Overlay zoning involves placing additional requirements for environmental or other purposes on portions of existing zoning districts. The standards for the overlay zone are then added to the standards of the original zone. This technique is also appropriate in protecting environmentally sensitive areas with geographic boundaries that do not coincide with the underlying zoning district. Floodplain overlay zones are a common use of this type of zoning.

A wellhead protection overlay zone might include requirements such as:

• prohibition of certain uses;
• reduced densities;
• limits on amounts of impervious surface;
• special requirements for septic systems;
• strict control of hazardous and toxic materials storage and management; or
• special stormwater and waste disposal provisions