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Estimation of the Prevalence of Undocumented and Abandoned Rural Private Wells in McDonough County, Illinois.


Abandoned wells are a known safety and public health hazard. Their danger received national attention in 1987 when Baby Jessica fell into an abandoned well and the country followed her eventual rescue (Kennedy, 1987), but many years later, children are still falling into wells, a known hazard (Apel, 2015, among others). Aside from the physical hazard of falling into them, abandoned wells can also have a detrimental effect on groundwater quality, such as when surface pollutants enter an aquifer via unfilled abandoned wells (Gass, Lehr, & Heiss, 1977).

Illinois did not begin requiring permits for installation of water wells until the 1960s (Wilson, Rennels, & Roadcap, 2013), so many of the wells in the state are undocumented. The number of abandoned wells in Illinois has been estimated to be in the thousands (Hendrickson, Erickson, & Narve, 1996) and many of these wells were never documented. For example, a well survey in parts of three Illinois counties identified 1,706 total wells. Of these, 788 were not previously documented in the Illinois State Water Survey (ISWS) database (Wilson et al., 2013).

Although this type of well survey is the most accurate method of determining the abundance of undocumented wells, it is both costly and time-consuming to conduct. For this reason, a low-cost technique to estimate the prevalence of undocumented private water wells in a rural setting was developed that relies upon the assumed relationship between the number of structures in an area and the number of wells. This estimation method is not designed to locate individual wells, but to identify areas that are likely to contain undocumented and/or abandoned wells and warrant further investigation. This type of information could be useful to local health departments and/or companies planning to develop rural properties.


Well Data

A spreadsheet containing all well records of private wells (pumping less than 75 gal/ min) in McDonough County, Illinois, as of September 2015, was provided by the ISWS. The well record information required for this study included the location of the well, date of installation, and the date of sealing if the well was sealed.

Although there was very little documentation regarding the location of private wells in Illinois prior to the 1930s, a survey of private water wells was conducted in 1934 that included 4 of the 16 townships in McDonough County (Illinois State Water Survey [ISWS], 1935). A total of 276 farm or rural wells were identified during the survey. Most of the rural wells (86%) were installed in glacial deposits with depths ranging from 12-90 ft (ISWS, 1935). For the purposes of this study, it was assumed that no wells were missed during the well survey, so the number of wells reported for these four townships was the actual number of wells in 1934. Wells with no installation date were assumed to be older than 1934.

Structure Data

Historical plat books with buildings marked in the rural parts of the county were used to determine the number of structures in the study area. As the plat books do not show individual structures inside city limits, any 1-[mi.sup.2] Public Land Survey System (PLSS) section that contained any portion of the city limits of any town were excluded from the study (Figure 1). Plat books that identified structures were not available for the year of the well survey (1934), so it was necessary to use plat books from 1919 (Howat & Son, 1919) and 1954 (Rockford Map Publishers, 1954) to estimate the number of structures at the time of the well survey. The most recent plat book available for McDonough County that included structures on the map (Rockford Map Publishers, 1997) was used when estimating the likelihood of abandoned wells in the county.


Previous researchers have used aerial photographs, topographic maps, plat maps, or a combination of these resources to identify likely locations of water wells (Blomquist, 1984) or petroleum wells (Aller, 1984; Stout & Sitton, 1984). Our basis for the method used to estimate undocumented wells relies on an assumed ratio between water wells and structures (e.g., houses, barns, churches). As this ratio can change through time as farming practices change (e.g., fewer barns and outbuildings used than in the past), the estimate of undocumented wells was computed for 1934, the time of the aforementioned well survey. Specifically, the four townships within the county that were part of the 1934 well survey were used to establish the ratio of wells to structures in the rural portions of the county at that time.

After scanning the plat maps from 1919 and 1954, GIS software was used to create a shapefile for both years with the locations of each structure marked. The number of structures per 1-[mi.sup.2] PLSS section was determined for the years 1919-1954, and these numbers were used to estimate the number of structures in 1934 through interpolation. PLSS sections were chosen as the base area for computing the well-to-structure ratio because some of the wells in the study area were located by section and township only. The ratio determined for the four surveyed townships was then applied to the remaining 12 townships in the county to estimate the number of undocumented wells in 1934. The well-to-structure ratio was not the same for each of the four surveyed townships, so a range of estimates of undocumented wells was computed using the highest and lowest calculated ratios.

