MONITORING WELLS
A “monitoring well” is an excavation that is drilled, cored, bored, washed, driven, dug, jetted, or
otherwise constructed to extract groundwater for physical, chemical, or biological testing. Any
excavation, regardless of the method of construction, depth, depth or lack of casing, or length of time the
excavation is used, is a monitoring well if the excavation is constructed to remove one or more samples of
groundwater for testing.
A monitoring well must be constructed by a registered monitoring well contractor or licensed well
contractor.
A permit is required prior to the construction of a monitoring well except for monitoring wells sealed
within72 hours of the start of construction. The permit requirements are located in Minnesota Rules,
part 4725.1830.
4725.6450 APPLICABILITY AND USE.
This part applies to monitoring wells as defined in Minnesota Statutes, section
103I.005, subdivision 14.
In addition to the general construction, repair, maintenance, and sealing
requirements in parts 4725.2010 to 4725.3875, a monitoring well must be
constructed, repaired, maintained and sealed in accordance with this part. A
monitoring well is exempt from the requirements in parts 4725.4050 to 4725.6050.
A monitoring well that is not in use must be sealed.
A monitoring well is “in use” if it is sampled on a scheduled basis.
STAT AUTH: MS s 103I.101; 103I.111; 103I.205; 103I.221; 103I.301; 103I.401;
103I.451; 103I.501; 103I.525; 103I.531; 103I.535; 103I.541; 103I.621; 144.05;
144.12; 144.122; 144.383; 157.04; 157.08; 157.09; 157.13
HIST: 17 SR 2773; 18 SR 1222; 33 SR 211
4725.6500 [Repealed, 17 SR 2773]
4725.6600 [Repealed, 17 SR 2773]
4725.6650 CONSTRUCTION OF MONITORING WELLS.
Subpart 1. Casing. Casing for a monitoring well must be steel or plastic casing
meeting the standards of parts 4725.2250 to 4725.2650, or stainless steel or flush
threaded polyvinyl chloride meeting the standards of this subpart.
A. A monitoring well may be constructed with flush threaded polyvinyl chloride
(PVC) casing if:
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(1) the screen intersects the surface of the water table at the time of
installation and the well is constructed so the joint between the two deepest casing
sections is above the surface of the water;
(2) the total depth of the monitoring well is 50 feet or less;
(3) the monitoring well is completed in unconsolidated materials; and
(4) the flush threaded PVC casing used meets the standards of ASTM F480-02,
and the standards in Schedule 40 as referenced in ASTM Standard D1785-04.
FLUSH THREADED CASING
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Flush-threaded casing may be used only in water-table (unconfined) aquifers. Flush threaded casing
may not be used below a perched aquifer.
The 50-foot distance refers to the maximum depth of the bore hole including casing, screen, and
gravel pack below the screen.
The entire well casing, screen, and gravel pack must be completed in unconsolidated materials.
Flush threaded casing must not be used in a well completed in bedrock.
Flush threaded casing may only be used for monitoring wells and environmental bore holes under
these conditions. It may not be used for other types of wells or borings such as remedial wells, and
may not be used under conditions other than those in (1) through (4) above.
The 2008 revisions required for the first time that flush threaded casing meet the ASTM F480
standard. This standard has been required for solvent-welded plastic casing since 1978.
It is recommended to use casing which meets ANSI/NSF Standard 61-2003e or the health effects
portion of ANSI/NSF Standard 14-2003. This provides some assurance that chemicals will not leach
from the casing and affect the water quality.
B. A monitoring well may be constructed with stainless steel casing meeting
ASTM Standard A312/A312M-04b, having at least ANSI Schedule 5 for welded
joints and ANSI Schedule 40 for threaded joints.
