A EPA COMPLIANCE ADVISORY -SKSSKSKK
Reducing Significant Non-Compliance with National Pollutant Discharge Elimination System Permits
EPA Document # 305F21001	April 2021
Compliance Tips for Small, Mechanical Wastewater
Treatment Plants
Background on this Compliance Advisory
This advisory is directed to owners and operators of small publicly owned
wastewater treatment works (POTWs) and small private wastewater
treatment plants, both commonly referred to as wastewater treatment plants
(VWVTPs). It is intended to provide small VWVTPs with information that will
help them comply with their National Pollutant Discharge Elimination System
(NPDES) permit effluent limits. Smaller VWVTPS are a particular focus of an
EPA National Initiative to reduce significant non-compliance (SNC) because
60% of recent NPDES SNC violations occurred at these facilities. EPA
reminds VVWTP operators of their responsibility to fully comply with their
NPDES permits, and that compliance assistance is available. As a result of
EPA's focus in this important area, NPDES permittees, regardless of facility
size or type, will see EPA and states putting increased emphasis on
identifying, addressing and resolving SNC violations using enforcement and
other compliance tools. Note that, while this alert focuses on operational issues, some operators of small mechanical
VWVTPs are also failing to submit required discharge monitoring reports (DMRs), or are submitting incomplete or
inaccurate DMRs that can mask serious violations If you are having trouble completing or submitting your DMRs, contact
your permitting authority and request assistance. Increased compliance will improve surface water quality and reduce
potential impacts on drinking water supplies. For more information about EPA's efforts to reduce SNC,
+see: Reducing Significant Non-Compliance with National Pollutant Discharge Elimination System (NPDES)
Permits.
Surface Water Pollution from Small WWTPs
Pollutants commonly discharged by small VWVTPs at SNC violation levels include oxygen-demanding substances (e.g.,
biochemical oxygen demand (BOD), chemical oxygen demand (COD)), total suspended solids (TSS), pathogens (i.e.,
fecal coliform/E. coli), nutrients, and total residual chlorine. The tables included below provide information on violation
causes and potential solutions. Table 1 (below) starts by outlining some common issues experienced at VWVTPs that can
cause serious permit limit exceedances.
Table 1. WWTP Processes and Common Issues
WWTP Process
Common Issues That Can Lead to Noncompliance
Primary Treatment
(solids settling and
sludge removal)
>	Bar screen broken
>	Clarifier/sedimentation tanks out of service
>	Short circuiting of wastewater flow
>	Broken/uncalibrated process controls
Secondary
Treatment
>	Inadequate retention time and pH buffering (alkalinity), low food to mass
ratio, low soluble BOD (low influent loading)
>	Insufficient aeration/dissolved oxygen
>	Inadequate process control tools and methods
>	Clarifiers out of service
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(conversion of
pollutants into less
noxious substances)
> Solids loss from clarifiers
Tertiary Treatment
(filtration)
>	Filters (clogged) bound by sludge
>	Hydrogen sulfide generation in the carbon contactor
Disinfection
Chlorine
UV
>	No chlorine
>	No dechlorination
>	Chlorine contact tank full of biological solids
>	Poor effluent transmittance
>	Build-up of scale on bulbs
>	Electricity is off
Common Underlying Causes of Effluent Violations at Small WWTPs
Small systems often have difficulty keeping trained operators and obtaining adequate funding for operations,
maintenance, and system upgrades needed to achieve and maintain compliance. Table 2 can serve as a critical starting
point for identifying solutions to common causes of effluent violations. (Before making any major process or operation and
maintenance changes, operators are advised to check with their permitting authority.)
Table 2. Effluent Violations at Small WWTPs: Root Causes and Potential Solutions
Topic
Common Root Causes
Recommended Potential Solutions
Resource
scarcity
Resource scarcity may
involve one or more of the
following conditions:
>	Inadequate funding or
community commitment
to make resources
available for infrastructure
upgrades and/or
maintenance.
>	inadequate funds or
ability to hire and retain
certified operators.
>	inadequate funds to hire
contract wastewater
engineers to provide
operational oversight.
>	Lack of public awareness
of the need to invest in
infrastructure upgrades
and/or maintenance.
