Introduction
As a benefit to members of the National Ground Water Association, this document provides best
suggested practices for water well drilling contractors on procedures to follow when managing
a flowing artesian well. The best preparation is to understand geologic conditions in the area.
If artesian conditions are known to exist, contractors need to be prepared for potential flow, plan
for off-site water discharge, and follow best practices.
Definitions
Artesian Well:
An artesian well is not necessarily a flowing well. Artesian implies there is a confining bed
and the water level (potentiometric surface) of the well rises above the top of the aquifer
(Figure 1). A flowing well means specifically that water flows out the top of the well without
the use of a pump.
Confined Aquifer:
A confined aquifer, also called an artesian aquifer, is one restricted by an impermeable layer
both on the top and bottom. The potentiometric surface in a well constructed in a confined
aquifer reflects the pressure exerted from being forced between two layers. The upper confining layer prevents the water from rising upward (confines the water) to the static water level
Figure 1. A confined aquifer condition with an artesian flowing well.
NGWA Best Suggested Practice
Managing a Flowing Water Well
Approved by NGWA
Board of Directors:
3/9/2010
of the aquifer. When an aquifer is found between two impermeable layers, both the aquifer
and the water are said to be confined.
Confining Bed:
A confining bed is a layer of geologic material with low permeability that restricts water
movement. There are two types of confining beds—aquitards and aquicludes. An aquitard is
a layer of geologic material that does not produce appreciable amounts of water, but may be
capable of transmitting water to adjacent aquifers. In other words, an aquitard slows the movement of groundwater, but does not prevent water from moving. An aquiclude is a formation
that does not allow any significant amount of water to pass through it.
Potentiometric Surface:
The level to which water will rise above the top of a confined aquifer. This is described as the
static water level of the confined aquifer.
Permeability:
Permeability is the ability of a formation to transmit water. It reflects the amount of interconnected spaces that exist in a formation. Generally, coarse, clean formations will have a higher
permeability than those that contain a mixture of sand and clay.
Porosity:
Porosity is the amount of void spaces in a rock or soil.
Unconfined Aquifer:
An unconfined aquifer does not have an overlying impermeable geologic layer above the aquifer (confining bed). In an unconfined aquifer, the level of water measured in a well reflects the
true water level in the aquifer. For this type of aquifer, the water table forms the upper surface
of the zone of saturation, and well water will not rise above the level of the water table without
pumping.
Unconfined aquifers usually occur near groundwater discharge regions such as rivers or
lakes. Rainwater enters/infiltrates/recharges the ground and reaches the water table following
a delineated path as represented by the solid flow lines in Figure 2. The dashed equipotential
Figure 2. An unconfined aquifer condition.
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lines in the figure are lines of equal water pressure or static water level. Artesian conditions
exist because the static water level is greater than the ground surface elevation. When these
conditions exist and the aquifer is punctured, pressure will bring water above the land surface
until equilibrium is reached.
Why Some Wells Flow and Resulting Implications
Many flowing wells are the result of aquifers confined by a confining bed such as clay or shale
when the potentiometric surface (static water level) is above the top of the aquifer and land surface.
Flowing wells may occur miles away from the nearest confining bed where the water surface rises
above the land elevation. Such water table flowing wells are usually found at lower elevations which
may be within groundwater discharge areas, potentially creating surface water bodies. These wells
are more likely to occur where there is significant relief in the land surface topography.
Water doesn’t actively discharge unless an opening exists in ground surface topography, such
as the case with a spring or a well. Soil adds too much frictional resistance, therefore confining
the ability of water to flow upward. The presence of a well replaces the geologic material and
thus eliminates most of the resistance to upward flow. It provides a conduit for the groundwater
to travel to the surface.
Most problems associated with flowing wells result from improper discharge controls. If the
well is improperly constructed or maintained when a well is valved to stop or reduce flow, water
may flow around the casing or come to the surface in the vicinity of the well. In these instances,
water may discharge along the outside casing area or near the well through porous soils either by
channeling, wetting, or flooding the soil around the well.
