Investigations of impingement of aquatic organisms at the Calvert Cliffs Nuclear Power Plant, 1975–1995

Abstract

The Calvert Cliffs Nuclear Power Plant (CCNPP) in Maryland began commercial operation in 1975. The once-through cooling system pumps Chesapeake Bay water at a maximum rate of 73 m 3 /s (2.4×10 6 gallons per min) to the condensers, a total equal to 0.7% of the average tidal flow in the area. From 1975 to 1995, impingement monitoring was conducted at CCNPP. The 21-year record is one of the most extensive of its kind in the utility industry. A total of 73 species of fish were identified. Often, five species accounted for over 90% of the total number of fish collected in any year. Estimates of total annual fish impingement ranged from 79,000 to over 9.6 million with a 21-year average of 1.3 million fish per year. Total impinged biomass was less variable with a range of 1300 to 18,600 kg/yr (9100 kg/yr avg.) Six different survival studies were conducted at CCNPP and species-specific impingement tolerances were determined. Eleven of the 14 species caught most often had survival rates over 50% and blue crabs demonstrated greater than 99% survival. When total impingement estimates are adjusted to account for survival, the fish impact is reduced by over 73%. This impact is small compared with commercial and recreational fishing and other natural causes of mortality. In addition, many of the significant impingement collections were episodic events correlated with high temperature and low dissolved oxygen conditions in the intake water. The Maryland Department of Natural Resources has concluded that CCNPP impingement losses are small and do not represent a significant impact to fish populations in the mesohaline regions of the Chesapeake Bay.