Storage Tanks
February 1995

TNRCC Regulation VI, 116.111(3) states that the proposed facility will utilize Best Available
Control Technology (BACT), with consideration given to the technical practicability and
economic reasonableness of reducing or eliminating the emissions from the facility.  

The BACT determination is performed on a case by case basis. BACT is subject to change at any
time.  The applicant is encouraged to contact the New Source Review Program of the TNRCC to
determine current BACT requirements prior to submitting a permit or amendment application.
The following table should be consulted to determine whether or not a proposed storage tank
meets what the TNRCC currently considers BACT for storage tanks.

Vapor Pressure of        Storage Capacity    Type of        Primary   Secondary 
Compound at Storage           (gallons)        Tank            Seal             Seal
Conditions            

<0.5 psia                                Any                All

>= 0.5 psia                   <25,000             All

>= 0.5 psia                   > = 25,000               EFR      Mechanical Shoe Rim-Mounted
                                        EFR      Liquid-Mounted  Rim-Mounted
                                        IFR       Mechanical Shoe       None
                                        IFR       Liquid-Mounted        None
                                        IFR        Vapor-Mounted  Rim-Mounted

Notes: 
EFR - External Floating Roof Tank
IFR - Internal Floating Roof Tank
All - EFR, IFR and Fixed Roof Tank

EFR Comments:  
Vapor-Mounted seals are not accepted by the TNRCC as a Primary Seal. Shoe-Mounted seals
and Weather Shields are not accepted by the TNRCC as Secondary Seals. Credit is given for
reduction of wind effects when geodesic domes are used.

IFR Comments: 
A Vapor-Mounted Primary Seal alone is not accepted by the TNRCC. Shoe-Mounted seals and
Weather Shields are not accepted by the TNRCC as Secondary Seals. Double wiper seals are
acceptable provided both seals are rim-mounted. Double wiper seals are considered to be vapor-mounted primary seal with a rim-mounted secondary seal.

A Weather Shield is generally not impermeable to vapors and is not approvable as a secondary
seal unless specifically reviewed and determined to be vapor-tight.

Shoe-Mounted Secondary Seals do not form a barrier from the rim of the roof to the inside wall
of the tank shell and are therefore not accepted by the TNRCC.