guide to well drilling for groundwater … guide to well drilling for groundwater development...
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GUIDE TO WELL DRILLING
FOR GROUNDWATER DEVELOPMENT
October 2016
i
GUIDE TO WELL DRILLING
FOR GROUNDWATER DEVELOPMENT
Prepared by
Utah Division of Water Resources
1594 West North Temple, Suite 310
P.O. Box 146201
Salt Lake City, Utah 84114-6201
October 2016
ii
PREFACE
This document was prepared to help sponsors, engineers, project managers, and interested
individuals understand the important topic of well design and construction. This “Guide to Well
Drilling” is meant to provide the basic information needed to become familiar with the orderly
progression of steps that will lead to the design and construction of an operational and successful
well.
Sections 1 and 2 describe the process and the regulations one must follow in order to drill a well
in the State of Utah. Information in Section 1 pertains to those who seek financial assistance for
well drilling from the Utah Board of Water Resources. Section 2 provides information
concerning the Division of Water Rights, which regulates all well drilling activities in the state.
In addition, Section 2 provides information concerning the Division of Drinking Water, which
regulates the drilling and construction of drinking water wells. Sections 3, 4, and 5 briefly
introduce the hydrogeologic setting of Utah groundwater environments, the tools that can be
used in locating a well, and items that should be included in a subsurface investigation leading to
aquifer characterization. The remaining sections in this guide (Sections 6 – 12) discuss steps in
the same order that a set of specifications for well drilling would follow.
It is natural for anyone who witnesses a drill rig in action to feel curious about the process and
even experience a level of excitement in anticipation of seeing water flow from the ground.
As mentioned above, this document is meant to be instructional and to remove some of the
mystery that surrounds the exploration for and the development of an amazing natural resource –
groundwater. Becoming familiar with the process of well design and construction can result in
more successful wells being drilled. To that end, we submit this document for your perusal.
iii
ACKNOWLEDGEMENTS
This guidebook was prepared under the direction of Bill Leeflang, Assistant Director of the Utah
Division of Water Resources (UDWRe), by a project team consisting of the following staff
members:
Dan Aubrey - Section Chief Geologist
Carl Ege - Project Geologist
Staff members from the Investigation & Development and Planning sections of the UDWRe and
Jim Goddard from the Division of Water Rights provided significant assistance with reviewing
and editing the document for publication.
Cable Tool drilling rig, drilling an irrigation well in Santaquin, Utah.
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Table of Contents
1. UTAH BOARD OF WATER RESOURCES GUIDELINES .............................................................. 1
2. LEGAL REQUIREMENTS ................................................................................................................... 4
3. UTAH GROUNDWATER ..................................................................................................................... 5
4. WELL LOCATION ................................................................................................................................ 6
5. SUBSURFACE INVESTIGATION ...................................................................................................... 8
6. METHODS OF DRILLING .................................................................................................................. 9
1. Cable Tool ...................................................................................................................................... 10
2. Direct Air Rotary ............................................................................................................................ 11
3. Direct Mud Rotary ......................................................................................................................... 12
4. Dual-wall or Dual-tube Reverse Circulation ................................................................................ 13
5. Dual Rotary .................................................................................................................................... 14
6. Flooded Reverse Rotary ................................................................................................................. 14
7. WELL PLUMBNESS AND ALIGNMENT ....................................................................................... 16
8. WELL CASING .................................................................................................................................... 18
9. WELL SCREEN/PERFORATED CASING ...................................................................................... 22
10. ARTIFICIAL FILL MATERIAL ..................................................................................................... 27
11. WELL DEVELOPMENT .................................................................................................................. 29
1. Bailing ............................................................................................................................................ 29
2. Mechanical surging ....................................................................................................................... 30
3. Pumping with Backwashing .......................................................................................................... 30
4. High Velocity Hydraulic Jetting .................................................................................................... 31
5. Air Lift ............................................................................................................................................ 32
6. Chemical Treatment ....................................................................................................................... 32
12. PUMP TEST ........................................................................................................................................ 34
1. Step Drawdown Test ....................................................................................................................... 34
2. Constant Rate Test ......................................................................................................................... 34
3. Recovery Test .................................................................................................................................. 34
13. GLOSSARY......................................................................................................................................... 36
14. REFERENCES .................................................................................................................................... 39
15. APPENDIX .......................................................................................................................................... 41
1
1. UTAH BOARD OF WATER RESOURCES GUIDELINES
All sponsors who seek funding from the Board of Water Resources (Board) for a well drilling
project must follow Board guidelines:
1. The sponsor must have a licensed engineer or geologist under contract who will design and
supervise construction of the well.
2. Plans and specifications prepared by the sponsor’s consultant must adhere to appropriate
technical standards and shall be stamped and signed by a Utah registered Professional
Engineer (PE) or Professional Geologist (PG).
3. Prior to soliciting bids, plans and specifications must be received, reviewed, and approved by
UDWRe and all other state and federal agencies that have regulatory or funding involvement
in the project.
4. All well drilling projects are to be awarded to a qualified (licensed) drilling contractor based
on competitive bids.
5. In all cases, the sponsor must comply with laws governing design and construction as well as
the statutory requirements placed on the Board and UDWRe.
The guidelines listed above apply equally to both test wells and production wells. For more
information about the Utah Board of Water Resources loan program, go to
www.water.utah.gov/board/GUIDELINES032015.pdf.
The Board expects sponsors to assume financial risk until they have demonstrated the ability of
the well and the aquifer to yield the desired amount of water. This frequently results in the
sponsor hiring a groundwater consultant to investigate aquifer potential at the proposed well site
and the drilling of a test well, which is a smaller diameter, less expensive exploration/pilot hole
(see Figure 1-1). Test wells provide the following vital information:1
1. Determines the material make-up of the subsurface by taking representative samples at
regular intervals from the surface to total depth.
2. Identifies aquifer structure: thickness of water bearing material, intervening clay layers, and
areal extent to the degree possible.
3. Defines aquifer characteristics: confined or unconfined conditions, porosity, permeability,
and with multiple test wells the hydraulic gradient.
4. Determines depth to the static water level and phreatic surface of each aquifer encountered.
5. Provides the opportunity to conduct geophysical surveys in the open, uncased borehole.
6. Facilitates the recovery of water samples from potential aquifers to determine water quality
parameters.
7. Most importantly, a pump test must be conducted to determine if yield from the aquifer
matches design or desired production.
Information that comes from the test well drilling process is very important to the overall success
of the groundwater development plan, so a test well should always be considered. The need to
drill a test well is determined when there is a lack of the critical information necessary to design,
construct, and equip a successful production well. In these situations, the Board has taken the
position that the sponsor is responsible to prove that the project is feasible. This is especially
true when no other wells are located in the vicinity of a proposed production well; when
information concerning aquifer composition, depth, thickness, areal extent, and productivity is
2
missing; and when groundwater levels are unknown. In these cases, the new well becomes
exploratory in nature2 and will be considered by the Board as a test well.
The Board will only fund a test well if it meets all of the following conditions:
1. A pump test demonstrates the ability of the aquifer to produce the design quantity and quality
of water.
2. The test well is included in the Feasibility Report as an item listed in the cost estimate.
3. The test well is described in the Project Description section of the Feasibility Report.
4. The test well is discussed in the Letter of Conditions.
The following is an example of how a test well can be characterized in the Letter of Conditions:
“A test well shall be drilled at the same location and to the same depth as the proposed
production well. An appropriate pump test shall be conducted and the water sampled and tested
to demonstrate that it meets the standards of quality and quantity required by the sponsor.” The
Board will only cost-share in the completion of a successful test well.
Figure 1-2 is a river basin map of Utah showing areas of board member jurisdiction. Perspective
sponsors must contact their board member for approval of an application prior to submission to
UDWRe.
Figure 1-1 - Test well being drilled in Bountiful, Utah.
3
Figure 1-2 – 2016 River basin map of Utah showing areas of board member jurisdiction.
Link to the map can be found at http://www.water.utah.gov/Board/RDist0513.pdf
4
2. LEGAL REQUIREMENTS
Groundwater, like surface water, must be
appropriated in accordance with existing laws.
Under subsection 73-2-1(4)(b) of the Utah Code,
the State Engineer, as Director of the Utah
Division of Water Rights (UDWRi), is required to
make rules regarding well construction and related
regulated activities and the licensing of water well
drillers and pump installers (see Figure 2-1).
