Determination of Fecal Coliform Loading and its Impact on River Water Quality for TMDL Development
The reach of Red River of the North flowing through the Cities of Fargo, ND and Moorhead, MN has been impaired due to the fecal coliform. Analyses of water quality samples and rainfall data showed that high coliform concentration in the river was related to rain events, and runoffs from the urban areas are major sources of fecal coliform contamination. To determine the fecal coliform total maximum daily load (TMDL) and to develop an implementation plan for water quality improvement, an extensive water quality sampling and model simulation program was carried out to calculate storm runoff flow rates, fecal coliform loads from the runoffs, and their impact on Red River water quality.
The Storm Water Management Model (SWMM) was used to simulate the runoff flow rates and fecal coliform concentrations from different drainage areas under various rainfall conditions. Hydrographs and pollutographs generated by the model were used to determine the average daily fecal coliform load from each drainage area and the total load to the Red River. Steady state water quality model, QUAL2E, was employed for determining the impact of storm water runoff on Red River fecal coliform concentration. Event mean concentration (EMC) was used as a tool to link dynamic SWMM model to steady state QUAL2E model. The runoff sampling and modeling results were used to analyze the effect of rainfall properties on fecal coliform EMC. The study also identified sanitary sewer bypass as the potential source of high fecal coliform concentration in the River.
The Red River of the North, located in the north-central plains of the United States, plays an important rule in the regional development and is used for water supply, irrigation, industry, livestock, and recreation. The reach of the Red River main stem that flows through the Fargo, ND and Moorhead, MN areas was identified as impaired for its designated use due to high fecal coliform concentrations. Under the Clean Water Act, a pollutant-specific total maximum daily load (TMDL) needs to be developed. Led by Minnesota Pollution Control Agency (MPCA), a project team was assembled with participation of North Dakota Department of Health, Cities of Fargo and Moorhead, River Keepers, a voluntary group, and North Dakota State University (NDSU). Researchers from the NDSU Civil Engineering Department were responsible for determining fecal coliform loads from various sources and simulate its impact on the Red River water quality. The results of this study are presented in this paper.
The Red River formed at Wahpeton, ND and Breckenridge, MN by the confluence of the Ottertail and Bois de Sioux rivers flows northward through the Red River Valley and drains into Lake Winnipeg in Canada. It flows across the flat, former bottom of the ancient glacial Lake Agassiz with average relief of only 2-3 feet per mile towards the river and 1-2 feet per mile northwards. The Red River forms the boundary between North Dakota and Minnesota as it meanders for 394 river miles (mi) to the Canadian border, a path that is nearly double the straight-line distance. The river flow rate varies greatly through out a year. Snow melting in the spring often causes flood conditions and rainfalls in early summer result in high river flows (Stoner et al., 1993). During the dry months of a year, the river flow rate can be very low, especially in the upper portion of the river, causing water shortage concerns. The area is renowned for its harsh and long winters with an annual average temperature of only 41.0◦F. A map of the Red River Basin is shown in Figure 1, with the impaired reach area highlighted.