Environmental Impact Statement - radioactive monticello

Environmental Impacts of Operation
In addition to elevated temperatures, entrained organisms are exposed to biocides and
mechanical stresses. Experimental studies using fathead minnow (Pimephales promelas) fry
demonstrated that up to 11.8 percent survived temperature elevations of 25.6 to 41.60 F; while
8.5 to 42.4 percent showed signs of mechanical damage from passing through the condensers.
The incidence of external injuries for fish that were alive at recapture was only approximately
2 percent (Knutson et al. 1976). However, survival was found to be very low (0.0 to
1.6 percent) when ambient river temperatures were 55.00 F or higher or when the change in
temperature was 59.40 F (Knutson et al. 1976). Overall, it was concluded that sublethal thermal
and mechanical effects would result in long-term survival of less than 10 percent of entrained
fishes (Knutson et al. 1976).
Entrainment monitoring was also conducted at Monticello between April 23 and
September 4, 1976, for the CWA 316(b) Demonstration. This sampling period encompassed a
low-flow year in the Mississippi River. Therefore, Monticello withdrew a relatively high
percentage of river water, and consequently, entrainable organisms (Amish et al. 1978). During
the year, an average of 19.3 percent of the Mississippi River flow passed though the plant,
ranging from a high of 36 percent in August 1976 to a low of 7 percent in April 1976 (Amish et
al. 1978).
In the 1976 study, 2.83 million young-of-the-year fish and 1.08 million fish eggs were estimated
to have been entrained at Monticello. The predominant species entrained as larvae were
879,000 logperch (Percina caprodes) (31.8 percent); 633,000 shorthead redhorse (22.4
percent); 388,000 unidentifiable darters (13.7 percent); and 308,000 unidentifiable minnows
(10.9 percent). The eggs were not identified to species (Amish et al. 1978). The maximum
number of equivalent adult fish estimated to have been lost due to this entrainment was
250,124 fishes, including 218,000 logperch, 9230 shorthead redhorse, 1410 darters, and
13,600 minnows (Amish et al. 1978).
Generally, buoyant eggs are the only ones capable of being entrained at Monticello. Most fish
species in the area of Monticello have adhesive eggs. Therefore, it was assumed that
free-floating eggs were either diseased or accidentally removed from the riverbed by current
and scouring action. These eggs would have had a naturally low potential for survival (Knutson
et al. 1976).
To interpret the impacts of entrainment on fish community species populations and structure,
entrainment losses must be compared to the distribution, abundance, and life cycles of the
species that occur near Monticello. The ultimate impact of entrainment losses must be
evaluated in terms of a system's resiliency (i.e., environmental stability, productivity, population
compensation, and ecological and economic importance of the individual species) (Noguchi et
al. 1985). The fish community has been persistent and stable since the plant became
operational; and species composition has been similar between locations upstream and
downstream of the Monticello site (Xcel Energy 2004). Based on the CWA 316(b)
Demonstration (Amish et al. 1978), the Minnesota Pollution Control Agency concluded that
entrainment at Monticello does not pose a substantial detrimental effect on the fish population
August 2006 4-15 NUREG-1437, Supplement 26 1