WELL AND BORING GENERAL CONSTRUCTION AND USE
REQUIREMENTS
4725.2010 APPLICABILITY.
The general construction and use requirements specified in parts 4725.2010 to
4725.3875 apply to all wells and borings except exploratory borings regulated
under chapter 4727. The additional requirements or exemptions in parts
4725.4050 to 4725.6050 apply to water-supply wells. The additional requirements
or exemptions in part 4725.6150 apply to dewatering wells. The additional
requirements or exemptions in parts 4725.6450 to 4725.6850 apply to monitoring
wells and cased environmental bore holes. The additional requirements or
exemptions in part 4725.7050 apply to vertical heat exchangers. The additional
requirements or exemptions in part 4725.7250 apply to elevator borings. The
additional requirements or exemptions in part 4725.7450 apply to environmental
bore holes.
This portion of the rules (Minnesota Rules, parts 4725.2010 to 4725.3950) applies to all wells and borings
including water-supply wells (including public and private water supplies, sandpoints, dug wells,
irrigation wells, remedial wells, and heat pump wells), monitoring wells, dewatering wells, environmental
bore holes, elevator borings (excavations for elevator cylinders, “jack holes”), and vertical heat
exchangers. Rule parts after Minnesota Rules, part 4725.3875, include additional requirements or
exemptions for specific types of wells or borings.
The rules in Minnesota Rules, Chapter 4725, apply to new construction, repair, and sealing of existing
wells and borings.
Minnesota Rules, Chapter 4727 contains the rules pertaining to exploratory borings (metallic minerals,
petroleum, kaolin apatite, diamonds, graphite, and gemstone exploration drilling). Copies of Minnesota
Rules, Chapter 4727 may be found online at www.revisor.mn.gov/rules or obtained from the MDH Well
Management Section.
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.541; 103I.621; 144.05; 144.12;
12.122; 144.383; 157.04; 157.08; 157.09; 157.13
HIST: 17 SR 2773; 18 SR 1222; 33 SR 211
4725.2020 INTERCONNECTION OF AQUIFERS PROHIBITED.
Subpart 1. Aquifer interconnections. A well or boring must not be constructed to
interconnect aquifers separated by a confining layer or interconnect an
unconsolidated aquifer and a bedrock aquifer.
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Subpart 1a. Open bore hole, gravel pack, or screen in a confining layer. A well
or boring must not have open bore hole, gravel pack, or screen extending through
more than:
A. ten feet of a confining layer, except for the Decorah or Glenwood
formations;
B. two feet of the Decorah or Glenwood formations; and
C. 50 percent of the confining layer.
The commissioner may establish less stringent standards than identified in this
subpart where protective conditions exist or unique characteristics of the confining
layer exist, including low permeability overlying materials, favorable groundwater
gradients, the presence of fractures or permeable horizons in the confining layer,
or reduced contaminant loading in recharge areas. The areas subject to less
stringent standards under this provision will be designated on a map published by
the commissioner, along with the standards that do apply to those areas.
Subp. 2. [Repealed, 33 SR 211]
Subp. 3. [Repealed, 33 SR 211]
A “confining layer” means a stratum of a geologic material that restricts vertical water movement. A
confining layer includes: (A) a stratum at least 10 feet in vertical thickness of unconsolidated materials or
bedrock that has a vertical hydraulic conductivity of 10-6 (0.000001) centimeters per second or less; (B) a
stratum at least 10 feet in vertical thickness of clay, sandy clay, or silty clay as defined by the United
States Department of Agriculture in Handbook 18; or (C) a stratum at least 10 feet in vertical thickness of
the St. Lawrence or Eau Claire sedimentary bedrock formation, or a stratum at least 2 feet in vertical
thickness of the Decorah or Glenwood sedimentary bedrock formation, as described in “Geology of
Minnesota: A Centennial Volume “ by Sims P. K. and Morey, G.B., pages 459-473, “Paleozoic
Lithostratigraphy of Southeastern Minnesota” by George Austin, which is incorporated by reference. The
publication is available at the Minnesota Geological Survey, MDH, or through the Minitex interlibrary
loan program. Water level or piezeometric surface differences, water quality differences, and groundwater
age dating are other measurements that can be used to identify and define confining layers.
The preferred method of constructing a well or boring through a confining layer is to drive or grout an
outer casing into the confining layer, drill open hole through the confining layer, install an inner casing
through the confining layer, and fill the annular space with grout. The rules allow a casing to be driven
through a confining layer in unconsolidated formations. The rules also allow the drilling of a rotary bore
hole through a bedrock or unconsolidated confining layer if casing is placed and grouted through it.
Clay, silty clay, or sandy clay are the most common confining materials in unconsolidated formations
(glacial drift). Confining layers in unconsolidated materials must be sealed by driving casing through it,
by filling the annular space with bentonite grout, cement-sand grout, or neat-cement grout, or by filling
the annular space below a depth of 50 feet with drill cuttings (except for monitoring wells and cased
environmental bore holes where grout is required). The use of cuttings is not recommended due to
bridging concerns and concerns about the confidence of their placement at depths greater than 50 feet.
Neat-cement grout, cement-sand grout, or bentonite grout is recommended in unconsolidated formations.
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Shale, siltstone, or layers of sandstone and shale or siltstone are the most common confining materials in
bedrock formations. Casings that are installed through a bedrock confining layer must be installed in a
bore hole 3.0 inches larger than the outer diameter of the casing/coupling (except for casings deeper than
100 feet and larger than 12 inches where a 3.5-inch bigger hole is required) and the annular space must be
grouted with neat-cement grout or cement-sand grout.
