[Federal Register Volume 61, Number 216 (Wednesday, November 6, 1996)]
[Notices]
[Pages 57425-57429]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-28430]


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ENVIRONMENTAL PROTECTION AGENCY
[FRL-5646-6]


Questions and Answers Regarding Implementation of an Interim 
Permitting Approach for Water Quality-Based Effluent Limitations in 
Storm Water Permits

AGENCY: Environmental Protection Agency.

ACTION: Notice.

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SUMMARY: Notice is hereby given that the Environmental Protection 
Agency (EPA) has developed a set of questions and answers to assist 
municipalities and permitting authorities in implementing its recent 
policy outlining an interim approach for incorporating water quality-
based effluent limitations into storm water permits.

Background and Purpose

    On August 26, 1996, the EPA published in the Federal Register (61 
FR 43761) a policy outlining an interim approach for incorporating 
water quality-based effluent limitations into National Pollution 
Discharge Elimination System (NPDES) storm water permits. The policy 
was developed to address the variable nature of storm water discharges, 
and the typical lack of information on which to base numeric water 
quality-based effluent limitations (expressed as concentration and 
mass). The policy addresses issues related to the type of effluent 
limitations that are most appropriate for NPDES storm water permits to 
provide for the attainment of water quality standards. Since the policy 
only applies to water quality-based effluent limitations, it is not 
intended to affect technology-based limitations, such as those based on 
effluent guidelines or the permit writer's best professional 
judgements, that are incorporated into storm water permits.
    Based on numerous requests for additional information regarding the 
implementation of the policy, the EPA has developed the following set 
of questions and answers. For convenience, the policy is also reprinted 
below.

Policy Statement

    In response to recent questions regarding the type of water 
quality-based effluent limitations that are most appropriate for 
National Pollutant Discharge Elimination System (NPDES) storm water 
permits, the Environmental Protection Agency (EPA) is adopting an 
interim permitting approach for regulating wet weather storm water 
discharges. Due to the nature of storm water discharges, and the 
typical lack of information on which to base numeric water quality-
based effluent limitations (expressed as concentration and mass), EPA 
will use an interim permitting approach for NPDES storm water permits.
    The interim permitting approach uses best management practices 
(BMPs) in first-round storm water permits, and expanded or better-
tailored BMPs in subsequent permits, where necessary, to provide for 
the attainment of water quality standards. In cases where adequate 
information exists to develop more specific conditions or limitations 
to meet water quality standards, these conditions or limitations are to 
be incorporated into storm water permits, as necessary and appropriate. 
This interim permitting approach is not intended to affect those storm 
water permits that already include appropriately derived numeric water 
quality-based effluent limitations. Since the policy only applies to 
water quality-based effluent limitations, it is not intended to affect 
technology-based limitations, such as those based on effluent 
guidelines or the permit writer's best professional judgement, that are 
incorporated into storm water permits.

[[Page 57426]]

    Each storm water permit should include coordinated and cost-
effective monitoring program to gather necessary information to 
determine the extent to which the permit provides for attainment of 
applicable water quality standards and to determine the appropriate 
conditions or limitations for subsequent permits. Such a monitoring 
program may include, ambient monitoring, receiving water assessment, 
discharge monitoring (as needed), or a combination of monitoring 
procedures designed to gather necessary information.
    This interim permitting approach applies only to EPA, however, EPA 
also encourages authorized States and Tribes to adopt similar policies 
for storm water permits. This interim permitting approach provides 
time, where necessary, to more fully assess the range of issues and 
possible options for the control of storm water discharges for the 
protection of water quality. This interim permitting approach may be 
modified as a result of the ongoing Urban Wet Weather Flows Federal 
Advisory Committee policy dialogue on this subject.

Questions and Answers

    Question 1: Must EPA require that storm water dischargers, 
industrial or municipal, be subject to numeric water quality-based 
effluent limitations (expressed as concentration and mass) in order to 
attain water quality standards (WQS)?
    Answer 1: No. Although National Pollutant Discharge Elimination 
System (NPDES) permits must contain conditions to ensure that water 
quality standards are met, this does not require the use of numeric 
water quality-based effluent limitations. Under the Clean Water Act 
(CWA) and NPDES regulations, permitting authorities may employ a 
variety of conditions and limitations in storm water permits, including 
best management practices, performance objectives, narrative 
conditions, monitoring triggers, action levels (e.g., monitoring 
benchmarks, toxicity reduction evaluation action levels), etc., as the 
necessary water quality-based limitations, where numeric water quality-
based effluent limitations are determined to be unnecessary or 
infeasible.

