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 T type screens (eight per unit). Each wedgewire screen is 7 2 - inch in diameter with an effective length of 144 inche s (actual overall length is 240 inches including the nose cones ) and i s 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 f eet per second (fps). Units 3 and 4 at Eddystone were built after Units 1 and 2 , and the cooling water intake structure design include d 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 vel o city of approximately 0.88 fps at design flow and mean low water level. Larvae of t essellated darter (32%), American shad (13%), Cyp rinidae (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 s tudy 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) . T he 6.35 mm s lot width cylindrical wedgewire screens installed and operated at Units 1 and 2 of Eddyston e 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 reducti on 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 Eddys tone 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. Co mparison 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 Reductio n for WWS n Mean Density

(n/100 m 3) n Mean Density (n/100 m 3) Egg 7 0.8 1 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 Ex celon Generation Company, LLC