Safeguarding Against Natural Hazards and Extreme Weather Events: A Resource Guide for Onsite Wastewater Treatment Systems


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Safeguarding Against Natural Hazards
and Extreme Weather Events:

A Resource Guide for Onsite Wastewater
Treatment Systems





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SAFEGUARDING AGAINST NATURAL
HAZARDS AND EXTREME WEATHER EVENTS:

A Resource Guide for Onsite Wastewater
Treatment Systems

POTENTIAL IMPACTS TO ONSITE WASTEWATER TREATMENT SYSTEMS (OWTS):

Explore how sea level rise, increased precipitation, extreme temperatures, wildfires,
and drought may impact OWTS. Three broad categories are used to organize

and simplify a spectrum of interrelated impacts:

1.1	Saturated drainfields 		4

1.2	Diminished treatment capacity		7

1.3	Infrastructure damage 		9

HOW COMMUNITIES CAN PREPARE:

Learn steps communities can take to prioritize preparedness:

2.1	Community planning 		11

2.2	Infrastructure considerations		14

2.3	Policy approaches		18

2.4	Education and outreach		21

References	23

Appendix 1: Background Information on Impacts 	 27

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INTRODUCTION

Onsite wastewater treatment systems (OWTS), also referred to as septic systems or decentralized systems,
treat wastewater and return the treated effluent to the environment. Due to natural hazards and extreme
weather, wastewater treatment systems, including centralized systems and OWTS, may become impaired
and require greater oversight or more frequent infrastructure adjustments to ensure proper performance.
Wastewater treatment system failure can cause the release of untreated wastewater into the environment,
increasing the risk of pathogen exposure and contamination of soils, surface waters, and groundwater.
The vulnerability of these systems is dependent on several factors, such as location, use, and infrastructure
condition. For example, when exposed to changing environmental conditions, outdated and poorly
maintained systems may see greater performance impacts than properly maintained systems. Adapting
wastewater systems to be more resilient requires homeowners and communities to identify current and
anticipated impacts and devise individual and community-specific mitigation strategies.

PURPOSE AND AUDIENCE

This resource guide is for state, Tribal, and local governments that regulate onsite wastewater treatment
systems, as well as onsite wastewater professionals. The guide covers OWTS impacts resulting from
sea level rise, increased precipitation, extreme temperatures, wildfires, and drought. Then, the guide
outlines potential steps that communities can take to increase the resilience of their OWTS. Specific
examples focus on community planning, infrastructure considerations, policy approaches, and
education and outreach. The information in this guide is not meant to be exhaustive, and there may
be other impacts and mitigation steps worth considering.

BACKGROUND

The U.S. Environmental Protection Agency (EPA) estimates that about 20 percent of U.S. households
use OWTS (U.S. EPA, 2002). Some communities rely exclusively on OWTS (U.S. EPA, 2024a).
Conventional OWTS digest organic matter and separate floatable materials (e.g., oils and grease) from
solids in a septic tank. The liquid (known as effluent) is discharged from the septic tank into a series
of perforated pipes buried in gravel, chambers, or other special units designed to slowly release the
effluent into the soil. There must be ample soil depth above the local/seasonal water table for
wastewater to be adequately treated before it enters the groundwater. Other site-specific conditions
can impact where OWTS can be located, including soil composition, vertical separation distance
to bedrock, and proximity to drinking water wells. Currently, OWTS are regulated and designed based
on standards created at the state, county, and local levels.

Some methods for wastewater site evaluations use outdated assumptions or older protocols.

It is critical that decisions about OWTS adaptations or the need to install new equipment be based
on community specific information. For more information on potential impacts from sea level rise,
increased precipitation, extreme temperatures, wildfires, and drought, please see Appendix 1.
Community education is also critical to help OWTS users understand anticipated impacts and
equip them with mechanisms for adaptation.

