Chapter 5Oil/Water Separators
Chapter 5Oil/Water Separators
Chapter 5Oil/Water Separators
5.1 Introduction
The intended use of an oil/water separator(s) (OWS) determines whether the separator is subject to the
SPCC regulations and, if so, what provisions are applicable. This chapter explains the applicability of the SPCC
rule to OWS, and clarifies the exemption for certain uses, including equipment, vessels, and containers that are
not specifically called “OWS” but perform oil/water separation, such as water clarifiers at wastewater treatment
plants. This chapter also discusses the alternative compliance options for flow-through process vessels at oil
production facilities.
Table 5-1 below outlines the SPCC rule applicability for various uses of OWS. Only OWS used exclusively
to treat wastewater and not used to satisfy any requirement of 40 CFR part 112 are exempt from all SPCC
requirements. OWS used in oil production, recovery or recycling and to meet the secondary containment
requirements of the rule are not exempt.
Table 5-1: SPCC rule applicability for various uses of OWS.
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The §§112.8(c) and 112.12(c) provisions for bulk storage containers do not apply because oil/water separators at these facilities
function as oil-filled manufacturing equipment and are not bulk storage containers.
Section 5.3 discusses the exemption for the use of an OWS as wastewater treatment.
Section 5.4 addresses applicable SPCC requirements for the use of an OWS as secondary
containment.
Section 5.5 discusses applicable SPCC requirements for the use of an OWS at oil production
facilities.
Section 5.6 discusses applicable SPCC requirements for the use of an OWS at oil recovery or
recycling facilities.
Section 5.7 describes required documentation for OWS and the role of the EPA inspector in
reviewing facilities with OWS.
Subject to §112.7
requirements including
§112.7(c) general
secondary containment
Enhanced gravity separators allow the separation of smaller oil droplets within confined spaces. These
separators use a variety of coalescing media and small diameter cartridges that enhance laminar flow and
separation of smaller oil droplets that accumulate on the separator surface for removal. Figure 5-6 shows
coalescing plates in the middle compartment (separator designs may vary).
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Other types of separators include vortex separators, which combine gravity with centrifugal forces.
OWS are flow-through equipment in which wastewater enters the separator and treated water exits the
separator typically on a continual basis. To be effective, the OWS is sized appropriately in order for the unit to
separate and contain the intended oil capacity, in addition to the flow-through wastewater quantity. Also, the
design flow rate of the OWS is carefully considered when specifying a wastewater treatment system, as a flow
rate above the maximum rate of the separator will cause the discharge of accumulated oil and/or untreated
wastewater. The specifications from OWS manufacturers typically outline these and other design factors and
considerations, along with operation and maintenance requirements, to ensure that the OWS is correctly
constructed and operated for its intended use.
5.3.2 Applicability of the SPCC Rule to OWS Used for Wastewater Treatment
Section 112.1(d)(6) exempts “any facility or part thereof” that is used exclusively for wastewater
treatment and is not used to meet any other requirement of the rule (excluding oil production, recovery, and
recycling facilities). There are components of wastewater treatment facilities, such as treatment systems at
publicly owned treatment works (POTWs) and industrial wastewater treatment facilities treating oily
wastewater, that likely meet the two criteria for this exemption. OWS used exclusively for wastewater
treatment are flow-through separators and are not engaged in a static process in an isolated container. For
example, the presence of a water sump in a bulk storage container does not constitute wastewater treatment.
POTWs and other wastewater treatment facilities may have bulk storage containers and oil-filled
equipment, as well as exempt OWS. The capacities of the bulk storage containers and oil-filled equipment are
counted to determine whether the facility is subject to the requirements of the SPCC rule. The presence of an
OWS at an otherwise regulated facility does not exempt the entire facility from the SPCC rule requirements.
Such OWS capacity does not count toward the overall storage capacity of the facility, and only that equipment
used for oil/water separation is not subject to any rule provisions. At wastewater treatment facilities, storage
capacities to be counted include bulk storage containers, hydraulic equipment associated with the treatment
process, containers used to store oil that feed an emergency generator associated with wastewater treatment,
and slop tanks or other containers used to store oil resulting from treatment. All separate containers used to
store oil recovered by the separation process and all other equipment or containers at a regulated facility that
do not qualify for the wastewater treatment exemption are required to meet the applicable SPCC requirements
(67 FR 47069, July 17, 2002).
