Opinion ID: 785093
Heading Depth: 3
Heading Rank: 3

Heading: Intake velocity

Text: 56 UWAG argues that there is insufficient support in the record for Track I's through-screen velocity limit of .5 ft/s. See 40 C.F.R. § 125.84(b)(2), (c)(1). 57 Through-screen velocity, as its name implies, is the velocity of water at the point it moves through an intake point. The velocity of water a short distance away from the intake point (the approach velocity) increases as the same quantity of water is forced (because of screens or other devices that take up space) to flow through a smaller surface area. The record reveals that the higher the velocity of the water moving into an intake system, the greater the pressure on organisms near the intake point, and the more of them that will be impinged and entrained. See Public Comment & Response No. 014.018, at 1437-38. Ninety-six percent of surveyed fish species can swim faster than.5 ft/s, however, meaning they can escape an intake structure that withdraws water at that velocity (or slower). Notice of Data Availability, 66 Fed.Reg. 28,853, 28,864 col. 3 (May 25, 2001) [hereinafter NODA]. A survey of facilities constructed in the last 15 years demonstrates that most 31 subject to the Rule already comply with the .5 ft/s through-screen requirement. 58 UWAG argues that the relevant velocity is the approach velocity, because that is what the fish experience before they are swept into the intake, when they may still be able to escape. UWAG Br. at 32. Basing the regulation on the through-screen velocity allegedly adds an unnecessary measure of stringency to the regulation. 32 The EPA responds that it chose a through-screen velocity limit (and not an approach velocity) as the appropriate measure because through-screen velocity is easier to measure accurately, many recently constructed facilities are designed to meet through-screen velocity limits, and it provides a margin of safety, as the actual through-screen velocity will only increase as a screen becomes occluded by debris and the area through which water can pass is further reduced. The fact that a minority of facilities do not presently meet this requirement, of course, says nothing about whether the required technology is the best or available. 59 Accordingly, we think the EPA's choice of velocity limit was reasonable.