These rules are promulgated pursuant to Section
73-3-25. The purpose is to assist in the orderly
development of underground water; insure that
minimum construction standards are followed in
the drilling, construction, deepening, repairing,
renovating, cleaning, development, pump
installation/repair, and abandonment of water wells
and other regulated wells; prevent pollution of
aquifers within the state; prevent wasting of water from flowing wells; obtain accurate records of
well construction operations; and insure compliance with the State Engineer’s authority for
appropriating water.3
An application must be filed with the UDWRi indicating that the owner desires to make an
appropriation through the drilling of a well. It must specify the location, amount of water
desired, purpose for which the water will be used, and other pertinent details. After the
application has been advertised and protests, if any, have been heard, UDWRi will notify the
owner that the application is either accepted or rejected.2 If accepted, the applicant is given
permission to drill and a Start Card is issued to the owner and to his licensed well driller who has
been selected through the competitive bid process.4 Drilling commences once stamped plans and
specifications for well drilling, construction, development, and testing have been reviewed and
accepted by the UDWRe.5
After the well has been drilled and the water put to the “beneficial use” stated in the application,
the owner must file a Proof of Beneficial Use. This includes exact water measurements, maps
showing place of use, and other final details. When these requirements are completed, UDWRi
will issue a Certificate of Beneficial Use, which is evidence of the ownership of a perfected
water right.2 Wells being designed and drilled as a municipal drinking water source must also
follow the Administrative Rules promulgated by the Utah Division of Drinking Water, based on
administrative rules R309-515 Source Development and R309-600 Source Protection (see Figure
2-1).
Another layer of governance pertaining to drilling a well resides in the local (city/county) health
departments, many of which have well-specific regulations. Frequently, these regulations
include: depth of surface seal, mandatory seal inspection, and water quality standards that must
be met before a well can be used. Almost all well setback requirements (property boundary,
septic, sewer, feed lots, PCS’s, etc.) are promulgated at the local health department level.
Figure 2-1 - Administrative rules governing well
drilling, source development for municipal wells, and
source protection. Both are required reading for
design engineers.
5
3. UTAH GROUNDWATER
Groundwater is a very important resource for the State of Utah. Here in Utah’s semi-arid
climate, many are dependent upon groundwater daily. Groundwater is the only source of
drinking water for many Utah communities. According to the Utah Division of Drinking Water
wells, springs, and tunnels numerically make up more than 96 percent of the water sources used
by public-water systems in Utah.6 Volumetrically, groundwater withdrawn from wells accounts
for over half of the reliable water supply for public community systems in the state.7
Groundwater as a resource is under increasing pressure due to recurring droughts and continuing
development.6
Groundwater is found in several different types of aquifers in Utah (see Figure 3-1). Over 94
percent of the groundwater withdrawn is from unconsolidated basin-fill deposits.8 These
unconsolidated deposits consist of boulders, cobbles, gravel, sand, silt, and clay or a mixture of
some or all of these materials. The largest yields of groundwater are obtained from coarse-
grained materials sorted into layers of uniform grain size. A small percentage of wells in Utah
are found in consolidated bedrock aquifers. Types of bedrock that have the highest yields of
groundwater are basalt, which contains fractures or joints, limestone, which contains solution
enlarged fractures, and sandstone, which may contain open pore space between grains of sand
and open fractures.9
Figure 3-1 - Confined and Unconfined Aquifers in Unconsolidated Basin Fill.4
6
4. WELL LOCATION
“Sometimes the proper location of a well becomes a
difficult problem. The owner primarily wants water in
the needed quantities and at a point where it can be
economically conveyed to the distribution system or
reservoir. To drill a well at a given location because it is
close to a supply main or reservoir may be false
economy if one is likely to get a dry hole.” 2
Selection of a well location should be based on technical
criteria rather than on convenience alone.10 The site
selection process should begin before drilling is planned.
Tools used as guidance in the well location selection
process include:
1. Well logs of previously drilled groundwater
production wells located near the potential well site
are found on the UDWRi web page
www.waterrights.utah.gov. Well logs, which are
public records pertaining to the drilling and
construction of wells, are vital sources of information.
From these logs one can obtain insight into the
location and depth of the well; depth, thickness, and
description of unconsolidated and/or consolidated
units penetrated; water level variations as successive
strata are encountered; yields from water bearing
formations penetrated and the corresponding
drawdown; the form of well construction; and pump
test data of the well upon completion.11 (See
Appendix for sample well logs).
2. Geologic maps and reports of the area describe both
alluvium and bedrock (see Figure 4-1). These include
reports or maps that cover the drainage basin up-
gradient of the proposed well site. Geologic maps
show the location where consolidated rock formations
and unconsolidated sediment outcrop on the surface,
including their strike and dip directions.11 Geologic
maps will also show the location of faults, which are
likely the location of some springs. Surface outcrops
can indicate possible areas of recharge for an aquifer
and the direction of water flow in the aquifer.
Geologic maps that have been published for the State
of Utah can be found on the Utah Geological Survey
(UGS) webpage www.geology.utah.gov/apps/intgeomap/. The Utah Quaternary fault and fold
database webpage, www.geology.utah.gov/resources/data-databases/qfaults/, can be very
helpful in locating these structures that frequently influence groundwater movement.
“Groundwater can be found
almost anywhere under the
earth’s surface. There is,
however, much more to
groundwater exploration than
the mere location of subsurface
water. The water must be in
large quantities, capable of
sustained flow to wells over
long periods at reasonable rates,
and of good quality.
To be reliable, groundwater
exploration must combine
scientific knowledge with
experience and common sense.
It cannot be achieved by mere
waving of a magic forked stick
as may be claimed by those who
practice what is variously
referred to as water witching,
water dowsing, or water
divining.”11
Groundwater
Exploration
Figure 4-1 - Geologic map of Utah
7
3. Geologic cross-sections provide some of the main
clues on potential groundwater conditions for an
area. They specify the character, thickness, and
sequence of underlying geologic formations.11
4. Aerial photographs can provide valuable
information on terrain characteristics that have a
significant bearing on the occurrence of
groundwater.11 Information obtained from stereo
pairs in a preliminary investigation can greatly
reduce or help focus the scope of work. For a quick
aerial overview of a site, Google Earth can be very
helpful.
5. Groundwater reports that discuss aquifers and
groundwater development in the area of
investigation. Many reports are available on the
UDWRi web page: www.waterrights.utah.gov and
on the UGS website: www.geology.utah.gov.
6. USGS website www.groundwaterwatch.usgs.gov
contains annual water level data from observation
wells. Accompanying hydrographs for each well
demonstrate groundwater level trends in response to
changes in precipitation, groundwater recharge, and
groundwater withdrawal.
7. Surface geophysical survey data and reports may
provide information on the stratigraphy and
structure of the local geology and aquifer. Faults,
fractures, folds, etc. can be found using geophysical
methods. These methods include seismic refraction
or reflection, gravimetric, electromagnetic, and
electrical resistivity.
To determine whether the desired amount of
groundwater is available at a particular location and
whether it is of suitable quality, drillers and
groundwater consultants rely on prior knowledge of
the local groundwater system, experience gained in
similar areas, and a diverse array of information
gathered from the sources listed above.12
Sites being analyzed as potential production well
locations should demonstrate some reasonable
expectation of providing sufficient water, meet
regulatory requirements, and not pose unacceptable
health or safety risks to future water users. For public-
supply wells, the proposed location must allow for a
defensible wellhead protection delineation that does not include multiple pollution sources.1
Design and construction of a
production well begins when a
licensed, professional consultant is
engaged to design the well and
oversee the work of the licensed
well driller.
A suitable well location is
determined to meet the specified
purposes of the well and fill the
needs of the sponsor. This is
followed by preparation of a
preliminary design. For large
production wells and especially
where groundwater levels and
aquifer properties are unknown, a
small-diameter pilot hole or test
well is drilled. With information
obtained from the test hole, aquifer
dimensions and make-up,
groundwater levels, and water
quality can be determined at
various depths.
Utilizing the information produced
from this subsurface investigation,
optimization of the final well
design (plans and specifications)
for the specific hydrogeologic
conditions at the site is
accomplished. Appropriate
materials (casing, screen, and
gravel pack) can be ordered in a
timely fashion prior to the final
drilling.
Once the well is drilled/reamed to
the design diameter and depth, the
driller installs well casing and well
screen to match the location in the
subsurface of productive and non-
productive zones. Gravel/filter
pack is then installed, the driller
develops the well, and conducts a
pump test.