>	Operators are not given
the resources needed to:
purchase process control
testing equipment,
treatment chemicals or
haul sludge.
»
»

For help and information on
funding sources, such as loans,
grants, accessing State Revolving
Funds, bonds, etc., contact your
local Environmental Finance
Center.
Determine if user fees need to be
increased to cover operation,
maintenance, and replacement
costs of treatment equipment.
Use asset management to pursue
and achieve sustainable
infrastructure. Draft
budget based upon
Asset Management
»
Encourage best planning and management practices by
implementing Capacity, Management. Operation and
Maintenance (CMOM) programs.
Explore the Water Finance Clearinghouse.
Educate municipal leadership.
Engage the public by conducting public outreach and
education on benefits and true costs of wastewater
collection, transmission, and treatment. Develop an insert
for the wastewater billing or post information on the utility's
website.
Operation
Problems
Jr Operator error is often
due to lack of training or
being over-extended.
Ir Errors may also occur
when written standard
>	Seek training among the many low or no cost online
sources, such as WaterOperator.org - Process Control
Resources.
>	Join listservs and organizations that conduct training such
as U.S. EPA NPDES Traininc, your state permitting
a wastewater
proper operations and maintenance:
for Water and Wastewater Utilities.
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Table 2. Effluent Violations at Small WWTPs: Root Causes and Potential Solutions
Topic
Common Root Causes
Recommended Potential Solutions
operating procedures
(SOPs) and documented
operational data are not
available or are not
implemented.
>	Plant configuration may
lack operational flexibility.
>	Operational issues, such
as manifold blower(s)
used to run all air
components and cycled
on and off to optimize
biological treatment; airlift
return activated sludge
(RAS) pumps are out of
service.
>	Operators may need
more training on activated
sludge process control
and troubleshooting,
which is critical to
compliance.
»
»
1
agency, professional associations such as Association of
Clean Water Administrators (ACVVA), Water Environment
Federation (WEF), National Association of Clean Water
Agencies (NACWA), American Water Works Association
(AWWA) or your local technical assistance providers like
Rural Community Assistance Partnership (RCAP) and the
National Rural Water Association (NRWA),
Seek collaboration with neighboring operators with similar
conditions or process units. Consult with your state or
EPA Region, who can use an ECHO-gov CWA NPDES
National POTW Pairing Dashboard to help put you in
touch with operators at similarly sized plants that are
successfully meeting their effluent limits.
Develop written SOPs using resources at WEF.org or EPA
Guidance for Preparing SOPs.
Seek training on troubleshooting: Troubleshooting
Noncompliance at the Smallest Wastewater Treatment
Plants: Part I and Troubleshooting Noncompliance at the
Smallest Wastewater Treatment Plants: Part II.
Lack of operator training
on its use, failure to follow
best management
practices, or lack of
Equipment	preventative maintenance
failure	planning and/or
implementation.
> Improper design
installation, and/or
construction.
>	Seek lessons learned from other operators of new
systems.
>	Find training on best practices for operating and
maintaining treatment systems with new technology.
>	Develop an asset management system that incorporates
operation and maintenance plans and tracks equipment
that may be nearing end of life and will require capital
investment: Developing an Asset Management Program.
>	Encourage best planning and management practices by
implementing Capacity, Management, Operation and
Maintenance (CMOM) programs.
Significant
changes in
system
influent
volume or
strength
>	Changes to the influent
volume and strength are
influenced by increased
or decreased population,
new or fewer industrial
users, or excessive wet or
dry weather.
>	Widespread
implementation of low-
flow fixtures can also
contribute to reduced
influent volume.
> Provide education about regionalization: Consolidation of
Water and Wastewater Systems: Options and
Considerations.
For
communities
that have a
decreased
population:
>	Seek
technical
assistance
and
evaluate
how
current
system can be modified to effectively treat the current
influent level and strength.
>	Hire an engineer:
http://wateroperator.Org/Portals/1/Documents/10112.pdf
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Table 2. Effluent Violations at Small WWTPs: Root Causes and Potential Solutions
Topic
Common Root Causes
Recommended Potential Solutions
For communities that have increased population:
>	Seek education on financing for expansion and new
technology: contact your local Environmental Finance
Center.
