Illinois State Water Survey (ISWS) findings of a study on arsenic in drinking water from wells near Tolono, IL showed no discernable pattern of elevated arsenic levels except in the small subdivision south of Tolono where the safe drinking water issue was initiated, according to Walt Kelly, ISWS groundwater geochemist.
Last October, the ISWS Public Service Laboratory discovered that a homeowner south of Tolono had well water arsenic levels that tested 344 parts per billion for the outdoor water supply and 154 parts per billion for the indoor water supply, which runs through a water softener. Both levels far exceed the federal standard maximum of 10 parts per billion for drinking water.
Investigating further, Kelly and Tom Holm, ISWS geochemist, collected samples from 17 wells in March and April and accessed a database to evaluate 54 samples from Tolono and the surrounding area. They found that 25 samples had arsenic concentrations above the federal standard, and eight samples had arsenic levels that exceeded 50 parts per billion.
“The findings are typical of other studies in that, for the most part, the high concentration levels are not located in one area, but are spread out,” Kelly said. “There is a lot of hit and miss.”
The subdivision where the initial sample was taken had higher arsenic concentration levels than surrounding areas, indicating a “warm spot,” Holm said. Arsenic “hot spots” with extremely high arsenic concentrations in groundwater are found in Bangladesh, for example. All wells in this location were drilled to the same depth, which may explain this phenomenon.
The ISWS study showed a relationship between well depth and arsenic concentrations in that the samples with the highest arsenic concentrations (above 40 parts per billion) were from wells between 165 and 180 feet deep. These results suggest that a specific sand layer in the geologic layer is the location where arsenic is plentiful.
“Wells screened in the shallower sand layers sometimes have arsenic concentrations greater than 10 parts per billion, but levels are rarely above 30 parts per billion,” Kelly said. “It is important to note that not all wells drilled to the deeper sand layer have excessively high arsenic levels.”
Arsenic is found naturally in geologic layers in Illinois. As groundwater flows through these layers, the arsenic may dissolve in water under certain conditions; the presence of organic matter seems to be an important variable. The contaminant has no smell or taste in drinking water.
Solving the problem of high arsenic levels in drinking water is no easy task since water softening in the home does not appear to reduce levels. In some locations, wells could be drilled to a deeper or shallower level. Reverse osmosis may be an effective point of use method to significantly reduce arsenic in water.
Many homeowners in the Tolono area have elected to tap into the city water supply, which is supplied by Illinois-American Water in Champaign. Illinois-American gets their water from the Mahomet Aquifer.
While city water treatment plants are required to meet federal and state regulations, there are no regulations for private wells. Homeowners are responsible for having their well water tested to ensure that it is safe to drink.
The ISWS Public Service Laboratory (PSL) tests well water for a small fee. Contact the PSL at 217-333-9321; http://www.isws.illinois.edu/chem/psl. The ISWS is a division of the Prairie Research Institute in the University of Illinois at Urbana-Champaign.