Examples of wastewater treatment OWS that may be eligible for the exemption of §112.1(d)(6) include:
OWS at a wastewater treatment facility;
Grease traps that intercept and congeal oil and grease from liquid waste; and
A separate container storing oil removed from an exempt separator is considered a bulk storage
container and is subject to the SPCC rule requirements. Furthermore, OWS exempted from the SPCC rule may be
subject to other federal, state, and local regulations. For example, many exempted wastewater treatment OWS
are within wastewater treatment facilities or parts thereof subject to the National Pollutant Discharge
Elimination System (NPDES) requirements under section 402 of the Clean Water Act (CWA). NPDES (or an
approved state permit program) ensures review and approval of the facility’s wastewater treatment plans and
specifications, as well as operation/maintenance manuals and procedures, and requires a Storm Water Pollution
Prevention Plan, which may include a Best Management Practice (BMP) Plan. 103 P
Additionally, some facilities may be subject to pretreatment standards promulgated under §307(b) of
the CWA. Pretreatment standards apply to “indirect discharges” that go first to a POTW via a collection system
before being discharged to navigable waters. The General Pretreatment Regulations for Existing or New Sources
of Pollution, found at 40 CFR part 403, prohibits an indirect discharger from introducing into a POTW a pollutant
that passes through or interferes with treatment processes at the POTW, and also sets the framework for the
implementation of categorical pretreatment standards. Specifically, 40 CFR 403.5(b)(6) prohibits the
introduction into a POTW of “petroleum, oil, non-biodegradable cutting oil, or products of mineral oil origin in
amounts that will cause interference or pass through.”
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BMPs are operational conditions that may supplement or constitute effluent limitations in NPDES permits. Under §402(a)(2) of
CWA, BMPs may be imposed in addition to effluent limits when the EPA Administrator determines that such conditions are
necessary to carry out the provisions of the Act. See discussion of authority for NPDES and BMP provisions in the preamble to
the 2002 final SPCC rule, 67 FR 47068.
a does not meet the definition of a “loading/unloading rack.” Sufficient secondary containment for a grease trap unloading area may be provided by acti
5.3.3 Wastewater Treatment Exemption Clarification for Dry Gas Production Facilities
A dry gas production facility is a facility that produces natural gas from a well (or wells) from which it
does not also produce condensate or crude oil that can be drawn off the tanks, containers or other production
equipment at the facility. Since no oil is being “produced” at these dry gas facilities they may be eligible for the
wastewater treatment exemption because they are not “oil production, oil recovery, or oil recycling facilities.”
Produced water containers used exclusively for wastewater treatment at dry gas production facilities are not
excluded from the wastewater treatment exemption (69 FR 29728, May 25, 2004). These produced water
containers are eligible for the wastewater treatment exemption and therefore do not count toward oil storage
capacity and are not subject to the rule’s requirements.
It should be noted that in the 2008 amendments to the SPCC rule (73 FR 74236, December 5, 2008), EPA
added the term “condensate” to the definition of production facility. The purpose of this amendment was to
clarify that certain gas facilities (i.e., wet gas facilities) that produce oil in the form of condensate are oil
production facilities and may be subject to the SPCC rule. As oil production facilities, wet gas facilities are not
eligible for the waste water treatment exemption.
At 69 FR 29730, EPA stated that
“...[in] verifying that a particular gas facility is not an ‘oil production, oil recovery, or oil recycling facility,’
the Agency plans to consider, as appropriate, evidence at the facility pertaining to the presence or
absence of condensate or crude oil that can be drawn off the tanks, containers or other production
equipment at the facility, as well as pertinent facility test data and reports (e.g., flow tests, daily gauge
reports, royalty reports or other production reports required by state or federal regulatory bodies).”
The corresponding anticipated flow rate of the drainage system to the separator; and
The appropriate capacity of the OWS for oil and for wastewater.
