EPA/600/R-07/034A
A Screening Assessment of the Potential
Impacts of Climate Change on the Costs of
Implementing Water Quality-Based Effluent
Limits at Publicly-Owned Treatment Works
in the Great Lakes Region
External Review Draft Report
U.S. Environmental Protection Agency
Office of Research and Development
National Center for Environmental Assessment
Global Change Research Program
John Furlow, Thomas Johnson, Britta Bierwagen
and
ICF International
1725 Eye St, NW
Washington, DC 20006
J. Randall Freed, Jeremy Sharfenberg, Chiara D'Amore, Sarah Shapiro
September, 2006
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PREFACE
The Environmental Protection Agency's Global Change Research Program (GCRP) is an
assessment-oriented program within the Office of Research and Development that focuses on
assessing how potential changes in climate and other global environmental stressors may impact
water quality, air quality, aquatic ecosystems, and human health in the United States. The
Program's focus on water quality is consistent with the Research Strategy of the U.S. Climate
Change Research Program - the federal umbrella organization for climate change science in the
U.S. government - and is responsive to EPA's mission and responsibilities as defined by the
Clean Water Act and the Safe Drinking Water Act. The GCRP's water quality assessments also
address an important research gap. In the 2001 National Assessment of the Potential
Consequences of Climate Change in the United States (Gleick and Adams, 2000), water quality
was addressed only in the context of the health risks associated with contaminated drinking
water. A comprehensive assessment of the potential impacts of global change on water quality
was not included.
Since 1998, the National Center for Environmental Assessment's office of the GCRP has
assessed the consequences of global change on water quality. Through its assessment projects,
this Program has provided timely scientific information to stakeholders and policy makers to
support them as they decide whether and how to respond to the risks and opportunities presented
by global change. This report assesses the potential effects of climate change on the costs
implementing water quality-based effluent limits at publicly owned treatment works (wastewater
treatment facilities) in the Great Lakes Region. Water treatment infrastructure was identified as a
priority concern because water treatment is an essential service necessary to protect public health
and ecosystems. Investments in water treatment infrastructure are also capital-intensive, long-
term in nature, and irreversible in the short- to medium term. Decisions made today will thus
influence the ability of treatment facilities to adapt to changes in climate for many years into the
future.
The report is a screening level analysis intended to determine the scope and magnitude of global
change impacts rather than a detailed assessment of specific impacts and adaptation measures.
Together with a companion report addressing the potential effects of climate change on
combined sewer overflow (CSO) events, this report fulfills a GCRP 2006 Annual Performance
Measure to complete "two external review draft reports detailing the possible impacts of global
change on combined sewer overflows in key regions, and the possible effects of climate change
and variability on operations and management of publicly operated treatment works (wastewater
facilities) for OW and EPA Regions. "
Peter Preuss, Ph.D.
Director
National Center for Environmental Assessment
Office of Research and Development
U.S. Environmental Research Program
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Screening Analysis: Climate Change impacts on Costs of implementing WQBELs at F'OTWs
1 Acknowledgements
2
3 We are very grateful for the many thoughtful comments and suggestions made by staff from the
4 EPA Global Change Research Program and ICF International in developing and conducting this
5 work. In particular, we thank Susan Julius, Jordan West, and Chris Pyke from the EPA Global
6 Change Research Program. We are also very grateful for the many excellent comments and
7 suggestions provided by five peer reviewers of this report: Joel Allen (US EPA, NRMRL/WQMB),
8 Patrick Bradley (US EPA, OW/WPD), Chris Weaver, (AAAS/US EPA), Christopher Nietch (US EPA,
9 ORD/NRMRL/WSWRD/WQMB), and Russell Martin (US EPA Region 5).
10
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Executive Summary
Climate is a major factor influencing the amount, timing, and quality of water available meet
human needs (Gleick 2000). During the last century, much of the U.S. experienced increased
ambient air temperatures and altered precipitation patterns (NAST 2000). Projections of future
climate suggest these trends are likely to continue, and potentially accelerate during the next
century. Future changes in climate could thus impact water quality management.
Streamflow is strongly influenced by precipitation intensity and frequency, air temperature, and
various natural and anthropogenic factors affecting watershed hydrologic processes. Projected
impacts of climate change on streamflow include changes in both the total amount and temporal
variability of flow. Climate change is expected to increase the proportion of rainfall occurring in
high intensity events (US GCRP 2000), resulting in increased stormwater runoff and high flow
events. At the same time, a shift towards more intense storms will decrease infiltration and
groundwater recharge, resulting in reduced low flow periods between events.
Increased temperatures in the GLR will also result in increased evapotranspiration. As a result,
more precipitation will be lost to the atmosphere and less will run off into streams and rivers,
especially during the summer and early fall months when low flow periods are most likely to
occur. Increased temperatures would also mean a shift in the form of precipitation - more would
fall as rain and less as snow. As a result of this shift, and an earlier melt of the snowpack in the
spring, streamflows during the summer are likely to be reduced in the GLR (US GCRP 2000).
Publicly owned treatment works (POTWs) discharge billions of gallons of effluent daily to
receiving water bodies throughout the U.S. One of the principal pollutants associated with
POTW effluent is organic matter. Naturally occurring microbial populations in receiving waters
consume dissolved oxygen (DO) as they decompose organic matter. Low DO is a significant
problem for aquatic ecosystems and is a leading cause of impairment for water bodies listed
under Section 303(d) of the Clean Water Act (CWA).
The design characteristics of POTWs are directly tied to hydroclimatological metrics such as
daily precipitation and receiving water low-flow conditions. Generally, these systems are
designed to handle storm or flow events of a given intensity, duration, and frequency, and there
is an implicit assumption that precipitation and flow are constant over time. Potential changes in
climate could reduce low-flow conditions in receiving waters, reducing the dilution of effluent,
and increasing the likelihood of DO impairment below POTW discharge locations.
Under the CWA, all point source discharges must obtain a National Pollutant Discharge
Elimination System (NPDES) permit, which specifies limits on pollutant concentrations or loads
in the discharge. If it is determined that a discharge has the reasonable potential to cause or
contribute to an exceedance of a water quality standard (WQS), the discharger's NPDES permit
must contain a water quality based effluent limit (WQBEL) for that pollutant. Current guidance
established by the EPA's Office of Water for implementing WQBELs recommends the use of the
7-day averaging period, 10-year recurrence interval low flow (7Q10) as the design flow for
establishing assimilative capacity and WLAs for a water body. If climate change results in
reductions in low flow volume, and therefore assimilative capacity, WQBELs would need to be
more stringent, and treatment costs would increase.
The Intergovernmental Panel on Climate Change (IPCC) Regional Assessment of Vulnerability
for North America (Mulholland and Sale 1998) found that climate change may lead to a
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reduction in summer baseflows, which will reduce the assimilative capacity for wastewater
effluents and exacerbate existing or produce new water quality problems. In the Great Lakes
Region, it has also been estimated that climate change could decrease annual freshwater flows
into the Great Lakes from streams and rivers by 20% (US EPA 2001). It is thus possible that low
flow conditions, including 7Q10 events, will decrease throughout the region.
The objective of this research was to characterize the scope and magnitude of climate change
impacts on operating costs' at POTWs discharging to rivers and streams in the Great Lakes
Region (GLR). This effort was designed to be a screening study, focusing on costs of treating a
single pollutant (BOD5), from a single point source category (POTWs), for only those facilities
in the GLR most likely to be subject to water quality based effluent limits (POTWs discharging
to water bodies listed as impaired for DO or related impairments). The study focused on 147
POTWs identified as discharging to impaired receiving waters in the GLR.
Although WQBELs have been established for many dischargers, it is still the case that even
where WQBELs are appropriate, many permits are still based on technology-based effluent
limits (TBELs). Thus, before estimating the cost of more stringent treatment standards associated
with climate change, it was first necessary to estimate the treatment efficiency (and associated
cost) required for full implementation of WQBELs under current climate conditions. Then,
starting from the baseline conditions, we estimated the cost of more stringent WQBELs resulting
from potential climate change-related decreases in receiving stream flow.
A bounding analysis framework was used to evaluate scenarios for (1) treatment requirements
associated with WQBEL implementation under current climatic conditions (referred to as BL-
WQBEL) and (2) more stringent treatment requirements associated with climate change (referred
to as CC-WQBEL). Two BL-WQBEL scenarios, (assuming more and less stringent requirements
to meet WQBELs), and two CC-WQBEL scenarios (assuming high and low estimates of
decreases in 7Q10) were assessed.
Based on two case studies of TMDL implementation, values of 12 percent and 50 percent were
chosen to represent the range of incremental increase in BOD5 removal efficiency, beyond
TBELs, that will typically need to be attained by POTWs to meet WQBELs in reaches impaired
for dissolved oxygen {i.e., the BL-WQBEL). Based on an EPA estimate of potential reductions
in annual streamflow in the GLR (US EPA 2001), and a study by Eheart et al. (1999) of potential
climate change-related effects on the Sangamon River (IL), values of 20 percent and 57 percent
were chosen to represent low and high decrements in 7Q10 low flow events resulting from
climate change. The incremental changes in WQBELs required due to climate change (CC-
WQBEL) were assumed to be linearly proportional to changes in streamflow.
