My Aquifer > For Private Well Owners > How can my well become contaminated?
Your well may become bacteriologically contaminated in one or more of the following ways:
1. The well may not have a vermin-proof cap, allowing insects that carry bacteria to enter the well.
2. There is a source of contamination, such as a septic system, too close to the well or the well casing isn't deep enough to assure that recharge water receives sufficient filtration to remove bacteria.
3. The well may be constructed using poor sanitary practices. New wells often show contamination because:
- The drillhole was contaminated by dirty tools, pipe or drilling water
- New piping, pump or pressure system components were not disinfected prior to use, assembly or installation
Note The state well code requires disinfection of new wells, pumping equipment and water systems prior to use.
4. Contaminated surface water or groundwater can enter an improperly constructed well in the following ways:
- Dug wells walled with boards, brick, stone or tile sections permit unfiltered surface water and near-surface waters to seep into the well through cracks in the wall .
- Casing improperly sealed into the rock and/or unconsolidated geological formation may permit surface water or contaminated groundwater to move vertically downward, contaminating good aquifers.
- The well casing doesn't extend far enough above the ground allowing surface water to enter the well or because a hand pump base doesn't have a watertight seal where it attaches to the casing.
- The well top ends in a nonconforming well pit subject to flooding or seepage of contaminated groundwater.
- Old well casings may rust through, leaving holes near the ground surface where surface water or near-surface waters can seep in and contaminate deeper groundwater.
- The aquifer supplying the well is fractured rock, which has poor water-filtering properties.