Assessment of Land Availability for Future On-lot Septic Systems.

On-lot septic systems (OLS) are recognized by public health and environmental protection officials as cost effective and permanent approaches to treating wastewater for rural areas. According to US Census data, approximately 1/4 of the estimated 115 million occupied homes in the United States were served by OLS. The percentage varied from 55% in Vermont to 10% in California. In Pennsylvania 1/4 of the 4.5 million housing units had OLS. With rapid expansion of development into rural areas in Pennsylvania and reliance on OLS, land availability has become an issue for future development. This study used geographic information systems to assess the availability of land in south eastern and south central Pennsylvania for three types of common OLSs varying in soil conditions required for installation and operation. The analysis excluded land that was already developed, protected, or within existing municipal sewer service boundaries. The remaining land, deemed suitable for future development, was analyzed for soil suitability using OLS suitability ratings for each soil map unit in USDA-NRCS digital 1:24000 SSURGO soil survey data. Results showed that, for 642 municipalities investigated, the median percentage of available land area that could be developed with OLS was 63% of total land area. Of the land available for development, on average, only 0.2% had slight limitations for in-ground-bed system, 21% for elevated sand mounds, and 38% for drip irrigation systems.  Significant variability existed among municipalities in land area with different limitations for different septic systems, ranging from no suitable land in some municipalities to 99% of available land suitable for OLS.