3-84 



average basis, the temperature increase due to operation of the gen- 

 erating station is probably less than IF (0.6 C) at the water quality 

 monitor . 



The NAI thermal surveys conducted during July, August, and 

 October 1976 give quantitative information about the extent of the 

 generating station thermal plume. The results of the surveys conducted 

 during October 13, 1976, are shown in Figures 3-24 through 3-27. At 

 slack low water, a small plume is apparent near the discharge point 

 (Figure 3-24) . Its maximum surface temperature rise was about 5 F 

 (2.8 C) above ambient. The percentage of the surface area of the inner 

 harbor bounded by the 4 F AT isotherm is less than 0.1%. The 3, 2 and 1 F 

 (1.7, 1.1 and .6 C) AT isotherms bound 0.4, 0.6, and 1 percent respect- 

 ively of the inner harbor surface area. Cross-sectional data show the 

 plxome to have been a near surface feature (Figure 3-24) . Temperatures 

 representing AT's of 3 to 5 F (1,7 - 2.8 C) occupied the upper 4 m of 

 the water colxmn. From 4 to 7m, AT's were 2 to 3 F. Below the 7 m 

 depth, temperatures were at or very close to ambient. 



At maximum flood tide, the plant's thermal plume was less con- 

 centrated, due to greater mixing with ambient waters (Figure 3-25) . The 

 temperature rise directly above the discharge point was about 3 F, with 

 the 3 F AT isotherm enclosing less than 0.1% of the inner harbor surface 

 area. The 1 to 2 F AT portion of the plume water was observed to curve 

 across the navigation channel and up toward Long Wharf, with the 1 F AT 

 isotherm enclosing 2.4% of the inner harbor area. The cross-sectional 

 presentation shows the pl\ime concentrated near the discharge, with 

 dilution down to less than 1 F AT occurring only a short distance from ' 

 the plume axis. 



At high water slack (Figure 3-26) , the maximim surface temp- 

 erature increase was 2 F, but covered a very small surface area near the 

 discharge (less than 0.1%). The 1 F AT isotherm covered 2.2% of the 

 area of the inner harbor. Cross-sectional data show that the thermal 

 pliome intersected the bottom directly in front of the discharge. At 



