of a material that is compatible with the contaminants and are
capable of holding the pressure and volume of the pumping system under
worst case scenarios. If designers use a pneumatic-pumping system, the
lines must be capable of holding the pressure of the regulated compressed
air source. If designers use a submersible pump, the lines should be able
to hold the pump pressure if the flow is blocked at the treatment location.
Designers should use the working pressure rating, and not the burst
pressure rating, when assessing the pressure capability for manifold lines. .
If heat tape is used, steel or other materials should be used instead of
PVC. If a buried plastic pipe is used, a steel wire should be placed in
the upper part of the trench before backfilling so that a metal detector
can be used to locate the trench at a later time.
Note: Burying a steel wire is unnecessary at sites where reinforced
concrete pavement is used, since the metal detector will only "see"
the rebar.- '.
Flow Meter. A flow meter should be installed on the system to measure the
amount of pumping from each well. It should be a totalizing-flow meter
that indicates the total fluid pumped.
Product Storage Tank. A product tank is needed to contain the pumped
product. See Attachment 2 for related rules.
Product Separator Systems. Product separator systems are tanks which allow
separation of pumped product and water from total-fluids pumping systems.
The tank may be baffled to limit mixing, and a coalescing separator may be
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Guidanc* for Groundwatar Extraction and Product Recovery Sy items Fag* 27
used when the flow rates are too high for effective separation in a tank.
See Attachment 2 for related rules.
Control Panel. The control panel should be,designed specifically for each
site. A panel with the appropriate sensors can provide the following:
Automatic shut off, if the well is dewatered.
High-/low-level sensors to turn a product pump on and off.
. • Treatment system operation.
Auto shut off for full-product tank.
Auto shut off for overflow on separator tank.
Other equipment control, such as blowers for vacuum-enhanced
product recovery systems.
Other data collection devices, such as an hour meter on pump.
operation, automatic telemetry for data transmission over the
phone line, and possibly automatic data collection for water
parameters (Ph, conductivity, etc.).
4.5 Groundwater Extraction System Design Report.
In some cases, the remediation system design is included in a comprehensive
report with the results of the investigation. In other cases, the design
is submitted separately. The design of the recovery well(s) must be
submitted and approved prior to implementation, as required by Chapter
NR 141. A report that includes the design of a groundwater extraction
system should include the following information:
Discussion.
Plume Capture. Designers should discuss the assumptions used
to calculate the total groundwater extraction rate. Designers
should also include a discussion of the'geologic and
hydrogeologic conditions and reasons why the plume-capture
calculation method is appropriate.
Design of the Wells. Extraction well details include the
following:
—. bore-hole diameter,
— screen length and diameter,
— slot size, .
— casing depth, diameter and material
— filter pack and seal depths and specifications, and
— the drilling method.
Development method and planned disposition of development water
should also be discussed.
Manifold Design. The discussion should include the following:
- pipe type,
— materials of construction,
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Guidance for Groundw«t«r Extraction and Product R»cov«ry Sy»t«a» page 28
t
— diameter(s), '
— location of valves, and ' *- "
— a description of instrumentation for measuring flow rate.
Designers should discuss the depth of the manifold if it is
buried.
• Pumping System Specifications. The discussion should include
. total anticipated gallons per minute and anticipated drawdown
•in each extraction well.
Product Recovery. Designers should evaluate whether or not a
product recovery system is necessary for the site.
• Operations and Maintenance Plan. The discussion should include
a brief discus.sion of maintenance activities and frequency of
site visits.
Monitoring. The designer should propose a monitoring program
for selected monitoring wells at the site that accurately
measures the performance of the system. The DNR may require
modifications to the proposed plan prior to implementation.
See Subsection 5.4 for recommended progress report contents.
Figures.
Designers should include a map of proposed well locations drawn
to scale with the following information:
— locations of proposed and existing groundwater extraction
wells;
— locations of monitoring well(s);
— locations of. the manifold and instrumentation;
— location of the treatment system (if used) and the
location of water discharge to sewer or surface waters;
— location(s) of suspected and/or known contaminant
source(s) (if differing contaminant types are present at
a site, des'igners should identify the contaminant type at
each source location);
— free product zone (if present);
— groundwater contamination zone;
— groundwater extraction system capture zone under all
anticipated shifts in the groundwater table under a given
pumping rate;
— scale, north arrow,' title block, site name, and key or
legend; ' •.
— any other pertinent site information.
Designers should include a current water-table map with the
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Guidance for Groundwatar Extraction and Product Racovary Syatacu
date of water-level measurements.
Fag* 29
Tables.
A process-flow diagram indicating the piping layout with1
instrumentation and key components should, also be included.
The report should include a table of water levels/elevations
from all wells, over the life of the project.
If floating product is present at the site, designers should
include a table of product thicknesses over the life of
project. This table can be combined with the water-level
table.
Appendices.
Plume-capture calculations for determining the well location(s)
and the groundwater extraction rate should be included in the
report. If plume capture-calculations are based on
computerized modeling, the computer output should be included.
The calculations determining hydraulic conductivity should be
included, or a reference to the report that includes that data.
