Minnesota Administrative Rules
Agency 144 - Health Department
Chapter 4725 - WELLS AND BORINGS
WATER-SUPPLY WELLS
Part 4725.5550 - WATER-SUPPLY WELL DISINFECTION

Subpart 1. Disinfection procedure.

A water-supply well must be disinfected according to this part. A disinfection procedure is presumed adequate when one or more water samples collected as specified in part 4725.5650 indicate the absence of total coliform bacteria.

Subp. 2. Disinfection of new well or pump.

A person installing a new well or pump must ensure that the well is pumped until three volumes of the water contained in the well are pumped or until the water is as clear as groundwater conditions allow. After pumping, the person installing a new well or new pumping equipment must disinfect the well and pumping equipment with chlorine at a concentration sufficient to produce at least 50 parts per million of free chlorine in all parts of the well. The chlorine solution must contact the well surfaces above the static water level. The chlorine solution must remain in the well at least two hours before pumping all the chlorinated water from the well and the solution from the distribution system.

Subp. 3. Disinfection during repair or modification.

A person repairing or modifying a well or pump must disinfect the well as specified in subpart 2 or disinfect at the start of the repair or reconditioning by applying chlorine at a concentration sufficient to produce 200 parts per million free chlorine in all parts of the well for the period of the well repair or reconditioning operation. Before taking water samples or returning the well to use, all chlorinated water must be pumped from the well and distribution system.

Subp. 4. Disinfection materials.

Chlorine materials must meet the requirements of ANSI/NSF Standard 60-2016 as determined by a person accredited by ANSI or be registered by the United States Environmental Protection Agency according to the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), section 3(c)(7)(A), as an antimicrobial pesticide for use in potable water Chlorine compounds with additives such as perfumes or algaecides must not be used for disinfection. An alternate disinfection material may be used if the material is a biocide meeting the material and use standards of this part and provides biocidal activity equivalent to the chlorine concentrations and contact times required in this part.

Subp. 5. Chlorine in solid form.

Chlorine compounds in solid form used to comply with subparts 2 and 3 must be dissolved in potable water prior to placement in a water-supply well or circulated in the well to contact all well surfaces above the static water level, except that:

Subp. 6. Remedial well exemption.

The requirement to disinfect a water-supply well does not apply to a remedial well if the disinfection will interfere with water quality analysis or create dangerous reactions with contaminants.