vvEPA
United States
Environmental Protection
Agency
Study of the Agricultural and Wildlife Water
Use Subcategory (40 CFR 435 Subpart E)
April 2025
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U.S. Environmental Protection Agency
Office of Water (4303T)
1200 Pennsylvania Avenue, NW
Washington, DC 20460
EPA-820-R-25-004
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Contents
1. Introduction and Summary 1
2. Existing Effluent Limitations Guidelines for Oil and Gas Extraction and Subpart E Requirements 3
2.1 Clean Water Act 3
2.1.1 Types of ELGs 3
2.1.1.1 Best Practicable Control Technology Currently Available 4
2.1.1.2 Best Available Technology Economically Achievable 4
2.1.1.3 New Source Performance Standards 4
2.1.1.4 Pretreatment Standards for Existing Sources 4
2.1.1.5 Pretreatment Standards for New Sources 5
2.2 Oil and Gas Extraction Effluent Guidelines 5
3. Industry Profile 7
3.1 Summary of Permits 7
3.1.1 Description of State Issued Permits 7
3.1.1.1 California 7
3.1.1.2 Colorado 7
3.1.1.3 Texas 8
3.1.1.4 Utah 9
3.1.1.5 Wyoming 9
3.1.1.6 Montana 10
3.1.1.7 New Mexico 10
3.1.2 Description of Federally Issued Permits 11
3.1.2.1 EPA Region 8 11
3.1.2.2 EPA Region 9 12
3.1.3 Variability across permits 12
3.2 Company Information 13
3.2.1 Supermajor, Major, and Independent 13
3.2.2 Upstream, Midstream, and Downstream 14
3.2.3 Oil and Gas Companies in Major Production Basins West of the 98th Meridian 14
3.2.3.1 Permian 14
3.2.3.2 Williston 14
3.2.3.3 Denver-Julesburg 14
3.3 Oil and Gas Production for Existing Subpart E Permittees 14
4. Produced Water Characterization 17
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4.1 Produced Water Volumes 17
4.2 Discharge Volume Data 17
4.3 Discharge Constituent Data 19
4.3.1 Discharge Monitoring Reports 19
4.3.2 FracFocus 20
4.3.3 Reported Substances Used in Hydraulic Fracturing 21
5. Environmental Assessment 24
5.1 Produced Water Discharges to Surface Water 24
5.1.1 Immediate Receiveing Waters of Produced Water Discharges 24
5.1.2 Impairment Status of Immediate Receiving Waters of Produced Water Discharges 25
5.1.3 Environmental and Human Health Impacts Associated with Produced Water Discharges ...26
5.1.3.1 Aquatic Organism and Ecosystem Impacts 27
5.1.3.2 Terrestrial Organism and Ecosystem Impacts 32
5.1.3.3 Human Health Impacts 37
6. Produced Water Treatment Technologies 41
6.1 Technologies at Current Subpart E Sites in Wyoming 41
6.2 Pilot Treatment Systems 43
7. References 47
List of Figures
Figure 1. Map of 98th Meridian 6
Figure 2. Constituent Concentrations in Wyoming Subpart E Discharges from DMRs (2021 - 2023) 20
Figure 3. Receiving Waters Listed in DMRs with Discharges of Produced Water from Subpart E Oil and Gas
Facilities in Wyoming 25
Figure 4. Schematic of a Typical Heater Treater 41
Figure 5. Typical Skim Pond with Bird Netting at a Wyoming Production Site 42
Figure 6. Sulfides Treatment Basin at a Wyoming Production Site 42
Figure 7. Typical NPDES Subpart E Outfall in Wyoming 43
Figure 8. Permian Basin Produced Water Characterization Data (Xu 2022) 44
Figure 9. Texas Pacific Water Resources Pilot Treatment Train 45
Figure 10. Texas Pacific Water Resources Pilot Treatment Schematic 46
List of Tables
Table 1. Reported Oil and Gas Production for NPDES Permittees in Wyoming in 2023 15
Table 2. Estimated Produced Water and Hydrocarbon Production in Select States (2021) 17
Table 3. Estimated Subpart E Produced Water Discharge by Company in Wyoming 18
Table 4. Number of FracFocus Disclosures by State 21
Table 5: Lists of Compounds Used Nationwide in Hydraulic Fracturing 22
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Abbreviations
API
American Petroleum Institute
ATTAINS
Assessment and Total Maximum Daily Load Tracking and Implementation System
BADCT
Best Available Demonstrated Control Technology
BAF-UF
Biologically Active Filtration - Ultrafiltration
BAT
Best Available Technology
BBL
Barrel (measure of oil and produced water volume)
BPJ
Best Professional Judgment
BOD
Biochemical Oxygen Demand
BPT
Best Practicable Control Technology
Bq/kg
Becquerel per kilogram
CAS
Chemical Abstracts Service
CDPHE
Colorado Department of Public Health & Environment
COMID
Common Identifier
COWDF
Commercial Oilfield Wastewater Disposal Facility
CWA
Clean Water Act
CWT
Centralized Waste Treatment
CWTF
Commercial Wastewater Treatment Facility
DBP
Disinfection Byproducts
DMR
Discharge Monitoring Report
ELG
Effluent Limitations Guidelines
EROD
Ethoxyresorufin-O-deethylase
GWPC
Ground Water Protection Council
IARC
International Agency for Research on Cancer
IOGCC
Interstate Oil and Gas Compact Commission
Mcf
Thousand cubic feet (measure of gas production)
MSDS
Material Safety Data Sheet
NHD
National Hydrography Dataset
NOI
Notice of Intent (to discharge)
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NPDES
National Pollutant Discharge Elimination System
NSPS
New Source Performance Standards
PAH
Polycyclic Aromatic Hydrocarbon
PEG
Polyethylene Glycol
PFAS
Per- and Polyfluoroalkyl Substances
POTW
Publicly Owned Treatment Works
PSES
Pretreatment Standards for Existing Sources
PSNS
Pretreatment Standards for New Sources
RN
Registry Number
SDS
Safety Data Sheet
TBEL
Technology-Based Effluent Limitation
TCEQ
Texas Commission on Environmental Quality
TDS
Total Dissolved Solids
THM
Trihalomethane
TSS
Total Suspended Solids
USFWS
United States Fish and Wildlife Service
USGS
United States Geological Survey
VOCs
Volatile Organic Compounds
WET
Whole Effluent Toxicity
WOGCC
Wyoming Oil and Gas Conservation Commission
WOTUS
Waters of the United States
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1. Introduction and Summary
This report presents the findings of the Environmental Protection Agency (the EPA) study of discharges of
produced water from oil and gas extraction activities under 40 CFR 435 Subpart E. The report was
prepared by the EPA staff in the Office of Water, Regions 4, 6, and 8, and the Office of Research and
Development. The EPA regulates discharges of wastewater from industrial categories to surface waters
through effluent limitations guidelines (ELGs) pursuant to the Clean Water Act (CWA). See CWA sections
301, 304, and 306, 33 U.S.C. 1311, 1314 and 1316. These technology-based regulations are incorporated
into National Pollutant Discharge Elimination System (NPDES) permits.
The regulations at 40 CFR 435 Subpart E allow for discharge of produced water from onshore facilities
into navigable waters west of the 98th meridian if the produced water is of good enough quality for use in
agriculture or wildlife propagation and the produced water is actually put to such use during periods of
discharge. These onshore facilities are engaged in the production, drilling, well completion, and well
treatment in the oil and gas extraction industry. The EPA promulgated the Subpart E regulations in 1979.
Many changes have occurred in the oil and gas industry since that time. This study evaluates whether
there are available and economically achievable treatment technologies that can reduce the discharge of
pollutants from this industry. It also informs whether updates to the Subpart E regulations may be
warranted.
The EPA periodically reviews the existing ELG regulations and updates them, as appropriate. The ELG
Program Plan, published every two years, identifies existing industries selected for regulatory revisions
and new industries identified for regulation. The ELG Plan provides a rulemaking schedule for any such
activities.
This study does not announce any regulatory actions regarding 40 CFR 435 Subpart E. Readers should
consult the latest ELG Program Plan and supporting documentation to obtain information regarding the
EPA's planned ELG regulatory decisions (see https://www.epa.gov/eg/effluent-guidelines-plan).
The EPA's study found the following:
The EPA identified 188 existing NPDES individual permits for facilities under Subpart E. An additional 6
facilities are covered under a general permit.
Most of the existing Subpart E permitted facilities are located in Wyoming. Second to Wyoming, Colorado
has the next most existing Subpart E permitted facilities. The EPA is aware of one Subpart E NPDES permit
that has been issued in California, Texas, and Utah, respectively. There are also several permit
applications for discharge that have been submitted to regulatory agencies in Texas and New Mexico as
of March 2024.
The companies that currently hold Subpart E NPDES permits range in size from small entities that employ
just a few people and produce a few thousand barrels of oil per year, to large corporations that produce
millions of barrels of oil and millions of cubic feet of gas with hundreds of millions to billions of dollars in
revenue and thousands of employees.
The typical pollutants that are regulated in existing Subpart E NPDES permits include oil and grease, total
dissolved solids (TDS), chloride, sulfate, specific conductance and total radium 226.
Subpart E facilities that the EPA visited during this study utilize chemicals such as emulsion breakers,
corrosion inhibitors, scale inhibitors, water clarifiers, and biocides to aid in oil recovery and to reduce
bacteria growth and scaling in wells and in oil and produced water separation, collection, and distribution
equipment. In some cases, these chemicals are added to the produced water just upstream of the
discharge.
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Subpart E facilities typically use oil water separation and skim pits/ponds to treat produced water. Some
facilities employ aeration for sulfide reduction. The EPA is aware of one existing facility that plans to
utilize reverse osmosis membrane filtration, with additional pretreatment steps to prevent membrane
fouling.
Since produced water in the Permian basin contains significant quantities of salts, as well as pollutants
such as ammonia that can be toxic to aquatic organisms, it is expected that technology used to treat
Permian basin produced waters to discharge quality will be different than what is typically used for
existing Subpart E dischargers in other basins. This is reflected in the pilot treatment systems that are
being tested in the Permian and in the permit applications for these produced waters.
There are a number of pilot-scale treatment systems being tested on Permian Basin produced water. The
EPA expects that data from these pilot projects will be available throughout 2025 and beyond.
The EPA identified research that indicates the potential for adverse environmental and health impacts
(carcinogenic and non-carcinogenic) when aquatic organisms (e.g., fish, shellfish, and amphibians),
terrestrial organisms (e.g., livestock and birds), and humans are exposed to produced water from the oil
and gas extraction industry. While there are few studies that have evaluated these effects in current
Subpart E discharges, the findings do reinforce the need for treatment of produced water prior to
discharge to the environment.
In aquatic organisms, health impacts associated with exposure to produced water include changes in
cardiac function, metabolic processes, hormone levels, cell viability, development, and immune function.
For terrestrial organisms, health impacts associated with exposure include sudden death and
reproductive, neurological, gastrointestinal, musculoskeletal, and upper respiratory issues, as well as
hypothermia and drowning in birds.
In humans, exposure to produced water is associated with the increased risk of cancers, such as leukemia,
lymphoma, and bladder cancer, and neurological, respiratory, vascular, dermatological, and
gastrointestinal health issues, as well as birth defects in children.
The environment can be adversely impacted by produced water due to alterations in the composition and
function of microbial communities in water and soil, reduced growth and bioaccumulation of toxins in
crops, accumulation of toxins in soil and sediment, and soil sodification1.
Stakeholders have indicated that with proper treatment and risk management, produced water can
potentially be used to augment conventional water supplies for human and environmental end uses,
particularly in the more arid Western U.S. where a significant amount of oil and gas production occurs
1 Sodification refers to a process where soil becomes saturated with sodium ions. The accumulation of sodium ions
in soil impacts the soil's physical and chemical properties and can lead to a loss of soil fertility and reduced plant
growth.
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2. Existing Effluent Limitations Guidelines for Oil and Gas
Extraction and Subpart E Requirements
2.1 Clean Water Act
Congress passed the Federal Water Pollution Control Act Amendments of 1972, also known as the Clean
Water Act (CWA), to "restore and maintain the chemical, physical, and biological integrity of the Nation's
waters." 33 U.S.C. 1251(a). The CWA establishes a comprehensive program for protecting our nation's
waters. Among its core provisions, the CWA prohibits the discharge of pollutants from a point source to
waters of the United States (WOTUS), except as authorized under the CWA. Under section 402 of the
CWA, discharges may be authorized through a National Pollutant Discharge Elimination System (NPDES)
permit. The CWA also authorizes the EPA to establish nationally applicable, technology-based ELGs for
discharges from different categories of point sources, such as industrial, commercial, and public sources.
Furthermore, the CWA authorizes the EPA to promulgate nationally applicable pretreatment standards
that restrict pollutant discharges from facilities that discharge wastewater to WOTUS indirectly via
publicly owned treatment works (POTWs), as outlined in CWA sections 307(b) and (c), 33 U.S.C. 1317(b)
and (c). The EPA establishes national pretreatment standards for those pollutants in wastewater from
indirect dischargers that may pass through, interfere with, or are otherwise incompatible with POTW
operations. Pretreatment standards are designed to ensure that wastewaters from direct and indirect
industrial dischargers are subject to similar levels of treatment. In addition, POTWs are required to
implement treatment limitations applicable to their industrial indirect dischargers to satisfy any local
requirements.
Direct dischargers (i.e., those discharging directly from a point source to surface waters rather than
through POTWs) must comply with effluent limitations in NPDES permits. Discharges that flow through
groundwater before reaching surface waters must also comply with effluent limitations in NPDES permits
if those discharges are the "functional equivalent" of a direct discharge from a point source to a WOTUS.
Indirect dischargers, who discharge through POTWs, must comply with pretreatment standards.
Technology-based effluent limitations (TBELs) in NPDES permits are derived from ELGs (CWA sections 301
and 304, 33 U.S.C. 1311 and 1314) and new source performance standards (CWA section 306, 33 U.S.C.
1316) promulgated by the EPA, or based on best professional judgment (BPJ) where the EPA has not
promulgated an applicable effluent guideline or new source performance standard (CWA section
402(a)(1)(B), 33 U.S.C. 1342(a)(1)(B); 40 CFR 125.3(c)). Additional limitations based on water quality
standards are also required to be included in the permit in certain circumstances (CWA section
301(b)(1)(C), 33 U.S.C. 1311(b)(1)(C); 40 CFR 122.44(d)). The EPA establishes ELGs by regulation for
categories of point source dischargers, and these ELGs are based on the degree of pollution control that
can be achieved using various levels of pollution control technologies.
The EPA promulgates national ELGs for major industrial point source discharger categories for three
classes of pollutants: (1) conventional pollutants (i.e., total suspended solids (TSS), oil and grease,
biochemical oxygen demand (BOD5), fecal coliform, and pH), as outlined in CWA section 304(a)(4) and 40
CFR 401.16; (2) toxic pollutants (e.g., toxic metals such as arsenic, mercury, selenium, and chromium;
toxic organic pollutants such as benzene, benzo-a-pyrene, phenol, and naphthalene), as outlined in
section 307(a) of the Act, 40 CFR 401.15 and 40 CFR part 423, appendix A; and (3) nonconventional
pollutants, which are those pollutants that are not categorized as conventional or toxic (e.g., ammonia-
nitrogen, per- and polyfluoroalkyl substances (PFAS), total dissolved solids (TDS)).
2.1.1 Types of ELGs
The EPA develops technology-based ELG regulations based on the performance of control and treatment
technologies. The legislative history of CWA section 304(b), which is the heart of the ELG program,
describes the need achieve higher levels of pollutant control through research and development of new
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processes, modifications, replacement of obsolete plants and processes, and other improvements in
technology, while also accounting for the cost of pollutant controls. Legislative history and case law
support that the EPA need not consider water quality impacts on individual water bodies as ELGs are
developed.
There are many TBELs that may apply to a discharger under the CWA. As discussed below, there are four
types of standards applicable to direct dischargers and two types of standards applicable to indirect
dischargers.
