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GIS Mapping For Source Water Protection

The Safe Drinking Water Act (SDWA) amendments of 1996 require assessment of the susceptibility of surface drinking water supplies to quality degradation and contamination. An important tool being used by communities for source water assessment and protection is a geographically-linked database in a geographical information system (GIS) map of the watershed.

GIS can enhance the ability of communities to track, maintain and analyze data about land features and human activities that contribute to erosion and rainfall runoff to water sources. By enabling better source water protection decisions, episodes of drinking water contamination can be prevented, and an improved source water quality is maintained, leading to reduced drinking water treatments costs.

Hanover has measured high levels of turbidity in its drinking water source. All the drinking water for Hanover comes from two watersheds that surround three reservoirs. Wright-Pierce assisted in obtaining a grant through the New Hampshire Department of Environmental Services, and matching funds from the Hanover Water Works Company, to create a computerized map of these two watersheds. The map and analysis was created with ESRI’s ArcGIS by Wright-Pierce.

Factors in the data layers were ranked according to their potential to threaten water quality; these included proximity to the water source or tributary streams, slope, soil type, land cover, and the presence of known hazards. GIS enabled the ranked factors to be combined and overlaid on the base map. This analysis visually highlighted those areas that may constitute a threat to water quality.

  

GIS map visually highlights
areas that may consitute a threat
and ranks them according to their
potential to threaten water quality.
Project Highlights

Background

The town of Hanover was required by SDWA mandates to assess the contamination risk of the town's surface drinking water supplies.

Challenges

  • Drinking water comes from two watersheds surrounding three reservoirs.
  • Measured high levels of turbidity in drinking water source.

Solutions

  • Development of a computerized map of the two watersheds.
  • Watershed maps highlight areas with potential to impact water quality.
  • Creation of a GIS database providing a sound basis for zoning, economic development, and land use decisions that affect water quality, and ultimately the cost of treating water for drinking.
  • Wright-Pierce assisted in obtaining a grant through the NHDES and matching funds from the Hanover Water Works.