Finally, in an effort to estimate the number of abandoned wells, the ratio of estimated wells to structures was recomputed for each PLSS section in the county for the year 1997. The 1997 plat book was used because it is the most recent plat book that included structures on the map. A section that displayed a high well-to-structure ratio was presumed to be an area that has a high likelihood of containing an abandoned well. Any well-to-structure ratio >2 was considered high, as most rural lots contain, at most, one well for the residence and potentially one well for livestock.

To determine the well-to-structure ratio as of 1997, the well records between 1935-1997 were added to the estimated number of wells in 1934. Any records of wells sealed between 1935-1997 were then subtracted from this total and the resulting number was divided by the number of structures present in the PLSS section in 1997. It should be noted that the number of wells in a section are probably underestimates, because well records were not required by law to be submitted to the ISWS until the 1960s, making well records between the years 1935 and the 1960s incomplete (Wilson et al., 2013).

Results and Discussion

Undocumented Well Estimates for 1934

The ratios of wells to structures determined for the four townships included in the 1934 well survey ranged from 0.39-0.62 with a mean of 0.49, so there were roughly two structures per well in 1934 (Table 1). The low, mean, and high well-to-structure ratios were used to compute the low, medium, and high estimates of undocumented wells for the remaining 12 townships in the county by multiplying the ratio by the estimated number of structures and subtracting the number of well records in the townships (Table 2). A map constructed using the mean well-to-structure ratio of approximately 0.5 shows that the estimated number of undocumented wells are evenly distributed around the county, ranging from 0-6 wells per 1-[mi.sup.2] PLSS section (Figure 2).

The estimates of the number of undocumented wells per section were not rounded to whole numbers so that false patterns due to rounding up or down from 0.5 would not be created. The number of documented well records in each of these townships was very low, ranging from 1-12, so nearly all of the wells in these 12 townships were undocumented in 1934. The roughly 650-1,100 estimated undocumented wells are only for the rural parts of the county that were included in this study. There are undoubtedly many more undocumented urban wells, so these figures represent conservative estimates for township-wide undocumented wells.

Identification of Potentially Abandoned Wells as of 1997

The well-to-structure ratios for each township as of 1997 (Table 3) were greater than those computed for 1934, with a mean (1.08) that is more than double the 1934 value. A well-to-structure value near 1 was not surprising considering the changes in farming practices between 1934-1997. For example, in 1930 there were 2,433 farms in the county (Illinois Cooperative Crop Reporting Service, 1970), but only 726 farms remained in 1997 (Census of Agriculture, 1997), with the result that farms were much larger in 1997. Specifically, in 1930 only 10.9% of the farms in the county were greater than 260 acres in size (Illinois Cooperative Crop Reporting Service, 1970), whereas in 1997 that percentage had increased to 50.7% (Census of Agriculture, 1997). Additionally, the increasing emphasis on growing crops versus raising livestock (Table 4) meant less need for buildings to house farm animals, thus fewer farm structures per well.

Although modern farms with larger acreages and fewer buildings per lot than in the past led to the nearly 1:1 ratio of wells to structures, when the ratios were computed for each PLSS section within the county, some areas with a higher-than-average ratio of wells to structures were identified (Figure 3). If the ratio of wells to structures was >2, then the section was flagged as potentially containing an abandoned well.

A closer examination of the flagged PLSS sections showed that many of the highest ratios of wells to structures were in areas that did not show all of the structures present on the plat map, such as trailer parks and rural housing developments with small tracts of houses. Each of these anomalously high sections was scrutinized to see if they were, in fact, evidence for an abandoned well. For example, a rural PLSS section between the cities of Colchester and Macomb (Figure 4) had a well-to-structure ratio of 10.5 (7 document wells, 3.5 estimated wells, 1 structure) but on an aerial photo of the same area, as many as 20 houses can be identified. Rather than being a section with a high likelihood of abandoned wells, this area might actually have more undocumented wells than estimated, as there are many houses.

The identification of likely areas containing abandoned wells was more successful for rural parts of the county that have not experienced the construction of housing developments. For example, a section in the northeast portion of the county with a well-to-structure ratio of 2.5 had as many as six farmsteads on historic plat maps, but only two remained by 1997 (Figure 5). This portion of the county was part of the 1934 well survey, so the locations of five wells are known (open white triangles on Figure 5). Three of the wells are near existing structures and presumably are still in use. ISWS records show that one of the remaining wells was sealed in 2005, but the location of the 5th well (north-center of the section) is presently cropland with no existing structures, suggesting that it was abandoned and filled at some point.

