Sampling Frequency 



Starting in 1972, impinged organisms were collected over 24-h, 

 identified to species and counted daily. In March 1977 the counting 

 frequency was reduced to three 24-h samples per week. The basis for 

 this change was documented in a letter to the NRC justifying a change to 

 the ETS. Using data collected in 1973-75 at Unit 1, mean daily impinge- 

 ment estimates for each month based on 7 counts/week were compared to 

 mean daily estimates extrapolated from three counts/week assuming these 

 counts had been made on Monday, Wednesday, and Friday only. For winter 

 flounder the percent difference ranged from 0.0 to 83.4. The average 

 percent difference was 27.3, 18.3 and 15.0 respectively for the years 

 1973-75. 



Since these calculations included winter flounder only, additional 

 analyses were subsequently conducted covering the dominant species as 

 well (NUSCo 1979). Results based on 1973 and 1974 data showed that mean 

 differences between actual monthly totals (7 days/week) and estimates 

 based on three counts/week would range from 20-50% depending on the 

 species (Table 2). At this level of effort greater than 85% of all 

 species impinged would be represented. For levels of effort less than 

 3 days/week, the error associated with the estimated monthly totals 

 would increase rapidly. 



After the March 1977 program change, the design of impingement 

 monitoring programs received considerable attention in the scientific 

 literature. A thorough review of the subject was provided by Murarka et 

 al. (1978) and Kuman and Griffith (1978). For the purposes of this 

 review, a technique outlined by El-Shamy (1979) was used to further 

 evaluate the present sampling effort at Millstone. 