Many OWS used for secondary containment are installed in areas where they may receive considerable
flow from precipitation. If the precipitation flow rate exceeds the maximum design rate of a separator, it may
discharge accumulated oil and/or untreated wastewater to navigable waters or adjoining shorelines. In this case,
the separator may be an inappropriate choice for secondary containment. The specifications from OWS
manufacturers outline these and other design factors as important items to consider when determining the use
of a given OWS for a given application. Additionally, the manufacturer specifies the maintenance requirements
to ensure proper operation of the separator.
When OWS are used to meet SPCC requirements, they must be properly operated and maintained to
ensure they will perform correctly and as intended under the potential discharge scenarios it is aimed to address
(e.g., §§112.7(c), 112.8(c)(2), and 112.12(c)(2)). Required OWS capacities should always be available (i.e., oil
should not continually accumulate in the separators over a period of time such that the required storage
capacities would not be available if an oil discharge were to occur within the drainage areas).
The use of OWS as a method of containment may be risky as they have limited drainage controls to
prevent a discharge of oil and their reliability rests heavily on proper maintenance. This is particularly true when
using a separator to meet the sized secondary containment requirements for large bulk storage containers, as
separators are not typically designed to accommodate a worst case discharge of oil. EPA inspectors noting this
containment configuration should closely inspect the device and review records associated with documenting
the design criteria of the equipment and the routine maintenance performed on such equipment.
Oil contained in the separator does not count toward facility total oil storage capacity
Do not require additional secondary containment (i.e. tertiary containment) for the separator
Remember to observe the effluent treatment systems associated with bulk storage containers to prevent discharges to
navigable waters or adjoining shorelines.
5.4.2 Applicability of the SPCC Rule to OWS Used to Meet Specific SPCC Secondary
Containment Requirements
Section 112.7(c) requires “appropriate containment and/or diversionary structures or equipment to
prevent a discharge as described in §112.1(b).” OWS may be used to satisfy this requirement for onshore or
offshore facilities. These separators must be constructed to contain oil and prevent an escape of oil from the
system prior to cleanup in order to comply with the secondary containment provision for which it is intended
(§112.7(c)). A description explaining how the OWS complies with secondary containment provisions, and how it
is operated and maintained, should be included in the SPCC Plan. BMPs or operation and maintenance (O&M)
manuals that detail operation and maintenance procedures for OWS used specifically for secondary
containment may be referenced in the SPCC Plan and maintained separately.
ater separators
dary containment would typically be located in undiked areas, to supplement drainage systems. The requirements for secondary containment systems d
h a diked area which are used exclusively for treating dike discharge effluent are subject to the wastewater treatment exemption, as described in Sectio
Section 112.7(h)(1) requires “a quick drainage system” for areas where a tank car or tank truck loading
or unloading rack is present. OWS may be used as part of a quick drainage system to meet this requirement. This
containment system must hold at least the maximum capacity of any single compartment of a tank car or tank
truck loaded or unloaded at the facility (§112.7(h)(1)).
Sections 112.8(b), 112.9(b), and 112.12(b) set forth design specifications for drainage systems
associated with secondary containment at onshore facilities. Environmentally equivalent measures can be used
to satisfy these requirements (see Chapter 3: Environmental Equivalence, Section 3.3.1). For example, facilities
might use ponds, lagoons, or catchment basins as part of the design of facility drainage systems. Alternatively,
OWS might serve as environmentally equivalent measures to the ponds, lagoons, or catchment basins required
by §§112.8(b)(3) and 112.12(b)(3). In this instance, EPA recommends that these separators be designed to
handle the expected flow rate and volume of oil and water generated by facility operations. When certifying a
facility’s SPCC Plan, the PE must verify that OWS are adequately designed, maintained, and operated to provide
environmentally equivalent protection (in accordance with §112.7(a)(2)) under the potential discharge scenarios
they are aimed to address.
Sections 112.8(c)(2), 112.8(c)(11), 112.12(c)(2), and 112.12(c)(11) require that all bulk storage
containers be provided with secondary containment for “the entire capacity of the largest single container and
sufficient freeboard to contain precipitation.” OWS may be used to meet these requirements, but must be
appropriately sized. These separators must be capable of handling the oil and precipitation from the general
drainage area and additional oil from any accidental discharge from the largest bulk storage container located
within the drainage area for which the separator provides secondary containment. Good engineering practice
would suggest that the use of OWS to meet the specific secondary containment provisions be on a very limited
basis and typically with smaller capacity container storage areas. See the example scenario in Figure 5-7 that
calculates the required capacity of an OWS used as secondary containment for a drum storage area.
