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The sampling method proposed by Iso-soil is a stratified method, that will respect the US-EPA statement: “When a plume is heterogeneous, it is best to consider the behaviour of the contaminant in each flow path instead of trying to predict the average behaviour of the entrire plume.” However, instead of one biodegradation rate keyed to one point, e.g. in this case a well, the Iso-soil stratified approach leads to one estimated mean biodegradation (with corresponding confidence interval) for all points (e.g. wells) within a particular stratum.
The Iso-Soil approach will consider the entire plumeas equal to the study area defined for CSIA after the hydrogeology, geochemistry and concentration field has been determined.This will also be consistent with the US-EPA guidelines.  The number of observations generated from one sampling event in time according to this design, i.e. 12 – 20 would probably in most cases be sufficient for the entire plume, with the possible exception when several strata are used in a stratified approach, to comply with the Iso-soil design for estimating the mean.
From a comparison between the proposed Iso-soil sampling design and the US-EPA guidelines under the assumption that the US-EPA guidlines are adhered to with regard to number of samples and location of these samples, one can see the following advantages with the iso-Soil approach:

•    The costs and spatial resolution of a given sampling design is totally transparent
•    The sampling program will always provide data that can be used for deriving mean concentrations and isotopic signatures with accompanying confidence intervals for the whole study area and its strata (if any)
•    The sampling program will always provide data to make inferences from using different statistical tests e.g. comparing means, testing hypotheses etc

The research has received funding from the European Community's Seventh.
Framework Programme FP7/(2009-2012) under grant agreement no 212781.