REQUIRED MARKINGS ON STAINLESS STEEL PIPE
American Society for Testing and Materials (ASTM)
STANDARD A312-86a
Pipe manufactured in conformance with this specification shall be marked with the following
information:
1. The manufacturer's name or brand;
2. The manufacturer's private identifying mark;
3. Identification of seamless or welded;
4. The specification number and grade; for grades TP304H, TP316H, TP321H, TP347H, TP348H, and
S30815; the marking shall also include the heat number and heat treatment lot identification; and
5. Pipe larger than NPS 4 shall include the weight.
Marking shall begin approximately 12 inches from the end of each length of pipe. For pipe less than
NPS 2 and pipe under 3 feet in length, the pipe's required information may be marked on a tag securely
attached to the bundle or box in which the pipes are shipped.
A table of ANSI pipe schedules is included in the appendix.
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Subp. 2. Grouting of annular space. The annular space of a monitoring well
must be grouted from ten feet or less above the screen or open bore hole to the
established ground surface according to part 4725.3050, except that no cuttings
from the bore hole must be added to the grout. Neat-cement or cement-sand grout
may terminate at the base of the manhole or vault for an at-grade installation.
The grouting requirement applies to all monitoring wells constructed by a method which creates an
annular space (auger, rotary, etc.). Casing may be driven if the driven casing is installed in accordance
with Minnesota Rules, part 4725.3050.
Unlike other wells and borings, cuttings may not be used to grout a monitoring well or cased
environmental bore hole.
The provision to allow neat-cement or cement-sand grout to terminate 6 inches below a vault or manhole
is to prevent frost damage to the well and vault.
Bentonite chips may be used in place of bentonite pellets as an intermediate seal between a gravel pack
and the grout. It should be noted that this is the only permitted use of bentonite pellets or chips. Chips or
pellets may not be used to seal or grout a well or boring.
Grout must not be poured; it must be emplaced through a tremie pipe, except where the depth of the space
to be grouted is 10 feet or less.
Subp. 3. Exception to drilling fluids. Drilling fluids used to construct a
monitoring well must comply with part 4725.2950, except that a free chlorine
residual is not required.
Monitoring wells may be constructed with drilling water which does not contain a free chlorine residual
and the wells do not have to be disinfected upon completion. However, bacteria, including iron or other
slime-producing bacteria, are usually introduced into a well when constructed. These bacteria can lead to
erroneous water quality results, bio-fouling of the well, and decreased well life. Disinfection can greatly
reduce these problems.
Subp 4. Screen or open hole across an unconsolidated formation and bedrock
contact. A monitoring well, that is constructed to monitor contaminants at the
water surface, by placing a screen or open hole across the contact of an
unconsolidated formation and bedrock according to part 4725.6050, subpart 3, is
exempt from part 4725.2020, subpart 1.
STAT AUTH: MS s 103I.101; 103I.111; 103I.205; 103I.221; 103I.301; 103I.401;
103I.451; 103I.501; 103I.525; 103I.531; 103I.535; 103I.541; 103I.621; 144.05;
144.12; 144.122; 144.383; 157.04; 157.08; 157.09; 157.13
HIST: 17 SR 2773; 18 SR 1222; 33 SR 211
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4725.6700 [Repealed, 17 SR 2773]
4725.6750 [Repealed, 17 SR 2773]
4725.6755 PROTECTION OF MONITORING WELLS.
Subpart 1. Casing, protective casing, and capping. The inner casing of a
monitoring well, and when installed, the protective outer casing as specified in
subpart 2, item B, with bentonite grout in the annular space, must be covered with
a cap or cover in accordance with part 4725.2250, subpart 17. The protective
outer casing may be covered with an overlapping cap or cover without a
compression gasket.
Both the casing and the protective casing must be capped or covered in accordance with Minnesota Rules,
part 4725.3150, which requires a weatherproof and insect proof threaded connection, welded connection,
rubber expansion sealer, bolted flange with rubber gasket, overlapping cap with compression gasket, or
pump. Either the protective casing (“pro-top”) or the casing (“riser”), but not necessarily both, must be
secured with a tamper-proof closure consisting of a locked cap, or wrench-tightened, threaded metal cap.
