4725.4550 MINIMUM PROTECTIVE DEPTH.
A potable water-supply well must be cased to a depth of at least 15 feet from the
established ground surface. The top of a gravel pack must terminate at least 15 feet
below the established ground surface.
This applies to water-supply wells used to provide water for human consumption, food or medicinal
preparation, or that are connected to plumbing fixtures such as sinks or faucets accessible for
consumption. This rule part requires a minimum of 15 feet of watertight casing not including the casing
above ground or the screen.
The 15-foot minimum casing does not apply to borings or nonpotable wells such as dewatering wells,
monitoring wells, remedial wells, or irrigation wells.
“Established ground surface” is defined in these rules to mean the intended or actual finished grade
(elevation) of the surface of the ground at the site of a well or boring. This includes built up grades with
pavers, brick, stone, landscape rock, concrete or other materials.
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; 33 SR 211
4725.4600 [Repealed, 17 SR 2773]
4725.4650 SEDIMENT IN POTABLE WATER-SUPPLY WELLS.
The following requirements apply to a new potable water-supply well.
This applies to new water-supply wells used to provide water for human consumption, food or medicinal
preparation, or that are connected to plumbing fixtures such as sinks or faucets accessible for
consumption. The requirement does not apply to existing wells which are rescreened, redrilled or
redeveloped. The requirement does not apply to irrigation, remedial, or other types of wells.
A. A water-supply well must be developed to remove drilling fluid, native silts
and clays deposited during drilling, and the predetermined finer fraction of the
natural formation or the gravel pack.
Development is the process of agitating the formation to remove drilling fluids, sediment in the screen or
bore hole, loose sediment in the formation, and fine formation material that can pass through the screen or
gravel pack. The object in a screened well is to remove the fines near the bore hole to grade the formation
particles from larger to smaller away from the screen.
Development techniques include over-pumping, surging with a bailer or surge block, air lift pumping,
jetting, use of compressed gasses or dry ice, use of sonic tools, and explosives. Hydrofracturing may be
considered a development tool in some cases. The most common technique is over-pumping, which while
being simple and possibly inexpensive, is one of the least effective techniques. Over-pumping with the
well pump can lead to damage of the pump. Jetting while airlift pumping is one of the better techniques.
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B. A new water-supply well must not produce a sustained quantity of more than
five milligrams per liter (mg/l) of sand, or more than 200 mg/l of silt and clay as
defined in part 4725.1851, subpart 4, item A for potable water at the design
capacity of the well, except when geological conditions preclude meeting the
standard, and the well owner, licensee, and commissioner agree to accept the
sediment in a stipulated agreement.
The rule is based on a sustained yield of sand, not a momentary excess due to a pump start or flushing of
settled sand in the water system. The rule is also based on the design capacity of the original pump.
Installation of a larger pump would make this requirement not applicable.
Sediment can rapidly damage pumps, piping, fittings, screens, equipment, and fixtures such as
dishwashers and washing machines. In excessive amounts, sediment can cause erosion of the annular seal,
subsidence and collapse. Sediment can provide locations for organisms to grow and make disinfection
very difficult. Where possible, it is recommended that all wells, not just potable water-supply wells,
produce less than 5 mg/L of sand and less than 200 mg/L of silt and clay.
The standards are based on weight per volume; 5 milligrams of sand or 200 mg/L of silt and clay in 1 liter
(approximately 1 quart) of water. The amount of sand can be accurately determined by measuring the
weight of sand in a known volume of water. A Rossum sand tester or Imhoff cone can be used to
determine sand content. A rough estimate of the sand content can be made by collecting a liter sample of
water, allowing the sand to settle to the bottom of the container, and counting the number of sand grains.
Typically, 5 mg/L of sand will equal 10 to 40 sand grains, depending on the grain size and mineral type.
Another estimate can be obtained by collecting 20 gallons of water. Five mg/L of sand is approximately
equal to a circle of sand the size of a dime in 20 gallons of water.
Two hundred milligrams per liter of silt or clay is more difficult to visually estimate without laboratory
analysis, because of the variation in material and grain size. However, 200 mg/L of silt, when completely
settled, is roughly equal to a circle of sediment the size of a nickel in 1 liter of water. When shaken,
200 mg/L of silt and clay in one liter of water appears visibly cloudy, so much so that most persons will
not drink water with 200 mg/L of sediment.
Certain geologic conditions such as some flowing well areas, finely laminated sediments, or weathered
interbeds of clay may not supply acceptable quantities of water and still meet the sediment standards. In
such cases, a stipulated agreement between the well owner, licensee, and the commissioner may be
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
4725.4700 [Repealed, 17 SR 2773]
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4725.4750 LEAD PROHIBITION IN POTABLE WATER-SUPPLY WELLS.
Materials used in construction of a potable water-supply well that contact water
must not exceed eight percent lead except that solders and flux must not contain
more than 0.2 percent lead.
Lead packers can no longer be used to connect or seal screens to a casing. Alternative devices such as
neoprene rubber k-packers are available for this purpose.
Particular attention should be paid to red brass fittings, which commonly contain more lead than yellow
brass and may exceed the 8 percent standard. Lead-free brass compounds, such as silicon brass, are
becoming increasingly available.
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
4725.4800 [Repealed, 17 SR 2773]
4725.4825 NONPOTABLE WATER-SUPPLY WELLS.
Subpart 1. Construction. A water-supply well used to provide water for
nonpotable purposes such as irrigation, heating and cooling, or industrial
processing, that is not used for purposes listed in part 4725.0100, subpart 35a,
must be constructed according to parts 4725.2010 to 4725.5550, except parts
4725.4550, 4725.4650, and 4725.4750.
Nonpotable water-supply wells (such as irrigation or industrial process waters) must be constructed to the
general wells and borings standards and the water-supply well standards, except that the 15-foot
minimum casing requirement of Minnesota Rules, part 4725.4550, the development and sediment
standards of Minnesota Rules, part 4725.4650, and the lead standard of Minnesota Rules, part 4725.4750
do not apply.
Subp. 2. Interconnection prohibited. A nonpotable well or water system must not
be interconnected with a potable well or water system except as provided in part
4725.3350.
Minnesota Rules, part 4725.3350 requires backflow prevention according to the Minnesota Plumbing
Code.
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Subp. 3. Identification required. A nonpotable well water system providing
water to a building with a potable water system, or accessible to the public, must
be marked as nonpotable according to part 4715.1910.
The Minnesota Plumbing Code, part 4715.1910, requires that in a building which has both potable and
nonpotable water systems, both systems must be marked. The Minnesota Plumbing Code identifies two
types of markings; color and metal tags. Color markings require potable pipes to be marked green and
nonpotable to be marked yellow. The entire pipe can be marked, or 3-inch wide color bands placed at
25-foot intervals and where pipes pass through walls, roofs, or floors. Metal tags must be 3-inch diameter
round tags bearing the legend “safe water” for potable piping, and 4-inch equilateral triangles bearing the
legend “nonpoptable water.” The tags must be placed at 25-foot intervals, and where the pipe passes
through a wall, roof, or floor.
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;
HIST: 33 SR 211
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