United States Office of
Environmental Protection Solid Waste and
Agency Emergency Response
! VEPA - DIRECTIVE NUMBER: 9441.01-91
TITLE:
Açplicability of the “Mixture” Rule to Petroletin
Refinery Waste .zater Systans
APPROVAL DATE: July 5, 1991
EFFECTIVE DATE: July 5, 1991
ORIGINATING OFFICE: WaSte IdentificatiQ Brar h,
Characterization and Asses nt
Division, Office of Solid Waste
FINAL
El DRAFT
STATUS: 0 A- PendIng 0MB Approval
0 B - Pending AA-OSWER Approval
REFERENCE (Other Documents):
9441.29—85 ipplicability of “Mixture” and “Derived Fran”
Rules to Petrole n Refinery Wastewater Systeiis
OSWER OSWER ‘ OSWEIT{ OSWER
DIRECTIVE bIRECTIVE DIRECTIVE

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United States nvironmental rOtectio4, Agency
Washenglon DC 20460
&ERA OSWER Directive Initiation Request
Ii Dtr rie Numbe
I 9441.01-gi
(

2. Oi1 natoi’ Inloimatlon
Name of Contact Person Ma4 Code lOffic.
I Qs—333 I QJ /QSW/çJ D/WIB
‘Telephone Code
FTS: 382—4800
3 r u
Applicability of tt “Mixture” Rule to Petroleun Ref inery
Wastewate.r Systøtts
4 Summary 01 Directive (ui ude bnef statement of purpose)
Directive clarifies Iu the mixture rule ur ier 1CR applies to listed hazardous
waste cxdes for F037 ar* F038. Purpose is to respaxxl to API’s r uest for
clarification is of
S Keywords
wa.stewater treathent systan / petroleun refirEry / mixture rule / 1 A / HW listings
6a. Does This Directive Supersede Previous Directive(s)? No Yes Whit directt’ . (number, title)
b Does p1.men s Directive(s)? Yes What *ectrve (number, title)
9441.29—85
7 Draft Level
A - Signed by MJD&A B - Signed by Office Director C - For Review & Comment 0-In Development
I
18. Document to be distributed to States by Headquarters? Yes No
This Request Mests OSWER Olr.ctlv.s Syst.m Format Standards.
IDa le
9 Signature of Lead Office Directives Coordinator
L n T. 7/8/91
10 Name and Title of Approving 0 ici l
Date
Sylvia K. Lt .zrance, Director, Office of Solid Waste 7/5/91
EPA Form 1315-17 (Rev. 5-87) Previous editions are obsolete
Os
WER Os
WER OS
WER
0
VE
DIRECTIVE
DIRECTIVE
DI
RECTIVE

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# 9441.01—91
ST ç
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON DC 20460
,
oF IC O
SOLO W2.STE 2. O ME” NC $PC\SE
ii 51991
MEMORANDUM
SUBJECT: Applicability of the “ i ure” Rule To Petroleum
Refinery Wastewa s
FROM: Sylvia K. Lowr ce
Office of Solid W
TO: Director, Waste anagement Division
Regions I - X
Last fall, EPA added two wastes, F037 and F038, generated in
the treatment of petroleum refinery wastewaters to the list of
hazardous wastes under 40 C.F.R. 261.31 (55 Fed. Req. 46354,
November 2, 1990). Since then, we have received requests for
clarification concerning the application of the “mixture rule” to
these listings. This memorandum is intended to provide guidance
on this question.
In a December meeting with the American Petroleum Institute
(API) and my staff, API discussed what it viewed as a potential
conflict between the language of the listing that limits the
listed wastes to those generated upstream of aggressive
biological treatment units and the preamble discussion of the
interaction between the “mixture rule” and the listing. .PI
explained its fear that introduction of a particle of the sludge
to non-hazardous wastewater would taint the wastewater and thus
convert any downstream units into hazardous waste treatment
facilities.
The discussion of the mixture rule in the preamble to the
final regulation does not reflect any change in the Agency’s
position about how the mixture rule works and the circumstances
in which a non-hazardous wastewater, i.e., non-listed wastewater,
that generates a listed waáte would become hazardous.
- In response to an expression of concern about this matter in
comments filed on the rule, EPA (Response to Comments Background
Document) indicated as follows:

