Some discharges are sources of toxicants only. If they are dispersed they 
tend to go far afield until particulates from other sources send them 
eventually to the sea bed. If the toxicant is not dispersed it leaves its 
signature in the near field sediments as a "hot spot." 
Toxicants attached to very fine grain or low density materials can be 
carried anywhere in the Sound by the net circulation and kept in suspen¬ 
sion by the tidal current turbulence. These materials may wander into 
the rural appended embayments far from urban sources. However, if the 
local sources of clean sediment material in these rural embayments is 
large in comparison to the advected supply, these embayments will have 
low concentrations of toxicants in the sediment. 
The laying down of toxicants in the sediments is a physical mechanism for 
cleansing the Sound. Eventually the toxicants are forced to sufficient 
depth that they no longer interact with the water or the biota. As the 
input of toxicants is decreased natural sedimentation processes will tend 
to decrease the concentration of toxicants at the sediment-water interface 
providing humans do not interfere with the sediment supply. Increasing 
the clean sediment supply increases the sedimentation rate and also de¬ 
creases the sediment toxicant levels. The depth of the Sound allows much 
of the sedimentation processes to progress with no interference to 
shipping. In the urban industrailized port areas sediment and toxicant 
accumulation may produce shoaling that requires dredging. It is in these 
areas that disturbance of the sediments makes toxicants again available to 
the water and biota. Special handling is required to minimize impacts of 
dredging and dredged material disposal. 
Puget Sound is a magnificent and dynamic estuarine environment. Annually 
it receives enough river water to form a layer 65 ft. thick over its entire 
surface. This fresh water is combined with seawater by turbulent mixing 
derived from tidal currents. The presence of this fresh water requires 
that a net circulation exists that transfers a diluted surface layer sea¬ 
ward and allows seawater in at depth to replenish the seawater carried out 
in the surface mixture. There is also the driving force of denser oceanic 
water at depth on the Strait side of the entrance sill trying to displace 
the less dense water at depth in the main basin. Both the rates of ad¬ 
dition of river water and the supply rate and density of the oceanic waters 
have seasonal cycles. The Sound continually tries to adjust its proper¬ 
ties towards an equilibrium as fresh water input and oceanic water supply 
changes in time. This makes the net circulation flows variable in time. 
In the attempt to keep up with the circulation driving forces, Puget Sound 
reaches its most diluted stage in February about one month after the maxi¬ 
mum wintertime precipitation period. At this time about 1 cubic nautical 
mile of its total of 26.5 cu. nautical miles is stored fresh water. In 
late October or early November before river flow has appreciably in¬ 
creased the Sound is at its saltiest having given up its stored fresh water 
and replaced it with the upwelled oceanic type water that entered at its 
maximum rate in August and September displacing the resident water upwards 
9 
