3
Modeling Fish Entrainment and
Impingement Impacts: Bridging
Science and Policy
Webb Van Winkle and John Kadvany
46
3.1 Introduction
Impingement and entrainment at cooling-water intake systems (CWIS) are
two sources of potential mortality for fish. Impingement occurs when fish
are trapped or pinned by the force of the intake flow against the intake
screens at the entrance of a facility’s CWIS. Mortality can be high, but
numerous technologies have been developed to successfully reduce at a
reasonable cost both the number of fish impinged and the mortality of those
fish that are impinged (Taft 2000). Entrainment occurs when fish eggs
and larvae are taken into a facility’s CWIS, pass through its heat exchanger,
and are pumped back to the water body with the discharge from the
facility. Mortality can approach 100% for sensitive species and life stages.
However, for many species, mortality for those eggs and larvae entrained
can be reduced when facilities are operated to reduce exposure of entrained
organisms to potentially lethal high temperature, to large changes in
temperature, and to toxic chemicals (Dey et al. 2000; Mayhew et al. 2000).
Substantially reducing the number of eggs and larvae entrained, however,
is difficult to achieve at a reasonable cost for power plants with oncethrough cooling systems. This cost difference between mitigation technologies for entrainment as compared to impingement, in combination with the
uncertain ecological impact created by entrainment, has led to a good deal
of the difficulty and controversy surrounding the regulations associated
with Section 316(b) of the Clean Water Act of 1972.
The entire 316(b) text from the 1972 Clean Water Act is remarkably brief:
“Any standard established pursuant to section 301 [regulating effluent
limitations] or section 306 [describing effluent performance standards]
of this Act and applicable to a point source shall require that the location,
design, construction, and capacity of cooling water intake structures reflect the best technology available for minimizing adverse environmental
impact” (USEPA 2000). The key terms “best technology available” (BTA),
“minimizing,” and “adverse environmental impact” (AEI) are not further defined. Without a characterization of AEI, it is not known what to
Modeling Fish Entrainment and
Impingement Impacts: Bridging
Science and Policy
Webb Van Winkle and John Kadvany
46
3.1 Introduction
Impingement and entrainment at cooling-water intake systems (CWIS) are
two sources of potential mortality for fish. Impingement occurs when fish
are trapped or pinned by the force of the intake flow against the intake
screens at the entrance of a facility’s CWIS. Mortality can be high, but
numerous technologies have been developed to successfully reduce at a
reasonable cost both the number of fish impinged and the mortality of those
fish that are impinged (Taft 2000). Entrainment occurs when fish eggs
and larvae are taken into a facility’s CWIS, pass through its heat exchanger,
and are pumped back to the water body with the discharge from the
facility. Mortality can approach 100% for sensitive species and life stages.
However, for many species, mortality for those eggs and larvae entrained
can be reduced when facilities are operated to reduce exposure of entrained
organisms to potentially lethal high temperature, to large changes in
temperature, and to toxic chemicals (Dey et al. 2000; Mayhew et al. 2000).
Substantially reducing the number of eggs and larvae entrained, however,
is difficult to achieve at a reasonable cost for power plants with oncethrough cooling systems. This cost difference between mitigation technologies for entrainment as compared to impingement, in combination with the
uncertain ecological impact created by entrainment, has led to a good deal
of the difficulty and controversy surrounding the regulations associated
with Section 316(b) of the Clean Water Act of 1972.
The entire 316(b) text from the 1972 Clean Water Act is remarkably brief:
“Any standard established pursuant to section 301 [regulating effluent
limitations] or section 306 [describing effluent performance standards]
of this Act and applicable to a point source shall require that the location,
design, construction, and capacity of cooling water intake structures reflect the best technology available for minimizing adverse environmental
impact” (USEPA 2000). The key terms “best technology available” (BTA),
“minimizing,” and “adverse environmental impact” (AEI) are not further defined. Without a characterization of AEI, it is not known what to