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E D 9441.01—9].
—2—
With respect to the commenter’s concern that all
downstream units would be regulated as hazardous as a
consequence of application of the mixture rule, the
Agency feels that the following points should be made.
Generation of a waste does not occur until deposition.
It is Agency policy that no mixing occurs in a
wastewater treatment unit that manages a non-hazardous
[ nonlisted) liquid waste even if that liquid generates
a hazardous sludge that settles to the bottom of the
unit, unless that sludge is in some way dredged up and
physically mixed with the liquid. If the Agency did
not interpret the mixture rule in this manner, there
would be no point in carefully limiting listings to
include sludges but exclude wastewaters. The position
of the Agency in expanding the listing was to ensure
the regulation of similarly composed sludges,
regardless of where they are generated.
This is consistent with EPA’s previous discussions of the
applicability of the mixture rule with respect to petroleum
refinery wastewater separation sludges. (See attached December
7, 1984 Office of Solid Waste and Emergency Response Memorandum,
Subject: Region VIII Policy for the Permitting of Refinery Oily
Wastewater Treatment Ponds). Further, the Agency’s position is
fully explored in the extended discussion of the rule in the
final rule concerning the delay of closure for hazardous waste
management facilities. See 54 . g. 33376, 33387 (August l4’ .
1989). There, the Agency rejected the position that when non-
hazardous waste and a listed hazardous waste are co—mingled and
co—managed in the same unit under any circumstances, the entire
mixture is considered a listed waste.
The Agency has consistently interpreted the mixture
rule not to apply where a non—listed waste is
discharged to a unit (i.e., surface impoundment) even
if that liquid generates a hazardous sludge, unless the
sludge is in some way “mixed” with the liquid (e.g.,
scoured as a result of operations in the unit). If the
Agency did not interpret the mixture rule in this
manner, there would be no point in carefully limiting
listings to include sludges but exclude wastewater.
The discussion goes on to recognize that there is a continuum
between sludge, the sludge/liquid and the liquid. Within the
sludge/liquid interface there may be some mixing but not “mixing”
so as to convert the liquid from non—hazardous waste to
hazardous. Only in the e rent of scouring or other physical
mixing would the mixture rule come into play.
Were any mixing to occur, it would be confined to the
liquid/sludge interface. Levels of hazardous
constituents escaping from the hazardous sludge to the
non-hazardous liquid are not likely to pose an

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L J # 9441.01—91
-3-
appreciable risk to human health and the environment.
Should the impoundment be dredged so that scouring or
other physical mixing occurs, the mixture rule would
come into effect. 54 E . B . 33388.
Under the policy explained above, for example, it is
unlikely that any increased turbidity associated with the
introduction of water from storm events would create the
necessary scouring or physical mixing described above so as to
convert non—hazardous wastewater to hazardous. Similarly, for
example, the small amount of resuspension of primary sludge
associated with the normal operation of a properly designed
wastewater treatment system would not render the wastewater
hazardous.
cc: RA’s Region I-X
Richard Witt (LE—l32S)

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D # 9441,.O1—91
Ii ’ .
?
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
____ WASHINGTON, 0 C 20460
t( ’ DEC 7 1984
OPIICE O
SOt.i0 WAS1I AP O IM(RGENC’v ESPONS
MEMORANDUM
SUBJECT: Region VIII Policy for the Permitting of Refinery
Oily Waatewater Treatment Fonda
FROM: John H. Skinner, Director
Office of Solid Waste (WH-562)
TO: Robert L. Duprey, Director
Region 8
Air and Waste Management Division (8AW-WM)
We have reviewed the proposed Region VIII position
discussed in your memos dated May 1 and October 12, 1984 that
define permitting coverage of refinery wastevater treatment
ponds. As your staff may have informed you, there have been
several meetings between my staff and yours to discuss this
problem. We have also met with Chevron, Phillips, Toeco and
API and, separately, with Region IX to discuss the issue. We
share your concern about the threat posed to ground and surface
waters by some of the unlined wastewater ponds that treat or
store oily wastewaters. However, we believe that the similarity
of downstream unit sludges (in terms of lead and chromit levels)
to those found in the API Separator are not a sufficient basis
for defining the material in the downstream units as API
Separator Sludge. In fact, the similarity of these sludges was
a significant factor in our decision to move forward on an
expanded listing to regulate these pond sludges.
Specifically, we are planning in a forthcoming listing to
regulate oil/vate.r/solids separation sludges generated in the
wascewater treatment system prior to biological treatment. This
listing was origfnally proposed in November of 1980. We expect
to issue a notice identifying all of the available data in support
of the listing and to provide ,some clarifications in response to
previous comment s. Current plans are to promulgate that listing
by late s mer.
While the listing revision should cover most sludges generated
in these ponds, we realize chat does not address your short term
problem. We do have some suggestions in this regard. Section
206 of the Hazardous and Solid Waste Amendments of 1984 provides