Well Design and
Construction
8
5. SUBSURFACE INVESTIGATION
Once the well location has been chosen, a subsurface
investigation is conducted to identify and characterize the
soil stratigraphy of the site and identify the units that
need further investigation (see Figure 5-1). This work
begins with drilling test wells to determine depths to
groundwater, quality of groundwater, and the physical
character and thickness of aquifers without the expense of
a larger production well.13 During drilling of a test well,
a detailed log should be completed that indicates the
depths of the geologic formations encountered including
when and where samples were taken. Samples should be
routinely collected at 5 or 10-foot intervals, at any change
of formation, and at each 5-foot interval within water
bearing strata (see Figures 5-2 and 5-3). The samples
should be placed in a bag or container and each should be
properly labeled with well location, name or number of
the well, depth interval, date taken, and name of the
sampler. On small projects the scope of the work is
generally reduced, but in no way should a subsurface
investigation be eliminated. The owner cannot afford to go in blindly without knowing what the
subsurface conditions are.2
Other ways to determine geologic conditions in the borehole are to incorporate borehole
geophysical methods. Borehole geophysical survey logs and reports are extremely useful in
determining the effectiveness of well construction. When completed, these logs provide
excellent information on the lithology, porosity, moisture content, diameter of the well, etc.
Types of geophysical logs that are most commonly used include: spontaneous potential, single-
point resistance, normal-resistivity, gamma, neutron, caliper, and deviation.
Figure 5-1 - Subsurface Investigation
conducted near Brigham City, Utah.
Figure 5-2 - Grab bag samples taken during a
subsurface investigation near Bountiful, Utah.
Figure 5-3 - Chip tray samples taken during
subsurface investigation near Bountiful, Utah.
9
6. METHODS OF DRILLING
Various methods of drilling are commonly used in Utah in the construction of a water well.
Different methods have been developed because geologic conditions vary from hard bedrock
such as granite, to unconsolidated sediments such as alluvial sand or gravel.1 There is no single
method that is best suited for all geologic conditions that a driller may experience. In most
cases, the drilling contractor who is experienced in the area is the best qualified individual to
select the method of drilling. Successful drilling is a skill developed from extensive experience
and good engineering practices.1 The four most common drilling methods in Utah during the
2015 calendar year included air rotary in all its forms (47%), cable tool (20%), mud rotary
(18%), and dual rotary (12%). See Figure 6-1 for the full breakdown.
The most common air rotary systems used in Utah include direct air rotary, dual rotary, and dual-
wall reverse air rotary. These systems can be further enhanced by coupling technology such as
down-hole hammers, drill-through casing drivers, and under-reamer systems (e.g., Odex, Tubex,
Centrex).
Figure 6-1 – Graph showing the number and percent of well drilling activities by type from the Utah
Division of Water Rights website: http://www.waterrights.utah.gov/wellinfo/stats2k/default.asp
10
1. Cable Tool
Cable Tool, also known as percussion drilling,
is used in many parts of the world for the
construction of a water well (see Figure 6-2). In
Utah, cable tool is the second most common
drilling practice. Although it is commonly the
slowest drilling method, cable tool drilling is
less costly, inexpensive to operate, provides
excellent samples, and is suitable for many
geologic conditions.
The drilling is performed by percussion with
heavy tools in the form of a blunt chisel (see
Figure 6-3). Wells are constructed by
alternately lifting and dropping these tools,
which are suspended on a wire cable so that
with each stroke the drill bit strikes the bottom
of the hole. The design of the wire cable causes
the bit to twist approximately ¼ revolution per
drop, creating a drilling-like action. The raising
and dropping of the bit loosens unconsolidated
sediments (clay, sand, or gravel) and breaks up
rock into cuttings.
The drill cuttings are mixed with water by the
driller to create a slurry that must be removed
from the hole. The slurry is collected by
removing the tools and lowering a bailer on a
separate bailing line to the bottom of the hole.
The bailer (see Figure 6-4) is usually a 10 to
25-foot long steel tube that is brought to the
surface, where it is dumped in a constructed pit
or trough. Samples of the cuttings are
retrieved during this process. Tools for
drilling and bailing are suspended on separate
lines spooled on independent hoisting drums.
In unconsolidated sediment, the casing is
driven down the hole as work progresses to
prevent the hole from collapsing and to
prevent surface or subsurface water
contamination. Well casing used in this type of drilling operation ranges from 4 to 24 inches in
diameter.10 Prior to driving the casing, a drive shoe of hardened steel is fastened to the bottom of
the first length of the casing to protect it from damage.14 The typical cable tool drilling
procedure involves boring past the end of the casing, bailing the hole to remove the cuttings,
Figure 6-2 – Cable Tool drilling rig, drilling
an irrigation well in Santaquin, Utah.
Figure 6-3 – Cable Tool bit
Source: UDWRi (Jim Goddard photo).
11
driving the casing, cleaning the hole,
then continuing to drill.14 The driving,
drilling, and bailing operations are
repeated over and over until the well has
reached the prescribed depth.
Advantages of cable tool drilling include:
(1) low cost – 1/5 cost of rotary drilling,
(2) low maintenance, (3) less water is
required, (4) highly suitable in remote
areas, (5) rig can be operated by a single
person, (6) excellent samples, (7) drilling
tools easy to clean, (8) advances casing
in unconsolidated formations, and (9)
easy installation of monitoring casing
and risers.15 Disadvantages include: (1)
slow drilling speed - 1/7 as fast as rotary
drilling, (2) very low penetration rates in hard
bedrock, (3) restricted to steel casing material
only, and (4) noise and vibrations can be significant.16
2. Direct Air Rotary
Air rotary is the most common drilling
method in Utah, mainly due to its
versatility and adaptability. Direct air
rotary is the most basic form of air
rotary drilling. In air rotary drilling, air
serves as the fluid and excavation is
achieved in exactly the same manner as
the mud rotary method (see Figure 6-5).
Air is forced down the drilling pipe and
out through holes at the bottom of the
rotary bit.10 The air functions both to
cool the drill bit and force cuttings up
and out of the hole. Air rotary rigs
typically employ a tophead drive
system as opposed to a table drive
system common with mud rotary. A
tophead drive can move up and down
the rig mast, making adding and
removing drill pipe much faster and more effective. This method is primarily limited to drilling
in consolidated or cemented formations where the risk of borehole caving is minimal. Direct air
rotary is not typically used to drill in unconsolidated deposits unless other attachments to the
system are included. Also, in order to cut down on dust, aid the removal of cuttings, and
stabilize the borehole, water and foam (surfactant) is added to the compressed air stream.17
Figure 6-4 - Cable Tool bailer dumping cuttings that
were removed from the bottom of the hole.
Figure 6-5 – Air Rotary installing a groundwater monitoring well in a
residential area. Source: EDPS Environmental Drilling & Probing
Services, LLC (www.edpssoutheast.com).
12
The versatility and adaptability of air rotary allow the
system to add features to adapt to most drilling
conditions. In order to drill in unconsolidated
formations, a drill-through casing driver is often used
that allows the driller to drive casing behind the bit as
drilling progresses. This gives the advantage of cable
tool in that the driven casing allows the borehole to be
stabilized during drilling.17
When drilling in hard consolidated rock or
cobbles/boulders, a down-the-hole hammer (DTH) can
be installed in place of a tricone bit (see Figure 6-6).
This is essentially a pneumatic hammer, similar to a
jackhammer with case-hardened carbide buttons being
actuated by the compressed air of the drill rig. Air
hammers are available in 3 to 17-inch diameter and
can provide 800 to 2,000 strokes/min.23
Advantages of air rotary include (1) drilling in
bedrock and consolidated formations, (2) versatility
and adaptability, (3) fast drilling rates, (4) fast
mobilization and demobilization, (5) good sample
collection and groundwater identification, (6) can
estimate groundwater yield while drilling, (7) lost circulation usually not a problem, and
(8) wells develop faster because drilling mud is not used.17 Disadvantages of air rotary include:
(1) the cost to purchase a large capacity air compressor, (2) high operation and maintenance
costs, (3) formation restrictions unless equipped, and (4) blow out zones unless equipped.17
3. Direct Mud Rotary
Mud Rotary is a rapid method of drilling
in unconsolidated materials (see Figure 6-
7). This drill method operates
continuously with a hollow rotating bit
through which drilling fluid slurry is
forced. The drill bit most commonly used
is a tri-cone roller bit (see Figure 6-8).
