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INNOVATIVE RESEARCH FOR A SUSTAINABLE FUTURE
FLOODPLAIN WASTE WATER RE-USE AND INDIRECT DISCHARGE
Wastewater Treatment Plants Using Indirect Discharge

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Figure 1: The distribution of wastewater treatment plants that discharge indirectly into floodplains across
the U.S. based on proximity to rivers and streams using data from three of the EPA's most recent voluntary
Clean Watersheds Needs Survevs.
Background
Communities across the nation are
implementing innovative approaches
to re-use and gain benefits from
discharged treated wastewater.
Typically, wastewater undergoes
primary and secondary treatment;
facilities may also utilize tertiary
treatment to reduce specific pollutants,
like nutrients. These treatment
methods ensure that effluent meets or
exceeds water quality standards prior
to discharge directly into rivers,
streams, or other receiving waters.
Alternatively, indirect discharge of
water is way to transport effluent over
land via open channels, often through
floodplains to streams, rivers, or other
water bodies. Permit standards for
effluent quality have traditionally been
designed for discharge directly into
flowing waters. Direct discharge
methods utilize a mixing zone where
some pollutants are diluted to
permissible concentrations. However,
some facilities request and receive
permits to indirectly discharge their
effluent over land to provide
environmental benefit from water re-
use.
To ensure safe water resources and
protect our nation's water from excess
pollution, research is ongoing to
evaluate and identify potential risks
and benefits of water re-use and
indirect discharge. Discharging over
land allows effluent to interact with
sediment plants, and the environment
where the water can support habitat or
ecosystems that need water. Given the
complexity of water movement and
chemical changes unique to over-land
discharge in floodplains, it is
important to understand how effluent
will move, change, and affect
groundwater and nearby water bodies.
Indirect Discharge
Potential benefits of indirect discharge
include increased availability of water
for habitat or irrigation, improved
water quality through plant uptake or
microbial reduction of pollutants, and
even recharge of depleting aquifers.
Because indirect discharge can
naturally reduce pollutants, indirect
discharge is sometimes compared to
expensive tertiary treatment methods.
Still, concerns over nutrient and metal
accumulation, as well as other
unforeseen contamination of soil and
groundwater make this an important
area of research to support existing
and future discharge decisions.
To understand how common indirect
discharge is and to evaluate the risk to
our nation's water, we must know
where and how frequently the method
is utilized. Currently, no public dataset
provides information on all
wastewater treatment plants, their
treatment level, and discharge method.
However, the EPA's Clean
Watersheds Needs Survey (CWNS)
provides valuable information on a
subset of publically owned treatment
works that are seeking funds from the
federal govermnent.
Across the United States
Using data from the CWNS between
2004 and 2012, we compared the
frequency and distribution of indirect
dischargers relative to direct
dischargers across the nation. We
show which of these facilities are
utilizing indirect discharge near rivers
and streams (within 100m; Figure 1).
The sites are nationally dispersed with
higher frequencies surrounding
metropolitan areas.
Approximately 3% of treatment plants
included in the CWNS utilized
indirect discharge (Figure 2). This
proportion remained relatively
constant accross the survey years. Of
those using indirect discharge, almost
none were noted as treating for
nutrient removal.
1
U.S. Environmental Protection Agency
Office of Research and Development