Observed impacts, such as sea level rise, increased precipitation, extreme temperatures, wildfires,
and drought may interfere with an OWTS's functionality. Communities may be affected by multiple
impacts simultaneously (i.e., cumulative impacts). Some Florida communities, for example, face both
sea level rise and extreme precipitation events. OWTS in these communities are likely to experience
saturated drainfields, infrastructure damage, and saltwater intrusion, all impacting treatment and
operation (Miami Dade County, 2018). In regions affected by extreme heat and wildfires, warmer soils
may impact microbial activity, and wildfires may damage OWTS equipment. Understanding OWTS
characteristics, vulnerabilities, and location can help communities identify anticipated impacts
and potential adaptation strategies.

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1. POTENTIAL IMPACTS TO OWTS

1.1 Saturated Drainfields

SEA LEVEL RISE

Sea level rise can cause the water table to rise in coastal areas. This change can reduce the vertical
separation distance (VSD) from groundwater to the drainfield area of an OWTS, inhibiting effective
treatment and creating a direct pathway for pollution to reach groundwater sources, as shown in Figures 1
and 2. Water tables can increase by 31 to 35 percent of the rate of sea level rise, which effectively
reduces the VSD and site suitability (Cox et al., 2020; Mihaly, 2018). Sea level rise can also increase
saltwater intrusion into groundwater, which impacts soil structure and can reduce a drainfield's ability
to effectively treat wastewater. Communities can help increase resilience to saturation and protect
treatment capabilities by increasing the VSD required in regulations that govern OWTS or by requiring
treatment technologies that allow for a shallower VSD.

Properly Functioning System	Failed System Saturated Drainfield

Figure 1: OWTS with a properly functioning drainfield.

Green circular graphics represent beneficial microbes
that aid in the treatment of wastewater.

Figure 2: OWTS with a saturated drainfield.

Green circular graphics represent beneficial microbes
that aid in the treatment of wastewater.

4

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There is significant reliance on OWTS along the East Coast (Figure 3). Approximately 50 percent
of homes in New England states and the Carolinas rely on OWTS (Mihaly, 2018; University of North
Carolina, 2021). New rural developments continue to use OWTS, particularly in areas experiencing
sea level rise, including New England, the mid-Atlantic and southeastern states, and island
communities such as Hawai'i and Puerto Rico (NAHB, 2023; U.S. Census Bureau, 2022).

Drainfield soil saturation from increased precipitation reduces the ability of OWTS to remove nutrients,
bacteria, and other pathogens in wastewater. Saturation reduces soil adsorption and impairs
interactions with microbes living in the soil.

After floods, the water table can rise and cause OWTS backups, which expose residents to sewage.
Soil saturation increases the risk of exposure to insufficiently treated wastewater that percolates
to the surface or runs off into adjacent surface water and groundwater. Exposure to wastewater puts
people and animals at risk for wastewater-borne diseases. Human health impacts from contaminated
water can also quickly become a concern when homeowners or tenants resort to improper disposal
of waste through primitive means, such as buckets, during an OWTS backup or failure.

Saturated and failing OWTS drainfields can also contaminate nearby water bodies with excessive
nutrients. Higher water tables facilitate the movement of nutrients to adjacent water bodies, which
can lead to algal blooms and low oxygen levels, both of which negatively impact nearby aquatic
species (University of North Carolina, 2021).

Figure 3: OWTS distribution in the United States.

Source: U.S. EPA, 2002.

INCREASED PRECIPITATION

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CASE STUDY

Monitoring OWTS Vertical Separation Distance
During Extreme Weather

In September 2018, Hurricane Florence hit North Carolina's coast and delivered
more than 30 inches of rain (National Weather Service, 2018). Researchers
monitored groundwater levels at three OWTS sites to assess how the rainfall
affected VSD before, during, and after the hurricane (Humphrey et al., 2021).

Site 1 was located near the top of sloped terrain, and therefore had a relatively
deep VSD. Sites 2 and 3 were situated on flat interstream divides, which
contributed to their relatively shallow VSDs.