Photocopies of hand written calculations and graphs are
acceptable, IF THE CALCULATIONS ARE LEGIBLE. The initials and
date of the person performing a quality assurance/quality
control (QA/QC) check of all calculations should be included.
Calculations estimating the drawdown in the extraction well(s)
should be included.
Designers should include calculations used to select the pumps;
the type, size, manufacturer, and model of the pump; and the
performance curve that is provided by the manufacturer of the
pump.
If a product recovery system is included in the system design,
designers should include the type and specifications of the
product pumps, the associated piping specifications, the
specifications for the product tank, and disposition of
recovered product.
Designers should include calculations for determining the
filter pack, well-screen slot-size, and entrance velocity. The
grain-size analysis should also be included.
A copy of the WPDES permit application, permit, request to a
POTW, or approval letter from a POTW should be included.
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Chiidcnc* for Grcnmdw«t»r Extraction mnd Product R«cov«ry Symtooa t*ge 30 _
5.0 Operation of a Groundwater Extraction System.
When a system is designed properly for the site, the system is likely to
operate as expected. If the remediation system operator finds a method of
operating the system more efficiently at any time, the system operator
should evaluate those changes and submit them to the DNR for review prior
to implementing the-changes.
Generally, the. operation of a groundwater extraction system includes |
periodic maintenance visits.
.,
5.1 On-site Tests After Installation of the Extraction System.
- ^ • .0
After the groundwater extraction and treatment/disposal system is *
installed, designers should conduct a pumping test in a single extraction
well as part of start-up operations to confirm the hydraulic conductivity
estimate. This pumping test is not necessary if a 72 hour pumping test (24
hours for confined conditions) — at a flow rate that is at least 25 percent
of the final remediation system pumping rate — was previously performed at
the site.
A confirmation pumping test should be conducted for a minimum of 48 hours.
This test does not need the frequency of water-level measurements that a . v
predesign test requires because this test is used only to verify previous ,. '
aquifer-testing results. In most cases, using popper tapes or water-level
indicators are sufficient for this test, instead of using pressure
transducers. Recommended frequency of water-level measurements for all , ' ;
wells at a generic site includes the following: ' •/'
• Water-level measurements should be collected as rapidly as
practical in all wells for the first two hours of operation.
It is most important to frequently collect the measurements
from the extraction well and nearby monitoring wells.
Water-level measurements should be collected every hour for the
next eight hours of operation.
Water-level measurements should be collected at least twice a
day for the next two to four days.
•The system operator should leave the system in operation after the data is
collected because the confirmation pumping test is not as important as the
remediation system operation. Because the system continues to operate,
recovery data cannot be collected. If multiple wells are installed, the
start-up testing sho'uld only be conducted in a single well. After the
,' start-up testing is completed, the operator should bring the additional
wells on-line.
Because long-term data is available, using the Jacob straight-line method
to calculate transmisivity of monitoring well data may be sufficient if the
u value is less than 0.05. Using the new transmisivity value, the system
operator should prepare a new plume-capture calculation to ensure the
pumping rate is sufficient.
If a soil venting system is installed at the site, it should remain off
during the start-up testing of the groundwater extraction system. This
allows the aquifer to respond to the groundwater extraction system alone. i
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Guidance fox Groundwatcr Extraction and Product R»cov«ry Syst«n» Page 31
5.2 As-Builts Submittal.
• Designers should submit as-built information in a report after the
groundwater extraction system construction is complete. Because most of
the information is in the design report, a separate submittal is usually
not necessary, unless requested by the DNR. In most cases, the as-built
information should be included in the first progress report after start-up.
The as-built information includes the following:
Results of on-site testing discussed in Subsection 5.1.
• . 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 groundwater extraction wells;
— locations of monitoring wells;
— the manifold and instrumentation locations;
— suspected and/or known source location(s) (if differing
contaminant types are present at a site, identify the
contaminant types at each source location);
— zone of soil contamination;
— zone of groundwater contamination;
- zone of free product (if present);
- scale, north arrow, title block, site name, and key or
legend; and
— any other pertinent site information.
Groundwater extraction well construction diagrams, boring logs,
development information, and any other information required by
Chapter NR 141.
Any other pertinent information.
5.3 Groundwater Maps.
During regular site.visits, water levels should be measured in all .
monitoring wells. . Water-level maps should be prepared on a monthly basis
for the first three months and quarterly thereafter. The maps should be
used to assess the remediation system's ability to capture the plume. If
the capture zone is insufficient, additional measures may be necessary,
such as additional extraction wells and/or higher pumping rates.
If system operators use a soil venting system, vacuum-enhanced product
recovery system, or air sparging system in conjunction with a groundwater
extraction system, they should periodically shut off these systems long
enough to allow the water table to respond to only groundwater extraction.
After the water table has stabilized, operators should -then collect water-
level data and use it to calculate water elevations to produce the water-
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Guidinc* for Groun
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Guidance for Groundwater Extraction and Product Recovery Systems ' Page 33
text. The first progress report after pump start-up should
also include a water-table map describing conditions
immediately prior to pump start-up.