For comparison purposes, another rural section of the county with a well-to-structure ratio of 2.5 (7.5 wells, 3 structures) was identified from an area that was not included in the 1934 well survey and therefore has fewer documented wells (Figure 6). This section has 3 documented wells and an additional 4.5 estimated wells based upon the prevailing well-to-structure ratio for the county. The wells that were likely associated with the former structures shown on older plat maps have presumably been abandoned and/or filled, but there is no record of sealing in the ISWS well records.

Local Geology and Potential Contamination Sources

The U.S. Environmental Protection Agency (U.S. EPA) toxic release inventory for McDonough County identified only two potential industrial sources of potential water pollution (U.S. EPA, 2018); the potential sources are located in the cities of Macomb and Bushnell. Oil wells are present in the southwest portion of the county that tap a reservoir that is approximately 500 ft deep (Illinois State Geological Survey, 2018). As most of the farm or rural wells (86%) identified during the 1934 well survey in McDonough County were shallow dug, bored, or well-point types ranging from 12-90 ft deep (ISWS, 1935), they are fed by aquifers within glacial deposits. Wells in glacial deposits typically tap unconfined aquifers that are recharged from the infiltration of local precipitation and are parts of local flow systems (Fitts, 2012).

Therefore, the most likely potential sources of contamination to the abandoned or undocumented wells would be from the ground surface through infiltration of nonpoint source agricultural chemicals (e.g., herbicides, pesticides, fertilizer) or from feed lots and septic tanks. Water in local ground water flow systems generally travels from the point of infiltration to the nearest surface water body (lake or stream), so any human exposure to contamination of abandoned wells in the study area would most likely occur in active wells that are located between the abandoned well and a nearby stream.


The total population in McDonough County increased by 20% between 1930-2000, but the population in the rural townships analyzed in this study decreased by 48% during the same time period (Illinois Cooperative Crop Reporting Service, 1970; U.S. Census, 2000). In the process, a large number of rural wells were abandoned. The technique developed in this study could be used as another tool--along with existing methods that employ aerial photographs, topographic maps, plat maps, or a combination of these resources--to identify likely locations of undocumented or abandoned water wells.

Many of the private well records in Illinois are not documented because submittal of their records to ISWS was not mandated until the 1960s (Wilson et al., 2013). The well-to-structure ratios established for rural McDonough County could be used to estimate undocumented wells in other areas of rural Illinois using old plat books from the local area. The average well-to-structure ratio changed from approximately 0.5 in 1934 to approximately 1 in 1997; however, the ratio was >5 in some PLSS sections within the county. The 1997 values are conservative estimates of undocumented wells, as they include only some of the wells installed between 1935 and the 1960s, when well drilling reports were first mandated. The assumption that a high (>2) well-to-structure ratio was an indicator or the likelihood of a PLSS section containing an abandoned well proved to be valid in the rural portions of the county, but was not as successful in areas surrounding towns.

The techniques used in this study could be applied to other areas of Illinois that are predominately involved in cropland and pasture activities. Identification of areas that have a high likelihood of containing undocumented and/or abandoned wells could be useful to county and municipal health departments, particularly when rural property is being developed (e.g., housing tracts, concentrated animal feeding operations).

If access to rural properties can be granted, future research might include a door-to-door well survey of randomly selected PLSS sections to test the accuracy of the number of undocumented wells estimated in this study. Additionally, a site survey could be conducted of areas that have been identified as likely locations of abandoned wells to see if any evidence of a well exists. Ml

Acknowledgements: The authors thank Keisuke Nozaki (Western Illinois University GIS Center), Ken Hlinka (ISWS), Linda Zellmer (Western Illinois University Library), and Bill Cook (Western Illinois University Library Archives) for their assistance acquiring the data used in this study. Additionally, this article benefitted from comments of the anonymous reviewers during the manuscript submission process.

Corresponding Author: Steve Bennett, Department of Geology, Western Illinois University, 1 University Circle, Macomb, IL 61455.



