MN Well Driller cheat sheet

Minimum annular seal (grout) for a drilled well is 20 ft below land surface; where the upper 20 ft contains unconsolidated material, the seal must extend to at least 10 ft into the confining layer or bedrock, per Minnesota Rules 4725.

Casing must extend at least 12 in. above the finished grade or floor; in areas subject to flooding, casing must terminate at least 2 ft above the 100-year flood elevation (verify current rule text).

Grout volume for an annulus = 0.7854 x (hole diameter squared minus casing outside diameter squared) x sealed length, with diameters in consistent units; add a 10-15% excess for lost circulation and washout.

Neat cement grout mix: 1 bag (94 lb) Portland cement to no more than 6 gal water; bentonite may be added up to 5% by weight of cement for shrinkage control.

Cement grout must be placed by pumping from the bottom up through a tremie pipe; free-fall dumping into the annulus is not acceptable because it bridges and segregates.

A well must be disinfected with a chlorine solution of at least 100 mg/L (typically 50-100 ft of water column strength) with a minimum 12-hour contact time before sampling; sample only after chlorine demand is satisfied.

Screen and gravel pack sizing: pack material is selected so the screen opening retains 90% or more of the filter pack; the pack is sized to the formation's 50% retained size (D50).

Well development continues until the discharge is clear of sediment; surging, bailing, or jetting must not be so aggressive that it causes formation collapse or grout damage.

Driller must keep a log of overburden and bedrock materials, depths, casing, screen, and grout quantities; the log is filed with the state and provided to the owner.

Abandonment requires removing the pump, drop pipe, and wiring first; the casing is then either removed or perforated and filled so the entire borehole is sealed.

Sealing material for abandonment is typically neat cement grout, sand-cement grout (not more than 1 part sand to 1 part cement), bentonite chips, or bentonite slurry placed from the bottom up.

Bentonite chips are placed by gravity and must be poured slowly to avoid bridging; the seal must extend from the bottom of the well to land surface.

An unsealed flowing well or a well with artesian pressure must be sealed with grout weighted or placed to control flow; a flowing well cannot be abandoned by simply capping it.

A minimum 20-ft surface seal is required on all new wells, and the seal must be continuous and free of voids; a dry annular space is not a substitute for grout.

Grout must be allowed to set at least 24 hours (longer for large volumes or cold weather) before drilling continues or the well is developed.

Abandonment must be reported to the Minnesota Department of Health within 30 days of completion, with the sealing method and materials documented.

A well that is temporarily out of service must be maintained with a watertight cap and the casing intact; it is not considered abandoned until it is permanently sealed.

Sealing a well in a confined aquifer requires the seal to extend through the confining layer to prevent cross-contamination between aquifers.

Minnesota Rules Chapter 4725 governs wells and borings; Minnesota Statutes Chapter 103I is the enabling well law.

A person may not construct a well without a license or without working under a licensed well contractor; the contractor is responsible for the work and the required reports.

Well construction and sealing records must be submitted to the Minnesota Department of Health within 30 days of completing the work.

A property owner may construct a well on land they own and occupy for domestic use only if they obtain a permit and meet the rule requirements; this is a narrow exception, not a general exemption.

Wells must be located at least 50 ft from a septic tank and at least 50 ft from a soil treatment system; greater setbacks apply to certain contamination sources and must be verified in the current rule.

A well must be at least 20 ft from a property line unless the adjoining owner consents in writing, and must not be located in a floodway or area subject to surface water ponding.

The Department of Health may require a variance for nonstandard construction; a variance must be requested in writing and approved before the work is done.

Well contractors must carry the required insurance and must notify the state before beginning certain types of work; failure to file reports can result in enforcement action.

Local units of government may adopt more stringent well ordinances than the state rule; the driller must follow the stricter local requirement.

A new well must be sampled for coliform bacteria and nitrate after disinfection and before the well is placed in service; results are reported to the owner and the state.

The nitrate standard for drinking water is 10 mg/L as nitrogen (NO3-N); a result above that level requires the owner to be advised not to use the water for infants under 6 months.

Coliform bacteria must be absent; a positive total coliform result requires resampling and, if confirmed, correction of the well or treatment.

Samples must be collected in sterile containers supplied or approved by the laboratory, with the sample taken from a tap or the wellhead after the pump has run long enough to purge the line.

Chlorine residual must be absent at the time of sampling; residual disinfectant can mask or interfere with the bacteriological test.

Arsenic, manganese, and radon are common Minnesota groundwater concerns; arsenic has a maximum contaminant level of 10 micrograms per liter.

A well with a confirmed bacteriological problem must be disinfected and retested; if the problem persists, the driller must investigate the casing, seal, and wellhead for defects.

Water quality results must be kept by the contractor and provided to the well owner; the state maintains a database of well records and water quality results.