• . A total contaminant removal, graph, with time on the horizontal
axis and cumulative contaminant removal in pounds or gallons on
the vertical axis should be included in the figures. This
graph should include the free-product recovery, the total
dissolved-phase recovery, and the sum of the two.
Tables.
A table of water levels/elevations and product levels or
thicknesses from all wells at the site should be included.
A table of groundwater chemistry data from monitoring and
extraction wells should also be included.
.Other Information.
• If analytical data is available from a laboratory, the lab
reports should be included.
• A discussion of sampling procedures, analytical procedures,
etc. is not required in each report, but operators should
include a reference to the report that lists the procedures.
Any other pertinent information or data should be included.
In all projects that include groundwater extraction, designers should
report the groundwater discharge to the DNR Wastewater program or to the
local POTW. Groundwater reporting requirements are not satisfied by
reporting to the LUST, ERR, or Superfund program.
5.5 Project Close Out.
See Chapter 10 of the Guidance for Conducting Environmental Response
Actions for project close-out procedures. Long-term monitoring or
additional corrective actions may be necessary.
Note: At the time this document was finalized, Chapter 10 has not
been completed.
All wells should be.abandoned in accordance with NR 141.25 upon final
proj.ect closeout. .
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Guidance for Groimdwater Zxtracticm and Product Recovery Systems Face 34
6.0 References. ' - • \
Bear, J. 1979. Hydraulics of Groundwater. McGraw-Hill Inc., New York,
N.Y. ••-.••'••
Cooper, H.H, Bredehoeft, J.D., and Fapadopulos, I.S. 1967. Response of a
Finite Diameter Veil to an Instantaneous Charge of Water. Water Resources
Research. Volume 3, -Number 1, pages 263 to 269.
Bouwer, H. and Rice, R.C. 1976. A Slug Test for Determining Hydraulic
. Conductivity of Unconfined Aquifers with Completely or Partially
Pene.trating Wells. Water Resources Research. Volume 12, pages 423 to 428.
Bouwer, H. 1989. The Bouwer and Rice Slug Test - An Update. Ground
Water, Volume 27, Number 3, Pages 304 to 309. •
Domenico, P.A. and Schwartz, F.W. 1990. Physical and Chemical
Hydrogeology. John Wiley and Sons, Inc. New York, New York.
Driscoll, F.G. 1986. Groundwater and Wells, Second Edition. Johnson
Division, St. Paul, Minnesota.
EPA, 1990, Basics of Pump-and-Treat Ground-Water Remediation Technology.
EPA/600/8-90/003, March 1990.
Farr, A.M., Houghtalen, R.J., and D.B. 1990. Volume Estimation of Light
Nonaqueous Phase Liquids in Porous Media. Ground Water, Volume 28, .
Number 1, Pages 48 to 56.
Fetter, C.W. 1988. Applied Hydrogeology, Second Edition. Merrill
Publishing Company, Columbus, Ohio.
Fetter, C.W. 1993. Contaminant Hydrogeology. Macmillan Publishing
Company, New York, New York.
Freeze, R.A. and Cherry, J.A. 1979. Groundwater. Prentice Hall Inc.,
Englewood Cliffs, NJ.-
Grubb, S. 1993. Analytical Model for Estimation of Steady-State Capture
' Zones of Pumping Wells in Confined and Unconfined Aquifers. Ground Water,
Volume 31, Number 1, Pages 27 to 32.
Hughes, J.P., Sullivan, C.R., and Zinner, R.E. 1988. Two Techniques for
Determining the True. Hydrocarbon Thickness in an Unconfined Sandy Aquifer.
Proceedings of the Conference on Petroleum Hydrocarbons and Organic
Chemicals in Ground Water: Prevention, Detection and Restoration, November
1988, Pages 291 to '. 314.
Javandel, I. and Tsang, C. 1986. Capture Zone Type Curves: A Tool for
Aquifer Cleanup. Ground Water, Volume 24, Number 5, Pages 616 to 625.
Karasaki, K., Long, J.C.S., and Witherspoon, P.A. 1988. Analytical Models
of Slug Tests. Water Resources Research, Volume 24, Number 1, pages 115 to
126. '
Kemblbwski, M.W. and Chiang, C.Y. 1990. Hydrocarbon Thickness Fluctuations .
in Monitoring Wells. Ground Water, Volume 28, Number 2, Pages 244-252.
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Guidance for Groundwatar Extraction and Product Recovery Systems ~ • • , Page 35
Kruseman, G.P. and de Ridder, N.A. , 1990. Analysis and Evaluation of
Pumping Test Data, Second Edition. International Institute for Land
Reclamation and improvement, Wageningen, The Netherlands.
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.
Neuman, S.P.,1974. Effect of Partial Penetration on Flow in Unconfined
Aquifers Considering Delayed Gravity Response. Water Resources Research,
. Volume 10, Number 2.' Pages 303 to 312.
Neuman, S.P., 1975. Analysis of Pumping Test Data From Anisotropic
Unconfined Aquifers. Considering Delayed Gravity Response. Water Resources
Research, Volume 11,"Number 2. Pages 329 to 342. ,
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.