The drilling fluid is composed of water or
water mixed with bentonite clay. The
mud is forced down the drilling pipe and
out through holes at the bottom of the
rotary bit.10 The drilling mud serves
several functions: (1) prevents collapse
and stabilizes the borehole (2) reduces
water loss to the formations by caking the
borehole wall, (3) removes cuttings from the
drill hole, (4) suspends cuttings when drilling
Figure 6-7 - Mud Rotary drilling rig. Source:
Pacific Drilling Company
(www.pacdrill.com).
Figure 6-6 – Downhole Hammer (DTH)
Source: UDWRi (Jim Goddard) photo.
13
fluid circulation stops, (5) cools and lubricates the drill stem and bit, and (6) facilitates the
collection of geologic data.14 Cuttings loosened by the bit are carried upward by the rising mud.
No casing is required during the drilling process but is added later after the drilling is completed.
Advantages of mud rotary drilling include: (1) fast
and efficient means of drilling, (2) adaptable to a
wide variety of geologic conditions, (3) no
temporary casing is needed, (4) casing is installed
after drilling, (5) convenient access of geophysical
survey logging equipment (resistivity or gamma-
gamma).16 Disadvantages include: (1) drill rigs are
costly and high maintenance (2) poor sample
collection, (3) poor groundwater identification in
locating water bearing zones, (4) formation
plugging from the mud that may interrupt the water
flow in the aquifer and decrease water production in
the well, (5) complicated drilling fluid management
that requires a significant amount of water to mix
mud and maintain circulation, (6) need to remove
mud cake during well development, (7) problem of lost circulation in highly permeable
sediments or karst formations, and (8) increased development time.17
4. Dual-wall or Dual-tube Reverse Circulation
Dual-wall or Dual-tube Reverse Circulation rotary is another
adaptation of the air-rotary method of drilling (see Figure 6-9).
This method is mainly used for test wells, and depths of up to
1,000 feet (305 m) can be achieved.1 Instead of using a single
wall drill pipe, this drilling technique uses a specialized dual wall
drill pipe (see Figure 6-10). High-pressure air or water is
pushed/forced down the annular space between the inner and
outer pipes and the cuttings are lifted up the inner pipe.19
Continuous samples are discharged through a cyclone separator
assembly. A top-head
drive rotates the entire
drill string, including the
drill bit.
Several advantages of
dual wall reverse
circulation include: (1)
reduces erosion potential
of the borehole, (2) great
for sample identification,
and (3) better able to
recognize zones with
groundwater potential.20
Figure 6-8 - Typical mud rotary tri-cone button
bit, note ports used to circulate fluids.
Source: DTH Drilling Accessories
(www.gettechequipments.com)
Figure 6-9 – Dual-Wall Reverse
Circulation. Source: Groundwater
and Wells by Fletcher G. Driscoll.
Figure 6-10 – Typical dual-wall pipe used
in this drilling method. Source: UDWRi
(Jim Goddard) photo.
14
Disadvantages include: (1) limited to borehole diameters of 10 inches or less and (2) more
expensive than other drilling techniques.20
5. Dual Rotary
The dual rotary drilling method consists of two rotary
drives (lower and upper). The lower rotary drive
advances steel casing through unconsolidated
material. The top rotary drive contains a head that
simultaneously handles a drill string equipped with
either a down-the-hole hammer, drag bit, or tri-cone
bit.17 Figure 6-11 shows a typical dual rotary rig.
Cuttings are removed using air from the on-board
compressor and/or auxiliary compressor(s). High-
pressure air is pushed/forced down the inner pipe and
cuttings are lifted up in the annular space between the
inner and outer pipes. The casing can be advanced
ahead of the bit or the drill bit can be advanced ahead
of the casing for faster drilling.
Dual rotary rigs come in various sizes, including the
DR-12, DR-24, DR-24HD, and DR-40.17 The DR
stands for dual rotary and the number indicates the
maximum diameter (in inches) of the casing that can
be installed. Several advantages of dual rotary
include: (1) fast drilling speed, (2) can drill through
very coarse-grained material including boulders, (3)
installing and welding casing is efficient, (4) drill
holes can be drilled at an angle (up to 45 degrees),
and (5) samples are representative of the formation being drilled.17 The main disadvantage for
this drilling method is expense.
6. Flooded Reverse Rotary
Reverse circulation is another variation of
air-rotary drilling. It is more related to
mud rotary drilling than air rotary drilling
due to the fact that drilling fluid (mainly
water) is required. This method of drilling
is used for deep, large diameter, high
capacity wells in unconsolidated
formations.19 In reverse circulation
drilling, large table drive rigs utilize both
fluid and air. Instead of circulating the
drilling fluid through the pipe and up the
outside of the pipe (as in mud rotary), the Figure 6-12 – Flooded Reverse Circulation drill rig
drilling a culinary well. Source: UDWRi (Jim Goddard)
photo.
Figure 6-11 - Dual Rotary drill rig.
Source UDWRi (Jim Goddard) photo.
15
method is reversed. Fluid is supplied down through
the area between the wall of the hole and the drill
pipe and it is then sucked/blown up, together with
the cuttings, through the hollow drill stem and out a
discharge pipe to the surface (see Figures 6-12 and
6-13). Elevated hydrostatic borehole pressure and
low downhole velocity stabilizes the borehole to
where casing is not needed to keep the borehole
from collapsing.20
Reverse circulation generally requires mobilizing a
support vehicle, auxiliary vehicle, compressors, and
the drill rig (see Figure 6-14). The support vehicle
contains diesel fuel and water tanks for resupplying
the drill rig, as well as tools if maintenance is
needed on the rig. The auxiliary vehicle carries the
auxiliary and booster engines. These engines are
connected to the drill rig by high pressure air hoses
when drilling is in progress.
Several advantages of flooded reverse rotary
include: (1) sample recovery, (2) borehole stability
in unconsolidated deposits, (3) larger diameter/deep
holes without casing, and (4) screen and gravel
pack are used. Disadvantages include: (1) the rig
components are large and expensive, (2) risk of
borehole collapse, (3) a large water supply is needed,
(4) large mud pits are required, (5) more personnel
are required to operate the rig, and (6) drill sites can be inaccessible due to the large rig size.16
Figure 6-13– Schematic drawing of a Flooded
Reverse Circulation drill rig drilling a culinary well.
Source: UDWRi (Jim Goddard) photo.
Figure 6-14– Flooded Reverse Circulation drill rig drilling a culinary well with
compressors, etc. Also, notice the sound curtains in place to reduce the noise of the
drilling operation. Source: UDWRi (Jim Goddard) photo.
\
16
7. WELL PLUMBNESS AND ALIGNMENT
Plumbness is defined as the quality of being plumb and vertical, with an orientation toward the
gravitational center of the earth (see Figure 7-1). The plumbness of a well is determined by the
horizontal deviation (drift) from the center point at the top of the well, to the center point at the
bottom of the well. The American Water Works Association (AWWA) standard is common in
the water well industry and is widely used by municipalities, private utilities, industry, and
consultants. It allows a maximum horizontal drift of 2/3 the inside diameter of the well casing per
100 feet.21
Alignment is defined as the state of being arranged in a straight line. Alignment of a water well
refers to the path a well’s casing and screen take from the top of the well to the bottom of the
well. The alignment tolerance in the AWWA standard requires the free passage of a 40-foot
long section of pipe (called a dummy) with a width of no more than ½ inch less than the inside
diameter of the well. This test requires the dummy to freely pass through that portion of the well
where the pump will be set, with no binding or obstructions.21
Plumbness (deviation from the vertical) and alignment (straightness) of the well are issues of
importance with respect to the installation of a pump in the well. In particular, line shaft-type
pumps are much more sensitive to the alignment issue than are submersible pumps. With a
rotating shaft extending from the surface to the bowl assembly (sometimes hundreds of feet
down in the well), wells in which line shaft pumps are to be installed must be held to tighter
tolerances than wells with submersible installations.22
Plumbness and alignment of a well are never perfect. Conditions that cause wells to become
crooked or out of plumb include the nature of material being drilled, trueness of the well casing,
tension of the cable tool drilling line, and pull-down force on drill pipe in rotary drilling.10
Solutions for these problems vary as widely as do the conditions which cause the problems, but
generally with skill and reasonable care on the part of the driller during drilling and well
construction, the problems can be avoided. With the proper tools, preparation, and skill, wells
sufficiently straight and plumb for suitable pump installation and service can be constructed in
almost every situation.10
A basic plumbness and alignment standard and test might be that the completed well is
sufficiently plumb and straight so that there will be no interference with installation, alignment,
operation, or future removal of the permanent pump. The standard for acceptance would be that
the pump is successfully installed with sufficient clearance and does not touch the casing at any
time during installation. Good quality control by the driller should include a periodic check of
the plumbness of the cable or drill string suspended in the hole.10
A plumbness and alignment test may be specified as part of construction, with a standard that all
casings and liners be set round, plumb, and true to line as defined by the specifications.