2.1.1.1 Best Practicable Control Technology Currently Available
Traditionally, the EPA defines Best Practicable Control Technology (BPT) effluent limitations based on the
average of the best performances of facilities within the industry, grouped to reflect various ages, sizes,
processes, or other common characteristics. The EPA may promulgate BPT limitations for conventional,
toxic, and nonconventional pollutants. In specifying BPT, the EPA considers several factors: the cost of
achieving effluent reductions in relation to the effluent reduction benefits, the age of equipment and
facilities, the processes employed, engineering aspects of the control technologies, any required process
changes, non-water quality environmental impacts (including energy requirements), and such other
factors as the Administrator deems appropriate. If, however, existing performance is uniformly
inadequate, the EPA may establish limitations based on higher levels of control than what is currently in
place in an industrial category, when based on an agency determination that the technology is available in
another category or subcategory and can be practicably applied.
2.1.1.2 Best Available Technology Economically Achievable
The Best Available Technology (BAT) represents the second level of stringency for controlling the direct
discharge of toxic and nonconventional pollutants. Courts have referred to this as the CWA's "gold
standard" for controlling discharges from existing sources. In general, BAT represents the best available,
economically achievable performance of facilities in the industrial subcategory or category. As the
statutory phrase intends, the EPA considers the technological availability and the economic achievability
when determining what level of pollution control represents BAT. Other statutory factors that the EPA
considers in assessing BAT are the cost of achieving BAT effluent reductions, the age of equipment and
facilities involved, the process employed, potential process changes, and non-water quality
environmental impacts, including energy requirements, and such other factors as the Administrator
deems appropriate. The Agency retains considerable discretion in assigning the weight to be accorded
these factors. The EPA usually determines economic achievability based on the effect the cost of
compliance with BAT limitations has on overall industry and subcategory financial conditions.
BAT reflects the highest performance in the industry and may reflect a higher level of performance than is
currently being achieved based on technology transferred from a different subcategory or category,
bench scale or pilot plant studies, or plants located in foreign countries. BAT may be based upon process
changes or internal controls, even when these technologies are not common industry practice.
2.1.1.3 New Source Performance Standards
New Source Performance Standards (NSPS) reflect effluent reductions that are achievable based on the
Best Available Demonstrated Control Technology (BADCT). Owners of new facilities have the opportunity
to install the best and most efficient production processes and wastewater treatment technologies. As a
result, NSPS should represent the most stringent pollutant controls attainable through the application of
the BADCT for all pollutants (that is, conventional, nonconventional, and toxic pollutants). In establishing
NSPS, the EPA is directed to take into consideration the cost of achieving the effluent reduction and any
non-water quality environmental impacts and energy requirements.
2.1.1.4 Pretreatment Standards for Existing Sources
The CWA calls for the EPA to issue pretreatment standards for discharges of pollutants to POTWs.
Pretreatment standards for existing sources (PSES) are designed to prevent the discharge of pollutants
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that pass through, interfere with, or are otherwise incompatible with the operation of POTWs.
Categorical pretreatment standards are technology-based and are analogous to BPT and BAT; thus, the
Agency typically considers the same factors in promulgating PSES as it considers in promulgating BAT. The
General Pretreatment Regulations, which set forth the framework for the implementation of categorical
pretreatment standards, are found at 40 CFR part 403. These regulations establish pretreatment
standards that apply to all non-domestic dischargers.
2.1.1.5 Pretreatment Standards for New Sources
Section 307(c), 33 U.S.C. 1317(c), of the CWA calls for the EPA to promulgate Pretreatment Standards for
New Sources (PSNS). Such pretreatment standards must prevent the discharge of any pollutant into a
POTW that may interfere with, pass through, or may otherwise be incompatible with the POTW. The EPA
promulgates PSNS based on BADCT for new sources. New indirect dischargers have the opportunity to
incorporate into their facilities the BADCT. The Agency typically considers the same factors in
promulgating PSNS as it considers in promulgating NSPS.
2.2 Oil and Gas Extraction Effluent Guidelines
The EPA first developed the oil and gas extraction effluent guidelines in the 1970's. In 1979, regulations
promulgating BPT limitations for the offshore (Subpart A), onshore (Subpart C), coastal (Subpart D) and
agricultural and wildlife water use subcategories (Subpart E) were finalized (see 44 FR 22069, April 13,
1979). A 1993 amendment promulgated BAT, BCT and NSPS requirements for offshore facilities (see 58
FR 12454, March 4, 1993). In 1996, an amendment was published that added BAT, BCT, NSPS, PSES, PSNS,
and revised BPT limitations for coastal facilities (see 61 FR 66086, December 16, 1996). A 2001
amendment added requirements for the discharge of synthetic-based drilling fluids and other non-
aqueous drilling fluids in certain coastal and offshore waters (see 66 FR 6850, January 22, 2001). A 2016
rulemaking established pretreatment standards (PSES and PSNS) prohibiting the discharge of wastewater
pollutants from unconventional oil and gas extraction facilities under Subpart C to POTWs (see 81 FR
41845, June 28, 2016).
There are three subcategories that apply to onshore activities (Subpart C, E, and F). The regulations at 40
CFR 435 Subpart C prohibit the discharge of wastewater pollutants from onshore facilities into navigable
waters from any source associated with production, field exploration, drilling, well completion, or well
treatment (i.e., produced water, drilling muds, drill cuttings, and produced sand). Standard practice in the
industry for managing produced water from onshore activities is disposal via underground injection or re-
use in the oil field for enhanced oil recovery, drilling or hydraulic fracturing. Some produced water from
onshore facilities is also indirectly discharged via POTWs. Some is also used for dust suppression and road
deicing.
The regulations at 40 CFR 435 Subpart E allow for discharge of produced water from onshore facilities
into navigable waters west of the 98th meridian (see Figure 1) if the produced water is of good enough
quality to be used for wildlife or livestock watering or other agricultural uses and the produced water is
actually put to such use during periods of discharge (40 CFR 435.51). These facilities are engaged in the
production, drilling, well completion, and well treatment in the oil and gas extraction industry. The
Subpart E regulations contain a daily maximum BPT effluent limitation of 35 mg/L of oil and grease
applicable to produced water. The Subpart E regulations do not contain BAT limitations for existing
sources, and do not contain NSPS limitations for new sources. The Subpart E regulations also do not
contain pretreatment standards for indirect discharge via POTWs.
Another subpart (Subpart F - Stripper Subcategory) applies to onshore facilities that produce 10 barrels
per well per calendar day or less of crude oil and which are operating at the maximum feasible rate of
production and in accordance with recognized conservation practices. These facilities are engaged in
production, and well treatment in the oil and gas extraction industry. Subpart F does not contain effluent
limitations. Any limitations are developed by the permitting authority on a case-by-case basis.
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Figure 1. Map of 98th Meridian
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3. Industry Profile
3.1 Summary of Permits
All oil and gas operations west of the 98th Meridan can manage produced water under 40 CFR 435
Subpart E if the produced water has a use in agriculture or wildlife propagation and the produced water is
actually put to such use during periods of discharge. Currently, all states with areas west of the 98th
meridian except New Mexico are delegated to issue NPDES permits for oil and gas. However, the EPA only
identified active permits issued for discharges under 40 CFR 435 Subpart E in California, Colorado, Texas,
Utah, and Wyoming. From record reviews and discussions with state regulatory agencies, the EPA
identified 176 active individual permits under Subpart E issued by primacy states. For Indian country and
states that do not have primacy, the EPA issues the permits. From records reviews, the EPA identified 12
permits issued in Indian country. In many cases, there may be multiple discharge points/outfalls covered
under a single permit. A February 4, 2025, search of the Integrated Compliance Information System (ICIS)
database did not identify any active permits outside of California, Colorado, Texas, Utah and Wyoming.
The State of Montana issues a general permit for produced water discharges, although not under Subpart
E.
3.1.1 Description of State Issued Permits
The EPA reviewed all active Subpart E permits that it identified and summarized permit requirements
such as regulated pollutants and chemical disclosure requirements and whether the permit requires
whole effluent toxicity (WET) testing. The below summary is of permit requirements and does not
incorporate any permit application requirements. Some additional states (Montana and New Mexico)
that currently do not have Subpart E permits but have other relevant permitting information are
summarized as well.
3.1.1.1 California
The NPDES Program has been delegated to the State of California for implementation through the State
Water Resources Control Board (State Water Board) and the nine Regional Water Quality Control Boards
(Regional Water Boards), collectively Water Boards. The EPA identified one active permit (CA0050628)
issued to Sentinel Peak Resources California LLC. Segregation of flowback and chemical additive
disclosure are not required, however, acute and chronic WET testing is required twice per year.
Segregation of Flowback
Not addressed in the permit.
Chemical Additive Disclosure
Not addressed in the permit.
WET
Acute and Chronic Testing is required twice per year (see Table E-3 of the permit).
The permit states that: "Acute toxicity shall be assessed by the survival of aquatic organisms in 96-hour
bioassays of undiluted waste and survival shall be no less than:
70 percent, minimum for any one bioassay; and
90 percent, median for any three consecutive bioassays.
There shall be no chronic toxicity in the effluent discharge."
3.1.1.2 Colorado
NPDES permits in Colorado are issued by the Colorado Department of Public Health & Environment
(CDPHE). CDPHE has both a General Permit and Individual Permits issued under 40 CFR Part 435 for
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discharges of produced water. There are six operators permitted under the General Permit and one
Individual Permit issued under Subpart E.
General Permit Requirements
Segregation of flowback is not required, however, disclosure of chemical additives is required in the
permit application. Acute and chronic WET testing is required quarterly.
Segregation of Flowback
Segregation is not required. The permit instead states "Consistent with the scope of the oil and gas
extraction point source category established by the EPA in the development of Federal Effluent Limitation
Guidelines (ELGs), produced water discharges associated with production of crude petroleum and natural
gas, drilling oil and gas wells, and oil and gas field exploration services are included within the scope of
the permit. In addition to formation water, produced water may be commingled with injection water, any
chemicals added downhole, chemicals added during the oil-water separation processes, or chemicals
added during the treatment process."
Chemical Additive Disclosure
The permit states that: "Chemicals that may be present in the discharge, whether added during
exploration/production, or after the formation water has reached the surface of the well, will be provided
in the permit application with each chemical's Material Safety Data Sheet (MSDS)."
WET
The permit requires acute and chronic quarterly WET testing, however the Division has the authority to
"vary the frequency as stated in the WET Policy."
CDPHE Individual Permit
Colorado has issued one individual permit (C00000051) to POC-I, LLC. Segregation of flowback and
disclosure of chemical additives is not required, but chronic WET testing is required monthly.
Segregation of Flowback
Not addressed in the permit.
Chemical Additive Disclosure
Not addressed in the permit.
WET
The permit states that: "The permittee shall conduct the chronic WET test using Ceriodaphnia dubia and
Pimephales promelas, as a static renewal 7-day test using three separate grab samples. The permittee
shall conduct each chronic WET test in accordance with the 40 CFR Part 136 methods described in Short-
term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Water to Freshwater
Organisms, Fourth Edition, October 2002 (EPA-821-R-02-013) or the most current edition."
3.1.1.3 Texas
Effective January 15, 2021, the onshore portion of oil and gas permitting became under the jurisdiction of
TCEQ. The EPA identified one individual permit (TX0140153) that has been reissued by the Texas
Commission on Environmental Quality (TCEQ) to Dorchester Operating Company, LLC. An additional eight
permits have expired and are administratively continued or terminated. The EPA is also aware that as of
early 2025, TCEQ has seven pending Texas Pollutant Discharge Elimination system (TPDES) permit
applications for produced water discharges under Subpart E for operations in the Permian Basin.
For onshore permits in Texas, the EPA Region 6 requires at a minimum the following permit conditions:
A reasonable potential analysis to evaluate the presence of toxic pollutants (127 priority pollutants).
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Screening for minerals such as chlorides, sulfates, and TDS are performed to determine whether a
permit limit or further study of the receiving stream is required.
Modeling (and monitoring) may also be performed for facilities that may negatively affect a water
body's dissolved oxygen levels in receiving waters. Results are evaluated to determine what effluent
limits are needed to maintain appropriate dissolved oxygen levels. Numerical models or other
techniques are used to develop permit limits for oxygen-demanding constituents, in order to ensure
the attainment of numerical criteria for dissolved oxygen.
WET testing either acute or chronic depending on the permit writer's discretion.
Monitoring and reporting requirements for other pollutants may also be performed to collect data
that may be used to make informed decision during the next permit cycle.
A letter of certification for the agricultural and wildlife use subcategory stating the beneficial use of
the produced water.
Segregation of Flowback
Not addressed in the permit.
Chemical Additive Disclosure
Not addressed in the permit.
WET
WET testing is required with the type (acute or chronic) up to the discretion of the permit writer.
3.1.1.4 Utah
Currently, the Utah Department of Water Quality has issued one Utah Pollutant Discharge Elimination
System (UPDES) permit under Subpart E to Scout Energy Management LLC for its produced water
discharge (UT0000035). Segregation of flowback and chemical additive disclosure are not required,
however, chronic WET testing is required semi-annually.
Segregation of Flowback
Not addressed in the permit.
Chemical Additive Disclosure
Not addressed in the permit.
WET
The permit states that: "Effective immediately, and lasting through the life of this permit, there shall be
no acute or chronic toxicity in Outfall 001 as defined in Part VI and determined by test procedures
described in Part I. C.5.a of this permit." Chronic WET testing is required semi-annually.
3.1.1.5 Wyoming
The Wyoming Department of Environmental Quality only issues individual permits under Subpart E for
discharges. There is currently no general permit. The EPA identified 172 permits that that contain a total
of 431 outfalls. Wyoming permits state that: "Development of permit limits involves considering all
federal and state regulations and standards and incorporates the most stringent requirements into the
permit. The effluent limits established in this permit are based upon Chapters 1 and 2 of the Wyoming
Water Quality Rules and Regulations, 40 CFR Part 435 Subpart E, and other evaluations conducted by
WDEQ related to this industry." Prohibition of flowback is required, however, disclosure of chemical
additives is not required, and WET testing is not universally required.
Segregation of Flowback
Wyoming permits state that permits do not cover activities associated with discharges of drilling fluids,
acids, stimulation waters or other fluids derived from the drilling or completion of the wells.
Chemical Additive Disclosure
9
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Not addressed in permits.
WET
Wyoming permits can have acute WET monitoring if the permit application reveals the permittee is using
treatment formulations which may be toxic (e.g., flocculants, anti-scalants, antimicrobial compounds,
etc.) or if they are near Class 2 waterbodies. Class 2 waterbodies are defined by Wyoming as those waters
"known to support populations offish and/or drinking water supplies and are considered to be high
quality waters." WET monitoring and limits are implemented on Class 2 waters consistent with
Wyoming's water quality standards regulations.
Additionally, some permit may remove previous WET testing if the permittee's compliance history
indicates there is no toxicity (i.e., passing test results) or the produced water discharge and/or treatment
chemicals have not changed.
3.1.1.6 Montana
The Montana Department of Environmental Quality permits all discharges of produced water under a
state-issued, General Permit for Produced Water, Permit No. MTG310000 for discharges to state waters
only (i.e., non-navigable waters). Therefore, these permits are not issued under Subpart E as the
discharges do not discharge to navigable waters. As of January 2025, there were 30 operators issued
authorization to discharge under this non-NPDES Produced Water Discharge Permit.
In the general permit, produced water is defined as "the water (brine) brought up from the hydrocarbon-
bearing strata during the extraction of oil and gas, and may include formation water, injection water, and
any chemicals added downhole or during the oil/water separation process."
Segregation of flowback and WET are not required, however, chemical additive disclosure and chemical
and additive reporting are required.
Segregation of Flowback
Not addressed in the permit.
Chemical Additive Disclosure
The permit states that: "Applicants must disclose all chemicals and additives used at all leases and
facilities that discharge produced wastewater: all product names, recommended uses, manufacturer, and
Safety Data Sheets (SDSs). An SDS is acceptable for submission if it contains the information required
above." The permit also states that: "The permittee shall submit to DEQ the list of all chemicals and
additives used when submitting the [notice of intent] NOI; the volume of each liquid chemical and
additive used; the mass of each solid chemical and additive used (if dissolved into a solution, provide the
resulting solution concentration or ratio); and a list of the leases and facilities where the chemicals and
additives are being used." In addition, the permit states: "The permittee shall submit to DEQ annually the
Safety Data Sheets (SDSs) or Material Safety Data Sheets (MSDSs) for each chemical and/or additive used
during the year."