Groundwater rose 4.9, 5.6, and 5.9 feet at the three sites, respectively, within the
first nine hours of the storm, greatly decreasing the VSD at each site. Groundwater
did not inundate the drainfield at Site 1 because, just prior to the storm, the water
table had been 13 feet below the drainfield. However, groundwater inundated the
drainfields at Sites 2 and 3, which caused groundwater contamination. Groundwater
even surfaced at Site 2 for 12 consecutive hours, and the velocity and flow from
the storm led to contaminated water dispersion over a large area. The groundwater
at each site did not return to pre-storm levels until 27,40, and 25 days after the
storm, respectively (Humphrey et al., 2021).

6

Figure 4: House in Horry County, South Carolina, flooded during Hurricane Florence.
Hurricane Florence multi-sensor rainfall estimates, September 18, 2018, 2pm EDT.

Source: Natural Weather Service, 2018. House photograph credited to Jonathan
Lamb, NWS; Rainfall map produced by National Weather Service Eastern Region
Headquarters.

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1. POTENTIAL IMPACTS TO OWTS

1.2 Diminished Treatment Capacity

7

SEA LEVEL RISE AND INCREASED PRECIPITATION

The availability of oxygen in soils is critical for the function of the different bacteria species that
destroy pathogens and transform nutrients in wastewater. When soils are saturated with water due
to sea level rise and/or increased precipitation, the soil oxygen levels in OWTS become depleted
due to the displacement of air, which reduces aerobic microbial activity and diminishes wastewater
treatment capacity. Some research has indicated that OWTS generally take two to seven days
to recover and return to normal function after inundation events, depending on the soil type,
its drainage characteristics, and proximity to surface water (University of North Carolina, 2021).

EXTREME TEMPERATURE

Increased temperatures impact OWTS in both positive and negative ways. Increased air
temperatures warm soils, which can increase microbial activity and aid in wastewater treatment.
However, increased air temperatures can also increase oxygen demand and compromise aerobic
microbial activity, which impacts OWTS biochemical processes (Mihaly, 2018; Cooper et al., 2016)
Decreases in the effectiveness of OWTS treatment can lead to wastewater-borne disease
outbreaks and pollution of nearby water bodies.

Figure 5: Algal blooms in Lake Erie, Ohio (left), and Shelburne Pond, Vermont (right).

Source: U.S. EPA (left), Lisa B. (right).

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Some lab studies show that changes in biochemical oxygen demand (BOD5) and oxygen levels can
affect nitrogen and phosphorous removal (Cooper et al., 2016). Dispersion of nutrient-rich waters
from OWTS may cause algal blooms in adjacent water bodies and hypoxic conditions for aquatic
ecosystems (Figure 5; Mihaly, 2018). Since underground treatment processes can be complex and
influenced by many variables, close evaluation of real-world performance may be needed. To develop
solutions that work for local conditions in areas vulnerable to extreme temperatures, state and local
agencies may want to test and monitor technologies that provide advanced treatment for nutrient
removal.

Figure 6: Wildfire-damaged property with OWTS in Vacaville, California, following the LNU Lightning
Complex Fire. Professional inspection is often required to assess OWTS condition post-fire.

Source: Marcia Parker, 2020.

INCREASED WILDFIRES

Wildfires alter the mass, activity, and biodiversity of microbial communities in near-surface soil
(Barreiro & Dfaz-Ravina, 2021). It may take five to 10 years for the topsoil and subsoil layers to fully
recover from a wildfire, especially an extreme one, and in some cases the soil may be permanently
altered (Barreiro & Diaz-Ravina, 2021).

Wildfires can also lead to soil compaction and reduced OWTS function. High-intensity fires can
cause an increase in soil bulk density because of the collapse of soil aggregation and the destruction
of soil organic matter and pore space. This impact leads to an increase in the hydrophobicity of soil
particles, resulting in decreased water infiltration (Agbeshie et al., 2022). The toppling of trees during
a wildfire can damage OWTS, especially in cases where a tree's roots extend into the drainfield.
The loss of vegetation, as well as the large volume of water used during firefighting activities,
can make areas affected by wildfires more susceptible to erosion. More research can be beneficial
to determine the full extent of the impact of wildfires on the treatment capacity of OWTS.

