Environmental Impact Statement - radioactive monticello

Description of Site and Environment
spathula) were absent in the upper reaches of the Mississippi River due to river blockage at
St. Anthony Falls. However, the construction of St. Anthony Falls Lock and Dam in 1963
removed this barrier to fish passage. As a result, species such as channel catfish, flathead
catfish (Pylodictis olivaris), gizzard shad, northern hog sucker, golden redhorse (Moxostoma
erythrurum), and white crappie (Pomoxis annularis) now occur above St. Anthony Falls. The
Coon Rapids Dam (RM 866), located approximately 12 mi upstream from St. Anthony Falls,
remains a barrier to upstream movement; although some fishes can circumvent the dam at
times (e.g., during floods) (Hatch et al. 2003). This may account for the presence of channel
catfish, northern hog sucker, white crappie, and, most recently, flathead catfish near Monticello.
The major primary producers within the Monticello area are periphyton. The periphyton
community consists of diatoms, blue-green algae, green algae, and golden algae; periphyton
contributes an estimated 60 to 82 percent of the primary production in the Monticello area.
Nearly 150 species of periphyton were collected near Monticello between 1968 and 1976, and
were dominated by diatom species throughout the year. During the summer, blue-green algae
were co-dominant with diatoms (Amish et al. 1978). Peak periphyton production occurs in
summer. Species composition was found to be similar between preoperational and operational
years (Amish et al. 1978). Phytoplankton is generally not abundant in flowing waters. Most of
the phytoplankton that occurs in the main river channel originates from backwater areas and
from periphyton scour. Phytoplankton in the Upper Mississippi River is dominated by diatoms
and green algae, and contributes 18 to 40 percent of the primary productivity in the Monticello
area (Amish et al. 1978).
Between 1968 and 1970, the only macrophytes found in the immediate area near Monticello
were the American pondweed (Potamogeton nodosus), sago pondweed (Stuckenia pecinatus),
and antifever fontinalis moss (Fontinalis antipyretica). The macroscopic green alga Cladophora
glomerata also occurs in the area. Overall, macrophytes abundance is low in the Monticello
area due to fast-moving currents and shifting sand and gravel substrates (Amish et al. 1978).
Zooplankton populations are limited within the main channel of the Mississippi River near
Monticello due to high gradients. Near Monticello, the zooplankton community is comprised of
protozoans, rotifers, cladocerans, and copepods (Afzal et al. 1975; Amish et al. 1978).
The benthic macroinvertebrate community near Monticello includes oligochaetes (aquatic
annelid worms), mayflies, caddisflies, aquatic beetles, midges, black flies, aquatic snails, and
fingernail clams (Amish et al. 1978). The non-channel areas of the Upper Mississippi River
consistently support more species than the main channel area (USGS 1999). Near Monticello,
66 genera of macroinvertebrates were collected in the backwaters, while only 24 genera were
collected from the main channel (Amish et al. 1978).
The Upper Mississippi River contains a rich assemblage of freshwater mussels. Historically, as
many as 50 species of mussels have been documented from the Upper Mississippi River, but
only 30 species have been reported in recent surveys. Many are rare (e.g., listed as
endangered, threatened, or of special concern by one or more states [USGS 1999]). The
August 2006 2-21 NUREG-1437, Supplement 26 1