WET
Not addressed in the permit.
3.1.1.7 New Mexico
As of January 2025, there have not been any Subpart E permits issued in New Mexico. However,
stakeholders have indicated that there is one application in development for discharge of produced water
under Subpart E in New Mexico.
10
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3.1.2 Description of Federally Issued Permits
The EPA issues Subpart E permits in Indian country when the Tribes do not have primacy. Currently, the
EPA has 12 permits issued in Indian country.
3.1.2.1 EPA Region 8
The segregation of flowback is required, or disclosure of chemicals is required if segregation does not
occur. Acute WET testing is required for 10 of the 11 permits. Chemical additives are not required to be
disclosed universally.
Wind River Indian Reservation
On the Wind River Indian Reservation, EPA Region 8 currently has 10 Subpart E permits issued.
Segregation of Flowback and Chemical Inventory Reporting Requirement
For permits requiring Chemical Inventory Reporting, the language states, "The Permittee shall maintain
an inventory of the quantities and concentrations of the specific chemicals used to formulate well
treatment and workover fluids (defined below). Unless these fluids are segregated, the Permittee shall
submit the following information with the DMR, to the extent such information is obtainable after making
reasonable inquiries to suppliers: all chemical additives in the well treatment or workover fluid, their
trade names, purposes, supplier, CAS number, concentrations and amounts. The type of operation that
generated the well treatment or well workover fluids shall also be reported. To the extent a Safety Data
Sheet (SDS) contains the information required above, it may be submitted for purposes of complying with
this provision. For purposes of this provision, well treatment and workover fluids will be considered
segregated if the Permittee takes steps to recover a volume of fluid equivalent to the volume of the well
treatment or workover fluid used in the job."
'"Well treatment fluids' means any fluid used to restore or improve productivity by chemically or
physically altering hydrocarbon-bearing strata after a well has been drilled."
"'Well workover fluids' means salt solutions, weighted brines, polymers, or other specialty additives used
in a producing well to allow for maintenance, repair or abandonment procedures."
Chemical Additive Disclosure
Not addressed in the permits.
WET
Acute WET testing is required in nine of 10.
Crow Indian Reservation
On the Crow Indian Reservation, EPA Region 8 has issued one Subpart E permit. This permit requires WET
testing, segregation of flowback or chemical additive disclosure if segregation does not occur, per- and
polyfluoroalkyl substances (PFAS) monitoring, and to report any changes in chemical additives from the
time of permit development (i.e., chemical disclosure).
Segregation of Flowback
The permit states that: "The Permittee shall maintain an inventory of the quantities and concentrations of
the specific chemicals used to formulate well treatment and workover fluids (defined below). Unless
these fluids are segregated, the Permittee shall submit the following information with the DMR, to the
extent such information is obtainable after making reasonable inquiries to suppliers: all chemical
additives in the well treatment or workover fluid, their trade names, purposes, supplier, CAS number,
concentrations and amounts. The type of operation that generated the well treatment or well workover
fluids shall also be reported. To the extent a Safety Data Sheet (SDS) contains the information required
above, it may be submitted for purposes of complying with this provision. For purposes of this provision,
11
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well treatment and workover fluids will be considered segregated if the Permittee takes steps to recover
a volume of fluid equivalent to the volume of the well treatment or workover fluid used in the job."
'"Well treatment fluids' means any fluid used to restore or improve productivity by chemically or
physically altering hydrocarbon-bearing strata after a well has been drilled."
"'Well workover fluids' means salt solutions, weighted brines, polymers, or other specialty additives used
in a producing well to allow for maintenance, repair or abandonment procedures."
Chemical Additive Disclosure
The permittee must submit any changes to the chemical additives it submitted to the EPA when the
permit was developed. If the permittee uses any additional chemicals from those disclosed above during
the permit term, the permittee must submit notification of those additional chemicals to the EPA per the
Planned Changes provision in Parts 8.1 and 8.1.1. of the permit.
WET
Chronic WET is required in the permit.
3.1.2.2 EPA Region 9
Navajo Nation
EPA Region 9 has one permit issued in Navajo Nation that has two outfalls. Segregation of flowback,
chemical additive disclosure, and WET testing are not required in the permit.
Segregation of Flowback
Not addressed in the permit.
Chemical Additive Disclosure
Not addressed in the permit.
WET
Not required in the permit.
3.1.3 Variability across permits
The current regulation for discharges under Subpart E does not specify how permitting authorities should
make a determination of 'good enough quality' to be used for wildlife or livestock watering or other
agricultural uses. This has led to variability in the requirements of Subpart E permits among permitting
authorities (i.e., states and EPA). The EPA has identified multiple factors that contribute to these
variabilities, including but not limited to:
Permit application data,
The type of beneficial use (i.e., wildlife propagation or agriculture),
Classification and water quality standards of receiving waters,
Chemistry of source water for hydraulic fracturing, and
Innate formation fluid quality.
EPA identified specific variability in how state permitting authorities permit the discharge of produced
water, particularly related to the definition of produced water, produced water effluent limits, chemical
additive disclosure, monitoring requirements (including PFAS and WET), and prohibition of discharge of
flowback after hydraulic fracturing and maintenance processes.
Permit Limits
In Wyoming, water quality standards for produced water discharges are contained in every permit. For
other permitting authorities, the water quality standards for the receiving water body are used to set
produced water effluent limits and monitoring requirements. The only consistent requirement is an oil
12
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and grease effluent limitation and a requirement for a beneficial use. For instance, some permits require
quarterly WET monitoring, whereas others require a one-time WET test or there is no WET test
requirement. A large number of permits do not require screening for toxic pollutants, chemical
disclosure, segregation of flowback or chemical additive disclosure after hydraulic fracturing, or
monitoring for PFAS.
Additional Challenges
Permit applications do not require the disclosure of production wells that contribute to the produced
water discharge. Many permittees have both underground injection wells and discharge permits to
manage the produced water. From discussion with multiple operators, what method is used for disposal
can vary over time for each production well. This creates a challenge in determining when flowback after
hydraulic fracturing and maintenance processes could be discharged. Generally, there is no definition in
permits of when flowback and maintenance activities ends (e.g., equal volume recovered as used in a
hydraulic fracturing job). Therefore, there is potential for chemical additives from these operations to be
present in produced water that is being discharged.
Another challenge permit writer's face is determining "good enough quality" for the agricultural and
wildlife use. The EPA has developed a tool to aid permit writers in making these determinations (see
https://www.epa.gOv/eg/oil-and-gas-extraction-effluent-guidelines#bene-use-tool). However, there is a
lack of data for constituents found in produced water related to crop health, ecotoxicology, livestock
impacts, and other information that is necessary to make an adequate determination of "good enough
quality."
In most cases, produced water that meets established water quality criteria for discharge often will
contain an unpredictable and complex mixture of chemical additives and naturally occurring constituent
for which no water quality standards and analytical methods exist. These concerns related to the
unknown chemistry of produced water and the limited amount of data regarding treatability of produced
water, particularly regarding reduction of toxicity, creates a challenge for regulators to determine
treatment approaches and effectiveness. These knowledge gaps further complicate understanding
treatment technology effectiveness to address potential human health and aquatic toxicity concerns
resulting from discharges.
3.2 Company Information
There are many oil and gas producing basins located in the Western states. How produced water is
managed depends on many factors, including the quality and quantity of produced water and the
availability of management and disposal options. The EPA has not conducted a comprehensive evaluation
of produced water generation and management for purposes of this report. However, a brief discussion is
provided of some of the major basins, the companies operating in those basins, and produced water
generation for select basins to provide perspective on factors that are important for the EPA's
consideration of Subpart E regulations. For a comprehensive discussion of broader national produced
water issues, see the reports prepared by the Ground Water Protection Council (GWPC, 2019 and GWPC,
2023).
3.2.1 Supermajor, Major, and Independent
Supermajor integrated oil and gas companies are defined as being involved in each segment of the
industry and typically having market capitalization of $100 billion or more. Often, these are international
companies. Major oil and gas companies are defined as typically having market capitalization of $10
billion to $100 billion. Whereas, independent companies focus on one segment of the industry and are
defined as a producer who does not have more than $5 million in retail sales of oil and gas in a year or
who does not refine more than an average of 75,000 barrels per day of crude oil during a given year.
13
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3.2.2 Upstream, Midstream, and Downstream
Upstream companies focus on exploration and production. Globally, most crude oil production is
controlled by National Oil Companies, which includes The Organization of Petroleum Exporting Countries
(OPEC), or integrated international oil companies. Upstream companies benefit from high oil and gas
prices and high volumes. Other metrics include rig count and capital spending. Midstream companies
handle the transportation and storage of oil and gas. This segment is made up of many independent
transportation operators. Oil and gas volumes are important to midstream companies, and prices as they
relate to volume: if the price drops so low that upstream companies stop producing, midstream
companies are not needed for transportation. Downstream companies manage the refining and
marketing of oil and gas. There is lower market concentration in the downstream segment than the
upstream segment. Downstream companies benefit from profit margins where they can sell their refined
products for more than the cost of acquiring the crude resources. Other metrics include the number and
size of refineries.
3.2.3 Oil and Gas Companies in Major Production Basins West of the 98th Meridian
According to the Institute for Energy Economics and Financial Analysis (IEEEFA), Enverus, and Rextag, the
major oil and gas production basins west of the 98th meridian, and the major companies operating in
those basins, include the following:
3.2.3.1 Permian
The Permian Basin is located in west Texas and southeastern New Mexico. Some of the major oil and gas
companies with significant holdings in the Permian Basin include Chevron, ExxonMobil, Occidental
Petroleum (Oxy), ConocoPhillips, Diamondback Energy, Apache, and Pioneer Natural Resources, with
Chevron holding the largest percentage of acreage in the region. According to East Daley Analytics, the
Permian Basin produced 6.1 million barrels per day of crude oil in 2023. The basin also produced 11.5
billion cubic feet per day of associated natural gas in 2023.
3.2.3.2 Williston
The Williston Basin includes areas in Montana, North Dakota and South Dakota. Some of the major oil and
gas companies with significant holdings in the Williston Basin include Hess, ExxonMobil, EOG Resources,
Continental Resources, Enerplus Resources USA, Hunt Oil and Whiting. The Williston Basin produced
approximately 1.57 million barrels of oil equivalent per day in 2023. The Bakken Shale is the predominant
source of oil and gas in the Williston Basin.
3.2.3.3 Denver-Julesburg
The Denver-Julesburg basin is located in northeastern Colorado and southeastern Wyoming. Major oil
and gas holdings in the Denver-Julesburg (DJ) Basin include Oxy, Chevron and Civitas. Other majors
include Bonanza Creek Energy, PDC Energy, EOG Resources and Whiting Petroleum. According to East
Daley, the Denver-Julesberg produced approximately 0.630 million barrels of oil per day in 2023.
Additionally, the U.S. Energy Information Administration estimated the production value closer to 0.670
million barrels of oil per day and 1.53 million barrels of oil equivalent per day in 2023.
3.3 Oil and Gas Production for Existing Subpart E Permittees
EPA collected data on oil and gas production for Subpart E permittees. The analysis was limited to
Wyoming since the majority of existing Subpart E permits are located in that state. Wyoming is a major
hydrocarbon producing state. Oil production has been steadily increasing in Wyoming over the past 20
years. While oil production was about 51.8 million BBLs in 2005, it increased to over 96 million BBLs in
2023. Gas production, on the other hand, has been steadily decreasing since 2009. After reaching a peak
of over 2.5 billion Mcf, producers reported just over 1.2 billion Mcf of gas production to the Wyoming Oil
and Gas Conservation Commission (WOGCC) in 2023 (see pipeline.wyo.gov for production data and
graphs). The Wyoming State Geological Survey (January 2024) attributed the decrease in gas production
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to a lack of new gas wells being drilled and the declining rate of production from existing wells. The
increase in oil production is attributed to new drilling activity, particularly in the Powder River Basin.
As part of an economic analysis to support development of ELGs, the EPA typically evaluates factors such
as industry revenues and incremental costs to understand whether additional treatment is economically
achievable for an industry consistent with the CWA statutory factors (see section 2 for more information).
For studies, the EPA may conduct a screening-level analysis to understand the economics of a particular
industry. For this study, the EPA conducted a screening-level analysis to determine oil and gas production
(as a proxy for revenue) for companies with current Subpart E permits in Wyoming. The EPA obtained oil
and gas production data from WOGCC (see pipeline.wyo.gov). The EPA used 2023 as an example year
since this was the most recent full year of data available when the EPA began the study in 2024. The EPA
then summed oil and gas production by company. This was done by cross-referencing the production
data by company with active Subpart E permits2 to obtain total production for each company in Wyoming
that had an active NPDES permit in 2024. Some permittees were not found in the WOGCC production
data, indicating that these companies may be engaged in other activities (such as water services or
produced water treatment) or did not report any oil and production in 2023.
From this analysis, the EPA identified 82 companies that had 172 NPDES permits in Wyoming in 20243. Of
these 82 companies, 74 reported nonzero oil production and 39 reported nonzero gas production in
2023. Total reported oil production in 2023 in Wyoming for these 74 companies was 20,518,911 BBL
(about 21% of statewide oil production) and total reported gas production in 2023 in Wyoming for these
39 companies was 155,912,209 Mcf (about 13% of statewide gas production). The results of the EPA's
analysis of oil and gas production for Wyoming Subpart E permittees can be found in Table 1.
Table 1. Reported Oil and Gas Production for NPDES Permittees in Wyoming in 2023
Company Name
Barrels Oil
2023
Mcf Gas
2023
Company Name
Barrels Oil
2023
Mcf Gas
2023
AETHON ENERGY OPERATING
LLC
107,978
10,797,780
MEERKAT LOGISTICS AND
OPERATIONS LLC
1,742
-
AMWEST PETROLEUM INC
N/A
N/A
MERIT ENERGY COMPANY
5,276,571
2,733,055
ANTHILLS PRODUCTION
2,137
-
MID-CON ENERGY
OPERATING LLC
92,020
35,085
Anticline Disposal, LLC
N/A
N/A
NEPECO
6,399
-
ANTLER ENERGY LLC
5,450
603,224
NEW ERA PETROLEUM INC
19,820
-
ARNELL OIL COMPANY
40,110
-
NEW HORIZON
RESOURCES LLC
28,498
34,853
ATR ENERGY CORP
27,202
O'BRIEN ENERGY
RESOURCES
CORPORATION
14,384
BATAA OIL INC
6,240
2,343
OIL MOUNTAIN ENERGY
INC
15,132
-
BEREN CORPORATION
15,186
-
OSAGE PARTNERS LLC
4,340
-
BIG MUDDY OPERATING LLC
46,635
-
OTTINC
4,120
-
BITTERROOT ENERGY PARTNERS
LLC
4,399
3,335
PETROLEUM RESOURCE
MANAGEMENT CORP
1,278
1,513
BLACK BEAR OIL CORPORATION
135,128
362,331
PETROX RESOURCES INC
32,746
-
2 Note that in some cases there were differences in the name of companies reported in the WOGCC production data
and the name of permittees contained in the WY DEQ permit data. In these cases, EPA used the company name
from the WOGCC production data to prepare data summaries contained in this report.
3 EPA used a snapshot of permits obtained from WY DEQ in September 2024 to generate estimates for this report.
WY DEQ provided an updated count in April 2025 that indicated there were 188 permits held by 97 companies.
15
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Table 1. Reported Oil and Gas Production for NPDES Permittees in Wyoming in 2023
Company Name
Barrels Oil
2023
Mcf Gas
2023
Company Name
Barrels Oil
2023
Mcf Gas
2023
BLACK GOLD SERVICES INC
18,514
3
PGC LLC
-
-
BLACKTHUNDER OIL LLC
10,357
-
PINE HAVEN RESOURCES
LLC
48,694
-
BREITBURN OPERATING L.P.
