Arsenic is one of the most common natural contaminants of groundwater in Illinois, and weve done several studies on it, so I anticipate Ill be writing a lot of posts about it on this blog. I was prompted to write one today because of the recent discovery of a high arsenic area near Champaign. As was reported in our local paper, The News Gazette, Sunday February 28, 2011, a domestic well in Tolono that was recently sampled had an arsenic concentration of about 300 ug/L, about 30 times the drinking water standard of 10 ug/L (equivalent to 10 ppb), and the highest arsenic level Ive ever seen in Illinois. By 50%!
The Water Surveys Public Service Laboratory (PSL) has provided well water analyses for citizens of Illinois for over 100 years, but its only been in the past 5 or 6 years that weve had the analytical capability to detect arsenic at low levels (the current detection limit is around 1 ug/L, about 100 times better than it used to be). So every now and then the PSL measures a high arsenic level. But 300 ug/L, that was startling. Were planning on sampling a number of wells in the area to see if we can find the extent of the arsenic contamination. A few other nearby wells also had elevated arsenic levels, in the 80-100 ug/L range, and a Water Survey monitoring well a couple of miles southeast of the very high well had an arsenic concentration of 23 ug/L.
One of the problems with arsenic is its high degree of spatial variability. In a study a few years ago in Champaign and Tazewell Counties (southeast of Peoria), we sampled about 100 wells. Using those samples and data from the health department and other sources we hoped to discover spatial and depth trends for arsenic that would help guide well drillers and homeowners (heres a link to the report we produced). Unfortunately, the variability was so great that we cannot make any meaningful predictions about where elevated arsenic is found. Check out the map below:
The numbers are arsenic concentrations and the green lines represent a distance of 100 m (~300 ft). All of these wells were of similar depth. As you can see, even within a distance of 100 m, wells with arsenic well above the standard are very close to some with little arsenic.
More on arsenic in later posts. If you want to have your well water tested, contact the PSL at (217) 333-9234.