Assessing the Status of Onsite Wastewater Treatment Systems in the Alabama Black Belt Soil Area

This study for the first time evaluated the soil suitability for onsite wastewater treatment systems (OWTS) within the Alabama Black Belt region and assessed the current status of those OWTS within this area. A local OWTS soil suitability rating system was developed based on current Alabama OWTS regulations and was compared with the existing nationwide Natural Resources Conservation Service soil limitation rating system based on their soil assessment results over the study area. Both rating systems indicate that a large percentage (52%-89%) of land within the study area should not be recommended for conventional OWTS. However, OWTS are widely used and aging in this region. Raster-based OWTS-soil suitability rating system results and US Census-derived demographics were combined in a GIS to prioritize the study area in terms of potential public health threat from OWTS. Although the results lack field verification, two parallel strategies to limit the public health risk from OWTS malfunction are suggested: to extend municipal sewer service to high-risk city fringe areas and to subsidize system retrofit, repair, or replacement of aged OWTS with alternative engineered systems for rural households. Although this study only focused on the Alabama Black Belt area, the presented GIS and demographic methods can be referenced by other regions for similar OWTS assessment purposes.