&EPA
United States
Environmental Protection
Agency
Model NPDES Permit for
Discharges Resulting From
The Cleanup of Gasoline
Released From
Underground Storage Tanks
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PART I
INSTRUCTIONS FOR MODEL NPDES PERMIT PACKAGE FOR DISCHARGES
RESULTING FROM THE CLEANUP OF GASOLINE RELEASED
FROM UNDERGROUND STORAGE TANKS
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TABLE OP CONTENTS
Page
1.0 INSTRUCTIONS FOR MODEL NPDES PERMIT PACKAGE 1-1
1.1 NPDES PERMITTING AUTHORITY 1-2
1.1.1 NPDES Permit Application Requirements 1-3
1.2 MODEL NPDES PERMIT 1-3
1.2.1 Authorization to Discharge 1-4
1.2.2 Effluent Limitations and Monitoring Requirements... 1-4
1.2.3 Standard Conditions 1-5
1.2.4 Special Conditions 1-5
1.3 FACT SHEET 1-6
1.4 DECISION TOOL FOR DEVELOPING WATER QUALITY-BASED
EFFLUENT LIMITATIONS 1-6
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1.0 INSTRUCTIONS FOR MODEL NPDES PERMIT PACKAGE
This package was developed to assist U.S. Environmental Protection Agency
(EPA) Regional and State permitting authorities in writing National Pollutant
Discharge Elimination System (NPDES) permits for direct discharges to surface
waters resulting from the cleanup of gasoline from leaking underground storage
tank (UST) sites.
The UST program originally was mandated under Subtitle I of the Resource
Conservation and Recovery Act of 1976 (RCRA) to regulate the installation,
operation, and closure of USTs. The Hazardous and Solid Vaste Amendments of
1984 (HSWA) strengthened the existing RCRA provisions to provide for a com-
prehensive regulatory program to address USTs and releases of regulated sub-
stances (primarily petroleum products) into the environment. Like other RCRA
programs, States may be authorized by EPA to implement their own UST programs.
When a release is detected, the enforcement agency (either EPA or its
delegated State) has the authority to require the owner/operator to conduct a
release response and corrective action to cleanup the release. Depending on
the situation, the EPA or delegated State may choose to conduct the release
response or corrective action. Any discharge to surface waters occurring
during a release response or corrective action would be subject to regulation
under an NPDES permit.
This Model Permit package is only intended for use at facilities where
gasoline has been released and the cleanup (or corrective action) involves a
release or discharge of waters and wastewaters to surface waters. It is not
intended for use at sites where nongasoline products are the primary source of
contamination (e.g., jet fuels, fuel oil, diesel fuel, etc.). This package
consists of four documents. Part I, Instructions for Model NPDES Permit
Package, briefly describes NPDES permit requirements. The remaining three
documents are briefly described below:
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• Part II - Model NPOES Permit For Discharges Resulting From The Cleanup
Of Gasoline Released From Underground Storage Tanks
• Part III - Fact Sheet For Model NPDES Permit For Discharges Resulting
From The Cleanup Of Gasoline Released From Underground Storage Tanks
• Part IV - Decision Tool For Developing Water Quality-Based Effluent
Limitations.
The UST Model Permit Package is available on diskette in WordPerfect*
version 4.2. In addition, the Model Permit Package can be made available in
IBM® Document Control Architecture revisable-format-text (DCA RFT) or ASCII
formats for use on IBM PC (or compatibles) or for Apple Macintosh® computers.
1.1 NPDES PERMITTING AUTHORITY
This Model Permit is intended for use in developing individual, site-
specific NPDES permits. NPDES permit application requirements (discussed in
Section 1.1.1 below) may vary depending upon the NPDES permitting authority.
Under the NPDES Program, a total of 57 jurisdictions are regulated including
the 50 States plus the District of Columbia, Puerto Rico, the Virgin Islands,
American Samoa, Guam, West Marinaras, and U.S. Trust Territories. Thirty-nine
of these jurisdictions have the authority to conduct their own NPDES program.
In the remaining 18 jurisdictions, EPA is responsible for implementing the
NPDES program.
According to 40 CFR §122.28, States can apply for the authority to issue
general NPDES permits. General permits apply the same set of limitations to a
group of dischargers that discharge the same types of vastes, require the same
effluent limitations or operating conditions, and require similar monitoring.
The information provided in this Model Permit Package may also be used as the
basis for developing a general permit. Thirteen NPDES-approved States have
the authority to issue general permits. EPA can issue general permits in all
of the 18 jurisdictions where EPA is the permitting authority. Currently,
general permits cannot be issued in 26 jurisdictions.
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1.1.1 NPDES Permit Application Requirements
Dischargers must submit an NPDES permit application before an individual
NPDES permit can be issued. The information provided in the permit applica-
tion serves as one source of data for developing NPDES permit requirements.
States may have their ovn permit application forms and requirements but must
request from the applicant as a minimum, the information required by the
Federal NPDES regulations.
Some of the major constituents of gasoline can be detected by analytical
methods for volatile organlcs. Analytical methods are specified at 40 CFR
Part 136. Certain other chemicals (e.g., xylene) should be tested for if the
applicant believes that other substances are present in the discharge, for
which there are no approved analytical methods. For these other substances,
the applicant is required to use another suitable analytical method. One such
method that is particularly suitable for potential gasoline constituents is
EPA Method 8240. This method is an approved RCRA method for the analysis of
volatile organic compounds such as xylene.
The data provided in the NPDES permit application should be carefully
reviewed by the permit writer. Specifically, information such as discharge
flow rates and the presence of toxic pollutants should be carefully evaluated.
For example, the effluent limits in the Model Permit may be modified to
account for the presence of additional pollutants. Similarly, the monitoring
requirements may need to be modified based upon unique discharge characteris-
tics (e.g., batch discharges).
1.2 MODEL NPDES PERMIT
This Model Permit is based on the approach taken, in part, by several
States and EPA Regional Offices. Vhile a Model Permit may not be applicable
in every situation, the information contained in this Model Permit Package
should serve as a framework for the permit writer and expedite the NPDES
permit issuance process. Key elements of the Model Permit include chemical-
specific effluent limitations, standard conditions, and special conditions
including Best Management Practices (BMPs) and biomonitoring requirements.
These elements are recommended for inclusion in all NPDES permits for
discharges from the cleanup of gasoline-related UST sites.
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This Model Permit was-, based principally on guidance provided by the NPDES
regulations and the Training Manual For NPDES Permit Writers, EPA Office of
Water and Permits, May 1987. However, the Model Permit should be modified to
conform with State regulations and policies, air and ground-water protection
strategies or requirements, or site-specific conditions. This Model Permit
differs from most NPDES permits in that gasoline cleanups typically last for
one or two years while most NPDES permits are issued for a five year period.
Due to this shorter time span, biomonitoring requirements may need to be
altered or deleted in some cases. The following subsections highlight four
major components of the Model Permit.
1.2.1 Authorization to Discharge
The "Authorization to Discharge" section of the Model Permit must be
completed by the permit writer. In order to fill in this section the
following information must be provided:
• Name and Address of Facility
• Outfall Designations
• Receiving Water Name and Present/Future Water Quality Standard
Classification of Receiving Water
• Effective Date of Permit
• Expiration Date of Permit.
1.2.2 Effluent Limitations and Monitoring Requirements
Part I of the Model Permit provides technology-based effluent limitations
and monitoring requirements for surface water discharges from corrective
actions at gasoline underground storage tank sites. Specifically, effluent
limitations have been developed for benzene and the aggregate parameter 8ETX
(benzene, ethylbenzene, toluene, and the xylenes). The technology basis used
to develop these limits is free product recovery, followed by air stripping.
These effluent limits are based on the characterization of constituents
commonly found in gasoline as described in the Fact Sheet (listed in Tables
3-1, 5-1, and 5-2 of the Fact Sheet). Additional site-specific constituents,
such as gasoline additives, may be reported in the sampling data required as
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part of the NPDES permit application. Should this occur, the permit writer
may need to develop additional effluent limitations.
NOTE: An optional set of effluent limitations has also been developed
based upon consideration of the potential impacts of treatment costs,
particularly on smaller firms that ovn retail motor fuel outlets. These
optional effluent limitations, based upon a reduction in air stripping
efficiency, could be used by permit writers if a firm could not afford
the cost of compliance with the more stringent effluent limitations.
However, if these optional effluent limitations, as with all technology-
based limitations, would result in the exceedance of water quality
standards and/or endanger aquatic life, human health, or the environment,
then water-quality based limitations should be established.
Weekly flow and chemical-specific monitoring is recommended based on EPA
guidelines. In addition, chronic toxicity testing requirements are recom-
mended and provided in the permit. Alternative approaches to establishing
biomonitoring requirements, such as the whole effluent toxicity screening
approach, are provided in the Fact Sheet.
1.2.3 Standard Conditions
The standard conditions established in Part II of the Model NPDES Permit
are based on those required in 40 CFR §122.41. Standard conditions may vary
from State to State. Therefore, the permit writer is free to substitute State
requirements for the Standard Conditions in this Model Permit as appropriate.
1.2.4 Special Conditions
Part III of the Model Permit requires the permittee to develop a Best
Management Practices (BMP) plan. In addition, biomonitoring is recommended
for inclusion in each gasoline UST cleanup NPDES permit. The Fact Sheet
provides additional guidance for developing and implementing biomonitoring
requirements. Additional special conditions may be required to address
site-specific problems. The conditions presented in this Model Permit are
severable, which means if one condition is proven to be invalid the other
conditions still hold. Regions and States may choose to incorporate addi-
tional requirements in accordance with their own policies on BMPs and bio-
monitoring requirements.
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1.3 FACT SHEET
The NPDES regulations [40 CFR §124.8(a)] require the preparation of a
Fact Sheet for every major NPDES permit to document the facts, methodology,
and basis used to develop the permit. For purposes of this Model Permit it is
assumed that the discharge from an UST cleanup may constitute a major point
source discharge. Therefore, a Fact Sheet has been prepared as part of this
package that provides a rationale for the effluent limitations, monitoring
requirements, and special conditions set forth in the Model Permit. This Fact
Sheet should be reviewed carefully by the permit writer before using the Model
Permit. The rationale given in the Fact Sheet may need to be modified to
account for site-specific considerations.
1.4 DECISION TOOL FOR DEVELOPING WATER QUALITY-BASED EFFLUENT LIMITATIONS
Both the Clean Water Act and NPDES regulations require all NPDES permits
to include effluent limitations to achieve applicable State water quality
standards. Since State standards are typically specified on a site-specific
basis, water quality-based effluent limitations have not been developed for
this Model Permit. However, a Decision Tool for addressing site-specific
water quality criteria is presented for use by State and EPA Regional permit
writers. This Decision Tool includes EPA's ambient water quality criteria for
the protection of aquatic life and human health for benzene, ethylbenzene,
toluene, xylene, and naphthalene, the only constituents of gasoline for which
water quality criteria have been established.
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MODEL NPDES PERMIT FOR DISCHARGES RESULTING FROM THE
CLEANUP OF GASOLINE RELEASED FROM UNDERGROUND STORAGE TANKS
AUTHORIZATION TO DISCHARGE UNDER THE
NATIONAL POLLUTANT DISCHARGE ELIMINATION SYSTEM
In compliance with the provisions of the Federal Water Pollution Control Act,
as amended (33 U.S.C. Section 1251 et seq., hereinafter the "Clean Water Act"
or "Act"), and attendant regulations incorporated by the U.S. Environmental
Protection Agency under Title 40 of the Code of Federal Regulations,
(Name of Discharger) (hereinafter "Permittee")
is authorized to discharge from (description of facility), located at
(insert Address)
to the receiving waters named (identify) in accordance with
effluent limitations, monitoring requirements, and other conditions set forth
in Parts I, II, and III herein. The permit consists of this cover sheet, Part
I - 1 page, Part II - 13 pages, and Part III - 3 pages.
All references to Title 40 of the Code of Federal Regulations are to regula-
tions that are in effect on the effective date of this permit. Unless other-
vise specified herein, all terms are defined as provided in the applicable
regulations in Title 40 of the Code of Federal Regulations.
This permit shall become effective on (insert date). This permit and the
authorization to discharge shall expire at midnight (insert date) .
Date Director
(or Other Authorized Official)
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Page 1-1
Permit No.
PART I
EFFLUENT LIMITATIONS AND MONITORING REQUIREMENTS; Outfall 001 -
discharge resulting from gasoline underground storage tank corrective
actions.
During the period beginning on the effective date of the permit and
lasting through the term of this permit, the permittee is authorized to
discharge treated vater and vastevater that has been contaminated by
gasoline.
Such discharges shall be limited and monitored by the Permittee as
specified below:
Effluent Characteristic
Flow, MGD
Benzene
Total BETX*
Discharge Limitations
Hicrograms per Liter
Daily Avg. Daily Max.
Report Report
5 5
100 100
Monitoring Requirements
Measurement
Frequency Sample Type
1 per week 'Continuous
1 per week Grab
1 per veek Grab
The pR shall neither be less than 6.0 standard units nor greater than 9.0
standard units and shall be monitored once per veek by grab sample.
There shall be no discharge of floating solids or visible foam in other
than trace amounts.
Samples taken in compliance vith the monitoring requirements specified
above shall be taken at the following location(s): nearest accessible
point after final treatment but prior to actual discharge or nixing vith
the receiving vaters.
* BETX shall be measured as the sum of benzene, ethylbenzene, toluene, and
xylenes. EPA methods 602, 624, or 1624 shall be used for the measurement
of benzene, ethylbenzene, and toluene. EPA method 8240, or an equivalent
method, shall be used for the measurement of xylenes including ortho-,
meta-, and para-xylene. (Note: Depending on Regional/State policy, EPA
Method 8240 may be used as a substitute or equivalent for the CUA methods
602, 624, or 1624 required under the CWA in 40 CFR Part 136.)
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Optional Page 1-1
Permit No.
