vvEPA
United States
Environmental Protection
Agency
Office of
Solid Waste and
Emergency Response
DIRECTIVE NUMBER:
9483.01(84)
TITLE: E: Permitting of Hazardous Waste Treatment/Storage
' Tanks " ' ~ "
APPROVAL DATE: 2-23-84
EFFECTIVE DATE: 2-23-84
ORIGINATING OFFICE: E:, off ice of -solid waste
0 FINAL
D DRAFT
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STATUS [ C ]r i Bf^ Pending" AAf OSWER ^approva
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REFERENCE (btfter documents):
OSWER OSWER OSWER
/£ DIRECTIVE DIRECTIVE Di
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PARTS 264 AND 265 SUBPART J - TANKS DOC: 9483.01(84)
Key Words: Minimum Shell Thickness, Tank
Regulations: RCRA Subpart J, 40 CFR 264.194(b), 270.14(b)(50)
Subject: Permitting of Hazardous Waste Treatment/Storage Tanks
Addressee: Regional RCRA Branch Chiefs
Originator: John H. Skinner, Director, Office of Solid Waste
Source Doc: #9483.01(84)
Date: 2-23-84
Summary:
Establishing Minimum Shell Thickness
Subpart J standards require that a minimum shell thickness be specified in
the permit for all regulated hazardous waste storage/treatment tanks, except for
covered underground tanks that cannot be entered for inspection. The applicant
must demonstrate to EPA that the tank complies with all applicable standards
before the decision to permit the tank is made. The applicant should obtain
current thickness data from the pre-permit inspection and include it in the
Part B application.
In general, RCRA-related metal tanks should not have a shell thickness of
less than 1/8 inch. The permit writer can use different methods to determine
the appropriate thickness for metal tank shells depending on size, shape, and
age. S/he can use standard industry codes, but these may not be practical in
some cases.
The permit writer can establish minimum shell thickness for fiberglass-
reinforced polyester (FRP) tanks and concrete tanks, once the tank is inspected,
by subtracting a small amount from the actual measured shell thickness (less
than O.I inch for FRP tanks and less than 10 percent for concrete tanks). The
applicant should line or coat concrete tanks with a compatible material to
prevent possible migration of hazardous wastes through its walls.
Tank Inspections
The applicant should conduct an initial inspection prior to the issuance of
a draft permit. This inspection should include draining the tank, examining the
tank interior, and measuring shell thickness through ultrasonic or some other
non-destructive test method.
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Continued from Document 9483.01(84)
The inspection plan, required by §270.14(b)(5), must contain detailed
procedures for conducting periodic, comprehensive inspections for each per-
mitted tank, and should specify the procedures for emptying the tank, methods
for performing the inspection (which should include an inspection of the tank
interior), and a-prescribed methodology for performing shell thickness measure-
ment* if the internal inspection indicates deterioration that would lead to
thinning of the tank wall to less than the minimum thickness prescribed in the
permit.' The Downer/ opera tor should perform periodic inspections; at least once
every two years, unless s/he can demonstrate that a more lengthy interval is
appropriate. Tanks storing or treating corrosive wastes, heated and/or pres-
surized tanks, tanks with relatively thin shells, fiberglass tanks, and concrete
tanks should be considered for more frequent inspections. The frequency of
comprehensive internal inspections should be established on a case-by-case
basis.
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9483.01 (34)
^^ o I f*- Q - -
^3 198'
.•:t.: i' .vANnr.'f;
nn f «r:nJ.t.t inrj of Hazardous w«ato»
Tanks
hi!o-i: John h. Skinner, L-irector
office of Solid Waste
TO: ' Wogional PCRA Brancn Chiefs
This memorandum provides guidance to permit writers on several
issues regarding permitting ot" hazardous waste treatment and
storage tanks. Several of the current PCRA Subpart J standards,
particularly the requirements nor minimum shell thicknesses and
farioaic inspections, have boen difficult to implement and have
in some cases been resolved differently by the regional offices.
Several regions have requested guidance on these regulatory re-
quirements to provide a more consistent national approach to
permitting RCRA regulated tanks.
The following guidance is applicable only to tanks permitted
under the current Subpart J standards.
bstaolishing Minimum Shell Thicknesses
The current Subpart J standards require that a minimum shell
thickness be specified in the permit t'or every regulated hazardous
waste storage/treatment tank'. This requirement applies to all
tanks (except for covered underground tanks that cannot be entered
tor inspection), and it cannot be waived.
The current, actual shell thickness of each tank should be
determined prior to the issuance of a draft permit. It is essential
that the applicant demonstrate to KP\ that the tank complies with
all applicable standards before the decision is made to permit the
tank. Current thickness data should Lie obtained from the pre-permit
inspection, and included in the Part B application (-see dis-
cussion below).
Sevoral methods can be used to determine the appropriate
mininun thickness for netal tank shells. Standard formulas can
bo used, such as the formula specified in the API Code 650. This
formula (also presented in the early "Tommy Tank" guidance)
should be used, however, only for very large (over 50,000 gallon
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capacity) non-yrossurized metal tanUs. For smaller rretal tanks,
the thicknesses prescribed in the r;L 142 code can be used, even
tncu'.jh this cede is intended primarily for tanks storing ignitable
Liquids. Other cedes for more specialized tanks, such as the
AhME iSnction VIII cede fcor pressure vessels, can also be used
tor certain types of tanks". It should be understood that the
shell thicKndsses prescribed in industry cedes are ninipium thick-
nesses to ensure structural integrity, and do not inclur.o allowance
for corrosion.
