Texas Natural Resource Conservation Commission
                     Interoffice Memorandum

To:  Interested Parties
Through:  Steve Hagle, P.E., New Source Review (NSR) Program
            Technical Specialist Director
From:  Susan Blevins, P.E., Dale Beebe-Farrow, P.E. and Dana
         Vermillion, P.E., NSR Program
Date:  April 13, 1995
Subject:  Reduction Credit for Annual Flange Monitoring

The NSR program has reviewed the question of an appropriate
reduction credit for annual instrument monitoring of flanges
at a 500 ppm leak detection limit.  After careful
consideration, a seventy-five percent reduction credit will
replace the thirty percent credit currently allowed for annual
flange monitoring at a leak detection limit of 500 ppm.  

This determination is based on information contained in the
1993 Environmental Protection Agency (EPA) document "Protocol
for Equipment Leak Fugitives" and a limited amount of actual
monitoring data for flanges submitted to NSR for evaluation. 
The control effectiveness percentages given in the protocol
document are based on the type of facility, monitored data and
a reduction in the percentage of leakers.  This defers from
the traditional NSR approach of allowing a reduction from the
Synthetic Organic Chemical Manufacturing Industries (SOCMI)
and petroleum refinery factors.  Since it is considered
preferable to allow a single reduction credit for both
chemical facilities and petroleum refineries, a lower common
denominator was used to establish the reduction credit.  The
seventy-five percent reduction credit will be suitable for
both types of facilities.  This will also allow some
conservatism to accommodate its application to old and new
facilities, address concerns regarding the low monitoring
frequency and make allowance for the differing approaches used
by the EPA and TNRCC to assign reduction credits.  

If you should have any questions regarding this determination,
please contact one of the individuals listed above.