616,872
4,460,991
POC-I LLC
10,508
-
CARBON CREEK ENERGY LLC
-
58,826,907
PRINCIPLE PETROLEUM
LLC
96,694
-
CAROL-HOLLY OIL
CORPORATION
13,793
8,703
RANCH OIL COMPANY
29,899
-
CHAPMAN OIL COMPANY
3,109
-
RED TIGER OIL & GAS LLC
129,759
-
CITATION OIL & GAS
CORPORATION
1,163,145
247,803
RICHARDSON OPERATING
CO
96,920
399,247
CLOUD PEAK OPERATING LLC
8,850
-
SEEDY DRAW LLC
7,694
-
CODY ENERGY INC
4,173
103,578
SEP - Pass Creek, LLC
N/A
N/A
CONTANGO RESOURCES LLC
5,256,487
66,873,506
SHADCO
N/A
N/A
D90 ENERGY LLC
46,087
297,102
SIMON OIL LLC
40,071
-
DAU BE COMPANY THE
53,891
-
SIX BAR OIL LLC
60,625
-
DENBURY ONSHORE LLC
2,448,914
2,307,569
SOUTH PASS PETROLEUM
INC
2,334
103,360
DIAMOND OIL & GAS LLC
17,489
158,608
SPELLBOUND ENERGY LLC
84,597
-
E & BNATURAL RESOURCES
MANAGEMENT
271,432
1,026
SUNSHINE VALLEY
PETROLEUM
111,784
374,979
ELLWOOD EXPLORATION LLC
20
-
TR OPERATING LLC
45,964
-
ENERGY EQUITY COMPANY
-
5,415
TRIBAR RESOURCES LLC
47,242
5,454
EVEREST OIL & GAS LLC
15,439
-
TRUE OIL LLC
1,107,795
1,110,202
GRANITE CREEK ENERGY LLC
205,772
7,141
UNDERWOOD OIL & GAS
580
-
HADLEY/JACKSON ENERGY LLC
14,384
-
USA ENERGY LLC
14,041
6,233
Homer Dean Oil Company
N/A
N/A
VALKYRIE OPERATING LLC
128,800
41,025
IRON CREEK PROPERTIES INC
2,877
12
VAQUERO BIG HORN LLC
338,217
-
J & J PRODUCTION LLC
1,846
-
VERMILION ENERGY USA
LLC
975,831
3,868,331
JP OIL WYOMING LLC
43,888
67,519
VORTEX PETROLEUM INC
7,137
-
LOIL OIL LLC
70,099
150,503
WASHBURN LEE
1,339
-
M & K OIL COMPANY LLC
319,074
953,242
WESCO OPERATING INC
321,645
803,816
M2S OIL LLC
5,974
-
WESTERN AMERICAN
RESOURCES LLC
18,075
32,676
MAXIM DRILLING & EXPLINC
14,325
81,306
WHITE ROCK OIL & GAS
LLC
132,572
12,452
MAXIMUS OPERATING LTD
132,523
29,981
WYOIL CORP
13,245
-
Data from WOGCC production reports in 2023.
N/A means company was not found in WOGCC production data in 2023.
- Means that the company reported no production during the year.
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4. Produced Water Characterization
4.1 Produced Water Volumes
The best source for data on volumes of produced water brought to the surface is the Ground Water
Protection Council's Reports on Produced Water (GWPC, 2023). However, that data uses a 2021 baseline
production year and is reported on a state-by-state basis. In addition, not all states require producers to
report produced water generation, so developing national estimates pressents several challenges. Given
continued growth in production in the Permian Basin, it is expected that current produced water volumes
from Texas and New Mexico may be higher than the 2021 GWPC estimates. Given that most major
production basins straddle state boundaries, a comparison of state production data is provided in Table 2
for selected states.
Table 2. Estimated Produced Water and Hydrocarbon Production in Select States (2021)
State
Number of Wells
Producing
Volume of Produced
Water Brought to
Surface (bbl/year)
Volume of
Hydrocarbon
Produced
New Mexico
62,405
1,600,878,600
451,085,590 BBL
2,421,424 MMCF
North Dakota
18,163
643,154,596
405,127,827 BBL
1,075,538 MMCF
Oklahoma
48,492
1,744,894,591
148,337,393 BBL
2,544,913 MMCF
Texas
203,207
8,107,645,550
1,724,402,106 BBL
10,741,016 MMCF
Wyoming
27,171
1,559,881,944
85,290,133 BBL
1,081,393 MMCF
Source GWPC 2023
BBL = Barrel4; MCF = Thousand Cubic Feet5; MMCF = Thousand MCF
4.2 Discharge Volume Data
The EPA evaluated discharge monitoring reports (DMR) to determine reported discharge volumes by
permittee for Wyoming discharges6. To resolve any potential reporting errors in DMRs that could reduce
the accuracy of produced water discharge flow estimates, the EPA also performed a cross-check with
NPDES permits and other documentation, such as inspection reports and permit quality reviews. The EPA
then summed discharge volumes by company name. As an additional data quality check, the EPA also
compared the company-level discharge volumes with the quantity of produced water reported to
WOGCC as part of the production reports. This check helped identify any instances where reported
discharge volumes exceeded produced water generation and allowed for additional adjustments to be
made using other data sources. However, the EPA notes that these data may still contain inaccuracies and
therefore should only be considered estimates of actual discharge volumes by company. Despite these
limitations, however, this evaluation of discharges by permittee and by company can inform the
evaluation of potential produced water treatment technology costs.
4 BBL = barrel, a unit of volume for oil and produced water, 42 gallons.
5 A unit of natural gas production.
6 Since little produced water is discharged under Subpart E in other states, the EPA limited this analysis only to
Wyoming.
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Table 3 presents the estimated average daily discharge (based on 2021, 2022 and 2023 DMRs), and the
number of Subpart E permits held by the 82 companies identified in the EPA's analysis. Some permittees
reported zero discharge during the reporting years, resulting in estimates of zero GPD for the average
produced water discharge. The EPA estimated that daily produced water discharges in Wyoming for these
82 companies, based on DMRs, is approximately 39 million gallons per day (or approximately 935
thousand barrels per day). Based on WOGCC data, Wyoming producers reported generating
approximately 1.63 billion barrels of produced water in 2023, which on average would be about 4.5
million barrels (187 million gallons) per day. Therefore, approximately 21% of produced water is
discharged under Subpart E in Wyoming based on EPA's analysis.
Table 3. Estimated Subpart E Produced Water Discharge by Company in Wyoming
Company Name
Average
Discharge
(GPD)
Number of
Subpart E
NPDES
Permits
Company Name
Average
Discharge
(GPD)
Number of
Subpart E
NPDES
Permits
AETHON ENERGY OPERATING
LLC
1,149,195
2
MEERKAT LOGISTICS AND
OPERATIONS LLC
3,359
1
AMWEST PETROLEUM INC
0
1
MERIT ENERGY COMPANY
12,002,500
12
ANTHILLS PRODUCTION
7,028
1
MID-CON ENERGY
OPERATING LLC
16,201
1
ANTICLINE DISPOSAL, LLC
0
1
NEPECO
37,389
1
ANTLER ENERGY LLC
8,000
2
NEW ERA PETROLEUM
INC
110,844
1
ARNELL OIL COMPANY
32,222
2
NEW HORIZON
RESOURCES LLC
170,000
1
ATR ENERGY CORP
16,250
1
O'BRIEN ENERGY
RESOURCES
CORPORATION
67
1
BATAA OIL INC
15,418
3
OIL MOUNTAIN ENERGY
INC
110,500
1
BEREN CORPORATION
223,763
2
OSAGE PARTNERS LLC
0
4
BIG MUDDY OPERATING LLC
0
2
OTT INC
0
1
BITTERROOT ENERGY
PARTNERS LLC
821
2
PETROLEUM RESOURCE
MANAGEMENT CORP
17,278
1
BLACK BEAR OIL
CORPORATION
244,844
4
PETROX RESOURCES INC
72,688
1
BLACK GOLD SERVICES INC
0
1
PGC LLC
0
1
BLACKTHUNDER OIL LLC
191,580
3
PINE HAVEN RESOURCES
LLC
994
3
BREITBURN OPERATING L.P.
3,484,006
6
POC-I LLC
4,214
4
CARBON CREEK ENERGY LLC
7,444
1
PRINCIPLE PETROLEUM
LLC
1,081,282
5
CAROL-HOLLY OIL
CORPORATION
23,394
3
RANCH OIL COMPANY
293,593
2
CHAPMAN OIL COMPANY
30,000
1
RED TIGER OIL & GAS LLC
0
1
CITATION OIL & GAS
CORPORATION
5,145,556
5
RICHARDSON OPERATING
CO
198,217
2
CLOUD PEAK OPERATING LLC
213,727
1
SEEDY DRAW LLC
0
1
CODY ENERGY INC
1,366
1
SEP - Pass Creek, LLC
27,031
1
CONTANGO RESOURCES LLC
3,054,977
9
SHADCO
0
1
D90 ENERGY LLC
630,271
2
SIMON OIL LLC
125,896
3
18
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Table 3. Estimated Subpart E Produced Water Discharge by Company in Wyoming
Company Name
Average
Discharge
(GPD)
Number of
Subpart E
NPDES
Permits
Company Name
Average
Discharge
(GPD)
Number of
Subpart E
NPDES
Permits
DAU BE COMPANY THE
683,389
1
SIX BAR OIL LLC
7,703
1
DENBURY ONSHORE LLC
1,064,617
2
SOUTH PASS PETROLEUM
INC
1,022
1
DIAMOND OIL & GAS LLC
166,250
1
SPELLBOUND ENERGY LLC
0
1
E & BNATURAL RESOURCES
MANAGEMENT
50,472
3
SUNSHINE VALLEY
PETROLEUM
21,202
1
ELLWOOD EXPLORATION LLC
7,933
1
TR OPERATING LLC
711,633
3
ENERGY EQUITY COMPANY
0
1
TRIBAR RESOURCES LLC
1,381,722
1
EVEREST OIL & GAS LLC
302,939
1
TRUE OIL LLC
27,417
1
GRANITE CREEK ENERGY LLC
949,289
1
UNDERWOOD OIL & GAS
0
1
HADLEY/JACKSON ENERGY LLC
44,667
2
USA ENERGY LLC
227,117
5
Homer Dean Oil Company
5,400
1
VALKYRIE OPERATING LLC
674,682
6
IRON CREEK PROPERTIES INC
30,000
1
VAQUERO BIG HORN LLC
3,362,222
6
J & J PRODUCTION LLC
8,222
1
VERMILION ENERGY USA
LLC
0
2
JP OIL WYOMING LLC
222,000
2
VORTEX PETROLEUM INC
32,000
1
LOIL OIL LLC
110,000
2
WASHBURN LEE
0
1
M & K OIL COMPANY LLC
20,017
7
WESCO OPERATING INC
0
1
M2S OIL LLC
105,900
2
WESTERN AMERICAN
RESOURCES LLC
17,640
1
MAXIM DRILLING & EXPLINC
0
1
WHITE ROCK OIL & GAS
LLC
138,500
1
MAXIMUS OPERATING LTD
0
1
WYOIL CORP
126,561
1
Values are estimated based on Discharge Monitoring Reports
Zero values indicate that the permittee reported no discharge during the reporting years of 2021, 2022 and 2023.
4.3 Discharge Constituent Data
There are several sources of produced water quality data available. The EPA previously summarized
national data on produced water characteristics (see USEPA, 2020) and therefore does not include a
comprehensive evaluation of produced water characterization data in this report. Instead, the discussion
presented here focuses on pollutants in existing Subpart E discharges based on DMRs. In addition, the
EPA provides a summary of FracFocus disclosure data as an indicator of the constituents that may be
found in produced water more broadly.
4.3.1 Discharge Monitoring Reports
The EPA retrieved DMR data for active permits in Wyoming to evaluate the concentration of various
pollutants in reported discharges. As described above, the parameters regulated (and, therefore,
monitored) in these permits vary; however, most DMRs contained data for chloride, oil and grease, and
sulfide. Many DMRs also contained data for radium 226, total dissolved solids and sulfate. A select few
DMRs also contained data for other pollutants. Figure 2 presents the DMR effluent data for the most
commonly analyzed pollutants for the reporting years 2021 - 2023 for Wyoming Subpart E permittees.
19
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The boxes present the 25th, 50th and 75th percentile concentrations and the whiskers present the
minimum and maximum concentrations of all non-zero values for a given constituent.
10000
1000
100
E
T3
ra
CC
10
"aS
E
0.1
0.01
0.001
0.0001
0.00001
Oil & Grease Ra226 Sulfide Sulfate
(1362) (587) (2342) (663)
[1135] [586] [2244] [660]
Constituent
(Number of Obsevations)
{ Number of Nonzero Observations)
TDS
(325)
[325]
Chloride
(862)
[860]
Figure 2. Constituent Concentrations in Wyoming Subpart E Discharges from DMRs (2021 - 2023)
4.3.2 FracFocus
The FracFocus Chemical Disclosure Registry (https://fracfocus.orR/) is a publicly accessible online
database managed by GWPC and the Interstate Oil and Gas Compact Commission (IOGCC). Oil and gas
operators can use the database to disclose information about water and chemicals used in hydraulic
fracturing fluids at individual wells, which is required in many states where oil and gas production occurs.
Twenty-two states recommend or require such disclosures using FracFocus, with at least 17 states
mandating them (Trickey et al., 2020). Each disclosure details several parameters about a given site: dates
of operation, locational data, company/operator, well name, American Petroleum Institute (API) well
number, vertical depths, base fluid volumes, and fluid composition. Fluid composition is further detailed
by trade (product) name, supplier (manufacturer), purpose, compound name / Chemical Abstract Service
(CAS) Registry Number, and relative percentage of total fluid (by mass). This provides regulators and the
public with access to important information about well locations, operations, and chemical use.
However, certain limitations of the database may affect its use for regulatory, research, and public
outreach efforts. Disclosure is not required by every state, limiting its coverage, and the information
captured within each disclosure can vary, including the potential to withhold certain ingredient
20
-------
information. This is typically regarding proprietary business information and can include compound
identifications, mass contributions, and functional purposes within the injection fluid. Maintenance
chemicals (compounds used throughout the operation of a site after the initial stage) are also not
disclosed, and disclosures do not reflect any redactions, corrections, or changes to formulations over
time. Additionally, the database is provided as-is without quality-control procedures that promote data
reliability (e.g., deduplication of records, cross-validation of chemical names and CAS numbers, or well
location verification checks).
Table 4 aggregates and summarizes the disclosures from FracFocus databases through the open-source
project Open-FF (https://open-ff.com/). Data was accessed January 27, 2025, and is presented as-is. The
EPA has not linked actual FracFocus disclosures with specific Subpart E discharges as part of this study.
However, the data on number of disclosures is informative for purposes of highlighting where hydraulic
fracturing operations are occurring, and therefore where FracFocus disclosure data may provide
information that will inform any future EPA actions.
Table 4. Number of FracFocus Disclosures by State
State Number of Disclosures State Number of Disclosures
Texas
109,159
Montana
876
Colorado
20,340
Kansas
858
Oklahoma
18,839
Virginia
617
North Dakota
16,757
Alaska
264
New Mexico
13,522
Mississippi
171
Pennsylvania
11,140
Alabama
169
Wyoming
6,490
Kentucky
51
Utah
5,782
Michigan
31
Louisiana
4,372
Nebraska
14
California
3,769
Nevada
4
Ohio
3,502
Illinois
3
West Virginia
3,435
Indiana
2
Arkansas
2,870
Idaho
1
4.3.3 Reported Substances Used in Hydraulic Fracturing
Table 5 details a cross-walking of known substances reported to be used in hydraulic fracturing
operations nationwide with lists of constituents in several federal and international sources (such as
regulated pollutants or hazardous substances). The aggregated chemicals were assembled through the
EPA's CompTox Chemicals Dashboard (https://comptox.epa.Rov/dashboard/) from other existing lists of
hydraulic fracturing chemicals7 and in-progress research, deduplicated via unique DTXSID8, and assigned
to a new list denoted 'HFRLISTS'. This was then compared against other existing chemical lists that may
indicate potential risks to human and/or ecological health. For each, a description of the cross-walking
category and the number of applicable compounds is provided. Given that some categories may be
subjective, narrowly focused, or depend on molecular structure, some categories may not fully represent
7 List codes for preexisting lists on Dashboard: EPAHFR, EPAHFRTABLE2, FRACFOCUS, CALWATERBDS
8 Distributed Structure Searchable Toxicity substance identifiers (DTXSID) are unique substance identifiers, where a
substance can be any single chemical, mixture, polymer, or chemical family.