Analysis

    A. The Clean Water Act does not require numeric effluent 
limitations.
    Section 301 of the CWA requires that discharger permits include 
effluent limitations necessary to meet State or Tribal WQS. Section 502 
defines ``effluent limitation'' to mean any restriction on quantities, 
rates, and concentrations of constituents discharged from point 
sources. The CWA does not say that effluent limitations need be 
numeric. As a result, EPA and States have flexibility in terms of how 
to express effluent limitations.
    B. EPA's regulations do not always require numeric effluent 
limitations.
    EPA has, through regulation, interpreted the statute to allow for 
non-numeric limitations (e.g., ``best management practices'' or BMPs, 
see 40 CFR 122.2) to supplement or replace numeric limitations in 
specific instances that meet the criteria specified at 40 CFR 
122.44(k). This regulation essentially codifies a court case addressing 
storm water discharges. NRDC v. Costle, 568 F.2d 1369 (D.C. Cir. 1977). 
In that case, the Court stated that EPA need not establish numeric 
effluent limitations where such limitations were infeasible.
    C. EPA has interpreted the statute and regulations to allow BMPs in 
lieu of numeric limitations.
    EPA has defended use of BMPs as a substitute for numeric 
limitations in litigation involving storm water discharges (CBE v. EPA, 
91-70056 (9th Cir.)(brief on merits)) and in correspondence (Letter 
from Michael Cook, EPA, to Peter Lehner, NRDC, May 31, 1995). EPA has 
found that numeric limitations for storm water permits can be very 
difficult to develop at this time because of the existing state of 
knowledge about the intermittent and variable nature of these types of 
discharges and their effects on receiving waters. Some storm water 
permits, however, currently do contain numeric water quality-based 
effluent limitations where adequate information exists to derive such 
limitations.
    Question 2: Has EPA provided guidance on a methodology for deriving 
numeric water quality-based effluent limitations?
    Answer 2: Yes, but primarily for continuous wastewater discharges 
at low flow conditions in the receiving water, not intermittent wet 
weather discharges during high flow conditions. Regulations at 40 CFR 
122.44(d) specify the requirements under which permitting authorities 
establish water quality-based effluent limitations when a facility has 
the ``reasonable potential'' to cause or contribute to an excursion of 
numeric or narrative water quality criteria. In addition, EPA guidance 
in the Technical Support Document for Water Quality-Based Toxics 
Control (TSD) and the NPDES Permit Writers Training Manual, 
supplemented with total maximum daily load (TMDL) and modeling 
guidance, supports issuing permits that include numeric water quality-
based effluent limitations. This guidance was based on crafting numeric 
water quality-based effluent limitations using TMDLs, or calculations 
similar to those used in developing TMDLs, and wasteload allocations 
(WLAs) derived through modeling. EPA expects the Urban Wet Weather 
Flows Federal Advisory Committee (60 FR 21189, May 1, 1995) will review 
this issue at greater length and may provide recommendations on how to 
proceed.
    Question 3: Why can numeric water quality-based effluent 
limitations be difficult to derive for storm water permits?
    Answer 3: Storm water discharges are highly variable both in terms 
of flow and pollutant concentrations, and the relationships between 
discharges and water quality can be complex. The water quality impacts 
of storm water discharges are related to the uses designated by States 
and Tribes in their WQS, the quality of the storm water discharge 
(e.g., conventional or toxic pollutants conveyed to the receiving 
water) and quantity of the storm water (e.g., erosion and loss of 
habitat caused by increased flows and velocity). Uses may be impacted 
by both water quality and water quantity. Depending on site-specific 
considerations, some of the water quality impacts of storm water 
discharges may be more related to the physical effects (e.g., stream 
bank erosion, streambed scouring, extreme temperature variations, 
sediment smothering) than the type and amount of pollutants present in 
the discharge. For municipal storm water discharges in particular, the 
current use of system-wide permits and a variety of jurisdiction-wide 
BMPs, including educational and programmatic BMPs, does not easily lend 
itself to the existing methodologies for deriving numeric water 
quality-based effluent limitations. These methodologies were designed 
primarily for process wastewater discharges which occur at predictable 
rates with predictable pollutant loadings under low flow conditions in 
receiving waters. Using these methodologies, limitations are typically 
derived for each specific outfall to be protective of low flows in the 
receiving water. Because of this, permit writers have not made wide-
spread use of the existing methodologies and models for storm water 
discharge permits. In addition, wet weather modeling is technically 
more difficult and expensive than the simple dilution models generally 
used in the permitting process.
    Question 4: Has EPA previously recognized the technical difficulty 
in deriving numeric water quality-based

