December 2008, Vol. 20, No.12
The Role of GIS in Distributed, Decentralized Wastewater Management
In the 1997 Response to Congress on Use of Decentralized Wastewater Treatment Systems, the U.S. Environmental Protection Agency determined that “with the technology now available, adequately managed decentralized systems can protect public health and the environment as well as provide long-term solutions for the nation’s wastewater needs.” The key words in this statement are “adequately managed.” The charge to meet this need often falls to local jurisdictions, typically county health or planning departments, to ensure that the decentralized infrastructure (generally onsite or small cluster systems) is managed both administratively by the jurisdiction and operationally by a private operator or service district.
Management and tracking capabilities within various counties can range from basic to very sophisticated. The range of capability tends to be driven by budgets, staffing, information technology, and political structure or leadership. The implementation or use of a geographical information system (GIS) can enable these responsible parties to better manage and share information on various aspects of their decentralized wastewater systems.
A GIS is an information system used to input, store, retrieve, manipulate, analyze, and output geographically referenced data to support decision-making for planning and management of land use, natural resources, environment, transportation, infrastructure, administrative, or other records.
A GIS references real-world spatial data elements (also known as graphic or feature data elements), which can be on or below the ground, to a common coordinate system. These features, such as buildings, lakes, manholes, ownership parcels, and soil series boundaries, usually are separated into different thematic layers, which can be turned on and off much as one would with computer-
assisted design software.
The power of GIS is its ability to store attribute data (descriptive information) about the feature data elements on a map. Having the database linked to the graphic elements enables the GIS user to retrieve information quickly, query the database based on user-defined criteria (such as what is there, when it was installed, and required maintenance), analyze spatial relationships between layers of data (for example, on soils, topography, and groundwater) and output the information in a tabular or map format (to analyze information, create reports, schedule maintenance letters, etc.). By displaying this in the most informative visual format, information can be easily interpreted and understood, particularly in public settings and decision-making sessions of local officials.
GIS software packages most commonly used by counties can be operated on nearly any personal computer and will work with all the common database programs. Most counties have parcel mapping and digital orthophotography of their land areas. These two components form the primary platform for a wastewater management program. Other common information that can be incorporated includes contour, soil, wetland, vegetation, and groundwater mapping that is usually available from various county departments.
When this information is incorporated into a GIS format, each nonmunicipally served tax parcel can be attributed with a wide variety of information. This information can include predevelopment site conditions or, for developed areas, information relative to existing onsite wastewater systems. In either case, the GIS platform can be used for distributed and decentralized wastewater system planning and management purposes.
Today, it is imperative to evaluate proposed development relative to compatibility with existing growth, transportation corridors, and public services and to minimize impacts on the environment, all while accommodating the end user. GIS technology can play a key role in evaluating the receiving environment for new or existing development. The receiving environment includes a site’s physical features, soil characteristics, and groundwater and bedrock conditions beneath the site.
The U.S. Natural Resources Conservation Service (NRCS) recently developed a Web site that provides access to all mapped areas in the United States (more than 95% of all counties; see websoilsurvey.nrcs.usda.gov/app). NRCS collects a large volume of data related to various soil physical and chemical properties, land features, hydrology, depth to bedrock and water table, and engineering test data for specific soil series.
In addition to collected data, NRCS also provides the data in tabular format with its associated interpretations of these data. The tabular data can be resorted by various site and soil characteristics pertinent to waste-water treatment. Selected criteria can be resorted for application with either performance or prescription codes. Finally, the information can be mapped in the GIS platform. The resulting maps can be used as a guidance tool for making planning decisions for new development and for identifying areas of environmental concern relative to existing development. These maps can be incorporated into a management tracking system for individual wastewater treatment systems.
The other aspect of adequately managed decentralized systems addresses existing or soon-to-be-installed systems. Again, the GIS platform can serve as “information central” for the responsible management entity (RME). Management information can include simple inventory (for example, Is there a system here?), permit number, installation date and inspection reports, system specifics (tank size, manufacturer, location, drainfield size and location), service providers (site evaluator, designer, installer, pumper), maintenance schedules and reports, and performance data, such as flow and sampling results.
Currently, various software programs incorporating GIS are being developed by the private sector that are Internet-accessible, allow direct input by service providers, and provide property owner communication for onsite wastewater systems. Public or private management staff will retain system control and have electronic data storage and retrieval, as well as inventory, maintenance, and operational reporting at their command.
Using GIS applications for waste-water management enables counties to provide planning services or at least allow access to information for small, unsewered communities, sanitary districts, lake districts, county- and state-owned facilities, and other RMEs with limited assets. The information also can be provided to private parties, including developers and commercial and private landowners. GIS applications can be an invaluable tool to give counties and other RMEs the ability to manage decentralized wastewater systems more efficiently to ensure protection of public health and the environment and provide a long-term wastewater solution.
Rick Apfel is senior soil scientist and manager of wastewater at Ayres Associates Inc. (Madison, Wis.).