Sections 112.8(c)(9) and 112.12(c)(9) require that the facility owner/operator observe effluent
treatment facilities frequently enough to detect possible system upsets that could cause a discharge as
described in §112.1(b). Separators should be monitored on a routine schedule, and collected oil should be
promptly removed, as appropriate, and in accordance with manufacturers’ specifications and maintenance
instructions as described in the Plan, in order to ensure the proper operation and capacity of the equipment.
When OWS are used to meet secondary containment requirements, their capacities do not count
toward a facility’s overall storage capacity. Any volume of oil that would flow into these separators would come
from another source within the drainage areas and are already counted in the facility storage capacity
determination. However, slop tanks or other containers used to store waste oil that is transferred out of these
separators do count toward the facility’s total storage capacity. Furthermore, the SPCC rule does not require
redundant secondary containment around OWS used for secondary containment (i.e., tertiary containment is
not required).
Figure 5-7: Example calculation of secondary containment for a drum storage area using an
oil/water separator.
The following example includes an oil/water separator used to provide secondary containment for a drum storage area:
Scenario: An automotive facility stores up to 10 55-gallon containers of lubricating oil in its outdoor drum storage area.
This undiked area drains to an oil/water separator. The total drainage area served by the oil/water separator is 70 feet x
100 feet.
Applicable secondary containment requirements: The 55-gallon containers are bulk storage containers, subject to the
sized secondary containment requirements of §112.8(c)(2). In this case, the facility is using the oil/water separator to
meet the secondary containment requirements. Therefore, the separator must be designed and sized to handle the
capacity of the largest container in the area, plus sufficient freeboard to contain precipitation.
Note that because the drum storage area is undiked, the requirements at §112.8(b)(3) and (4) also apply.
Calculation of OWS capacity: After a review of historical precipitation data for the vicinity of the facility, the PE
determined that a peak rainfall intensity is 0.6 inch per hour is the most reasonable design criterion for this undiked
area, based on local conditions. The site is 100 percent impervious nd therefore the full volume of precipitation that
falls on the drainage surface is expected to flow into the oil/water separator.
Volume of largest container in area = 55 gallons
Drainage surface area = 70 ft x 100 ft = 7,000 ft 2
Precipitation volume (per hour) = 7,000 ft2 x (0.6 in /12 in=0.05 ft) = 350 ft3
Precipitation volume (per hour) in gallons = 350 ft 3 x 7.48 gal/ft3 = 2,618 gallons
Total volume = 55 gal + 2,618 gal = 2,673 gallons
Flow rate = 2,673 gallons / 60 minutes/hour = 44.6 gallons/minute
The OWS must be capable of handling a flow-rate of 44.6 gallons per minute. Additionally, the OWS must have
sufficient oil storage capacity within the unit to provide storage for 55 gallons of oil plus a reasonable safety to account
for oil accumulated from the drainage area itself.
Conclusion: Based on these calculations, the facility has specified a cylindrical separator sized to handle a flow rate of
55 gallons per minute and providing a total volume of 550 gallons, including an oil storage capacity of 110 gallons prior
to the recommended pump out. The oil/water separator is maintained so as to preserve storage within the unit at all
times under normal operating conditions (pump out is scheduled for 35 gallons). For additional protection, the outlet of
the separator is equipped with an afterbay in which absorbent materials are placed.
s what differentiates flow-through process vessels from other bulk and end-use storage containers, such as produced water containers. Produced water
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An emulsion is a colloidal suspension of a liquid within another liquid. In this case, small droplets of oil are dispersed
through water.
Figure 5-8: Low pressure free-water knockout. Figure 5-9: Two-phase oil/water separator.
Figure 5-10: Gun barrel oil/water separator. Figure 5-11: Three-phase oil/water separator.