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1. POTENTIAL IMPACTS TO OWTS

1.3 Infrastructure Damage

SEA LEVEL RISE AND INCREASED PRECIPITATION

Coastal erosion, a consequence of sea level rise and other factors, can uncover OWTS tanks
and piping, rendering them inoperable (University of North Carolina, 2021). When intense precipitation
compounds with storm surge events, it can lead to flooded OWTS and destructive erosion. These
events can scour, expose, and degrade OWTS infrastructure (Capps et al., 2020). Additionally,
if OWTS are not anchored properly into the ground, sea level rise and flooding can raise the water
table and push OWTS components upward in the soil, potentially damaging inlet and outlet pipes,
along with other infrastructure. In steep areas, extreme single- or multi-day precipitation events
can impact soil composition and lead to landslides, damaging OWTS.

INCREASED WILDFIRES

Although they are largely located belowground, OWTS are susceptible to the impacts of wildfires.
For example, wildfires can destroy OWTS equipment by melting plastic and fiberglass components,
control valves, and purge valves that are located above ground. Fires can even melt components
that are several feet underground, such as risers and diversion valves between tanks and drainfields.
The weight of equipment used to suppress wildfires, such as fire and brush trucks, may damage
OWTS since their locations are often undefined (Steinkraus, 2018).

OWTS equipment that is destroyed by wildfires will likely need to be replaced, causing system
shutdowns that may have both short- and long-term implications, including potential human
exposure to untreated wastewater.

Wildfires strip areas of vegetation that help to hold soils in place. Therefore, erosion and
mudslides are common in areas recently affected by wildfires and heavy rainfall. After a wildfire,
OWTS can be buried in multiple feet of mud and pollute nearby waterways with sediment
and nutrients (Steinkraus, 2018).

INCREASED DROUGHTS

Droughts can cause groundwater levels to drop, which may lead to land subsidence over time.
Subsidence can damage OWTS pipes or compromise the structural integrity of other treatment
components (Hughes et al., 2021). When drought occurs in shrink-swell soil types, changes in
volume in response to moisture content can cause large cracks to form in the soil, potentially
creating pathways for wastewater to travel rapidly with limited treatment.

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10

Boulder County Public Health Response
to OWTS Damage from Natural Disasters

After several disasters in recent years, including the costliest wildfire in Colorado
history, Boulder County has focused on policies that support recovery and
rebuilding to limit environmental and health impacts from OWTS damaged by
natural disasters. The county overhauled its preparedness documents and created
a "Water Quality Playbook." Designed for environmental health specialists and
county leadership, it includes important information and procedures related
to addressing OWTS after a disaster and serves as a repository for recent lessons
learned. The Water Quality Playbook includes policy and primacy considerations,
immediate response priorities, and short- and long-term recovery strategies
(including internal public health risk assessments). In addition to developing the
Playbook, Boulder County amended land use codes to reduce uncertainty around
the use of undocumented OWTS after damages from wildfire.

To speed up recovery following disasters and reduce the number of homes using
unpermitted OWTS in the county, Boulder County amended its policy to permit
accessory dwelling units (ADUs) on properties destroyed by fire that had previously
relied on OWTS. ADUs are permitted to remain as permanent structures after
the home is rebuilt, which has resulted in an increase in OWTS permit revisions
for larger systems that support both ADUs and rebuilt homes. Permitting costs
remain in place for homeowners building expanded homes post-recovery,
but permitting costs to reconnect homes are waived to ease the burden on
homeowners rebuilding homes the same size or smaller. As seen in Figure 7, this
has resulted in an increase in the number of issued permits.



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Figure 7: Boulder County
OWTS permits issued from
2010 through 2023 in the
Marshall Fire Area.

Source: Data analysis conducted
by Boulder County Public Health.

Note: The Marshall Fire began
on December29,2021.
A significant increase in OWTS
permit issuance can be seen
following the fire.

Year of Issuance

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2. HOW COMMUNITIES CAN PREPARE

2.1 Community Planning

Inventories of existing OWTS help communities assess performance, condition, and locations of systems
when conducting resilience planning. Integrating this type of data into community planning for infrastructure
projects can enable planners to incorporate positive impacts for the community served by OWTS. Geographic
information system (GIS) mapping of OWTS allows communities to focus on addressing the actual flooding
and saturation observed in their area. For example, potential impacts from natural hazards and extreme
weather may be dependent on local hydrologic conditions, so targeted site-specific approaches may
be more cost effective than implementing changes universally.

