Q3: Oral Presentation C Friday, 9:30 10:00 am C French River Room

Using GIS as a Tool to Manage Northern Minnesota's On-site Wastewater Treatment Systems

Richard J. Otis, Timothy Barnett
Ayres Associates
2445 Darwin Road
Madison, WI  53704

Over 25% of existing homes in the U.S. rely on onsite systems to treat and disperse the household wastewater into the environment. Traditionally, these onsite systems have been prescriptive designs that protect public health by discharging partially treated wastewater below the ground surface in infiltration trenches located some distance from private wells. Because of the reliance of the system on the soil to accept the wastewater, these systems can be used only on lots with suitable site and soil characteristics. 

Increasingly, there is pressure to develop beyond the reach of existing sewer systems because of the high costs of conventional sewerage. Today, approximately 37% of new homes in the U.S. use onsite systems. With this increased development pressure, the availability of suitable sites is becoming limited and more marginal lands are used where onsite system failures are more frequent. The failures create environmental as well as public health problems.

Federal, state, and local governments are recognizing that sewers are not the wastewater solution for many small communities and rural areas. However, onsite system practices must change if public health and the environment is to be protected adequately. Conversion from prescriptive onsite system codes where suitable sites must be available to use the approved designs to performance codes where suitable systems must be designed to build on the available sites is occurring. But this change increases the complexity of administering onsite system permitting programs substantially. Performance standards for the onsite systems will depend on the environmental sensitivity of sites to wastewater discharges, proximity wellhead protection zones, densities of homes, etc. Better tools are needed by the counties to assist in the consistent administration of a performance-based program.

This paper will describe a GIS based tool to evaluate environmental sensitivities, establish performance standards for systems, plan for future development, assess performance of existing systems with respect to site conditions, and track permits and maintenance records. This is an essential tool if onsite wastewater systems are to be sustainable substitutes to central sewerage.