Kalman Filter Method for Estimating Organic Contaminant Concentrations in Major Chesapeake Bay Tributaries

Concentrations of toxic organics (atrazine, metolachlor, fluoranthene, and total polychlorinated biphenyls) in fluvial transport were obtained for the Susquehanna, Potomac, and James Rivers during 1992−1993. These three tributaries constitute ca. 75% of the total riverine basin area supporting the Chesapeake Bay watershed. Across all basins a total of 26 samples was acquired. Owing to the recent focus on development of a predictive capability for assessing concentration levels in this watershed, the data were used as the basis for predicting concentrations using a Kalman filter. Prediction was obtained for months where the actual concentration was unknown and, using substitution, for selected months when the concentration was measured. A total of 92 comparisons were made across all tributaries and compounds using substitution. For known concentrations, a filtered or smoothed value was also obtained that reflects the correction due to the estimated noise in the measurements and the underlying environmental system. Examination of the contaminant concentration values in a predictive fashion, using substitution, suggests that they are mainly within a factor of 4−5 of the measured concentration in most cases. This is well within the accuracy goals for this watershed.