Bacteria contamination is viewed as a serious health and water quality issue for the 20 mile long Norwalk River.  This statistical analysis of a multi-year analytical data set included looking at the land use in the watershed to find patterns indicating sources of bacterial contamination.

The watershed encompasses nearly 40,000 acres across seven municipalities, and is a mix of developed (31.5%), forested (48.7%) and wetland (3.4%) parcels. Turf, grass, agriculture and the like constitute the remaining (16.4%) land area. About 56% of the homes are connected to the public sewage systems, with the remaining 44% using septic tanks.  Sources of bacterial contamination in surface water can emanate from both types of systems, along with non-point sources such as untreated stormflow.  In addition, water treatment plants are not required to disinfect their discharge between October 1st and April 30th—a period when beaches and local shellfish beds are closed.

Since 1998, the Harbor Watch/River Watch program has monitored a number of water quality parameters on the river, including the bacterial indicators of fecal coliforms and Escherichia coli (E. coli).  This data analysis evaluated the following questions:

1. Are fecal coliforms and E. coli affected by wastewater treatment plants?
2. Do different sampling sites have different patterns and trends and is there a site which can represent the whole river?
3. Is there a seasonal pattern (higher in summer and lower in winter)?
4. Have concentrations of E. coli and fecal coliforms increased since 1998?
5. Can E. coli and fecal coliforms be predicted by streamflow?
6. Can E. coli and fecal coliforms be predicted by ambient water quality parameters?
7. Is there impact from rainfall?

Based on a statistical analysis of the data, it was determined that water treatment plant protocols did affect bacteria levels in the Norwalk River.  Of particular note were the concentrations from the Ridgefield water treatment plant during the periods when water was not disinfected.