due to its higher temperature. Thus, it would lie on top of, and 

 move over, the older effluent water. Dye studies clearly showed 

 the formation of this midwater layer of lighter effluent and its 

 moving out of the harbor on ebbing tides. This layer acted as a 

 buffer zone and impeded vertical mixing of the deeper effluent. 

 Internal convection cells within the effluent were also prevented 

 from mixing with the overlying water. As the hot, high-saline 

 water came in contact with ambient water the least conservative 

 parameter, temperature, was the first to change. As heat was lost 

 the high-saline effluent became denser and sank away from the inter- 

 face thus slowing further cooling. 



When the desalination plant shut down, the effluent stratum dis- 

 appeared from the harbor within 24 hours. Some of the effluent 

 water must have persisted longer than 24 hours, however, based on 

 known flushing rates and the known volume of effluent. 



The mean depth of the top of the effluent stratum was 18 feet 

 (5.49m), the average thickness of the effluent layer was 4.6 feet 

 (1.4m) and its volume was 20,615 cubic feet (0.58 million cubic 

 meters). Tidal flushing was only 10,756,080 cubic feet (0.30 million 

 cubic meters) per day and it is questionable if wind-driven currents 

 could account for the dissipation of the remaining 10 million cubic 

 feet. Probably, once the thermal barrier was eliminated, vertical 

 mixing was accelerated. Some effluent cooled and remained stagnant 

 in the deeper pockets but the remainder probably mixed with the 

 surface water. The effluent stratum, however, lost its identity 

 and was not detectable hydrographically after 24 hours. 



The effluent production, including the entrained ambient water, was 

 about 20 million cubic feet (0.57 million cubic meters) per day which 

 was ample to reestablish the effluent layer within one day. Once the 

 layer of 20 million cubic feet (0.57 million cubic meters) was estab- 

 lished in Safe Harbor, there must have been some 20 million cubic feet 

 of effluent per day mixing with the ambient water and possibly passing 

 through the approach channel to deeper water. 



Failure to find the effluent beyond 2,000 feet (600 meters) past the 

 edge of the turning basin indicated it was probably mixing with the 

 surface water to a point where it was not detectable by the hydro- 

 graphic methods employed. That some effluent mixed with the surface 

 water was sliown by copper analysis of the sediments of the flats to 

 the west of the turning basin (where the surface harbor water moves 

 over the flats under prevailing wind conditions). These sediments 

 showed much more copper than the upcurrent flats to the east. High 

 copper levels in shallow water areas inside the harbor (see below) 

 also indicated presence of the effluent in shallower water. 



The effluent stratum was plotted in real time using the Westinghouse 

 thermister array and was calculated from water measurements taken 

 twice weekly at all stations. Figure 13 shows the monthly average 



50 