In oil production separators, the momentum of the fluid flow is absorbed at the inlet, thereby reducing
the fluid viscosity and allowing oil, gas, and water to separate out of solution. Gas then rises and flows out at the
top of the separator, while oil and water fall to the lower portion of the vessel and coalesce in separate areas.
With the appropriate settling time, the more dense free water settles beneath the less dense oil. Liquid levels
are maintained by float-actuated control valves or dump valves. As the different pre-set liquid levels are
reached, dump valves discharge water and oil from the separator to appropriate storage areas:
Water is discharged from the bottom of the separator to a water tank;
Gas flows continuously out at the top of the separator to sales, a meter run, a flare, or a
recovery system.
5.5.2 Applicability of the SPCC Rule to OWS Used in Onshore Oil Production
OWS used in oil production count toward the total storage capacity of the facility and must be
considered when determining if a facility is regulated by the SPCC rule in accordance with §112.1(b) and (d)(2)
and the definition of storage capacity in §112.2. In determining applicability of any container for calculating the
total facility storage capacity, the preamble to the 2002 rule states:
The keys to the definition are the availability of the container for drilling, producing, gathering, storing,
processing, refining, transferring, distributing, using, or consuming oil, and whether it is available for one
of those uses or whether it is permanently closed. Containers available for one of the above described
uses count towards storage capacity; those not used for these activities do not. Types of containers
counted as storage capacity would include some flow-through separators, tanks used for “emergency”
storage, transformers, and other oil-filled equipment. (67 FR 47081, July 17, 2002)
Take corrective action or make repairs to flow-through process vessels and any associated
components as indicated by regularly scheduled visual inspections, tests, or evidence of an oil
discharge; and
Promptly remove or initiate actions to stabilize and remediate any accumulations of oil
discharges. P
It is important to note that the general secondary containment requirements under §112.7(c) still apply
to flow-through process vessel OWS in addition to the alternative requirements described above. The secondary
containment system must be designed to address the typical failure mode, and the most likely quantity of oil
that would be discharged, and can be either active or passive in design (see Chapter 4: Secondary Containment
and Impracticability, Section 4.8.1).
Furthermore, the owner/operator of the facility must install sized secondary containment and comply
with bulk storage container inspection requirements (§112.9(c)(2) and (c)(3)) for flow-through process vessels
within six months of a discharge(s) from flow-through process equipment as described below and a report must
be submitted to the RA in accordance with the requirements of §112.4:
More than 1,000 U.S. gallons of oil in a single discharge to navigable waters or adjoining
shorelines, or
More than 42 U.S. gallons of oil in each of two discharges to navigable waters or adjoining
shorelines within any twelve month period.
This excludes discharges that are the result of natural disasters, acts of war, or terrorism. When
determining the applicability of this SPCC reporting requirement, the gallon amount(s) specified (either 1,000 or
42) refers to the amount of oil that actually reaches navigable waters or adjoining shorelines not the total
amount of oil spilled. EPA considers the entire volume of the discharge to be oil for the purposes of these
reporting requirements.
nks, dryers, heat exchangers, and distillation columns) are not subject to the more stringent sized secondary containment and inspection requirements r
potential to immediately discover and correct a discharge at non-production facilities than at oil production facilities, which are generally unattended. F
5.5.3 Applicability of the SPCC Rule to OWS Used in Offshore Oil Production
Offshore production facilities are subject to requirements under §112.11 of the SPCC rule, which are
tailored specifically for the offshore operating environment. Therefore, OWS used at off-shore oil production
facilities are not eligible for the alternate compliance option in §112.9(c)(5) as described in Section 5.5.2. Flow-
production facilities. Production facilities are normally unattended and therefore lack constant human oversight
and inspection. Produced water generated in the production process normally contains saline water as a
contaminant in the oil, which in addition to the toxicity of the oil might aggravate environmental conditions in
the case of a discharge (67 FR 47068, July 17, 2002). In some areas of the United States, produced water is fresh
and may be discharged for beneficial use (e.g., irrigation or water for livestock) in accordance with federal and
state regulatory requirements.
Therefore, a facility that stores, treats, or otherwise uses produced water remains subject to the rule.
Produced water containers at onshore oil production facilities are bulk storage containers and are therefore
subject to the applicable requirements in §112.9(c), including the requirement for sized secondary containment.