Unexpected Artesian Flowing Well Conditions
Sometimes artesian conditions are not discovered until they are found at the site while drilling. Flowing artesian conditions are realized when the borehole yields an instant flow (sometimes
preceded by a dramatic loss in drilling fluid). Three steps should be taken when these conditions
become evident: control the flow, secure the casing or borehole, and protect the rig.
The flow may be reduced by extending the casing near or above the artesian head pressure or by
increasing the density of water in the casing.
Identifying Artesian Flowing Well Conditions
Areas known to produce flowing artesian conditions can be managed by implementing a clearly
defined plan to deal with impending flow. Information is available from local and state records that
can aid in deciding if the area is prone to flowing wells. If information is not available in a specific
area, recognizing the geologic formations will simplify identification of flow zones.
Construction in Areas of Artesian Flow
When artesian conditions are expected, a general template can be applied to properly construct
a well. While this method should yield positive results, individual results may vary due to local
conditions. Check local regulations and code prior to implementing any plan.
Construction in a Confined Aquifer
Special well construction techniques for flowing wells should prevent upward flow of water along
the outside of the well casing. Figure 3 illustrates a step-by-step example of such construction. An
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Figure 3. Construction in a confined aquifer.
outer borehole should be constructed about halfway through the confining bed (A). Surface casing
is then installed and sealed in place with appropriate grout (B). An inner enlarged borehole is then
constructed through the remainder of the confining bed to the top of the aquifer (C). An intermediate
well casing should be set to the top of the aquifer and driven into the production zone and sealed in
place with appropriate grout (D). After the appropriate grout has set, an open drill hole is constructed
into the aquifer (E).
Construction in an Unconfined Aquifer
There is no confining bed in the water table. For rotary mud drilling, it may require circulating
a heavier than normal mud during drilling and using a temporary surface casing to prevent hole
collapse.
Flow Control with Drilling Mud
To control free-flowing wells, the driller can use drilling mud of sufficient weight to counteract
the pressures in the aquifer. When controlling pressure with drilling mud, it is imperative to keep
in mind that weight is the determining factor, not thickness. Mud thickness and weight are not
always directly related, so the two should not be confused.
One gallon of water weighs 8.34 pounds per gallon. Freshly prepared drilling mud that is
properly mixed will weigh about 9 pounds per gallon. A mud balance or other accurate weighing
system is essential to determining the weight of mud.
The first factor to consider when determining the weight of mud to be used is to identify the
height water will rise above the ground surface when the aquifer is tapped. Once the potentiometric level has been determined, the mud weight can be calculated. The formula for calculating the
required mud weight is: (1) determine the height (in feet) the water will rise above ground level;
(2) add this number to the depth (in feet) to the top of the flowing aquifer; (3) decide how far
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below ground level (in feet) the water in the well should be kept; (4) subtract this number from the
depth (in feet) to the top of the flowing aquifer; (5) then multiply the sum of adding the depth to
the flowing aquifer to the height the flowing water will reach by the number 8.34 (the weight of a
gallon of water); and (6) divide the product of the calculation in step 5 by the sum of subtracting
the distance below ground level for the fluid level in the well from the depth to the top of the
flowing aquifer.
Example: If it is found that the aquifer is 75 feet deep and water in the neighbor’s well rises
3 feet above ground and the fluid in the well is to be kept 2 feet below ground level, the new mud
weight would need to be 8.34 × (3 feet + 75 feet) divided by (75 feet – 2 feet) = 8.9 pounds per
gallon.
Flow Control with Packers
Flowing artesian pressure can sometimes be too strong for the techniques mentioned earlier and
an inflatable packer is needed to seal the borehole so the annular space can be grouted. The inflatable packer is installed in the well below the level of the annular space. The packer is installed on
a pipe which will provide a path for the water to continue to flow after the packer is inflated. The
pipe, with the packer, extends up and out of the well. A valve is installed on this pipe to control
the flow. When the packer is lowered to the correct location in the well, the packer is inflated. The
inflated packer prevents the water from flowing into the annular space. With the water no longer
flowing in the annular space, the grouts can be placed and allowed to set in the annular space.
