E. Nizeyimana et al., STATEWIDE GIS CENSUS DATA ASSESSMENT OF NITROGEN LOADINGS FROM SEPTICSYSTEMS IN PENNSYLVANIA/, Journal of environmental quality, 25(2), 1996, pp. 346-354
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.