A recent article in the Chicago Tribune indicated that Chromium VI had been detected in the City of Chicago’s drinking water at a level of 0.18 ppb. Based on the proximity of the City of Evanston’s water intakes to Chicago’s and similarities in the water treatment processes, city staff assumed that the level of Chromium VI in the Evanston drinking water would be approximately the same as Chicago’s.
“As previously reported, the City of Evanston has annually tested for total chromium in their drinking water since 1979 as required by the United States Environmental Protection Agency (USEPA).,” explained Utility Department Director Dave Stoneback. “ The chromium in Evanston’s water has always been below this detection level and reported as non-detectable or less than 5.0 parts per billion (ppb).”
Total chromium is comprised of hexavalent (Chromium VI) and trivalent (Chromium III). Again, it should be noted that the USEPA only requires that total chromium levels be tested.
The current US Environmental Protection Agency (EPA) and Illinois EPA maximum contaminant level (MCL) for chromium is 100.0 ppb. This standard is established in the National Primary Drinking Water Regulations and all public water supplies must abide by these regulations. MCLs are established to protect human health based on what the EPA believes, given present technology and resources to detect and treat, is the lowest level to which water systems can reasonably be required to remove a contaminant.
Recently the Evanston Water Utility had tests performed on its finished water. In samples collected January 26, 2011, using the same laboratory and lab method as the Environmental Working Group (the group quoted in the Tribune article), the level of Chromium VI (hexavalent) was determined to be 0.27 ppb,” added Stoneback.
The laboratory also indicated that the total Chromium level of this same sample was 0.20 ppb. These test results provide an indication of the margin of error in the testing methods when sampling for such miniscule detection levels in the parts per billion range.
“As a point of reference, a part per billion is equivalent to 1 second in 32 years,” explained Stoneback.
“The Water Utility is committed to testing for both total and hexavalent Chromium on a quarterly basis in accordance with a USEPA request for all large water utilities. The results of these quarterly tests will be available on the City of Evanston’s website at www.cityofevanston.org/utilities as they become available,” concluded Stoneback.
The results of the samples of the finished water indicate that the water from the Evanston Water Utility is still some 99.73% below the current Safe Drinking Water Act standard of 100 ppb for total Chromium.