The test for plumbness and alignment is made following construction of the well, and before test
pump equipment is installed. Any test or tests for acceptance should be part of the written
specifications for well construction.10
17
Figure 7-1 – A plumb hole is one that follows a vertical
line from the ground surface to the earth’s center.
Source: Groundwater and Wells by Fletcher G. Driscoll.
18
8. WELL CASING
Casing is an important component in
well construction. The best well casing
is standard seamless steel (see Figure
8-1). “All steel casing installed in
Utah shall be in new or like-new
condition, being free from pits or
breaks, clean with all potentially
dangerous chemicals or coatings
removed…” and “shall meet or exceed
the minimum American Society For
Testing And Materials (ASTM),
American National Standards Institute
(ANSI), or American Water Works
Association (AWWA) standards for steel pipe …”.3 Steel casing must have a specified wall
thickness depending upon its diameter and depth of placement in the well (see Table 1). The
most common materials from which casing is made are carbon steel and plastic (most commonly
but not exclusively PVC). PVC casing used in water wells must be schedule 80 or SDR 17 or
thicker walled.
Table 1
Minimum Wall Thickness for Steel Well Casing
Depth
Nominal
Casing
Diameter
(inches)
0
to
200
(ft)
200
to
300
(ft)
300
to
400
(ft)
400
to
600
(ft)
600
to
800
(ft)
800
to
1000
(ft)
1000
to
1500
(ft)
1500
to
2000
(ft)
2 .154 .154 .154 .154 .154 .154 … …
3 .216 .216 .216 .216 .216 .216 … …
4 .237 .237 .237 .237 .237 .237 .237 .237
5 .250 .250 .250 .250 .250 .250 .250 .250
6 .250 .250 .250 .250 .250 .250 .250 .250
8 .250 .250 .250 .250 .250 .250 .250 .250
10 .250 .250 .250 .250 .250 .250 .312 .312
12 .250 .250 .250 .250 .250 .250 .312 .312
14 .250 .250 .250 .250 .312 .312 .312 .312
16 .250 .250 .312 .312 .312 .312 .375 .375
18 .250 .312 .312 .312 .375 .375 .375 .438
20 .250 .312 .312 .312 .375 .375 .375 .438
22 .312 .312 .312 .375 .375 .375 .375 .438
24 .312 .312 .375 .375 .375 .438 … …
30 .312 .375 .375 .438 .438 .500 … …
Figure 8-1 - Stockpile at well site of 20-inch diameter casing.
Note casing has beveled ends to facilitate welding.
19
Steel casing and plastic casing each have advantages and disadvantages as follows:
Steel has higher strength, it is suitable for all drilling methods, there are no impacts from heat of
hydration resulting from the curing of cement grouts, and wells can be deepened, repaired, and
redeveloped without damaging the casing. Steel casing does corrode over time yielding rusty
water.20
PVC is non-corroding, resulting in fewer water quality complaints, it costs less than steel casing,
and is more easily joined and installed. Plastic casing has lower strength, it cannot be driven but
only placed in open boreholes. Once in place the well cannot be deepened or aggressively
cleaned/rehabilitated without chancing damage.20
The terms casing and pipe are often confused. There is a distinguishing difference between pipe
and casing. Steel pipe is manufactured in cylindrical form, whereas steel casing is made
cylindrical by a fabricator from steel sheets or plates. Steel casing is fabricated to resist external
and vertical forces, while steel pipe is fabricated to resist internal burst forces.10
Casing is installed in wells for the following reasons: 1. To stabilize the walls of the borehole by preventing collapse.
2. To seal the well against infiltration of surface water and undesirable groundwater.
3. To allow groundwater access to the well through post placement perforations (cable-
tool wells).
4. To facilitate the installation of screen and gravel pack.
5. To provide a channel for conveying groundwater to the surface.
6. To provide housing for the pump and pump components.
Individual sections of steel casing
must be joined. The two most
common methods are welding and
threading. Welded casing joints are
aided by the presence of beveled
ends which helps to assure deep,
uniform seams (see Figure 8-2).
Plastic casing sections are joined
and made water-tight by the use of
solvent.10
Surface/conductor casing must be at
least 4 inches larger in diameter than
the casing that houses the pump. It
should extend to a depth of at least
100 feet for culinary wells, 30 feet
for other wells (see Figures 8-3 and 8-
4), and must be withdrawn during
placement of the surface seal, which shall consist of neat cement grout, sand cement grout,
bentonite grout, or unhydrated bentonite.3 This process prevents surface contamination from
moving downward, accessing the well, and it prevents artesian aquifers from leaking upward
around the well casing.3
Figure 8-2 - Welding steel casing sections together, prior to
being lowered into the well. Source: Steffl Drilling & Pump
(www.waterwelldrilling.com)
20
21
22
9. WELL SCREEN/PERFORATED CASING
To fulfill their function of providing access to groundwater in aquifers, wells must allow
groundwater to enter through their structural components (casing and/or screen). Once inside the
well groundwater comes in contact with the pump. To facilitate the movement of groundwater
into the well, various types of openings and methods of their fabrication have been developed.
Openings in steel casing can be installed either before placement in the well or after. Factory
slotted casing can be delivered to the work site for joining and placement in the well; in-addition
slots can be cut into the casing with a torch or saw after it has been delivered to the well site.
Casing that has been advanced as the well was being drilled, typically via cable tool or rotary rig
with a casing driver, can be perforated in place using a tool referred to as a Mills Knife or Mills
Perforator. For driven casing using an air rotary rig, a pneumatic perforator is used instead of a
Mills Knife. In addition, down-hole explosive shot perforators can be used to create openings in
steel casing. In some instances, the casing is left open on the bottom. Water enters the casing
through the open unplugged casing. Manufactured, continuous slot, wire-wrapped screen
(Figure 9-1) is installed after the well has been drilled.
In plans and specifications, the following
information is necessary:22
1. The type of screen:
a. Wire-wound, continuous slot screen (see
Figure 9-1) b. Factory slotted steel casing (see Figures 9-2
to 9-5)
c. Pneumatic, Mills Knife, or shot perforated
steel casing (see Figures 9-6 and 9-7)
d. Unplugged, open bottom production.
2. Aperture (slot/perf.) size, slot length, and
number of perforations per round per foot.
3. Diameter of the screen. (Doubling the screen
diameter provides about a 10% increase in
yield.)
4. Screen length. (Doubling the screen length can double the yield.)
5. Material of the screen:
a. Stain-less steel,
b. Carbon steel (casing)
c. PVC (plastic)
6. Method of installation:
a. Lowered into the well and secured by allowing the native aquifer materials to collapse
against it,
b. Lowered into the well and secured by placing engineered filter pack around it,
c. Lowered into the well and then pulling back the casing to expose screen and filter pack to
the aquifer,
d. Perforating in-place casing.
Figure 9-1 - Continuous slot, wire-wound
manufactured screen. Source: Hightop Metal
Mesh (www.wedgewire.org)
23
The most important functions of well screen include the following:
1. Allows water to enter the well,
2. Restricts sediment migration into the well (particularly sand-size particles),
3. Minimizes friction loss (well loss) in and near the well,
4. Determines/regulates entrance velocity.
The well owner and engineer will need to determine if perforated casing or well screen is better
suited for the particular well they are designing. Well efficiency, function, durability, and
operation are based on this important decision. The following are reasons that engineered screen
should always be considered first and foremost:
1. The amount of open space is much greater in engineered screen (such as wire-wound,
continuous slot screen). The most efficient well is one where the porosity of the aquifer
material is roughly equal to the open area (%) of the screen/perforation, which means the
screen is not an impediment to the flow of water into the well. About the only screen that
can come close to the porosity of a good sand/gravel aquifer (30%) is continuous slot, wire-
wrapped screen (Figure 9-1). Louver style, factory perforated screen is the next closest
(Figure 9-3)20.
