From Well Services
Protect and maintain your wellhead. The cap covering a well may be a small part of the overall household water well system, but is an extremely important one. A properly installed well cap separates potential pollutants from you drinking water. The cap, which should be sealed tightly at all times, keeps out everything from liquid contaminants to bugs that can crawl inside a well and wreak havoc. It is imperative that your wellhead be protected against contamination at all times.
Therefore, it should be covered with a weather tight, vermin proof cap. Another very important component is the extension of the water well casing. The extension should be at least 12” above the grade in order to prevent any surface water runoff from entering inside of the well and causing contamination problems. Check the well cap from time to time. Make sure that it is sealed tightly, and look for cracks and evidence of tampering. Take care when working or mowing or snow blowing around the wellhead.
Also, practice safe water habits. Do not landscape around the well cap. If you landscape your yard, make sure there is not a low area near the well where rain water could collect. Rain water can carry pollutants that can seep into a well. And when working with oil and gasoline, or mixing herbicides or pesticides, do so over concrete so spills can’t seep into the ground.