A cost model was developed to translate the estimates of BOD5 removal efficiency into estimates
of annual cost. The cost model provided an estimate of cost versus removal efficiency as a
function of POTW size (effluent flow). The annual cost of achieving the high and low range
values for BL-WQBEL and CC-WQBEL was then estimated for each of the 147 POTWs, and
expressed in terms of incremental cost.
1 Throughout this report, the term "operating costs" is used to represent annualized capital plus operating and
maintenance (O&M) costs.
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Results indicate that if WQBELs were implemented under current climate conditions, costs
summed across all 147 POTWs are estimated to increase by $14 million (= 4%) to $59 million (=
17%) per year over TBEL levels (for the low end and high end, respectively). This is equivalent
to an average annual cost increase of $95,000 to $400,000 per facility over TBEL levels.
Accounting for climate change (i.e. due to reduced 7Q10 streamflow in receiving waters) would
increase the incremental cost of implementing WQBELs summed across all 147 POTWs by an
additional $8 million (= 2%) to $97 million (= 24%) per year over the current cost of
implementing WQBELs. This is equivalent to an average annual cost increase of $54,000 to
$660,000 per facility over the current cost of implementing WQBELs.
As a general screening analysis, these results suggest that climate change could have a
significant effect on two of EPA's most important water programs - NPDES permitting and
POTW financing through the State Revolving Fund (SRF). Given the limited scope of the
analysis (e.g. it addresses only one pollutant, one source type, one region, and only includes
POTWs discharging to impaired streams) - it is likely that these cost estimates do not reflect the
full scope of climate change impacts on WQBEL implementation.
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Table intents
Preface i
Acknowledgements ii
Executive Summary ii
Table of Contents vii
1. Introduction 1
1.1 WQBELs and the TMDL Program 2
1.1.1 Watersheds and Management Practices 2
1.1.2 Designation of Water Quality Limited Stream Reaches (303(d)) list 3
1.1.3 Approaches to Allocate Loads 3
1.2 Municipal Wastewater Treatment 4
1.2.1 Municipal Wastewater Pollutants 4
1.2.2 Overview of Typical Treatment Systems 5
1.2.3 Effluent Guidelines 5
1.3 Impacts of Climate Change on the Hydrologic Cycle 6
1.4 Climate Change Adaptation and Water Resource Decision-making 7
2. Methods 8
2.1 POTW Identification 8
2.1.1 Water Quality Limited Stream Reaches (303(d) list) 8
2.1.2 POTWs on DO-impaired Reaches 9
2.2 Development of the Cost Curve 10
2.2.1 National Research Council Equations 11
2.2.2 Scaling Equations 12
2.2.3 Characterizing POTW Rates of Discharge 14
2.3 WQBEL Implementation in Current Climate (BL-WQBEL) 14
2.4 WQBEL Implementation in Future Climate (CC-WQBEL) 16
2.4.1 Impact on Low Flows 16
2.4.2 Proportional Impact on Effluent Limit 17
2.4.3 Incremental Treatment Cost Analysis 17
3. Results and Discussion 18
3.1 Impacts of Climate Change on Costs to Achieve WQBELs 18
3.2 State Distribution 20
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3.3 Study Limitations and Future Research 20
3.3.1 Limitations 20
3.3.2 Future Research 21
4. Conclusions 23
Literature Cited 24
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1. Er kIiI'J!,ii»iiu
Climate is a major factor influencing the amount, timing, and quality of water available meet
human needs (Gleick 2000). During the last century, much of the U.S. experienced increased
ambient air temperatures, sea level rise, and altered precipitation patterns (NAST 2000).
Projections of future climate suggest these changes are likely to continue, and potentially
accelerate during the next century. Future changes in climate thus could have a major impact on
water quality management.
Water quality management infrastructure typically have long lifetimes, significant capital costs,
and design characteristics that are directly tied to hydroclimatological metrics such as daily
precipitation and receiving water low-flow conditions. Generally, these systems are designed to
handle storm or flow events of a given intensity, duration, and frequency, and there is an implicit
assumption that precipitation and flow are constant over time.
Publicly owned treatment works (POTWs) are examples of such water quality management
systems. POTWs have a significant impact on water quality because they discharge billions of
gallons of effluent daily to receiving water bodies throughout the U.S. Potential changes in
climate could reduce low-flow conditions in receiving waters, reducing the dilution of effluent,
and increasing the likelihood of water quality impairment below POTW discharge locations.
Under the CWA, all point source discharges must obtain a National Pollutant Discharge
Elimination System (NPDES) permit, which specifies limits on pollutant concentrations or loads
in the discharge. If it is determined that a discharge has the reasonable potential to cause or
contribute to an exceedance of a water quality standard (WQS), the discharger's NPDES permit
must contain a water quality based effluent limit (WQBEL) for that pollutant. Section 303 also
establishes the Total Maximum Daily Load (TMDL) program, which requires states to determine
the maximum allowable amount of a pollutant an impaired water body can receive and still meet
water quality standards. WQBELs may be established regardless of whether a TMDL has been
developed for the receiving stream, but if a TMDL has been developed, WQBELs are the
regulatory mechanism by which waste load allocations (WLAs) for point source dischargers are
implemented.
WQBELs are developed under the assumption that pollutant loads should not exceed the
assimilative capacity of streams during low-flow conditions. Current guidance established by the
EPA's Office of Water for implementing WQBELs and TMDLs recommends the use of the 7-
day averaging period, 10-year recurrence interval low flow (7Q10) as the design flow for
establishing assimilative capacity and WLAs for a water body. Future increases in temperature
together with changes in the pattern of rainfall are likely to result in decreased low flow events in
much of the U.S. If climate change results in reductions in low flow volume, and therefore
assimilative capacity, WQBELs would need to be more stringent, and treatment costs would
increase.
The objective of this research was to characterize the scope and magnitude of climate change
impacts on operating costs at POTWs in the Great Lakes Region (GLR). This effort was
2 Throughout this report, the term "operating costs" is used to represent annualized capital plus operating and
maintenance (O&M) costs.
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designed to be a screening study, focusing on costs of treating a single pollutant (BOD5), from a
single point source category (POTWs), for only those facilities in the GLR most likely to be
subject to water quality based effluent limits (POTWs discharging to water bodies listed as
impaired for DO or related impairments). The study also addressed only facilities discharging to
rivers and streams whose discharge limits are sensitive to changes in low flow conditions,
(facilities discharging to lakes were not included).
This line of investigation is timely given the gap between anticipated funds available and funds
needed to finance improvements in wastewater treatment infrastructure. The Clean Water Needs
Survey (CWNS) released in 2004 indicates that $57 billion will be required for improving
wastewater treatment systems in the U.S. over the next 20 years (US EPA 2003), well beyond
the funds available through the State Revolving Fund (SRF), the principal source of funds for
these improvements. The extent to which climate change could widen this funding gap is an
important issue for EPA as well as state and local governments.
I I '1." I -1 I and the 11 - III III * III I" 1 >«ram
In this section, we describe some of the key features of WQBELs, focusing on their relationship
with the TMDL program. In many cases, WQBELs are in place because a TMDL has been
developed. WQBELs may be required, however, regardless of whether a TMDL has been
developed for the receiving stream (or whether the receiving water body has been listed as
impaired). Assumptions about WQBEL implementation in this study are related to the TMDL
program in the following way:
Estimates of the baseline treatment efficiency to meet WQBELs are based on data from
the TMDL program
The set of POTWs analyzed were selected because they discharge to impaired receiving
waters where TMDLs have been or will be developed
1,1,1 Watersheds ami Management Practices
The formulation of water quality management plans in the United States is driven by U.S. EPA
rules and guidance for the determination of TMDLs, a calculation of the maximum amount of a
pollutant that a water body can receive and still meet water quality standards. The Clean Water
Act, section 303, requires that states establish water quality standards, and if standards are not
met, then a TMDL must be developed.
The TMDL process integrates and evaluates all potential sources of a pollutant impacting a water
body, and is a water quality-based approach to implementing water quality standards. It is
applied to an entire watershed or drainage basin whenever possible, but may also be applied to
water body segments with individual or multiple pollutant sources. The TMDL process provides
the basis for determining whether a proposed discharge of a pollutant has the potential to cause
or contribute to an excursion of water quality standards. If a discharge poses a reasonable
potential for exceeding a standard, the TMDL process is used to determine the WQBELs for all
sources of that pollutant to assure compliance with water quality standards. If not, the watershed
or water body segment is not water quality limited for that pollutant (Bromberg 1996).