[[Page 57427]]

effluent limitations for storm water discharges?
    Answer 4: Yes. EPA recognized the technical difficulty in deriving 
numeric water quality-based effluent limitations for wet weather 
discharges in its brief on the merits in Citizens for a Better 
Environment (CBE) v. United States Environmental Protection Agency, 91-
70056 (9th Cir.) and in the Great Lakes Water Quality Guidance (58 FR 
20841, April 16, 1993).
    In the CBE case, EPA explained why it was technically infeasible to 
derive numeric water quality-based effluent limitations for the 
discharge of metals in storm water into South San Francisco Bay and 
asserted that a water quality-based effluent limitation could take the 
form of a narrative statement, such as a BMP, if it was infeasible to 
derive a numeric limitation. In explaining its arguments in the CBE 
case, EPA cited 40 CFR 122.44(k)(2), which provides that BMPs may be 
imposed in NPDES permits ``to control or abate the discharge of 
pollutants when * * * [n]umeric effluent limitations are infeasible.''
    In the Great Lakes Water Quality Guidance, EPA did not extend the 
method for calculating wasteload allocations, the basis for numeric 
water quality-based effluent limitations, to storm water or combined 
sewer overflow (CSO) discharges because the varying nature of these 
discharges is inconsistent with the assumptions used in developing the 
guidance. The Great Lakes Water Quality Guidance defers to national 
guidance and policy on wet weather and does not seek to establish a 
separate and distinct set of wet weather requirements. EPA expects the 
Urban Wet Weather Flows Advisory Committee to provide recommendations 
about how to address the broader technical issues involved in achieving 
compliance with WQS in a wet weather context.
    Question 5: What are the potential problems of using standard 
methodologies to derive numeric water quality-based effluent 
limitations for storm water permits?
    Answer 5: Correctly derived numeric water quality-based effluent 
limitations provide a greater degree of confidence that a discharge 
will not cause or contribute to an exceedance of the WQS, because 
numeric water quality-based effluent limitations are derived directly 
from the numeric component of those standards. In addition, numeric 
water quality-based effluent limitations can avoid the expense 
associated with overly protective treatment technologies because 
numeric water quality-based effluent limitations provide a more 
precisely quantified target for permittees. Potential problems of 
incorporating inappropriate numeric water quality-based effluent 
limitations rather than BMPs in storm water permits at this time are 
significant in some cases. Deriving numeric water quality-based 
effluent limitations for any NPDES permit without an adequate effluent 
characterization, or an adequate receiving water exposure assessment 
(which could include the use of dynamic modeling or continuous 
simulations) may result in the imposition of inappropriate numeric 
limitations on a discharge. Examples of this include the imposition of 
numeric water quality criteria as end-of-pipe limitations without 
properly accounting for the receiving water assimilation of the 
pollutant or failure to account for a mixing zone (if allowed by 
applicable State or Tribal WQS). This could lead to overly stringent 
permit requirements, and excessive and expensive controls on storm 
water discharges, not necessary to provide for attainment of WQS. 
Conversely, an inadequate effluent characterization could lead to water 
quality-based effluent limitations that are not stringent enough to 
provide for attainment of WQS. This could result because effluent 
characterization and exposure assessments for discharges with high 
variability of pollutant concentrations, loadings, and flow are more 
difficult than with process wastewater discharges at low flows.
    Question 6: How are water quality-based effluent limitations 
developed for combined sewer overflow (CSO) discharges?
    Answer 6: The CSO Control Policy issued by EPA on April 19, 1994 
(59 FR 18688) provides direction on compliance with the technology-
based and water quality-based requirements of the CWA for communities 
with combined sewer systems. The CSO Policy provides for implementation 
of technology-based requirements (expressed as ``nine minimum 
controls'') by January 1, 1997.
    In addition, under the CSO Policy, communities are also expected to 
develop long-term control plans that will provide for attainment of WQS 
through either the ``presumption approach'' or the ``demonstration 
approach.'' Under the presumption approach, CSO controls would be 
presumed to attain WQS if certain performance criteria are met. A 
program that meets the criteria specified in the CSO policy is presumed 
to provide an adequate level of control to meet the water quality-based 
requirements of the CWA, provided the permitting authority determines 
that such presumption is reasonable based on characterization, 
monitoring, and modeling of the system, including consideration of 
sensitive areas. Under the demonstration approach, the permittee would 
demonstrate that the selected CSO controls, when implemented, would be 
adequate to meet the water quality-based requirements of the CWA.
    The CSO Policy anticipates that it will be difficult in the early 
stages of permitting to determine whether numeric water quality-based 
effluent limitations are necessary for CSOs, and, if so, what the 
limitations should be. For that reason, in the absence of sufficient 
data to evaluate the need for numeric water quality-based effluent 
limitations, the Policy recommends that the first phase of CSO permits 
(``Phase I'') contain a narrative requirement to comply with WQS. 
Further, so-called ``Phase II'' permits would contain water quality-
based effluent limitations, as provided in 40 CFR 122.44(d)(1) and 
122.44(k), that may take the form of numeric performance or design 
standards, such as a certain number of overflow events or a certain 
percent volume capture. Generally, only after the long-term control 
plan is in place and after collection of sufficient water quality data 
(including applicable wasteload allocations developed during a TMDL 
process) would numeric water quality-based effluent limitations be 
included in the permit. This would likely occur only after several 
permitting cycles.
    Question 7: If BMPs alone are demonstrated to provide adequate 
water quality protection, are additional controls necessary?
    Answer 7: No. If the permitting authority determines that, through 
implementation of appropriate BMPs required by the NPDES storm water 
permit, the discharges have the necessary controls to provide for 
attainment of WQS and any technology-based requirements, additional 
controls need not be included in the permit. Conversely, if a 
discharger (municipal or industrial) fails or refuses to adopt and 
implement adequate BMPs, the permitting authority may have to consider 
other approaches to ensure water quality protection.
    If, however, the permitting authority has adequate information on 
which to base more specific conditions or limitations, such limitations 
are to be incorporated into storm water permits, as necessary and 
appropriate. Such conditions or limitations may include an integrated 
suite of BMPs, performance objectives, narrative standards, monitoring 
triggers, numeric water quality-based effluent limitations,