The basal St. Peter sandstone formation contains sufficient shale to act as a confining layer in parts of
southeastern Minnesota; particularly in the seven-county twin cities area. In general, and especially where
characteristics of a confining layer occur, the MDH recommends that wells not interconnect the St. Peter
and Prairie du Chien formations, and that annular spaces through the basal St. Peter be filled with neatcement grout.
Dakota County Environmental Services delegated well program has studied the characteristics of the
Prairie du Chien (Shakopee and Oneota formations) and the Jordan formation. They have observed
enough differences of water quality, water level, and water transmission to consider the Shakopee
formation to be hydraulically separated from the Jordan formation by the Oneota. The Dakota County
well program does not allow interconnection of the Shakopee and Jordan. For more information contact
the Dakota County Environmental Services Department.
This rule allows an open hole or screen to penetrate no more than 50 percent of a confining layer, not to
exceed 10 feet. In the Decorah and Glenwood formations, the open hole or screen may penetrate no more
than 50 percent of the confining layer, not to exceed 2 feet. This is largely designed to accommodate
monitoring and other investigative purposes. The intent should not be to design water-supply wells to
pump water from confining layers.
Wells and borings may only be open to one aquifer. Open bore holes, well screens, nonwatertight casing,
or gravel packs may not be placed across a confining layer. Well screens may not be placed in two
different aquifers separated by a confining layer. Confining layers may be saturated and may produce
limited quantities of water but still function as confining layers.
Interconnection of two or more wells or borings completed in different aquifers through piping manifolds
or other means is prohibited and is discussed in Minnesota Rules, part 4725.3350
The provisions of this part do not apply if the commissioner of health has published a map detailing
different construction standards from those contained in this rule part.
In the mid-1990s, in response to issues raised by drilling contractors about identifying the St. Lawrence
formation and its confining properties in southern Minnesota, the MDH and the Minnesota Geological
Survey conducted a study to determine where the St. Lawrence formation was present, and where it
serves as a confining layer. In 1996, the MDH (i.e., the commissioner) released a well construction map
directing well and boring contractors how to construct wells that encountered the St. Lawrence formation
in parts of Scott, Le Sueur, Blue Earth, Nicollet, and Sibley Counties in southern Minnesota. The map is
entitled “MDH, St. Lawrence Project, Well Construction Plate, March 22, 1996.” The map depicts
where the St. Lawrence formation is absent, where it is present as the first bedrock formation encountered
while drilling, and where it is present and covered by younger bedrock formations. The map directs well
and boring contractors how to construct wells and borings into, or through the St. Lawrence formation.
Copies of the map are available from the MDH Well Management Section. A similar study with
accompanying maps is being completed in the metropolitan twin cities area.
A geologic column of southeastern Minnesota is included in the appendix.
181
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.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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4725.2050 USE OF WELLS OR BORINGS FOR DISPOSAL OR INJECTION
PROHIBITED.
A well or boring must not be used for disposal or injection of surface water,
groundwater, or any other liquid, gas, or chemical, except for groundwater
thermal exchange devices, drilling fluids, vertical turbine prelubrication water,
treatment chemicals, priming water, water used for hydrofracturing, and water
used for disinfection in accordance with parts 4725.1831, 4725.2950, 4725.3250,
4725.3725, 4725.5050, 4725.5475, and 4725.5550. This does not prohibit the
injection of air for drilling, development, or sparging.
Disposal or injection of wastes is primarily regulated by the MPCA. Rules of the MPCA, Minnesota
Rules, part 7060.0600, specifically prohibit the discharge of sewage, industrial wastes, or other wastes
into the zone of saturation through wells. Chapter 7060 may be viewed at www.revisor.mn.gov/rules.
The well and boring rules prohibit injection wells and borings. A well or boring may not be used to
inject surface water, groundwater, water from roof drains or other rainwater collection systems,
agricultural drainage, chemicals, or wastes into an aquifer. The injection of dye-tracing chemicals,
nutrients, organisms, or other materials for groundwater contamination remediation in a well or boring is
also prohibited by this rule part; however, a variance may be granted for these purposes in certain
circumstances.
This rule does not prohibit a person from introducing water into a well or boring for drilling operations,
disinfection, hydrofracturing, development, slug tests, inspections, repair operations, or for permitted
groundwater thermal exchange devices. This rule also does not prohibit a person from introducing
approved treatment chemicals like chlorine or acid into a well or boring for development, repair, or
rehabilitation.
A. Water used to cool parts of engines, air compressors or other equipment, or
air conditioning equipment must not be returned to a well or any part of a potable
water system except if permitted as a groundwater thermal exchange device under
part 4725.1831 and Minnesota Statutes, section 103I.621.
A groundwater thermal exchange device is an installation that pumps groundwater from a supply well
through a heat exchanger and then returns the water to the aquifer via a well, called an injection well.
Minnesota Rules, part 4725.1831, details the permit process and the piping requirements. The water must
not come in contact with hazardous materials and must be clean when returned to the aquifer.
B. A well may be used for the injection of water to conduct a slug test if the
injected water was originally taken from that well or is potable water.
A slug test measures the response of an aquifer when a volume of water is either added to, or removed
from, a well. The information generated is used to determine the hydraulic conductivity of the aquifer.
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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.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
4725.2100 [Repealed, 17 SR 2773]
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