Under the CWA, all point source discharges must obtain a National Pollutant Discharge
Elimination System (NPDES) permit, which specifies limits on pollutant concentrations or loads
in the discharge. For those waters not listed as impaired, WQBELs may still be imposed through
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Screening Analysis: Climate Change impacts on Costs of implementing WQBELs at F'OTWs
the NPDES permitting process. If technology-based effluent limits (TBELS) are deemed
insufficient to attain water quality goals, the CWA (section 303(b)(1)(c)) and NPDES regulations
(40 CFR 122.44 (d)) require that the permit writers develop more stringent WQBELs designed to
ensure that water quality standards are attained (US EPA 1984).
1.1.2 Designation of Water Quality l imited Stream Reaches (303(d)) list
Section 303(d) of the Clean Water Act (CWA) requires that states, territories, and authorized
tribes create lists of impaired waters. For these impaired waters, each state must establish a
TMDL which specifies the point and non-point source pollutant loadings which will bring the
water body into compliance. Currently, these entities must submit to EPA a complete listing of
impaired waters within their jurisdictions every two years. A "303(d) impaired water body" is
one that is not meeting Water Quality Standards (WQS) despite implementation of existing
pollution control measures.
The 303(d) listings and methodology must be approved by the EPA. If EPA determines that the
states, territories, and authorized tribes are not making progress towards the creation of a 303(d)
list, they can intervene and complete the listing process. After the impaired listing process, these
jurisdictions generally have 8-13 years to establish a complete set of TMDLs for a given reach
(US EPA 2002b).
1.1.3 Approaches to Allocate Loads
The WQS for a water body are based on its designated use classification. A TMDL is the
maximum amount of a given pollutant that a water body can receive and still meet the WQS for
its designated use. The TMDL is the sum of loadings from point sources (such as POTWs and
industrial facilities) and non-point sources (such as urban and agricultural runoff, and natural
sources). TMDLs are required to contain a margin of safety to account for modeling and
measurement error and seasonal variations, which in most cases can be integrated into the
TMDL by using conservative estimates for the waste load allocation (WLA) for point sources
and load allocation (LA) for non-point sources. TMDLs are calculated according to the following
formula:
TMDL = IWLA + ILA + MOS
Where:
WLA = Wasteload allocation from point sources
LA = Load allocation from non-point sources, includes natural loadings
MOS = Margin of safety
Allocating the load reductions across sources is considered by many to be the most challenging
aspect of the TMDL program, with many complex technical and equity issues. There are 19
different allocation schemes that can be used, ranging from equal load allocation to equal cost
allocation (US EPA 1991). In the NPDES permitting process, the WLA for a POTW becomes
the basis for the legally enforceable WQBEL. The following are some of the factors that make
load allocation technically challenging:
The objective is generally to meet a water quality standard at all points throughout the
stream reach. Water quality is rarely uniform throughout the reach, however, and some
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sources usually have a greater influence than others on the locations with poorest water
quality.
A unit of load reduction for one source may not be technically or economically feasible at
another source.
One of the key factors driving a WQBEL determination for a stream or river is the amount of
water available to assimilate the pollutant load. For most pollutants, critical loads are determined
for a low-flow design period, during which the in-stream dilution provided by the waterway is at
a minimum. EPA recommends a design upstream flow for acute aquatic life criteria at the 1Q10
(1-day low flow over a 10-year period) and for chronic aquatic life criteria at the 7Q10 (7-day
low flow over a 10-year period) (US EPA 1995; US EPA 2006).
Dissolved oxygen (DO) is a key indicator of the health of a water body which, when depleted,
can pose chronic health effects to aquatic ecosystems. Concentrations of DO in the water are
reduced by the presence of organic matter, which is consumed by naturally occurring aerobic
microbes in the water. Nutrients in the water, such as nitrogen and phosphorus, also influence
DO concentrations through the facilitation of algal growth, which consumes oxygen at night
during the respiration phase of the photosynthesis-respiration cycle. A typical DO water quality
standard to sustain fish and aquatic life is 5 mg/1, though this may be set higher or lower
depending on state water quality goals and the designated use of the water body (US EPA 2000).
Because reduced DO results in chronic effects, the low-flow design period used for this study is
the 7Q10 low-flow event.
I Municipal Wastewatr i 11 n > :atment
1.2.1 Municipal Wastewater Pollutants
The primary contaminant in municipal wastewater is organic matter. When organic matter
reaches a stream or river, the decomposition process reduces the aqueous concentration of DO.
Increases in air temperature may induce a shift in aquatic biota by increasing surface water
temperatures, resulting in lower DO saturation concentrations and increased rates of BOD
decomposition (Morill et al. 2005). The standard measurement for the level of organic matter in
municipal wastewater is the 5-day biochemical oxygen demand test (BOD5). This is a measure of
the dissolved oxygen consumption for a known volume of wastewater over a 5-day incubation
period at 20° C.
In 303(d) reaches impaired for low DO, TMDLs are typically specified in terms of BOD5
loadings. Although in some cases excessive nitrogen or phosphorous loadings may be the cause
of DO impairment, in this study the focus is only on BOD5. The average influent BOD5
concentration for municipal wastewater is 215 mg/1 (US EPA 1998b), and the wastewater can be
treated through several processes.
There are many other pollutants of concern in POTW effluent, most commonly suspended solids
and microbial pathogens; however, the scope of this study is limited to BOD5.
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1.2.2 Overview of Typic itnient Systems
The BOD5 treatment process at POTWs is organized into a stepwise regimen of primary,
secondary, and advanced levels. Primary treatment generally consists of a screening process to
remove large objects from the influent and is then followed by a settling tank, which allows
suspended solids to settle out and be removed as sludge. This level of treatment has an average
BOD5 removal efficiency of approximately 43%, which varies depending on influent and plant
characteristics (US EPA 1998b).
Secondary treatment is typically comprised of an activated sludge system that follows primary
treatment. After primary treatment the influent goes through an aeration process to facilitate
aerobic bacterial digestion, and then a secondary settling tank for the further removal of
suspended solids. Often, a portion of these solids is returned to the influent at the aeration
process to further facilitate the bacterial digestion process (the remaining solids are managed as
biosolids or sludge). Combined with primary treatment, at the end of this step the average BOD5
removal efficiency is about 85%, but again the level varies depending on influent and plant
characteristics (US EPA 1998b).
There are also advanced primary and advanced secondary treatment systems where various
chemical steps can be added to increase BOD5 removal efficiency of these processes, generally
by increasing settling rates. Advanced primary treatment can reach removal efficiencies close to
secondary, and advanced secondary treatment can exceed 90% removal efficiency. Advanced
treatment to further reduce BOD5 concentrations beyond that of advanced secondary can include
filtration and reverse osmosis, and can reach BOD5 removal efficiencies of 95% and beyond
(Metcalf and Eddy 2003).
1.2.3 Effluent Guidelines
Great strides have been made over the last 30 years in the average level of municipal wastewater
treatment as a result of the combination of federal regulations for POTWs to meet secondary
treatment standards (see 40 CFR Part 133) and the more than $60 billion in grants from the
federal government for treatment plant construction and other related projects (US EPA 1998c).
Under the secondary treatment standards, discharge permits must require POTWs to meet a BOD
effluent standard of 30 mg/1 and a BOD5 removal efficiency standard of 85%. There are some
allowances for reduced levels of treatment that are granted on a case-by-case basis (e.g.,
situations where pre-existing treatment is close to these standards, episodic high flow during rain
events, low BOD5 influent concentration, or extreme geographic and climatic characteristics). In
such situations, allowances can only be made if it is determined that the increased pollution will
not adversely impact the receiving body of water (US EPA 1984).
As a result of some POTWs operating below the CWA standards, and some operating above
them, the average level of treatment for all POTWs throughout the nation is 85% removal
efficiency of BOD5 (US EPA 1998b). Compared to historical levels, the reduced BOD5 loading
to our nation's streams and rivers has produced an increase in DO levels, and thus an
3 It should be noted that there are other treatment processes, such as chlorination (to treat bacteria) and sludge
processing, which are not discussed in this memo because they do not directly relate to BOD5 removal and effluent
quality.
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improvement in overall water quality. Of a set of 311 impaired reaches below POTW outfalls
monitored by the EPA throughout the US, 69% showed an improvement in worst-case DO
levels, with an increase in minimum DO levels from an average of 4.1 to 7.2 mg/1 for the top 25
improving reaches (US EPA 1998b). However, even with this progress, there are many streams
and rivers that are still impaired. The current implementation of TMDLs for bodies of water
throughout the nation is a comprehensive attempt to improve water quality in thousands of
stream reaches, and it will require treatment beyond secondary treatment standards for thousands of
POTWs.
L Impacts of Climate Change on th i! 'i tlogi- '-V:le
Streamflow is strongly influenced by precipitation intensity and frequency, air temperature, and
various natural and anthropogenic factors affecting watershed hydrologic processes. Projected
changes in climate are thus likely to have a significant impact on the amount and seasonal
variability of streamflow.
Climate change is expected to increase the proportion of rainfall occurring in high intensity
events (US GCRP 2000). This will tend to increase storm water runoff during events, resulting in
increased high flow events without necessarily increasing the amount of water available. A shift
towards more intense storms will also decrease infiltration and groundwater recharge. Low flow
periods occur when there is little or no precipitation, and streamflow is supplied by groundwater.
