GIS Analysis of Nitrate in Oregon Domestic Wells: Capturing Exposure through Innovative Drinking Water Policy

Nitrate contamination of groundwater is a serious problem in Oregon, as most Oregonians rely on groundwater for household drinking water. In 1989, Oregon legislature passed a law requiring that any seller of a property with a private well must test the well water for nitrate and coliform bacteria before transferring ownership of the property. Sampling results are submitted to the state health department.

The purpose of this study was to analyze the spatial distribution of private wells in Oregon that exceed the USEPA Maximum Contaminant Level or the State Maximum Measurable Contaminant Level and compare these data to groundwater sampling data, designated groundwater management areas, and land use data. This study sought to: (1) determine if there are areas in Oregon where nitrate-contaminated wells are clustered and if these clusters co-locate with other data trends; (2) serve as an exploratory tool for identifying a public health concern that can be followed up with comprehensive analytical studies or focused education outreach; (3) critique the utility of Oregon's Real Estate Transaction (RET) law and attendant database as a means of identifying and monitoring wells that are not regularly monitored. Data were analyzed for statistical and spatial analyses using SAS and ArcGIS.

Preliminary results indicate that several clusters of contaminated private wells exist in Oregon outside of areas where remediation efforts have been implemented and are co-located with coliform clusters, groundwater sampling exceedances and agricultural land use. Policy implications will also be discussed in light of these findings.