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              1The design of this network is described in detail in the 1996 IGPA Biennial Report
Illinois Groundwater Protection Program Report-January 1998 Page 27
The CDC awarded an additional grant to IDPH in 1994 to survey and sample a minimum of eight wells
in each county to obtain background information on the incidence of contamination in private wells in the
state which were not affected by the flood. A total of 818 private wells were surveyed and sampled. In
this study, IDPH analyzed water samples from these wells for coliform bacteria and nitrate concentration.
Coliform bacteria were found to be present in 44 percent of wells tested; E. Coli (15 percent), and 15
percent had nitrate levels above 10 mg/l as N. The well construction types showing the greatest degree
of coliform contamination were dug and buried wells with 86 percent and 66 percent, respectively.
Together, drilled and driven wells had a 24 percent contamination rate. This generally corresponded with
the results obtained from the survey of flooded wells.
As part of the 818 CDC well study, IDOA tested water samples for atrazine and alachlor utilizing
immunoassay methods. Atrazine was detected in 4.1 percent of the water samples. None of the
laboratory test results exceeded the atrazine MCL which is 3 ppb. Owners/users whose wells tested
positive for atrazine were given the opportunity to have their wells resampled by IDOA and analyzed for
the presence of atrazine and three atrazine metabolites as part of a CIBA Corporation sponsored atrazine
water well study. Ninety-two wells were sampled in this secondary study which will assist the U.S. EPA
in the evaluation of re-registration issues relative to atrazine. The report for this study is in final preparation
by CDC.
During June and July of 1995, in conjunction with local health departments, a follow-up survey of selected
water wells from the first 818 well survey was performed in accordance with protocol developed by CDC.
A total of 365 wells were surveyed and sampled, and each of these wells was resampled within two weeks
after the initial sampling. Water samples were analyzed by IDPH for coliform bacteria and nitrate
concentration. The laboratory results were sent to CDC for their analysis. Health questionnaires for
households served by these wells were completed by local health departments conducting the data
collection activities. The report for this study is also in final preparation by CDC.
In conclusion, no correlation could be found between persons drinking water from contaminated wells and
illness, and there were no adverse health affects related to drinking water. A survey of the flooded wells
indicated that physical damage to the wells was minimal. The flood did not appear to have an impact on
the quality of water from wells that were flooded. In fact, the amount of contamination was similar to that
found in those surveyed wells that were not flooded. This may reflect the fact that most homeowners had
thoroughly flushed and disinfected their wells in accordance with Department-issued news releases and the
advice of state and local health departments, prior to consuming the water. The study indicates that the
groundwater quality in the area of the flood was not adversely affected by the flood waters.
CWS Ambient Groundwater Monitoring Network (CWS Ambient Network) - The Illinois EPA
continues to maintain the CWS Ambient Network.1 This statistically designed network of monitoring
stations has been linked with detailed assessment information and represents the entire population of CWS
wells and principal aquifers in Illinois. (see Figure 2)