If a higher proportion of total precipitation is delivered in intense events, unless total
precipitation increases significantly, low flow periods between events will thus likely decline.
Increased temperatures in the GLR will result in increased evapotranspiration. As a result, more
precipitation will be lost to the atmosphere and less will run off into streams and rivers,
especially during the summer and early fall months when low flow periods are most likely to
occur. Increased temperatures would also mean a shift in the form of precipitation - more would
fall as rain and less as snow. As a result of this shift, and an earlier melt of the snowpack in the
spring, streamflows during the summer are likely to be reduced in the GLR (US GCRP 2000).
In many areas of the US, groundwater levels are predicted to decline over the next 100 years as a
result of climate change (US GCRP 2000). A reduction in groundwater levels would have the
greatest impact during the dry summer season when many streams and rivers are dependent on
groundwater as a source of baseflow.
Extreme low flow conditions tend to be correlated with poor water quality due to reduced
dilution of point source pollutants in receiving waters (US EPA 1998a). The Intergovernmental
Panel on Climate Change (IPCC) Regional Assessment of Vulnerability for North America
(Mulholland and Sale 1998) found that climate change may lead to a reduction in summer
baseflows, which will reduce the assimilative capacity for wastewater effluents and exacerbate
existing or produce new water quality problems. In general, water quality problems associated
with human impacts on water resources via wastewater discharges (e.g., low dissolved oxygen
levels and high contaminant concentrations resulting from wastewater effluents) will be
exacerbated more by reductions in streamflow, particularly during summer baseflow periods,
than by other changes in hydrologic regimes (Mulholland and Sale 1998). More severe droughts,
particularly in summer, could result in reduced water quality (e.g., lower dissolved oxygen [DO]
concentrations, reduced dilution of effluents) and impaired habitat (e.g., drying of streams,
expansion of zones with low dissolved oxygen concentrations, water temperatures exceeding
thermal tolerances).
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1 -4 Climate Change Adaptation and Water Resour I cision-making
To focus decision support resources where they will have the most benefit, it is helpful to
identify situations where decisions are sensitive to climate-related factors, and where significant
resources will be invested (e.g., Purkey et al. in press; Freed and Sussman in press).
Based on these criteria, the TMDL program is a good candidate for decision support because:
1. Decisions are often dependent on climate-sensitive flow parameters, such as the
frequency or severity of low-flow conditions;
2. The establishment and implementation of TMDLs is a high-priority for state and federal
partners; and
3. TMDLs are associated with long-term, investments that are expected to perform for
decades into the future.
Furthermore, the focus of this study on one category of discharger, POTWs, is warranted
because:
1. POTWs are a major source of point source discharges throughout the U.S.;
2. POTWs are managed by public agencies through decision-making processes that can be
influenced by EPA;
3. Many POTWs have relatively similar treatment processes (and thus can be analyzed in a
relatively straightforward way); and
4. POTWs are the subject of strategic analysis at the Agency due to the large gap in SRF
available versus funds needed for treatment improvements.
Although relevant to many parts of the United States, this study focuses on POTWs in the Great
Lakes Region (GLR). The focus on the GLR results from EPA's long-term interest in this area
through its responsibilities to the first national assessment of the impacts of climate change on
the United States (US GCRP, 2000), and because EPA maintains strong working relationships
with key stakeholders in the region.
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2. Methods
The methodology for estimating the potential impacts of climate change on the cost of
implementing WQBELs started with identifying POTWs on impaired reaches using the 303(d)
listings for each GLR state and the industrial facilities database (IFD). This process identified a
set of 147 POTWs to be included in the analysis. The next step was to estimate treatment costs
for these POTWs at varying levels of BOD5 removal efficiency. A cost-treatment efficiency
curve for BOD5 removal that could be scaled to various sizes of POTWs was developed using
published POTW operation cost functions for capital and operations and maintenance
expenditures (NRC 1993, Qasim 1999). By combining these cost functions, a model was created
to estimate operating costs for a range of POTW capacities that was inclusive of all active
POTWs identified using the IFD and 303(d) listings.
Although WQBELs have been established for many dischargers, it is still the case that even
where WQBELs are appropriate, many permits are still based on technology-based effluent
limits (TBELs). Thus, before estimating the incremental cost of more stringent treatment
standards associated with climate change, we had to first estimate the treatment efficiency (and
associated cost) required for full implementation of WQBELs under current climate conditions.
Then, starting from the baseline conditions, we estimated the cost of more stringent WQBELs
resulting from potential climate change-related decreases in receiving stream flow.
Establishing WQBELs is a complex and site-specific activity. To simplify the system and make
the analysis tractable, we applied a bounding analysis framework to evaluate combinations of
scenarios for (1) treatment requirements associated with baseline WQBEL implementation
(referred to as BL-WQBEL) and (2) more stringent treatment requirements associated with
climate change (referred to as CC-WQBEL). We developed two BL-WQBEL scenarios (less
stringent/ more stringent) and two CC-WQBEL scenarios (low decrement in 7Q10/ high
decrement in 7Q10), for a total of four combinations, and analyzed costs for each combination.
2.1 POTW Identification
2,1,1 Water Quality Limited Stream Reaches (303(d) 1st)
Initially, all of the POTWs in the GLR that discharge into receiving waters with existing water
quality impairment were considered for inclusion this study. This initial list was pared down to a
smaller set using criteria described below. The Great Lakes Region was defined using the border
established by the Great Lakes Regional Climate Change Assessment (see
http://www.geo.msu.edu/glra/region/region.htmn. This region includes the states of Michigan,
Minnesota and Wisconsin in their entirety, as well as counties within Illinois, Indiana, New
York, Ohio, and Pennsylvania that border the Great Lakes.
Impaired reaches were defined as those listed on the 303(d) list of impaired waters developed by
each state as required under the CWA. The 303(d) database includes data on the basic attributes
for each impaired reach, as well as the location of the reach (i.e., the spatial element). Multiple
reach records exist where more than one impairment has been identified for a reach segment. The
impairment type was linked to the spatial element by linking the LIST ID field of the
impairment list, which includes the impairment type(s) according to EPA and the state for each
reach segment, to the ENTITY ID of the 303(d) table.
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The focus of this assessment was narrowed to those impairment types related to dissolved
oxygen (DO) levels. The relevant impairment type as listed by EPA is "Organic Enrichment/Low
DO." Corresponding state impairment types are:
-Biochemical Oxygen Demand
-Biological Oxygen Demand
-BOD
-BODs
-CBOD
-Chemical Oxygen Demand
-Dissolved Oxygen
-Eutrophic
-Eutrophication
-Hypoxia
-Low Oxygen
-Organic Enrichment
-Organic Enrichment / Low Dissolved Oxygen
.Organic Enrichment / Low DO
-Oxygen Demand
-Sediment Oxygen Demand
-Sludge / Sediment
-TOC Trend
-TSI
-Low Dissolved Oxygen
The list of water quality-limited reaches was further narrowed to include only creeks, streams,
and rivers, as the calculation of assimilative capacity in lakes is not related to changes in low-
flow conditions. It should be noted that some of the larger POTWs in the GLR discharge directly
to the Great Lakes. Given that POTWs discharging to lakes were omitted from this study, it is
likely that there was an undersampling of the largest POTWs in the region.
This screening resulted in the identification of 2,351 reach segments water quality-limited for
DO within the study area. However, many of these records represent segments of the same river
or stream reach. When grouped by Reach ID (from the "ReachFile 1" data set), the number of
reach segments was reduced to fewer than 250 individual existing impaired reaches.
2.1.2 POTWs on DO-impaired Readies
Given the list of 250 DO-impaired reaches in the GLR, the Industrial Facilities Discharge (IFD)
database was queried to pinpoint POTWs4 discharging to these waters. This database contains
spatial locations for industrial or municipal point sources discharging to surface waters. These
data include multiple SIC (Standard Industrial Classification) codes for each facility, of which
the code "4952" was used to identify POTWs.
Facilities were identified with primary and secondary SIC codes equal to "4952." A half mile
buffer was then created around DO-impaired reaches using a GIS (ESRIARCGIS), and all
POTWs located within this half-mile buffer were identified. This resulted in the selection of 235
POTWs located within a half-mile of a DO-impaired stream reach. Nine POTWs discharging to
impaired lakes were eliminated from the analysis.
Due to error associated with the spatial locations of the facility database, this number provides a
reasonable approximation, but should not be considered precise. Additionally, the buffer does
not take into account the relative position of the facility to the stream, viz., whether it is
downstream or upstream or whether it may be releasing directly to the stream or to a tributary of
the stream.
4 This database can be found on the EPA Office of Water BASINS CDROM series with documentation available
online at http ://www. epa. gov/waterscience/basins/metadata/ifd. htm.
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Figure 1 shows the location of POTWs within a half mile of an impaired reach within the GLR.
