Water Well Construction

The protection of water quality in drilled wells

Improper well construction or the failure to carry out routine prevention maintenance on a well can result in contaminated water.

Factors contributing to the deterioration of drilled well water quality

A poorly maintained or constructed well can result in the bacterial and/or chemical contamination of its water.  One of the most common causes of contamination is foreign materials and surface waters in the immediate vicinity of a well having direct access into the well.

In Ontario, drilled wells are constructed using a variety of drilling machines that produce holes of varying diameters, and are usually lined with a steel casing.  Problems due to surface water contamination occur when the sealing around the outside or top of the casing is not watertight.  Damage such as cracking of old cement grouting or corrosion can also allow surface water to enter such a well.

Indicators that sealing around the well casing may be inadequate and surface contamination may be gaining access to the well include:

• Presence of coliform bacterial in counts exceeding recommended limits set by health authorities

• Changes in the appearance or physical quality of the water, such as turbidity, colour, taste or odour, especially after a rainstorm or snow melt

• Rapid or large changes in the well water level, especially after a rainstorm or snow melt

• Cascading, seeping or stagnant water and/or staining inside the casing in a well pit

• The presence of biological material, such as animals insects or roots, in a well pit

• Unsealed or parted joints or cracks in the casing wall or cover

• A cracked or damaged well cap

• Settlement of soils around the well casing at ground level or around the old well pit

• The casing is noticeably heaved or loose in its seal, or water is bubbling up around casing

• An absence of any sanitary well seal or vermin-proof or watertight well cap over the casing set at an appropriate height about the land surface level

• Change in the chemical quality of the well water detected through laboratory analysis

Preventive maintenance measures

Well owners should be aware of the measures that should be taken for the care and maintenance of a well to ensure it provides good quality water.

• Protect against contaminants
  To safeguard a well supply, do not do anything near the well that might result in contamination.  Do not store, use or dispose of refuse, manure, petroleum products, salt, pesticides, paint or any other potential contaminant in the vicinity of the well.  When mixing pesticides or paints, the water supply line from the pressure system should be equipped with backflow device to prevent water from flowing back down the well.
   

• Watch for signs of damage
  The well cap must be securely in place and vermin-proof.  If the cap is damaged, cracked or missing, replace it immediately so that contaminants will not have direct access to the well.  The well cap must be a minimum o 40 centimeters above land surface level.  The well air vent must be shielded and screened to prevent the entry of any materials into the well.

All wells that have been repaired must be chlorinated.  It is to recommend that the well water be tested for portability immediately after the work has been completed.  Proper evacuation of the chlorinated water out of the well must be conducted before the well water is consumed or used.

Resources

Ministry of Environment web site www.ene.gov.on.ca