The National
Pollutant Discharge Elimination System (NPDES) derives from the Clean Water
Act. According to the EPA:
“The Clean Water Act prohibits anybody from discharging
"pollutants" through a "point source" into a "water of
the United States" unless they have an NPDES permit. The permit will
contain limits on what you can discharge, monitoring and reporting
requirements, and other provisions …”
“The program was created in 1972 by the Clean Water Act
and is authorized to state governments by EPA. An NPDES permit is typically a
license for a facility to discharge a specified amount of a pollutant into a
receiving water under certain conditions. The two basic types of NPDES permits
issued are individual and general permits.”
EPA writes that point source “means any discernible,
confined and discrete conveyance, such as a pipe, ditch, channel, tunnel,
conduit, discrete fissure, or container. It also includes vessels or other
floating craft from which pollutants are or may be discharged. By law, the term
"point source" also includes concentrated animal feeding operations,
which are places where animals are confined and fed. By law, agricultural
stormwater discharges and return flows from irrigated agriculture are not
"point sources."
EPA writes that a pollutant is “includes any type of
industrial, municipal, and agricultural waste discharged into water. Some
examples are dredged soil, solid waste, incinerator residue, sewage, garbage,
sewage sludge, munitions, chemical wastes, biological materials, radioactive
materials, heat, wrecked or discarded equipment, rock, sand, cellar dirt and
industrial, municipal, and agricultural waste. By law, a pollutant is not
sewage from vessels or discharges incidental to the normal operation of an
Armed Forces vessel, or certain materials injected into an oil and gas
production well.”
EPA also defines NPDES as follows:
“The national program for issuing, modifying, revoking and
reissuing, terminating, monitoring and enforcing permits, and imposing and
enforcing pretreatment requirements, under Sections 307, 402, 318, and 405 of
the CWA.”
Whether one
needs an NPDES permit or not depends on whether the pollutant is discharged into
a water of the United States (WOTUS). In that case, a permit is required. A
permit may be required for discharging into a storm sewer. A permit is generally
not required for discharging into a municipal sewer system but there are specific
requirements. NPDES permits are issued by EPA regional offices or to state
agencies given primacy by the EPA. NPDES permits specify acceptable levels of
pollutants. These levels may be changed to reflect new understanding and new pollutants
may be added. Other permit conditions may include requiring best management
practices. NPDES permits are generally good for five years and may be renewed thereafter.
There are two
types of NPDES permits: an individual permit and a general permit. An individual
permit is issued for site-specific conditions usually from a single discharger
based on information gathered from the discharger. General permits are issued
for “multiple dischargers with similar operations and types of discharges
based on the permit writer’s professional knowledge of those types of
activities and discharges.” This foreknowledge and better understanding of
types of processes and sizes and types of discharges, for example, means that general
permits are issued faster than individual permits. If you know your type and
size of operation with known composition and volume of wastewater you will likely
learn whether you are covered under a general permit.
Source: Scope and Framework of the NPDES Program. U.S. EPA. Overview of EPA, the Clean Water Act, and the National Pollutant Discharge Elimination System (NPDES) Program
Source: Scope and Framework of the NPDES Program. U.S. EPA. Overview of EPA, the Clean Water Act, and the National Pollutant Discharge Elimination System (NPDES) Program
Source: Scope and Framework of the NPDES Program. U.S. EPA. Overview of EPA, the Clean Water Act, and the National Pollutant Discharge Elimination System (NPDES) Program
Operators discharging
wastewater under a general permit submit a notice of intent (NOI) after the
general permit is issued, indicating their intent to be covered under the
general permit. In the case of an individual permit an operator is required to
apply for the permit at least 180 days before any there are any discharges into
the environment. EPA gives public notice of NPDES NOIs and permit applications
via notices in a major local newspaper, usually in the legal section of the
classified ads, or in an official publication such as the Federal Register.
The U.S. EPA
has different NPDES permits for different types of operations that produce
wastewater. There are different permits for animal feeding operations, publicly
owned treatment works, mining and manufacturing, new facilities, existing
facilities, process wastewater vs. non-process wastewater, stormwater
discharges associated with industrial activity, and new and existing operations
for treating domestic sewage.
NPDES Permit Administration by EPA or State Agency and
Water Quality Determination
The regulating
agency given authority, whether the U.S. EPA or the state agency, receives and
reviews the applications and NOIs, considering any recent rule updates or administrative
updates. Effluent limits are of two types and may change. The two types are technology-based
effluent limits (TBELs) and water quality-based effluent limits (WQBELs). These
are both considered for each discharge. A pre-permit inspection is typically done
after all of the permit or NOI information is submitted. The permits consider
federal effluent guidelines (FEGs). U.S. EPA developed TBELs for 58 industrial
sectors and these limits must be met without dilution from other waste streams.
WQBELs characterize both the effluent and the receiving waters. The waste load
is calculated to determine how much wastewater the receiving water can receive without
negatively affecting water quality. Thus, both the waste load and the condition
of the receiving water are considered in the permitting. The receiving water
may be a pond, lake, river, stream, shallow groundwater, or delineated wetland.
When there is insufficient data, the estimates are calculated conservatively.
If it is determined that TBELs are insufficient to prevent a harming level of
pollution, then WQBELs are utilized as the effluent limits. The U.S. EPA guidance
for states on water quality has three components:
• Magnitude—The level of pollutant (or pollutant
parameter), generally expressed as a concentration, that is allowable.
