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Data analysis is the step in the process when the data collected from the ToxWatch monitoring network is examined to determine what information can be gleaned from it. This usually involves statistical analysis to develop an average concentration over the given period of time and comparing these numbers to toxicity information and screening levels. Two of IDEM’s regular data analysis project are:
Each month IDEM produces the ToxWatch Monthly Screening Report. The purpose of this internal report is to check for unusually high readings at monitors to see if any immediate action is necessary to protect human health and the environment.
This is accomplished by comparing the concentrations recorded for the month against a set of screening levels calculated by IDEM each year. These screening levels are not health protective. (although IDEM does compare readings to health protective levels as well) The screening levels are based on 5 years of historical concentrations of each pollutant at each monitoring location. They are based on a non-parametric outlier test called the “Sprent Test.” This test is set up to identify readings that are roughly two standard deviations above the mean.
IDEM has been performing regular monthly screenings of the ToxWatch data since 2008 and has yet to encounter an event that required immediate action.
In early 2010 IDEM released the ToxWatch Data Analysis Report. This report was a detailed analysis of a decade’s worth of air toxics monitoring results, covering 1999 to 2008. This report looked at trends in the data and compared concentrations to health protective data.