Environmental Impact Statement - radioactive monticello

Description of Site and Environment
Monticello site, and there are no significant changes proposed to the limits and conditions of the
air permit.
2.2.5 Aquatic Resources
The principal aquatic resource in the vicinity of Monticello is the Mississippi River, which is the
source and receiving body of the water for the Monticello cooling system. The main aquatic
habitats on the Monticello site are the Mississippi River and the cooling-system discharge canal.
The discharge canal is approximately 1000 ft long by 200 ft wide at the surface, sloping down to
a width of 92 ft on the bottom. It is 18 ft deep at the center. In 1980, an overflow weir was
added to the discharge canal that closely approximates the shoreline of the Mississippi River.
The weir was added to minimize cold shock mortality from sudden plant shutdowns within the
discharge canal and in the river area adjacent to the discharge (MPCA 1979). It allows normal
outflow of water while reducing the movement of fish into the discharge canal (NMC 2005a).
The transmission lines associated with Monticello cross several streams and rivers. The
Monticello-Elm Creek-Parkers Lake line crosses Otter Creek, County Ditch #9, Crow River,
Rush Creek, and Elm Creek; while the Monticello-Sherburne County-Coon Creek line crosses
the Mississippi River, Elk River, St. Francis River, Tibbits Brook, Trott Brook, and the Rum
River. Transmission line right-of-way maintenance activities in the vicinity of stream and river
crossings employ procedures to minimize erosion and shoreline disturbance While encouraging
vegetative cover.
The Monticello plant facilities are located on the southern bank of the Mississippi River in
Wright County at Mississippi River Mile 900. Near Monticello, the Mississippi River is broad and
turbulent. The average river velocity varies from about 1.5 to 2.5 ft/s. The river 1.5 mi
upstream to 1.5 mi downstream of the plant loses 10 ft in elevation, resulting in rapids and
current velocities that exceed 4.9 ft/s (NMC 2005a). The main channel of the Mississippi River
is approximately 980 ft wide in the vicinity of the Monticello site. This portion of the river is also
shallow, averaging about 6.2 ft deep (Knutson et al. 1976). Within backwaters and protected
shoreline areas, the river is less than 2 ft deep with silt and mud substrates, whereas the main
channel substrates consist of gravel, rubble, and boulders with some sand (Afzal et al. 1975).
River flow past Monticello averages 7217 cfs, which meets the NRC's annual flow criterion for
classification as a small river. Flow has ranged from a minimum of 240 cfs to a maximum of
51,000 cfs. It exceeds 1100 cfs 90 percent of the time, and 300 cfs 99 percent of the time.
Ambient river temperature in summer averages 71 OF, while winter temperatures are at freezing
(32°F) (NMC 2005b).
A number of physical and chemical stresses have caused major changes and modifications to
the aquatic resources within the Upper Mississippi River Basin. Dams and six associated
headwater reservoirs occur on the Mississippi River between its headwaters at Lake Itasca and
St. Anthony Falls Lock and Dam (river mile [RM] 854) near the Twin Cities. However, as the
August 2006 2-19 NUREG-1437, Supplement 26 I