STATEWIDE GIS CENSUS DATA ASSESSMENT OF NITROGEN LOADINGS FROM SEPTICSYSTEMS IN PENNSYLVANIA/

Despite the role of septic systems in surface and groundwater N contam ination, little statewide information has been collected or is availab le on the amount of N pollution from septic systems. This study report s on the development of a methodology to assess N released from septic systems at the state level and presents results of N loading estimate s in Pennsylvania watersheds. The methodology describes steps to compu te N loadings per watershed unit area within a Geographic Information System (GIS) framework based on (i) information on septic systems and population from the 1990 Census data, (ii) soil limitations to proper purification of septic system effluent acquired from the State Soil Ge ographic (STATSGO) data base, and (iii) daily N estimates per capita i n septic system effluent from the literature. In this study, watershed s were ranked from 1 to 104 and grouped into three significantly diffe rent classes (high, medium, and low) according to their N loadings. Th e N loading ranges corresponding to these classes were 1.16 to 0.71 kg ha(-1) yr(-1), 0.56 to 0.41 kg ha(-1) yr(-1), and 0.38 to 0.03 kg ha( -1) yr(-1), respectively. High-producing watersheds were generally loc ated in suburbs adjacent to larger metropolitan areas. The watershed r anking, groups, and N loading results provided by this methodology can be combined with similar information from agriculture, atmospheric de position, etc. in the attempt to account for all sources of nonpoint N pollution in a state or region.