OPTIONAL EFFLUENT LIMITATIONS FOR DISCHARGES RESULTING
FROM THE CLEANUP OF GASOLINE RELEASED FROM UNDERGROUND STORAGE TANKS
PART I
A.
EFFLUENT LIMITATIONS AND MONITORING REQUIREMENTS! Outfall 001 -
discharge resulting from gasoline underground storage tank corrective
actions.
During the period beginning on the effective date of the permit and
lasting through the term of this permit, the permittee is authorized to
discharge treated water and vastevater that has been contaminated by
gasoline.
Such discharges shall be limited and monitored by the Permittee as
specified below:
Effluent Characteristic
Flow, MGD
Benzene
Total BETX*
Discharge Limitations
Micrograms per Liter
Daily Avg. Daily Max.
Report Report
50 50
750 750
Monitoring Requirements
Measurement
Frequency Sample Type
1 per week Continuous
1 per week Grab
1 per week Grab
The pH shall neither be less than 6.0 standard units nor greater than 9.0
standard units and shall be monitored once per week by grab sample.
There shall be no discharge of floating solids or visible foam in other
than trace amounts.
Samples taken in compliance with the monitoring requirements specified
above shall be taken at the following location(s): nearest accessible
point after final treatment but prior to actual discharge or mixing with
the receiving waters.
* BETX shall be measured as the sum of benzene, ethylbenzene, toluene, and
xylenes. EPA methods 602, 624, or 1624 shall be used for the measurement
of benzene, ethylbenzene, and toluene. EPA method 8240, or an equivalent
method, shall be used for the measurement of xylenes including ortho-,
meta-, and para-xylene. (Note: Depending on Regional/State policy, EPA
Method 8240 may be used as a substitute or equivalent for the CVA methods
602, 624, or 1624 required under the CVA in 40 CFR Part 136.)
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PART II
MODEL NPDES PERMIT POR DISCHARGES
RESULTING FROM THE CLEANUP OF GASOLINE
RELEASED FROM UNDERGROUND STORAGE TANKS
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Page II-l
Permit No.
PART II
STANDARD CONDITIONS
SECTION A. GENERAL CONDITIONS
1. Duty to Comply
The Permittee must comply with all conditions of this permit. Any permit
noncompliance constitutes a violation of the Clean Vater Act and is grounds
for enforcement action, for permit termination, permit revocation and permit
reissuance, or modification, or for denial of a permit renewal application.
2. Toxic Pollutants
The Permittee shall comply with effluent standards or prohibitions established
under Section 307(a) of the Clean Vater Act for toxic pollutants within the
time provided in the regulations that establish those standards or pro-
hibitions, even if the permit has not yet been modified to incorporate the
requirement.
3. Penalties for Violations of Permit Conditions
Any person vho violates a permit condition is subject to a civil penalty not
to exceed $10,000 per day for each violation. Any person who willfully or
negligently violates permit conditions is subject to a fine of not less than
$2,500 nor more than $25,000 per day for each violation, or by imprisonment
for not more than 1 year, or both.
4. Duty to Reapply
(a) If the Permittee wishes to continue an activity regulated by this permit
after the expiration date of this permit, the Permittee must apply for and
obtain a renewal permit. The Permittee shall submit a new application at
least 180 days before the expiration date of this permit, unless permission
for a later date has been granted by the Director.
(b) Where EPA is the Permit Issuing Authority for the renewal permit, the
terms and conditions of this permit continue in force under 5 U.S.C. Section
558(c) until the effective date of the new permit (or permit denial) only if
the Permittee has submitted a timely and complete application under 40 CFR
Section 122.21 for a renewal permit and the Permit Issuing Authority, through
no fault of the Permittee, does not issue a new permit (or deny the permit)
before the expiration date of this permit. The permit continued under
5 U.S.C. Section 558(c) remains fully effective and enforceable, including
subject to the actions set forth in 40 CFR §122.6(c).
5. Duty to Mitigate
The Permittee shall take all reasonable steps to minimize or prevent any
discharge in violation of this permit that has a reasonable likelihood of
adversely affecting human health or the environment.
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Page II-2
Permit No.
6. Permit Actions (Modification, Revocation and Reissuance, or Termination)
(a) This permit may be modified, revoked and reissued, or terminated for
causes (as described in 40 CFR Sections 122.62, 122.63, and 122.64),
including, but not limited to: violation of any terms or conditions of this
permit; obtaining this permit by misrepresentation or failure to disclose
fully all relevant facts; or a change in any condition that requires either a
temporary or permanent reduction or elimination of the permitted discharge.
The filing of a request by the Permittee for a permit modification, revocation
and reissuance, or termination, or a notification of planned changes or
anticipated noncompliance, does not stay any permit condition.
(b) Notwithstanding Paragraph II-A-6(a) above, if a toxic effluent standard
or prohibition (including any schedule of compliance specified in such
effluent standard or prohibition) is established under Section 307(a) of the
Clean Water Act for a toxic pollutant that is present in the discharge and
such standard or prohibition is more stringent than any limitation for such
pollutant in this permit, this permit may be modified or revoked and reissued
to conform to the toxic effluent standard or prohibition.
(c) Nothwithstanding Paragraph II-A-6(a) above, this permit may be modified,
or alternatively revoked and reissued, to comply with any applicable effluent
standard or limitation issued or approved under Sections 301(b)(2)(A), (C),
(D), (E), and (F), or 304(b)(2) of the Clean Water Act, if the effluent
standards or limitation so issued or approved contains different conditions or
is otherwise more stringent than any effluent limitation in this permit; or
controls any pollutant not limited in this permit.
7. Effect of Permit/Other Lavs
(a) Issuance of this permit does not convey any property rights of any sort,
or any exclusive privileges, nor does it authorize any injury to persons or
property, or invasion of other private rights, or any infringement of Federal,
State, or local laws or regulations.
(b) Nothing in this permit shall be construed to preclude the institution of
any legal action or relieve the Permittee from any responsibilities,
liabilities, or penalties established pursuant to any applicable State lav or
regulation under authority preserved by Section 510 of the Clean Water Act.
(c) Nothing in this permit shall be construed to preclude the institution of
any legal action or relieve the Permittee from any responsibilities,
liabilities, or penalties to which the Permittee is or may be subject to under
Section 311 of the Act.
(d) Except as provided in permit conditions on "Upsets," Paragraph II-B-4
below, and pH Excursions, Paragraph II-C-7(c) below, nothing in this permit
shall be construed to relieve the Permittee from civil or criminal penalties
for noncompliance with a permit condition.
(e) Pursuant to Section 509(b)(l)(F) of the Clean Water Act, a challenge to
the validity of permit conditions, including the effluent limitations in Part
I-A of this permit, shall not be a defense to an enforcement action under
Section 309 or 505 of the Clean Water Act. Each and every violation of a
permit condition is subject to an enforcement action.
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Page II-3
Permit No.
(f) 'Compliance with the terms of this permit does not constitute a defense to
any action brought under Section 504 of the Clean Water Act, or any other lav
governing protection of public health or welfare, for any imminent and
substantial endangerment to public health or welfare.
8. Onshore or Offshore Construction
This permit does not authorize or approve the construction of any onshore or
offshore physical structures or facilities or the undertaking of any work in
any waters of the United States.
9. Inspection and Entry
The Permittee shall allow the Director, or an authorized representative, upon
the presentation of credentials and other documents as may be required by law,
to:
a. Enter upon the Permittee's premises where a regulated facility or
activity is located or conducted, or where records must be kept under
the conditions of this permit;
b. Have access to and copy, at reasonable times, any records that must
be kept under the conditions of this permit;
c. Inspect at reasonable times any facilities, equipment (including
monitoring and control equipment), practices, or operations' regulated
or required under this permit; and
d. Sample or monitor at reasonable times, for the purposes of ensuring
permit compliance or as otherwise authorized by the Clean Water Act,
any substances or parameters at any location.
10. Severability
The provisions of this permit are severable, and if any provision of this
permit, or the application of any provision of this permit to any
circumstance, is held invalid, the application of such provision to other
circumstances, and the remainder of this permit, shall not be affected
thereby.
SECTION B. OPERATION AND MAINTENANCE OF POLLUTION CONTROLS
1. Proper Operation and Maintenance
The Permittee shall at all times properly operate and maintain all facilities
and systems of treatment and control (and related appurtenances) that are
installed or used by the Permittee to achieve compliance with the conditions
of this permit. Proper operation and maintenance also includes adequate
laboratory controls and appropriate quality assurance procedures. This
provision requires the operation of back-up or auxiliary facilities or similar
systems that are installed by a Permittee only when the operation is necessary
to achieve compliance with the conditions of the permit.
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Page II-4
Permit No.
2. Need to Halt or Reduce not a Defense
It shall not be a defense for a Permittee in an enforcement action that it
would have been necessary to halt or reduce the permitted activity in order to
maintain compliance with the conditions of this permit.
3. Bypass of Treatment Facilities
a. Definitions
(1) "Bypass" means the intentional diversion of waste streams from any
portion of a treatment facility, which is not a designed or
established operating mode for the facility.
(2) "Severe property damage" means substantial physical damage to
property, damage to the treatment facilities that renders them
inoperable, or substantial and permanent loss of natural resources
that can reasonably be expected to occur in the absence of a bypass.
Severe property damage does not mean economic loss caused by delays in
production.
b. Bypass Not Exceeding Limitations
The Permittee may allow any bypass to occur that does not cause
effluent limitations to be exceeded, but only if it also is for
essential maintenance to ensure efficient operation. These bypasses
are not subject to the provisions of Paragraphs c. and d. of this
section.
c. Notice
(1) Anticipated bypass. If the Permittee knows in advance of the need for
a bypass, it shall submit prior notice, if possible at least ten days
before the date of the bypass; including an evaluation of the
anticipated quality and effect of the bypass.
(2) Unanticipated bypass. The Permittee shall submit notice of an
unanticipated bypass as required in Paragraph II-D-6 (24-hour notice).
d. Prohibition of Bypass
(1) Bypass is prohibited and the Permit Issuing Authority may take
enforcement action against a Permittee for bypass, unless:
(a) Bypass was unavoidable to prevent loss of life, personal injury,
or severe and extensive property damage;
(b) There were no feasible alternatives to the bypass, such as mainte-
nance of sufficient reserve holding capacity, the use of auxiliary
treatment facilities, retention of untreated wastes, waste haul-
ing, or maintenance during normal periods of equipment downtime.
This condition is not satisfied if adequate back-up equipment
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Page II-5
Permit No.
should have been installed in the exercise of reasonable engi-
neering judgment to prevent a bypass that occurred during normal
periods of equipment downtime or preventive maintenance; and
(c) The Permittee submitted notices as required under Paragraph b. of
this section.
(2) The Permit Issuing Authority may, within its authority, approve an
anticipated bypass, after considering its adverse effects, if the
Permit Issuing Authority determines that it will meet the three
conditions listed above in Paragraph d.(l) of this section.
4. Upsets
"Upset" means an exceptional incident in which there is unintentional and
temporary noncompliance with technology-based permit effluent limitations
because of factors beyond the control of the Permittee. An upset does not
include noncompliance to the extent caused by operational error, improp-
erly designed treatment facilities, inadequate treatment facilities, lack
of preventive maintenance, or careless or improper operation. An upset
constitutes an affirmative defense to an action brought for noncompliance
with such technology-based permit limitations if the requirements of 40
CFR Section 122.Al(n)(3) are met. (Note that this provision does not
apply to water quality requirements).
5. A Schedule of Maintenance
Any maintenance of facilities, which might necessitate unavoidable
interruption of operation and degradation of effluent quality, shall be
scheduled during noncritical water quality periods and carried out in a
manner approved by the Permitting Authority.
6. Removed Substances
This permit does not authorize discharge of solids, sludge, filter back-
wash, or other pollutants removed in the course of treatment or control of
wastewaters to waters of the United States unless specifically limited in
Part I.
SECTION C. MONITORING AND RECORDS
1. Representative Sampling
Samples and measurements taken as required herein shall be representative of
the volume and nature of the monitored discharge. All samples shall be taken
at the monitoring points specified in this permit and, unless otherwise
specified, before the effluent joins or is diluted by any other wastestream,
body of water, or substance. Monitoring points shall not be changed without
notification to and the approval of the Permit Issuing Authority.
2. Sampling Points
All samples shall be taken at the monitoring points specified in this permit
and, unless otherwise specified, before the effluent joins or is diluted by
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Page II-6
Permit No.
any other vastestream, body of vater, or substance. Monitoring points shall
not be changed vithout notification to and the approval of the Permitting
Authority.
3. Flov Measurements
Appropriate flow measurement devices and methods consistent with accepted
scientific practices shall be selected and used to ensure the accuracy and
reliability of measurements of the volume of monitored discharges. The
devices shall be installed, calibrated, and maintained to ensure that the
accuracy of the measurements is consistent with the accepted capability of
that type of device. Devices selected shall be capable of measuring flows
with a maximum deviation of less than ± 10 percent from the true discharge
rates throughout the range of expected discharge volumes. Guidance in
selection, installation, calibration, and operation of acceptable flow
measurement devices can be obtained from the following references:
(1) "A Guide of Methods and Standards for the Measurement of Vater Flow,"
U.S. Department of Commerce, National Bureau of Standards, NBS Special
Publication 421, May 1975, 97 pp. (Available from the U.S. Government
Printing Office, Washington, DC 20402. Order by SD Catalog No.
C13.10:421).
(2) "Vater Measurement Manual," U.S. Department of Interior, Bureau of Re-
clamation, Second Edition, Revised Reprint, 1974, 327 pp. (Available
from the U.S. Government Printing Office, Washington, DC 20402.
Order by Catalog No. 127.19/2.-V29/2, Stock No. S/N 24003-0027).
(3) "Flow Measurement in Open Channels and Closed Conduits," U.S.
Department of Commerce, National Bureau of Standards, NBS Special
Publication 484, October 1977, 982 pp. (Available in paper copy or
microfiche from National Technical Information Service (NTIS),
Springfield, VA 22151. Order by NTIS No. PB-273 535/5ST).