Once the sealing grouts are secure in the annular space, the packer is deflated and removed. The
water can continue to flow from the well through the casing, but the flow around the casing has
been stopped.
Note: If the flow from the well is substantial, with the packer inflated and the flow from the
well controlled, a valve can be installed on the casing to accommodate the flow and pressure
(see Flow Control After Construction on page 6).
Casing Selection
All local, state, or federal regulations should be considered when considering casing selection.
Casing selection is determined by proper environmental consideration or driller application.
Various casing manufacturers offer tools to aid in the selection process for casing specific to your
situation and geologic conditions. Water quality will determine if use of PVC, fiberglass, stainless,
or black steel is more appropriate.
Construction—Annular Grouting
Large artesian flows may require special techniques to regain control including pressure grouting with neat cement, weighting agents in the grout to depress the flow, quicker setting cements
such as high-early, and accelerators such as calcium chloride or heated water. Using grout to fill
the annular space between the casing and open borehole has four main functions:
1.To provide support for the casing
2.To prevent fluid movement to the surface and between formations
3.To prevent pollution of fresh water formations
4.To prevent casing corrosion.
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Each sealing material has certain characteristics and distinctive properties; accordingly, one material may be especially suited for doing a particular job. The selection of the material must therefore
be based on the construction of the well, the nature of the formations penetrated, the material and
equipment available, the location of the well with respect to possible sources of contamination,
and the cost of doing the work. All work should be conducted in accordance with any local, state,
or federal regulations and code.
Flow Control After Construction
Uncontrolled flow from the well is undesirable and in many situations violates applicable codes.
Water flowing from a well normally will not have sufficient volume and/or pressure to provide for
the needs of the water system for which the well was constructed. A pump is required to provide
the volume and/or pressure to meet the requirements of the water system.
When the well has a limited head, extending the existing water well casing a few feet can overcome the head. The water will fill the casing to a level below the top of the casing and the flow out
of the well is stopped. In areas where freezing temperatures occur, the wellhead will have to be
protected from the freezing.
In situations where the head is such that it is not practical to extend the casing to the required
height but the flow and head is limited, a seal-type device can be installed in the casing to eliminate
the water flowing out of the casing. Normally these sealing devices will have a smaller diameter
pipe, with an in-line valve on the smaller pipe, penetrating the seal device. This arrangement allows
for the opening of the valve to allow water to flow from the well. The smaller diameter pipe provides
a means for controlling the flow of water from the well and significantly reduces the head pressure
on the sealing device. The sealing device is installed in the casing with the valve open. That allows
for the water to flow from the well, which reduces the pressure from the well to “push” the sealing
device out of the well. With the pressure reduced and the water being diverted away, the sealing
device can be installed and affixed in place. Once the sealing device is secure, the valve can be
closed and the water is stopped from flowing out of the well. If there is an approved use for the water
flowing from the well, this arrangement will provide that option. Since there will always be water in
the pipe from the valve down, that area will have to be protected from freezing.
In situations where the flow is substantial, a valve can be affixed to the casing to control the
flow.
Abandonment
In the situation where a flowing well must be abandoned, every effort should be taken to ensure
the aquifer remains in pristine condition, surface intrusion is not possible, and flow is arrested.
Once flow is under enough control to permit working in the well, final abandonment can proceed
after which the casing may be cut off at or below ground level.
The flowing artesian well with improperly sealed casing and with water escaping around the
outside of the casing either to the surface or to another formation presents a special problem.
Grout must be still for the initial set to take place, otherwise it washes out. A necessary first step
in bringing the flow under control is to establish a permanent seal between the casing and the point
or interval from which the water is escaping. In order to place this seal effectively, the flow must
be stopped or the water level lowered in the well. This can be accomplished by several methods.
The method or methods used will depend in part on the piezometric or shut-in pressure of the well
and the depth to which the water level must be lowered. Some of these are:
1. Pumping nearby wells, producing the same effect
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2.Setting an inflatable packer at the depth necessary to stop the flow and pump the sealing grout
through the packer to seal off the water-producing zone (see Flow Control with Packers)
3.Extending the casing to stop the water flow (see Flow Control After Construction).