Of this set, only 184 POTWs were determined to be active. Thirty seven of the 184 active sites
were very small (discharge less than 0.1 MGD), and were excluded from analysis due to
concerns that the cost model would not be valid for very low discharge rates. This resulted in a
set of 147 POTWs that were selected for inclusion in the study.
Figure 1. POTWs on Stream and River Reaches Impaired by Low DO in the Great Lakes Region
Great Lakes Study Area
DO-impaired Lake
DO-impaired Reach
POTW
5
2.2 Development of the Cost Curve
To estimate the cost associated with incremental POTW treatment efficiency improvements, a
cost curve was developed expressing the unit cost of treatment (including annualized capital
costs and operating and maintenance (O+M) costs) per 1000 gallons treated for operating a
POTW at a given level of treatment (expressed as percent removal of BOD5). Capital costs
include the annual costs of loan repayment for construction and equipment needs for the POTW.
Operation and maintenance (O+M) costs consist of employee salaries, general upkeep of the
plant, sludge disposal, electricity consumption, and other expenditures that occur on a regular
basis that are essential for plant operation.
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2,2,1 National Research Council Equations
The cost curve was estimated using data published in 1993 by the National Research Council
(NRC), based on an extensive POTW survey conducted by MIT in 1990, and another survey
conducted by the NRC in 1991 (NRC 1993). These surveys were combined with expert technical
analysis to produce estimated annual capital and O+M costs for multiple treatment scenarios and
their respective BOD5 removal efficiencies (NRC 1993). The assumptions used by the NRC in
determining these costs were an interest rate of 8% for a 20 million gallon per day (MGD)
facility and a design lifetime of 20 years. Land costs were excluded from the capital cost
functions. For this study, cost estimates were adjusted to 2006 dollars to account for inflation.
The NRC identified 10 types of treatment systems, and estimated the cost for each, as well as the
removal efficiency for BOD, suspended solids, phosphorus, nitrogen, and other pollutants. The
systems range from primary treatment only (system 1) to a system with chemically enhanced
primary treatment, biological treatment, nutrient removal, high-dose lime treatment, filtration,
granular activated carbon, and reverse osmosis (system 10). These systems span BOD5 removal
efficiencies of 30 to 100 percent. Significant performance data exist only for Systems 1 through
4, and are well characterized in the two POTW surveys. Systems 5 through 10 are uncommon,
and the treatment efficiency and costs for those systems were based on literature reviews and
professional judgment (NRC 1993). Several of these more advanced (and costly) systems are
designed primarily to remove pollutants other than BOD5, however, and thus are not viable
options from a cost-effectiveness standpoint for reducing BOD5. Thus only 4 systems were
considered as alternatives for managing BOD in this study.
The systems corresponding to the range of interest for BOD5 removal efficiency are listed in
Table 1, and have removal efficiencies ranging from 78% to 98% removal. Table 1 also lists the
annual costs for the treatment systems; the NRC provided the costs as a range, and the costs
shown represent the midpoint of the range. The cost model uses an important assumption: within
each interval of treatment efficiency, it was assumed that the cost of BOD5 removal is linear
between each point generating a continuous function, i.e., there is a continuous rate of cost
increase as removal efficiency increases (rather than a stepwise function5). The cost curve is
shown in Figure 2, which also includes points for two treatment systems outside the 78% to 98%
range of interest in this study.
5 The results of the analysis could be quite different if the removal efficiency increases were handled as step
functions, though it is hard to estimate the net effect of such a change in methodology.
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Table 1. Wastewater Treatment Cost and Level of Treatment for a 20 MGD POTW
Treatment System (and NRC BODs Removal Total Annual Cost (1991$ per Million
System Number) Efficiency Gal treated)
High-dose Chemical Primary (2b) 78% $700
Conventional Primary plus Biological 92% $1,030
(3)
Chemically-enlianced Primary plus 95% $1,100
Biological Treatment (4)
Nutrient Removal plus Gravity 98% $1,625
Filtration (6)
Source: (NRC 1993).
Figure 2. Cost Curve for a 20 MGD POTW
$3.00
$2.50
"is $2.00
o
o
| $1.50
~V)
o $1.00
$0.50
$0.00
Estimated BOD5 Removal Cost
Design Flow = 20 MGD, Costs in 1991$
¦ BOD5 Removal Cost
Source: NRC 1993.
50
60
70
80
90
100
BOD5 % Removal
2.2.2 Scaling Equations
The NRC cost functions supply useful information on the cost of various treatments for a given
design flow (20 MGD), but the NRC report does not provide information that can be used to
estimate costs for different plant capacities. Due to the influence of economies of scale, the
treatment costs for smaller plants are higher than those for larger plants on the basis of dollars
per 1000 gallons treated. To estimate costs for a range of plant sizes, scaling factors were derived
based on a series of 28 cost approximation equations for POTWs (Qasim 1999). These equations
were largely derived from an EPA report on municipal wastewater treatment (US EPA, 1976).
For each of the cost elements, which range from activated sludge treatment to support personnel,
a pair of equations is presented - one for capital cost and one for annual O+M cost. All of the
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cost elements are a function of daily design flow (Q); in many cases, the functions are
exponential, with the exponents ranging from 0.43 to 2.
Scaling factors using the Qasim equations were developed for each of the four NRC treatment
systems, across the range of plant capacities for the set of 147 POTWs in our study (from 0.1
MGD to 10 MGD). There were an additional 37 active POTWs with flows less than 0.1 MGD
that were not evaluated because they were outside the functional range of the Qasim equations.
Scaling factors were determined for each plant as follows:
1. The capital costs for construction were annualized using the same approach as NRC, i.e.,
assuming an interest rate of 8% and a lifetime of 20 years.
2. The total annual costs were calculated as the sum of annualized capital plus annual O+M
cost, for each cost element, for 20 different design flows (19 within the range of POTWs
within the sample (viz., 0.1 to 10 MGD) and 20 MGD, the value provided by NRC).
3. From the 28 Qasim cost elements, those that were likely to correspond to each of the four
NRC treatment systems were selected.
4. For each of the four treatment systems that mirrored the NRC systems, the costs were
summed across the relevant cost elements for each of the 20 design flows. For example,
the conventional primary plus biological system has 13 cost elements; summing the total
system cost for plants with capacity of 1 MGD and 20 MGD, the results are $732 per
year per 1000 gallons design flow and $209 per year per 1000 gallons design flow,
respectively.
5. A "scaling factor" was developed throughout the flow range of interest, equal to the ratio
of cost at a given design flow to cost for a 20 MGD plant. For the example above, the
scaling factor is 3.51 (=$732/$209). The scaling factor was then multiplied by the NRC
cost estimate for the corresponding treatment system. In this example, the NRC cost
estimate for a conventional primary plus biological 20 MGD plant, adjusted to 2006$, is
$1.54 per 1000 gal treated. The scaled unit cost for a 1 MGD plant would be 3.51 * $1.36
= $5.40 per 1000 gal treated.
6. For each of the 147 POTWs, the treatment cost was calculated by continuous
interpolation across the range of treatment efficiencies, and multiplying flow by the unit
cost. For example, to estimate treatment cost for a 1.2 MGD plant for a target treatment
efficiency of 85%, the first step is to identify the "reference" flow (1 MGD is the closest
flow category calculated). The two treatment systems whose efficiency brackets the
target were then identified. In this case it would be high-dose chemical primary, at 78%
(with a cost of $3.72 per 1000 gal treated), and primary plus biological, at 92% (with a
cost of $5.39 per 1000 gal treated). The unit cost for 85% was determined by
interpolating ($4.35 per 1000 gal treated).
7. The annual cost for each POTW was estimated by multiplying unit cost by flow (in
thousand gallons). In the above example with flow of 1.2 MGD, annual cost would be
$1.91 million (= 1,200 thousand gal/day * $4.35 per thousand gal treated * 365 days/yr).
The actual costs of increasing removal efficiency will vary from plant to plant based on existing
POTW infrastructure and many complex, site-specific factors.
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2,2,3 Characterizing POTW Rates of Discharge
Of the 184 active POTWs in the study set, 166 had average daily effluent discharge values
reported in the IFD. For each of these 166 POTWs, the cost estimates were based on the reported
discharge rates.
For the remaining 18 active POTWs with no data on discharge rates, flow was estimated as
follows. Most of the active POTWs in the IFD database (including all 18 with no flow data) are
listed as either major or minor. It is generally the case that major POTWs have average daily
discharge rates greater than 1 MGD, while minor plants have average daily flows less than 1
MGD (US EPA, 1998c). There were 1 major and 17 minor plants for which there were no flow
values reported. The mean flow was calculated for each of the two sets (major and minor) with
flow data, and we assumed that the unknown plants have the mean flow for their set. For
reference, the total flow across all of the POTWs in the study set was considerable. Including the
18 for which no flow data were available, total flow for the 184 active POTWs in the GLR, in
water bodies impaired due to "Organic Enrichment/Low DO," is estimated to be 325 MGD.
