Impingement 



Impingement estimates were calculated from January 1975 to .December 1985 using daily cooling 

 water volumes (for 24 h starting at 0800 h). Over 100 taxa of fish and invertebrates have been impinged 

 over the past 10 years (Appendix IX). Impingement estimates for the selected taxa are presented in Table 

 1.1. Sand lance accounted for almost 50% of the total number impinged. Prior to 1984, sand lance 

 accounted for less than 1% of the total impingement (NUSCo 1986a). However, in 1984, an estimated 

 390,000 sand lance were impinged at Unit 2 during the week of July 18th. This estimate was based on a 

 single 24-h sample, and qualitative observations made during the remEiinder of the week indicated that the 

 numbers of impinged sand lance decreased rapidly thereafter. The sand lance is a schooling species (I^im 

 and Scott 1966) and a large school probably encountered the intake structures. A similar short-term large 

 impingement of a schooling species, Atlantic menhaden (Brevoorlia tyrannus) occurred in 1971 (NUSCo 

 1982b). At that time, approximately one million juvenile menhaden were impinged in August at Unit 1 

 (the only unit operating then). Excluding sand lance, seven fish taxa dominated the impingement collections 

 and accounted for over 90% of the fish impinged. These included winter flounder, silversides, grubby, 

 anchovies, Atlantic tomcod, cunner, and sticklebacks. Except for the cunner and anchovies, these species 

 were impinged in the winter months (December through March). The winter flounder was the most 

 abundant and accounted for approximately 20% of the annual impingement catch. 



There was no apparent trend for the total number of fish impinged annually during the two-unit 

 operational period (Table 13). Although impingement samples wrre collected only at Unit 1 after 1983, 



Table IV Annual impingement estimates Tor selected taxa impinged, calculated using (lows frnm 0800-0745 (Units 1 A 2 combined 

 by year except during 1984-85 when Unit 2 was estimated alone). 



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