Barr completed a total maximum daily load (TMDL) study of Nine Mile Creek in the southwest suburban area of Minneapolis. The study was conducted in cooperation with the Minnesota Pollution Control Agency (MPCA) for the Nine Mile Creek Watershed District. The creek was listed on the MPCA’s impaired-waters inventory for turbidity levels exceeding the Class 2B water quality standard of 25 NTUs (nephelometric units—turbidity is measured as the amount of light scattered in a water sample and reported as NTUs). The creek is also listed for chloride and fish index of biotic integrity (IBI). In response to these impairment listings, the watershed district authorized comprehensive stream and watershed assessments that include extensive field data collection followed by computer simulation and mass-balance modeling of streamwater-quality conditions to assess the management practices that must be implemented to restore the creek to compliance with MPCA standards.
The first phase of work involved characterization of stream hydrology and water-quality conditions, including chemical and biological water quality. Barr surveyed the physical characteristics of the stream according to the Rosgen stream classification system and installed three continuous-flow-gaging and automatic-sampling stations on the main stem and branches of the creek. We’re conducting year-round continuous discharge monitoring and episodic water-quality sampling—both baseflow and stage-activated storm event—for a wide variety of water-quality constituents. We’re also concurrently studying stream habitat and the benthic macroinvertebrate and fish communities of the creek to determine any possible biotic impairments related to urban stormwater runoff and road salt applications. Following MPCA protocols for fish-community sampling and physical habitat assessment for wadeable streams, Barr completed fishery surveys for the development of the Index of Biotic Integrity (IBI) scores throughout the watershed. The Nine Mile Creek Watershed District, MPCA and Barr completed a total TMDL analysis of Nine Mile Creek and its watershed to address the fish IBI listing on the MPCA’s Section 303(d) Impaired Waters list. Barr collected continuous turbidity data to show that the creek should be de-listed for turbidity. Working with data collected by our staff and the Metropolitan Council, Barr has prepared the watershed and stream characterization, stressor identification, and causal analysis/diagnosis for the biological impairments.
A detailed computer model (i.e., XP-SWMM) has been developed to simulate stream hydrology and its effect on aquatic habitat. Calibrated to observed conditions, this model can be operated in “what if” mode to evaluate the benefits of implementing various watershed best management practices (BMPs) designed to reduce the rates and volumes of watershed runoff. Stakeholder meetings were organized and conducted to inform interested parties about TMDL study progress and to gather public input about proposed BMPs. In addition, mass-balance modeling and a TMDL report for chloride was developed/approved and implementation planning was completed.