Operational costs were determined for the 147 POTWs with flows greater than 0.1 MGD. The
total flow for these 147 POTWs is estimated to be 324 MGD, or 99 percent of the 184 active
POTWs identified in our dataset.
2.3 'III Implementation in Current C limate I l " *1 III l i
To estimate the change in treatment costs attributable to climate change, two steps in incremental
treatment were characterized. First, it was necessary to estimate the incremental treatment
beyond TBELs associated with implementation of WQBELs under current or baseline climatic
conditions (referred to as BL-WQBEL). Second, it was necessary to estimate the additional
change in treatment necessary to meet more stringent WQBELs that account for climate change
{i.e., due to anticipated changes in receiving stream flow; referred to as CC-WQBEL).
There is currently very little information on BOD5 waste load allocations for POTWs, i.e., BL-
WQBELs. Although many reaches have been listed as impaired, many jurisdictions have yet to
implement mitigation measures, including those that result in more stringent standards for point
sources. The effort needed to achieve reductions in BOD to meet a WQBEL will vary based on
considerations such as streamflow, particularly low flow 7Q10, effluent loading, and the ambient
quality of receiving waters, as well as specific wasteload allocation approaches used by
individual jurisdictions. Experience gained from compliance with existing TMDLs can provide
some guidance.
A final report entitled Total Maximum Daily Loads for the Middle Cuyahoga River, published by
the Ohio Environmental Protection Agency (OH EPA) in March of 2000, examines TMDLs for
several pollutants related to DO and the subsequent effluent changes for POTWs (OH EPA
2000). The Middle Cuyahoga River is impaired by low DO concentrations due to organic and
nutrient enrichment and hydrologic modifications that reduce flow. The primary point source
contributors are 6 POTWs on the reach, with flows ranging from 0.004 to 5 MGD (OH EPA
2000). The report details two scenarios for TMDL implementation: current hydrologic
modifications are adjusted to increase stream flow, or current hydrologic modifications remain in
place. The hydrologic modifications include the removal of two small impoundments to restore a
more natural flow regime and a minimum flow release of 3.5 MGD from an upstream reservoir.
Currently, the reservoir can reduce flow to zero during dry periods.
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The calculated TMDL under the first scenario for CBOD5 is 735 kg/d; under the second scenario
it is 411 kg/d.6 The average projected CBOD5 effluent loading reductions for the 6 POTWs
under the first scenario are 13 percent, and 50 percent for the second scenario. Table 2 provides
details in terms of POTWs and existing BOD5 effluent limits and potential reductions under the
two TMDL scenarios. (OH EPA 2000). This report not only provides an example for high and
low bounds, it also demonstrates the importance of stream flow on the WQBEL.
Table 2. Example TMDL-Based Reductions in POTW CBODs Effluent Concentration.
Middle Cuyahoga River
POTW
Existing Permit1
(mg/L CBODg)
Scenario 1 (maintain
critical low flow) Limit
(mg/L CBODg)
Percent
Reduction
Scenario 2 (no hydrologic
changes) Limit (mg/L
CBODs)
Percent
Reduction
Fishcreek
10
10
0
5
50
Kent
10
10
0
5
50
Ravenna
10
8
20
5
50
Franklin
10
8
20
5
50
Akron
10
8
20
5
50
Twin lakes
10
8
20
5
50
Average
13
50
Christina River Basin
POTW
Existing Permit1
(mg/L CBODs)
Level 1 Limit (mg/L
CBODg)
Percent
Reduction
Level 2 Limit (mg/L CBOD5)
Percent
Reduction
Broad Run
25
25
0
22.95
8
PA American
15
12.3
18
11.07
26
Downingtown
10
8.9
11
6.38
36
Kennett
25
17.5
30
16.63
34
Meadowview2
22
22
0
22
0
Average
12
21
130-day average effluent concentration under the existing NPDES permit.
2 These are in BOD5. BOD5 values can be slightly higher than CBOD5 values because nitrogenous sources are included.
In a second example, EPA (US EPA 2002a) describes the TMDL process for the Christina River
Basin, located in Pennsylvania, Delaware, and Maryland. The Christina River is impaired by low
DO concentrations and nutrient loading. The report details two TMDL allocation scenarios -
"level 1" and "level 2" - involving 5 POTWs discharging to reaches within this basin. The
average projected effluent loading reductions for the 5 POTWs under the level 1 scenario are
12%, and for the level 2 scenario the average is 30%.
6 CBOD5 is carbonaceous biochemical oxygen demand, as distinct from total biochemical oxygen demand (BOD),
which includes both carbonaceous and nitrogenous oxygen demand. BOD and CBOD are the same if there is no
degradable nitrogen in the sample analyzed.
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Screening Analysis: Climate Change impacts on Costs of implementing WQBELs at F'OTWs
These examples suggest that there is a wide range in terms of incremental change in efficiency,
beyond TBELs, required to meet BL-WQBELs. For this study, it was assumed that the likely
costs were bracketed by values given in the two reports described above. Low-end and high-end
scenarios were evaluated. For the low end load reduction, a BL-WQBEL value of 12% was
selected (the average for POTWs in the Christina Basin for the less stringent scenario in that
study). A high end BL-WQBEL value of 50% (the reduction required of all POTWs in the
Middle Cuyahoga Basin for the more stringent scenario) was selected. Although these appear to
be reasonable for a screening analysis, it is important to note that actual effects of WQBEL
implementation at individual POTWs will vary greatly and may be beyond this range.
2.4 '.*1 '1 I - II implementation in Fnfnre Climsnt-' ¦-' "'"Ml-I' I -t
2,4,1 Impact on Low Flows
Uncertainty remains concerning the specific effects of climate change on streamflow in the GLR,
however, several factors suggest that low-flow episodes are likely to decrease (US GCRP 2000).
Because 7Q10 flows are based on low flow periods, an increase in the number of these periods
will result in a reduction of the 7Q10 flow value for a given reach. Given uncertainty in local
scale climate predictions, it is difficult to predict the effects of climate change on flows during
low-flow conditions. In this study we therefore adopted a bounding analysis framework, by
developing low and high end estimates of the effect of climate change on 7Q10 was developed.
Schoen et al. (2006) found that despite uncertainty in the prediction of low flow, in the Mid-
Atlantic low flows are likely to get lower as a result of climate change even though the annual
hydrograph is not driven by the snowmelt dynamics and the area is predicted to see increases in
precipitation. The study used a stepwise linear regression for predicting the future low-flow
statistic 7Q10. Based on four general circulation models, Schoen et al. (2006) found a decrease
in the 7Q10 over the 21st century and a corresponding need to reduce contaminant load in the
future to meet current water quality standards. In the earliest future time period, the predictions
of the four models indicate that the ratio of future to current TMDL could range from 0.8 to 1.0,
or a reduction of 20% to 0%.
More specific to the GLR, a general characterization of impacts of climate change in the region
estimated that annual freshwater flows into the Great Lakes from streams and rivers could
decrease by 20% (US EPA 2001). This value was used as the low end estimate of potential
changes in 7Q10 in the screening analysis.
The potential impacts of climate change on 7Q10 in the Sangamon River upstream of
Monticello, Illinois was investigated by Eheart et al. (1999). Four climate scenarios were used to
develop 99 years of synthetic weather data. The 4 scenarios evaluated were: 1) no change in
precipitation characteristics; 2) a reduction in the mean precipitation of 25%; 3) a doubling of the
standard deviation of precipitation; 4) a combination of scenarios 2 and 3. Results show clearly
that for the scenarios assessed, climate change is likely to have a significant effect on low-flow
conditions. The 7Q10 event in this basin decreased 63% in response to a 25% drop in
precipitation; decreased 57% in response to a doubling of the standard deviation of precipitation;
and decreased 84% in response to a 25% drop in precipitation and a doubling of the standard
deviation. Because it is not clear whether precipitation will decrease, the scenarios involving a
25% decrement in annual precipitation were regarded as being overly conservative for this
analysis. The doubling in the standard deviation in precipitation is quite plausible, however, so
57% was chosen as the high end value for the bounding analysis.
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Screening Analysis: Climate Change impacts on Costs of implementing WQBELs at F'OTWs
1 2,4,2 Proportional Impact on Effluent Limit
2 The bounding analysis developed for this report assumes that there is a direct linear relationship
3 between streamflow and the BOD5 WQBEL so that a 20% reduction in 7Q10 flow will require a
4 20% reduction in loading to maintain the same level of water quality. It is also assumed that the
5 reduction in basin-wide TMDL translates directly into a proportional reduction in BOD5
6 WQBEL from POTWs.
7 2,4,3 Incremental Treatment Cost Analysis
8 As previously discussed, the bounding analysis was based on two scenarios each for BL-
9 WQBEL and CC-WQBEL, i.e., each having a low end and high end value. The four values are
10 shown in Table 3.