Beyond assessing risk, OWTS inventories can also be used to inform policies and initiate monitoring programs
that help make communities more resilient. Routine monitoring is essential to ensure proper OWTS function
and identify issues before they affect public and environmental health. Communities can use geospatial
datasets to estimate the number of OWTS within jurisdictions, which can prove particularly useful in areas
where limited information about septic infrastructure is available (Capps et al., 2020).

An understanding of OWTS ownership and current statutes can help communities identify regulations that
need to be updated to account for projected impacts from natural hazards and extreme weather. OWTS are
regulated by states, Tribes, and local governments and maintained by property owners or regional management
entities. State and local officials, including health officials, are typically involved only when installing a new
system or when failures present community risks. However, these officials may need to expand their involvement
by developing or enhancing maintenance tracking programs to monitor wastewater treatment effectiveness.

HOW TO ASSESS RISK?

Use the Federal Emergency Management Agency (FEMA)'s Flood Mao Service Center to find your
community's flood map and assess local flood risk. The EPA's Creating Resilient Water Utilities (CRWU)
initiative provides drinking water, wastewater, and stormwater utilities with the practical tools, training,
and technical assistance needed to increase resilience to current and future climate conditions.

• Use CRWU's Climate Resilience Evaluation and Awareness Tool (CREAT) to assess potential
climate impacts and related risks. The tool guides users through a climate threat identification
process and the design of adaptation plans based on their selected threats. CREAT features a
series of five modules, a user-friendly interface, climate data projections, and monetized risk results.
CREAT also has import capacity and integrates with other EPA tools such as the Vulnerability
Self-Assessment Tool (VSAT) and Resilient Strategies Guide.

• Use CRWU's Climate and Weather Data Maps to review climate model projections and natural
hazard data, including projections and data for:

• Coastal flooding and sea level rise • Average temperatures and extreme heat

• Average precipitation and storm intensity • Wildfire conditions and risk for water utilities

• Frequency of storm surge flooding
and hurricane strikes

Explore real-world case studies of utilities addressing climate change challenges in the
Adaptation Case Studies Map for Water Utilities.

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Southern Rl OWTS

Worst Case Hurricane Surge
(Om SLR)

OWTS Impact Category

i Kilometers

Ephemeral
Moderate
Serious
Unknown

Figure 8: Modeled impacts of hurricane surge on OWTS in southern Rhode Island.

Source: Cox et a I., 2020.

Note: Sea level rise is abbreviated as SLR. Rhode Island is abbreviated as Rl.

Following natural disasters, communities may choose to survey and document damaged OWTS
to analyze them for factors contributing to failures and determine which systems might be most
vulnerable in the future. After Hurricane Sandy in 2012, the town of Charlestown, Rhode Island,
conducted a damage assessment that included damage to septic systems. Charlestown was also
included in the GIS-based modeling study shown in the Figure 8 map, which examined potential
impacts of natural disasters on OWTS in southern Rhode Island. For that study, researchers
identified properties with OWTS using available tax assessor property parcel maps from the
communities (Cox et al., 2020).

Communities can make efforts to identify at-risk OWTS (i.e., OWTS that are failing or prone to failure).
Identifying at-risk OWTS in small and disadvantaged communities can help officials proactively
address concerns, including failures that contribute to disease outbreaks and water pollution. In some
instances, communities with failing OWTS may be connected to centralized wastewater treatment
facilities (University of North Carolina, 2021). However, in many rural communities, connection
to centralized wastewater treatment facilities may be infeasible or cost prohibitive. These communities
may then need to focus their efforts on increasing OWTS resilience.

Regional community planning can encourage the development of cluster systems, which convey
wastewater from two or more households or buildings to a treatment and dispersal system located
on a suitable site nearby. Cluster systems allow for larger systems with increased flexibility to treat
multiple wastewater sources, including commercial sources. A larger, combined system serving
multiple lots can be easier to manage and protect from the impacts. Cluster systems also reduce
the maintenance burden on individual homeowners.