(4) "NPDES Compliance Flow Measurement Manual," U.S. Environmental
Protection Agency, Office of Vater Enforcement, Publication MCD-77,
September 1981, 135 pp. (Available from the General Services
Administration (8BRC), Centralized Mailing Lists Services, Building
41, Denver Federal Center, Denver, CO 80225).
4. Monitoring Procedures
Monitoring must be conducted according to test procedures approved under 40
CFR Part 136, unless other test procedures have been specified in this
permit.
5. Calibration
The Permittee shall periodically calibrate and perform maintenance on all
monitoring and analytical equipment used to monitor the pollutants discharged
under this permit, at intervals that will ensure the accuracy of measurements.
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Page II-7
Permit No.
6. Testing Variability Not a Defense
If the Permittee believes or has reason to believe that monitoring or sampling
results reflect an analytical variability so as to render the results
inaccurate, he may monitor or sample more frequently than required by this
permit. The validity of the testing results, whether or not the Permittee has
monitored or sampled more frequently, shall not be a defense to an enforcement
action under Sections 309 or 505 of the Clean Water Act.
7. pH Effluent Limitations Under Continuous Monitoring
Notwithstanding Part I of this permit, where the Permittee continuously
measures the pH of water and wastewater discharges pursuant to a requirement
or option in this permit, excursions from the range provided in Part I are
permitted, provided:
(a) The pH limitation in Part I of this permit is based upon a
requirement imposed under 40 CFR Part 401, Subpart N.
(b) The total time during which the pH values are outside the required
range of pH values shall not exceed 446 minutes in any calendar
month.
(c) No individual excursions from the range of pH values shall exceed 60
minutes.
(d) For purposes of this section, an "excursion" is an unintentional and
temporary incident in which the pH value of the discharge exceeds the
range set forth in Part I of this permit. The number of individual
excursions exceeding 60 minutes and the total accumulated excursion
time in minutes occurring in any calendar month shall be reported in
accordance with Paragraph II-D-4 of this permit.
8. Penalties for Tampering
The Clean Water Act provides that any person who falsifies, tampers with, or
knowingly renders inaccurate, any monitoring device or method required to be
maintained under this permit shall, upon conviction, be punished by a fine of
not more than $10,000 per violation, or by imprisonment for not more than 2
years per violation, or by both.
9. Retention of Records
The Permittee shall retain records of all monitoring information, including
all calibration and maintenance records and all original strip chart
recordings for continuous monitoring instrumentation, copies of all reports
required by this permit, and records of all data used to complete the
application for this permit, for a period of at least three years from the
date of the sample, measurement, report or application. This period may be
extended by the Permitting Authority at any time.
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Page II-B
Permit No.
10. Monitoring Records
Records of monitoring information shall include:
a. The date, exact place, and time of sampling or measurements;
b. The individual(s) who performed the sampling or measurements;
c. The date(s) analyses were performed;
d. The individual(s) who performed the analyses;
e. The analytical techniques or methods used; and
f. The results of such analyses.
11. Additional Monitoring by the Permittee
If the Permittee monitors any pollutant more frequently than required by this
permit, using test procedures approved under 40 CFR Part 136 or as specified
in this permit, the results of this monitoring shall be included in the
calculation and reporting of the data submitted in the Discharge Monitoring
Report (DMR). Such increased frequency shall also be indicated.
12. Averaging of Measurements
Calculations for limitations that require averaging of measurements shall
utilize an arithmetic mean unless otherwise specified by the Permitting
Authority in the permit.
SECTION D. REPORTING REQUIRHENTS
1. Change in Discharge
The Permittee shall give notice to the Permitting Authority as soon as
possible of any planned physical alterations or additions to the permitted
facility. Notice is required only when:
a. The alteration or addition to a permitted facility may meet one of the
criteria for determining whether a facility is a new source; or
b. The alteration or addition could significantly change the nature or
increase the quantity of pollutants discharged. This notification
applies to pollutants that are subject neither to effluent limitations
in the permit, nor to notification requirements under Section D,
Paragraph 10(a).
2. Anticipated Noncompliance
The Permittee shall give advance notice to the Permitting Authority of any
planned change in the permitted facility or activity that may result in
noncompliance with permit requirements. Any maintenance of facilities, which
might necessitate unavoidable interruption of operation and degradation of
effluent quality, shall be scheduled during noncritical water quality periods
and carried out in a manner approved by the Permitting Authority.
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Permit No.
3. Transfer of Ownership -or Control
A permit may be automatically transferred to another party if:
a. The Permittee notifies the Permitting Authority of the proposed
transfer at least 30 days in advance of the proposed transfer date;
b. The notice includes a written agreement between the existing and new
Permittees containing a specific date for transfer of permit
responsibility, coverage, and liability between them; and
c. The Permitting Authority does not notify the existing Permittee of its
intent to modify or revoke and reissue the permit. If this notice is
not received, the transfer is effective on the date specified in the
agreement mentioned in Paragraph b, above.
4. Reporting of Monitoring Results
Monitoring results obtained during the previous calendar quarter shall be
summarized for each month (each quarter if monitoring frequency is quarterly)
and must be reported on a Discharge Monitoring Report Form (EPA No. 3320-1),
postmarked no later than the day of the month following the completed calendar
quarter. Duplicate signed copies of these, and all other reports required by
Section D of Part II, Reporting Requirements, shall be submitted to the
Permitting Authority at the following addresses:
U.S. EPA Regional Office; State Office;
(insert address) (insert address)
5. Compliance Schedules
Reports of compliance or noncompliance with, or any progress reports on,
interim and final requirements contained in any compliance schedule of this
permit shall be submitted no later than 14 days following each schedule date.
Any reports of noncompliance shall include the cause of noncompliance, any
remedial actions taken, and the probability of meeting the next scheduled
requirement.
6. Twenty-Four Hour Reporting
The Permittee shall orally report any noncompliance that may endanger health
or the environment within 24 hours from the time the Permittee becomes aware
of the circumstances. A written submission shall also be provided within five
days of the time the Permittee becomes aware of the circumstances. The
written submission shall contain a description of the noncompliance, its
cause, and the period of noncompliance, including exact dates and times. If
the noncompliance has not been corrected, the written submission shall also
include the anticipated time it is expected to continue, and steps taken or
planned to reduce, eliminate, and prevent reoccurrence of the noncompliance.
The Permitting Authority may verbally waive the written report, on a
case-by-case basis, when the oral report is made.
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Permit No.
The following violations shall be included in the 24-hour report vhen they
might endanger health or the environment:
a. An unanticipated bypass that exceeds any effluent limitation in the
permit.
b. Any upset that exceeds any effluent limitation in the permit.
7. Other Noncompliance
The Permittee shall report, in narrative form, all instances of noncompliance
not previously reported under Section D, Paragraphs 2, 4, 7, and 8, at the
time monitoring reports are submitted. The reports shall contain the
information listed in Paragraph 8.
8. Other Information
Where the Permittee becomes aware that it failed to submit any relevant facts
in a permit application, or submitted incorrect information in a permit
application or in any report to the Permitting Authority, it shall promptly
submit such facts or information.
9. Changes in Discharges of Toxic Substances
The Permittee shall notify the Permit Issuing Authority as soon as it knows or
has reason to believe:
a. That any activity has occurred or will occur that would result in the
discharge, on a routine or frequent basis, of any toxic substance(s)
(listed at 40 CFR Part 122, Appendix D, Tables II and III) that is
not limited in the permit, if that discharge will exceed the highest
of the following "notification levels":
(1) One hundred micrograms per liter (100 ug/1);
(2) Two hundred micrograms per liter (200 ug/1) for acrolein and
acrylonitrile; five hundred micrograms per liter (500 ug/1) for
2,4-dinitrophenol and for 2-methyl-4,6-dinitrophenol; and one
milligram per liter (1 mg/1) for antimony; or
(3) Five (5) times the maximum concentration value reported for that
pollutant(s) in the permit application.
b. That any activity has occurred or will occur that would result in any
discharge, on a nonroutine or infrequent basis, of a toxic pollutant
(listed at 40 CFR Part 122, Appendix D, Tables II and III) that is not
limited in the permit, if that discharge will exceed the highest of
the following "notification levels:"
(1) Five hundred micrograms per liter (500 ug/1);
(2) One milligram per liter (1 mg/1) for antimony; or
(3) Ten (10) times the maximum concentration value reported for that
pollutant(s) in the permit application.
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Permit No.
10. Duty to Provide Information
The Permittee shall furnish to the Permitting Authority, vithin a reasonable
time, any information that the Director may request to determine whether cause
exists for modifying, revoking and reissuing, or terminating this permit, or
to determine compliance with this permit. The Permittee also shall furnish to
the Permitting Authority, upon request, copies of records required to be kept
by this permit.
11. Signatory Requirements
All applications, reports, or information submitted to the Permit Issuing
Authority shall be signed and certified.
a. All permit applications shall be signed as follows:
(1) For a corporation: by a responsible corporate officer. For the
purpose of this Section, a responsible corporate officer means:
(1) a president, secretary, treasurer or vice president of the
corporation in charge of a principal business function, or any
other person who performs similar policy or decisionmaking
functions for the corporation; or (2) the manager of one or more
manufacturing, production, or operating facilities employing more
than 250 persons or having gross annual sales or expenditures
exceeding $25 million (in second-quarter 1980 dollars), if
authority to sign documents has been assigned or delegated to the
manager in accordance with corporate procedures.
(2) For a partnership or sole proprietorship: by a general partner
or the proprietor, respectively; or
(3) For a municipality, State, Federal, other political subdivision,
public agency/agents thereof: by either a principal executive
officer or ranking elected official.
b. All reports required by the permit and other information requested by
the Permitting Authority shall be signed by a person described above
or by a duly authorized representative of that person. A person is a
duly authorized representative only if:
(1) The authorization is made in writing by a person described above;
(2) The authorization specifies either an individual or a position
having responsibility for the overall operation of the regulated
facility or activity, such as the position of plant manager,
operator of a veil or a well field, superintendent, position of
equivalent responsibility, or an individual or position having
overall responsibility for environmental matters for the company
(A duly authorized representative thus may be either a named
individual or any individual occupying a named position.); and
(3) The written authorization is submitted to the Permit Issuing
Authority.
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Permit No.
c. Certification. Any person signing a document under Paragraphs (a) or
(b) of this section shall make the following certification:
"I certify under penalty of lav that this document and
all attachments were prepared under my direction or
supervision in accordance with a system designed to
assure that qualified personnel properly gather and
evaluate the information submitted. Based on my inquiry
of the person or persons who manage the system, or those
persons directly responsible for gathering the informa-
tion, the information submitted is, to the best of my
knowledge and belief, true, accurate, and complete. I am
aware that there are significant penalties for submitting
false information, including the possibility of fine and
imprisonment for knowing violations."
12. Availability of Reports
Except for data determined to be confidential under 40 CFR Part 2, all reports
prepared in accordance with the terms of this permit shall be available for
public inspection at the offices of the Permitting Authority. As required by
the Act, permit applications and permit and effluent data shall not be
considered confidential.
13. Penalties for Falsification of Reports
The Clean Water Act provides that any person who knowingly makes any false
statement, representative, or certification in any record or other document
submitted or required to be maintained under this permit, including monitoring
reports or reports of compliance or noncompliance, shall, upon conviction, be
punished by a fine of not more than $10,000 per violation, or by imprisonment
for not more than 2 years per violation, or by both.
SECTION E. DEFINITIONS
1. Permit Issuing Authority
The Regional Administrator or his designee, unless at some time in the future
the State receives the authority to administer the NPDES program and assumes
jurisdiction over the permit, at which time the Director of the State program
receiving authorization becomes the issuing authority.
2. Act
"Act" means the Clean Water Act (formerly referred to as the Federal Water
Pollution Control Act) Public Law 92-500, as amended by Public Law 95-217,
Public Law 95-576 and Public Law 100-4, 33 U.S.C. 1251 et seq.
3. Concentration Measurements
a. The "average monthly concentration" is the sum of the concentrations
of all daily discharges sampled and/or measured during a calendar
month on which daily discharges are sampled and measured, divided by
the number of daily discharges sampled and/or measured during such
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Page 11-13
Permit No.
month (arithmetic ..mean of the daily concentration values). The daily
concentration value is equal to the concentration of a composite
sample or, in the case of grab samples, is the arithmetic mean
(weighted by flow value) of all the samples collected during the
calendar day.
b. The "maximum daily concentration" is the concentration of a pollutant
discharge during a calendar day. It is identified as "Daily Maximum"
in Part I of the permit and the highest such value recorded during the
reporting period is reported under the "Maximum" column under
"Quality" on the DMR.
4. Other Measurements
a. The effluent flow, expressed as MGD, is the 24-hour average flow
averaged monthly. It is the arithmetic mean of the total daily flows
recorded during the calendar month. Where monitoring requirements for
flow are specified in Part I of the permit, the flow rate values are
reported in the "Average" column under "Quantity" on the DMR.
b. An "instantaneous flow measurement" is a measure of flow taken at the
time of sampling, when both the sample and flow will be representative
of the total discharge.
c. Where monitoring requirements for pH or dissolved oxygen are specified
in Part I of the permit, the values are generally reported in the
"Quality or Concentration" column on the DMR.
5. Types of Samples
a. Grab Sample: A "grab sample" is a single influent or effluent portion
that is not a composite sample. The sample(s) shall be collected at
the period(s) most representative of the total discharge.
6. Calendar Day
A calendar day is defined as the period from midnight of one day until mid-
night of the next day. However, for purposes of this permit, any consecutive
24-hour period that reasonably represents the calendar day may be used for
sampling.
7. Hazardous Substance
A hazardous substance means any substance designated under 40 CFR Part 116
pursuant to Section 311 of the Clean Water Act.
8. Toxic Pollutant
A toxic or "priority" pollutant is one of 126 substances listed as toxic under
Section 307(a)(l) of the Clean Water Act.
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Page III-l
Permit No.
