Statistical process control in sediment pollutant analysis

Statistical process control (SPC) is proposed for application to monitoring environmental variables. SPC was used to identify long- and short-term trends and outliers of sediment cadmium (Cd) concentration at an ocean outfall and reference station on the San Pedro Shelf, California. SPC is based on parametric statistics, is easy to calculate, emphasizes visual display, and benefits from a suite of time-tested zone rules to objectively distinguish out-of-control conditions (OOC). Since temporal and spatial trends of sediment Cd obtained from SPC are consistent with conventional methods employed here, the advantages of SPC offer promise in analyses of environmental variables. Comments on management applications and quality control are included.