Microbial Water Quality Indicators in Groundwater Wells along a Rural- to Urban-Gradient in the Semiarid Southwest

Numerous studies have documented that urbanization increases the occurrence and loads of fecal indicator bacteria to surface waters. Researchers have also extensively studied the transport and survival of Escherichia coli and thermotolerant coliforms in saturated soils and have proposed that survival of these bacterial groups can have negative consequences for groundwater quality. Despite these concerns, stormwater runoff from urban areas is often actively managed as focused recharge to groundwater in semiarid environments. In the summer of 2008, we sampled 30 groundwater wells in Tucson, Arizona along a semi-rural to urban housing density gradient. The groundwater wells ranged in depth from 20 to more than 200 feet from the surface, and several of the wells were within close proximity to a recharge site for reclaimed municipal effluent water. All wells were sampled for total and fecal coliform bacteria and E. coli. In addition, bacteriophage analyses were performed on a subset of the wells. Intensive monitoring of groundwater quality, across a variety of housing densities, source waters, and soil types results in a modified hydrologic template that is useful for understanding the tradeoffs between urban storm-recharge and water quality.