Shepherd, R.G. 1989. Correlations of Permeability and Grain Size. Ground
Water, Volume 27, Number 5, Pages 633 to 638.
Strack, O.D.L., 1989. Groundvater Mechanics, Prentice Hall, Inc.,
Englewood Cliffs, NJ.
Testa, S.M. and Paczkowski, M.T. 1989!. Volume Determination and
Recoverability of Free Hydrocarbon. Ground Water Monitoring Review, Winter
1989, Pages 120 to 128.
Todd, D.K. 1980. Groundwater Hydrology, Second Edition. John Wiley &
Sons, Inc. New York, NY. •
Department of Natural Resources. 1993. Guidance for Treatment Systems for
Ground Water and Other Aqueous Waste Streams. PUBL-SW184-93.
Department of Natural Resources. 1993. Guidance for Design, Installation
and Operation of Soil Venting Systems. PUBL-SW185-93.
Wisconsin Administrative Code NR 112, Private and Non-Community Well
Construction and Pump Installation Code.
Wisconsin Administrative Code NR 141, Groundwater Monitoring Well
Requirements.
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Attachment 1
Waste Classification of Petroleum Products
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CORRESPONDENCE/MEMORANDUM-
State of Wisconsin
DATE: January 3, 1992 ' "-. | FILE REF: 4430
TO: District Solid & Hazardous Waste Program Supervisors
^
FROM: Paul P.
SUBJECT: Waste Classification of Petroleum Products
Recently there have .been several questions raised concerning the regulation as
hazardous waste of off-specification petroleum products. Please note that
products which meet the petroleum product specifications of ch. ILHR 48, Wis
Adm. Code are not covered by this memo. "Petroleum product", in this
instance, means a product regulated by DILHR under ch. ILHR 48, the Petroleum
Products Administrative Code. It does not include waste oil, waste gasoline
or sludges generated during underground tank closures, or media contaminated'
by petroleum products. Products may be off-specification due to water
content, ethyl alcohol content or a number of other reasons. The closure of a
petroleum product storage tank system may also result in the necessity to
manage petroleum products which do- not meet DILHR requirements for sale to
consumers. In many cases these materials can be (and currently are)
reintroduced into the petroleum product market place. The purpose of this
memo is to clarify our position on the management of off-specification
materials. Owners and responsible parties should be encouraged to recover
free product in tank closure situations. They should be required to conduct
this work in accordance with applicable rules and guidance.
If an off-specification petroleum product falls outside the scope of (no
longer meets the specification for its intended use) or cannot be further
managed (downgraded or blended to meet ILHR requirements) under ch. ILHR 48-,
Wis. Adm. Code, then it is considered to be a solid waste and falls within the
jurisdiction of the Department of Natural Resources. 'The generator must
determine if the waste, is hazardous and manage it accordingly. Options other
than disposal, such as the secondary fuel program, do exist for petroleum
waste that is hazardous waste.
Petroleum products that either meet the standards of ch. ILHR 48 Wis Adm
Code or those products that will be blended to meet the standards fall within
the jurisdiction of the Petroleum Inspection Program of DILHR. Wastewater-
gasoline/water interfaces; petroleum directly above the product/water
interface (within 2 inches per DILHR guidance); and sludges fall within the
scope of the Wisconsin Department of Natural Resources regulations as wastes.
The following requirements have been established by the DILHR Petroleum
Inspection Program for the handling and use of petroleum products under its
jurisdiction which are generated during tank system closures. They also apply
to the management of off-specification petroleum products. These requirements
reflect DILHR's authority under ch. 168, Wis. Stats, arid ch. ILHR 48 Wis
Adm. Code. '
1. The removal and transfer of any off-specification product destined for
use or return to a terminal or refinery must be by a tank vehicle which
complies with the "Standards for Tank Vehicles for Flammable and
Combustible Liquids; NFPA-385."
Printed oo
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Waste Classification - January 3, 1992 • . . • 2.
\
2. Off-specification product may be:
a. Returned to a terminal slop, tank, if a terminal will accept it.
b. Returned to a refinery, if the company will accept it.
3. Petroleum product removed from a tank system may be managed in the .,
following ways:
.a. Gasoline may be transferred to another facility for storage and use.
Storage must meet the standards established in the Flammable and
Combustible Liquids Code. In this case the material must meet
specifications of ch. I.LHR 48, Wis. Adm. Code. Gasoline may also be
transferred to another facility for blending. The blended product ,
must meet ch. ILHR 48, Wis. Adm. Code, specifications. . , ."
b. Terminals or refineries may purchase off-specification gasolines I
blend them with new gasoline at their facilities at a rate not to
exceed h of 1%.
c. Off-specification oils must be down-graded to #2 fuel oil. Products
classified as kerosene, #1 diesel, #1 fuel oil or #2 fuel oil may be
blended with new #2 fuel oil (at up to a 50% rate) and used or sold
for heating purposes.
, f-
d. Off-specification products heavier than #2 fuel oil may be blended'
with an equal or heavier stock, at up to a. 50% rate, and sold or
used for heating purposes.
e. Off-specification oils may also be sold without blending for
nonsensitive burner and heating use if the purchaser has established
itself as a qualified buyer/user with the DILHR District Petroleum
•Inspection Office.