The SPCC rule includes an alternative compliance option for produced water containers at onshore oil
production facilities in lieu of sized secondary containment.
For more information on the applicability of the SPCC rule as it relates to oil and water mixtures in
produced water or produced water containers, see Chapter 2: SPCC Rule Applicability, Sections 2.2.7 and 2.10.7.
For information on the secondary containment requirements that apply to produced water containers including
the alternative regulatory requirements, see Chapter 4: Secondary Containment and Impracticability, Section
4.8.2.
For OWS used in oil recovery or recycling, the OWS are considered oil-filled manufacturing equipment
and are subject to the provisions of §112.7 and applicable provisions of §112.8(b) and (d) for onshore petroleum
and non-petroleum facilities or §112.12(b) and (d) for onshore AFVO facilities. The Plan must address the
general requirements under §112.7 for the OWS including a description of how the facility complies with the
secondary containment requirement under §112.7(c).
Routine visual inspection of the oil/water separator, its contents, and discharges of effluent;
A drainage area that flows to the OWS and corresponding anticipated flow rate of the drainage
system to the separator;
Appropriate capacity of the OWS for oil, wastewater, and, if appropriate, precipitation;
Provisions for adequate separate storage capacity (based on the containment sizing required by
the rule) to contain oil recovered in the oil/water separator; and
A separate bulk storage container used to store oil following separation in any OWS (i.e., wastewater
treatment, secondary containment, or oil production) is subject to all applicable requirements of 40 CFR part
112, including §§112.8(c), 112.9(c), or 112.12(c) as appropriate.
For OWS used in oil production, the OWS are bulk oil storage containers to be included in the SPCC Plan.
The location of these containers must be indicated on the facility diagram and discussed in the general
requirements in accordance with §112.7(a)(3). For more information on facility diagrams, refer to Chapter 6:
Facility Diagram and Description. The Plan must also include a discussion of sized secondary containment
provided for OWS (§112.9(c)(2)), or, in the case where the owner/operator elects to comply instead with the
alternate requirements in §112.9(c)(5), include records to document implementation of the alternative
measures, including periodic inspection and/or testing for leaks, corrosion, or other conditions that could lead to
a discharge as described in §112.1(b); corrective action or repairs to flow-through process vessels and any
associated components as indicated by regularly scheduled visual inspections, tests, or evidence of an oil
discharge; and prompt removal or initiation of actions to stabilize and remediate any accumulations of oil
discharges associated with flow-through process vessels. The Plan must also address the general requirements
under §112.7 for OWS including a description of how the facility complies with the secondary containment
requirement under §112.7(c).
OWS (including those used in oil production) that are not eligible for the wastewater exemption must be
included in the oil storage capacity calculations for the facility (§112.1(b) and (d)(2) and the definition of storage
capacity in §112.2).
When an oil production facility Plan describes compliance with the alternative option for flow-through
process vessels in accordance with §112.9(c)(5), then the EPA inspector should verify that the requisite records
are included in the SPCC Plan (refer to Section 4.8.1 and 7.2.9 for a summary of the information to be provided
in the Plan).
If the owner or operator of the facility discharges into or upon a navigable water or adjoining shoreline
more than 1,000 U.S. gallons of oil in a single discharge, or more than 42 U.S. gallons of oil in each of two
discharges within a 12-month period from a flow-through process vessel, and is required to comply with
§112.9(c)(2) and 112.9(c)(3), the SPCC Plan must then describe the sized secondary containment and inspection
program provided for this equipment.
By certifying the SPCC Plan, a PE attests that the Plan has been prepared in accordance with good
engineering practice and with the requirements of 40 CFR part 112, and that the Plan is adequate for the facility.
Thus, if OWS uses are properly documented, they most likely will be considered acceptable by EPA inspectors.
However, if the documented uses of the OWS appear inappropriate to prevent spills from reaching navigable
waters or adjoining shorelines, appear to be incorrect, deviate from the use described in the Plan, are not
maintained or operated in accordance with the Plan, or the separator appears to be malfunctioning or out of
service, further follow-up action may be warranted. This may include requests for more information or for a Plan
amendment in accordance with §112.4(d).