Prediction of Soil Lead Recontamination Trends with Decreasing Atmospheric Deposition

Abstract

The mathematical model of soil mixing after atmospheric surface deposition developed in Drivas et al. (2011) is expanded here and applied to a case study of soil recontamination in areas near a lead smelter in Herculaneum, Missouri. Soil lead samples collected from the yards of several residences in Herculaneum between 2001 and 2009 show that recontamination of previously remediated yards has taken place. The model is used to predict a relative soil lead recontamination trend with time, based on the remediation date and decreasing smelter emissions over time. An average scaling factor between relative and absolute soil lead levels is derived based on over 1600 data points from 24 properties, using modeled air lead levels and the remediation date for each property. The scaling factor was used to predict soil lead recontamination trends at an additional six properties that were remediated in the mid-1990s. The predicted soil lead concentration vs. time curves match the time-trends in the soil data, explaining the observations that soil lead levels increased during the 2000s for properties remediated in 2001–2002, but decreased during the same time frame for properties remediated in the 1990s. The model can be used to predict expected recontamination trends under differing air deposition scenarios and to extrapolate expected recontamination trends into the future.