PART III
A. SPECIAL CONDITIONS
1. Best Management Practices Requirements
A Best Management Practices (BMP) plan shall be developed vithin one month
after the effective date of the permit and shall be implemented as soon as
practicable but no later than two months from the effective date of the
permit. The plan must address the following BMPs:
a. Prevention of run-on/interception of runoff: Technologies that are
designed to prevent or reduce run-on include dikes, diversion
channels, flood walls, terraces, grading, and revegetation.
Temporary diversion dikes, diversion channels, and terraces are con-
structed upslope of a site to direct run-on from offsite to a collec-
tion system or away from the site. Terraces are used in combination
with dikes or ditches to channel water stopped by the terraces away
from the site.
b. Prevention of infiltration: The primary method for preventing infil-
tration of onsite surface water is capping. Grading also helps to
minimize infiltration by maximizing the amount of water that will run
off without causing significant erosion. Revegetation can either
promote or minimize infiltration.
c. Collection and transfer of water: Several technologies can be used
to collect diverted water for discharge or transfer to a storage or
treatment system. Chutes (or flumes) and downpipes are designed to
transfer water away from diversion structures such as dikes or
terraces to stabilized channels or outlets. Vaterways can be used to
intercept or divert water as well as to collect and transfer water
diverted elsewhere.
d. Storage and discharge of water: Technologies for this purpose
include seepage basins and ditches, sedimentation basins, and storage
ponds. Their function depends on the level of contamination of the
water they receive. Seepage basins and ditches are used to discharge
uncontaminated or treated water down and away from the site. Sedi-
mentation basins are used to control suspended solid particles in
surface-water flow.
2. Reopener Clause
This permit shall be modified, or alternatively revoked and reissued, to
comply with any applicable effluent standard or limitation issued or approved
under Sections 301(b)(2)(C) and (D), 304(b)(2), and 307(a)(2) of the Clean
Vater Act, if the effluent standard or limitation so issued or approved:
a. Contains different conditions or is otherwise more stringent than any
condition in the permit; or
b. Controls any pollutant not limited in the permit.
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Permit No.
3. Chronic Toxicity Testing Requirements for Characterizing Effluent Toxicity
The Permittee shall perform toxicity testing, as described below, on the
discharge from Outfall 001.
a. The Permittee shall initiate the following series of tests as soon as
practicable, but within 30 days of the effective date of this permit
to evaluate toxicity of the discharge. Such testing will determine
if an appropriately dilute effluent sample affects the survival,
growth, or reproduction of the test species. All tests will be
conducted on 24-hour composite samples. A minimum of four replicates
will be used in each of the following tests. The Student's t test
shall be used to determine whether differences in control and
effluent data are significant.
(1) The Permittee shall conduct a seven-day Ceriodaphnia survival and
reproduction toxicity test on the final effluent diluted by
appropriate control water. Toxicity will be demonstrated if
there is a statistically significant difference at the 95-percent
confidence level in survival or reproduction between Ceriodaphnia
exposed to an appropriate control water and the final effluent.
All test solutions shall be renewed using an approved renewal
schedule. If, in any control, more than 20 percent of the test
organisms die, that test shall be repeated.
(2) The Permittee shall conduct a seven-day fathead minnow survival
and growth toxicity test on the final effluent diluted by
appropriate control water. Toxicity will be demonstrated if
there is a statistically significant difference at the 95-percent
confidence level in survival or growth between fathead minnows
exposed to an appropriate control water and the final effluent.
All test solutions shall be renewed using an approved renewal
schedule. If, in any control, more than 20 percent of the test
organisms die, that test shall be repeated.
b. The toxicity tests specified in Paragraph (a) above, shall be con-
ducted once per month for a period of one year following initiation
of the tests and once every six months thereafter for the duration of
the permit. Results shall be reported according to EPA/600/4-85/014,
Section 10 Report Preparation, and shall be submitted to EPA with the
monthly Discharge Monitoring Report. If any one test indicates the
effluent is toxic, another confirmatory chronic toxicity test using
the same species and the same methodology shall be conducted within
one week.
c. All test species, procedures, and quality assurance criteria used
shall be in accordance with Short Term Methods for Estimating the
Chronic Toxicity of Effluents and Receiving Waters to Freshwater
Organisms, Section 13; Ceriodaphnia Survival and Reproduction Test
Method 1002.0; Section 11; Fathead Minnow (Pimephales promelas);
Larval Survival and Growth Test Method 1000.0, EPA 600/4-85/04. The
selection of an appropriate control water for all toxicity tests
shall be submitted to EPA for review and approval prior to use.
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Page III-3
Permit No.
4. Modification of Honito.ring Requirements
a. After three months of weekly flov and chemical-specific monitoring,
the Permittee may submit a written request for reduced frequency of
monitoring requirements. The Permitting Authority may grant or
refuse the request based on site-specific conditions, as appropriate.
b. After three months of monthly toxicity testing as required in
Paragraph III-A-3, the Permittee may submit a written request for
cessation or reduction of biomonitoring requirements. The Permitting
Authority may grant or refuse the request based on site-specific
conditions, as appropriate.
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PART III
FACT SHEET FOR MODEL NPDES PERMIT FOR
DISCHARGES RESULTING FROM THE CLEANUP OF GASOLINE
RELEASED FROM UNDERGROUND STORAGE TANKS
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TABLE OF CONTENTS
Page
1.0 FACT SHEET FOR MODEL NPDES PERMIT FOR DISCHARGES RESULTING FROM
THE CLEANUP OF GASOLINE RELEASED FROM UNDERGROUND STORAGE TANKS 1-1
2.0 SCOPE OF THE PROBLEM 2-1
3.0 DISCHARGE CHARACTERIZATION 3-1
3.1 VOLUME OF DISCHARGE 3-1
3.2 CONSTITUENTS OF GASOLINE 3-1
3.3 POTENTIAL SOURCES OF DISCHARGE 3-4
4.0 TREATMENT TECHNOLOGIES 4-1
4.1 FREE PRODUCT RECOVERY 4-1
4.2 TREATMENT OF CONTAMINATED WATER AND WASTEWATERS ' 4-1
4.2.1 Air Stripping 4-2
4.2.2 Carbon Absorption 4-2
5.0 TECHNOLOGY-BASED EFFLUENT LIMITATIONS 5-1
5.1 SELECTION OF POLLUTANTS TO BE REGULATED 5-1
5.1.1 Solubility of Gasoline Constituents 5-1
5.1.2 Henry's Law Constants of Gasoline Constituents 5-4
5.1.3 Indicator Pollutants Recommended for Limitation 5-4
5.2 CALCULATION OF TECHNOLOGY-BASED EFFLUENT LIMITATIONS 5-8
5.2.1 Optional Effluent Limitations 5-9
5.2.2 Additional Effluent Limitations 5-10
5.3 TREATMENT COSTS 5-10
5.3.1 Costs of Selected Treatment Technologies 5-10
5.3.2 Air Emissions Control 5-12
5.3.3 Costs of Alternative Treatment Technologies 5-12
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TABLE OF CONTENTS
(Continued)
Page
6.0 BEST MANAGEMENT PRACTICES 6-1
7.0 MONITORING 7-1
7.1 FLOW MONITORING 7-1
7.2 CHEMICAL-SPECIFIC MONITORING 7-1
7.3 BIOMONITORING 7-2
8.0 REFERENCES 8-1
ii
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LIST OF TABLES
TABLE Page
3-1 CONSTITUENTS OF GASOLINE 3-2
5-1 SOLUBILITY OF CONSTITUENTS OF GASOLINE 5-2
5-2 HENRY'S LAV CONSTANTS FOR CONSTITUENTS OF GASOLINE 5-5
5-3 PURCHASE AND RENTAL COSTS FOR PRE-ENGINEERED PACKED COLUMN
AIR STRIPPER UNITS 5-11
5-4 RELATIVE COST FACTORS FOR TREATMENT OF GROUND WATER 5-14
7-1 RECOMMENDATIONS FOR WHOLE-EFFLUENT TOXICITY SCREENING 7-4
iii
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1.0 FACT SHEET FOR MODEL NPDES PERMIT FOR
DISCHARGES RESULTING FROM THE CLEANUP OF GASOLINE
RELEASED FROM UNDERGROUND STORAGE TANKS
Pursuant to the Clean Water Act (CWA), the U.S. Environmental Protection
Agency (EPA), or an EPA-approved State, is authorized to issue a National
Pollutant Discharge Elimination System (NPDES) permits for the discharge of
"pollutants" from any "point source" into "waters of the United States." CWA
301(b) requires all point sources that discharge directly to the waters of the
U.S. to meet technology-based effluent limitations and State water quality
standards for the discharge of pollutants. EPA has determined technology-based
effluent limitations through the development of National effluent limitations
guidelines for many specific categories of industries. However, national
effluent guidelines have not been promulgated for wastewater discharges
resulting from gasoline underground storage tank (UST) cleanups. Conse-
quently, this technology-based permit has been developed on a best profes-
sional judgment (BPJ) basis in accordance with 40 CFR 125.3. BPJ is used to
develop technology-based effluent limits in those cases where an effluent
guideline has not been promulgated for the industry and water quality
standards do not dictate limits more stringent than technology-based limits.
Water quality-based limitations should be used in a permit when
technology-based effluent limits are not stringent enough to protect the
"designated use" of the receiving waters (as determined by the State). Water
quality-based permits involve a site-specific evaluation of the discharge, the
State's water quality standards, the designated use of the receiving water,
and published EPA water quality criteria. Therefore, the Model Permit and
this Fact Sheet only address technology-based effluent limitations. Guidance
for addressing water quality considerations is included in Part IV - Decision
Tool for Developing Water Quality-Based Effluent Limitations.
1-1
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.2.0 SCOPE OF THE PROBLEM
It is estimated that 1.7 million underground storage tanks exist in the
United States. Based on data collected by EPA's Office of Underground Storage
Tanks (OUST) (Ref. No. 1)*, 15 percent of these tanks are currently leaking.
Gasoline leaks, have been cited in more than 70 percent of the reported release
incidents (Ref. No. 14). The OUST estimates that over the next 5 years,
approximately 200,000 cleanups will be conducted to mitigate releases of
petroleum-related products into the environment. Assuming that 70 percent of
all underground tank releases involve gasoline, then as many as 140,000
gasoline-related UST cleanups could occur over the next 5 years.
Any discharges to surface waters resulting from gasoline UST cleanups
fall under the auspices of the NPDES program. These discharges could include
treated ground water, storm water, and tank cleaning wastewaters. The
treatment technologies commonly employed for gasoline UST cleanups are
discussed in greater detailed in Section 4.0.
^Reference numbers correspond to the number assigned to each reference listed
in Section 8.0 of this Fact Sheet.
2-1
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3.0 DISCHARGE CHARACTERIZATION
The volume and nature of discharges resulting from gasoline UST
cleanups is expected to be highly variable. Based on available data, the
following sections briefly describe the volume and nature of the discharges
that would be .expected from gasoline UST cleanups.
3.1 VOLUME OF DISCHARGE
The volume of discharges generated from gasoline UST cleanups varies.
Such variation is due to site-specific factors such as the size of the
release, depth to ground water, etc. However, OUST estimates the typical flow
rate of treated water and wastewater discharges resulting from gasoline
cleanups falls in the range of three to 20 gallons per minute, or about 4,000
to 30,000 gallons per day (Ref. No. 2).
3.2 CONSTITUENTS OF GASOLINE
Available data that enumerate the constituents of gasoline was -reviewed,
based on the assumption that the same compounds identified in gasoline would
likely be found in treated water and wastewater resulting from gasoline clean-
ups. Those constituents are shown in Table 3-1. The chemical properties of
these constituents, such as solubility (in water) and volatility, have been
used to characterize the treatability of discharges resulting from gasoline
UST cleanups (see Section 5.0). It should be noted that lead is used as an
anti-knocking compound in gasoline. However, lead is present in gasoline as a
component of the organic compound tetraethyllead.
The characterization of gasoline shown in Table 3-1 is based on an
analysis of constituents commonly found in gasoline. However, little to no
data are available regarding the concentration of pollutants in treated water
and wastewater discharges from UST cleanups of gasoline. Similarly,
additional site-specific constituents, such as gasoline additives, may be
present. Some of these are proprietary additives for which little or no data
exist (Ref. No. 6).
3-1
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TABLE- 3-1. CONSTITUENTS OP GASOLINE
Gasoline Constituent Reference
Isobutane 3,4,5
n-Butane 3,4,5
Isopentane 3,4,5
n-Pentane 3,4,5
n-Octane 3
Benzene 3,4,5
Toluene 3,4,5
o-Xylene 5
m-Xylene 5
p-Xylene 5
n-Hexane 3,4,5
2-Methylpentane 3,4,5
3-Methylpentane 4,5
2,2-Dimethylhexane 5
2,4-Dimethylhexane 3
Ethylbenzene 3,4,5
2,2,4-Trimethylhexane 3
2,2,5,5-Tetramethylhexane 3
1-Hexene 3
1,3,5-Tritnethylbenzene 3
2,2-Dimethylpropane 4
2,2-Dimethylbutane 4
1,2,4-Trimethylbenzene 4
2,3-Dimethylbutane 5
2-Methylhexane 5
3-Methylhexane 5
2,3-Dimethylpentane 5
2,4-Dimethylpentane 5
2,2,4-Trimethylpentane 5
2,3,4-Trimethylpentane 5
2,3,3-Trimethylpentane 5
2,2,3-Trimethylpentane 5
2-Methyloctane 5
3-Methyloctane 5
4-Methyloctane 5
Cyclopentane 5
Methylcyclopentane 5
Methylcyclohexane 5
l,cis,3-Dimethylcyclopentane 5
Cyclohexane 5
n-Heptane 5
3-2
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TABLE 3-1. - CONSTITUENTS OF GASOLINE (Continued)
Gasoline Constituent Reference
l,cis,3-Dimethyl-cyclopentane 5
1,trans,3-Dimethyl-cyclopentane 5
Propylene 5
trans Butene-2 5
cis Butene-2 5
1-Pentene 5
trans Pentene-2 5
cis Pentene-2 5
2-Methylpentene-l 5
2-Methylpentene-2 5
1-Methyl, 3-Ethylbenzene 5
1-Methyl, 4-Ethylbenzene 5
1,2,4-Trimethylbenzene 5
Tetraethyllead 6
Naphthalene 5
3-3
-------
3.3 POTENTIAL SOURCES OF DISCHARGE
Discharges from gasoline UST cleanups can originate from one or more of
several sources. Examples of these sources include:
• Contaminated ground water that has been extracted and treated
• Contaminated storm water that has been collected and treated
• Wastewaters that are generated from tank cleaning operations
• Contaminated water that results from product recovery operations.