The casing must be covered with a watertight cap. “J”-plug type compression seals are allowed.
A monitoring well is not required to be vented but may be vented if desired. Vents must comply with the
water supply venting requirements of part 4725.5450. The practice of drilling a hole in the casing or cap
to vent the well is not approved.
A. Either the inner casing, or the protective outer casing must be closed with a
watertight, locked cap or a wrench-tightened, threaded metal cap.
Either the casing or the outer protective casing must have a locked or threaded metal cap; it is not
required that both caps be metal.
B. The top of the well must be constructed to prevent entry of flood waters
according to part 4725.4350, subpart 2.
These requirements apply only to monitoring wells and cased environmental bore holes located within the
designated 100-year flood plain.
The requirements in this subpart do not apply to a well located in an area protected by a flood control
structure accepted by the United States FEMA, as designated on a FEMA flood map
The “regional flood level” is the 100-year flood level. “Regional flood level” is defined in Minnesota
Statutes, section 103F.111, subdivision 10, to mean a flood that is representative of large floods known to
have occurred generally in the state and reasonably characteristic of what can be expected to occur on an
average frequency in the magnitude of a 100-year-recurrence interval. The regional flood is often referred
to as the “100-year flood.”
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Minnesota Rules, part 4725.4350, subpart 2 requires:
A. Extending the casing at least 5 feet above the regional flood level. Wells may also be completed by
installing a casing coupling 2 feet above the ground surface and extending the casing 5 feet above the
regional flood level. The casing extension may be removed for service. Pump wires may exit the
casing immediately below the coupling through a watertight connection;
B. Installing a watertight seal and extending the casing 10 feet above the established ground surface, if
the regional flood level is more than 5 feet above the established ground surface;
C. Installing an outer, neat-cement grouted protective casing in accordance with Minnesota Rules,
part 4725.6755 subpart 2, item B, extending the protective casing and well casing a minimum of
2 feet above the established ground surface, and installing a waterproof threaded cap or a waterproof
compression seal with drawbolts and a one-piece top plate on both casings. At-grade installations are
permitted when equipped with a waterproof vault and cap. Overlapping, nonthreaded caps; O-ring
seals; and nontapered threads, such as flush threads, are not permitted; or
D. Extending the casing a minimum of 2 feet above the established ground surface, installing a sealed
spool, or flowing well pitless unit, and installing a waterproof, nonvented compression seal with
drawbolt(s) and a compression gasket. Electrical wires must exit through a watertight compression
fitting. Packers or drawdown seals are not equivalent protection.
C. A monitoring well cased with plastic must be protected with an outer steel
protective casing as specified in subpart 2, item B.
Subpart 2, item B requires an outer, steel-protective casing. There are two exceptions to this requirement:
● This requirement does not apply to at-grade wells.
● A plastic casing may be protected by a concrete pyramid as described in subpart 2, item A if the
pyramid incorporates a Schedule 40 steel outer protective casing. Using this method, the steel casing
does not have to extend 4 feet below ground; instead it must extend at least to the base of the
pyramid.
Three posts are not equivalent to the grouted, protective casing or pyramid for plastic casing.
The options for capping are found in Minnesota Rules, part 4725.3150, and include a weatherproof and
insect proof threaded connection, welded connection, rubber expansion sealer, bolted flange with rubber
gasket, overlapping cap with compression gasket, or pump.
Subp. 2. Protection. A monitoring well must be protected by:
Every monitoring well (except at-grade wells) must be protected by one of three methods: concrete
pyramid, steel outer casing, or three posts. A diagram of the three methods follows item “C.”
