were selected based upon Nichoul (1975) and, although considered typical 

 for the mixed layer, represent the greatest uncertainty associated with 

 the above model. Typical current velocities in the BGOF range between 

 0.05 and 0.25 m/s (Hazelton Environmental Sciences Corporation 1980) and 

 were used in the model in conjunction with the average loading value at 

 the point source (~ 2. 5i produced water/second) to project worst-case 

 concentrations. The maximum zone of toxicity (assuming a 1$ 

 concentration of produced water in seawater to be toxic) was <1 m 3 . 

 Decreasing the diffusion rates each by an order of magnitude resulted in 

 the "potentially slightly toxic" volume increasing up to 5 m 3 , mostly in 

 the direction of current flow. Increasing the diffusion rates resulted 

 in a decrease in the potentially toxic volume, and in the limiting case, 

 approximated results from method one described above. 



The discharge of produced water had detrimental effects on the 

 biomass levels and production rates of the BGOF biofouling community; 

 but, using the 5$ level to determine differences, significant 

 alterations of the community were restricted to a vertical distance of 

 about 1 m and a horizontal distance of less than 10 m. These results, 

 which were obtained in-situ, agreed well with the projected zones of 

 "toxicity" described above for worst-case conditions. The near-surface 

 zones in the immediate vicinity of the outfall were characterized by the 

 virtual absence of any living large barnacles but small (usually dead) 

 barnacles were sometimes obtained in the collections taken there. 

 Organisms colonizing this area may do quite well until worst-case 

 hydrographic conditions occur. In addition, organisms colonizing this 

 zone were probably periodically subjected to nearly 100$ concentrations 

 of produced water when they are exposed in the troughs of waves. Based 

 upon recolonization information (Figure 24) , worst-case conditions were 

 apparently encountered more frequently in spring through fall periods 

 than during winter. The surface effect of produced water on 

 recolonization rates for spring to summer and summer to fall periods is 

 readily apparent in Figure 24. However, production rates beneath the 

 outfall at depths greater than 1 m were typically equal to, or greater 

 than, production rates on control structures at the same depths during 

 the same periods. Production rates at the surface beneath the outfall 

 were even greater than rates at the surface station on the control 

 structure during the fall to winter period. The fall to winter period 

 was one of high energy and turbulent mixing prevailed. The winter to 

 spring season was characterized by low production rates at all stations 

 throughout the field and no significat differences were apparent. 



Results of respirometry experiments indicated low rates of 

 biofouling primary production and that a stress response (increased 

 oxygen uptake) had been elicited from the communities subjected to 

 treatment. In retrospect, the stress response was attributable to the 

 fact that the concentration of produced water to seawater (10$ to 25$) 

 exceeded the 96-h LC50 value of most of the organisms being tested. For 

 example, a common amphipod ( Ja3sa falcata) of the biofouling community 

 suffered 100$ mortality when placed in a 10$ produced-seawater mixture 

 for 48 h. 



62 