11 Table 3. Bounding Analysis Values.
Low End
High End
BL-WQBEL (% with respect to pre-TMDL
case, TBEL)
12%
50%
CC-WQBEL (% with respect to current
7Q10)
20%
57%
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Screening Analysis: Climate Change impacts on Costs of implementing WQBELs at F'OTWs
3. Results ,-ri >J If! ^ scussi »in
3.1 Impacts of Climate Change on Costs to Achieve Ls
The baseline case removal efficiency for the water quality-based effluent limit was calculated
assuming that the pre-WQBEL baseline was the current national average level of BOD5 removal
efficiency, i.e., 85% (US EPA 1998b). For example, if a 50% reduction in BOD5 loading was
required to meet a WQBEL, a POTW currently operating at 85% removal efficiency would need
to increase its efficiency to 92.5% to meet the new effluent limits (i.e., a 50% reduction in the
15% that is currently discharged would require removal of an additional 7.5%, so total efficiency
would be 92.5%). Furthermore, if an additional 20% reduction was necessary due to a reduction
in the 7Q10 low flow event resulting from climate change (to meet the CC-WQBEL) this would
mean that a POTW operating at 92.5% removal would have to increase that to 94% to meet the
new effluent limits (i.e., a 20% reduction in the 7.5% that is then discharged would require
removal of an additional 1.5%, so total efficiency would be 94%). The cost model estimates the
cost for each POTW, based on removal efficiency and flow, and sums across all 147 POTWs for
each scenario.
Table 4 and Table 5 show the incremental cost results for the 147 POTWs in the GLR. The cost
results are reported with respect to a TBEL baseline, as well as incremental to the BL-WQBEL.
In the TBEL baseline, annual POTW treatment costs are about $345 million. If WQBELs were
implemented, costs are estimated to increase by $14 million to $59 million per year, or an
average of $95,000 to $400,000 per facility per year (for the low end and high end, respectively).
Table 4. Estimates of Annual Cost Summed Across All 147 POTWs to Meet Low End BL-WQBEL, with Low
End and High End Design Flow Reductions for CC-WQBELs.
Note: "wrt" = "with respect to."
Percent Change in
Load (BL-WQBEL
is wrt TBEL; CC-
WQBELs are wrt
BL-WQBEL)
Percent
Removal
Efficiency
Annual Cost
(Smillion)
Incremental Annual
Cost wrt TBEL ($
million)
Percent Cost
Increase wrt
TBEL
Incremental
Annual Cost wrt
BL-WQBEL ($
million)
Percent Cost
Increase wrt BL-
WQBEL
Pre TMDL case:
(TBEL
0%
85.0%
$345
NA
NA
NA
NA
BL-WQBEL with
TMDL Load
Reduction (low end)
12%
86.8%
$359
$14
4%
NA
NA
CC-WQBEL,
Design Flow Low
End: with TMDL
Load Reduction
20%
89.4%
$380
$36
10%
$21
6%
CC-WQBEL,
Design Flow High
End: with TMDL
Load Reduction
57%
94.3%
$414
$69
20%
$55
15%
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Screening Analysis: Climate Change impacts on Costs of implementing WQBELs at F'OTWs
Table 5. Estimates of Annual Cost Summed Across All 147 POTWs to Meet High End BL-WQBEL, with Low
End and High End Design Flow Reductions for CC-WQBELs
Percent Change in
Load (BL-WQBEL
is wrt TBEL; CC-
WQBELs are wrt
BL-WQBEL)
Percent
Removal
Efficiency
Annual Cost
(Smillion)
Incremental Annual
Cost wrt TBEL ($
million)
Percent Cost
Increase wrt
TBEL
Incremental
Annual Cost wrt
BL-WQBEL ($
million)
Percent Cost
Increase wrt BL-
WQBEL
Pre TMDL case:
Technology-Based
Effluent Limit
(TBEL)
0.0%
85.0%
$345
NA
NA
NA
NA
BL-WQBEL with
TMDL Load
Reduction (high
end)
50.0%
92.5%
$404
$59
17%
NA
NA
CC-WQBEL,
Design Flow Low
End: with TMDL
Load Reduction
20.0%
94.0%
$412
$68
20%
$8
2%
CC-WQBEL,
Design Flow High
End: with TMDL
Load Reduction
57.0%
96.8%
$501
$156
45%
$97
24%
wrt = with respect to.
Estimates of the incremental annual costs of complying with tighter effluent limits expressed as
the sum across all 147 POTWs and per POTW are summarized in Table 6. These values suggest
that reductions in the 7Q10 flows would add significantly to the costs of WQBEL
implementation. The cost results are driven primarily by the increment in treatment efficiency
that is required in each scenario and the marginal cost in that region of the cost curve. They also
reflect the fact that treatment improvements have a higher unit cost at the high end of the range
than the low end (e.g., it costs more to move from 94% to 96% efficiency than to move from
85% to 87%).
Table 6. Summary of Estimated Incremental (with respect to BL-WQBEL) Annual Costs for CC-WQBEL.
Low End CC-
WQBEL (20%
beyond BL-
WQBEL)
Low End CC-
WQBEL (20%
beyond BL-
WQBEL)
High End CC-
WQBEL (57%
beyond BL-
WQBEL)
High End CC-
WQBEL (57%
beyond BL-
WQBEL)
Sum Total Cost:
Average Cost per
POTW:
Sum Total Cost:
Average Cost per
POTW:
Low End BL-WQBEL
(12% beyond TBEL)
$21 million
0.14 million
$55 million
0.37 million
High End BL-WQBEL
(50% beyond TBEL)
$8 million
0.05 million
$97 million
0.66 million
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Screening Analysis: Climate Change Impacts on Costs of Implementing WQBELsat POTWs
The incremental costs associated with changes in design flow appear significant both in absolute
terms (millions of dollars) and relative terms (percentage of TBEL costs). In the scenarios
assessed here, implementation of WQBELs under current climatic conditions would increase the
annual costs POTWs in the GLR region by about 4 to 17% over TBEL levels. Accounting for
climate change (i.e. due to reduced 7Q10 streamflow in receiving waters) would increase the
incremental cost of implementing WQBELs by an additional 2 to 24% over the current cost of
implementing WQBELs.
3.2 State Distribution
Figure 3 shows that the distribution of costs is quite uneven across the states, using as an
example the scenario with low end Baseline Compliance and low end Compliance with Climate
Change. State costs are proportional to the number of POTWs in impaired reaches and their
flow. Ohio, which has made considerable progress in listing reaches, has about half of the
POTWs in DO-impaired reaches, and incurs about half of the costs under this analysis.
Figure 3. Distribution of Costs for All 147 POTWs by State: Low end Baseline Compliance, Low end
Compliance with Climate Change
$20,000,000 -J
$18,000,000
0)
to $16,000,000
= $14,000,000
° $12,000,000
1 $10,000,000
d)
§ $8,000,000
0
- $6,000,000
1 $4,000,000
c
<
$2,000,000
$0 J T 1 1 T T T T
Illinois Indiana Michigan Minnesota Ohio Wisconsin
3.3 Study Limitations and Future Research
3.3.1 Limitations
There are several limitations to consider when interpreting the results of this research. These
limitations are related to the analytic framework and the data. These limitations, along with the
screening-level findings, point to the potential for future research in this area.
LimitedPOTWSelection - This analysis only considers active POTWs on 303(d) listed
reaches in the GLR, and should be considered a screening level analysis. As a result, this
analysis looks only at a limited number of POTWs in a single region. Climate change
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Screening Analysis: Climate Change impacts on Costs of implementing WQBELs at F'OTWs
would likely impact more POTWs in the region as the reduction in low flows in general
(and 7Q10 flows in particular) would occur on all reaches, leading to more reaches being
listed as impaired and making additional POTWs subject to WQBELs. More
significantly, costs would be much higher if all sources, all impaired reaches, and all
pollutants were considered.
Load Allocation Assumptions - A proportional distribution of load reductions was
assumed across all BOD5 sources in an average reach. There will undoubtedly be great
variation in actual load allocations and resulting impacts on POTWs. Point source load
allocations for POTWS are likely to vary widely due to various considerations such as
treatment costs and load allocations for non-point source loads (e.g., agricultural or urban
runoff). As a result, the costs associated with meeting each stepwise increment in effluent
standards for a given POTW may not reflect what would likely occur. However, from the
regional screening perspective of this study, the proportional distribution of load
reductions is a reasonable assumption.
Cost Curve Assumptions - The cost curve integrates two unique sets of municipal
wastewater treatment cost functions created by the National Research Council (1993) and
Qasim (1999). These cost functions are assumed to apply uniformly to all POTWs
evaluated. The actual costs of increasing removal efficiency will vary from plant to plant
based on existing POTW infrastructure and many complex and site-specific factors.
However, there is reasonably good agreement between the NRC cost estimate and the
cost elements from Qasim, which provides a level of independent confirmation of their
accuracy.