As discussed in Section 1.1, any direct discharge to waters of the U.S. would
be subject to regulation under a NPDES permit.
3-4
-------
4.0 TREATMENT TECHNOLOGIES
The cleanup or "corrective action" for releases from gasoline USTs
usually involves two phases. The first phase includes actions designed to
immediately contain and control a release. The second phase involves
assessing and .developing long-term measures designed to rectify and mitigate
contamination to a level that will protect human health and the environment.
4.1. FREE PRODUCT RECOVERY
Where site conditions permit, an UST cleanup typically begins with
recovery of gasoline (known as free product) floating on the water table.
Prompt removal of free product can minimize the extent of soil and ground
water that may potentially be contaminated by an UST release.
Free product is often removed by digging a trench to intercept the flow
of floating gasoline or by pumping ground water to create a cone of depression
in the water table. In either case, the free product flows toward the
collection point where it is removed by pumping. The ongoing process of free
product removal often requires the pumping or collection of substantial
amounts of ground water which may contain dissolved gasoline constituents.
This water may require treatment prior to discharge. This Fact Sheet
describes two technologies commonly used to treat such water. These
technologies are air stripping and carbon adsorption.
4.2 TREATMENT OF CONTAMINATED WATER AND WASTEWATERS
As product recovery continues, a variety of aqueous wastestreams and
contaminated waters may require additional treatment (see section 3.3). There
are many treatment technologies and methods available that could remove
gasoline constituents from these aqueous wastestreams and contaminated waters
including air stripping, carbon adsorption, biorestoration, reverse osmosis,
steam stripping, ozonation, etc. Use of any one of these treatment
technologies will depend upon the site-specific factors involved in an UST
corrective action. For example, due to equipment and utility requirements,the
use of steam stripping is not practicable for emergency field use unless the
contaminated ground water can be transported form the site to a steam
4-1
-------
stripping facility (Ref. No. 7). However, air stripping and carbon adsorption
are the most cost-effective and widely used treatment technologies available.
In fact, these two technologies are used in over 95 percent of ground-water
cleanups and are applicable to most cases where gasoline has contaminated the
groundwater (Ref. No. 6). Therefore, both air stripping and carbon adsorption
are described below.
4.2.1 Air Stripping
Due to the high volatility of many of the soluble constituents of
gasoline that remain in contaminated water and wastewater, air stripping is an
efficient and cost effective wastewater treatment technology. Air stripping
is a proven, effective means to remove volatile organic compounds (VOCs) from
ground water. Less volatile compounds (e.g., compounds with low Henry's Law
Constants) are not as easily removed via air stripping. There are several
methods of air stripping including diffused aeration, tray aerators, spray
basins, and packed towers. Regardless of the configuration used, all air
stripping units provide contact between air and water to allow the volatile
substances to diffuse from the liquid to the gaseous phase (Ref. No. 6).
Air stripping transfers the pollutants removed from the contaminated
water into the air. In some cases, volatilized pollutants may require
additional treatment (e.g., vapor phase carbon adsorption) to control
pollutant discharges to air.
4.2.2 Carbon Adsorption
Activated carbon is widely used in the treatment of wastewater contami-
nated with gasoline (Ref. No. 6). This treatment may be used either separately
or in combination with air stripping to address air quality concerns that may
arise from volatilizing the constituents of gasoline. The process of
absorption onto activated carbon requires the wastewater to come into contact
with the carbon, which selectively adsorbs organic constituents by a surface
attraction phenomenon (due to chemical or physical properties). The organic
molecules are attracted to the internal pores of the carbon granules.
Adsorption depends on the strength of the molecular attraction between
4-2
-------
adsorbent and adsorbate, molecular weight, type and characteristic of
adsorbent, electrokinetic charge, pH, and adsorbent surface area.
Most waste treatment applications use granular activated carbon (GAC)
adsorption units. These units are generally used in a downflow fixed bed
series mode where the waste stream flows through a series of packed bed
reactors. Eventually the carbon surfaces become saturated with organic
molecules, and reach the "breakthrough" point. The carbon must be replaced
and disposed of or regenerated for treatment to continue.
Use of GAC may be limited by site-specific conditions and cost
considerations. For example, treatment of ground water with naturally high
iron and manganese levels can clog the carbon filters. In addition,
requirements for disposing of the spent carbon may add significantly to
treatment costs (see section 5.3.3).
4-3
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5.0 TECHNOLOGY-BASED EFFLUENT LIMITATIONS
After a gasoline UST release has occurred, free product floats on the
surface or ground water near the site where it is skimmed or recovered using a
product recovery system. While many gasoline constituents remain as part of a
free floating gasoline layer (as opposed to dissolving into the water), the
more soluble fractions of the gasoline can dissolve into the surface or ground
water. Dissolved gasoline constituents typically remain in oil/water
separator effluent at a concentration of 15 ppm (Ref. No. 6).
The technology-based effluent limitations developed in the Model Permit
were based on the use of an air stripping unit. Air stripping units have been
demonstrated to be effective in removing the same or similar pollutants that
are found in gasoline. In addition, air stripping units are widely used and
readily available, and are generally less expensive than other available
treatment technologies. It is important to note that EPA does not intend to
specify the actual treatment that must be used at gasoline UST cleanup sites.
Other treatment technologies, such as carbon adsorption and biorestoration,
have also been used to treat contaminated water and wastewater resulting from
gasoline UST cleanups. Air stripping units are only used as the technology-
basis for justifying BPJ effluent limitations that are achievable with an
existing treatment technology.
5.1 SELECTION OF POLLUTANTS TO BE REGULATED
As discussed in Section 3.0, the chemical properties of gasoline
constituents determine the treatability of these constituents. Constituent
treatability forms the primary basis for selecting pollutants for which
effluent limitations should be developed.
5.1.1 Solubility of Gasoline Constituents
Gasoline constituent solubilities in water are shown in Table 5-1.
Generally, the higher the solubility of a constituent in water, the more
difficult it is to remove the constituent from water using an air stripper.
5-1
-------
TABLE 5-1. -SOLUBILITY OP CONSTITUENTS OF GASOLINE
Gasoline Constituent
Solubility in Water
(mg/1)
Isobutane
n-Butane
Isopentane
n-Pentane
n-Octane
Benzene
Toluene
o-Xylene
m-Xylene
p-Xylene
n-Hexane
2-Methylpentane
3-Methylpentane
2,2-Dimethylhexane
2,4-Dimethylhexane
Ethylbenzene
2,2,4-Trimethylhexane
2,2,5,5-Tetramethylhexane
1-Hexene
1,3,5-Trimethylbenzene
2,2-Dimethylpropane
2,2-Dimethylbutane
1,2,4-Trimethylbenzene
2,3-Dimethylbutane
2-Methylhexane
3-Methylhexane
2,3-Dimethylpentane
2,4-Dimethylpentane
2,2,4-Trimethylpentane
2,3,4-Trimethylpentane
2,3,3-Trimethylpentane
2,2,3-Triraethylpentane
2-Methyloctane
3-Methyloctane
4-Methyloctane
Cyclopentane
Methylcyclopentane
Me thylcyclohexane
Cyclohexane
n-Heptane
48.9
61.4
47.8
38.5
6.57x10
1,780.0
515.0
175.0
162.0
198.0
9.5
13.8
12.8
-i
24
28
152.0
0.87
0.33
59.
69.
33.
18.
.5
,1
.2
.4
57.0
22
2
2
5
4
1
1
2
2
1.42
1.42
0.01
160.0
61.1
14.0
55.6
2.96
5
54
64
25
06
14
36
59
59
5-2
-------
TABLE 5-1. SOLUBILITY OF CONSTITUENTS OF GASOLINE (Continued)
Gasoline Constituent Solubility in Water
(mg/1)
l,cis,3-Dimethyl- 7.07
cyclopentane
1,trans,3-Dimethyl- 7.07
cyclopentane
Propylene 2006.0
trans Butene-2 430.0
cis Butene-2 430.0
1-Pentene 148.0
trans Pentene-2 203.0
cis Pentene-2 203.0
2-Methylpentene-l 78.0
2-Methylpentene-2 84.2
1-Methyl, 3-Ethylbenzene 40.0
1-Methyl, 4-Ethylbenzene 40.0
1,2,4-Trimethylbenzene 57.0
Tetraethyllead 0.80
Naphthalene 3,400.0
Source: Reference No. 8
5-3
-------
The three compounds of gasoline with the highest solubilities are naphthalene
(3,400 mg/1), propylene (2,006 mg/1) and benzene (1,780 mg/1). Propylene,
however, accounts for only 0.03 percent of gasoline (Ref. No. 5) and would not
be likely to dissolve into ground water in significant amounts. Naphthalene
is also a minor constituent of gasoline. Therefore, effluent limitations for
naphthalene and propylene were not included in this Model Permit. Benzene was
selected as the main pollutant of concern since it is a more significant
constituent of gasoline than naphthalene or propylene.
5.1.2 Henry's Law Constants of Gasoline Constituents
The Henry's Law Constant for each of the constituents of gasoline is
shown in Table 5-2 (Ref. No. 8). As discussed in Section 4.2, the Henry's Law
Constant describes the ease with which specific compounds can be removed by
air stripping. Compounds with lower Henry's Law Constants are more difficult
to remove by air stripping than compounds with higher Henry's Law Constants.
Where multiple volatile organic compounds are present, the compound with the
lowest Henry's Law Constant will generally be the limiting compound {Ref. No.
6). As shown in Table 5-2, benzene, ethylbenzene, toluene, the xylenes,
1,3,5-trimethylbenzene, and naphthalene have the lowest Henry's Law Constants.
While these compounds are the least strippable constituents of gasoline, all
of the gasoline constituents are within the range where air stripping is
considered to be effective (Ref. No. 6).
5.1.3 Indicator Pollutants Recommended for Limitation
Based on the chemical properties of gasoline constituents (i.e.,
solubility and Henry's Law Constants), there are several primary pollutants of
concern for discharges from UST cleanups:
• Benzene
• Propylene
• Ethylbenzene
• Xylene
5-4
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TABLE 5-2. HENRY'S LAV CONSTANTS FOR CONSTITUENTS OF GASOLINE
Gasoline Constituent
Henry's Law Constant (20°C)
(atm-m /mole)
Isobutane
n-Butane
Isopentane
n-Pentane
n-Octane
Benzene
Toluene
o-Xylene
m-Xylene
p-Xylene
n-Hexane
2-Methylpentane
3-Methylpentane
2 , 2-Dimethylhexane
2 , 4-Dimethylhexane
Ethylbenzene
2,2, 4-Trimethylhexane
2,2,5, 5-Te t rame thylhexane
1-Hexene
1 , 3 , 5-Tr ime thylbenzene
2 , 2-Dimethylpropane
2,2-Dimethylbutane
1,2,4-Trimethylbenzene
2 , 3-Dimethylbutane
2-Methylhexane
3-Me thylhexane
2 , 3-Dimethylpentane
2 , 4-Dimethylpentane
2,2, 4-Trimethylpentane
2,3, 4-Trimethylpentane
2,3, 3-Trimethylpentane
2,2, 3-Trimethylpentane
2-Methyloctane
3-Methyloctane
4-Methyloctane
Cyclopentane
Methylcyclopentane
Hethylcyclohexane
Cyclohexane
n-Heptane
0.9 to 1.0(1)
0.859
1.31
1.26
3.20
5.47x10
6. 65x10" 3
5. 20x10" 3
5.27xlO"3
5. 27x10" 3
1.86
1.53
1.07
2.28
3.55
8.74x10"
3.03
5.94
0.346
5. 70x10" 3
1.25
1.27
3.02xlO"2
0.993
1.73
1.42
1.81
1.61
2.34
1.24
1.28
1.52
2.56
2.48
2.64
0.144
0.250
0.374
0.194
2.04
5-5
-------
TABLE 5-2. HENRY'5 LAW CONSTANTS FOR CONSTITUENTS OF GASOLINE
(Continued)
Gasoline Constituent
Henry's Law Constant (20°C)
(atm-m /mole)
l,cis,3-Dimethyl-
cyclopentane
1,trans,3-Dimethyl-
cyclopentane
Propylene
trans Butene-2
cis Butene-2
1-Pentene
trans Pentene-2
cis Pentene-2
2-Methylpentene-l
2-Methylpentene-2
1-Hethyl, 3-Ethylbenzene
1-Methyl, 4-Ethylbenzene
Tetraethyllead
Naphthalene
0.468
0.47 to 0.50(2)
0.230
0.193
0.172
0.294
0.229
0.224
0.271
0.211
2.63x10
0.027 to .030(3)
3 x 10"2(4)
5.47 x 10
-2
(1)A1though no Henry's Law Constant was found for this compound, the number
shown was estimated based on the values for n-Butane and Isopentane.
(2)Although no Henry's Law Constant was found for this compound, the number
shown was estimated based on the value for l,cis,3-Dimethyl-cyclopentane.
(3)Although no Henry's Law Constant was found for this compound, the number
shown was estimated based on the value for 1-Methyl,3-Ethylbenzene.
