Sarah Germann
Source Area Determination and Water-Quality Statistics: Salt Creek Watershed, Porter County, Indiana.
BSES Senior Research 2005

Background

The Salt Creek watershed is located in Porter County Indiana and is part of the larger Grand Calumet River watershed (or the Coastal Zone area), which flows into Lake Michigan. The area historically has been an area of concern for environmental management. The Center for Geospatial Data Analysis is currently working on a project for the Indiana Department of Environmental Management to compile and analyze historical water quality data from the Coastal Zone Area; for my project I chose to work with a smaller watershed (Salt Creek) and conduct similar analyses.

The Salt Creek watershed covers 12.95% of the Coastal Zone Area and includes the streams Salt Creek, Pepper Creek, Clark Ditch, Hodsen Ditch, Damon Run as well as Loomis Lake, Sagers Lake, Lake Louise, and Silver Lake. Salt Creek flows into the Calumet River and was chosen for my project because of the varying nature of the basin.

The headwaters of Salt Creek sit in heavily populated areas as well as heavily farmed areas. Determining potential source areas for pollutants is usually divided into two categories: nonpoint sources and point sources. Nonpoint sources of pollution in the study area are runoff from farms and urban areas, nutrient and sediment runoff, and septic systems. Point sources are areas of high commercial/industrial use and high density residential areas, NPDES locations, and Toxic-Release Inventory locations (TRIs). ESRI ArcGIS was used to map and analyze both non-point source pollution and point source pollution in the Salt Creek Watershed. The iLITH water-wells were also mapped and analyzed as a

proxy for locations of septic systems. The spatial analyst tool in Arc GIS can be used to create a density layer of water-well locations, showing the density of potential septic system sites (nonpoint source pollution). Lastly, using the historical data collected on this project for several sampling sites, I could look at select parameters over time as well as analyze spatial trends. I looked at nitrates and E. coli. E. coli has historically been a problem in the study area. One analysis of E. coli was over about ten years for two sites, one at the headwaters and one downstream. The trend fluctuates seasonally, but the mean values for each year at each site were above the human contact standard of 235 cfu/100 mL sample. A second trend of E. coli was done spatially over several sampling sites for one select day. Nitrate values were also analyzed to observe any trends over time. Nitrate values fluctuate seasonally like the E. coli values; the trend of the mean values over time increases 0.073 mg/L*year.

Continuing at this rate the nitrate values would be over the MCL value of 10 mg/L in about 95 years. In light of this study of source area determination and surface water quality analysis, my recommendations are to have continuous long-term data collection to analyze trends in water-quality parameters over time and to have consistent water-quality monitoring at several sites to evaluate water-quality parameters spatially.