Convincing Your Town to Adopt a Wellhead Protection Ordinance

An Introduction to a Model Ordinance and Best Management Practices

How Groundwater Works

Water from all the oceans, seas, lakes, ponds, rivers, streams, clouds, glaciers and the ground are part of the global Water Cycle. It’s called a cycle because there is never any new water being created, it’s all the same water just being moved from place to place.

When precipitation occurs, water falls on the ground. Some of the water runs off on the surface, creating streams and rivers. Some water is captured and used by plants and animals. And some water gets soaked up by the ground. “Groundwater” is an important part of the water cycle. It can feed lakes and streams above the surface of the ground and aquifers below the surface of the ground. It provides a water source for plants to tap with their roots.

When plants use water it passes through them and is returned to the air in a process called transpiration. Eventually water returns to the air through evaporation, where clouds can form and the cycle starts all over again.

Graphic of the cone of depression around a well

Groundwater is an important part of the water cycle for people too. In Maine, over half of the population gets its drinking water from groundwater sources. People usually use wells to access groundwater. Wells tap into the groundwater and pump the water to the surface. When this happens, water in the aquifer rushes toward the well. As water is drawn towards the well it creates a cone shape. This is called the “Cone of Depression.” The area on the surface of the ground that is outlined by the top of the cone is called the ‘Zone of Contribution,” because it is this area that contributes surface water to the groundwater.

The land uses in the Zone of Contribution are important for groundwater quality. Potential sources of contamination can be spread throughout the zone of contribution. Anything that happens to spill onto the ground within the zone of contribution has a good chance causing groundwater contamination. Not only is that bad for human health, it can cost a lot of money to fix. Click on the right arrow below to see the Economic Impacts of Groundwater Contamination.

DWP Home | Page 3 of 10