CO-KRIGING TO INCORPORATE SCREENING DATA - HUDSON-RIVER SEDIMENT PCBS

Kriging methods of geostatistical analysis provide valuable techniques for analysis of sediment contamination problems, including interpolat ion of concentration maps from point data and estimation of global mea n concentrations. Sample collection efforts frequently include prelimi nary screening data of considerably more extensive coverage than the l aboratory analyses on which estimation is usually based. How should th ese be incorporated in kriging? Screening and laboratory analysis cons titute two separate estimates of the same spatial field but of very di fferent characteristics. A modified version of co-kriging is developed to include the imprecise screening information in the analysis of con taminant distribution. Use of the method is demonstrated on a data set of sediment PCB samples from the Upper Hudson River, for which prelim inary categorical mass spectrometry screening was used to select a sma ller set of samples for gas chromatograph analysis. The method is wide ly applicable to many situations of contaminant and natural resource e stimation.