Wastewater management on a cluster or community level can create job opportunities for service
providers and operators and offer potential economic opportunities for resource recovery, such
as the reuse of treated water for irrigation.

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Figure 9: Cesspools on Kauai in the Hawaiian Islands, color
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2. HOW COMMUNITIES CAN PREPARE

2.2 Infrastructure Considerations

Consistent infrastructure monitoring and
evaluation are critical to track information such
as OWTS location, age, condition, permits,
maintenance history, depth to water table,
and land surface elevation. The average
household septic system should be inspected
at least every three years by a septic service
professional (U.S. EPA, 2024i). Advanced
OWTS with electrical float switches, pumps,
or mechanical components should be
inspected more often, generally once a year.

ONSITE AND DECENTRALIZED WASTEWATER
TECHNOLOGY CLEARINGHOUSE

The Searchable Clearinghouse of Wastewater
Technology (SCOWT) provides onsite and
decentralized technology resources to assist
communities' decision-making processes.

CONVENTIONAL AND ALTERNATIVE OWTS

Information on the 10 most common types
of OWTS, including illustrations
and technological details, is available on
the EPA's septic system website

Table 1 provides a non-exhaustive list
of infrastructure considerations for OWTS.

The first section presents risk-based best
management practices to better protect

current systems. The second section focuses on redesign and reconfiguration options. The third section
focuses on advanced systems that may be considered, particularly when there are chronic system failures.

Figure 10: Flood-damaged advanced nitrogen reducing OWTS in coastal Rhode Island. Storm surge flooding
displaced buoyant components of the OWTS. This type of damage can be mitigated with proper anchoring.

Source: Matthew Dowling, 2012.

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Table 1: Infrastructure considerations to address the impacts on OWTS.

Risk-Based Best Management Practices (BMPs): Installing new OWTS
and related technologies can be cost prohibitive to homeowners.
Solutions to protect existing systems from the current
and anticipated effects of climate change may be preferable in these
cases to maximize results with minimum cost.

Risks Addressed

Protect OWTS from land disturbance and soil compaction
(Amador et al., 2015):

• Install enclosures or barriers to hold soil in place.

• Add items such as watertight lids and fencing.

• Elevate control panel boxes and electrical components.

Protect OWTS from rising waters:

• Anchor all buoyant components (e.g., fiberglass air-filled textile
filters, pump basins, etc.) to prevent floating during flood events.

• Properly grade and slope areas around septic system components
to reduce flood scouring.

• Brace septic system components properly to withstand saturated
soil conditions.

• Plant resilient native plants with shallow root systems to hold soils
and prevent erosion.

• Elevate all electrical components above base flood elevation.

• Add artificial buffers or swales to divert excess water from OWTS.

• Install backflow valves to prevent return flow and protect your
property from sewage backups.

Protect OWTS from power risks:

• Install backup power to ensure that systems remain operational
during power outages.

• Install power shutoffs for emergency situations.

Reduce the risk of OWTS failure:

• Use water efficiently to reduce the amount of wastewater
entering the OWTS. Learn more about how to conserve water
at the WaterSense website. Watersense. an EPA-soonsored
program, is both a label for water-efficient products and
a resource for helping you save water.

Key:

Sea Level

Precipitation

Temperature

Wildfires

Drought

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Table 1: Infrastructure considerations to address the impacts on OWTS.

OWTS Redesign/Reconfiguration: When BMPs do not address some of the
issues related to climate change, more costly projects may be required.

Risks Addressed

Increase OWTS treatment capacity:

• Install additional drain lines, larger septic tanks, and holding tanks.

• Elevate drainfields to create more VSD. A mound system is one
possible configuration for an elevated drainfield system.

Consolidate systems:

• Install cluster systems to consolidate treatment and dispersal off-lot.
Cluster systems help alleviate the challenges of small individual lots,
difficult soils, and sensitive locations. Maintenance responsibilities are
transferred from individual homeowners to a maintenance professional.

