A LOCAL ASSESSMENT OF IMPROPERLY ABANDONED WELLS IN LINN AND BENTON COUNTIES, OREGON

The purpose of this project is to locate and map improperly abandoned wells in Linn and Benton Counties of Oregon’s Willamette River Basin. Sections of these largely rural counties have as many as 50% fewer addresses as they have registered wells. Some of these sections are within older settlements that had established municipal water systems relatively late in their histories. Others contain unincorporated developments which, for various reasons, have had to drill new wells. Unfortunately, the precise locations of these defunct wells are often unknown.

Older, unused wells can conceivably be located too close to newer installations, such as feedlots or septic tank drain fields, or in areas since rezoned to industrial. If an unblocked passageway exists to the capture zone of such an unused well, whether on the surface or beneath it, then the opportunities for contamination of the groundwater and surface water exists. The percentage of these unused wells that are improperly sealed, and thus a possible source of groundwater contamination, and the precise locations of such wells, comprise the critical information that this project is documenting.

A variety of methods are utilized to determine the location of improperly abandoned wells. These include 1) canvassing landowners through direct contact and local media; 2) conducting spatial analysis using ArcGIS to identify possible abandoned wells based on proximity to contamination source, and local hydrogeologic conditions; 3) investigating existing Federal, State, and County land and water use records such as parcel maps, soil/drainage reports, and well logs; and 4) conducting field investigations to assess the condition of these wells and catalog them using Trimble Pathfinder Pro XR sub-meter mapping grade GPS, a Trimble Nomad field computer with ArcPad 8.0, and a Geometric Magnetometer.