A comprehensive mass balance of a watershed under steady state conditions

Blackstone River water quality data collected during three dry weather surveys of the river was used in a comprehensive mass balance of selected water quality constituents for the river under steady state conditions, and to develop a method that can be applied to separate point and non-point source loads to the river. Mass balances for the river reaches between each dry weather sampling station were completed which isolated point sources, resulting in the identification of those reaches that were major contributors of pollutant loads to the river. These non-point sources, and the point sources, were ranked according to their dry weather loads to the river, for each survey, and for the average dry weather pollutant load contributions. The Blackstone River QUAL2E dissolved oxygen model was reevaluated and an extensive series of sensitivity analysis runs were completed for the river. These runs were conducted to evaluate specific algal and kinetic coefficients used to calibrate the model to the river. Root Mean Square Error (RMSE) analysis was used to check the goodness of fit to the observed conditions. These validation methods proved that the model is calibrated for the river, and can be used by regulatory agencies to develop TMDLs for the watershed. A second verification method was developed that separated the reach sections into 14 individual water quality models, and these were used to predict the water quality conditions in the river for selected constituents. Comparing the predicted output versus the observed data for the river and each reach model showed that the difference was minor, with a small improvement in RMS Error for the reach models