INTRODUCTION 



The disposal of sewage in the sea and adjoining estuaries is wide- 

 spread. The outfalls are usually relatively close to shore and the sewage 

 is discharged at depths of 200 feet or less. The purpose of the study 

 undertaken by the Civil Engineering Laboratory (CEL) , Port Hueneme, CA, 

 and described in this technical note is to determine whether sewage 

 bacteria would survive for longer or shorter periods if the sewage were 

 discharged at greater depths, where there is less light, where the 

 pressure is greater and where the temperature is lower. Bacteria of the 

 species Escherichia coli, the most abundant bacterial species in human 

 wastes, were employed in the study as representative sewage bacteria. 



METHODS AND MATERIALS 

 Ocean Exposure 



Small containers of sewage bacteria were exposed in the ocean by a 

 team of Navy divers who had had extensive experience in conducting ocean- 

 ographic experiments. A modified aluminum LCM-8 was employed in the 

 undertaking. 



The exposure site was approximately 3 miles offshore, 5 miles 

 southeast of Point Mugu, California. The water depth was 1,300 feet. 

 Ocean exposure stations were established near the surface of the ocean 

 and at depths of approximately 200 feet and 1,000 feet. The exposure 

 stations were simply tethering hooks or loops for suspending samples at 

 various positions on a 1,000-foot line (Figure 1). The line was supported 

 from the surface by three steel drums serving as buoys (Figure 2). A 

 500-pound weight at the end of the line held it taut in the water 

 (Figure 3). The assembly was prevented from drifting by a separate 600- 

 foot-long line attached to the 500-pound weight on one end and to an 

 ocean-bottom anchor on the other. Powerful winches (Figure 4) were used 

 to raise and lower the assembly when samples were removed or placed in 

 the ocean. 



Bacterial Cultures 



Pure cultures of Seattle strain E. coli as supplied by Roche 

 Diagnostics, Division of Hof fman-LaRoche, Inc., Nutley, NJ 07110, were 

 employed in all of the experiments. The bacteria were supplied as 

 BACT-CHEK discs, which are composed of dried bacterial cells and have a 

 diameter of approximately 4 millimeters and a thickness of approximately 

 1/2 mm. Each disc contains 100,000 to 1 million viable microorganisms. 