Another key assumption in the application of the cost curve is that the curve itself is
continuous, and an increase in required BOD5 removal efficiency results in a simple
incremental shift up the curve to a new cost point. In reality, there is often a step-wise
function of cost relative to treatment efficiency. An upgrade in treatment capacity would
require a step up in cost and treatment efficiency (i.e., the nutrient removal, high lime, or
filtration system is either there or it is not). The assumption applied in this paper may
result in conservative cost estimates as the "full step" up to the costs of the upgrade to
increase removal efficiency is not applied, and only the incremental increase in cost is
considered. The use of a continuous cost curve provides a simplifying approach to
estimating costs and also relates to the proportional waste load allocation assumption
previously discussed. If a small POTW is currently operating at the maximum treatment
efficiency, and an increase in BOD5 removal efficiency would require a great step up in
costs, then it is less likely to have a stringent TMDL allocation because more cost-
effective sources would be targeted.
3,3.2 Future Research
The results of this screening level analysis indicate that there are considerable costs associated
with improving POTW infrastructure to meet more stringent WQBELs under future climate
change scenarios. The following are several opportunities to improve the accuracy and validity
of the estimates developed in this study.
Land Use Change - Future population growth and development along these streams and
rivers will result in increased BOD5 loading as these POTWs are expanded or new ones
are built. In fact, it is estimated that by 2025, national BOD loading will return to levels
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Screening Analysis: Climate Change impacts on Costs of implementing WQBELs at F'OTWs
seen before the enactment of the CWA even with continued increases in average
treatment efficiency (US EPA 1998b). This increase in overall loading will force even
stricter WQBELs and greater focus on non-point sources as treatment efficiencies for
point sources such as POTWs are pushed to their technical and economic limits. It would
be interesting to investigate how population growth and land use change would interact
with the drivers considered in this study. Furthermore, examining the impact of potential
changes in hydrology due to urbanization (e.g., the impact of increased temperature,
impervious cover on low flow events) and the potential impact Smart Growth programs
might have on the future of POTW systems might be illuminating in terms of developing
the most cost-effective path to long-term water quality improvement.
Uncertainty Analysis - This screening analysis is formulated as a bounding problem, with
high and low endpoints for two different system characteristics (i.e., implementation of
baseline WQBELs and effect of climate change on design flows). It would be
straightforward to describe these parameters as distributions, rather than simply point
values, and then carry out a simple Monte Carlo-type analysis to create a phase space of
outcomes. Such an analysis could be conducted in concert with expert elicitation on
several key inputs, such as the incremental stringency of WQBELs (compared to
TBELs), the shape of the cost curve beyond TBEL, and the effect of climate change on
receiving stream flow.
Climate Change Impact on Low Flow - There has recently been additional research
investigating the potential impacts of climate change on low-flow conditions (e.g.,
(Nelson et al. 2006). This research could contribute to a more accurate characterization of
the impact of climate change on 7Q10 flows.
WQBELs in Unimpaired Reaches - This study focused on implementation of WQBELs
in impaired reaches, where TMDLs will need to be developed. However, WQBELs may
also be imposed by permit writers in reaches that are not on the CWA 303(d) Impaired
Waters list, within essentially the same regulatory framework (and with potentially
similar effects of climate change on compliance costs) as described here. It would be
useful to determine how often WQBELs are currently (and potentially) implemented in
unimpaired reaches, and to adjust the cost estimates accordingly.
Other Pollutants - The focus of this assessment was limited to those impairment types
related to DO levels. Expanding the scope beyond DO-related impairments would
increase the number of reaches - and thereby POTWs - included in the assessment,
giving a more comprehensive view of potential impacts of climate change on these
systems.
Additional Pollution Sources - Effluent from POTWs is only one source of pollution that
impairs waterbodies. There are many industrial and agricultural sectors that discharge
significant pollutant loads. WQBELs will also affect the stringency of discharge permits
for these facilities. Expanding the scope to include additional source categories would
require creating additional cost curves for each sector evaluated.
Expanding the Geographic Scope - This study focused only on POTWs in impaired
reaches in the GLR. From the standpoint of more accurately estimating national costs, it
would be useful to develop a national-scale estimate of compliance costs.
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4 ons
Climate changes such as warming temperatures, "flashier" precipitation events, and lower low
flows will have significant impacts on water resources. Changes in these conditions have direct
implications for decisions water resource managers are making today, because long-term
investments, such as municipal wastewater treatment infrastructure, are expected to perform for
decades into the future. The effectiveness of these infrastructure investments will, in part, be
determined by their performance under future climate conditions that differ significantly from
conditions observed over the past century.
As a general screening analysis, the results of this study suggest that climate change could have a
significant effect on two of the most important water quality programs in the United States:
attaining water quality standards (through WQBELs in general and the TMDL program in
particular) and POTW financing. As the TMDL program grows and more impaired reaches are
listed, thousands of additional sources may be included. Furthermore, as required treatment
efficiencies become more rigorous, the cost of treatment grows dramatically, so that even small
increments associated with climate change-related reductions in low-flows may have significant
costs. This analysis, like that of Eheart et al. (1999) and Schoen et al. (2006), suggests that water
resource planners should account for the possibility that climate change will affect design flows
in impaired water bodies given that any change in future climate that results in significant
reduction in flows would affect assumptions made in WQBEL calculations, with negative
consequences for in-stream water quality.
As for POTW financing, given that the design lifetime of POTWs is many decades - long
enough for the effects of climate change to be manifested - this analysis also suggests that long-
range planning for the State Revolving Fund (Clean Water Act Title VI) and other POTW
financing mechanisms should be aware of the possibility that treatment efficiencies required to
meet WQBELs will need to be more stringent than previously recognized. Thus, costs of
treatment would be higher. The Clean Water Needs Survey (CWNS) released in 2004 indicates
that $57 billion will be required for improving wastewater treatment systems in the U.S. over the
next 20 years (US EPA 2003). The results of this study indicate that the costs of adapting to
climate change, in addition to meeting the requirements of future WQBEL implementation,
could be considerable.
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1 Literal eti
2 Bromberg, A. W. Total Maximum Daily Loads and Water Quality-Based Effluent Limits. 1.3.1.
3 7-8-1996. Albany, NY, New York State Department of Environmental Conservation. New York
4 State Department of Environmental Conservation Technical and Operational Guidance Series
5 (TOGS).
6
7 Eheart J., A. Wildermuth, and E. Herricks. 1999. The Effects of Climate Change and Irrigation
8 on Criterion Low Streamflows Used for Determining Total Maximum Daily Loads. Journal of
9 American Water Resources Association, 35:1365-1372.
10
11 Freed J. R. and F. Sussman. in press. Converting Research into Decision Support: Climate
12 Change Adaptation and Water Resources. Water Resources Impact.
13
14 Gleick, P. H. Water: the potential consequences of climate variability and change for the water
15 resources of the United States. 2000. Pacific Institute for Studies in Development, Environment,
16 and Security.
17
18 Metcalf and Eddy 2003. Wastewater Engineering: Treatment and Reuse, McGraw Hill Book
19 Company, New York.
20
21 Morill J. C., R. C. Bales, and M. H. Conklin. 2005. Estimating Stream Temperature from Air
22 Temperature: Implications for Future Water Quality. Journal of Environmental Engineering,
23 131:139-146.
24
25 Mulholland, Patrick J. and Sale, Michael J. Impacts of Climate Change on Water Resources:
26 Findings of the IPCC Regional Assessment of Vulnerability for North America. Water
27 Resources Update, Universities Council on Water Resources [112], 10-15. 1998.
28
29 NAST. US National Assessment of the Potential Consequences of Climate Variability and
30 Change. 2000.
31
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1 Nelson, Karen C., Palmer, Margaret A., Angermeier, Paul L., Pizzuto, James E., Moglen, Glenn
2 E., Dettinger, Michael, and Hayhoe, Katharine. Modelling the vulnerability of stream-fish
3 assemblages to urbanization and climate change. 5-15-2006.
4
5 NRC. 1993. Wastewater Management in Coastal Urban Areas. Pages 309-350 in National
6 Research Council, editor. National Academy Press.
7
8 OH EPA. Total Maximum Daily Loads for the Middle Cuyahoga River. 31. 2000.
9
10 Purkey, D R, Huber-Lee, A, Yates, D, Hanemann, M, and Julius, S H. Integrating a Climate
11 Change Assessment Tool into Stakeholder-Driven Water Management Decision-Making
12 Processes in California. To appear in a special issue of Water Resources Management, entitled
13 WARM/ Advances in Global Change Research, in press.
14
15 Qasim, S. R. Wastewater Treatment Plants: Planning, Design, and Operation. 309-350. 1999.
16 Technomic Publishing.
17
18 Schoen, E M. Potential Effect of Climate Change on Design-Period Low Flow in the Mid-
19 Atlantic US. In press . 2006.
20
21 US EPA. Areawide Assessment and Procedures Manual: Performance and Costs. 1976. United
22 States Environmental Protection Agency.
23
24 US EPA. NPDES Permit Writer's Manual. 1984. United States Environmental Protection
25 Agency.
26
27 US EPA. Technical Support Document for Water Quality-based Toxics Control. EPA/505/2-90-
28 001.1991. United States Environmental Protection Agency.
29
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