Formation staff developed and assembled multiple lines of technical evidence to prove that the source of lead contamination and elevated blood-lead levels in Omaha’s children was predominantly from the presence of lead-based paint on Omaha’s older homes and not from emissions of two former lead processing operations. Two- and three-dimension spatial analysis of chemical data was used to describe and quantify the physical links between historic source areas and yard soil contamination. Quantitative analysis/mass balance of historic and ongoing source contributions over time were utilized to support spatial analyses. Formation staff developed a defense for the claims and, most importantly, developed a “story” and supporting graphics that brought together multiple lines of evidence in a form that was readily understandable by a mediator.
Environmental Site Characterization (Geochemistry)
Formation staff investigated the potential sources of lead to residential soils using spatial analyses of lead distribution across the site coupled with forensic methods.
Electron microprobe analyses and scanning electron microscopy (SEM) methods were applied to confirm the presence of lead paint in soil samples from residential yards where lead concentrations exceeded the clean-up level selected by EPA. The same methods were also applied to demonstrate the absence of lead paint in soil samples from neighboring non-residential settings (e.g., parks) where lead concentrations were considerably lower than the clean-up level. The distinctive morphology of paint particles confirmed their identification based on lead speciation and concentration.
This approach resulted in successful demonstration that lead-based paint, rather than historical air emissions from a lead refinery, was typically the cause of elevated lead concentrations in residential-yard soil.