In Nova Scotia the regulations require that a minimum of 20ft of casing be installed with Bentonite grout in the annular area above the drive shoe and around the casing.
This is crucial especially in a sandy quick draining soil when bedrock is near the surface. Less so if bedrock is hundreds of feet below a clayey glacial till.
Brewster Well Drilling typically installs a minimum of 40ft of grouted casing to ensure your well will not be at risk of surface water infiltration.
Some signs of surface water infiltration include, presence of bacteria in water or high turbidity during or after a heavy rainfall.
There are options available to remediate a well that is being contaminated by surface water however taking the time to do it right the first time saves us all time and money in the end.