Figure 9-2 - Factory perforated casing. This style
is a bridge perforation. Source: ZhongXin Slotted
Screen Eng. Co. (www.slotted-liners.com)
Figure 9-3 - Factory perforated casing. This
style is a louver perforation. Source: Water
Well Screens (www.alibaba.com)
Figure 9-4 - Factory slotted steel casing. Source:
Well Casing Slotted Screen Pipe (www.alibaba.com) Figure 9-5 - Factory slotted PVC plastic well
casing. Note threaded ends for coupling. Source:
Slotted Vent Pipe (www.farwestcorrosion.com)
24
2. Slot size of the wire-wound, continuous slot screen is based on lab tests (gradations) of the
coarse-grained sediment recovered from the aquifer during drilling.
3. Properly selected slot size inhibits the migration of filter pack and fine-grained sand into the
well.
4. Engineered screen with its increased open space over perforated casing (see Table 2) allows
for a lower entrance velocity and thus less erosion and movement of sediment into the well.
Figure 9-6 - Description of form and function of the driller’s tool know as a Mills Knife or
Perforator Knife. Perforates slots in in-place casing. Typical slot sizes range from 3/8 inch X
3 inches to 3/8 inch X 4 inches and up to much larger size 5/8 inch X 3 inches.
See Figure 9-7 for depiction of actual size slots.
Source: Mills Machine Company Inc. (www.millsmachine.com)
25
For small diameter screens covered with wire mesh, the number of openings in the mesh per inch
are designated by slot numbers.1 Some of the common slot number sizes for continuous wrap,
wire-wound screen are shown in Figure 9-8.
Figure 9-8 - Slot openings in thousandths of an inch
(Slot No.) for common sizes of screen openings.
Source: Groundwater and Wells by
Fletcher G. Driscoll
Figure 9-7 - Common size slots installed in casing using a mills
knife perforator. Drawn to scale.
26
In summary, screen is designed to decrease sand production while providing the maximum yield
possible for the well owner. The screen slot number size is selected based on sieve analysis of
samples collected during drilling. Well yield depends on the open area-per-foot of screen, the
length of the screen, and the design entrance velocity.23
Table 2 Comparison of Open Space in Perforated Casing
(Figure 9-9)
Versus
Continuous Slot, Wire-Wound Screen
(Figure 9-10)
Diameter of
Casing/Screen
Size of
Perforation
Open Space
Per Perforation
Perforated Casing
Open Space
Per Foot*
Screen
Slot Size
Wire-Wrap Screen
Open Space
Per Foot
12 Inch 3/8” X 3” 1.1 inch2 11 in2/ft 0.020 in. 69 in2/ft
16 Inch 3/8” X 4” 1.5 inch2 15 in2/ft 0.020 in. 68 in2/ft
18 Inch 5/8” X 3” 1.88 inch2 18.8 in2/ft 0.020 in 76 in2/ft
*10 perforations per round per foot
Figure 9-9 - Mills knife perforated casing with
limited open space and no sand filtering.
Source: Clear Creek Associates
(www.clearcreekassociates.com)
Figure 9-10 - Engineered, continuous slot, wire-wrapped
screen. Maximum open space. Inhibits sand production.
Source: UBO Wedge Wire Screen (www.ubowedgewire.com)
27
10. ARTIFICIAL FILL MATERIAL
Once the well is drilled and screen and casing have been placed, gravel and/or coarse-grained
sand is introduced to occupy the annulus (space between the well screen, well casing, and
borehole wall, see Figure 8-3). Wells with no annulus such as those with driven casing (cable-
tool and air rotary rig with a casing driver) cannot accept artificial fill (see Figure 8-2). The
exception would be if screen is placed inside driven casing, then the casing is pulled back to
expose the screen, providing an annular space that could accept gravel fill. Two main reasons
exist for filling the annular space with engineered artificial fill:
1. The introduced material acts to stabilize and support the native material that makes up the
aquifer. This removes the tendency of the native materials to collapse against the screen and
casing and mitigates the possible damage that could result. When this is its primary purpose,
the introduced material is referred to as formation stabilizer.22
2. The engineered, introduced gravel serves to assist in filtering aquifer material, allowing only
the finest-grained sand, silt and clay size particles to be removed during well development,
while retaining the coarser sand-sized particles. In this instance, the artificially introduced
material is referred to as gravel pack or filter pack.22
Benefits of using properly sized, engineered gravel pack include:20
1. Having higher porosity materials next to the screen,
2. Provides higher hydraulic conductivity,
3. Increases yield,
4. Reduces entrance velocity,
5. Reduces drawdown,
6. Decreases sand production,
7. Results in faster development time,
8. Results in longer well life,
9. Results in easier grouting, and
10. Improves the effectiveness of any future well rehabilitation.
During the development process in a naturally developed well (where native materials are in
contact with the screen), the finer-grained sand, silt, and clay sized particles are removed from
the vicinity of the well screen, leaving a zone of coarser graded material around the well. This
cannot be achieved in a formation consisting of fine, uniform sand due to the absence of any
coarser material. The objective of gravel packing a well is to artificially provide the graded
gravel or coarser sand that is missing from the natural formation.11
The recommended procedure for determining appropriate grain size of the gravel pack is to
collect frequent, representative samples during drilling and then analyze them for grain-size
distribution (sieve analysis). This lab data is critical and is used to select both the appropriate
slot size for screen and also the best fit grain size for gravel pack. The gravel pack grain size and
gradation are designed by the project engineer to allow only the finest grains (fine-grained sand,
silt, and clay) to enter the screen during development, resulting in relatively sand-free water
being pumped during production.24 A rule of thumb is to design the gravel pack based on the
native formation material (sieve analysis), then design the screen based on the gravel pack for
90% retention. For a naturally developed well without gravel pack, designing the screen for
between 40% and 50% retention if the native material is uniform in size (well sorted).
28
The material chosen as filter pack is of utmost importance and needs to conform to the following
standards (see Figures 10-1 to 10-4): 10
1. Well-rounded grains that are smooth and uniform.
2. Contains no more than 2% by weight of angular materials that have flat surfaces, are thin or
elongate in shape.
3. Its composition should contain no less than a minimum of 95% siliceous material (quartz-rich
material). It should not contain more than 5% of calcareous material (limestone, calcite).
4. Individual particles need to be hard, having a Mohs Scale hardness of ≥ 7.
5. It should be dry, having first been washed clean to remove fine-grained silt and clay particles.
6. It should be uniform in size, unless a specific range in gradation is called for.
7. Prior to placement all filter material must be disinfected.
Figure 10-1 - Example of mostly rounded some
elongate but smooth gravel. High siliceous content.
Will be effective. Source: www.shutterstock.com
Figure 10-2 - Example of subrounded but smooth gravel
with some flat surfaces. Low siliceous content. Less
effective. Source: www.cranehardscapesupply.com
Figure 10-3 - Example of well rounded, smooth, uniform
sized gravel. High siliceous content. Will be effective.
Source: www.cranehardscapesupply.com
Figure 10-4 - Example of angular gravel. Flat
surfaces, ridges and corners. Will not be effective.
Source: www.stones4homes.co.uk
29
11. WELL DEVELOPMENT
Properly performed, well development improves the well in several very important ways:
1. Restores the physical characteristics of the aquifer to its pre-drilled condition, thus reversing
the effects of compaction, mud cake buildup, and infiltration of drilling fluids into the near-
well portions of the aquifer.24
2. Removes fine-grained material (sand, silt, and clay) from the aquifer near the well screen that
might otherwise enter the well and cause excessive wear on pump components.24
3. The filter pack and/or the native aquifer materials are disturbed sufficiently to cause the
coarser grained portion to settle around and stabilize against the screen or slotted casing.10
The expected, overall effect of well development is to increase well capacity by removing loose
material introduced during drilling, by loosening, or redistributing native materials compacted by
drilling and installation of casing, screen, and filter pack, and by removing fine-grained material
from the vicinity of the well screen.24
Among the commonly used and most effective methods of well development are the following:
1. Bailing – Repetitive use of the bailer, entering and exiting the well, loosens and removes
fine-grained material such as sand, silt and clay, and drilling fluid from the aquifer adjacent
to the perforated or screened intervals of the well. This well development method also
removes sediment suspended in the well. Bailing has the potential of damaging continuous
slot, wire-wound screen. It is most effective in cased wells where the aquifer is composed of
relatively clean, fines depleted, and permeable materials.24 This method is generally only
used with a cable tool drill rig (see Figure 11-1).
