Rapid Field Methods to Verify Reductions in Contaminant Release Rates in Source Areas of MGP Sites

摘要

The current work has primarily focused on determining the behavior of PAH’s and BTEX in lightly contaminated soils to establish the mechanisms related to contaminantsoil binding. This work ascertained that for a wide spectrum of contaminants, a given contaminant is desorbed from soil solids in a manner consistent with a two-compartment sorption system; for each compound in soil these compartments consist of rapid release fraction and a slow release fraction. Estimations of these fractions can be accomplished with a bench scale apparatus consisting of a modified zero headspace unit containing a semipermeable bag of resin to adsorb the contaminants released from soil solids and solubilized in the water fraction. The sorption to the resin is monitored for a duration of 15 days at regular time intervals. Based on the accumulation of contaminants onto the resin with time, a rapid-release and slow-release fraction can be estimated under the highly conservative condition of maximum driving gradients that establish maximum soil desorption rates. Graphs of cumulative contaminant loss from the soil can be plotted from the resin analysis data; this data can be used to estimate the fraction of contaminant concentrations that are in the rapid release compartment. This data is used to determine a “Release Index” for a particular soil sample. The Release Index parameter is site specific and is potentially useful in predicting the spatial distributions of source area contaminant. Research to date indicates that certain rapid field techniques for measuring vapor pressure have some potential for estimating rapid release fractions. At two manufactured gas plant sites where a number of soil samples were analyzed, the release index correlated well with certain vapor pressure measurement methods with an R2 > 0.9. The naphthalene release index in field was correlated with total vapor pressure and benzene release index was correlated with benzene vapor pressure measurements. The presentation will describe potentially useful techniques to describe the spatial distributions of rapidly released contaminants relative to the macro-geometries of source areas of contaminated sites.