ESTIMATES OF UNDOCUMENTED AND ABANDONED WATER WELLS IN MCDONOUGH COUNTY, ILLINOIS

Data from a well survey of McDonough County conducted in 1934 were used to develop a method of estimating the prevalence of undocumented private wells in the rural portion of the county. One-quarter of the townships in McDonough County were included in the well survey which, along with old plat books showing existing structures, was used to compute the ratio of wells-to-structures for the rural portions of the county. These ratios were applied to the portions of the county that were not included in the 1934 well survey to compute estimates of undocumented wells in 1934 ranging from 676 to 1,116 in the county.

The most recent plat books that include structures (1997) were used to compute well-to-structure ratios in 1997 by using the results of the 1934 estimate and incorporating records of well installation or well sealing for the years 1935 through 1997. High ratios (>2 wells per structure) in the rural parts of the county were assumed to provide evidence for the likely existence of abandoned wells or wells that were sealed without documentation. The maps of the well-to-structure ratios produced could be used by county or municipal health departments to identify the potential for abandoned wells in rural properties that are being developed (e.g housing tracts, CAFOs).

Potentially-abandoned wells in cities were not included in the above estimate because the plat books do not include structures within city limits. However, the 1934 well survey was conducted with such detail (sketches of lots with houses and distances marked) that aerial imagery was used to estimate that, in one small town, at least 27% (15 of 56) of the 1934 wells were potentially abandoned or were sealed without proper documentation.