VARIABILITY OF GROUNDWATER QUALITY BENEATH AN UNSEWERED RURAL SUBDIVISION

Population growth and urban expansion in many areas have resulted in residential development on formerly agricultural land, but there have been few studies of impacts of such developments on groundwater quality. To document the effects of this land-use conversion on groundwater quality, we initiated a monitoring program to collect water-quality data before, during, and after construction of a new, unsewered subdivision on agricultural land several miles outside of Madison, Wisconsin. The subdivision site lies in glaciated terrain over sandstone and dolomite. The water table ranges from 2 to 15 meters below the surface. The new homes are supplied by individual domestic wells, and dispose of their wastewater in individual septic systems.

Pre-construction groundwater quality varies in space and time and shows the effects of agricultural land use and nearby highway salting. Groundwater samples collected prior to subdivision construction contained variable amounts of chloride, nitrate, and atrazine, with concentrations ranging from below the level of detection to 296 mg/L, 30 mg/L as N, and 0.8 ug/L, respectively. Such high background nitrate and chloride concentrations may make it difficult to detect any future release of these contaminants from septic systems, lawn fertilization, or storm runoff once homes are built. However, septic systems can also release viruses, hormones, pharmaceuticals, and other household products to the environment. These contaminants may not only be better indicators of human waste in groundwater than nitrate or chloride, but they may also pose larger threats to groundwater quality and public health. We have conducted pre-construction screening for viruses and estrogenically active human hormones at the site, and investigated the potential applications for enzyme-linked immunosorbent assay (ELISA) test kits in future groundwater research. This project is continuing as new homes are constructed at the site.