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Lake Michigan—Bacteria TMDL
The Indiana Department of Environmental Management (IDEM) developed an E. coli TMDL for Indiana's Lake Michigan Shoreline and tributary waterbodies that appear on the 2002 section 303(d) list due to the fact that there have been an average of more than 15 beach closures per year at the National Seashore and state park during the 1990 to 2000 period from violations of E. coli water quality standards.
Potential point and nonpoint sources of pollution that were investigated were the following:
Point sources
- Wastewater treatment plants: None discharge directly to the lake and were investigated as tributary TMDLs.
- Combined Sewer Overflows (CSOs): None discharge directly to the shoreline waters were investigated as part of tributary TMDLs.
- Storm Water Phase II Communities: E. coli loadings to the Lake Michigan shoreline from most urban stormwater sources were included in the estimates of the tributary loads. Direct discharge of stormwater from these communities into the lake was not considered a significant source of E. coli.
Nonpoint sources (focus of this E. coli TMDL)
- Tributaries: Tributaries that enter Lake Michigan within Indiana include Burns Ditch, the Indiana Harbor Ship Canal, Trail Creek, and several smaller tributaries and man-made ditches. These were considered the most significant sources of E. coli to the shoreline.
- Residential septic systems: Since site-specific information on the location areas with high septic vulnerability was not available, estimates of E. coli loads were made.
- Wildlife: Wildlife populations and the amount of E. coli each organism contributed were estimated, then the results were compared to loads estimated from other sources. Raccoons, white-tailed deer, and seagulls were listed as potential sources of E. coli.
- Swimmers, beach sands, and algae: Daily E. coli loads from swimmers, beach restroom facilities, and sand/algae at each of the six major beaches (Mt. Baldy, Central Beach, Kemil Road Beach, Dune Acres Beach, California Avenue Beach, West Beach) were estimated.
- Boaters: Best professional judgment was used to estimate the load at Washington Harbor, Hammond Marina, and Robert A. Pastrick Municipal marinas.
- Boundary conditions: Since there was no data available regarding E. coli counts at the boundary conditions of the shoreline, a constant value was assumed for modeling purposes based on the average 1999 data at two western monitoring locations.
E. coli loading from streams entering Lake Michigan was based on observed data. Other sources quantified for the lakeshore model include wildlife, waterfowl, failing septic systems, swimmers, and boaters.
Environmental Fluid Dynamic Code (EFDC) was used as the modeling framework to support TMDL development. This is a hydrodynamic model for receiving waters which can model in 3-D, and can estimate the fate and transport of E. coli. This model involved the consideration of 4 major components (from April 1 to October 31, 1999 data): waterbody representation (shoreline and bathymetry); meteorological data; hydrologic flows; and representation of E. coli loadings.
Final TMDL load allocations for tributaries; residential septic systems; swimmers, beach sands, and algae at public beaches; boating activity and wildlife are indicated in the document.
Footnote: Indiana Department of Environmental Management. 2004. Lake Michigan Shoreline TMDL for E. coli Bacteria 