[[Page 57428]]

action levels, etc. Storm water permits may also need to include 
additional requirements to receive State or Tribal 401 certifications.
    Question 8: What is EPA doing to develop information about the 
linkage between BMPs and water quality and to facilitate a watershed-
based approach to storm water permitting?
    Answer 8: The Agency has cooperative agreements with WERF (Water 
Environment Research Foundation) and ASCE (American Society of Civil 
Engineers) to research which BMPs are most effective under which 
circumstances. The results of this research should provide permitting 
authorities and permittees with information about how to evaluate the 
effectiveness of different kinds of BMPs in different circumstances and 
to select the most appropriate controls to achieve water quality 
objectives. EPA also has cooperative agreements with the Watershed 
Management Institute and other organizations to conduct research over 
the next two to four years that will examine the capability of storm 
water BMPs to improve receiving water quality and restore/protect the 
biological integrity of those waters. EPA expects the Urban Wet Weather 
Flows Federal Advisory Committee to provide recommendations on how to 
permit storm water discharges on a watershed basis.
    Question 9: The interim permitting approach states that permits 
should include monitoring programs to generate necessary information to 
determine the extent to which permits are providing for the attainment 
of water quality standards. What types of monitoring should be included 
and how much monitoring is necessary?
    Answer 9: The amount and types of monitoring necessary will vary 
depending on the individual circumstances of each storm water 
discharge. EPA encourages dischargers and permitting authorities to 
carefully evaluate monitoring needs and storm water program objectives 
so as to select useful and cost-effective monitoring approaches. For 
most dischargers, storm water monitoring can be conducted for two basic 
reasons: (1) to identify if problems are present, either in the 
receiving water or in the discharge, and to characterize the cause(s) 
of such problems; and (2) to assess the effectiveness of storm water 
controls in reducing contaminants and making improvements in water 
quality.
    Under the NPDES storm water program, large and medium municipal 
separate storm sewer system permittees are required to conduct 
monitoring. EPA recommends that each such municipal permittee design 
the monitoring effort to be supportive of the goals and objectives of 
its storm water management program when developing such a program for 
the term of its NPDES permit. To accomplish this, a municipal permittee 
may use a variety of storm water monitoring tools including receiving 
water chemistry; receiving water biological assessments (benthic 
invertebrate surveys, fish surveys, habitat assessments, etc.); 
effluent monitoring; including chemical, whole effluent and visual 
examinations; illicit connections screening; and combinations thereof, 
or other methods. Techniques that assess receiving waters will help to 
identify the degree to which storm water discharges are contributing to 
any water quality problems. Techniques that assess storm water 
discharge characteristics will help to identify potential causes of any 
identified water quality problems. The municipal permittee, in 
conjunction with the applicable NPDES permitting authority, should 
determine which monitoring approaches would be most appropriate given 
the objectives of the storm water management program. If municipal 
permittees conduct ambient monitoring, it may be most cost-effective to 
pool resources with other organizations (including, for example, other 
municipalities, States, and Tribes) conducting monitoring within the 
same watershed. This could be best accomplished through a coordinated 
watershed monitoring strategy.
    For industrial storm water dischargers, monitoring may be required 
under the terms of an NPDES permit for storm water discharges. For 
those industrial storm water permits that do require monitoring, this 
is typically done to characterize contaminants that might be found in 
