Appendix 1: Geographic Information Systems (GIS) Appendix I. Geographic Information Systems (GIS)
Geographic information system (GIS) technology integrates, stores, analyzes, and displays both non-spatial and spatial geographic data. The capabilities and applications of this technology are vast and beyond the scope of this resource guide; however, this technology can be useful in the sanitary survey process.
GIS is a powerful communication and analytical tool. Maps or images created us- ing GIS are easily shared and understood. GIS can be used to identify properties with subsurface wastewater disposal systems with the highest potential risk of contaminat- ing neighboring water bodies (e.g., structures which sit on marginal soils for septic systems, are adjacent to surface water, and do not have sewer access). GIS is like a “data sandwich” where multiple sets of data are layered to illustrate patterns or pol- lution risk “hotspots” in the watershed. It can also help organize survey information and track the progress of remediation efforts.
GIS technology is used to investigate relationships or patterns in space. For purposes of the sanitary survey, the types of GIS layers of interest include, but are not limited to:
Watershed and sub-watershed boundaries (hydrography networks including rivers, streams, ponds, lakes)
River and stream features
Habitat (wildlife, wetlands, flood
plains, forest, grasslands, shellfish)
Digital elevation models (i.e., slope)
Overboard Discharge Units
Storm sewer/drain network
Outfalls- publicly owned
Marinas and other high-use areas
Water quality monitoring sites
What resources and data are available?
The standard GIS software is ArcGIS, available through ESRI (see also http://www.gis.com). Alternatives include other commercial packages, shareware, freeware, and beta software. Municipalities without GIS capacity may need to contract with environmental consultants, nonprofit organizations (e.g., regional planning commissions), educational institutions, etc. Depending on the watershed, the Maine Healthy Beaches Program may be able to provide GIS assistance.
Many spatial datasets (“layers”) are available from the Maine Office of GIS (MEGIS). The MEGIS coverage files include Level 6 sub-watershed boundaries (from 10,000 acres to 200,000 acres of land, or up to 300 square miles) with 12-digit USGS Hydrologic Unit Codes (HUCs) and Level 7 drainage boundaries (from 3,000 acres to 10,000 acres of land or 5 square
miles to 15 square miles) with 14 digit HUCs. The most useful scale for evaluation will depend on the particular area, and often the sub-watershed is sufficient.
Other useful GIS layers can be obtained through state and federal agencies, or at the regional and local level. The same list of contacts in Part I should be consulted for available data. In many cases, new layers can be created as part of the sanitary survey process, such as parcels with septic systems that have the highest risk of contaminating nearby water bodies, known problem areas, agricultural operations on land with sloping topography, monitoring sites with consistently high bacteria levels, intermittent stream flows, etc.
The Conservation Technology Support Program awards grants of equipment a n d s o f t w a r e t o t a x - e x e m p t c o n s e r v a t i o n o r g a n i z a t i o n s t o b u i l d t h e i r G I S c a p a c i t y .
US Geological Survey (USGS) and Natural Resource Conservation Service (NRCS) Watershed Numbering System
Bill Olsen, St. Lawrence University Libraries