T17 Assessing Vulnerability of Water Supply Wells from Wastewater: Sources, Contaminants, Tracers, and Pathways

Sunday, 19 October 2014
8:00 AM - 12:00 PM
114/115

IMPACTS OF A RURAL SUBDIVISION ON GROUNDWATER QUALITY: DOCUMENTING A TRANSITION FROM AGRICULTURE TO RESIDENTIAL LAND USE

Paper number: T17-5
Program: Technical Sessions
Time: 9:05 AM – 9:20 AM

Authors

Abstract

New rural subdivisions built on former agricultural land are common outside of rapidly growing cities. Typically, each home in the subdivision has an individual domestic well and onsite septic system. There is often concern that such subdivisions might contribute to groundwater contamination, but data to support or refute this idea are generally sparse. We have been studying a 78-acre rural subdivision located in southern Wisconsin in which 18 homes were constructed starting in 2003. Prior to construction, the site was instrumented with monitoring wells, some completed in unlithified sediment and others in the underlying bedrock. Initial monitoring in the early 2000’s showed that groundwater beneath the site had been impacted by previous agricultural use, with nitrate-N values as high as 30 mg/l and some detections of atrazine, an herbicide commonly used on corn.

Groundwater beneath the subdivision was monitored periodically from 2001 to 2012. The scope of monitoring increased in 2013 and 2014, when we collected and analyzed groundwater and soil water samples for emerging contaminants including human viruses, pharmaceutical compounds, pesticides, and artificial sweeteners as well as major ions and environmental isotopes.

Our data document long-term changes in groundwater quality. In some wells, nitrate-N and atrazine levels have declined substantially. However, atrazine, last used on the site prior to 2003, was still present in 2013 at trace concentrations throughout the site. Wastewater tracers show small but detectable impacts from septic effluent on groundwater quality, as human viruses, pharmaceutical compounds, and artificial sweeteners, all indicators of domestic wastewater, were present in several wells. Nitrate concentrations varied spatially and temporally, with some concentrations substantially above the 10 mg/l-N drinking water standard. Over a decade of monitoring shows that the transition from agricultural to residential land use is changing groundwater quality in both negative and positive ways.