Participatory Spatial Modeling and the Septic Dilemma

Whereas point sources of nutrients are quite well known and controlled, there is growing concern about non-point sources, especially those that are related to individual homeowners and citizens' practices. They seem to be the hardest to manage and reduce. On-site sewage disposal systems (OSDS) are among the major contributors to the nutrient pollution of surface and ground waters. In Calvert County, Maryland, up to 25% of the non point source nitrogen pollution originates from septic systems. A participatory landscape modeling approach has been used to analyze and visualize the impact of septic systems on the water quality entering the estuary. The landscape model tracks the fate of nutrients released from septic tanks and other non-point sources. A series of stakeholder workshops have been arranged to demonstrate, using the model, how septic discharges contribute to the water pollution in the estuary. Our results suggest that septic tanks are a less significant contributor to surface water nitrogen pollution in the short-term than was previously assumed whereas fertilizer runoff may be more important than previously thought. We are exploring how this participatory process can be used to influence decision-making and management policies in the County to reduce all sources of nitrogen to local waters.