INTRODUCTION 



Impingement on the screens of circulating water intake structures 

 is a visible and direct source of mortality to aquatic biota. Accordingly, 

 impingement rates have been monitored intensively at many estuarine and 

 coastal power plant sites to assess the potential for damage to localized 

 marine populations (Stupka and Sharma 1977; Uziel and Hannon 1979). At 

 Millstone, routine impingement sampling began at Unit 1 in 1972, although 

 some qualitative observations were made as early as 1971. Monitoring at 

 Unit 2 was initiated just prior to full-power testing in September 1975, 

 and at that time, the program was incorporated into the Environmental 

 Technical Specifications (ETS) for the site. 



The primary objective of impingement monitoring at Millstone has 

 been to quantify total annual, species specific, mortality. In addition, 

 means of minimizing this mortality have been evaluated experimentally 

 and appropriate plant design changes recommended where cost-effective. 

 Throughout the ten years of study, various program changes have been 

 implemented. The purpose of this report is to review and assess these 

 changes, evaluate the adequacy of the present program and discuss future 

 studies relative to Unit 3 operation. 



EVALUATION OF PROGRAM CHANGES 



The principle changes to the routine impingement program were made 

 in each of three areas, the frequency of counting, the manner in which 

 lengths were recorded, and the method for calculating monthly totals 

 (Table 1) . Each of these changes is discussed below. 