4. When off specification product quantities of 500 gallons or more are
removed from a tank system, the DILHR District Petroleum Inspection
Office must be contacted. Based upon the contact, the Petroleum
Inspection staff will determine the disposition of the product. The
staff may:" ' '
a. Sample and test the product to determine compliance with
ch; ILHR 48, Wis. Adm. Code, and then provide directions for
disposition.
b. Allow transfer of the product to another station or facility for use
or sale.
c. Classify the product as falling outside the scope of ch. ILHR 48,
Wis. Adm. Code (material is waste).
At locations where the gas is floating on the water table in sufficient
amounts for it.to be recovered by itself, it may be handled in accordance with
items 1 through 4 without obtaining a hazardous waste I.D. number. However,
once items ,. through 4 are no longer available options, then it is a waste
material and must be managed in accordance with item 5 (below) and chs. NR 600
to 685 Wis. Adm. Code.
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Waste Classification - January 3, 1992 3
*
5. Petroleum wastes (material that can't be blended or downgraded) pumped
directly from the ground into a tank without any treatment or separation
are solid waste .and must be managed as hazardous waste if they exhibit
the characteristic of ignitability (in the future,; these may be TCLP
hazardous wastes). This material cannot be sold for use by consumers
under any circumstances.
This issue was previously addressed prior to this in a joint memo from
Barb Zellmer and Mark Giesfeldt to you dated December 7, 1990. For ease of
reference the two pertinent items from that memo are repeated below. You may
wish to review your.. copy of that memo for other related information.
-Is 'petroleum product which is recovered from the water table a
waste?. '' —
»»•••.•:.•. .tp*.. .... . ••
;•• Petroleum product recovered from the water table is a waste only if It
cannot be used as a product. The factsheet titled "Managing Petroleum
Products" provides guidance on blending "old" petroleum from tanks with
new product, and returning petroleum to terminal "slop tanks."
NOTE: There may be taxation issues which apply to recovered product.
This should be checked with the Department of Revenue. .-
9. What if a recovery system recovers both free product and groundwater?
Systems which recover both free product and groundwater may require an
EPA identification number for on-site separation tanks because product
separated in the tank may be a hazardous waste if it is unsuitable for
fuel purposes. Refer to the "Managing Petroleum Products" factsheet
regarding allowable petroleum uses . Recovered groundwater may be
directly discharged to a sanitary sewer following approval from a
publicly owned treatment plant. If groundwater is recovered at a .site
which does not fall under the TCLP deferral and it is transported by
tanker to a wastewater treatment system TCLP analysis is required and a
hazardous waste transportation license may be needed.
Discharge of groundwater to surface water requires a WPDES permit. If
the contaminated water is treated to meet WPDES permit limits TCLP
requirements would not apply. Refer to the July 9, 1990 memo from
Ken Wiesner. for additional wastewater guidance."
A copy of the factsheet "Managing Petroleum Products" is attached.
Facilities which have a gasoline water separation system following the tank in
which the contaminated groundwater/gasoline mixture is pumped, need to obtain
an EPA I.D. number and report the activity. The recovered petroleum material
may be handled in a manner consistent with items 1 through 4 previously
addressed. This could be viewed as legitimate recycling under the hazardous
waste program. The operation would be covered by ch. NR 625, Wis. Adm. Code -
Hazardous Waste Recycling.
U.S. EPA does not regulate off -specification petroleum products that are not
-considered to be waste. When an off -specification petroletun product is a
hazardous waste and is burned for energy recovery it is regulated in
accordance with the recycling provisions of 40 CFR Part 26 6 -Standards for the
management of specific hazardous wastes and specific types of hazardous waste
management facilities -subpart D. Both state and federal rules require both
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Waste Classification - January 3, 1992 4.
generators and transporters of hazardous waste fuel (secondary fuel) to comply
with applicable hazardous waste management standards. .-
In conclusion, off-specification petroleum product that cannot be blended or
downgraded is considered a solid waste. The generator must determine if the
waste is hazardous arid manage it accordingly. Options such as the hazardous
waste fuel (secondary fuel) program do exist for petroleum waste that is
hazardous. For example, WR&R, Avganic, and Milwaukee Solvents all have
secondary fuel programs.
At this time, D1LHR .is also working on its own formal rule interpretation on
the management,of off-specification petroleum products. When it is finalized,
we will forward a copy of it to you.
if you have questions do not hesitate to contact Ed Lynch at (608) 266-3084 or
Laurie Egre at (608) 267-7560.
v:\9202\sw9petwa.ekl
cc: Barb Zellmer - SW/3
Mark Giesfeldt - SW/3
Pete Flaherty - LC/5
Patti Hanz - LC/5
Bill Morrissey - DILHR
Hazardous Waste Unit Supervisors
t(Gordon, Lynch, Ebersohl, Polczinski, Jerow & Degen)
Environmental Response Unit Supervisors
(Egre, Balloti, Strauss, Schmidt, Urben, McCutcheon, Gutknecht,
Kendzierski & Evans)
Hazardous Waste Section (routed).
