Impacts of Privately Sewered Subdivisions on Groundwater Quality in Dane County, Wisconsin

Urban development of rural areas is probably the most significant land-use issue in Wisconsin and in many other parts of the United States. Although new residential developments near urban centers typically use city water and sewer services, rural developments usually rely on private water-supply wells and on-site wastewater-treatment systems. Conventional septic tank and leach field treatment of wastewater can release contaminants such as nitrate, bacteria, viruses, and hazardous household chemicals to groundwater systems, posing potential threats to nearby wells and surface water. Potential groundwater contamination is often cited as justification for discouraging or prohibiting new unsewered rural developments, particularly in environmentally sensitive areas with high water tables or shallow bedrock. New on-site treatment technologies have been developed in recent years to more effectively treat domestic wastewater. In 2000, the State of Wisconsin adopted Chapter Comm 83 (Wisc. Adm. Code, 2000), which permits the use of these alternative systems in areas where conventional systems are prohibited. To date, there have been few field studies to assess the performance of these systems. This project was a long-term monitoring study to document groundwater conditions before, during, and after construction of an unsewered subdivision that employs alternative onsite wastewater-treatment technologies. The first stage of the project documented the preconstruction groundwater conditions that have resulted from previous agricultural land use. We also examine the implications of these preconstruction results for identifying and interpreting changes that result from conversion of agricultural land to an unsewered subdivision.