(4)Reference No. 6
Source: Reference No. 8
5-6
-------
• Toluene
• 1,3,5 - Trimethylbenzene
• Naphthalene
The Model Permit includes effluent limitations for the aggregate parameter of
benzene, ethylbenzene, toluene, and the xylenes (BETX). In addition, a
limitation for benzene has been developed for use as an indicator parameter
for the removal of propylene, 1,3,5-trimethylbenzene, and naphthalene. As an
indicator, it is assumed that if benzene is removed, then the other compounds
with similar treatability characteristics will also be removed. The primary
advantage of using an indicator parameter is the reduction of monitoring
required to ensure compliance. In addition, an indicator can be used for
constituents for which no EPA approved analytical methods are available for
monitoring.
A traditional approach to limiting effluent contaminated with gasoline or
other fuel oils has been to limit BETX. This approach stems from petroleum
industry practices for determining the quality of fuels by measuring BETX.
Monitoring and limitation of BETX in discharges from gasoline UST corrective
actions is prudent for several reasons. First, the composition of gasoline is
highly variable and for some gasoline products any one of the four BETX
constituents can be the predominant constituent. Second, EPA has promulgated
or proposed water quality criteria for benzene, ethylbenzene, toluene, and the
xylenes. Except for naphthalene, criteria have not been proposed for the
other constituents of gasoline. Finally, as shown in Table 5-2, benzene,
ethylbenzene, toluene, and the xylenes are gasoline constituents with low
Henry's Law Constants. Therefore, limitation of the aggregate parameter,
BETX, is provided in this Model Permit. On a site-specific basis, however, it
may be more appropriate to individually limit ethylbenzene, toluene, and
xylenes in addition to benzene.
In addition to BETX, the Henry's Law Constants for 1,3,5-
trimethylbenzene and naphthalene are relatively low, as compared to other
constituents contained in gasoline. The Merck Index (Ref. No. 19) states that
1,3,5-trimethylbenzene is "practically insoluble in water..." but may be
5-7
-------
soluble in benzene. Furthermore, naphthalene is insoluble in water, but
soluble in both benzene and toluene. Therefore, benzene is considered an
appropriate indicator parameter for 1,3,5-trimethylbenzene and naphthalene.
That is, if benzene is sufficiently treated or removed, then 1,3,5-
trimethylbenzene and naphthalene should also be removed. In addition,
naphthalene is. considered to be a minor constituent in gasoline, accounting
for less than 1 percent of the total gasoline product (Refs. No. 3 and 5).
The removal of benzene is also an indicator of the removal of propylene.
As discussed in Section 5.1.1, propylene is slightly more soluble in water
than benzene. However, propylene has a much higher Henry's Law Constant.
Consequently, propylene is more amenable to treatment, by air stripping, than
benzene. Therefore, removal of benzene is assumed to be indicative of the
removal of propylene. As such, benzene is limited in this Model Permit.
5.2 CALCULATION OF TECHNOLOGY-BASED EFFLUENT LIMITATIONS
A recent EPA publication (Ref. No. 6) on UST cleanup technologies
estimates that 15 ppm (or 15 mg/1) of dissolved product remains in ground
water following free product recovery, under optimal operating conditions.
Case studies have documented dissolved hydrocarbon levels of 2 to 10 mg/1
after free product recovery was completed (Refs. No. 6, 18, and 20). These
values have been used to estimate that the potential influent levels of total
BETX into an air stripper (or other wastewater treatment system) varies from 2
to 15 mg/1. Vendors report that the potential removal efficiency of BETX
using a commercially available air stripper unit is 99.5 percent. If air
stripping is applied to influent BETX levels of 15 mg/1, the stripped
effluent would contain 0.075 mg/1 (or 75 ug/1) total BETX. One case study
reported air stripper performance capable of reducing hydrocarbon influent
levels of 4 to 6 mg/1 to less than 100 ug/1 after initial startup and
shakedown testing was completed (Ref. No. 18). However, product recovery and
air stripping technologies may not always occur under optimal conditions.
Therefore, the total BETX discharge limit is 0.1 mg/1 (or 100 ug/1). This is
in keeping with total BETX effluent limitations currently required by EPA
Region 1 (Ref. No. 20) and the State of Louisiana (Ref. No. 22).
5-8
-------
Influent concentrations of benzene, which have rarely exceeded 1 mg/1 in
the State of Maryland, would be stripped to 0.005 mg/1 (or 5 ug/1) at 99.5
percent efficiency (Ref. No. 21). Therefore, the limit of 5 ug/1 was chosen
for benzene. Further, EPA Region 1 (Ref. No. 20) and the States of Maryland
(Ref. No. 21) and Nebraska (Ref. No. 23) have all indicated that dischargers
in their jurisdictions have been able to meet the 5 ug/1 limit for benzene.
5.2.1 Optional Effluent Limitations
Permit limitations based on BPJ must be achievable with existing
technology at a reasonable cost. Based on data contained in the Regulatory
Impact Analysis of Technical Standards for Underground Storage Tanks (Ref. No.
1), over 75 percent of retail motor fuel outlets (which accounts for the
majority of gasoline USTs) in the U.S. are either owned or operated by
businesses meeting the Small Business Administrations's definition for small
businesses. Almost one-half of these own a single outlet with assets totaling
over $400,000. Therefore, many of the smaller firms may be severely affected
by the cost of compliance with the effluent limitations established in Section
5.2. Therefore, optional technology-based effluent limitations have been
developed for discharges from gasoline UST cleanups where these costs will
severely hinder a firm's ability to perform the remedial cleanup activities.
The same treatment technologies (i.e., free product recovery followed by
air stripping) were used to establish the optional effluent limitations.
However, the optional limitations are based on a 95 percent removal efficiency
for both benzene and BETX. Using the same influent concentrations described
in Section 5.2, the resultant effluent limitations will be 50 ug/1 for benzene
and 750 ug/1 for BETX. This relaxed removal efficiency for benzene and BETX
reduces the capital and operating costs for air stripping. This cost savings
could be realized through a reduction in the tower height and packing depth,
or a reduction in power requirements because a lower air-water ratio can be
used, or both. For example, assuming the benzene influent concentration and
all other operating conditions (e.g., loading rate, air-water ratio) remain
the same, the depth of packing could be reduced by about 7 feet if the desired
removal efficiency requirements were reduced from 99.5 percent removal to 95
percent removal.
5-9
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5.2.2 Additional Effluent. Limitations
The Daily Discharge limits set forth in Part I of the Model Permit
restrict benzene and total BETX. In addition, pH is limited to the widely-
accepted range of 6-9 standard units established for most industrial point
source categories.
Some NPDES permit writers may be concerned about the potential presence
of lead in gasoline at UST sites. In gasoline, however, lead is present as
tetraethyllead (TEL) a component of an organic compound and thus not amenable
to traditional metals removal technologies such as pH adjustment, flocculation
and sedimentation. Based on the Henry's Law Constant for TEL, it would likely
be removed by air stripping. TEL is also amenable to treatment by GAC, as
discussed earlier in Section 4.2 (Ref. No. 6). Permit writers may consider
applying monitoring requirements for lead, if lead is expected to be present
in gasoline contaminated ground water in concentrations or quantities of
concern.
5.3 TREATMENT COSTS
The following subsections briefly describes the cost of implementing
product recovery, air stripping and carbon adsorption technologies.
5.3.1 Costs of Selected Treatment Technologies
According to Cleanup of Releases from Petroleum USTs; Selected
Technologies (Ref. No. 6) the costs for free product recovery equipment will
vary according to the methods chosen for remediation (e.g., surface vs.
subsurface). Generally, the purchase costs will range from $6,000 to $10,000
for product recovery equipment.
Numerous literature sources report capital and operating and maintenance
(O&M) costs for air stripping treatment systems. However, the literature
reports costs for permanent structures rather than more flexible equipment.
Because flexible equipment is more appropriate for use over the relatively
short duration of many UST corrective actions, cost data has been collected
for this Model Permit from vendors for pre-engineered, sled-mounted air
stripping units (Ref. No. 10). Table 5-3 presents a summary of these costs,
including total purchase costs and estimated annual operation and maintenance
5-10
-------
TABLE 5-3. PIKBASB AND RENTAL COSTS PCR PRE-OGDHHED PtOfD OOUIK AIR SHOPPER WETS
Ul
i
Air Stripper
Design Flow
(gallons/minute)
3-20
3-20
30
30
15-60
15-60
150
150
Tower
Height/Diameter
(feet)
18.5/1
28.5/1
16/1
19/1
12.5/2
22.5/2
11/3
19/3
Packing Height
(feet)
D
21
11
14
8
16
5.5
13.5
Total Purchase
Cost (S)1
6,000
8,595
5,150
5,400
8,450
11,700
7,900
12,900
Estimated Annual
Monthly Rental Operations and
Cost ($)2 Maintenance Costs ($)
1,160
NA
1,400
1,400
1,699
NA
1,800
1,800
1,200
1,700
1,030
1,080
1,690
2,340
1,580
2,580
NA - Not Available
1 Does not include delivery, installation, engineering, and contingency costs. These costs are estimated to be about 30-50 percent
of purchase cost.
2 Rental costs will vary according to the length of rental time. At least a 6 month rental period was assured.
3 Operational and maintenance costs are highly variable; assumed to be 20 percent of total purchase cost based on vendor estimates.
-------
costs. In addition, if the corrective action is anticipated to be a
relatively short term cleanup, the owner/operator or cleanup contractor may
consider renting an air stripping treatment system. Therefore Table 5-3 also
presents monthly rental costs.
Effluent limitations for pH are established as 6.0 (minimum) and 9.0
(maximum) standard units based on available pH adjustment technologies. These
technologies include acid and/or base addition, the costs of which are inci-
dental to the overall costs of treating water and wastewater prior to
discharge.
5.3.2 Air Emissions Control
Emissions of volatile organ!cs from wastewater treatment systems may
impact local air quality. Carbon adsorption can be used to treat vapors
containing volatile organics that are emitted from air strippers in those
areas of the Nation where such controls are necessary (Ref. No. 7). Based on
the procedures outlined in Underground Storage Tank Corrective Action
Technologies (Ref. No. 7), costs for control of air emissions are estimated
below for three daily discharge flows:
Discharge Flow
<50,000 gpd
500
150,000 gpd
5,000
750,000 gpd
8,000
Airflow rate, cfm
Capital Cost $40,000 $75,000 $100,000
Annual Operating and
Maintenance Cost $6,000 $60,000 $100,000
5.3.3 Costs of Alternative Treatment Technologies
Free product recovery followed by air stripping is the treatment tech-
nology used as a basis for the development of effluent limitations in the
Model Permit. Carbon adsorption and biological treatment technologies are
also reported, in the literature, as examples of appropriate treatment
5-12
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technologies for discharges resulting from gasoline underground storage tank
cleanups.
The use of GAC may substantially increase treatment costs. Capital costs
may be twice to four times those capital costs generally needed for use of air
stripping treatment units. Operation and maintenance (O&M) costs incurred
when using GAC may increase to up to eight times the O&M cost of air
stripping. This eight-fold increase in O&M costs is due to the need to renew
the GAC carbon and dispose of spent carbon. These relative costs are shown in
greater detail in Table 5-4.
5-13
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TABLE 5-4. RELATIVE COST FACTORS FOR TREATMENT OF GROUND WATER
Technique
Air stripping
Air stripping &
vapor-phase GAC
Air stripping &
liquid-phase GAC
Air stripping &
Relative Cost
Capital
1*
2.0
3.0
4.0
Factors
O&M2
1*
3.0
3.0
5.0
O&M
(RCRA)
1
4.0
4.5
7.5
liquid-phase &
vapor-phase GAC
Liquid GAC only 1.5 4.0 8.0
*Assigned
Cost factors indicated are relative to air stripping.
O&M costs for GAC include costs for carbon replacement/regeneration.
Indicates cost if spent carbon must be treated as a hazardous waste under
RCRA.
Source: Reference No. 6
5-14
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6.0 BEST MANAGEMENT PRACTICES
The Model Permit requires the permittee to develop a Best Management
Practices (BMP) plan to minimize potential for release of pollutants from
corrective action activities. BMPs are designed to minimize contamination of
surface waters, as a result of cleanup operations. In addition, BMPs such as
diversion and collection of runoff, prevent offsite transport of surface
waters that may have become contaminated. The BMPs set forth in Part III,
Section A.I, of the Model Permit are based on recommendations provided in the
OUST document entitled Underground Storage Tank Corrective Action Technologies
(Ref. No. 7).
6-1
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7.0 MONITORING
Monitoring is the primary means of ensuring that the permit limitations
are met. It is also the basis for enforcement actions against permittees who
are in violation of their permit limits. State and EPA Regional offices
usually recommend monitoring frequencies based on the design capacity of the
treatment facility (Ref. No. 12).
The permittee may request reduced frequency of monitoring requirements
(or elimination of toxicity monitoring requirements) after 3 months of the
effective date of the permit. Part IV, Section A.4 of the Model Permit allows
the permittee to collect data sufficient to demonstrate that the treatment
system is performing well. After a review of discharge data collected over a
3 month period, the Permitting Authority may reduce the frequency of, or
eliminate monitoring requirements.
7.1 FLOW MONITORING
Weekly flow monitoring is recommended for discharges less than 100,000
gallons per day (Ref. No. 12). Since discharges from gasoline UST cleanups
are expected to be approximately 30,000 gallons per day (see Section 3.1), the
Model Permit requires weekly flow monitoring.
7.2 CHEMICAL-SPECIFIC MONITORING
Chemical-specific monitoring is recommended on a quarterly basis for
flows less than 100,000 gallons per day (Ref. No. 12). However, high
concentrations of hydrocarbons are expected to be present in water and
wastewater resulting from UST site corrective actions. Therefore weekly
chemical-specific monitoring is recommended.
Chemical-specific monitoring is required for benzene, ethylbenzene,
toluene, and the xylenes. Analytical methods 602, 624, and 1624 are approved
under authority of the CWA for analyses of benzene, ethylbenzene, and toluene.