21
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the number of possible compounds and are presented for comparison purposes only. These results are
aggregated for all production wells across the country and limited to data reported in the FracFocus
database. The EPA did not attempt to correlate individual wells with Subpart E permits as part of the
study. Therefore, for this study, the EPA did not determine which of these substances might be present in
current (or future) Subpart E discharges. However, the evaluation characterizes classes of chemical
compounds that might be present, and, therefore, might require treatment as part of any future
regulatory revisions.
Table 5: Lists of Compounds Used Nationwide in Hydraulic Fracturing
Aggregate List Name
List Code
Description
Number of
Compounds
40 CFR 355 Extremely Hazardous
40CFR355
Extremely Hazardous Substance
41
Substance List and Threshold
List and Threshold Planning
Planning Quantities
Quantities; Emergency Planning
and Release Notification
Requirements; Final Rule. (52 FR
13378)
Clean Water Act (CWA) Section
CWA311HS
Clean Water Act (CWA) Section
106
311(b)(2)(A) list
311(b)(2)(A) list of hazardous
substances
Department of Homeland
DHSCHEMS
Department of Homeland Security
57
Security Chemicals of Interest
Chemicals of Interest: Appendix A
to Part 27 of the Code of Federal
Regulations (CFR)
EPA Regional Screening Levels
ORNLRSL
Chemicals associated with the
300
Data Chemicals List
Regional Screening Levels (RSLs)
Generic Tables
EPA List of Hazardous Air
EPAHAPS
Under the Clean Air Act, EPA is
72
Pollutants
required to regulate emissions of
hazardous air pollutants. This is
the list of pollutants in the
February 4, 2022, final rule
EPAECOTOX: Ecotoxicology
ECOTOX_v6
Ecotoxicology knowledgebase
884
knowledgebase version 6
(ECOTOX) is a comprehensive,
publicly available knowledgebase
providing single chemical
environmental toxicity data on
aquatic life, terrestrial plants and
wildlife.
Health-Based Screening Levels
HBSL
Health-Based Screening Levels
173
for Evaluating Water-Quality
(HBSLs) are non-enforceable
Data
water-quality benchmarks
IARC: Group 1: Carcinogenic to
IARC1
This is the list of chemicals
16
humans
identified by the International
Agency for Research on Cancer
(IARC), in their monographs, as
Carcinogenic to humans
IARC: Group 2A: Probably
IARC2A
This is the list of chemicals
12
carcinogenic to humans
identified by the International
Agency for Research on Cancer
(IARC), in their monographs, as
Probably carcinogenic to humans
22
-------
Table 5: Lists of Compounds Used Nationwide in Hydraulic Fracturing
Aggregate List Name
List Code
Description
Number of
Compounds
IARC: Group 2B: Possibly
IARC2B
This is the list of chemicals
44
carcinogenic to humans
identified by the International
Agency for Research on Cancer
(IARC), in their monographs, as
Possibly carcinogenic to humans
List of CERCLA Hazardous
40CFR302
List of CERCLA Hazardous
199
Substances (40 CFR 302)
Substances associated with 40 CFR
302
NIOSH: immediately Dangerous
NIOSHIDLH
The immediately dangerous to life
150
to Life or Health Values
or health (IDLH) values are used by
the National Institute for
Occupational Safety and Health
(NIOSH) as respirator selection
criteria.
PFAS| EPA: PFAS structures in
PFASSTRUCTV5
List consists of all records with a
30
DSSTox (update August 2022)
structure assigned, and using a set
of substructural filters and percent
of fluorine in the molecular
formula.
EPA PFAS chemicals without
PFASDEV3
List of PFAS chemicals without
2
explicit structures v3
explicit structures - polymers and
other UVCB chemicals (Last
Updated March 23rd, 2024)
Toxic Substances Control Act
PFAS8a7
List of PFAS chemicals that meets
26
Reporting and Recordkeeping
the TSCA section 8(a)(7) rule
Requirements for Perfluoroalkyl
structural definition of PFAS
and Polyfluoroa 1 kyl Substances:
Section 8(a)(7) Rule List of
Chemicals
State-Specific Water Quality
SSWQS
EPA has compiled state, territorial,
141
Standards Effective under the
and authorized tribal water quality
Clean Water Act (CWA)
standards that EPA has approved
or are otherwise in effect for Clean
Water Act purposes.
EPA: Chemical Contaminants -
CCL5
The Contaminant Candidate List
18
CCL 5
(CCL) is a list of contaminants that
are known or anticipated to occur
in public water systems. Version 5
is known as CCL 5.
EPA: Drinking Water Standard
EPADWS
The EPA's Drinking Water Standard
81
and Health Advisories Table
and Health Advisories Table
summarizes EPA's drinking water
regulations and health advisories,
as well as reference dose (RFD)
and cancer risk values, for drinking
water contaminants.
23
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5. Environmental Assessment
The EPA compiled information on what surface waters currently receive produced water discharges, the
condition of those waters, and potential environmental and human health impacts associated with
produced water. The results of EPA's research are discussed below.
5.1 Produced Water Discharges to Surface Water
5.1.1 Immediate Receiveing Waters of Produced Water Discharges
As discussed in further detail in section 3.1, most facilities currently discharging produced water under
Subpart E are in Wyoming. Therefore, the EPA focused its data collection and mapping of surface waters
on those receiving produced water discharges from facilities in Wyoming.
For these facilities, the EPA collected information from 2021-2023 DMRs on the receiving waters of
produced water discharges, by facility and outfall. Receiving waters are reported in the DMR data by their
common identifier (COMID).9 The receiving waters were then mapped using the flowlines included in the
United States Geological Survey (USGS)'s National Hydrography Dataset (NHD), which are differentiated
by COMID. For some of the facilities, the COMID was not provided for the receiving waters. In these
cases, the EPA determined the receiving water's COMID by first mapping the facilities' outfalls by their
reported latitude and longitude in DMRs. The latitude and longitude points were then overlaid with the
NHD receiving water data for relevant NHD regions in Wyoming to determine the receiving water COMID
that each permit feature is within. The COMIDs for receiving waters containing outfalls were then also
mapped using the flowline information from NHD. Figure 3 presents the flowlines (in blue) for receiving
waters in Wyoming with produced water discharges. For additional context, Figure 3 also shows the
location of the receiving waters within relevant NHD HUC10 watershed regions in Wyoming.
9 A COMID is a unique identification number used to delineate a specific segment of a surface water.
24
-------
Montana
1
*
<
c
&
Idaho
\
r
K
(
-v
S1
*
\ A
lr . ; N -
~ "\
*'¦ -v ^
* <5
' - <
-*v4
South Dakota
/ s
tn *-
s *¦
Nebraska
¦'
*
Wyoming
i
>V "
Legend
Receiving COMC-
V \J ¦ ']¦ /
/ )
@ Region 10
0Req»onl6
Utah
Colorado
Q Region 17
Figure 3. Receiving Waters Listed in DMRs with Discharges of Produced Water from Subpart E Oil and
Gas Facilities in Wyoming
5.1.2 Impairment Status of Immediate Receiving Waters of Produced Water Discharges
Under section 303(d) of the CWA, surface waters that have been assessed by states as not meeting
established water quality standards for their designated uses are listed as "impaired". Determining
whether a surface water receiving produced water discharges from an oil and gas facility is listed as
impaired is helpful for understanding which receiving waters may be most sensitive to pollution from
these facilities.
To determine the impairment status of receiving waters with produced water discharges from oil and gas
facilities in Wyoming (see section 5.2), the EPA used the EPA's Assessment, Total Maximum Daily Load
(TMDL) Tracking and Implementation System (ATTAINS) spatial dataset to identify whether receiving
waters with existing impairments overlapped with the receiving waters in Wyoming identified as receiving
produced water discharges. For receiving waters where there was an identified overlap, the ATTAINS
Assessment Attribute Summary Table provided information on the pollutant groups associated with the
impairment. It is important to note that even if an immediate receiving water is not listed as impaired in
ATTAINS, it does not mean there are no water quality issues. ATTAINS does not capture water quality
issues for waterbodies in states that have not adopted the EPA's CWA section 304(a) aquatic life water
quality criteria for pollutants of concern or that may not have the resources to comprehensively assess all
waterbodies and/or a broad scope of pollutants. Additionally, several pollutants of concern in produced
water (e.g., TDS, sulfate, etc.) do not have aquatic life criteria recommended by the EPA under the CWA
section 304(a). Therefore, while the ATTAINS data is helpful for an initial screening level analysis of
potential water quality issues in immediate receiving waters of produced water discharges for oil and gas
25
-------
facilities, additional information and analysis is needed to definitively determine whether immediate
receiving waters without impairments have water quality issues.
Of a total of approximately 140 impacted immediate receiving waters, the EPA identified seven with
303(d) impairments. Four of the seven immediate receiving waters were identified as being impaired due
to pathogens, one was listed for impairment due to sediments, and two were listed as impaired for
multiple pollutant groups - oil and grease and toxic organics, and oil and grease and metals (other than
mercury), respectively. As some of these contaminants (oil and grease, toxic organics, and metals) are
found in produced water, the ATTAINS results suggest produced water discharges may be contributing to
the impairment of these immediate receiving waters.
5.1.3 Environmental and Human Health Impacts Associated with Produced Water
Discharges
The EPA's literature review identified research that indicates the potential for adverse environmental and
human health impacts (carcinogenic and non-carcinogenic) when aquatic organisms (e.g., fish, shellfish,
and amphibians), terrestrial organisms (e.g., livestock and birds), and humans are exposed to produced
water from oil and gas operations. Additionally, the literature indicates that features of aquatic
ecosystems (e.g., microbial communities and aquatic vegetation) and terrestrial ecosystems (e.g., crops,
soil, and sediment) can be adversely impacted from exposure to produced water. The following sections
discuss the evidence of adverse impacts for aquatic organisms and ecosystems (section 5.1.3.1),
terrestrial organisms and ecosystems (section 5.1.3.2), and humans (section 5.1.3.3).
Due to a lack of research on impacts associated with Subpart E produced water discharges in Wyoming,
the EPA relied on research - both observational and experimental - that analyzed impacts associated
with exposure to produced water through other pathways (disposal pits, spills, or indirect discharges of
produced water from CWT facilities to surface water) and in other areas of the United States and North
America where oil and gas extraction occurs. Given that the chemical composition of produced water
varies geographically and across facilities, the impacts to aquatic and terrestrial organisms and
ecosystems and human health discussed in the research may differ from impacts associated with Subpart
E produced water discharges in Wyoming. Due to this, the results discussed in this section are included in
the report to provide an overview of the potential range of impacts associated with produced water
exposure. As pollutants discussed in these studies overlap with pollutants in Subpart E discharges in
Wyoming, or other areas of the United States where Subpart E discharges might occur in the future,
these findings can inform decisions on risk management as Subpart E produced water discharges are
considered.
With appropriate treatment and risk management strategies, produced water can potentially be used to
augment conventional water supplies, particularly in the more arid Western U.S. where a significant
amount of oil and gas production occurs (Bureau of Reclamation, 2011). With an estimated 13 billion
barrels (1,320,167 acre-feet) of produced water generated per year in the Western U.S. in 2021 (see
section 4.1 for more information), produced water could help offset water demands and the over
allocation of water supplies. As discussed in the 2011 Bureau of Reclamation report, the primary uses of
water in the Western U.S. are for public supply, industrial uses and mining, and thermoelectric power, as
well as irrigation and livestock and agriculture which are currently considered beneficial uses for
26
-------
produced water discharges under Subpart E.10 The use of produced water for current and future potential
beneficial uses will likely depend on the volume of water available, the quality of the water, and the
proposed end use (Bureau of Reclamation, 2011).
5.1.3.1 Aquatic Organism and Ecosystem Impacts
The literature on impacts to aquatic organisms and ecosystems from produced water focuses on impacts
to fish, shellfish, amphibians, aquatic vegetation, and microbes. The studies identified by the EPA are
primarily experimental studies which evaluate changes in certain health outcomes (acute and/or chronic)
in aquatic organisms and environmental outcomes after exposure to produced water occurs. The findings
of these studies, organized by impacted group, are described here.
Impacts to Fish
Studies evaluating impacts to fish from exposure to produced water were primarily experimental studies
that analyzed the potential toxicity of pollutants in produced water to various fish species through
changes in specific health endpoints. Studies focused on impacts to rainbow trout11 and zebrafish, as
these are common model fish species. While the toxic effects of produced water exposure on fish were
found to be chemical composition- and species-dependent, exposures to produced water were generally
found to impact cardiac function, metabolic processes, hormone levels, and cell viability.
Rainbow Trout
Folkerts et al. (2023) analyzed impacts to later cardiac function and development in rainbow trout
exposed in ovo at select critical points in cardiac development to differing dilutions of untreated
produced water from the Devonian-aged Montney Formation in Alberta, Canada and lengths of time
(acute versus chronic exposure). Cardiac development effects were measured in the juvenile rainbow
trout approximately eight months post-fertilization through assessing fish swimming performance,
aerobic scope, and cardiac structure. After eight months, rainbow trout exposed to a solution of five
percent produced water for 48 hours (acute exposure), three days post-fertilization (dpf) or 10 dpf,
experienced significantly reduced swimming performance and aerobic scope. When exposed to a solution
of 2.5 percent produced water for 48 hours, rainbow trout exposed at three dpf also experienced
significantly reduced swimming performance and aerobic scope, although rainbow trout exposed at 10
dpf did not experience as significant effects. In all acute treatments of produced water, changes in heart
muscle tissue were observed in rainbow trout after approximately eight months, specifically decreases in
compact myocardium thickness. Additionally, rainbow trout exposed to a solution of one percent
produced water for 28 days (chronic exposure) showed similar cardiac function and developmental
impacts observed for acute exposures.
Weinrauch et al. (2021) analyzed impacts to nutrient and metabolic dynamics in the liver in rainbow trout
following acute exposure to diluted samples of untreated produced water from the Devonian-aged
10 These use categories align with the use categories the USGS recorded in its 2015 and 2020 assessments of water
use in the U.S. (USGS, 2023).
11 The EPA has an approved method for the use of rainbow trout to assess acute aquatic toxicity effects of pollution
as part of WET testing (40 CFR 136.3). The EPA currently does not have an approved method for evaluating chronic
aquatic toxicity effects using rainbow trout as part of WET testing. Therefore, chronic aquatic toxicity effects
discussed in the literature are likely not covered by the results of the WET testing presented in the permits
discussed in section 3.1.
27
-------
Montney Formation in Alberta, Canada. Immediately after a 48-hour exposure to a solution of 7.5 percent
produced water, induction ofxenobiotic metabolism12, measured by ethoxyresorufin-O-deethylase
(EROD) activity and abundance of mRNA cypla, increased by 8.8-fold and 10.3-fold, respectively. Three
weeks post-exposure, these returned to baseline levels in the rainbow trout. After exposure to solutions
of 2.5 percent and 7.5 percent produced water, the ability for cells in the liver to absorb glucose
increased by 6.8-fold and 12.9-fold, respectively; the ability for cells in the liver to absorb alanine was
variable after exposure to the solutions. These results indicated that aerobic metabolism was maintained
in rainbow trout following exposure to produced water as well as the processing of glucose. Additionally,
analyzed the synthesis of glucose in the liver following exposure to solutions of 2.5 percent and 7.5
percent produced water and found that gluconeogenesis decreased by approximately 30 percent
immediately following exposure to the 2.5 percent produced water solution and decreased by
approximately 20 percent three weeks after exposure to the 7.5 percent produced water solution. The
ability for the liver to synthesize amino acids increased two-fold three weeks after exposure to the 7.5
percent produced water solution. Overall, this study indicated that exposure to produced water can alter
metabolism in the liver of rainbow trout, although homeostasis generally returns after three weeks post-
exposure.
