Conceptual Site Model - Argonne National Laboratory

WVDP Phase 1 CSAPperformance will be compared with FIDLER detector performance for an area of the premises known tohave Cs-137 surface soil contamination present. The methods for this comparison are explained in detailin Section 6.11. If the results are that the FIDLER provides sufficiently low MDC levels for Cs-137, onlya FIDLER will be deployed for the remainder of gross gamma survey work. Alternatively, if the 2 in. × 2in. detector proves capable of identifying Cs-137 at levels that would be CG w concerns and that theFIDLER cannot identify, then both a FIDLER and a 2 in. × 2 in. NaI detector will be used for GWS.Because of the range of field conditions and data collection requirements that fall under the CSAP,providing details about all potential detectors and their performance characteristics is beyond the scope ofthis document. However, for each field data collection activity conducted under the CSAP, a fieldsampling plan will be prepared. If the field work includes the collection of scanning data, the detector(s)to be used will be identified, their deployment configurations and protocols specified, their MDCsestimated, and appropriate QC details provided.11.3 BackgroundThe GWS data from the reference area will be used to evaluate the gross activity detector response forsurface soils with background conditions. Gross activity from a survey of the background area will exhibitvariability that is a product of both counting errors and the natural variability in gross activity present inbackground soils. Section 6.7.1 of MARSSIM provides a general methodology for identifying anomalousmeasurement results in the presence of background conditions. As an example, a measurement greaterthan three standard deviations above average background gross activity levels would be highly unlikelyunless either one was in an area with different background conditions or contamination was present.Because of the variety of surface cover that is present on the WVDP premises, background detectorresponses are expected to also vary significantly depending on the nature of the surface being scanned.While a surface soil reference area will be established and a background detector response developed foreach detector used on the WVDP premises (see Sections 8 and 11.5), this reference area background willbe directly applicable only to comparable areas of the WVDP premises where other types of ground coversuch as pavement or hardstand material are not present.Because of varying background conditions and because areas where contamination is present in surfacesoils may have more than one gamma-emitting radionuclide above background conditions, it will not bepossible to establish a unique field investigation level for determining when contamination is present thatRev. 1 83