During our annual surveys of stream sediment chemistry, concentrations of Total PAHs (the sum of 16 compounds) generally range from <1mg/kg to over 200 over the past 15 years (Fig. 1). A screening value of 23 mg/kg is used as a threshold, above which, aquatic life use is expected to be negatively effected (Probably Effects Concentration, or PEC), and most of our data falls below this value. However there are a number of locations that have exceeded this value one or more times, and we are looking at these sites carefully for temporal trends and potential best practices that will address the source of PAHs to these sites.
Figure 1: Box plot of total PAH (mg/Kg) collected in EII sampling from 1996-2010. Black diamonds represent means, notched lines represent medians, and small circles represent outliers.