Additionally, an experimental study by Hu et al. (2022) examined impacts to cells (cell viability and
damage to the cell plasma membrane) from rainbow trout after exposure to treated and untreated
produced water samples from the Permian Basin. Cell lines were exposed to solutions between five and
50 percent whole produced water, produced water treated for organic compounds (produced water -
inorganic fraction), and produced water treated for salts (produced water - salt control). After exposing
cell lines to solutions of five to 10 percent whole produced water, produced water - inorganic fraction,
and produced water - salt control, the authors observed no significant change in cell viability. A significant
decrease in cell viability was observed after exposing cells to solutions of 20 to 50 percent whole
produced water, produced water - inorganic fraction, and produced water - salt control, with whole
produced water exhibiting the greatest toxicity to cells. For example, when exposed to solutions of 30
percent whole produced water, produced water - inorganic fraction, and produced water - salt control,
cell viabilities were 26.9 percent, 43.1 percent, and 53.2 percent, respectively. The higher toxicity of
whole produced water compared to produced water - inorganic fraction suggested that organic
compounds in produced water had a stronger lethal effect on cell viability, although inorganic
compounds likely also effected toxicity. Additionally, Hu et al. (2022) found that when cell lines were
exposed to solutions of 50 percent whole produced water, produced water - inorganic fraction, and
produced water - salt control, all resulted in cell viabilities of less than 10 percent. The authors concluded
that these results showed that high salinity was the predominant driver of toxicity at 50 percent dilution
of all three types of produced water. Similar trends were observed when analyzing whether exposure to
produced water would cause damage of the cell plasma membrane in the rainbow trout cells.
Zebrafish
Folkerts et al. (2019) collected samples of untreated produced water from a single horizontal hydraulically
fractured well from a basin in Alberta, Canada at different points in time in the production process (1.33,
72, and 228 hours post-well production onset) and conducted an experimental study to determine the
toxicity of produced water to aquatic organisms, including early life-stage zebrafish and rainbow trout,
and to determine whether toxicity was a function of when the produced water was generated in the
12 Induction ofxenobiotic metabolism refers to the process by which certain enzymes involved in the metabolism of
foreign substances are increased in response to exposure to various chemicals.
28
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production process. The analysis of the produced water samples showed that samples collected later in
the production process had higher levels of inorganics (CI, Na, Ca, K, and Mg ions and TDS), while samples
collected earlier in the production process had higher levels of organics (polyethylene glycols [PEGs] and
polycyclic aromatic hydrocarbons [PAHs]). Exposing the aquatic organisms to 30ml_ of the various
produced water samples showed that toxicity was to a certain extent species-specific; zebrafish had lower
lethality concentrations than rainbow trout. Although, trends in toxicity across the exposed aquatic
organisms showed the samples of produced water from early in the production process had the highest
toxic potential, indicating that in addition to high salinity, organics associated with produced water
provide a significant contribution to toxicity in exposed aquatic organisms.
Another experimental study analyzed the potential acute and sublethal toxicity of suspended solids13 in
untreated produced water from the Devonian-aged Montney Basin in Alberta, Canada on early life-stage
zebrafish (Lu et al., 2021). To study the acute toxicity, zebrafish embryos were exposed to suspended
solids from one to 96 hours post-fertilization (hpf). The assessment showed concentration-dependent
acute toxicity to the embryos; significant correlations were found between mortality of exposed embryos
and the concentration of suspended solids in produced water at three exposure concentration (12.5
mg/mL, 25 mg/mL, and 50 mg/mL), with 50 mg/mL suspended solids causing 100% mortality in the
embryos. Sublethal toxicity was analyzed by exposing larval zebrafish to produced water sediment
mixtures at two selected doses (1.6 and 3.1 mg/mL). At both doses, sublethal health effects observed in
the larval zebrafish included increased EROD activity, as well as transcriptional alterations in xenobiotic
biotransformation, antioxidant response, and hormone receptor signaling genes.
Impacts to Shellfish
The EPA identified one study that analyzed impacts to freshwater mussels from exposure to radium,
strontium, and metals associated with legacy treated produced water discharges (originating from the
Marcellus Basin) from a CWT facility to the Allegheny River (Pankratz and Warner, 2024). Samples of the
streambed sediment, mussel soft tissue, and the mussel hard shell were collected upstream, at the CWT
facility outfall, 0.5km downstream, and 5km downstream and tested for radium isotopes (226Ra and 228Ra).
Samples of sediment, mussel soft tissue, and mussel hard shell collected at the CWT facility outfall did not
have significantly different levels of radium isotopes compared to upstream samples, which the authors
noted was likely due to previous remediation efforts at the outfall. Compared to samples collected
upstream from the CWT facility outfall, levels of both radium isotopes were significantly greater in the
sediment, mussel soft tissue, and hard-shell samples collected 0.5km downstream from the outfall.
Compared to sampled upstream from the CWT facility outfall, mussel hard shells were found to have
greater levels of 226Ra up to five kilometers downstream of the CWT facility outfall. Analyzes were also
performed on the mussel soft tissue and mussel hard shell to determine levels of strontium isotopes (87Sr
and 86Sr) and heavy metals (cadmium). Pankratz and Warner (2024) found that the mussel soft tissue and
hard shell 87Sr/86Sr ratios and the metal to calcium ratios (Na/Ca; K/Ca; and Mg/Ca) downstream of the
CWT facility outfall were like those observed in produced water from the nearby Marcellus Basin. A
similar conclusion was drawn from the analysis of the 228Ra/226Ra ratios in the mussel soft tissue and hard
shell downstream of the CWT facility outfall. The findings of this study indicate the potential for retention
13 The study used filtered suspended solids from six produced water samples collected from two hydraulic fracturing
wells in Alberta, Canada (Lu et al., 2021). In the suspended solids samples, 10 of 16 parent polyaromatic
hydrocarbons (PAHs), which are priority pollutants for the EPA, were detected; four alkyl PAHs were also frequently
detected in the suspended solids samples (Lu et al., 2021).
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in sediment and bioaccumulation in freshwater mussels of pollutants found in produced water. An
experimental study conducted in 2021 also showed the potential for radium, strontium, and heavy metals
like cadmium to accumulate in freshwater mussel soft tissue and concluded testing for the presence of
these pollutants could be a biomonitoring tool to assess potential impacts from produced water
discharges from oil and gas production (McDevitt et al., 2021).
Impacts to Amphibians
In addition to the Tornabene et al. (2023) study that analyzed changes in microbial community structure
on amphibian skin from exposure to pollutants in produced water (discussed below), the EPA identified
an experimental study analyzing changes in development and immune function in a species of frog
(Xenopus laevis) after being exposed to pollutants associated with produced water (Robert et al., 2019).
At three-weeks old, tadpoles were exposed for three weeks to a mixture of 23 pollutants associated with
produced water that were diluted into their housing water. One group of tadpoles was exposed to a
solution with a final concentration of 0.1 |ag/ml_ of each constituent chemical and another group of
tadpoles was exposed to a solution with a final concentration of 1 |ag/ml_ of each constituent chemical. A
third group of tadpoles was used as a control and exposed to a solution of 0.2 percent ethanol. Once the
tadpoles completed metamorphosis and reached adulthood, the frogs exposed to the chemical mixture
were assessed for potential developmental and immune impacts. Frogs exposed to the chemical mixture
at both concentrations were not found to experience a significant increase in mortality or delay in
metamorphosis compared to the control group, although the frogs did experience significantly decreased
whole body weight at the end of metamorphosis when compared to the control group. Additionally,
compared to the control group, frogs exposed to the chemical mixture at both concentrations
experienced perturbation in immune homeostasis as evidenced by an observed decrease in the relative
number of immune cells produced in the spleen, with the decrease being significant in frogs exposed to
the 0.1|ag/ml_ solution during development. Lastly, compared to the control group, frogs exposed to the
chemical mixture at l|ag/ml_ exhibited weakened antiviral immune response given that they experienced
increased viral load when infected by the ranavirus FV3. The findings of this study suggest that exposure
of frogs in early life stages to chemicals in produced water can lead to long-term development and
immune impacts.
impacts to Aquatic Vegetation
Studies analyzing impacts of produced water on aquatic vegetation primarily focused on changes in
growth for various species of algae. Hu et al. (2022) examined the potential toxicity, evaluated through
measuring growth inhibition, of green microalgae (Scenedesmus obliquus) when exposed to whole
produced water, produced water - inorganic fraction, and produced water - salt control from the
Permian Basin. When exposed to each type of produced water at increasing fractions between five and
50 percent dilution, the growth inhibition rate of the green microalgae increased significantly, indicating a
dose-response relationship. Hu et al. (2022) posited that the significant inhibition effect observed was
likely due to increased salinity in the produced water samples, which caused irreversible damage to the
green microalgae and resulted in the breakdown of cells. The authors also noted that exposure to
produced water - salt control resulted in slightly higher toxicity to the green microalgae than exposure to
whole produced water. For example, when exposed to solutions of 30 percent whole produced water and
produced water - salt control, the growth inhibition rates were 68.4 percent and 72.9 percent,
respectively. Hu et al. (2022) concluded that this was likely due to the high concentrations of ammonium
present in the whole produced water compared to the produced water - salt control, which could
promote algal growth and inhibit the adverse effects of whole produced water on the green microalgae.
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Additionally, when the green microalgae were exposed to solution of 30 percent whole produced water
and produced water - inorganic fraction, the authors observed growth inhibition rates of 60.8 percent
and 39.2 percent, respectively. Based on these results, the authors also concluded that organic
compounds in whole produced water also have a significant effect on toxicity. This finding is like that of a
study conducted by He et al. (2019), which observed an approximately 30 percent decrease in the growth
inhibition rate of green microalgae once produced water had been treated to remove organics. Another
study by Sambusiti et al. (2020) found that exposure to a synthetic produced water with various organic
compounds and very low salinity was highly toxic to microalgae (Pseudokirchneriella subcapitata).
Microbial impacts
Studies on microbial impacts primarily evaluated how exposure to produced water may change the
structure and function of aquatic microbial communities. These studies observed associations between
increases in pollutants associated with produced water in surface water and changes in microbial
structure and function that can indicate potential changes in respiration, nutrient cycling, and markers of
stress in aquatic ecosystems (Tornabene et al., 2023; Fahrenfeld et al., 2017). One other study focused on
determining what pollutants in produced water may be most toxic to microbes in surface water, finding
that salinity and organic compounds in produced water contributed significantly to toxicity (Hu et al.,
2022).
Tornabene et al. (2023) analyzed changes in microbial community structure (in terms of phylotypes) in
sediment, water, and on amphibian skin in wetlands in the Prairie Pothole Region of the U.S. (North
Dakota and Montana) that are impacted by produced water from oil and gas production in the Williston
Basin. The study primarily focused on the impacts of increases in chloride, strontium, and vanadium
concentrations in wetlands associated with produced water. Tornabene et al. (2023) found that increases
in chloride had minimal effect on the diversity and richness of the microbial communities in water and on
amphibian skin; increases in chloride were associated only with differences in the structure of all three
microbial communities and reduced microbial diversity of sediment communities. Stronger effects were
generally observed between increases in heavy metals (strontium and vanadium) concentrations and the
structure, richness, and diversity of microbial communities. Increases in strontium and vanadium were
associated with increased differences in the structure of the three microbial communities. Increases in
strontium concentrations were associated with decreased richness and diversity in the three microbial
communities, while increases in vanadium concentrations were weakly associated with increased
diversity in the three microbial communities. The authors concluded the association between vanadium
concentrations and diversity was likely spurious given the concentrations of vanadium were much lower
than strontium.
Fahrenfeld et al. (2017) also assessed changes in microbial community structure and function in water
and sediment from exposure to pollutants associated with treated produced water from oil and gas
operations in West Virginia. Water and sediment samples were collected from the upstream and
downstream reaches of a stream running through a produced water disposal site, as well as from a
control reach. Compared to the control reach, the water quality in the downstream reaches was
characterized by increased conductivity, as well as two times the level of ions like chloride, ten times the
level of sodium, and five to six times the level of barium. Given that these are contaminants associated
with produced water, the authors determined the downstream sites to be impacted. Compared to the
upstream and control reaches, impacted downstream reaches were found to have different microbial
structures in both water and sediment communities that were unique to each site. Additionally,
compared to the upstream and control reaches, changes in genes in the microbial communities were
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observed in the downstream reaches, particularly increases in dormancy, sporulation, methanogenic
respiration, cadmium resistance, and genes related to stress responses (aromatic metabolism, sulfur
metabolism, and nitrogen metabolism). Additionally, increases in antimicrobial resistance-related arcB
and maxB genes in the microbial communities in the downstream reaches were observed, although the
overall abundance of such genes did not increase. The authors noted antimicrobial resistance has been a
concern with reports of the use of biocides in oil and gas operations.
Additionally, Hu et al. (2022) examined the impacts of treated and untreated produced water
(bioluminescence inhibition) from the Permian Basin on a luminescent bacterium (Vibiriofischeri).
Exposure to a solution of five to 10 percent whole produced water did not cause significant
bioluminescence inhibition in the bacterium, indicating that water comprised of five to 10 percent whole
produced water was not very toxic. For whole produced water, the bioluminescence inhibition level
increased significantly when bacterium were exposed to solutions of 20 percent or more whole produced
water. Hu et al. (2022) attributed this increase in toxicity to the increase in salinity of the solution. The
major role of salinity in determining toxicity was confirmed when comparing the bioluminescence
inhibition level of bacterium exposed to a solution of 20 percent whole produced water (38.6 percent)
and the bioluminescence inhibition level of bacterium exposed to a solution of 20 percent produced
water - salt control (33.2 percent). Hu et al. (2022) also found that organic compounds, particularly PAHs,
in produced water may significantly contribute to acute toxicity of the bacterium as the bioluminescence
inhibition level was higher for bacterium exposed to a solution of 20 percent whole produced water than
for bacterium exposed to a solution of 20 percent produced water - inorganic fraction. Additionally, Hu et
al. (2022) found that the bacterium experience a bioluminescence inhibition level of 85 percent when
exposed to solutions with 40 percent whole produced water, produced water inorganic - fraction, and
produced water - salt control, again indicating the significant role salinity plays in toxicity of produced
water.
5.1.3.2 Terrestrial Organism and Ecosystem Impacts
The research on impacts to terrestrial organisms and ecosystems from produced water focuses on
impacts to livestock (e.g. cattle), birds, crops, sediment, and soil. The studies identified by the EPA are a
mix of observational and experimental studies which evaluate changes in certain health outcomes (acute
and/or chronic) in livestock and birds and environmental outcomes for plants, sediment, and soil after
exposure to produced water occurs. The findings of these studies are organized by impacted group.
Impacts to Livestock
The EPA's research into potential impacts to livestock resulted in identification of two observational
studies which assessed impacts to livestock such as cattle, horses, sheep, llama, and chickens after
exposure to produced water from oil and gas operations (Bamberger and Oswald, 2012; Bamberger and
Oswald, 2015). These studies found that exposure to produced water was associated with increased
incidence of health issues in livestock such as sudden death and reproductive, neurological,
gastrointestinal, musculoskeletal, and upper respiratory issues, as well as increases in stillbirths among
calves born to cattle exposed to produced water ((Bamberger and Oswald, 2012; Bamberger and Oswald,
2015).
Bamberger and Oswald (2012) conducted an observational study of health effects among livestock
(cattle, horses, sheep, llama, and chickens) exposed to produced water from oil and gas operations in
Colorado, Louisiana, New York, Ohio, Pennsylvania, and Texas. The most common exposure pathway for
the livestock was through consumption of water from wells and/or springs and ponds or creeks
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contaminated by produced water. The health effects reported by farmers to the researchers primarily
occurred among livestock located within one to three miles of oil and gas drilling operations. Health
impacts reported from exposure to contaminated water for cattle included sudden death (usually within
one to three days after exposure), reproductive issues, reduced milk production, neurological issues,
inhibited growth, gastrointestinal issues, and upper respiratory issues. For bred cattle that were exposed
to contaminated water, farmers reported increased incidence of stillborn calves with and without
congenital abnormalities (e.g., cleft palate and white and blue eyes). In the few cases of stillborn births
that could be diagnosed, veterinarians identified acute liver or kidney failure as the most common cause.
