Document ID: EPA-HQ-OW-2008-0667-2877
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2012-06-12T04:00Z

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, species 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 Canyon Power Plant (DCPP) is located on the Pacific coast in
San Luis Obispo County, California.  The plant has a very high capacity
factor and an intake design volume of 2,500 million gallons per day
(mgd).  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):

 

This variation in data from a single state clearly demonstrates the
importance of site-specific impingement assessments.  

A facility such as DCPP, with average daily 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 success – the
plant’s annual impingement losses are approximately 710 pounds per
year (2 pounds or 12 fish per day), while circulating approximately 2.5
billion gallons of water per day.  The open ocean environment means that
most species are adapted to large changes 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 losses 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 any concerns for sensitive fish species. Further,
developing additional criteria that account 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) Initiative comments filed related to the proposed rule
and suggested 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 impingement losses measured at DCPP and the characteristics of
fishes collected during associated studies demonstrate that the
facility’s current design achieves a level of impingement that should
qualify for a de minimis exemption.  EPA should consider a
facility-specific de minimis exemption for the impingement mortality
standard 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.

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