Hazardous Waste Specialists
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Attachment!
DBLHR's Design Criteria for Process Equipment Buildings
Associated with Environmental Remediation of UST/AST Sites
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SAFETY * BUILDINGS DIVISION
201 E. Washington Avenue
P.O. Box 7969
Madison, Wisconsin 53707
State of Wisconsin ;
Department of Industry, Labor and Human Relations
. Program Letter 10- UST/AST Program
ILHR 10 POSITION STATEMENT
Design Criteria for Process Equipment Buildings Associated With Environmental
Remediation of UST/AST Sites
Issue
Soil and groundwater contamination remediation practices include several processes which
involve the potential hazards from flammable/combustible liquids and associated vapors.
The equipment associated with these processes often is protected from the weather
elements by enclosure within a building, which serves to trap vapors posing a greater hazard.
Presently this type of facility escapes direct code application due to the unique nature and
limited application. The building code does not clearly identify this type of structure and it's
respective use within the scope of the individual chapters. Proper design criteria is subject to
individual interpretation and discretion. The state has experienced approximately six fires or
explosions within buildings of this type within the past two years. Representatives of firms
designing and constructing remediation facilities have requested guidance in applicable rules
and fire prevention measures.
A work group was created to address the use and hazards associated with buildings
enclosing remediation equipment and associated process. The work group determined that
pump and treat, vacuum pumping, and free product removal processes pose a significant
fire/explosion risk due to the existence of flammable or combustible liquids and/or flammable
fumes or vapors. It was also determined that these facilities have very similar hazard
characteristics, therefore making a single design standard applicable ito all three processes.
*
The work group evaluated the physical characteristics of the equipment and the operating
and maintenance practices associated with the respective process.es. The design
recommendations are based upon the requirements within Wisconsin Administrative Codes
and National Standards: ILHR 50-64, ILHR 10, NFPA 30, and NEC NFPA 70. The building
and its operation meet the definition of process in NFPA 30 (1990 Edition) Chapter 5 .
Operations. The facility design standard in Chapter 5-3 is used to establish the basic criteria
for the remediation building. Due to the limited size of the building, the respective
remediation activities, and the reduced degree of risk, some of the requirements of NFPA 30
Chapter 5 are not practical.
RECEIVED
MAY26I993
' EMEflG & REMEDIAL RESPONSE SECTiOi-'
[ i .JR OF SOLID & HAZRO WAS"*?
sun
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Design Criteria
Setback
Building construction
Electrical
Venting of building
Tank construction
Tank located inside of
building
(A) NFPA 30-5-3.1.1 and Table 5-3.1.1 address the process
vessel, in this application the flammable/combustible liquid
collection tank. Tanks < 275 gallon capacity must be located 5'
from property line and 5' from any public way or important
building; a tank 276 to 750 gal. 10' from property line and 5' from
a public way and important building.
(B) NFPA 30 - 5-3.1.3 requires that liquid processing equipment,
such as pumps, heaters, filters, exchangers, etc., shall not be
located closer than 25' to property lines that can be built upon or
to the nearest important building. The philosophy is that such
equipment is more prone to leakage than the process tank. This
spacing requirement may be waived where the exposures are
protected by a blank wall having a fire resistive rating of not less
than 4 hours.
Tanks located outside of
building.
Product & vapor piping
Sirice remediation buildings dontain the process vessel and J
the} liquid processing equipment, the most restrictive setback
of 25V(B-abiove) shall apply, i t : : r
NFPA 30 - 5-3.2.1: Processing buildings or structures shall be of
fire resistive or non combustible construction.
Electrical area classification NEC article 514 and NFPA 30 Table
5-3.5.3. .
Electrical emergency shut-down in exterior locked cabinet or in
adjacent building if 24 hour access.
NFPA 30-5-3.3. Natural gravity or mechanical ventilation
capable of maintaining a minimum of 1 CFM/ft2. 18" AFF. Areas
that may pose temperatures above the flash point of the liquid
shall be ventilated at a rate sufficient to maintain the
concentration of vapors within the area at or below 25% of the
lower flammable limit
UL or similar listing for product contained within.
Vessels larger than 60 gallons. NFPA 30-4-4.1.2 4" curb.
Breach in floor for plumbing must be protected by 4" lip or be
sealed against liquids.
Tank must be vented to the outside of the building.
Secondary containment
Collision protection if in traffic area.
All piping and joint compounds shall be compatible with the
product.
Vent piping shall be of steel or approved metal construction only.
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Drum storage inside of
buildings
Drum storage outside of
building
Signage
Notification
Retroactivity
Inside storage of drums containing Class I or II liquid product
resulting from the remediation process .is not recommended, but
is not prohibited if the walls and ceiling are of a 1 hour fire
resistive rating.: ,;d
Drums that are being filled must have adequate venting to
prevent excessive pressure from rupturing the container.
Drums shall be stored in compliance with MFPA 30-4-8 Outdoor
Storage.
NFPA 704 placard.
WARNING - No Smoking.
24 hour notification number.
