Abstract

 The Bear Creek drainage district, located in Oakland and Macomb Counties in southeast Michigan, encompasses 19 square miles of concentrated residential, commercial and industrial development. The drainage district is served by 29 smaller county drains that are tributary to Bear Creek. The goal of the current work in the district is to identify and eliminate sources of E. coli contamination in the Creek. The first step is to identify sources of E. coli entering the watercourse through systematic sampling and testing of the Bear Creek and its tributaries.
The water quality data collected in Bear Creek indicates that the E. coli levels increase during wet weather. The cause of this increase is likely caused by (i) sewage entering the storm drains, (ii) bacteria washed off the land surface into drainage systems with the storm water, and/or (iii) re-suspension of bacteria associated with sediments deposited in the collection system.
Four of the large drains that contribute to Bear Creek pass under a major road through inverted siphons. Sediments accumulate in the siphons, which are continuously under water. It was postulated that these sediments serve as a source for bacteria. A diver was contracted by Macomb County Public Works Office to sample the sediments that have accumulated in each siphon. The results of the sampling indicated that high levels of bacteria - in some cases over 2,000,000 cfu/100g - exist in the sediments.
  Sediment samples were also collected at ten locations in the open portion of Bear Creek. A hand auger was used to collect two samples from a depth of 8-12" of sediment from each location. Samples were divided according to sediment type and placed into separate containers. Typically the upper layer was comprised of sand and gravel, while the bottom layer was silt or clay. E. coli levels in the upper layer averaged over 60,000 cfu/100 g, while the lower layer contained an average of about 27,000 cfu/100 g.