A. surrounding the casing with a concrete pyramid or cone that has horizontal
dimensions of at least 24 inches by 24 inches at the established ground surface,
that rises 12 inches above the established ground surface at the casing, and has a
base with a mass of at least three cubic feet below the established ground surface;
B. installing a steel outer casing meeting the material standards of part
4725.2350 that is at least 3.0 inches in diameter greater than the inner casing, that
extends at least two feet above and four feet below the established ground surface,
and that has bentonite grout, neat-cement grout, or cement-sand grout in the
annular space between the casings from the bottom of the outer casing to the
established ground surface; or
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C. placing three posts at least four inches square or four inches in diameter
around the well at equal distances from each other and two feet from the casing.
The posts must extend two feet above and four feet below the established ground
surface or to a depth of two feet if each post is set in concrete to a depth of two
feet. The posts must be made of reinforced concrete, decay-resistant wood, or
ASTM Schedule 40 steel pipe capped with an overlapping, threaded, welded steel
or iron cap, or be filled with cement.
Standard dimension 4 x 4’s (which measure 3-1/2” x 3-1/2” inches) are acceptable.
STAT AUTH: MS s 103I.101; 103I.111; 103I.205; 103I.221; 103I.301; 103I.401;
103I.451; 103I.501; 103I.525; 103I.531; 103I.535; 103I.541; 103I.621; 144.05;
144.12; 144.383; 157.04; 157.08; 157.09; 157.13
HIST: 17 SR 2773; 33 SR 211
378
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4725.6775 REPAIR; SEALING OF MONITORING WELL.
A monitoring well owner must repair or seal a damaged monitoring well within
seven days after the property owner becomes aware of the damage.
The property owner is responsible for well repair and sealing unless a written agreement exists between
the property owner and well owner in accordance with Minnesota Statutes, section 103I.205,
subdivision 8, and Minnesota Rules, part 4725.1830, item D. The requirements for well repair are found
in Minnesota Rules, part 4725.3750.
STAT AUTH: MS s 103I.101; 103I.221; 103I.301; 103I.621; 144.05; 144.12;
144.383; 157.04; 157.08; 157.09; 157.13
HIST: 17 SR 2773
4725.6800 [Repealed, 17 SR 2773]
4725.6850 AT-GRADE MONITORING WELL.
Subpart 1. At-grade termination. A monitoring well must terminate at least 12
inches above the established ground surface unless the commissioner determines
that no location exists for such a well to provide monitoring information equivalent
to an at-grade well.
A permit must be submitted and approved prior to constructing a monitoring well or converting an
existing monitoring well to at-grade. The permit application for an at-grade well must contain a map
showing the location of the at-grade well and providing documentation as to why the well cannot be
completed above-grade and as to the traffic hazard presented by an above-grade completion.
Monitoring wells may terminate at-grade in flood areas subject to the conditions detailed in Minnesota
Rules, part 4725.6755.
Subp. 2. Termination location; map. A monitoring well casing may terminate atgrade only on a roadway, sidewalk, driveway, or a parking area. The location of
the well identified by unique well number must be marked on a scaled map with
angles and directions from surveyed property corners, a permanent benchmark, or
the corners of a permanent structure. The map must be submitted to the
commissioner with the well record
At-grade wells are allowed only on areas with vehicular traffic. This includes paved or gravel roads
with vehicle traffic, ramps or sidewalks with wheelchair traffic, or airport runways or taxiways, where
termination of the casing above-grade creates a safety hazard that cannot be mitigated. At-grade wells are
not allowed at locations which do not have vehicular traffic such as grassed or “green” areas like
boulevards or lawns. At-grade termination may be allowed by variance in situations such as athletic
playing fields, or on certain rights-of-way where above grade termination presents a safety hazard.
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Minnesota Statutes, section 219.50, prohibits obstructions within 8-1/2 feet of the center line of a railroad
track. At-grade monitoring well, remedial well, environmental bore hole, and dewatering well casing
termination will be allowed within 8-1/2 feet of the track center line without a variance.
