Dissolved oxygen modeling of the Blackstone River (northeastern United States)

A dissolved oxygen model, QUAL2E, has been calibrated and validated to the Blackstone River, using the data collected in 1991 for the Blackstone River Initiative — Dry Weather Study. Physical representation of the river is accomplished using the data from previous studies. Flow profiles have been developed using the average daily flows of the three permanent United States Geological Survey (USGS) gaging stations and five wastewater treatment plants on the Blackstone River. These flow profiles have been verified by the success of the model to simulate a conservative parameter, chloride and independent flow measurements. The calibration and validation of the model for dissolved oxygen involved a stepwise approach to simulate each source and sink of dissolved oxygen. This has been accomplished by progressively defining atmospheric reaeration, oxygen depletion due to carbonaceous biochemical oxidation demand, nitrification, sediment oxygen demand and algal photosynthesis and respiration. The success of the model can also be judged by the ability of the model to represent the system under different conditions. During additional validation with data sets from 1980, the model was successful in predicting conditions prior to a previous waste load allocation for the largest point source. Statistical tests of the model results and the observed data have been performed for the 1991 surveys with a median relative error of approximately 10%. A brief assessment of the 7Q10 flows indicates violations of the dissolved oxygen criteria of 5.0 mg/l occurring downstream of the Woonsocket wastewater treatment plant. Minor violations occur in Massachusetts upstream of four impoundments.