• Design shared systems to pool financial resources so that climate
change resilient features can be incorporated.

• Consider whether advanced treatment options like membrane
technologies can be integrated into cluster systems to generate
treated wastewater for reuse (University of North Carolina, 2021).

Figure 11: Example of septic system installation.

Source: SimplyCreativePhotography

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Table 1: Infrastructure considerations to address the impacts on OWTS.

Advanced Solutions: Advanced systems may be required for
properties that experience chronic system failures, especially those
that have low soil permeability or that are situated near high

water tables, in coastal regions, or in elevated areas near streams Risks Addressed

or creeks. These are locations where OWTS failures are likely to
pollute well water and affect adjacent water body quality
(U.S. EPA, 2024j).

Increase treatment and/or capacity:

• Add advanced treatment systems with natural or synthetic media
that utilize oxygen to improve total treatment.

• For properties near water bodies that are prone to nutrient
contamination, upgrade OWTS to advanced nutrient removal
treatment systems, such as passive nitrogen-reducing biofilters
or recirculating sand filters (U.S. EPA, 2024j; Southeast New
England Program, 2021; Stony Brook University, n.d.).

The Massachusetts Alternative Seotic Svstem Technoloav Center
provides information on onsite treatment technologies for nutrient
removal and beyond.

• Use nature-based solutions to help treat effluent from OWTS,
particularly on a community scale. Examples of nature-based
solutions include treatment wetlands and facultative ponds
(The Nature Conservancy et al., 2021).

Limit flooding impacts/prevent drainfield oversaturation:

• Use curtain drains, fill caps, and silt applications to help divert
stormwater and groundwater from the drainfield during heavy
precipitation events (University of North Carolina, 2021).

• Install alternative dispersion for drainfields, such as shallow
pressurized drainfields or drip dispersal, which are installed
closer to the surface than conventional OWTS and may be less
impacted by rising groundwater levels.

Explore water reuse and conservation applications to address site/

geographical constraints:

• Investigate regulatory and technical feasibility for water reuse
systems that treat wastewater for specific end uses, such as toilet
flushing or irrigation. Source separation may be necessary to focus
on the reuse of gray water (i.e., household wastewater from sinks,
washing machines, and showers).

• Employ water conservation measures to reduce wastewater volumes,
which may allow for reduced drainfield size. WaterSense makes it
easy to find and select water-efficient products.

WaterSense labeled oroducts are backed bv indeoendent.
third-party certification and meet the EPA's specifications for
water efficiency and performance.

• Where appropriate and approved, use innovative decentralized
methods, such as incineration, biodigestion, and waste recovery
systems, to reduce nutrient loading from OWTS.

Key:

Sea Level

Precipitation

Temperature

Wildfires

•iy," Drought

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2. HOW COMMUNITIES CAN PREPARE

2.3 Policy Approaches

OWTS are regulated by states, Tribes, and local governments.

The EPA does not regulate OWTS. Depending on the state,
cities and towns may have the authority to establish OWTS
standards that address local conditions and needs. States
can periodically review their onsite wastewater system
design regulations to ensure protection of human and
environmental health. States can also assess the ability
of their wastewater infrastructure financing and funding
programs to fund OWTS construction, upgrades, and repairs. Onsite wastewater professionals and
health regulators can adopt new OWTS technologies if regulatory requirements are in place, they
have the support of state and local agencies, and sufficient funding is present.

Most OWTS are selected, approved, and installed based on current site conditions (e.g., VSD, soil
morphology, lot size, wastewater quantity). Long-term climate change projections are typically not
considered during this process. Wastewater managers can proactively take steps now to adapt to
future climate change events. For example, managers could require extra VSD buffers for areas
anticipating higher water tables due to sea level rise.

To allow for adequate treatment, state regulations require OWTS to have a specific VSD, measured
from the bottom of the drainfield to the water table or to a restrictive layer such as bedrock. VSD
requirements for several states are included in Table 2. VSD requirements are determined from
measurements related to soil profile depth or soil characteristics (e.g., texture and structure).
OWTS might not meet VSD requirements if proper soil characteristic determinations are not used.
States may consider revisiting regulatory VSD requirements on a regular basis and requiring soil
science training for design professionals.