EPA Method 8240 is an approved RCRA method for the analysis of ortho-, meta-,
and para-xylene which are reported as "total xylenes" or "xylene." EPA Method
8240 should be used to test "xylenes" unless State or EPA Regional policies
specify alternative analytical methods. EPA Method 8240 can also be used to
7-1
-------
analyze for benzene, ethyliienzene, and toluene. Depending upon EPA Regional
or State policy, the permit writer may opt to substitute Method 8240, when
using the Model Permit for the CWA methods generally required under the NPDES
program. Hence the permittee would not be required to perform two tests to
report the required data for benzene, ethylbenzene, toluene, and total
xylenes. Method 8240 is described in Test Methods for Evaluating Solid Waste
Volume IA; Laboratory Manual Physical/Chemical Methods (Ref. No. 15).
Grab sample collection is required based on procedures recommended in the
EPA Handbook for Sampling and Sample Preservation of Water and Wastewater
(Ref. No. 13).
7.3 BIOMONITORING
In the absence of information on the toxicity of a specific discharge the
EPA recommends biological monitoring requirements (Ref. No. 11). There are
three principal reasons for generating biomonitoring data:
1) to ascertain whether a permittee exceeds the narrative no toxics water
quality standard and thus needs water quality-based permit limits for
toxicants
2) to identify a sensitive test species for toxicity monitoring purposes
3) to generate data on the variability of effluent toxicity.
Permits can be and are routinely issued with data generation requirements
described in Part III, Special Conditions, of the permit to augment the limits
imposed on other parameters. These testing procedures require permittees to
generate data on their effluent so that the permit writer can determine
whether additional permit limits or controls will be necessary to meet other
statutory requirements, such as water quality standards.
This data generation mechanism should result in subsequent modification
of the NPDES permit if the data generated show unacceptable toxicity. Should
toxicity be demonstrated, the permit writer should consider developing site-
specific water quality-based limits (see Part IV - Decision Tool for
Developing Vater Quality-Based Limitations).
7-2
-------
The biomonitoring requirements set forth in Part III(A)(3) of the Model
Permit were adapted from EPA guidance on developing water-quality based
permits (Ref. No. 11). Specifically, chronic aquatic life toxicity testing is
required to characterize effluent toxicity. As an alternative, the permit
writer could use the whole-effluent toxicity screening procedure that is
recommended in. the EPA Technical Support Document for Water Quality-Based
Toxics Control (Ref. No. 24). This approach, provided in Table 7-1, allows
for decisions to be made regarding toxic impact early in the testing process.
Effluents with low potential for instrearn toxicity can be eliminated as a
priority or given a low priority for further analysis.
States may also have their own toxicity testing requirements that can be
substituted as appropriate. One such approach has been successfully used in
the State of North Carolina and has been included for consideration as an
alternative for gasoline UST cleanups. The State of North Carolina developed
a standard approach to whole-effluent toxicity testing that is based on the
instream waste concentration (IWC) resulting from a discharge. The IWC, which
is expressed as a percentage, is calculated by dividing the effluent flow or
discharge flow by the sum of the receiving water low flow (defined as 7Q10 low
flow) plus the effluent flow. Depending upon the IWC, one of three types of
toxicity tests are generally required (Ref. No. 16):
• If the IWC exceeds 1 percent, then the permittee is required to
perform the Ceriodaphnia Pass/Fail chronic toxicity test. This static
renewal test is conducted at the IWC and runs for 7 days. Passing the
Pass/Fail chronic test means there is no observable inhibition of
reproduction or significant mortality at the IWC.
• If the IWC is between 0.25 and 1 percent, then the permittee is
required to perform a static, nonrenewal, 48 hour acute toxicity test.
This test is conducted over a range of effluent concentrations using
either Ceriodaphnia dubia or Daphnia pulex. To pass, the 48 hour
concentration of effluent lethal to 50 percent of the organisms (LC50)
must be greater than or equal to the IWC (expressed as a
concentration).
• If the IWC is less than 0.25 percent, then a short term Pass/Fail
acute toxicity test must be performed by the permittee. This static
nonrenewal test uses either the fathead minnow (Pimephales promelas),
Daphnia pulex, or Ceriodaphnia dubia, and runs for 24 hours; typically
at 90 percent of the effluent concentration. This test is failed if
it is determined that mortality in the effluent treatment is
significantly different than the control population (measured using
the Student's test and a 99 percent confidence interval).
7-3
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TABLE 7-1. RECOMMENDATIONS FOR WHOLE-EFFLUENT TOXICITY SCREENING
Individual Dischargers - Compare receiving water flow rate (in terms
of whatever water quality-based design low flow is specified by the
State) to average effluent flow rate.
- If dilution exceeds 10,000 to 1, and there is a reasonably rapid
mix of the effluent outside of the rapid initial dilution area in
the receiving water, then the effluent should be given a low
priority for any further attention.
- If dilution is less than 10,000 to 1, or mixing is not rapid and
toxicity within a plume is of concern, then toxicity screening
tests should be performed.
- If dilution is between 1,000 to 1 and 10,000 to 1, or a poorly
mixed effluent plume in a large receiving water (>10,000 to 1
dilution) is of concern, conduct acute toxicity screens as follows:
1. Collect four to six effluent samples on one day (grab or short
term composite), quarterly. Conduct screening tests (24-hour)
in 100% effluent, using a daphnid and a fish, on each sample.
2. If 50% mortality or greater is observed in three samples, the
potential for toxicity is assumed and further testing is
required.
3. If 50% mortality or greater is observed for two or fewer
samples, the discharge should be given a low priority for
further analysis.
- If dilution is less than 1,000 to 1, conduct chronic toxicity
screens (short term chronic tests are recommended) as follows:
1. Collect four to six effluent samples (24-hour composite) on four
to six successive days. Conduct static screening tests (seven-
day) in 100% effluent, using a cladoceran and a fish, on each
sample.
2. If a 50% or greater effect is observed between controls and test
organisms, the potential for toxicity is assumed and further
testing is required.
3. If less than 50% effect is observed, the discharge should be
given a low priority for further analysis
Acute tests can be used in these dilution situations, but it should be
noted that there will be cases where no acute toxicity is measured but
the effluent is chronically toxic.
7-4
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TABLE 7-1. RECOMMENDATIONS FOR WHOLE-EFFLUENT TOXICITT SCREENING
(Continued)
- Where dilution is less than 100 to 1, the use of a toxicity-
testing-based screening procedure is not recommended. Screening
has already been accomplished through dilution analysis. Even in
discharge situations where no toxicity is observed in screening
tests, the narrow margin between effect concentration and available
dilution suggests more complete effluent toxicity characterization
is mandatory. If uncertainty factors are applied in a 100 to 1
discharge situation, dilution alone would mandate further testing.
Where very limited dilution is available, it is recommended that
toxicity-testing screening be skipped and the discharger be
required to begin DEFINITIVE DATA GENERATION procedures (see Ref.
No 24).
Ambient Toxicity Analysis - Use ambient toxicity analysis to identify
areas of instream toxicity associated with specific dischargers. This
analysis may be most useful when conducted by the regulatory agency,
but dischargers may be required to conduct the tests in conjunction
with effluent tests. A systematic plan for identifying problem areas
is recommended. This procedure is useful for multiple source
discharge situations. The analysis should be conducted concurrently
with discharge-specific screening and must be done at low flow
conditions. A procedure is described in Appendix C (contained in Ref.
No. 24).
Source: Reference No. 24.
7-5
-------
8.0 REFERENCES
1. Regulatory Impact Analysis of Technical Standards for Underground
Storage Tanks. Prepared for the EPA Office of Underground Storage
Tanks by ICF, Inc. August 24, 1988.
2. Based on SAIC conversations with EPA staff members, Office of Under-
ground Storage Tanks.
3. Based on draft data submitted to EPA, Office of Underground Storage
Tanks by Camp, Dresser and McKee, Inc. (1987).
4. Guard, H.E. James, N.G., Roy B. Laughlin, Jr. Characterization of
Gasolines, Diesel Fuels and Their Water Soluble Fractions. Naval
Biosciences Laboratory, Naval Supply Center, Oakland, CA. September
1983.
5. Fate and Transport of Substances Leaking from USTs; COM Draft Report
January, 1986.
6. Cleanup of Releases From Petroleum USTs: Selected Technologies. EPA
Office of Underground Storage Tanks, (EPA/530/UST-88/001) April 1988.
7. Underground Storage Tank Corrective Action Technologies. Hazardous
Waste Engineering Research Laboratory, ORD/Office of Underground
Storage Tanks/OSWER (EPA/625/6-87-015) January 1987.
8. Quantitative Structure Activity Relationship System (QSARS) Data
Base. Environmental Research Lab, EPA Office of Research and
Development, Duluth, MN.
9. Quality Criteria For Water 1986. EPA Office of Water Regulations and
Standards (EPA 440/5-86-001) May 1, 1987.
10. Delta Cooling Towers, Inc.; Ground Water Technology, Inc.
11. Permit Writer's Guide to Water Quality-Based Permitting for Toxic
Pollutants. EPA Office of Water (EPA 440/4-87-005) July 1987.
12. Training Manual for NPDES Permit Writers. EPA Office of Water
Enforcement and Permits. May 1987.
13. Handbook for Sampling and Sample Preservation of Water and Waste-
water. U.S. Environmental Protection Agency (EPA-600/4-82-029)
September 1982.
14. Summary of State Reports on Releases from Underground Storage Tanks.
EPA Office of Underground Storage Tanks (EPA/600-M-86/020) August
1986.
15. Test Methods for Evaluating Solid Waste Volume IA: Laboratory Manual
Physical/Chemical Methods. EPA Office of Solid Waste and Emergency
Response (SW-846) November 1986.
8-1
-------
16. North Carolina Whole Effluent Toxicity Program. North Carolina
Division of Environmental Management, Biological Services Unit,
(Undated).
17. Kirk-Othmer Encyclopedia of Chemical Technology, Third Edition,
Volume 11. John Wiley & Sons, 1980.
18. Oil Spill Conference Proceedings, sponsored by USEPA, U.S. Coast
Guard; American Petroleum Institute held in Los Angeles, CA, February
25-28, 1985.
19. The Merck Index, Tenth Edition. Merck and Company, Inc. 1983.
20. Science Applications International Corporation. Based on memos and
telephone conversations with EPA Region I, Industrial Permits
Section.
21. Science Applications International Corporation. Based on memos and
telephone conversations with the Maryland Department of the
Environment.
22. Science Applications International Corporation. Based on memo
submitted by the Louisiana Department of Environmental Quality,
Office of Water Resources, Permits Section.
23. Science Applications International Corporation. Based on memos and
telephone conversations with the Nebraska Department of Environmental
Control, Water Quality Division.
24. Technical Support Document for Water Quality-Based Toxics Control.
EPA Office of Water, September 1985.
'25. Lange's Handbook of Chemistry, Thirteenth Edition McGraw-Hill Book
Company, 1985.
8-2
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PART IV
DECISION TOOL FOR DEVELOPING WATER
QUALITY-BASED EFFLUENT LIMITATIONS
-------
TABLE OF CONTENTS
Page
1.0 DECISION TOOL FOR DEVELOPING WATER QUALITY-BASED EFFLUENT
LIMITATIONS 1-1
1.1 BACKGROUND 1-1
1.2 METHODOLOGY 1-4
1.3 DISCHARGES FROM GASOLINE UNDERGROUND STORAGE TANK CLEANUPS. 1-7
1.4 DISCUSSION 1-9
-------
LIST OF TABLES
Table Page
1-1 WATER QUALITY CRITERIA FOR POLLUTANTS IN DISCHARGES
FROM GASOLINE UST CLEANUPS 1-8
1-2 RECEIVING STREAM FLOW REQUIRED TO ACHIEVE WATER
QUALITY CRITERION FOR BENZENE 1-10
ii
-------
1.0 DECISION TOOL FOR DEVELOPING WATER
QUALITY-BASED EFFLUENT LIMITATIONS
This document defines a procedure for deciding whether water quality-
based effluent limitations should be required in a NPDES permit for discharges
resulting from the cleanup of gasoline from leaking underground storage tank
(UST) sites.
The development of one-hour maximum and four-day average water quality-
based effluent limitations according to guidance set forth in the EPA
Technical Support Document for Water Quality-Based Toxics Control (September
1985), or TSD, requires site-specific information. Certain assumptions have
been made to simplify the application of this Decision Tool to a wide variety
of site-specific conditions and circumstances in a manner consistent with the
way the majority of the States now develop water quality-based effluent
limitations. The site-specific information required for this simplified
approach is limited to effluent flow, effluent concentration, and receiving
water flow. Where the simplifying assumptions are not applicable, the
procedure developed here for use as a Decision Tool should be modified
accordingly. The simplifying assumptions and the limits they place on the
application of the Decision Tool are summarized following the discussion of
the methodology and its application to leaking UST cleanups.
1.1 BACKGROUND
Both the Clean Water Act and promulgated Federal regulations require that
all NPDES permits include limitations to achieve all applicable State water
quality standards. Further, NPDES permits must include limitations that
reflect any total maximum daily loads or wasteload allocations set by EPA or
States to achieve applicable water quality standards.
EPA's policy and legal basis regarding the use of State water quality
standards to set NPDES permit limits on toxicants is provided by the Office of
Water's Policy for the Development of Water Quality-Based Permit Limits for
1-1
-------
Toxic Pollutants, 49 FR 9016, March 9, 1984. In part, this policy states
that:
Where violations of water quality standards are identified
or projected, the State will be expected to develop water
quality-based effluent limits for inclusion in any issued
permit. Where necessary, EPA will develop these limits in
consultation with the State. Where there is a significant
likelihood of toxic effects to biota in the receiving
water, EPA and the States may impose permit limits on
effluent toxicity and may require an NPDES permittee to
conduct a toxicity reduction evaluation (TRE). Where
toxic effects are present but there is a significant like-
lihood that compliance with technology-based requirements
will sufficiently mitigate the effects, EPA and the States
may require chemical and toxicity testing after instal-
lation of treatment and may reopen the permit to incorpo-
rate additional limitations if needed to meet water
quality standards. [Toxicity data, which are considered
"new information" in accordance with 40 CFR 122.62(a)(2),
could constitute cause for permit modification where
necessary].