The at-grade well location map must be submitted with the well construction record. It is not required to
survey the location, but it is required to provide accurate measurements of the well location in relation to
permanent landmarks.
Subp. 3. Construction. An at-grade monitoring well must be constructed as
specified in this subpart.
A. At-grade well casing must terminate no lower than the established ground
surface.
As indicated in the diagrams below, the casing must terminate no lower than “at” or flush with grade, not
in a pit, or below ground level. The top of the manhole or vault must be raised at least 2 inches above the
surrounding grade.
B. The well must be contained in a protective manhole cover or vault. The top
of the manhole cover or vault must be no less than two inches above the
established ground surface.
A list of manholes and vaults meeting the standards of these rules is included in the appendix of approved
materials.
C. The established ground surface must be sloped to divert surface water or
spills away from the well and to allow for traffic movement and snow plowing.
D. The manhole cover or vault must be installed in a concrete pad at least four
inches in thickness and four feet square or four feet in diameter and of sufficient
load-bearing capacity to support vehicular traffic.
Asphalt, gravel, or materials other than concrete are not allowed to support the vault. A precast concrete
pad may be installed, but the pad must be firmly bedded.
The top of the concrete pad must be sloped away from the well in all directions. If the well is installed on
sloping ground, the pad is not required to be level, but can be sloped to match the slope of the
surrounding grade.
If the well will be located in an existing concrete surface, a 4-foot section of the existing concrete must be
removed in order to slope the pad away from the well in all directions. If the existing concrete has
adequate drainage, a variance may be applied for to cut a smaller hole and support the vault by use of a
flange, cemented pins, or other means.
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E. The manhole cover or vault must be labeled with the words “Monitoring
Well” cast or stamped in letters at least one centimeter or one-half inch in height.
The triangular symbol denoting “monitoring well” is not equivalent to the words “monitoring well.” Atgrade installations for environmental bore holes, remedial wells, or dewatering wells must also be
marked, either with a standard vault marked “monitoring well” or preferably permanently marked
denoting the type of well or boring. The marking may be factory cast, stamped with a die into the cap or
flange, stamped on a metal plate attached to the cap or flange, or marked with a weld bead.
F. All materials used to construct the manhole cover or vault must be resistant
and impervious to water, petroleum products, and chemicals likely to be present.
G. The manhole cover or vault must have a watertight, impervious compression
O-ring or gasket.
H. The manhole cover or vault must meet AASHTO Standards H20-44 and
M306-04.
I. The well casing must be secured with a locking cap or cover according to
part 4725.2250, subpart 17. The manhole cover or vault must be secured with a
lock or tamper-resistant bolts.
The well casing must have a key or combination lock. A threaded cap or bolted cap is not sufficient.
J. The well label must be placed on the well casing, manhole cover, or vault, or
the unique well number may be stamped on the vault.
COMPLETION OF AT-GRADE VAULTS IN WINTER
Contractors have requested that the MDH allow postponement of pouring at-grade protective pads during
subfreezing weather. Concerns for vehicular damage to the well, paving over or burying of the well, or
runoff into the well has led the department to deny these requests. The protective pad, vault, and
watertight seals must be installed upon completion of drilling and before the well is used.
Options for legally completing at-grade wells in subfreezing weather include:
● Use of concrete accelerators, thermal blankets, heated enclosures;
● Replacement of frozen fill;
● Use of a precast pad;
● Postponement of drilling until warmer weather; or
● Completion of the well above-grade until warmer weather.
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383
STAT AUTH: MS s 103I.101; 103I.111; 103I.205; 103I.221; 103I.301; 103I.401;
103I.451; 103I.501; 103I.525; 103I.531; 103I.535; 103I.541; 103I.621; 144.05; 144.12;
144.383; 157.04; 157.08; 157.09; 157.13
HIST: 17 SR 2773; 33 SR 211
4725.6900 [Repealed, 17 SR 2773]
4725.7000 [Repealed, 17 SR 2773]
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