the industrial runoff and/or to assess the effectiveness of the 
industrial storm water pollution prevention plan in reducing these 
contaminants. This typically involves end-of-pipe chemical-specific 
monitoring. End-of-pipe monitoring may be more appropriate for an 
industrial facility than for a municipal permittee, given the 
industrial facility's more discrete site characteristics, which make 
management strategies such as collection and treatment more feasible. 
Industries, for the most part, have readily defined storm water 
conveyances into which runoff flows from discrete drainage areas. 
Industries may more readily identify and control existing on-site 
sources of storm water contamination or provide collection and 
treatment within these discrete drainage areas to control pollutant 
concentrations in their storm water discharges.
    EPA and other organizations are currently working to improve 
approaches for monitoring storm water and the potential effects upon 
water quality. These new approaches are called storm water program 
``environmental indicators.'' Environmental indicators are designed to 
be more meaningful monitoring tools that storm water dischargers can 
use to conduct storm water monitoring for the purposes described above. 
A manual describing each of the recommended storm water program 
environmental indicators is being prepared by the Center for Watershed 
Protection in Silver Spring, Maryland. That manual is expected to be 
ready by the end of August 1996 and should provide useful information 
for storm water dischargers contemplating the need to develop a cost-
effective, meaningful storm water monitoring program. In addition, EPA 
expects the Urban Wet Weather Flows Federal Advisory Committee to 
provide recommendations on how to better monitor storm water and other 
wet weather discharges using a watershed approach.
    Question 10: Does this interim permitting approach apply to both 
storm water discharges associated with industrial activity and storm 
water discharges from municipal separate storm sewer systems?
    Answer 10: Yes. The interim permitting approach is applicable to 
both discharges from municipal separate storm sewer systems and storm 
water discharges associated with industrial activity (as defined by 40 
CFR 122.26(b)(14)). The interim permitting approach would not affect, 
however, permits that already incorporate appropriately derived numeric 
water quality-based effluent limitations. Since the interim permitting 
approach only addresses water quality-based effluent limitations, it 
also does not affect technology-based effluent limitations, such as 
those based on effluent limitations guidelines or developed using best 
professional judgement, that are incorporated into storm water permits. 
In addition, particularly for some industries, adequate information may 
already have been collected with which to assess the reasonable 
potential for a storm water discharge to cause or contribute to an 
excursion of a WQS, and from which a numeric water quality-based 
effluent limitation can be (or has been) appropriately derived. An 
adequate amount of storm water pollutant source information may also 
exist with which to assess the effectiveness of the industrial storm

[[Page 57429]]

water control measures in complying with the limitations and in 
reducing storm water contaminants for protecting water quality.

DATE: The policy was signed by the Assistant Administrator for Water on 
August 1, 1996.

FOR FURTHER INFORMATION CONTACT: Copies of the policy with the 
questions and answers are available by writing the U.S. Environmental 
Protection Agency, Water Resources Center, Mail Code 4101, 401 M 
Street, SW, Washington, D.C., 20460, or by calling (202) 260-7786. If 
you have additional questions about the policy, please contact, Bill 
Swietlik, Storm Water Phase I Matrix Manager, Office of Wastewater 
Management, at (202) 260-9529 or William Hall, Urban Wet Weather Flows 
Matrix Manager, Office of Wastewater Management, at (202) 260-1458, or 
by Internet at [email protected].

    Dated: October 11, 1996.
Michael B. Cook,
Director, Office of Wastewater Management, Designated Federal Official.
[FR Doc. 96-28430 Filed 11-5-96; 8:45 am]
BILLING CODE 6560-50-P