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### MEMORANDUM
Tetra Tech, Inc. 400 Red Brook Blvd., Suite 200 Owings Mills, MD 21117 phone 410 - 356 - 8993 fax 410 - 356 - 9005 DATE: August 2 1 , 2008 TO : Paul Shriner, EPA FROM : Henry

L atimer, Blaine Snyder, and Ann Roseberry L incoln SUBJECT: H o lding time s to evaluate post
- impingement mortality Clean Water Act §316(b) requires an examination of impacts on the aquatic community from impingement and entrainment related to withdrawal of cooling water. As part of evaluating the impact that a coolin g water intake structure (CWI S) has on the aquatic community , the number and ty pes of organisms (fish and shellfish) impinged and entrained b y that structure are often quantified. Depending on the types of screens, screen wash s ys tems, fish return s ys tems , and operations at the facility in question it may also be useful to quantify impingement survival rates. Because impingement survival rates are influenced b y the physical design and operations of the CWI S as well as by the species and conditions within the source water (e.g., high vs. low debris load), impingement survival is ty pically facility
- specific. Therefore, the measurement of impingement survival rates can be useful in developing a more refined understanding of mortality associated with impingem ent at a facility . This memorandum addresses2

suggested holding times to use in evaluating post
- impingement latent mortality of fish and shellfish. McLaren and Tuttle (2000) held fish for 96 hours post
- impingement to evaluate latent mortality associated with impingement on 1 mm Ristroph
- ty pe traveling screens at the Somerset Station (281 MGD intake, 625 MW coal
- fired plant on Lake Ontario). Survival of impinged fish did not include evaluation of effects of passage through the 300 m fish return pipe. Sim ilarly , Thompson (2000) reported that fish and shellfish were held for 96 hours post
- impingement to evaluate mortalit y associated with impingement and return to the source water at the Carolina Power & Light Company ’s Brunswick Steam Electric Plant in North Carolina. Ronafalv y et al. (2000) held fish for 48 hours post
- impingement to evaluate mortalit y at the Salem Generating Station in New Jersey. A holding time of 24 hours post
- impingement was used by Black (2007) to evaluate the mortality of various fis h species in a laboratory setting. This study

was also different from some of the facility

studies in that the laboratory setting allowed for fish not subject to impingement to be used as controls to quantify mortality associated with holding conditions. Laboratory studies such as this one fail to completely replicate conditions in the field such as survival under varying temperatures and additional phy sical damage related to debris loading on the traveling screen. Further, this study did not consider a potentially

large source of stress on impinged organisms ; passage through a fish
- return sy stem. Although laboratory studies are necessary

and appropriate for use in evaluating the ability

of various technologies to reduce stresses to fish and shellfish re lated to impingement, survival data from studies such as this should only be used to evaluate the relative magnitude of stress related to each technology for a given species. Because of the site
- specific nature of impingement mortality and additional stre sses to which fish and shellfish are exposed on site (e.g., temperature, debris, etc.), laboratory
- derived survival data should not be used to estimate impingement survival at a given facility . A single review of post
- impingement mortalit y studies is av ai lable in the literature. EPRI (2003) evaluated 65 different impingement survival studies conducted at 29 different3

power generation facilities in North America. This review determined that these studies used post
- impingement holding times ranging from le ss than 24 to 108 hours (with one study that held organisms for over 200 hours). The plurality of these studies (approximately

30 of 65) held fish for 96 hours to evaluate post
- impingement mortality (approximate values are used here as data were presented graphicall y). It also appears that 11 studies only

evaluated instantaneous mortality and 10 studies evaluated mortality at 48 hours post
- impingement. The remaining studies held fish for an intermediate period between 24 and 84 hours post
- impingement. Using data from two different studies that collected mortality data (corrected using control organism s ) ; EPRI (2003) also evaluated the percentage of latent mortality observed at various time intervals. This evaluation indicated that most latent mortality effects can be observed within 96 hours post
- impingement. Further, it appears that for some species onl y approximately 60% of latent mortality

is accounted for at 48 hours post - impingement. For more fragile species, the majority of mortalit y associated with impingement is likely

to occur within the first 24 to 48 hours. Thus, it appears that use of a minimum holding time of 48 hours is necessary to ensure that the majorit y of initial and latent mortality

