Wedgewire Screen Larval Entrainment Reductions at Eddystone Generating Station 

Apr 2005 – Apr 2006

A recent (20 April 2005 through 28 March 2006) full-scale evaluation of 6.35 mm cylindrical wedgewire 

screens was performed at the Eddystone Generating Station located on the Delaware River Estuary in 

Pennsylvania (Veritas et al. 2008). This evaluation supports the applicability of the wedgewire 

performance curve to full scale screens of similar design being considered for IPEC. The original 

cooling water intake structure for Eddystone Units 1 and 2 was located in a shoreline bulkhead, and was 

equipped with conventional 9.5 mm (3/8-inch) mesh traveling screens with no design or operational 

modifications to reduce impingement or entrainment. In the early 1990s, the intake for Units 1 and 2 was 

modified by removing the traveling screens and installing sixteen narrow slot cylindrical wedgewire Ttype screens (eight per unit). Each wedgewire screen is 72-inch in diameter with an effective length of 

144 inches (actual overall length is 240 inches including the nose cones) and is equipped with 6.35 mm 

(0.25 inch) wedgewire screening with the slots oriented radially around each screen and the long axis of 

the cylinder aligned parallel to the sweeping flow. The average through-screen velocity is approximately 

0.4 feet per second (fps). 

Units 3 and 4 at Eddystone were built after Units 1 and 2, and the cooling water intake structure design 

included several structural modifications specifically to reduce impingement and entrainment. Units 3 and 

4 employ conventional 9.5 mm (3/8-inch) mesh traveling screens, with a through-screen velocity of 

approximately 0.88 fps at design flow and mean low water level. 

Larvae of tessellated darter (32%), American shad (13%), Cyprinidae (9%), striped bass (9%), white 

perch (7%), Morone spp. (55%), and American eel (5%) were the predominant fish taxa observed in the 

entrainment samples collected during a year-long entrainment study performed from April 2005 through 

March 2006 at Eddystone Units 1 and 2, with the peak period of entrainment abundance occurring from 

early May through mid-July (Table 2-5 in Veritas et al. 2008). The 6.35 mm slot width cylindrical 

wedgewire screens installed and operated at Units 1 and 2 of Eddystone Generating Station were 

estimated to reduce total annual entrainment of fish eggs and larvae combined by 60% from baseline, 

with a 95% confidence interval of 48 to 71% (Table 5.2, Veritas et al. 2008). The 60% reduction in 

entrainment estimated for the 6.35 mm CWW screens installed and operated at Eddystone Units 1 and 2 is 

a unique and site-specific application of these CWW screens in combination with the actual flow 

reductions and other operational controls unique to that site. 

The entrainment reduction performance of the 6.35 mm CWW screens installed at Eddystone Units 1 and 

2 that is directly applicable to estimate performance at other facilities of different intake flows and 

operational procedures is based on the difference in density of fish eggs and larvae between 

simultaneously collected pairs of 2-hour entrainment samples. Only 10 eggs were collected throughout 

the year-long study (5 American shad, 1 tesselated darter, 1 white perch and 2 striped bass), and 867 

larvae were collected, so reduction calculations for this paired comparison were based solely on larvae 

(Table 1). In 374 pairs of simultaneously collected 2-hour entrainment samples collected from 20 April 

2005 through 5 April 2006 at Eddystone, the mean density of larvae entrained through the 6.35 mm slot 

width CWW screens at the Unit 1 and 2 CWIS was 82% lower than the mean density of larvae entrained 

simultaneously through conventional 9.5 mm (3/8-inch) mesh screens at the adjacent Unit 3 and 4 CWIS

(Table 1). These results from Eddystone demonstrate that a high percentage of larvae can avoid 

entrainment through full-scale cylindrical wedgewire screens operating under estuarine field conditions 

with a similar species composition as IPEC, even at a slot width of 6.35 mm. 
Table 1. Comparison of the number and density of fish eggs and larvae (all taxa combined) collected in 

374 pairs of simultaneously collected 2-hour entrainment samples taken at the Eddystone Unit 1 and 2 

bulkhead and the Unit 3 and 4 bulkhead during 20 April 2005 through 5 April 2006.

Life 

Stage

Wedgewire Screens at Unit 1 and 2 Conventional Screens at Units 3 

and 4 Percent 

Reduction 

for WWS

n

Mean Density

(n/100 m

3

) n

Mean Density

(n/100 m3)

Egg 7 0.81 3 0.68 N/A

Larvae 221 0.55 646 3.06 82%

Reference

Veritas Economic Consulting, Normandeau Associates Inc., and ARCADIS (Veritas et al.) December 

2008. Development of annual current and baseline impingement mortality and entrainment 

estimates. Eddystone Generating Station. Eddystone, PA. Prepared for Excelon Generation 

Company, LLC