Evaluating a chemical source-tracing suite for septic system nitrate in household wells

Abstract

Reducing human and ecological risks of groundwater nitrate contamination requires understanding the source of nitrate. Land use practices, such as agriculture and residential development, can increase groundwater nitrate concentrations. This study evaluated a chemical source-tracing suite that paired analysis of agricultural herbicide metabolites and human wastewater constituents. The source-tracing suite was tested in an area subject to nitrate from both agriculture and on-site waste ("septic") systems. Monitoring wells showed that agricultural contamination was deeper (>5 m) in the aquifer consistent with its origin a greater distance from wells and that on-site waste ("septic system") contamination was shallower in the aquifer (<3 m). Repeated sampling of seventeen household wells showed evidence of both agricultural and on-site waste contamination in wells with higher nitrate concentrations. The artificial sweeteners sucralose and acesulfame and the antibiotic sulfamethoxazole were the only septic system indicators consistently detected. Less persistent compounds, such as caffeine and acetaminophen, were never detected in the household wells indicating they were attenuated over the distance between septic system and well and reducing their utility as a tracer of septic system nitrate. Overall, there was a positive relationship between sucralose, acesulfame and nitrate in wells with low levels of agricultural contamination although the relationship varied between wells.

Keywords: Groundwater; Nitrate; Sweeteners; Tracers; Wastewater.