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**EPA’s Proposed Rule for Cooling Water Intake Structures at Existing and Phase I**

**Facilities; 316(b) Impingement Requirements**
**RE: The need to set a de minimis**  **standard Summary:**  Pacific Gas & Electric Company (PG&E) urges EPA to consider including a de minimis standard for impingement, so that facilities that substantially minimize impingement with existing technologies are provided an exemption. Large affected stakeholder organizations, including the Edison Electric Institute and the Utility Water Act Group, have expressed support for the concept of a de minimis exemption as well. PG&E believes such a determination should be made based on site

- specific factors and based on criteria that are consistent and verifiable. The different water bodies, specie s of concern, and seasonal dynamics affect impingement such that an appropriate de minimis exemption for one facility may be too restrictive at another and too large at another facility . Nevertheless, we would urge EPA to provide guidance to permitting authorities to ensure appropriate de minimis standards are developed. The Diablo Canyon Power Plant provides a sound example of a facility that can be instructive to the design of a metric to apply

on a site

- specific basis , or if EPA determines appropriate, could also apply as the basis for a national standard

. **Background:** The Diablo Can yon Power Plant (DCPP) is located on the Pacific coast in San L uis Obispo County , California. The plant has a very high capacit y factor an d an intake design volume of 2 ,5 00 m illion gallons per day (m gd) . The plant also demonstrates the lowest impingement biomass per million gallons circulated of all of the coastal plants in California that use once

- through cooling. There are 14 coastal power plants in California with 17 separate structures that have some level of fish impingement as a result of intake operations. The overall data from California demonstrates the wide variation in levels of impingement at facilities

- from over 32,000 pounds per year to as little as 77 pounds per year , as displayed in the table below ( See Attachment 1, Table E1

- 1 in August 18, 2011 PG&E comments to EPA) :2

This variation in data from a single state clearly demonstrates the importance of site

specific impingement assessments. A fa cility such as DCPP, with average dail y impingement of a dozen predominately juvenile fish, makes a strong case for a de minimis exemption. The intake at Diablo Canyon was designed to minimize impingement and the impingement numbers demonstrate its succes s
– the plant’s annual impingement losses are approximately 710 pounds per year ( 2 pounds or 12 fish per day), while circulating approximately 2.5 bil lion gallons of water per day . The open ocean environment means that most species are adapted to large ch anges in tides, as well as significant swells. Additionally, the plant’s low through

- screen velocity (average centerline between 0.78 and 1.02 fps) allows most fish to swim in and out of the bar racks. Establishing the de miminis standard for annual los ses should be based on estimates of impingement from power plants within a region withdrawing water from similar environments. Such a baseline can also help address an y concerns for sensitive fish species. Further, developing additional criteria that acco unt for the large differences in water intake is also appropriate. If EPA determined it appropriate to finalize a national de minimis standard, PG&E supports the Clean Energy Group’s 316(b) Initiative3

comments filed related to the proposed rule and sugges ted an annual impingement level of 2,000 pounds. Using such a number is reasonable when one considers the wide range of impingement levels across the country

. **Conclusion:** The low impi ngement losses measured at DCPP and the characteristics of fishes coll ected during associated studies demonstrate that the facility ’s current design achieves a level of impingement that should qualif y for a de minimis exemption

. EPA should consider a facility

- specific de minimis exemption for the impingement mortality stand ard that is based on a benchmark average impingement rate (biomass per volume of water circulated) and/or a general benchmark for annual total impingement losses of 2,000 pounds. We would be happy to discuss the design of such a benchmark further with EPA staff.