Notice to local fire department of installation, including name,
address and telephone number(s) for 24 hour notification.
Identify access to building, and shut-down process.
Twenty-four hour access or locked exterior panel.
Non complying electrical, non complying interior and/or tank
ventilation, fire department notification, and signage.
Plan review
ILHR 10 requires that the installation of tanks for the storage of flammable or combustible
liquids be submitted for plan review and approval to the authorized program operator for the
geographic fire jurisdiction of the site. The installation of the product storage tank and the
associated product piping and vent piping.shall be conducted by an ILHR 10 Certified
Installer.
Remediation buildings are designed to be temporary structures with an expected use life of 1
to 5 years. Local operators reviewing plans are directed to contsct the area DILHR
Tank Inspector when plans or on-s/te inspections reflect that the building may be over
built for the Intended remediation use. Characteristics that reflect a structure with a
questionable design may be: footings, overhead garage door, floor area, windows,
construction material; surface improvements, etc. DILHR should also be notified if the facility
appears to have components in place or design characteristics for the addition of utilities (eg.
sewer or water) at a later date.
Common remediation buildings are a windowless single story structure, on a floating cement
slab, less than 200 sq. ft floor area, with a single walk-through door.
William J. Mferrissey, Director
Bureau of Petroleum Inspection
and Fire Protection
'Sheldon Schall, Chief
Fire Protection and Storage Tank
Section
May 25, 1993
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Attachment 3
Two-dimensional Plume-Capture Calculations with Uniform
Horizontal Flow Under Static Conditions
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Wisconsin DHR - Guidance for Ground Hater Extraction and Product Recovery Systems - August 24, 1993 - Page 46.
Attachment 3
Two-dimensional Plume-Capture Calculations With Uniform
Horizontal Flow Under Static Conditions!
This method is usually used for sites with relatively high-hydraulic
conductivity and high natural groundwater migration rate. Refer to the
references for a further discussion of assumptions and applicability.
Key assumptions include the following:
Steady-state, no transient affects.
Location of a single, fully penetrating extraction well at the
coordinate origin in a confined aquifer.
Note: Although the method is for confined aquifers, since the
drawdown is less than 20 percent of the total-aquifer thickness
(in most cases), the method usually provides reasonable results
iri unconfined aquifers. If the drawdown exceeds 20 percent,
the method in Grubb (1993) or another method should be used.
Uniform horizontal flow (when no pumping occurs) from the
plus x direction towards the minus x direction; no water enters
the aquifer at the base.
No dispersion; assume that all contaminants travel on the
streamlines.
The aquifer is isotropic.
Equation 4.32 from Todd, (page 122) is:
Y- - ± mnrr . .
The method uses consistent units.
Q is the pumping rate,
K is the hydraulic conductivity,
b is the aquifer thickness,
i is the slope of the water table.
Solving for yL provides one-half of the capture zone width at an infinite
upgradient distance.-
The following equation 4.31 from Todd, page 121, provides the capture zone:
y _ I 2 it K b i I
• -r - tanl Q— y/
Solving for x, given different values for 7 (that are less than TL), the x
and y coordinates of specific points along the capture zone can be
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WtcooslD DXR - Guid«ic« for'Ground tfet.r Extraction and Product ft.cov.ry Sy.t«ns - August 24, 1993 - P^« 47.
calculated. Note: The tangent function uses radians instead of degrees.
To determine the stagnation point use equation 4.33 from Todd on page 123:
i
• '"-*'-" Q
• L 2 n K b i
An example and sample set of results are as follows:
. Assume the following:
Q. - 3850.3 cubic feet per day (corresponds to 20 gpm)
K - 35 feet per day (corresponds to 1.23 E-2 cm/sec)
i - 50 feet
i - 0.01
Solve for YL,
YL " ± 2 KQb i ' * 2 * 3355*'lo * 0.01 ~ 110'01 feet
Using differing positive values of y (less than FL), calculate x.
For instance at y - 100, x is:
*-
y x
(feet) (feet)
100 340.3
. 80 69.3
60 8.6
40 .. -18.3
20 -31.1
Because the capture zone is symmetrical, each data point can also be
plotted at the negative of the y value.
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Hiicociin DKR - Guidance for Ground Water Extraction and Product Recovery 8yatem» - August 24, 1993 - Page 48.
Solve for XL at the stagnation point. Note: The point at 7 - 0 is
the stagnation point downgradient of the extraction well,
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Figure A3-1
Plume Capture
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Figure A3-1
Plume capture
(-18,40)
-x
(-18,-40)'
(69, 80)
(9, 60)
-y
Recovery well at origin
Groundwater flow direction
(9, -60)
(69, -80)
Capture Zone
L_
0
20 40
Example based on
20 GMP pumping rate
35 feet/day hydraulic conductivity
50 foot aquifer thickness
0-01 water table slope
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Attachment 4
Two-dimensional Plume-Capture Calculation; wiith a
Horizontal Water Table Under Static Conditions
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Wiconiin DKR - <5uid«nc« for Ground W.t.r Extr.ction and Product R.cov.ry Sy«t«ns - August 24, 1993 - P.*. 52.
