Environmental Impact Statement - radioactive monticello

Environmental Impacts of Operation
(MPCA 1979). Under conditions of the current State of Minnesota NPDES permit, the location
and operation of the intake will continue to have minimal environmental impact.
During the course of the SEIS preparation, the staff considered mitigation measures for the
continued operation of Monticello. Based on the assessment conducted, the staff expects that
the measures in place at Monticello (e.g., the intake structure is situated in a location devoid of
unique spawning habitat and the capability of the plant to operate in a partial recirculation or
closed-cycle mode) provide mitigation for impacts related to entrainment. The staff concludes
that the potential impacts of entrainment of fish and shellfish in the early life stages into the
cooling water intake system are SMALL, and further mitigation measures would not be
warranted.
4.1.3 Impingement of Fish and Shellfish
For plants with once-through cooling systems, impingement of fish and shellfish on debris
screens of cooling water system intakes is considered a Category 2 issue, requiring a
site-specific assessment before license renewal. To perform this evaluation, the staff reviewed
the applicant's ER (NMC 2005a) and related documents [including the CWA 316(b)
Demonstration (Amish et al. 1978)]; visited the Monticello site; and reviewed the applicant's
State of Minnesota NPDES Permit No. 0000868, issued on August 22, 2002, and in force until
July 31, 2007 (MPCA 2002).
Condenser cooling water is withdrawn from the Mississippi River through an approach channel
angled at 810 to the shoreline (Amish et al. 1978). Water enters the intake over a concrete sill
equipped with a 12.5 ft wide stop log section in the center of the sill. After passing over the sill,
the water passes through a bar rack. The water is then diverted into two separate streams that
each pass through paired traveling screens with 3/8-in. mesh (NMC 2005a). The Mississippi
River is also used for service water cooling, screen wash, and fire protection (MPCA 2002).
The traveling screens at Monticello are normally rotated and rinsed every 12 hours, but run
continuously when the river temperature is higher than 50 0 F. The screen rinse sluiceway was
installed in 1973 to decrease mortality of impinged fish. During periods of continuous screen
washing, the sluiceway produces up to 95 percent survival of impinged fish (Amish et al. 1978).
Monticello may withdraw a maximum of 645 cfs for once-through or helper-cycle mode cooling
and plant process water from the Mississippi River. Special operating conditions are required
when the river flow is less than 860 cfs. For example, plant water intake may not exceed
75 percent of river flow when the river flow is less than 860 cfs but greater than 240 cfs (NMC
2005a). When river flow is less than 240 cfs, there are further restrictions, including use of a
closed-cycle mode of operation (NMC 2005a). Withdrawn water is returned to the river except
for that amount evaporated in the discharge canal and cooling towers. During 2002, the mean
river flow was 6351 cfs, while mean intake flow was approximately 529 cfs; similar means for
2003 were 4572 cfs and 491.9 cfs, respectively (Xcel Energy 2004).
NUREG-1437, Supplement 26 4-16 August 2006 1