Environmental Impact Statement - radioactive monticello

Environmental Impacts of Operation
4.1.1 Water Use Conflicts (Plants with Cooling Ponds or Cooling Towers Using
Makeup Water from a Small River with a Low Flow)
Water use conflicts for plants with cooling ponds or towers using makeup water from small river
with low flow is a Category 2 issue, requiring a site-specific assessment before license renewal.
Monticello utilizes cooling towers and withdraws make-up water from the Mississippi River
which has annual flow rate of less than the 3.15 x 1012 cubic ft per year threshold value in
10 CFR 51.53(c)(3)(ii)(A).
The impact of consumptive loss on the downstream riparian communities is associated with the
small difference it can cause in the river surface elevation. Section 2.2.2 describes Monticello
surface water withdrawal from the Mississippi River, which is regulated by the Minnesota
Pollution Control Agency (MPCA) NPDES permit and by the Minnesota Department of Natural
Resources (MNDNR) Surface Water Appropriations Permit. During normal conditions, river
flows in the Mississippi River exceed 860 cfs and cooling of circulating water meets NPDES
permit limits. Under these conditions, the NPDES permit allows Monticello to withdraw a
maximum of 645 cfs and Monticello operates in a once-through mode. When water
temperatures approach NPDES permit limits, Monticello operates: in helper cycle (see
Section 2.2.2) and some of the cooling water is passed through the cooling towers before
discharging into the discharge canal. United States Geological Survey (USGS) gage station
data is available approximately 26 mi upstream from Monticello since 1988 (Station 05270700,
Mississippi River at St. Cloud). This gage station represents a conservative estimate of flow, at
Monticello because this does not take into account additional flow inputs between the USGS
gage station and Monticello. Furthermore, review of the MNDNR online database of water
allocation permits indicate there are no significant surface water withdrawals between the
measuring station and the intake at Monticello (MNDNR 2005a). From September 1988
through September 2004, the maximum and minimum daily flows at the upstream USGS gage
station were 45,100 cfs and 1010 cfs, occurring on April 9, 1997, and August 24, 1989,
respectively (USGS 2005). A separate flow analysis was conducted by NMC in the ER using
data from USGS gage stations both upstream and downstream of Monticello. In this analysis,
the flow at Monticello was estimated based on its drainage area relative to the drainage areas
of the USGS gage stations. This analysis estimated the lowest daily river flow at 586 cfs (NMC
2005a). If the Mississippi River is between 240 and 860 cfs, NMC is only allowed to withdraw 75
percent of the river flow (see Section 2.2.2). At a river flow of 586 cfs, NMC is allowed to
withdraw 440 cfs. Under these conditions, and with an assumed evaporative loss of water from
the cooling towers of 18 cfs (AEC 1972), the consumptive loss due to evaporation from the
cooling towers represents four percent of the river flow, which is not considered significant.
The staff independently reviewed the NMC ER, visited the site, and reviewed the Monticello
NPDES permit, the Surface Water Appropriations permit, and other reports. Based on this
information, the staff concludes that the potential impacts of water use conflicts are SMALL.
During the course of this evaluation, staff considered mitigation measures for continued
'operation of Monticello. Based on this evaluation, the staff expects that the existing State
NUREG-1437, Supplement 26 4-12 August 2006 1