Of the seven cattle farms Bamberger and Oswald (2012) studied in the most detail, they found that, on
average, 50 percent of the herd was affected by sudden death and failure of survivors to breed after
exposure. For the other livestock included in the study, health effects reported after exposure included
neurological issues (horses and sheep), sudden death (chickens and sheep), gastrointestinal issues
(horses), dermatological issues (chickens), upper respiratory issues (llama), and musculoskeletal issues
(chickens and horses).
In another observational study conducted in 2015, Bamberger and Oswald assessed health effects among
livestock (cattle, horses, chickens, and goats) exposed to produced water from oil and gas operations in
Pennsylvania, Colorado, Arkansas, North Dakota, and New York at initial exposure and then, on average,
25 months later. The purpose of the research was to determine changes in livestock health effects over
long-term exposure and to assess whether changes in oil and gas operations (increase, no change,
decrease) impacted health outcomes for livestock. All reported livestock health impacts were within two
miles of an oil and gas operation. While livestock were exposed to produced water often through multiple
pathways, like Bamberger and Oswald (2012), most exposures were associated with consumption of
water from wells and/or springs and ponds or creeks contaminated with produced water. This exposure
often continued after the initial interview, as most farmers were not able to switch livestock to an
uncontaminated source of water. Additionally, like Bamberger and Oswald (2012), the most common
health impacts reported in livestock following exposure were reproductive, neurological, gastrointestinal,
respiratory, and growth issues, as well as reduced milk production. Changes in health impacts reported in
livestock were analyzed, on average, 25 months after exposure. The study found that, in that timeframe,
livestock exhibited a significant decrease in reproductive issues (although, farmers reported levels were
still above normal), a significant increase in respiratory issues, and a significant increase in growth issues.
Lastly, the results of Bamberger and Oswald's (2015) analysis of associations between changes in oil and
gas drilling activity and changes in health issues among animals (livestock and companion animal [e.g.,
dogs and cats]) showed that: increases in activity were associated with non-significant increases in health
issues; no changes in activity were associated with non-significant decrease in health issues; and
decreases in activity were associated with significant decreases in health issues.
Impacts to Birds
The EPA identified one study from the U.S. Fish and Wildlife Service (USFWS) in 2014 that analyzed
potential impacts to birds following exposure to produced water when it is stored in ponds prior to
discharge. The study determined that exposure to produced water can cause deteriorated health and
death in birds.
The study examined whether produced water from oil and gas operations could impact the health of
migratory bird populations. The study primarily focused on characterizing produced water stored in
evaporation ponds for removal of oil before discharge to surface waters at commercial and centralized
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oilfield wastewater disposal facilities (COWDFs)14 in Wyoming (USFWS, 2014). While the produced water
may be free of oil in the evaporation ponds, the water may still contain surfactants, geogenic chemicals,
and chemicals added during the oil and gas extraction process, and may also be hypersaline, all of which
can be hazardous to migratory bird populations that consume or come into physical contact with the
produced water. Therefore, the USFWS collected water samples from 31 COWDFs receiving produced
water between May 2009 and November 2012 to determine whether pollutants were present at levels
known to be toxic to birds. The results of the water sampling campaign showed that surface tension (a
way to measure the presence of surfactants) in all wastewater samples were above the threshold of 50
Dynes/cm which is associated with feather wetting in birds. Feather wetting causes feathers to become
waterlogged, resulting in hypothermia, or loss of buoyancy which can cause birds to drown. Additionally,
the wastewater was found to have high concentrations of chlorides, sulfates, and TDS. Concentrations of
sodium in one COWDF were above 17,000 mg/L which is the threshold for sodium toxicity in birds. In four
COWDFs, the water had TDS above 35,000 mg/L which classifies the water as hypersaline, which also
indicates the potential for sodium toxicity in birds, as well as salt encrustation in their feathers. Lastly, in
wastewater samples, thresholds for toxicity to birds were exceeded for arsenic (1,000 |ag/L), barium
(10,000 |ag/L), selenium (100 |ag/L), and boron (5,000 |ag/L).
Impacts to Crops
The EPA identified four studies that analyzed potential impacts to crops after irrigation with produced
water. The findings of the studies indicate that irrigating crops with produced water can affect plant
growth in terms of decreased rates of seed germination and reductions in biomass (Ben Ali et al., 2022;
Miller et al., 2020; Sedlacko et al., 2020). Additionally, the studies found that irrigating crops with
produced water is associated with diminished plant health, such as impaired photosynthesis,
interruptions to cell signaling, interruptions to protein synthesis, impaired plant respiration, the
accumulation of contaminants (e.g., heavy metals), and impaired metabolic function (Ben Ali et al., 2022;
Sedlacko et al., 2020; Sedlacko et al., 2022).
Ben Ali et al. (2022) examined impacts on the growth of five types of crops, western wheatgrass, alfalfa,
meadow bromegrass, Russian wildrye, and tall fescue when irrigated with desalinated produced water
treated by reverse osmosis, raw produced water that had been diluted, raw produced water, and tap
water from New Mexico. Ben Ali et al. (2022) observed that impacts to seed germination differed across
species depending on their tolerance to various levels of saline water15; as salinity increased, the
percentage of seeds that germinated for alfalfa, wheatgrass, bromegrass, and Russian wildrye decreased,
with no seeds germinating when irrigated with raw produced water. Due to its higher tolerance to
salinity, there was little change in the percentage of seeds that germinated for tall fescue as salinity
increased, even when irrigated with raw produced water. Similar patterns were observed between
increases in salinity and the amount of dry biomass for wheatgrass, bromegrass, Russian wildrye, alfalfa,
and tall fescue, with irrigation with raw produced water resulting in plant death except for tall fescue.
These findings are like those in a study conducted by Miller et al. (2020), which analyzed impacts to
growth of wheat following irrigation with solutions of one percent and five percent untreated produced
14 Commercial disposal facilities are operated for profit and receive produced water from one or more oil and gas
facilities, while centralized disposal facilities are owned and operated by the same oil and gas company that
operates the wells that generate the produced water (USFWS, 2014).
15 The salinity - measured as mg/L of TDS - of the various types of water used for irrigation were: reverse osmosis
desalinated water = 231 mg/L; tap water = 427 mg/L; diluted raw produced water = 1,400 mg/L; raw produced
water = 8,610 mg/L (Ben Ali et al., 2022).
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water from a well in the Denver-Julesburg Basin, a saltwater solution with salinity equivalent to the
solution of five percent produced water, and control irrigation water. Miller et al. (2020) observed that
with increased salinity of the irrigation water, wheat yields decreased, with the lowest yields observed for
wheat irrigated with the saltwater solution and the solution of five percent produced water. Additionally,
these findings are supported by a study conducted by Sedlacko et al. (2020) which examined impacts to
growth of sunflower and wheat plants after irrigation with tap water, solutions of 10 percent and 50
percent raw produced water, solutions of 10 percent and 50 percent treated produced water using
biologically active filtration followed by ultrafiltration (BAF-UF), and desalinated produced water using
electrodialysis. The produced water was collected from the Niobrara formation of the Denver-Julesburg
Basin. Sedlacko et al. (2020) observed that wheat and sunflower plants irrigated with solutions of 50
percent raw produced water and BAF-UF treated water displayed stunted growth, with reduced height
and leaf area, and had reduced biomass compared to wheat and sunflower plants irrigated with the tap
water control. Wheat and sunflower plants irrigated with solutions of 10 percent raw produced water,
BAF-UF treated water, and electrodialysis treated water also resulted in decreases biomass, but to a
lesser extent, indicating that salinity stress can affect plant growth.
In terms of plant health, Ben Ali et al. (2022) observed that as salinity in the irrigation water increased, so
did levels of sodium, calcium, magnesium, and chlorine, resulting in increased levels of these ions in plant
tissues for all species, which the authors noted may be associated with observed decreases in biomass.
Increases in magnesium ions were also associated with observed increases in chlorophyll content across
the five plant species. In bromegrass and tall fescue, increases in sodium ions in plant tissue were
associated in reductions in potassium ions. The uptake of potassium by plants is known to decrease with
increasing sodium concentrations and is associated with interruptions to photosynthesis regulation in
plants. Additionally, across all species, levels of manganese ions in the tissues decreased as the salinity of
the irrigation water increased. Decreased manganese in plants tissues is associated with impaired
photosynthesis. Across all species, Ben Ali et al. (2022) also observed decreases in phosphorous ions in
plant tissues with increasing salinity of the irrigation water. Reductions in phosphorous ions in plants are
associated with interruptions to cell signaling and protein synthesis. Reductions in zinc, iron, and sulfur,
which are important for plant growth, plant respiration, chlorophyll content and protein synthesis,
respectively, were observed across all species with increased salinity in the irrigation water, although a
decline in plant growth was not observed with the decrease in zinc and iron. Boron ions were also
observed to increase across the five plant species when they were irrigated with reverse osmosis
desalinated water and raw produced water, although toxic impacts were not observed. Sedlacko et al.
(2020) also observed changes in the ionome of wheat and sunflower plants that were exposed to
solutions of treated and raw produced water. Even at the lower levels of exposure to solutions of raw
produced water, BAF-UF treated water, and electrodialysis treated water, plants that were phenotypically
similar showed changes in ionome composition in terms of heavy metals, salts, and micronutrients, which
the authors suggested illustrates the impacts of irrigation with produced water on plant uptake,
translocation, and accumulation of chemicals. Additionally, in a study conducted by Sedlacko et al. (2022),
changes were observed in the metabolic function of wheat that was irrigated with diluted produced
water from the Niobrara formation of the Denver-Julesburg Basin (10 percent and 50 percent solutions),
independent of changes in metabolic function attributable to salinity stress when irrigated with a
saltwater solution equal in salinity to the solution of 50 percent produced water. Specifically, the
solutions of produced water were found to uniquely and significantly alter carbon, nitrogen, and lipid
metabolism in wheat irrigated with the solutions. Wheat irrigated with the solution of 50 percent
produced water experienced the most pronounced changes in metabolic function and impacts to survival,
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while wheat irrigated with the solution of 10 percent produced water exhibited some adaptive capacity to
survive despite the produced water stressors. Based on these findings, Sedlacko et al. (2022) concluded
that treatment of produced water, such as with nanofiltration or reverse osmosis, would likely be needed
to reduce metabolic impacts, improving plant health.
Land Impacts
The EPA identified five studies that analyzed impacts to sediment and soil from the discharge, leaching, or
application of produced water. Three of the studies focused on impacts to streambed sediment following
the discharge of produced water from CWT facilities that handle wastewater from oil and gas production
or from indirect contamination from leaching or spills at produced water disposal facilities. These studies
found that produced water that enters a stream can alter the composition of constituents in the
streambed sediment, increasing levels of salts, metals, and organic chemicals associated with produced
water from oil and gas production or organic compounds unique to oil and gas production (Burgos et al.,
2017; Van Sice et al., 2018; Orem et al., 2017). Two studies focused on impacts to soil after crops were
irrigated with produced water. These studies found that even when crops are irrigated with low-saline
produced water that has been blended with freshwater, constituents such as salt and boron can
accumulate over the long-term in soils, increasing risks of soil sodification, groundwater salinization, and
to plant health (Kondash et al, 2020; Miller et al., 2020).
Sediment
An observational study by Burgos et al. (2017) characterized contaminants in stream sediment between
10 to 19 km downstream of two CWT facilities that had previously discharged treated produced water
from the Marcellus Shale formation in Western Pennsylvania. Burgos et al. (2017) found that sediment
collected from layers corresponding to the years of maximum oil and gas production in the area
contained elevated levels of salts, alkaline earth metals (strontium, radium, and barium), and organic
chemicals (nonylphenol ethoxylates [NPEs] and PAHs). Additionally, researchers identified in these
sediments' isotopic ratios of 226Radium/228Radium and 87Strontium/86Strontium which correspond to
isotopes identified in the Marcellus Shale formation, suggesting the contaminants in the sediment likely
were sourced from produced water from the Marcellus Shale formation. A study conducted by Van Sice
et al. (2018) also looked at concentrations of radium in streambed sediment from the indirect discharge
of Marcellus Shale formation treated produced water from five centralized waste treatment (CWT)
facilities to downstream surface waters. The researchers collected sediment samples between 2011 and
2017 at locations within one and five kilometers from the point of discharge and within 58km
downstream of the point of discharge. The authors found that over the period the sediment samples
were collected, radium loadings to the stream decreased by approximately 95 percent, aligning with a
2011 voluntary request from the Pennsylvania Department of Environmental Protection that encouraged
recycling of produced water, rather than treatment and discharge, from unconventional oil and gas
operations. Despite this, the continued disposal of produced water from CWT facilities into the stream
was associated with radium concentrations near the point of discharge that were often hundreds of times
higher than background levels. For example, in 2014, near the point of discharge for two of the five CWT
facilities, sediments were found to have radium concentrations of 15,000 ± 200 becquerel per kilogram
(Bq/kg) and 24,600 ± 740 Bq/kg. Additionally, the researchers found that radium concentrations in
sediments downstream of the point of discharge were 1.5 times higherthan background concentrations.
Another study analyzed the composition of contaminants in stream sediment indirectly impacted (e.g.,
through leaching or spills) by produced water. Orem et al. (2017) analyzed streambed sediment samples
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collected from an unnamed tributary of Wolf Creek - near Fayetteville, West Virginia - upstream,
downstream, and near an underground injection disposal facility that handles produced water from
unconventional oil and gas operations in the Marcellus Shale formation. Unique to the sediments
collected downstream of the disposal facility, the researchers found several organic compounds including
diesel fuel hydrocarbons (e.g., pentacosane, Z-14-nonacosane) and halogenated hydrocarbons (e.g., 1-
iodo-octadecane, octatriacontyl trifluoroacetate, dotriacontyl pentafluoropropionate), in addition to
many chromatographically unresolved and unidentified hydrocarbons. This, the researchers suggested,
indicated that produced water from the unconventional oil and gas operations had indirectly entered the
stream and contaminants from the produced water were found in the sediment. The authors noted that
in the sediment, concentrations of the various organic compounds derived from unconventional oil and
gas operations were relatively low (less than 70 |ag/L/g [dry weight]), and assays of human cell lines
showed minimal effect when exposed to the sediment.
Soil
In parts of California, treated oilfield produced water is blended with freshwater and used to irrigate
crops. An observational study conducted in the Cawelo Water District in Kern County, California analyzed
impacts to soil quality from the use of blended produced water for irrigation of crops (Kondash et al.,
2020). Soil samples were collected from a field where hay was spray irrigated with produced water after it
was treated for oil and sites where crops were drip irrigated using produced water blended with
freshwater or local groundwater, and subsequently analyzed to quantify the concentration of salts,
metals, radionucleides (226Radium and 228Radium), and dissolved organic carbon. The researchers found
that, while none of the water quality parameters studied exceeded the current California irrigation quality
guidelines in the blended produced water, soils irrigated with the blended produced water had higher
concentrations of salts and boron compared to soil from crops irrigated with groundwater. This suggested
that while blended produced water may be low in salts and boron when they are applied, long-term
accumulation may occur in the soils its applied to which can result in long-term risks to soil sodification,
groundwater salinization, and plant health from boron toxicity. Miller et al. (2020) also found
accumulation of salts in soil when crops are irrigated with produced water and associated this with
diminished plant health. While soils irrigated with unblended produced water and blended produced
water contained 226Radium, 228Radium, and dissolved organic carbon, the concentrations were not
significantly different from soil irrigated with groundwater (Kondash et al., 2020).
5.1.3.3 Human Health Impacts
Through the literature review, the EPA identified research indicating potential adverse carcinogenic and
non-carcinogenic human health impacts associated with produced water from oil and gas operations. The
two major exposure pathways studied for human contact with pollutants in produced water are through
consumption of contaminated drinking water and inhalation of chemicals in produced water, such as
volatile organic compounds (VOCs), which is supported by a review of the literature conducted by Werner
et al. (2015). While studies on human health impacts from exposure to produced water are limited, the
studies the EPA found analyzed the potential for adverse human health impacts through inference when
chemicals that are well-known human hazards were identified in drinking water or air around produced
water disposal areas, and through experimental studies that analyzed non-carcinogenic and carcinogenic
health impacts when humans had come into contact with produced water or when human cells and
laboratory animals were exposed to produced water. The findings of the research are organized by
exposure pathway.
