(7) Structural Performance (Fig. 59). 



Figure 59. View showing effect of surface currents around 

 "monopod" post (August 1973). 



(a) Performance. Structural performance has been good, though design condi- 

 tions have not been experienced. During periods of vibration, motion has been slow and 

 regular; motion on nearby four-le^ed platforms has been more rapid and irregular. 



The impressed current system of cathodic protection was not satisfactory, and is being 

 modified and sacrificial anodes included. 



A 0.5-inch double plate has been installed around the center post in the tidal area for 

 erosion protection. 



(b) Maintenance. Regularly scheduled inspections, including divers' inspection, 

 has kept maintenance work to a minimum. 



(8) Effect of Structure on Environment. 



(a) Physical. Scour has taken place under the northwest comer of the pontoon 

 base to a depth of 10 feet. It is to be remedied with triangular concrete blocks surrounding 

 the area to deflect the current, with the space under the pontoon and in the immediate 

 vicinity to be filled with grout, both in plastic bags and pumped into place. 



Raw sewage is now being discharged at sea bottom level, but a sewage treatment plant is 

 under construction. 



(b) Biota. Because of the heavily silted water, this area has never been a good 

 fishing ground. Fish are in the area during salmon runs, apparently unaffected by erection of 

 the drilling structures. Waterfowl in the area are plentiful. 



(c) Aesthetics. Aesthetics have had little influence on the design of the 

 structures. 



106 



