Shallow Groundwater Sampling in Kane County, 2015

In October 2003, scientists from the Illinois State Water Survey (ISWS) sampled 75 shallow wells for water -quality analysis in Kane County to provide a “snapshot” of groundwater quality in these shallow aquifers, and to compare water quality from different pa rts and aquifers of Kane County. In the fall of 2015, the study was repeated to assess how groundwater quality had changed since 2003. Sixty -eight wells were sampled in 2015, 55 of which had been sampled in 2003. The quality of shallow groundwater in Kane County is generally good, especially in the western and central thirds of the county. However, the total dissolved solids (TDS) values of samples from the eastern third of the county were significantly higher than elsewhere in the county; chloride was the ion of greatest concern. Two- thirds of the samples from the eastern wells sampled had TDS and/or chloride concentrations above their drinking water standards. Road- salt runoff is most likely the major source of elevated TDS and chloride. Of the wells samp led in both 2003 and 2015, about 60 percent had higher TDS values in 2015, with three having increases greater than 100 mg/L. The average increase for the wells with increasing TDS values was 50 mg/L. The increase in TDS is entirely explained by increases in chloride and sodium concentrations, which increased in 78 percent and 59 percent of the wells, respectively. The average increase for wells with increasing values was 25.4 mg/L for chloride and 19.2 mg/L for sodium. The average rate of increase in chlor ide concentrations in the urban eastern third of Kane County was 3.9 mg/L/yr, which is similar to rates found in other studies in northeastern Illinois.