Attachment 4
Two-Dimensional Plume -Capture Calculat-inns vn-h ' a
Horizontal Water Table Urjrigr Static,
This method is usually used at sites with relatively low hydraulic
conductivity and minimal natural groundwater migration. Refer to the
references for a further discussion of assumptions and applicability.
Key assumptions include the following:
The water table is flat with no slope.
A single, fully penetrating extraction well is located at the
center 'of the contamination.
The aquifer is isotropic and unconfined,
Steady state; no transient affects.
Equation 4.18 from Todd (1980, page 118),
Q - -2 n r K h -g- ' i
The method uses consistent units.
Q is the pumping rate,
K is the hydraulic conductivity,
h is the aquifer thickness under static conditions,
dh/dr is the slope at a radial distance r.
Solve for Q, disregard the minus sign.
For a numerical example, assumptions include;
- distance to farthest point of contamination (r) is 50
feet;
- thickness of aquifer (h) is constant throughout at 35
feet prior to pumping;
hydraulic conductivity (K) is 3.5 feet per day
(corresponds to 1.23 E-3 cm/sec);
- an inward slope of 0.015 (dh/dr) is desired at the
perimeter. Note: This is SOX greater than the minimum
recommended in subsection 4.1;
- no water enters the aquifer at the base and there is no
infiltration;, and
• - drawdown at r is insignificant and 'is assumed to be zero,
Q - -2 n r K h -^- - -2 * it * 50 * 3.5 * 35 * 0.015 - 580 ~ —
Or (Jay
which corresponds to 3 gpm
After the flow rate is determined, the drawdown (s) in the well is
predicted to see if it is reasonable. Formula 3.7 on page 65 in .Kruseman
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Hi«ccra«in DHR - Guidance for Ground Water Extraction and Product Recovery Syatao* - Augu.t 24, 1993 - Fag* 53.
and de Ridder (1990) can predict drawdown assuming a long period of time
(such as a year). Note: Similar formulas are also given in Fetter (1988,
page 170), Driscoll (1986, page 219) and Freeze and Cherry (1979, page
Use consistent units.
2.3 Q I 2.25 T t 1
~ 4 n.T ^o / P-S"-/
Where T<-Kh-3.5*35- 122.5
Additional assumptions for the numerical example include;
- well radius (r) is 0.25 feet;
— storage or specific yield (S) is 0.2;
— time (t) is one year (or 365 days); and
— the well is adequately developed to be efficient.
- - 2.3 Q T__ / 2.25 T t
S 4 n T
I
/
2-3 * 580 I 2.25 * 122 * 365 I c n f
* it * 122.5 L°*l° / - 0.25* * 0.2 - / "' 6'° feet
4 * it * 122.5
Designers can then make a partial penetration correction, if necessary.
There is no ideal mathematical solution for an unconfined situation where
the screen is at the top of an aquifer. Designers should use a confined
solution, even though it is not mathematically correct, it is better than
no correction. An additional assumption for the example includes;
The plume is in the uppermost 20 feet of the aquifer,
therefore, the designer should select a 20 foot partially
penetrating well screen that intersects the water table at the
top of the screen.
In this example, Figure 9.35 in Driscoll (1986, page 2!>0) is used to
estimate the drawdown in a partially penetrating well. When calculating
the percentage of aquifer screened or the thickness of the aquifer (b) , use
the thickness of the aquifer and screen length under pumping (not static)
conditions. Since the aquifer is partially dewatered and the top of the
screen is set at the top of the static aquifer, both the aquifer thickness
and the effective screen length are shortened by the drawdown.
Therefore;
(h-s) is substituted for b,
h-s 35 - 6.0 ...
~~7 0725 H6
Therefore Curve E is used on Figure 9.35.
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Hi ic cms in DHK - Guidance for Ground Hater Extraction and Product Kacovcry System* - August 24, 1993 - Fag* 54.
Percentage of aquifer screened — 35*0 I g'o " 0.48 - 48 percent
From Figure 9.35, the percent of maximum specific capacity attainable is 70
percent.
Therefore the drawdown (s) is increased to, •
0.7
- 8.5
Where the term sp represents the drawdown in a partially penetrating well..
* ' •
It is generally good to have a minimum of 5 feet of screen in the aquifer
under pumping conditions. In the above numerical example, the predicted
drawdown is roughly 8.5 feet in a 20 foot screen, which means that there
will be roughly 11.5 feet of water in the screen. Subsection 4.2
recommends a maximum drawdown of 10 feet in water-table wells with no free
product. That is only a recommendation; economic considerations may
require fewer wells with greater drawdown in some situations. Remediation
system designers should use their professional judgement.
The method for partial penetration in Driscoll (1986) assumes confined
conditions, therefore, some error is likely when the method is applied to
unconfined situations, such as the above example. Another solution, using
different mathematical principles and assumptions, is included in Todd
(1980). -
Note: If the Kozeny Equation on page 250 in Driscoll is used, there is a
typographical error in early copies of the book. The term "... plus the
seventh root of ..." is wrong, it should be "... plus seven times the
square root of ..."
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