Environmental Impact Statement - radioactive monticello

Description of Site and Environment
2.2.3 Water Quality
Potential environmental issues associated with water quality at the Monticello plant include
surface water quality in the Mississippi River. During 2002 and 2003, the MPCA conducted
stream assessments under Section 305b of the Clean Water Act to estimate the extent to which
Minnesota water bodies meet the goals of the Clean Water Act and attain state water quality
standards (MPCA 2004a). The Mississippi River in the area of the Monticello plant is identified
as impaired; however, the MPCA is still developing its strategy for addressing these findings.
Table 2-2.
Circulating Water System Operating Modes
Operating Mode
Temperature and River Flow Conditions
OPEN CYCLE OR ONCE-THROUGH:
Water is withdrawn from and discharged directly to
the Mississippi River.
HELPER CYCLE:
WHEN:
- Discharge canal temperature is below permit
limits, and
- River flow exceeds 860 cfs.
WHEN:
Water is withdrawn from and discharged directly to - Discharge canal temperature approaches permit
the Mississippi River.
limits, and
Cooling towers cool water prior to discharge to the - Upstream river temperatures are consistently at
river. or above 68 0 F.
PARTIAL RECIRCULATION:
WHEN:
75% of the Mississippi River flow is withdrawn. - River flow is less than 860 cfs but greater than
Cooling towers are operating. A portion of the 240 cfs, and
cooled water is recirculated to the intake and the - River temperature is elevated.
remainder is discharged to the river.
Operating Mode
CLOSED CYCLE:
Cooling towers are operating and all cooled water is
recirculated to the intake, except for cooling tower
blowdown, which is discharged to the discharge
canal.
Temperature and River Flow Conditions
WHEN:
- River is at or less than 240 cfs, and
- River temperature is elevated.
Water quality discharges at Monticello are regulated by a NPDES permit with the MPCA. This
NPDES permit regulates effluent water quality to the Mississippi River and discharges from
certain in-plant processes. The NPDES permit also has monitoring, reporting, and permit limit
requirements on water quality parameters including chlorine, pH, temperature, total suspended
solids, oil and grease, and oxidants. Based on these monitoring reports, plant discharges are
NUREG-1437, Supplement 26 2-16 August 2006 1