Figure 11-1 - Dart valve and flapper valve style of bailers.
Source: Jim Goddard, Basic Water Well Design & Construction Part 1
30
2. Mechanical surging – This method employs the use of a
tool called a swab or surge block (see Figure 11-2). It is a
frequent method of well
development used with
cable tool or rotary drill
rigs.24 The repetitive
plunging action of
raising and lowering the
surge block in the well
forces water out into the
aquifer and then draws
the water back in. This
method of well
development minimizes
the stress to the aquifer
by uniformly
distributing the force
applied over the entire
open interval of the
well.24 Mechanical surging
loosens and removes fine-
grained material from the
aquifer and gravel pack,
pulling it into the well (see
Figure 11-3). To avoid sand-locking of the surge block
during development, surging starts at the top of the screened
interval and progresses downward to the bottom of the lowest
screen in the well.10 This procedure is repeated as
necessary.24 Loose materials in the well are subsequently
removed by use of a bailer or pump.
The most effective surging with a cable tool rig is by using a double-swab arrangement. A
swab or surge block is placed at each end of a ten-foot section of perforated pipe (see Figure
11-4). This tool is attached to pipe and lowered into the well to the level of perforated casing
or screen. The double swab is lifted up and down (typical cable tool motion). The turbid
water and sediment that is generated can be removed from the well via air lift or submersible
pump.
3. Pumping with Backwashing – Repetitive cycles of pumping followed by backwashing is an
effective method of well development. Pumping induces water, fine-grained material, and
drilling fluid to flow from the aquifer into the well. Backwashing, which occurs when the
pump (without a check-valve or foot-valve) is turned off, allows the water in the pump line to
Figure 11-2 - Typical surge block
used during well development to
remove sand and turbidity. Source:
Groundwater and Wells by Fletcher
G. Driscoll
Figure 11-3 - Well cut-away
showing surging action pulling
sand and silt into the well.
Source: Groundwater and Wells
by Fletcher G. Driscoll
31
fall back into the well, causing an outward surging of water into the aquifer.10 Backwashing
helps prevent bridging of groups of particles in the native materials of the aquifer or within
the filter pack.11
4. High Velocity Hydraulic Jetting – Treating the screen, filter pack, and aquifer with high
velocity jets of water directed horizontally through the screen openings is generally
considered to be the most effective method of well development.10 The effectiveness of this
method is increased if it is coupled with pumping water from the well at the same time that
the jetting operation is in progress.11 By pumping more water out of the well than is being
added by jetting, flow will be induced into the well from the aquifer and filter pack, thus
bringing the loosened and dislodged material into the well. This speeds up the development
process and makes it more efficient.11 The high velocity hydraulic jetting method is more
effective in wells constructed with continuous slot, wire-wound screens. The greater
percentage of open area in this type of screen permits a more effective use of the jet in
disturbing and loosening formation material, remaining drilling fluid, and mud cake over the
jetted water being dissipated by impinging on the solid areas of slotted casing.11 Jetting
should begin at the bottom of the screened interval and proceed toward the top. The tool is
Figure 11-4 - Double swab/surge block method of well development. Source: Roscoe Moss Company
32
rotated slowly and positioned at one level for not less than two minutes. The tool is then
moved upward to the next level, not more than six inches vertically from the previous jetting
level.10 This is a highly effective method of well development but it is rarely used due to its
high cost.
5. Air Lift – This form of development is very common with air rotary rigs. The drill pipe is
lowered into the well and the compressed air is turned on. This lifts, agitates, and blows
water out of the well (see Figure 11-5). This is continued at levels within the screen until the
water clears up (see Figure 11-6).
6. Chemical Treatment – During the development process, chemicals can be introduced to help
break up polymers, drilling mud, clay, and mud cake. Dispersants break down drilling fluids
and allow mobilization of residual clay-sized particles. Surfactants reduce the surface
tension of water, allowing for easier penetration of water-based chemical mixtures. Acids
chemically break apart encrustations upon and within the well screen structure and native
aquifer materials. Chlorine disinfects well components.
An important part in any well development method is that the work should be started slowly and
gently, then gradually increased in vigor as the well is developed.8 After the casing, screen, and
filter pack have been installed, one or more methods of development are employed. The
development phase is considered complete when specific capacity is stabilized, well efficiency is
maximized, turbidity is minimized, sand concentration is less than 5 ppm (Rossum Sand Tester
should be required), and when water quality parameters including temperature, pH, electrical
conductance, and total dissolved solids stabilize.20
Development of the well is a critical last step in well construction. Sufficient time and energy
should always be devoted to this step. The key to good well development is to impose both
Figure 11-5 - Air lift development after 30
minutes, yields turbid water carrying sediment.
Source: USGS
(pubs.usgs.gov/sir/2005/5065/htdocs/body1.html)
Figure 11-6 - Air lift development, in same well
after 4 hours yields clean water.
Source: USGS
(pubs.usgs.gov/2005/5065/htdocs/body1.html)
33
inward and outward velocity through the screen, gravel pack, and/or native aquifer material. The
goal is to produce an inward velocity that will exceed the intake velocity produced by the
permanent pump. The objective is to remove the finer portion of the surrounding sand/gravel
envelope plus repair any damage caused by drilling, such as removal of mud or other drilling
fluids that may have migrated into the native aquifer materials (see Figure 11-7).23
Figure 11-7 - Well development methods remove mud cake and fine-grained silt and sand, located adjacent to
the screen or gravel pack. Appropriately sized screen and gravel pack inhibit sand migration into the well.
Source: Groundwater and Wells by Fletcher G. Driscoll
34
12. PUMP TEST
Pump tests provide information that is useful in the long-term operation and maintenance of
wells, such as pumping rates versus drawdown (specific capacity), well efficiency, sustained and
transient yield, pump depth setting, and aquifer hydrologic characteristics. The type of tests
chosen are dependent upon the information desired, intended use of the well, costs, and logistical
considerations.10
There are several types of pump tests that can be conducted on a test well/production well. The
most common are:
1. Step Drawdown Test (also called Variable Rate Test) – In this test, a variable speed pump is
used and the well is pumped at three or more rates. Typical rates designated in step
drawdown tests are 1/3, 2/3, and full design rate. Other rates commonly designated are 1/2,
3/4,
full design rate, and 11/2 times the design rate. Pumping continues for each step/rate until
drawdown stabilizes. Once drawdown has remained stable for a specified period of time, the
flow is increased and pumping at the next step/rate commences.22
2. Constant Rate Test – For this test, pumping should commence and then continue at a
uniform rate of discharge until the cone of depression stabilizes or during expansion it
touches and responds to any boundary conditions that could affect future performance of the
well (either recharge boundary or discharge boundary). Typically, the duration of this test
does not exceed 24 hours for wells in confined aquifers (artesian conditions) and 72 hours for
wells in unconfined aquifers (water table conditions).10
3. Recovery Test – Recovery test measurements allow the transmissivity of the aquifer to be
calculated, thus providing an independent check of the pump test results. Recovery test
measurements are more reliable than pump test data because recovery occurs at a constant
rate, whereas a constant discharge during pumping is often difficult to achieve in the field.
During pump tests, pumping rate and water level measurements are taken and recorded at set
intervals as designated in the specifications (see Figures 12-1 to 12-3). Typical measurements
occur at set time intervals such as every 1 minute for the first 10 minutes, every 2 minutes for the
next 10 minutes, every 5 minutes for the next 40 minutes, every 15 minutes for the next hour,
every 30 minutes for the next 3 hours, and hourly for the remainder of the pump test.
The correlation of discharge rate in gallons per minute (gpm) and magnitude of drawdown (in
feet) provide a basis on which to purchase a permanent pump for the well. Pump test data give
guidance to determine the depth at which the pump must be set, the size of the pump required,
and the horsepower needed. Pumps are expensive and their selection and purchase should not be
made based on assumed conditions.2
Every properly conducted pump test will include a recovery test. The recovery test begins the
instant the pump is turned off at the conclusion of the pump test. Recovery measurements of the
rising water level in the well are to be recorded at the same frequency as those taken during the
pumping portion of the test.1 To ensure the most accurate recovery level measurements, a foot
valve must be installed so that at the conclusion of the pump test, when the pump is turned off,
the column of water in the casing does not fall back into the well. Following the pump and
35
recovery tests, a temporary metal cap is welded to the top of the well casing until the permanent
pump is ready for installation.
Figure 12-1 - Pump test, Garfield School District Well
near Escalante, Utah.
