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 andrnBTEX in lightly contaminated soils to establish the mechanisms related to contaminantsoilrnbinding. This work ascertained that for a wide spectrum of contaminants, a givenrncontaminant is desorbed from soil solids in a manner consistent with a two-compartmentrnsorption system; for each compound in soil these compartments consist of rapid releasernfraction and a slow release fraction.rnEstimations of these fractions can be accomplished with a bench scale apparatusrnconsisting of a modified zero headspace unit containing a semipermeable bag of resin tornadsorb the contaminants released from soil solids and solubilized in the water fraction.rnThe sorption to the resin is monitored for a duration of 15 days at regular time intervals.rnBased on the accumulation of contaminants onto the resin with time, a rapid-release andrnslow-release fraction can be estimated under the highly conservative condition ofrnmaximum driving gradients that establish maximum soil desorption rates. Graphs ofrncumulative contaminant loss from the soil can be plotted from the resin analysis data; thisrndata can be used to estimate the fraction of contaminant concentrations that are in thernrapid release compartment. This data is used to determine a “Release Index” for arnparticular soil sample. The Release Index parameter is site specific and is potentiallyrnuseful in predicting the spatial distributions of source area contaminant.rnResearch to date indicates that certain rapid field techniques for measuring vapor pressurernhave some potential for estimating rapid release fractions. At two manufactured gas plantrnsites where a number of soil samples were analyzed, the release index correlated wellrnwith certain vapor pressure measurement methods with an R2 > 0.9. The naphthalenernrelease index in field was correlated with total vapor pressure and benzene release indexrnwas correlated with benzene vapor pressure measurements.rnThe presentation will describe potentially useful techniques to describe the spatialrndistributions of rapidly released contaminants relative to the macro-geometries of sourcernareas of contaminated sites.