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1 D # 9441.01—91
2
that persons obtaining RCRA permits must undertake corrective
action for all releases of hazardous Constituents from any
solid waste management unit as a condition of obtaining the
RCR.A permit. Thus, if a refinery pond is releasing hazardous
constituents and the refinery seeks a RCRA permit for any
unit at that facility, the refinery would have to undertake
corrective action for the releases from the pond. (This could
be done either through the permit, or pursuant to an interim
status compliance order.) This principle applies even if the
pond is not considered to hold a hazardous waste, since Section
206 applies to releases of hazardous constituents from solid
waste management units.
A second option for addressing these pond sludges is to
regulate the wastes as hazardous based on their exhibiting one
or snore of the characteristics of hazardous waste (see 40 CPR
S261.21 —24). You mentioned this option in your recent letter
with respect to EP Toxicity. ifowever, your staff seems to have
overlooked corrosivity (high p0 has been found in some COD ponds)
and reactivity (S261.23(a)(5)). It is likely that some refinery
pond sludges will contain excessive levels of reactive sulfidee.
The final option that could be used to deal with downstream
impoundments and basins is applicability of the mixture rule. It
is imperative, however, that your staff understand the proper
framework for the application of the mixture rule. To maintain
that a pond is regulated because an API Separator is an inherently
inefficient unit and allows sludge to be carried through to a
pond, is inaccurate. Likewise, downstream oxidation ponds are
not regulated simply because they sometimes receive flow that
has bypassed the API Separator. In both cases, the listed API
Separator Sludge has not yet been generated. Rather, API
Separator Sludge is generated when it is deposited in the bottom
of an API Separator. The mixture rule is relevant only in those
cases where previously deposited sludge is scoured, resuspended,
and then carried out of the unit with the wastewater. If the
Region can make a case for scouring from a separator, the mixture
rule is applicable and the wastewater becomes a hazardous waste
until delisted or discharged to a stream subject to regulation
under the Clean Water Act.
The burden of proof in the demonstration of scouring is
upon the Agency. Such an argument, although technically complex,
can be made basea on well established hydrodynamic principles.
Realizing that there are limited resources and capability for
developing such art argument by the Regions. we have (at the
request of your staff) taken arf active role in the development of
guidance for the application of this argument. Attached to this
memo is a preliminary list of factors that may be required to
establish the occurrence of scouring frog a given separator.
These points are being provided at this time to facilitate the
initiation of information gathering in the more serious cases.

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# 9441.,O1—91
We have also requested that the Office of Waste Programs
Enforcement (OWPE) develop more thorough guidance. That effort
is being conducted by their contractor (Metcalf & Eddy). We
anticipate that your staff will be contacted by them in the near
future The contractor should be able to provide some direct
assistance to your staff in some specific cases, thereby serving
the dual purpose of training and resolution of specific factors
of concern. Mike Barclay (FTS: 475—8727) of OWPE is the Head-
quarters lead on that project and should be contacted for any
further Information. Ben Smith of my staff (FTS: 475—8551) is
our technical expert in this matter and the lead on our study
of petroleum refineries and their wastes. Do not hesitate to
contact him if additional questions arise pertaining to this or
other matters.
cc: PA’S Region I—X
Mike Barclay (OWPE)
Steve S verman (0CC)
Susan MangaflellO (ORC, Region VIII)

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Factors To Be Evaluated In Determining The potential For
separator Sludge Scouring
Sludge Accumulation Practices — Continuous sludge removal
from the separator rules out the occurrence of scouring.
At the other end of the spectrum are facilities that allow
sludge to accumulate to considerable depth. Accumulation
to a depth greater than 50% of the flow depth makes scouring
probable. Intermediate ranges of accumulation will prob-
ably depend more heavily on other factors.
• Plow variability — Unless overloaded, units with maximum—
to—minimum, flow ratios at the separator effluent of less
than 2 and inlet flow ratios of less than 4 are probably
not experiencing much resuspension of sludge.
• Poor Separator Design Or Operation — Factors contributing
to scour conditions include: excessive, inlet or outlet
zone turbulence; nominal horizontal velocities greater
than 30 feet per minute; nominal overflow rates (f low!
surface area) greater than 10,000 gallons per day/square
foot of basin; basins less than 30 feet in length; opera-
tion under pressure (e.g., with a backwater at the inlet
of a separator with a frozen surface), settling zone
turbulence (sometimes seen as bubbling with solids
entrainment).
o Separator Effluent Characteristics — Excessive weir loadings
(e.g., operation with a suppressed weir, flow depth greater
than a foot) facilitate carryover of resuspended particles.
Visible, large (diameter greater than 1/4 inch) sludge
particles in the separator effluent are strong evidence
of scouring associated with microbial degradation of
deposited sludge.
o Sludge Characteristics — Particle size distribution as
measured by wet sieve and hydrometer analyses is necessary
information to define scour conditions. The presence of
coke fines in the wastewater influent is also important
becauséth t size of particle (<.lrrun) is non—cohesive
and highly susceptible to resuspension.

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