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Water
Research has shown the potential for adverse health effects to occur in humans exposed to produced
water through consumption of contaminated drinking water. This research includes studies that evaluate
changes in risk or the incidence of adverse health impacts associated with exposure to produced water
from drinking water consumption, as well as studies that analyze the presence of pollutants in drinking
water contaminated with produced water that are known to cause adverse human health impacts.
To evaluate changes in risk, an observational study was conducted by Gaughan et al. (2023) to analyze
associations between exposure to pollutants in produced water and certain birth defects. The study
focused on infants born in Ohio from 2010 to 2017, corresponding to a period in which natural gas
production increased in Ohio by 30 percent. Of the 965,236 live births in Ohio during that period, 4,653
infants were born with birth defects. For the infants born with birth defects, the researchers estimated
exposure to pollutants from oil and gas operations based on maternal residential proximity at birth to
active oil and gas wells and using a metric specific to the drinking water exposure pathway that identified
oil and gas wells hydrologically connected to a residence. The researchers found that the odds an infant
would be born with any birth defect were, on average, 1.13 times higher in infants born to mothers living
within 10 km of an oil and gas well compared to infants born to unexposed mothers. The odds of an
infant being born with any birth defect were, on average, 1.3 times higher in infants born to mothers
living in a residence hydrologically connected to an oil and gas well compared to mothers living in
hydrologically unconnected residences. When analyzing the odds of an infant being born with a specific
birth defect, Gaughan et al. (2023) found that, on average, the odds were elevated that an infant would
be born with neural tube defects (1.57 times higher), limb reduction defects (1.99 times higher), and
spina bifida (1.93 times higher) if the infants were born to mothers living within 10 km of an oil and gas
well compared to infants born to unexposed mothers.
Additionally, Nagel et al. (2020) conducted a review of experimental studies evaluating the potential for
endocrine-mediated health impacts in humans from exposure to a mixture of 23 chemicals commonly
found in produced water from oil and gas operations. All studies reviewed used the same mixture of
chemicals at four environmentally relevant doses (0.01 mg/L mix, 0.1 mg/L mix, 1 mg/L mix, and 10 mg/L
mix) that represent concentrations of chemical found in surface water and groundwater in areas with
dense oil and gas operations and concentrations found in the produced water itself. In all studies, the
mixtures were comprised of the 23 chemicals in equal ratios. Additionally, all the studies look at in vivo
impacts to either laboratory mice and tadpoles or human tissue culture cells. In general, the various
mixtures of chemicals found in produced water exhibited potent antagonistic activity for the estrogen,
androgen, glucocorticoid, progesterone, and thyroid receptor when they were applied to the human
tissue culture cells. The researchers also administered the mixtures via drinking water to pregnant mice
and to tadpoles to determine how they might impact reproductive and developmental health.
Developmental exposure to the mixtures substantially impacted pituitary hormone concentrations,
reduced sperm counts, altered folliculogenesis, and increased mammary gland ductal density and
preneoplastic lesions in mice (Nagel et al., 2020). Additionally, exposure to the mixtures resulted in
altered energy expenditure, exploratory and risk-taking behavior, and impairments to the immune system
of mice, while frogs experienced altered basal and antiviral immunity (Nagel et al., 2020).
To evaluate the presence of chemicals in produced water that are associated with adverse health impacts
if consumed, Elliott et al. (2016) reviewed the potential for carcinogenic effects, particularly for risks of
childhood leukemia and lymphoma, from exposure to pollutants in produced water from oil and gas
drilling operations. Elliott et al. (2016) collected a list of 1,177 chemicals found in hydraulic fracturing
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fluid and wastewater from the EPA and assessed their carcinogenicity and potential for increased risk of
leukemia and lymphoma using monographs from the International Agency for Research on Cancer (IARC).
More than 80 percent of pollutants on the list were not evaluated by IARC, but Elliott et al. (2016)
identified 111 water pollutants evaluated by IARC, 49 of which were identified as known, probably, or
possible human carcinogens. Additionally, 17 water pollutants have evidence supporting an association
with an increased risk or leukemia or lymphoma, such as petroleum-related VOCs (e.g., benzene), metals
(e.g., cadmium), solvents (e.g., dichloromethane and tetrachloroethylene), and PAHs
(benzo[b]fluoranthene, dibenz[a,h]anthracene, and benzo[k]fluoranthene).
Landis et al. (2016) and Abraham et al. (2023) conducted experimental studies to quantify levels of
disinfection byproducts (DBPs) in drinking water impacted by produced water from oil and gas
operations. The generation of DBPs at drinking water treatment systems downstream of oil and gas
operations is a public health concern as epidemiological studies have shown that exposure to DBPs
through consumption of drinking water is associated with increased risk of bladder cancer, miscarriage,
and birth defects in humans (Abraham et al., 2023). Elevated bromide and iodide levels in water sourced
for drinking water is one way for DBPs, in this case, brominated DBPs and iodinated DBPs, to appear in
drinking water as conventional drinking water treatment processes do not remove bromide or iodide
before the water is disinfected through chlorination of chloramination processes. In 2012, the EPA
collected water samples from the Allegheny River in Pennsylvania at six sites downstream of a
commercial wastewater treatment facility (CWTF) that solely treats produced water from oil and gas
producers and impacts two public drinking water systems. The results of the sampling campaign showed
that discharges from the CWTF were associated with significant increases (39 ppb, 53 percent) in bromide
concentrations at public drinking water system intakes downstream compared to the upstream reference
values during periods of low river discharge (Landis et al., 2016). While high river discharges resulted in
lower absolute concentrations due to increased dilution capacity, samples taken at the nearest
downstream public drinking water system continued to show bromide concentrations that were above
upstream levels (7 ppb, 22 percent). With these bromide concentrations at drinking water intakes, Landis
et al. (2016) estimated modeled increases in total trihalomethanes (THM) of three percent and positive
shifts of between 41 to 47 percent to more toxic brominated THM. In an experimental study, Abraham et
al. (2023) simulated surface water impacted by produced water by diluting produced water generated in
Texas 100-fold with raw river water, resulting in a mixture with bromide concentrations approximately
three times greater than average levels of natural bromide found in surface water. The mixtures were
then treated using chlorination and chloramination processes and levels of brominated DBPs and
iodinated DBPs were compared to raw river water. Under both treatment processes, water impacted by
produced water generated 1.3 to five times more total DBPs compared to the raw river water, with
individual DBPs ranging from less than 0.1 to 122 |ag/L. Chlorinated waters were found to form the
highest levels of DBPs, including brominated THM exceeding the EPA's regulatory limit of 80 |ag/L.
Chloroaminated waters generated more iodinated DBPs and the highest levels of haloacetamides in
water impacted by produced water. Additionally, water impacted by produced water that was treated
through chlorination or chloramination had higher estimated cytotoxicity and genotoxicity than raw river
water that was treated, with chloroaminated water impacted by produced water having the highest
estimated cytotoxicity due to having higher levels of iodinated DBPs and haloacetamindes which are
more toxic than brominated DBPs.
Air
Humans may be exposed to pollutants in produced water through inhalation when compounds in the
produced water, like PAHs, are volatized during the disposal process (Moore et al. 2014). In their 2016
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study, Elliott et al. identified 29 air pollutants evaluated by the IARC, 20 of which were identified as
known, probably, or possible human carcinogens. Of the 20 pollutants, 11 had evidence of increased risk
for leukemia or lymphoma, such as 1,3-butadiene, benzene, formaldehyde, dibenz[a,h]anthracene,
tetrachloroethylene, and PAHs. Ma et al. (2022) analyzed the non-carcinogenic and carcinogenic risks to
human health from produced water during the disposal process. They focused on analyzing scenarios
where produced waters are stored in tanks and/or ponds and leaks occur. In estimating the non-
carcinogenic and carcinogenic risks for inhalation exposure from contaminated soil when leakages occur,
Ma et al. (2022) found that when exposed to compounds like VOCs (e.g., benzene) both risks increased
rapidly over time in all scenarios (after 10 days, 100 days, 1,000 days, and 10,000 days of leakage),
regardless of recharge rates, causing risk estimates to exceed stipulated thresholds by several orders of
magnitude. Ma et al. (2022) concluded that the results support that the inhalation pathway may pose the
greatest risk to human health with respect to VOCs in produced water that are more easily transferred
into the air.
Multiple Exposure Pathways
Humans can experience adverse health impacts associated with exposure to produced water through
multiple exposure pathways. As previously discussed, Bamberger and Oswald (2012) conducted an
observational study tracking the incidence of adverse health impacts among farmers in six states with
farms within one to three miles of an oil and gas drilling operation. Human exposure in the study mostly
occurred through using well or spring water that was contaminated with produced water for drinking,
cooking, showering, and bathing (Bamberger and Oswald, 2012). After using the water, farmers reported
to Bamberger and Oswald (2012) that they experienced adverse health impacts such as upper respiratory
issues (burning of the nose and throat), burning of the eyes, headache, gastrointestinal issues (vomiting
and diarrhea), dermatological issues (rash), and vascular issues (nosebleeds). In 2015, Bamberger and
Oswald conducted a longitudinal observational study that tracked the changes in health impacts among
farmers in six states with farms within two miles of an oil and gas drilling operation. Changes in health
impacts were tracked over 25 months and were analyzed along with changes in oil and gas drilling
operations in the area (Bamberger and Oswald, 2015). Human exposure in the study mostly occurred
through exposure to water from well or spring water, as well as pond or creek water, that was
contaminated with produced water or through exposure to air pollution from the oil and gas drilling
operations (Bamberger and Oswald, 2015). The most common adverse health impacts reported by
farmers were neurological issues (headache, dizziness, difficulty concentrating, short-term memory loss,
skin numbness and tingling, incoordination, seizures, and inability to stand), respiratory issues (burning in
the nose and throat, coughing, wheezing, difficulty breathing, and asthma), vascular issues (nosebleeds,
stroke), dermatological issues (hair loss and rashes), and gastrointestinal issues (vomiting, diarrhea,
cramping, weight loss, and weight gain), with no significant change in health issues over the 25 months
(Bamberger and Oswald, 2015). When changes in health impacts were analyzed with changes in oil and
gas drilling operations over the 25 months, Bamberger and Oswald (2015) found that: in areas where
industrial activity increased, there was an associated non-significant increase in incidence of health
issues; in areas where industrial activity did not change, there was an associated non-significant, small
decrease in incidence of health issues; and, in areas where industrial activity decreased, there was an
associated significant decrease in incidence of health issues.
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6. Produced Water Treatment Technologies
6.1 Technologies at Current Subpart E Sites in Wyoming
In Wyoming, the typical treatment used at Subpart E sites starts with separating the oil and gas from the
produced water. This is typically done using a heater treater (see Figure 4 courtesy of WA II CO), which is
a vessel that uses heat to decrease the viscosity of the oil and help emulsions separate. Gases and vapors
rise to the top and water accumulates at the bottom. Water is removed using a drain and then flows for
additional processing. Some sites also use gun barrel separators. After separation, produced water in
Wyoming is typically sent to ponds and/or tanks where additional oil removal is provided via gravity
separation and skimming (see Figure 5 for a photograph of a typical skim pond). Emulsion breaking
chemicals are typically used to help aid the oil/water separation, and additional chemicals such as
biocides and corrosion inhibitors can be used at various locations as well. In some cases, additional
treatment for sulfides control is accomplished via aeration, causing precipitates to form (see Figure 6 for
a photograph of a newly constructed sulfides treatment basin in Wyoming). After the skim ponds/tanks
(or after sulfides treatment, if present) produced water is typically discharged to the receiving water (see
Figure 7 for a photograph of a typical outfall in Wyoming). Additional treatment beyond these
technologies is generally not occurring in Wyoming. The EPA is aware of one company, however, that is
constructing a reverse osmosis treatment facility to provide additional treatment for produced water
prior to discharge to meet permit limits for chlorides.
Figure 4. Schematic of a Typical Heater Treater
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Figure 5. Typical Skim Pond with Bird Netting at a Wyoming Production Site
Figure 6. Sulfides Treatment Basin at a Wyoming Production Site
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Figure 7. Typical NPDES Subpart E Outfall in Wyoming
6.2 Pilot Treatment Systems
According to stakeholders, there is much interest in discharging produced water in other western states,
particularly in Texas and New Mexico. This is driven by factors such as increased production (and
associated increases in produced water generation), declining injection disposal capacity in some
formations, and water scarcity. There are several state consortia that have been formed in recent years
that are investigating topics such as produced water characteristics, cost and performance of treatment
technologies, and uses of produced water outside of the oil field such as irrigation, rangeland restoration,
industrial uses, and augmentation of existing water supplies. The produced water characteristics in areas
that are investigating discharge under Subpart E, such as the Permian Basin of Texas and New Mexico, are
very different than the characteristics of existing dischargers in Wyoming. In particular, concentrations of
TDS and chlorides in Permian Basin produced water are orders of magnitude higher than found in existing
discharges in Wyoming. See Figure 8 (Xu et a I, 2022) for select data from one study of produced water
characteristics in the Permian Basin16. The mean TDS concentration of 46 produced water samples from
five locations in the Permian Basin was 128,423 mg/L.
16 Total radium was calculated by the EPA as the sum of radium-226 and radlum-228.
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10000
1000
4s
100
10
Alkaiinity
Benzene
COD
IDS
Total Radium
IOC
Figure 8. Permian Basin Produced Water Characterization Data (Xu 2022)
As a result, produced water in these and other areas will likely require desalination to be of "good enough
quality" for use in agriculture or wildlife propagation, as well as other proposed beneficial uses in the
future, and to comply with water quality standards. Technologies under investigation include thermal
desalination and membrane-based processes. Permian produced water generally will also require varying
levels of pretreatment to protect the desalination step, particularly for membrane processes. In addition,
toxic compounds such as soluble organics and ammonia that can carry through the desalination step will
generally require polishing to protect aquatic resources. Recognizing that there is work to be done in this
area, entities have invested in work to develop and test treatment trains to economically treat produced
water. For example, several companies, in concert with the New Mexico Produced Water Research
Consortium, have been testing various technologies to treat produced water (see Delanka-Pedige et a I,
2024, Tarazona et al, 2024a, Tarazona et al 2024b, Van Houghton et al, 2024a, and Van Houghton et al
2024b). The EPA toured two of the pilot projects during the study. The first site that the EPA toured was
operated by NGL Water Solutions. The pilot treatment plant uses a multi-step treatment train
incorporating proprietary technologies, including biological treatment, membrane filtration and ion
exchange, to treat Permian Basin produced water. The second site that the EPA toured was operated by
Texas Pacific Water Resources. This pilot also uses a multi-step treatment train. Figure 9 shows the
various stages in the Texas Pacific pilot treatment process as well as the constituent categories that are
targeted for removal in the various unit processes. Figure 10 shows a schematic of the pilot treatment
train.
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Stage
Treatment process
Targeted constituents
1
Oxidation arid physical separation
Solids and oil
2
Coagulation arid filtration
Suspended solids, hydrocarbons, and iron
3
Freeze desalination
Dissolved solids
4
Filtration through anionic charged glass sand
media filter and activated carbon filter
Dissolved solids, inorganic compounds, volatile
organic compounds, microbial contaminants
5
Reverse Osmosis
Dissolved solids and organics
6
GAC + Disinfection via UV Light
Residual organic and inorganic compounds
and micro-organisms
Figure 9. Texas Pacific Water Resources Pilot Treatment Train
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SETTLING/
SEPARATION
TANK
' »*"
I J
RAW
PROquCED
WATER
WASTE
BRINE'SLUDGE «
REJECT BRINE LINE
Figure 10. Texas Pacific Water Resources Pilot Treatment Schematic
In addition to the two pilot projects that the EPA toured, the Agency met with several vendors during the
study to discuss planned, in-process, or completed pilot projects. These include Bechtel, Circle Verde,
Badwater Alchemy, and Devon Energy. The EPA expects that additional information and data from these
and other pilot projects will be available and in the public domain throughout calendar year 2025 and will
help inform any future Agency efforts.
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