Land Development

In natural environments, stormwater filters as it flows over native vegetation, and then through soils, before it reaches groundwater. Stormwater runoff from land development (including active construction sites) is a leading cause of water pollution nationally and the leading cause in New Hampshire. Stormwater can become polluted when it flows through streets, lawns, farms, construction sites and industrial areas. Risks for pollution rise higher when substances such as fertilizers, sediment (small soil particles), pesticides or oils are along the water's path.

If stormwater is left untreated, the pollutants it introduces can impact drinking water supplies, stream health, and aquatic and land-based wildlife. Unregulated land development can also increase the amount and rate of stormwater runoff which, in turn, can contribute to flooding in other areas.

Alteration of Terrain (AoT) permitting helps regulate stormwater control and treatment on larger sites. It helps govern "earth-moving" operations, such as gravel pits, as well as industrial, commercial and residential construction. Treatment options can be biological or physical. Management methods include rain gardens, infiltration ponds, gravel wetlands and other best management practices.

Other controls that help avoid increasing water runoff from land development sites include detention ponds and underground storage facilities. The same structures that provide treatment can also be used to store and control the rate of runoff.

Alteration of Terrain permits are required if a project proposes to disturb more than 100,000 square feet of contiguous terrain (50,000 square feet, if any portion of the project is within a protected shoreland). Disturbances greater than 2,500 square feet, over terrain with grades of greater than 25%, may also require these permits. AoT "General Permits by Rule" apply to smaller sites, which do not require applications or notifications.