Aller, L. (1984). Survey of available technologies for locating abandoned wells. Proceedings, 1st National Conference on Abandoned Wells--Problems and Solutions, Environmental and Groundwater Institute, University of Oklahoma, Norman, OK.

Apel, T. (2015, September 8). Boy, dog rescued from hole in Lincoln County. The Clarion Ledger. Retrieved from https://www.clarion

Blomquist, P. (1984). Abandoned water well inventory in Minnesota. Proceedings, 1st National Conference on Abandoned Wells--Problems and Solutions, Environmental and Groundwater Institute, University of Oklahoma, Norman, OK.

Census of Agriculture. (1997). Illinois--County data. U.S. Department of Agriculture, National Agricultural Statistics Service.

Fitts, Charles R. (2012). Groundwater science (2nd ed.). Waltham, MA: Elsevier.

Gass, T.E., Lehr, J.H., & Heiss, H.W. (1977). Impact of abandoned wells on groundwater (EPA-600/3-77-095). Ada, OK: U.S. Environmental Protection Agency, Office of Research and Development.

Hendrickson, H., Erickson, N., & Narve, M.A. (1996). Abandoned wells: Conducting a statewide well-sealing demonstration program. Paper presented at the Soil and Water Conservation Society, Ankeny, IA.

Howat, W.A. & Son. (1919). Farm ownership map and plat book guide of McDonough County, Illinois. Peoria, IL: W.A. Howat & Son.

Illinois Cooperative Crop Reporting Service. (1970). Illinois County agricultural statistics, McDonough County (Bulletin C-46). Illinois Department of Agriculture and U.S. Department of Agriculture.

Illinois State Geological Survey. (2018). Illinois oil & gas resources. Retrieved from

Illinois State Water Survey. (1935). A survey of the groundwater resources of Illinois. Champaign, IL: Department of Registration and Education, State Water Survey Division.

Kennedy, J.M. (1987, October 17). Jessica makes it to safety--After 58 1/2 hours. The Los Angeles Times. Retrieved from http://articles.

Rockford Map Publishers. (1954). McDonough County, Illinois, farm plat book and business guide: 1954. Rockford, IL: Rockford Map Publishers.

Rockford Map Publishers. (1997). McDonough County, Illinois, farm plat book and business guide: 1997. Rockford, IL: Rockford Map Publishers.

Stout, K.K., & Sitton, M.D. (1984). Locating abandoned oil and gas wells with historical aerial photos. Proceedings, 1st National Conference on Abandoned Wells--Problems and Solutions, Environmental and Groundwater Institute, University of Oklahoma, Norman, OK.

U.S. Census. (2000). Illinois County census data. Retrieved from

U.S. Environmental Protection Agency. (2018). 2016 Toxic release inventory factsheet--McDonough County, Illinois. Retrieved from ?pstate=IL&pYear=2016&pParent=NAT

Wilson, S.D., Rennels, K.L. & Roadcap, G.S. (2013). A water well inventory to assess potential conflicts from development of a well field in selected areas of McLean, Tazewell, and Woodford Counties, Illinois (Contract report 2013-03). Champaign, IL: Illinois State Water Survey. Retrieved from

Steve Bennett, PhD

Department of Geology

Western Illinois University

Chad Sperry, MS

GIS Center

Western Illinois University

Caption: FIGURE 1: Portion of the Plat Map Containing Bushnell, Illinois Note. Structures are depicted by black squares. As no structures are depicted within the city limits, we did not use any PLSS sections containing a portion of the city limits (sections 27, 28, 33, and 34 in this example) in this study.

Caption: FIGURE 2: Estimate of Undocumented Wells per 1-[mi.sup.2] Sections in McDonough County, Illinois Note. White squares represent areas that were excluded from the study analysis.

Caption: FIGURE 3: Ratio of the Number of Estimated Wells to Structures in 1-[mi.sup.2] Sections in McDonough County, Illinois Note. Sections with a ratio >2 are areas that are likely to contain abandoned wells. White squares represent areas that were excluded from the study analysis.

Caption: FIGURE 4: Plat Map Comparison to an Aerial Photo Note. This section had a very high well-to-structure ratio (10.5) due to the inaccurate structure information on the plat map compared with those identified on an aerial photo of the area (white squares).

