similar to the situation with other drinking water contaminants, the ability to detect trace concentrations of one part per billion, which is equivalent to one second in 32 years, or less,  has outpaced the science that can provide meaning to the significance of chronic exposures to these minute levels in drinking water.  Measuring total chromium levels below 1 ppb was not standard until the mid-1990s.  Previously, the detection ability was in parts per million, not billion.  Furthermore, few analytical labs are capable of measuring chromium 6 down to the proposed California public health goal.

Total chromium levels have been measured at Madison wells since at least the early 1970s, and the levels are relatively unchanged since that time.  The techniques and the methods for measuring chromium may have changed, but the concentrations have not.

Read more:  http://www.cityofmadison.com/water/waterQuality/ChromiuminWater.cfm