Two forms of State water quality standards for toxicants can be used to
set NPDES permit limits: numerical standards and narrative standards.
Numerical standards for some individual toxicants are contained in virtually
all State water quality standards. They are usually expressed as an instream
"not-to-be-exceeded" concentration of a toxicant (e.g., 0.019 mg/1 for total
residual chlorine).
All States also have narrative standards for pollutants. The most common
form of the narrative standard contains language establishing that the waters
are free from substances in amounts that will:
1. Settle to form objectionable deposits;
2. Float as debris, scum, oil, or other matter to form nuisances;
3. Produce objectionable color, odor, taste, or turbidity;
4. Injure, be toxic to, or produce adverse physiological responses in
humans, animals, or plants; and
5. Produce undesirable or nuisance aquatic life.
1-2
-------
States must also include a procedure for translating this "free from" language
into numerical "water quality criteria," from which can be derived water
quality-based effluent limitations. In addition, a State's water quality
standards rule is not considered administratively complete unless it contains
an antidegradation provision to protect existing water quality, where it is
better than the minimum required to support at least fishing and swimming.
Degradation only can be allowed when certain tests of social or economic
benefit are met. Those tests are set forth in Section 302(b) of the Clean
Water Act and the regulations developed to implement that section.
The standard under (4) above pertains to toxic effects and is an
important element in any effective toxics control strategy. This standard
should be used by States and EPA Regions to limit both individual toxicants
(where a toxic effect can be traced to a specific chemical for which no
standards or criteria exist) and whole effluent toxicity (where it is not
obvious which chemicals are causing toxicity or where the limitation of
generic effluent toxicity is more appropriate to that particular discharge
situation).
Clean Water Act Section 303(d)(l)(C) mandates that water-quality based
effluent limits more stringent than those required by Best Available
Technology (BAT) regulations be imposed on a site-specific basis to assure the
protection of receiving water quality with an ample margin of safety. Such
limits, developed by the States, are to be based on the capacity of receiving
waters to assimilate a particular toxic substance entering the system from all
well-characterized sources. The assimilative capacity of the receiving water
for a particular pollutant is defined in terms of the rate at which that
pollutant is degraded at a concentration equal to the water quality standard
or the existing concentration, whichever is lower under design low flow
conditions. That rate in pounds or kilograms per day is specified as the
Total Maximum Daily Load (TMDL).
The maximum load attributable to nonpoint sources (load allocation) is
then subtracted from the TMDL, and the difference is apportioned among point
sources according to an allocation rule. This is the point source waste load
allocation (WLA) for the particular substance and receiving water. TMDL/WLA-
1-3
-------
based toxic substance effluent limits are then incorporated into all affected
point source discharge permits.
NPDES permits must be developed and issued in accordance with current
permit issuance policies, including current Agency operating guidance, permit
issuance strategies, and State-specific agreements and workplans. Applicable
water quality standards and site-specific water quality data, as well as
effluent composition data, should be assessed during the permit issuance
process to determine whether water quality-based permit requirements for
toxics are necessary for a particular discharge.
This is particularly important for waterbodies that have been identified
as not achieving water quality standards pursuant to Section 304(1) of the
Clean Water Act. For each stream segment or waterbody identified, Section
304(1) requires that individual control strategies be developed to reduce the
discharge of toxic pollutants from point source discharges to the stream
segment or waterbody. In addition, NPDES permits incorporating all necessary
and appropriate elements should be developed for all point sources identified.
However, the requirement to-develop water quality-based effluent limita-
tions as necessary to achieve applicable water quality standards in the
receiving water is not limited to 304(1) waterbodies. The requirements of
Section 303(d)(l)(C) of the Clean Water Act apply to all U.S. waterbodies
whose water quality is protected under the Clean Water Act.
1.2 METHODOLOGY
The technology-based effluent limitations set forth in the Model Permit
are based on removal efficiencies of product recovery and air stripping
treatment systems. While use of such technologies may significantly reduce
the contaminant levels of the pollutants of concern, technology-based effluent
limitations may not adequately address water quality concerns of affected
receiving waters.
To guide NPDES permit writers in implementing the requirements of CWA
Section 303(d)(l)(C), EPA's Office of Water published the TSD. This guidance
1-4
-------
describes approved approaches for measuring or calculating the dimensions of
and dilution afforded by zones of initial dilution (ZIDs) and mixing zones.
This guidance also provides procedures for the calculation of chemical-
specific and whole effluent toxicity-based 1-hour maximum or 4-day average
effluent limitations, taking into account dilution within the ZID or mixing
zone, the applicable acute or chronic water quality criterion, effluent
composition variability, the receiving water flow, and the statistical
confidence level equivalent to an acceptable frequency of recurrence of
effluent limitation exceedance.
To quantify the relationship between the chemical-specific pollutant
loading rate from a single discharge, or from multiple discharges, and the
downstream receiving water quality at any point outside of the mixing zone,
the permit writer has several options. For toxic pollutant discharges to
rivers and run-of-river reservoirs, a simple mass balance equation can be
used. This equation is based on the assumption that the flow and pollutant
concentration of the effluent are fixed at their average values [i.e.,
constant average loading rate); the flow of the receiving water is treated as
a constant (generally the once-in-ten-year, 7-day (7Q10) drought flow is
applied for the chronic scenario and the once-in-three-year, 1-day low flow
(1Q3) is applied for the acute scenario); and the rates of pollutant
production, destruction, and storage within the system are assumed to be zero.
The simple mass balance equation as it applies to a single discharge and
assuming complete mixing is as follows:
Q. + Q
e
where: C - downstream concentration of pollutant
C = upstream concentration of pollutant
Qs = upstream design flow of receiving water
Ce = effluent pollutant-specific concentration limit
Qe = effluent design flow.
1-5
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In situations where only a fraction of the receiving water flow is
allocated for mixing to ensure that the mixing zone does not inhibit the free
passage of fish, then a factor "f" is used. This factor accounts for the
fraction of the upstream receiving water flow that constitutes the allocated
mixing zone. To ensure that applicable water quality criteria are achieved
downstream of the effluent discharge, C is defined such that:
C = f-VQC
where: WQC » the pollutant-specific water quality criteria to be
achieved in the receiving water
Rearranging and solving for the effluent concentration:
[f-VQC-(Qe + Qs)] - Cs-Qs
According to the TSD, the final effluent limitations should be derived
taking into account effluent variability. The more restrictive of the aquatic
acute, aquatic chronic or long-term human health-based 1-hour maximum and
4-day average limitations are then used as the basis for the final effluent
limitations. If the permit writer chooses not to address effluent varia-
bility, then acute aquatic and chronic aquatic or human health-based effluent
limitations should be treated as "not to exceed" levels. As most States use
the "not to exceed" approach, that approach will be followed here.
The above mass dilution equation is used to calculate 4-day average "not
to exceed" effluent limitations from the more protective of chronic aquatic
criteria or human health criteria, using the appropriate flow of the receiving
water and "f" is taken to be the fraction of the receiving water flow with
which the effluent mixes in the mixing zone.
The mass dilution equation can also be used to calculate 1-day maximum
effluent limitations. For this purpose, the upstream concentration is usually
assumed to be zero, the VQC becomes the acute aquatic criterion, and "f" is
taken to be the fraction of the flow of the receiving water with which the
1-6
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effluent mixes in the ZID.- In the absence of a ZID and mixing zone, however,
water quality criteria must be met at the end-of-pipe.
Where specific numerical criteria for a chemical or biological parameters
(such as toxicity) are absent or where exposure to multiple pollutants is
occurring via a complex effluent, compliance with the standards must be based
on the general narrative criteria and on protection of the designated use of
the receiving water. This standard is implemented via whole effluent toxicity
testing using short-term tests (e.g., %8 to 96 hour) to protect from acute
lethal effects at the edge of the ZID and long-term tests to protect from
chronic sub-lethal effects at the edge of the mixing zone. In both circum-
stances the testing includes exposure to effluent diluted with upstream
receiving water to the extent dictated by mixing within the ZID or within the
mixing zone under drought flow conditions.
1.3 DISCHARGES FROM GASOLINE UNDERGROUND STORAGE TANK CLEANUPS
For the pollutants known to be present in gasoline UST discharges (see
Part III - Fact Sheet), Federal water quality criteria have been developed
only for benzene, ethylbenzene, toluene and naphthalene. The water criteria
for each of these pollutants are shown in Table 1-1, as reported in Quality
Criteria for Water 1986 (EPA 440/5-86-001). The air stripping effluent
concentrations are reported in the Fact Sheet.
A comparison of water quality criteria to achievable undiluted air
stripping effluent concentrations (i.e., the technology-based effluent
limitations included in the Model Permit) reveals that only the water and fish
ingestion criteria for protection of human health would be exceeded for
benzene. A relationship for the downstream concentration of benzene is
established below. First, the assumptions explained in the legend below are
made, and the corresponding values are substituted in the mass balance
equation.
Cs = assumed zero
WQC = human health criterion for benzene (water and fish
ingestion) assuming an acceptable increased lifetime cancer
risk at 10
1-7
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TABLE 1-1. UffTER QUttJTY CRTEERIA FDR PttLUEANTS FWSENT IN DESOBABGES FRCH GASQLDE 1ST CLEANUPS
(Cbnoaitrations in
Aquatic Life Protection
Benzene
Ethylbenzene
Toluene
Xylene
Naphthalene
Priority
Pollutant
Yes,
Tes
Yes
No
Yes
Carcinogen
Yes
No
No
No •
No
r^sisri
Acute
Criteria
5.30*
32*
17.5*
2.3*
Marine
Acute
Criteria
5.10*
0.430*
6.30*
.620*
Marine
Chronic
Criteria
0.70*
5.0*
2.35*
Hunan Health Protection
Water and
Fish
Ingestion
0.00066**
1.4
14.3
Fish
Consumption
Only
0.040**
3.28
424
. * Means the data were insufficient to develop criteria; the value presented is the lowest observed effect level (L.O.E.L.).
** Human health criteria for carcinogens are generally reported for three risk levels; the value presented is for the 10- risk level.
-------
C = technology-based effluent concentration for benzene
f = assumed 1.0 (i.e., the entire upstream receiving water flow
is allocated for mixing).
C = f-VQC =
CsQs
(0.005 mg/1) Q
0.00066 mg/1 = or Qe = (0.152)QS
For the optional effluent limitations:
(0.05 mg/1) Qe
0.00066 mg/1 = — or Q = (0.013)QS
Q. + Q.
*s
The relationship between the effluent flow and the receiving stream flow
calculated above can also be expressed in tabular form. Table 1-2 shows the
receiving stream flow required to provide sufficient dilution to achieve the
water quality criterion for benzene.
It should be noted that while the benzene water quality criterion to
protect human health is lower than that to protect aquatic life, the potential
need for a whole effluent toxicity-based effluent limitation is not removed.
This is because of the potential complex composition of UST-contaminated
ground water even after treatment has been carried out utilizing the
equivalent of the best available technology. Whereas benzene, singly, is not
expected to be acutely or chronically toxic to aquatic life at effluent
concentrations necessary to protect human health, this situation may not
necessarily hold for other constituents that may be present. In the absence
of water quality criteria for all the potential contaminants present in the
effluent or in anticipation of a potentially additive or synergistic toxic
effect from the complex mixture, it is appropriate to also include a whole
effluent toxicity monitoring requirement in the permit.
1-9
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TABLE 1-2. RECEIVING STREAM FLOW REQUIRED TO ACHIEVE
WATER QUALITY CRITERION FOR BENZENE
Effluent Flow
(Gallons per
minute)
(Gallons per
day)
Receiving Stream Flow
(Gallons per
minute)
(Cubic feet
per second)
Air stripping effluent = 0.005 mg/1
1
5
10
20
50
100
1,440
7,200
14,400
23,800
72,000
144,000
7
33
66
132
329
658
0.015
0.07
0.15
0.29
0.73
1.47
Air stripping effluent = 0.05 mg/1 (optional effluent limitations)
r
5
10
20
50
100
1,440
7,200
14,400
28,800
72,000
144,000
77
334
769
1,538
3,846
7,692
C.17
0.83
1.7
3.4
8.6
17.1
1-10
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1.4 DISCUSSION . :
The use of the simple mass balance equation for calculating water
it
quality-based effluent limitations presupposes that the volumes of the ZID and
mixing zone have been defined and that the dilutions afforded by mixing within
those volumes have been accurately quantified. In many States no provisions
are made for ZIDs (acute limitations are met at the end-of-pipe) and the
mixing zone is defined as a function of the cross-sectional area of the
receiving water under 7Q10 conditions (e.g., 1/4 to 1/2). The length of the
mixing zone is often chosen based on a maximum allowable distance (e.g., 1000
meters). Complete mixing with the 7Q10 flow of the receiving water is assumed
to occur within the mixing zone.
For fast-flowing or highly turbulent rivers, the complete mix assumption
may be valid. But under 7Q10 conditions many rivers are slow moving and
relatively quiescent. Under these conditions, mixing can be slow. More'so
than for rivers and run-of-river estuaries, the assumption of uncomplies.ted,
rapid mixing with receiving water flow to achieve a chemical-specific or
narrative standard at the edge of the ZID or edge of the mixing zone is likely
to be inapplicable for lakes and Impoundments, or for estuaries and near-shore
ocean discharges. :
For complex mixing situations, permit writers should refer to the various
hydrodynamic mixing models, referenced in the TSD. Such situations include
submerged, low velocity discharges, particularly those with significant
temperature and or salinity differences than the surrounding water. The
application of the simple mass balance equation is inappropriate for these
situations. This is also true of surface discharges with the same properties.
In these circumstances it is necessary to conduct site-specific mixing studies
under conditions that represent a worst-case (e.g., maximum temperature and
density differences; lowest near-shore flow, tidal or wave action). The
general approach for performing appropriate mixing studies and reference to
more detailed guidance are contained in the TSD.
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