In wells in which the hydrostatic head producing the flow is low and in which there is no escape
of water below ground, the movement of water can be arrested by extending the well casing to
an elevation above the artesian pressure surface. This permits the placement of the sealing grout.
Or the flow of artesian wells to be sealed can be stopped with neat cement or sand-and-cement
grout pumped in by tremie under pressure. Alternatively, a suitable well packer may be placed at
the bottom of the confining formation immediately overlying the artesian water-bearing zone, and
sealing finished with conventional cement-based grout placement.
Wells with large holes or little or no grout or surface casing may be initially controlled by running a liner with a packer or an interval packer to slow inflow, then proceeding with killing and
sealing by pressure cementing.
The sealing of abandoned wells that have a rapid or high-volume movement of water between
aquifers or to the surface requires special attention and ingenuity, and should be conducted by a
water well contractor familiar with this type of work. The movement of water may be sufficient
to make the sealing with ordinary materials and by the usual methods impractical. Methodologies
such as a well packer or bridge may be used to restrict the flow, thereby permitting the placement
of appropriate sealing material (see Flow Control with Packers). If preshaped or precast plugs
are used, they should be several times longer than the diameter of the well to prevent tilting.
Any material used should be permanent and safe to leave in a potable water aquifer.
References (updated August 24, 2010)
Abbott, David. The Well Discussion. May 22, 2009.
Gaber, Michael S. Flowing Well Handbook. Michigan Department of Environmental Quality, Water
Bureau, Drinking Water and Environmental Health Section, Well Construction Unit. 2005.
Gass, Tyler E. “Ground Water by Gass: Artesian Aquifers.” Water Well Journal, November 1976: 28-29.
Groenewald, Leon. “Sealing of an Unexpected Artesian Borehole.” Borehole Water Journal, 2004: 2-3.
Jenkins, Jonathan T. “Best Suggested Practices: Flowing Wells Working Session.” National Ground Water
Association Convention and Exposition. Orlando, 2007.
Moody and Associates Inc. and National Ground Water Association. Aquifer Impact Evaluation from Oil
and Gas Development in the Jamestown, New York Area. Westerville: NGWA Press, 1982, 61.
Riewe, Tom. “Flowing Wells: Why Some Wells Flow.” News Bits, September 1987: 6-7.
Simpson, Howard E. “Reducing the Flow of Artesian Wells.” The Johnson National Drillers’ Journal, 1933: 5.
Smith, Stuart A. “Well and Borehole Sealing: Importance, Materials, Methods, and Recommendations for
Decommissioning.” Ground Water Publishing. January 1994.
Water Well Journal. “Jeremiah’s Well: Artesian Wells.” July 1987: 30-31.
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This document was prepared as the result of regular meetings of a task group composed of representatives from among the NGWA membership and duly affected individuals. These included:
Anthony E. Gilboy
Bill Niemans
Jack Henrich, MGWC
James M. Frazee Jr.
John J. Surinak
John Pitz, CPI
Kevin J. Stover
Lawrence H. LaChance, MGWC
Lester Ehorn
Lloyd H. Johnson
Richard Peterson
Scott Woolley
Compiled by Jonathan T. Jenkins (NGWA Staff)
Disclaimer:
This publication is a collaborative effort to try to set forth best suggested practices on this topic but individual situations and local conditions may vary, so members and others utilizing this publication are free
to adopt differing standards and approaches as they see fit. The Association and professionals mentioned
on page 6 assume no liability or responsibility for the contents of this publication. Only qualified personnel shall conduct any testing or inspection of the water well system for which they are qualified.4 All data
collected during a water well system inspection shall be representative of conditions observed on the date
of inspection. All local, regional, state, and federal code and regulations supersede these guidelines in the
instance of conflicting information.
Qualified shall mean knowledgeable and licensed, certified, or registered.
Copyright © 2016 by National Ground Water Association Press
ISBN 1-56034-019-3
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Published by: NGWA Press
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