Evaluating a low-cost method for identifying areas with failing septic systems in low-order watersheds

Abstract There are significant gaps in the ability to rapidly and affordably assess and identify areas of failing septic systems at fine spatial resolutions (< 1 km). This study evaluates a low-cost integrated method for identifying possible failing septic systems by: 1) using spatial metaanalysis to investigate the relationship between land cover, soil, and tax parcel data with the addition of in-situ high-resolution (50 m) nitrate data to identify localized hot spots of nutrient pollution that overlap with likely septic system locations; 2) prioritize the application of tests for Fecal Indicator Bacteria (FIB) only at these predetermined localized hot spots; 3) validate this integrated method against high-accuracy traditional water grab sampling methods of N and P concentration collected alongside the in-situ electronic measurement of relative nitrate change. Within a case example of the Fall Kill watershed, a suburban-rural watershed in New York, of the 17 observed in-stream spikes in relative nitrate concentration, nine of those spikes had strong evidence of possible septic influence based on FIB data, suggesting suboptimal septic systems pose a sizable threat to water quality. This low-cost and rapid approach to identifying likely locations of failing septic systems can help watershed groups elsewhere target education and mitigation strategies more efficiently.