If the plant design includes flexibility, there are operation
techniques that can expand capacity to treat high strength flow
and wet weather flow such as step feeding for high strength
waste streams and contact stabilization for wet weather flows.
For systems that have new or increased flow from industrial
users:
>	Establish a jretreatment program and revise the sewer
use ordinance.
>	Reduce influent strength by implementing septic hauling
for a portion of the wastewater.
Pass-through
and
interference
>	Pass-through and
interference from
industrial users and
institutions (high strength
or non-compatible
influent) can cause or
contribute to effluent
violations.
>	Small plants that accept
septage may experience
resultant effluent
violations.
»
effective municipal
level Enforcement
>
>
Design flaws
Plants may have design
issues:
>	With parallel treatment
trains, the flow splitting
may be poor.
>	Plant was designed using
a textbook number for
raw sewage composition,
which may lead to
unnecessarily high
capacity.
>	Lack of operational
flexibility such as airlift
pumps that cannot be
turned down; insufficiently
sized sludge holding
tanks.
»
Promote the use of operations manuals rather than
engineering manuals (e.g., Design Standards: Wastewater
Treatment Plants & Collection Systems < 100.000 gpd).
Adjust valves to improve splitting.
Explore operational changes to limit the effects of the
design flaws.
Take treatment units out of service during periods of low
loading.
In municipalities without a pretreatment program, consider
establishing a program )retreatment program.
Revise and enforce the sewer use ordinance.
Seek training for states
and municipalities on
pretreatment program
implementation,
including handling of
slug loads.
Conduct outreach on
Response Plans
(escalation of enforcement response against non-
complying Industrial Users).
Conduct an inventory of WWTPs and industrial users to
target likely impacts.
Implement best practices for sampling and treating
septage: Septage Management.
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Compliance and Financing Assistance Resources
In addition to the resources listed in Table 2, the following resources can help you correct violations and achieve
compliance.
Compliance Assistance Resources
P Reducing Significant Non-Compliance (SNC) with NPDES Permits - Resources for NPDES Permittees and Other
Organizations (https://www.epa.aov/enforcement/national-compliance-initiative-reducing-siqnificant-non-compliance-
snc-npdes-perm its')
P EPA Small and Rural Wastewater Systems Website and Tools (https://www.epa.gov/small-and-rural-wastewater-
svstems/tools-traininq-and-technical-assistance-small-and-rural)
S* WaterOperator.org is a free training resource portal for operators of small
systems
>	Rural Community Assistance Partnership Website
(https://www.rcap.org/)
S* National Rural Water Association Website (nrwa.org)
>	EPA National Pollutant Discharge Elimination System Website
(https://www.epa.gov/npdes/nationai-pretreatment-program-events-training-and-publications)
>	Activated Sludge Process Control and Troubleshooting Training Manual and Chart Methodology
(https://epa.ohio.gov/Portals/29/documents/CAU/Activated%20Sludge%20Process%20Control%20and%20Troublesh
ooting%20Manual.pdf)
>	NetDMR Support Portal (https://netdmr.zendesk.com/hc/en-us)
Potential Funding and Financing Sources
>	Funding Sources for Small and Rural Wastewater Systems (https://www.epa.gov/small-and-rural-wastewater-
systems/funding-sources-small-and-rural-wastewater-systems)
>	EPA Water Infrastructure and Resiliency Finance Center (https://www.epa.gov/waterfinancecenter/efcn)
>	Clean Water State Revolving Funds (www.epa.gov/cwsrf)
General References
§" U.S. EPA, 1998, How Wastewater Treatment Works... The Basics (EPA/833/F-98/002). Office of Water, Washington,
D.C. (https://www3.epa.gov/npdes/pubs/bastre.pdf)
§" U.S. EPA, 2004, Primer for Municipal Wastewater Treatment Systems (EPA/832/R-048/001). Office of Water,
Washington, D.C. (https://www3.epa.gov/npdes/pubs/primer.pdf)
Disclaimer
This Compliance Advisory addresses select provisions of EPA regulatory requirements using plain language. Nothing
in this Compliance Advisory is meant to replace or revise any NPDES permit, any EPA regulatory provision, or any
other part of the Code of Federal Regulations, the Federal Register, or the Clean Water Act. EPA recommends that
operators consult with their permitting agency prior to making major changes to their systems.
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