determine statistical significance. Ascophyllum mortality data are presented as the mean of years 1979-1986, 

 with vertical bars representing the range of values. As a special case, mortality at Fox Island excludes 

 1984 data, because the elimination oi Ascophyllum from FL in late summer of 1984 would bias comparisons 

 between F^'ox Island and other stations. 



RESULTS AND DISCUSSION 

 Temperature Data 



Ambient water temperature in the Millstone Bight area follows a predictable annual cycle. Maximum 

 daily average temperatures of 20-21 °C occur in August-September, with little variability among years. 

 Winter temperatures are more variable, ranging from to -1 °C in a cold year (e.g., 1977), to 3-4 °C in 

 a warm year (e.g., 1983); yearly minima occur in January- February. 



Condenser cooling water used by Millstone Units 1 and 2 is heated to 12-15 °C above ambient, 

 depending on reactor power level. Prior to August 1983, the heated effluent was discharged through a 

 single cut in the south end of the discharge quarry (Fig. 3); a second quarry cut was opened in anticipation 

 of the added volume of cooling water needed by Unit 3. 



With one cut open and either 1 or 2 units operating, the effluent plume was directed to Twotrce 

 Channel where it was subjected to tidal flushing. Water temperatures within 75 m of the cut (FL 

 A.Kcopliyllum station; Fig. 3) were 2-3 °C above ambient, and temperatures at FF, were within 1 "C of 

 ambient regardless of tidal stage (Fig. 4, regime 1). 



After the second discharge cut was opened the effluent plume lost half its momentum and mixed with 

 nearshore water, producing nearly isothermal temperatures along the shore between the cuts and the 

 southwest tip of Fox Island. During this time temperatures at Fox Island were 3-4 "C cooler than the 

 undiluted effluent (Fig. 4, regime 2), regardless of tidal stage. This resulted in temperatures at FF, 7-9 °C 

 above ambient when one Unit was operating (e.g., autumn of 1983), and 12-13 °C above ambient when 

 both Units were operating (e.g., most of 1984). Under these conditions, maximum water temperatures at 

 FF could exceed 30 °C. 