Tho use of standard industry codes nay not be practical for
'many metal tanks, such' as' irregularly shaped tanks, older tanks
not built to standard codes, and others. In such cases, permit
writers should specify a minimum thickness that is sufficient
not only to contain the liquid contents, but also to withstand
normal operational stresses and minor accidents (e.g., being hit
by a forklift), without massive failure. Discussions with various
industry officials have suggested that as a general rule, a metal
shell thickness of 1/8" (0.1J5") -3 a satisfactory minimum thick-
ness to provide an adequate deqr-.-e of safety against normal oper-
ational contingencies (this thickness would not be sufficient,
however, for pressurized tanks, or most large tanks of over
50,000 gallons capacity). Accordingly, it is recommended that
the minimum shell thickness specified in RCRA permits for metal
tanks be not less than 1/8". If a RCRA regulated tank is measured
and found to have a shell thickness of less than 1/8", the permit
writer should consider requesting that the applicant provide
additional information (such as-an engineer's certification) to
demonstrate that the tank is structurally sound and can withstand
normal operational streses and minor accidents.
For fiberglass reinforced polyester (FRP) tanks, the standard
formulas for determining. shell thickness based on structural
criteria, such as those used for metal tanks, are not appropriate.
Structural strength of FRP tanks is more a function of how the
tanks are manufactured (e.g., filament wound, fiber mat, etc.)
and the specific bonding resins used, rather than the thickness
of the wall. In general, the primary concerns for PKP tanks are
shell cracking (due to improper installation cr other causes) and
erosion of the resin layer of the interior tank wall surface.
Each FRP tank should be inspected internally prior to permitting
to determine if the inner resin layer is intact, or has deteriorated
or eroded such that glass fibers are exposed. FR? tanks which
exhibit deterioration of the inner resin layer, or other evidence
of wall deterioration, snould be repaired or taken out of service.
For FRP tanks in good condition, an appropriate approach to estab-
lishing minimum shell thickness is simply to subtract a snail
amount from the actual treasured shell thickness, to allow for
possible construction irregularities and/or sons limited erosion
of the( inner resin layer. This "allowance" should usually be
0.1" or less, since the inner resin layers c.f rvost fiberglass
tanks as manufactured typically do not exceed 0.1".
Minimum shell thicknesses for concrete tanks can be estab-
lished in a similar manner. Once the tank has been inspected
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IMUI" C.II t(JMI*.'S3 C«3II Ut: : Uv 3>JU<_ r. C i_ •_ L I Hj a n< V, I I A. i.ia i. Xa.«j«r (nw
rore than 1U%) tren the actual measured thickness of the tank
wall. Existing concrete tanks in good condition can, with few
exceptions, be presumed to have arterjuata "snell thickness",
since concrete tanks are typically designed tor substantially
greater than normal anticipated structural stresses.
A primary concern with concrete tanks is possible migration
oc Mflsarvicu.i waacod tnrough the walls ot the tan*. Conctfnta
tanks should be lined or coated with a compatible material
(even it the wastes are compatible with the concrete), unless
the applicant can aenonstrate that migration of wastes through
the tank walls, will not .occur over the. li.fe of. the. tank.
Tank Inspections
To ensure that regulated tanks are in compliance with
applicable RCRA standards, each tank should be thoroughly in-
spected by the applicant or another firm hired for the purpose,
prior to issuance of a draft pernit. This initial inspection
should involve draining the tank and examining the tank interior
tor leaks, cracks, corrosion, liner or coating failure and
other signs of deterioration. The inspection should also include
taking shell thickness measurements using ultrasonics or another
non-destructive test method. Attachment A presents suggested
methodologies for conducting ultrasonic shell thickness testing
for both vertical and horizontal metal tanks. Ultrasonic and
radiographic non-destructive testing must be performed by
qualified personnel. If the applicant proposes to use his own
personnel to perform such testing, he should be required to
demonstrate that those persons are competent in the use of the
test equipment,, through course work or other training or experience
The inspection plan required by §270 .14(b)(5) must contain
detailed procedures for conducting periodic, comprehensive
inspections for each permitted tank, as required in §264.194(b).
This periodic inspection should include a thorough inspection
of the tank interior. The inspection plan should specify the
procedures that will be used for emptying the tank, and the
methods to be used in performing the inspection. If the internal
inspection indicates evidence of significant corrosion, erosion
or other deterioration which would lead to thinning of the tank
wall to less than the minimum thickness prescribed in the permit,
the inspection plan should specify that the applicant shall
then perform shell thickness measurements according to a pre-
scribed methodology.
The frequency of the comprehensive internal inspection
should be established taking into account the age and general
condition of the tank, the material of construction and relative
compatibility with the wastes to be stored, waste temperature,
and other relevant factors. It is recommended that the periodic
inspections be performed at least once every two years, unless
the applicant can demonstrate that a more lengthy interval is
appropriate. More frequent inspections should be considered for
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sone tanks, including: tanks storing or treating corrosive
wastes, heated and/or pressurized tanks, tanks with relatively
thin shells, fiberglass tanks, concrete tanks.
Tank checklist
Attachment B is a checklist developed by Region I which can
be. a. useful tool for permitting tanks. The checklist can be
used by permit applicants as "a format for presenting the required
information for each tank to be permitted. It should be noted,
however, that some of the data asked for in the checklist are
not required by the regulations, and applicants should thus be
informed that use of the checklist is entirely optional. The
checklist can be sent to applicants along with other appropriate
guidance documents as part of the Part B call-in letter. Permit
writers can also use the checklist as a means of organizing the
information for each tank in the Part B application.
Attachments
cc: Regional Permits Section Chiefs
J. Lehman
S. Lingle
T. Grogan
P. Guerrero
B. Weddle
K. Gray
PAT staff
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