Caption: FIGURE 5: First Example Section With a High Likelihood of an Abandoned Well Note. The well-to-structure ratio was 2.5 (5 wells, 2 structures) as of 1997. This section was part of the 1934 well survey, so the locations of the wells are known. Two of the wells in the northwest quarter of the section (depicted by open triangles) were last near a structure on the 1962 plat map. One of these wells was sealed in 2005 and the other is presumed to be abandoned.

Caption: FIGURE 6: Second Example Section With a High Likelihood of an Abandoned Well Note. The well-to-structure ratio was 2.5 (7.5 wells, 3 structures) as of 1997; this section was not included in the 1934 well survey, so only 3 well records (depicted by open triangles) exist for this area. The wells that were presumable associated with the former structures might have been filled, although there is no record of their sealing.

Ratios of Wells to Structures for Townships in the 1934 Well Survey

Township    Structure Count    Estimate of   Documented    Ratio of
                               Structures     Wells in     Wells to
                                 in 1934        1934      Structures
           In year   In year
            1919      1954

T5N R1W      216       141         180           70          0.39
T7N R1W      177       155         126           78          0.62
T7N R2W      164       145         151           78          0.52
T7N R3W      182       164         153           64          0.42
Total        739       605         610          290       Mean = 0.49


Estimates of Undocumented Wells in 1934

Township   Estimate of    Well        Estimates of
           Structures    Records    Undocumented Wells
             in 1934     in 1934

                                   Low    Medium   High

T4N R1W        171          1       66      83      105
T4N R2W        174          6       62      79      102
T4N R3W        180          4       66      84      108
T4N R4W        179          2       68      86      109
T5N R2W        158         10       52      67       88
T5N R3W        186         11       62      80      104
T5N R4W        152         12       47      62       82
T6N R1W        161          6       57      73       94
T6N R2W        143         12       44      58       77
T6N R3W        111          2       41      52       67
T6N R4W        161          3       60      76       97
T7N R4W        139          3       51      65       83
Total         1,915        72      676     865     1,116


Ratios of Estimated Wells to Structures in 1997

Township    Estimated     Well       Sealed    Estimated
             Number      Records    Wells as     Wells
            of Wells      From      of 1997     in 1997

T4N R1W        86          34          0          120
T4N R2W        87          62          2          147
T4N R3W        90          50          0          140
T4N R4W        90          39          0          129
T5N R1W*       70          18          0          88
T5N R2W        79          47          1          125
T5N R3W        93          149         2          240
T5N R4W        76          52          0          128
T6N R1W        81          31          0          112
T6N R2W        72          29          0          101
T6N R3W        56          67          2          121
T6N R4W        81          30          3          108
T7N R1W *      78          39          2          115
T7N R2W *      78          44          0          122
T7N R3W *      64          42          0          106
T7N R4W        70          31          1          100
Total         1,251        764         13        2,002

Township    Structure    Ratio of
              Count      Estimated
             in 1997     Wells to

T4N R1W        129         0.93
T4N R2W        112         1.31
T4N R3W        99          1.41
T4N R4W        123         1.04
T5N R1W*       127         0.69
T5N R2W        109         1.15
T5N R3W        135         1.78
T5N R4W        128         1.00
T6N R1W        134         0.83
T6N R2W        112         0.90
T6N R3W        64          1.88
T6N R4W        116         0.93
T7N R1W *      104         1.11
T7N R2W *      138         0.88
T7N R3W *      107         0.99
T7N R4W        118         0.84
Total         1,855     Mean = 1.08

* Well numbers for these four townships were taken from
the 1934 well survey.


Agricultural Changes in McDonough County From 1930-1997

                       1930      1997     Percent Change
Cropland (acres)
  Corn                115,000   134,609         17
  Soybeans             4,200    128,736       2,965
  Wheat               28,800     2,215          a
  Oats                46,000      667          -99
  Hay                 28,200     9,151         -68
  Barley               3,500       0           -100
  Rye                  1,300       0           -100
  Total               227,000   275,378         21
Livestock (animals)
  All cattle          26,300    19,581         -26
  Milk cows           10,000      274          -97
  Hogs                115,500   33,390         -71
  Sheep                8,100     1,520         -81
  Horses              11,800      554          -95
  Total               171,700   55,319         -68
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Author:Bennett, Steve; Sperry, Chad
Publication:Journal of Environmental Health
Article Type:Report
Geographic Code:1U3IL
Date:Dec 1, 2018
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