associated with impingement is observed. The primary

concern related to longer holding periods is that holding conditions may be sufficiently stressful to cause additional mortality not related to impingement and passage through the fish
- return s ystem. Inappropriate crowding of organisms and/or insuff icient aeration and renewal of holding water can lead to elevated ammonia or depressed dissolved oxygen concentrations, the stress of which increase s in relation to holding time. Predation and aggressive interactions between individuals can also contribut e to mortality if care is not taken to separate “ incompatible ” species. Although mortality related to such aggressive interactions would be expected regardless of the holding period, mortality related to such interactions would likely increase with holdin g time. Therefore, regardless of the holding time selected , it is critical that conditions in which organisms are held to evaluate post
- impingement mortality do not artificially

enhance that mortality .4

Use of a 96 hour exposure period has also been recommended to account for latent mortality in acute toxicity

tests with fish (e.g., Ruesink and Smith, 1975). This 96 hour exposure period/holding time is consistent with the implementation of EPA’s acute whole effluent toxicity

(WET) test methods for fish (E PA 2002). Acute toxicity testing methodologies for fish used in NPDES permit compliance WET testing typi cally require an exposure period of 96 hours, although the methodology allows for use of exposure periods between 24 and 96 hours and exposures of 48 h ours are sometimes used. Further, some States (e.g., California) require the use of 96 hour WET testing in evaluation of potentially

toxic discharges (CRWQCB

– San Diego, 1995). The evaluation of post
impingement survival is slightly different than the e valuation of mortality related to exposure to toxic materials as the exposure period for WET testing is integral to the amount of stress to which the organisms are exposed (e.g., exposure to toxins continues for the entire test period) whereas the stress o f impingement and transit through a fish return s ys tem is discrete and occurs prior to holding. However, the goals of WET testing and post
- impingement survival studies are similar enough that the holding times used should be similar. Some organisms are k illed outright by impingement and passage through the fish
- return sy stem, while others are injured. Holding organisms for a set period following impingement and, ideally, passage through the fish
- return s ys tem allows quantification of any latent mortality associated with these injuries. Various holding times have been reported in the scientific literature and in industry reports. Based on reviews of these studies we conclude that a minimum post
- impingement holding time of 48 hours is necessary to adequat el y evaluate latent mortalit y associated with impingement and passage through a fish return sy stem. Caution should be taken to ensure that the conditions in the holding tank s ys tems do not cause additional stress (e.g., predation, aggressive interactions, low dissolved oxygen, high ammonia, etc.) which could relate to additional mortality that could be erroneousl y interpreted as the result of impingement. If possible, control tanks should be included with similar organisms that have not be en subject to impingement , and that control should be used to evaluate baseline mortality in5

the holding tanks. The control data should be used to normalize the observed mortality of fish/ shellfish that have been subject to impingement and passage through the fish return . Literature Cited Black, J.L . 2007. Laboratory evaluation of modified traveling screens for protecting fish at cooling water intakes. Graduate Thesis, University of Massachusetts Amherst. California Regional Water Qualit y Control Board (CRWQCB), San Diego Region. 1995. Water quality

control plan for the San Diego Basin (9). CRWQCB, San Diego Region, San Diego, CA. Electric Power Research Institute (EPRI). 2003. Evaluating the effects of power plan operations on aquatic communities: Summary of impingement survival studies. EPRI , Palo Alto, CA. Report 1007821. McLaren, J.B. and L.R. Tuttle, Jr. 2000. Fish survival on fine mesh traveling screens. Environmental Science & Policy 3 (Supplement 1): 369
- 376. Ronafalv y, J.P., R.R. Cheesman, and W. M. Matejek. 2000. Circulating water traveling screen modifications to improve impinged fish survival and debris handling at Salem Generating Station. Environmental Science & Policy 3(Supplement 1): 377
- 382. Ruesink, R.G. and L .L . Smith. 1975. The rel ationship of the 96
- hour LC 50 to the lethal threshold concentration of hexavalent chromium, phenol, and sodium pentachlorophenate for fathead minnows (

Pimephales promelas Rafinesque). Transactions of the American Fisheries Societ y: 567 - 570. Thompson, T. 2000. Intake modifications to reduce entrainment and impingement at Carolina Power & Light Company ’s Brunswick Steam Electric Plant, Southport, North Carolina. Environmental Science & Policy 3(Supplement 1): 417
- 424. U.S. Environmental Protection Agency . 2002. Methods for measuring the acute toxicity of effluents and receiving waters to freshwater and marine organisms, fifth edition, October 2002. EPA
- 821 - R - 02 - 012. Office of Water, Washington, DC.