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Facilities Included in the Clean Watershed Needs Survey
By providing information on both
nutrient treatment and discharge
methods at the facilities, the CWNS
provides a snapshot of how indirect
discharge is utilized throughout the
U.S. Still, the voluntary nature of the
survey may include potential regional
or frequency biases in what was
reported. Nonetheless, in 2012, 51%
of all treatment plants were
represented in the CWNS when
compared to the EPA's Facility
Registry Service (FRS) which
compiles all facilities subject to
enviromnental regulation.
Current Research Efforts
EPA scientists from the Office of
Research and Development are
studying the use of inland floodplains
as natural green infrastructure (GI) for
wastewater management, including an
evaluation of how natural GI, like
indirect discharge practices, influence
water quality.
Some of this work is being conducted
on the Yakima River floodplain in
Washington state, where researchers
are working with the City of Yakima
to evaluate how groundwater and
surface water quality responds to
indirect discharge on a newly restored
floodplain.
To examine the effects of indirectly
discharging treated effluent for
beneficial irrigation in a fanned
floodplain, scientists are working with
agricultural researchers in Chickasha,
Oklahoma. Soil, surface water, and
groundwater will be examined to
evaluate the potential risks for
contamination of receiving waters
when effluent is used to grow crops.
Some of the data gaps highlighted by
the CWNS are being addressed by the
EPA Office of Water's National Study
of Nutrient Removal and Secondary
Technologies. A survey to gather
basic information on discharge
procedures and nutrient removal from
all treatment works in the U.S. with a
National Pollutant Discharge
Elimination System (NPDES) permit
is in development. The new survey
will create a valuable dataset, enabling
a more comprehensive assessment of
wastewater treatment and effluent
quality in the U.S.
Nutrient Treatment
| None
¦	p
N
N and P
¦	NorP
Direct Indirect Other
Direct Indirect Other NA
Discharge Method
Direct Indirect Other
Figure 2: The number of wastewater treatment plants discharging directly into streams or rivers, indirectly into
floodplains, using other methods or not reporting their discharge method, according to data from the EPA's
most recent Clean Watersheds Needs Surveys. Few of the facilities using indirect discharge methods treated
effluent to remove nitrogen (N) or phosphorus (P).
The CWNS survey is a useful tool to
understand how effluent is managed
across the country. The survey collects
information on discharge method, but
it does not distinguish between
different reuse applications and
disposal methods or include treatment
plants that rely solely on land
application that are not point sources
or require a NPDES permit. However,
by using the existing survey results we
can better understand patterns and
anticipate research needs.
These efforts are important starts to
evaluate risks to different natural
resources and water, but continued
effort is needed to create a
comprehensive evaluation of indirect
dischargers across the nation.
Future Objectives
While we know that indirect discharge
to floodplain river systems can
provide many important benefits, few
studies have shown how these
practices stand up to risks over time
and space. Pollutants from effluent
such as nutrients, heavy metals,
pharmaceuticals, and organic
wastewater compounds can
accumulate in water and soil, affecting
human and ecosystem health.
Because many enviromnental factors
influence pollutants, their effects will
be evaluated to assess long-term
ecosystem and health risks.
Data collected from this and future
research efforts will continue to provide
a stronger foundation for assessing the
benefits and risks associated with the
use of wastewater effluent in floodplains
and other inland systems. These
research efforts are critical to help
support our obligation to sustain
protect, and preserve clean water across
the Nation.
DISCLAIMERS: This document has been
reviewed in accordance with U.S. Environmental
Protection Agency policy and approved for
publication. The data and information presented in
this document have been assessed by the EPA for
this work. However, neither EPA, EPA
contractors, nor any other organizations
cooperating with the EPA are responsible for
inaccuracies in the original data that may be
present.
REFERENCES:
EPA: Clean Watershed Needs Survey (2004, 2008, 2012)
https: //www. ep a. gov/ c wns
EPA: Nutrient Innovations Task Group. Report of the
State, An Urgent Call to Action (Aug 2009).
https://www.epa.gov/sites/production/flles/documents/nit
greport.pdf
EPA: National Study of Nutrient Removal and Secondary
Technologies, https://www.epa.gov/eg/national-study-
nutrient-removal-and-secondary-
techno logies#background
CONTACT INFORMATION:
Ken Forshay, Ph.D., Research Ecologist, EPA Office of
Research and Development. 580-436-8912,
F orshay. Ken@epa. gov
Shannon Donohue, Research Assistant, Oak Ridge
Affiliated Universities at the EPA Office of Research and
Development
Doug Beak, Ph.D., Geologist, EPA Office of Research
and Development
Charlotte Narr, Ph.D., Postdoctoral Research Associate,
National Research Council at the EPA Office of Research
and Development
2
U.S. Environmental Protection Agency
Office of Research and Development

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