Figure 12-2 - Pump test, Burr Desert Exploration Well
south of Hanksville, Utah. Note observation well in
background.
Figure 12-3 - Pump test, Fountain Green Irrigation Company Well, Fountain Green, Utah.
36
13. GLOSSARY
Annular Space (Annulus) – The space between the casing and/or screen and the wall of the
borehole or outer casing.
Aquifer – A water-bearing layer of unconsolidated sediment or bedrock that will yield water in
usable quantities to a well.
Aquiclude –A body of relatively impermeable unconsolidated sediment or bedrock that is
capable of absorbing water but will not transmit it in usable quantities to a well or spring.
Aquitard – A body of impermeable unconsolidated sediment or bedrock into and through which
no water moves.
Artesian Well – A well deriving its water from a confined aquifer in which the water level
(potentiometric surface) stands above the local water table.
Bailer – A length of pipe that is lowered into the well to retrieve water and sediment samples
from a borehole. Used primarily in cable tool drilling.
Basin-Fill – Most frequently refers to the unconsolidated sediment deposited in basins,
consisting of clay, silt, sand, gravel, cobbles, and boulders.
Bedrock – Rock that either lies under unconsolidated sediments or outcrops on the surface.
Caliper log – Type of geophysical log that measures the diameter of the uncased borehole.
Cone of Depression – A depression in the water table or potentiometric surface that has the
shape of an inverted cone and develops around a well from which water is being withdrawn.
Confined Aquifer – A water-bearing layer of unconsolidated sediment or bedrock in which the
groundwater is isolated below or between impermeable (clay rich) layers. In this setting,
groundwater is subject to pressure greater than atmospheric.
Confining Layer – A layer of unconsolidated sediment or a layer of bedrock of impermeable or
distinctly less permeable material that lies above and/or below one or more water-bearing zones
or aquifers.
Consolidated – Pertains to the solid or bedrock aquifers.
Drawdown – Lowering of water level in a well caused by pumping. It can also be stated as the
distance between the static water level and the surface of the cone of depression.
Drilling Fluid – A fluid that aids in the drilling of boreholes. Types of fluids that are used
include: air, water, and clay slurry.
37
Flowing Well – A well deriving its water from a confined aquifer in which the water level
(potentiometric surface) stands above the ground surface and thus flows freely.
Gamma log – A geophysical log where quantities are measured from naturally occurring
radiation coming from sediment surrounding the borehole.
Groundwater – Water present in the saturated zone of an aquifer.
Jetting – A method of well development where high velocities of water are directed horizontally
through the screen openings to loosen formation material, drilling fluid, or mud cake.
Karst – Subsurface topography created due to the dissolution of soluble rocks such as limestone.
Mohs Scale – A scale that characterizes the hardness of minerals based on their scratch
resistance. Magnitudes range from 1, the softest mineral (talc) to 10 the hardest mineral
(diamond). Quartz has a hardness of 7 and because of its durability makes the best gravel or
filter pack material.
Mud Cake – In mud rotary drilling, it is the layer of mud mixed with drill cuttings that adheres to
the borehole wall.
Neutron log – Type of geophysical log that measures the total porosity of the sediment under
saturated conditions.
Normal-resistivity log – Type of geophysical log that measures the electric properties of the
formation. These logs help identify permeable zones.
Perched Aquifer – Groundwater in an unconfined aquifer of limited lateral extent that is
separated from the main aquifer by a layer of impermeable (clay-rich) sediment.
Permeability – The capacity of a porous medium to conduct or transmit fluids.
Porosity – The voids or openings in a rock or sediment whether interconnected or isolated.
Potentiometric Surface – An imaginary surface representing the total head of groundwater in a
confined aquifer that is defined by the level to which water will rise in a well.
Sieve Analysis – Also known as a gradation test, is a procedure to evaluate the particle size
distribution of unconsolidated material, such as clay, silt, sand, or gravel. It provides the basis
for determining the particle size (gradation) of the artificial fill and for slot size of the screen.
Soil Stratigraphy – Natural layering in basin-fill sediment that results from deposition of eroded
material.
Specific Capacity – The rate of discharge of a water well per unit of drawdown, commonly
expressed in gpm/ft. It varies with duration of discharge.
38
Spontaneous potential log – Type of geophysical log that measures the electrical potentials that
result from chemical and physical changes at geologic contacts.
Surge Block – A flat seal that fits the casing interior and is operated like a plunger beneath the
water table.
Static Water Level – The level of water in a well that is not being affected by discharge.
Unconfined Aquifer – An aquifer where the water table is exposed to the atmosphere through
openings (such as wells) in the overlying sediment.
Unconsolidated – Pertains to sediment. The loose mantel of native materials that overlies
bedrock.
Water Table – The upper surface of groundwater in the saturated zone where the pressure is
equal to atmospheric pressure.
39
14. REFERENCES
1 Driscoll, F.G., 1986, Groundwater and Wells 2nd Edition; Johnson Screens, 1,089 pgs. 2 Shupe, Clarence, G., 1958, Drilling Wells For Ground Water Development. 3 State of Utah, 2011, Water Well Handbook. 4 NGWA at www.ngwa.org , accessed March 28, 2016. 5 Guidelines For Applicants Seeking Financial Assistance From The Board Of Water Resources,
at www.water.utah.gov/Board/MakeApp.html , accessed March 14, 2016. 6 Jensen, M.E., 2004, “President’s Message in Groundwater in Utah: Resources, Protection, and
Remediation”; Utah Geological Association Publication 31. 7 Division of Water Resources, 2014,”State of Utah Municipal and Industrial Water Supply and
Use Study Summary 2010”, 149 pgs. 8 Division of Water Resources, 2005, “Conjunctive Management of Surface and Groundwater in
Utah”, Utah State Water Plan, 115 pgs. 9 Burden, C.B. and others, 2015, “Groundwater Conditions in Utah, Spring 2015”; U.S.
Geological Survey, Cooperative Investigation Report No. 56, 136 pgs. 10 NGWA, 1998, Manual of Water Well Construction Practices 2nd Edition. 11 Gibson, U.P., Singer, R.D., 1971, Water Well Manual; Premier Press, 156 pgs. 12 Harter, Thomas, 2003, Water Well Design and Construction; Publication 8086 University of
California, Division of Agriculture and Natural Resources. 13 Todd, D.K., 1980, Groundwater Hydrology Second Edition. 14 State of Michigan, Water Well Drilling Methods: Online accessed March 8, 2016
www.michigan.gov/documents/deq/deq-wbdwehs-gwwfwim-section5_183030_7.pdf 15 Treadway, Carl, 1991, “Cable Tool Drilling, A viable drilling method for constructing
monitoring wells”: Water Well Journal, p. 56-59. 16 International School of Well Drilling Methods: Online accessed March 8, 2016
www.welldrillingschool.com/courses/pdf/DrillingMethods.pdf 17 Foremost Industries, LP, 2003, Benefits of Dual Rotary Drilling in Unstable Overburden
Formations: Online accessed August 1, 2016.
www.pierregagnecontracting.com/images/dr_benefits.pdf 18 Culver, Gene, “Drilling and Well Construction”: Oregon Institute of Technology TP65, p. 129-
163: Online accessed July 29, 2016.
www.oit.edu/docs/default-source/geoheat-center-documents/publications/geothermal-
resources/tp65.pdf?sfvrsn=2 19 Strauss, M. F., Story, S.L., and Mehlhorn, N.E., 1989, Applications of Dual-Wall Reverse
Circulation Drilling in Ground Water Exploration and Monitoring: Online accessed August 17,
2016. www.info.ngwa.org/GWOL/pdf/891149283.PDF 20 Goddard, Jim, Basic Water Well Design & Construction (Parts 1-3) Presentation: Utah
Division of Water Rights training. 21 DePonty, DePinto, Kornrumph and Glotfelty, 2013, Plumbness and Alignment Standards-
Analysis and Recommendations for Operational Applicability.
40
22 Rafferty, Kevin, Specification of Water Wells; ASHRAE Transactions. 23 NGWA, Design and Construction of Wells 24 Lapman, W.D., Wilde, F.D., and Koterba, M.T., 1997, Guidelines and Standard Procedures for
Studies of Ground-Water Quality: Selection and Installation of Wells, and Supporting
Documentation: USGS WRIR 96-4233.
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15. APPENDIX
Examples of well logs
Submitted to the Utah Division of Water Rights
Format of well logs has changed over time.
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43
44
45
46
47