Risk from pathogens and exposure to antibiotic resistance genes in private wells in southwest WI

Private wells supply water for rural residents of southwest Wisconsin, where fractured rock aquifers are vulnerable to contamination from septic systems and agriculture. Our recent research detected viral, bacterial, and protozoan pathogens in 66 of 138 private wells in the region, but the health risk associated with the contamination is unknown, reflecting the broader lack of knowledge about health risk associated with private well water. Pathogens originate in wastewater and manure, which were detected in study wells using microbial source tracking (MST). Wastewater and manure are also sources of antibiotic resistance genes (ARGs), but the relative contribution of various fecal sources to ARGs in groundwater is unknown. The proposed work addresses these two microbial threats to groundwater quality by building on an existing study. Objectives are to 1) quantify health risk from 10 pathogens detected in private wells, 2) evaluate well construction and geologic factors for pathogen contamination, and 3) assess ARG co-occurrence with human and livestock fecal contamination. Existing data will be combined with new analyses of archived samples to complete objectives at reduced cost. Risk will be calculated using quantitative microbial risk assessment (QMRA) based on completed pathogen measurements. Existing geology and MST data will be used to categorize risk by geology and fecal source. Archived samples will be tested for ARGs and examined for co-occurrence with human and livestock fecal contamination. The proposed work supports local and statewide efforts to improve groundwater quality by placing private well contamination data in the context of public health, which also addresses the national knowledge gap regarding health risk from private wells. Likewise, ARGs are emerging contaminants of concern relevant in rural areas affected by manure and wastewater. The study supports mitigation strategies by examining how fecal sources, geology, and well construction are related to contamination and health risk.