• Duration—The period of time (averaging period) over
which the instream concentration is averaged for comparison with criteria
concentrations.
• Frequency—How often criteria can be exceeded
These data may need to be determined in order to be considered.
EPA’s water quality is currently focused on 126 ‘priority toxic pollutants.’ Regulators
may apply both numeric criteria and narrative criteria to determine effluent limits for water quality. Numeric criteria are usually expressed in
the concentration of the pollutant in the wastewater or some similar
measurement. Narrative criteria are descriptions of the desired water quality goal.
Narrative criteria may be used when no numeric criteria have been established. WQBEL
variances may be granted to operations unable to fully comply if deemed
warranted.
WQBELs are an example
of a chemical-specific approach to water quality. Since
wastewater may have multiple toxic components, regulators may also consider a whole
effluent toxicity (WET) approach. This approach considers all the toxic
components of the wastewater as a whole. This approach also considers the effects
of the whole effluent on organisms. A third approach is a biological
approach, which is based on bioassessments that consider effects on the
receiving waters and its organisms such as toxicity. Monitoring and data
analysis may be used to determine whether there is a ‘reasonable potential’
to exceed applicable criteria (whether narrative or numerical). The table below
shows the strengths and limits of each of the three approaches and notes that
they can be combined into an integrated approach to water quality.
Projected
effluent quality (PEQ) is an estimate of treated wastewater quality before it’s
discharged into the environment. This is determined mathematically by plugging
numbers derived from gathered data into a formula then weighing them
statistically to arrive at the estimate. Some of the important variables in this
‘mass balance water quality equation’ are wastewater discharge flow rates and pollutant
concentrations, which together indicate the wastewater data component for
determining waste loading rate. The variables of the receiving water such as
flow rates, volume, composition, etc. are also considered in that
determination. The data are used to develop a Total Maximum Daily Load (TMDL)
for a pollutant. It is the maximum amount of pollutant allowable to prevent degradation
in water quality. Waters known to be impaired are required to have TMDLs for
pollutants established for them.
Some Household Sewage Treatment Systems Require NPDES
Permits
In rural areas, household sewage treatment systems, or septic systems, are very common. EPA regulates,
through state environmental agencies, larger sewage treatment systems and
certain household sewage treatment systems that are high risk with inadequate or
no soil absorption leach field treatment. These are covered under the domestic
sewage NPDES permit. Many of these older systems are grandfathered in and when
they need to be replaced the owners are permitted to do that with an NPDES regulated
system where the effluent is required to be sampled annually. This is the case
in Ohio, for example, where a general NPDES permit is issued for these systems.
Many of these samples of the discharged effluent still do not meet requirements
and with costs for sampling and testing the wastewater, some property owners ignore
and delay getting the required annual tests and paying for them. For most of
these systems, it is not practical or possible to replace them with less polluting
systems due to poor soil absorption qualities and/or lack of space for a
replacement system. In Ohio, these systems are required to be sampled annually. The
Ohio Health Department states on its website that:
“A homeowner that installs a replacement discharging
sewage treatment system, and in limited cases a new discharge on an existing
lot, must register for coverage under the general permit by submitting a notice
of intent to Ohio EPA along with a registration fee.”
Possible Future Changes in Water Quality Regulation
Water quality
standards are always changing as better scientific understanding arises. Three
areas where EPA is revising standards includes biological criteria, sediment
criteria, and wildlife criteria. Another that may emerge is numeric nutrient
criteria which considers the nutrients entering water bodies through sewage, agricultural
runoff, and other wastewater streams. Effects on organisms are considered in
biological criteria. Sediment criteria address the ability of sediment to receive,
concentrate, and re-release toxins back into the water. Wildlife criteria consider
the effect of polluted water on wildlife such as mammals and birds. Pollutant
effluent limits are also revised periodically. Reviews are either every 5 years
or every 3 years. Selenium, ammonia, cadmium, and mercury are examples of pollutants
with effluent levels that have been revised recently. When the effluent limits
change so do the allowable amounts of pollutants (TMDLs). For instance, in the late
1980s and 90s when allowable ammonia levels were lowered for wastewater
treatment plants, the rule resulted in improved water quality in Ohio’s large
rivers. Other things affecting those rivers that can be improved is better road
salt waste management and more removal of low-head, or low water dams.
Water and
wastewater reuse also has the potential to lead to better overall wastewater
management. Reuse for industrial process water for things like landscaping and irrigation
can have the effect of reducing potable water demand. Minerals, nutrients, and
energy can be extracted from wastewater inundated with sewage, industrial effluents,
or agricultural runoff. Biogas can be produced from wastewater treatment. Opportunities
to recover these from wastewater will no doubt grow in the future as we pursue
more functional circular economies. It is estimated that only about 11% of
wastewater globally is reused. This can grow significantly.
What is the Source of the Wastewater Covered by NPDES Permits?
The graph below from
2013 shows the wastewater sources by percentage of total volume. It shows that well
over half of the water under NPDES regulation is stormwater and most of that is
construction stormwater. The second graph shows the number of permits for different
types of facilities.
Source: Scope and Framework of the NPDES Program. U.S. EPA. Overview of EPA, the Clean Water Act, and the National Pollutant Discharge Elimination System (NPDES) Program
References:
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NPDES Overview: NPDES General Permit for Household Sewage Treatment Systems. Ohio Department of Health. NPDES Overview | Ohio Department of Health
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