Table 2: Examples of state vertical separation distance regulations for conventional systems.

State

State Regulation

VSD (inches)

Arizona

AAC R18-9-A312

60-120

Florida

AR 62E-6.006

24-42

Massachusetts

AR 301.12.212

48-60

Minnesota

AR 7080.2150

Nebraska

AR 124.4.002

North Carolina

15A NCAC 18A

12-18

Oregon

OAR 340-071-0220

24-48

Sources: Henneman, 2020; Mihaly, 2018; University of North Carolina, 2021.

Note: This table provides select examples and is not for regulatory use. State policies are subject

to change. Please refer to state regulations for specific requirements and terminology.

FUNDING FOR OWTS

Potential federal, state, Tribal,
and local funding sources for
OWTS construction, upgrades,
and repairs can be found on
the EPA's septic system website.

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State and local permitting authorities may want to explore and establish additional requirements
to further protect public and environmental health. For example, the city of Gloucester, Massachusetts,
adopted OWTS regulations that are stricter than those found in the State Environmental Code due
to unique site conditions, such as shallow VSD, rapid soil percolation, high groundwater tables, and
the presence of wetlands and fractured bedrock (Gloucester Health Department, 2008). Additionally,
the town of Rye, New Hampshire, requires that OWTS be pumped out once every three years in the
Parsons Creek Watershed (Mihaly, 2018; Town of Rye, 2016). Implementing these kinds of locally
based standards may be a challenge in under-resourced areas, but state funding assistance programs
may provide some support. Importantly, adequate staffing, funding, and expertise are necessary
for effective development and implementation of OWTS policies.

Examples of actions that health departments and OWTS regulatory authorities can take to prepare
for potential impacts of natural hazards and extreme weather include the following:

Improve new construction setback requirements to ensure that septic systems are placed
in areas that are not likely to flood or pond, consistent with climate change projections.

• For areas prone to flooding or other natural disasters, implement appropriate design

and construction standards or develop buyback programs to prevent building in these areas.

• Establish VSD requirements using projected high-water marks and increase VSD
requirements for tidally impacted groundwater tables using the FEMA flood zones as a guide.

Require advanced technological solutions designed to be resilient or to address local conditions
—especially in vulnerable, high-risk areas prone to failure (see Table 1).

• Monitor advanced systems for compliance with contaminant reduction benchmarks/
regulations and require corrective adjustments for systems not meeting standards.

• Work with other jurisdictions to develop best available technology lists to address
shared/common contaminant problems (e.g., nitrogen, phosphorus, pathogens).

[V[ Establish municipality data-sharing platforms and operation and maintenance plans to ensure
OWTS are functional and compliant.

• Require regular OWTS inspections, particularly for areas vulnerable to natural disasters.

• Offer incentives for inspection and pump-outs to establish routine maintenance
and encourage documentation of treatment and performance.

• Establish responsible management entities that operate individual OWTS as utilities

to reduce the burden on property owners and streamline system maintenance and data
collection.

-------
Sf Involve local governments, where appropriate, to leverage their regulatory authority
and ensure that OWTS are installed and managed properly.

• Require damage assessment inventories of systems impacted by hazards to help model future
impacts and identify design and installation practices that mitigate hazards. These inventories
can inform policy revisions.

• Use GIS mapping of OWTS and other contamination sources to track flood risk and highlight
potential areas of concern.

• Consider backup power requirements or incentives for individual and community systems
that experience climate impacts and rely on pump stations.

• Implement licensing requirements for OWTS professionals such as permitting staff, designers,
installers, and other service providers.

• Implement a title transfer program requiring septic system inspection during property sales
to ensure the OWTS is functioning properly. During inspections, consider assessing systems
or past impacts and future climate vulnerabilities as well.

CASE STUDY

Policy Change Efforts for Adaptation
in Nags Head, North Carolina

The town of Nags Head, North Carolina, is experiencing an increase in heavy
precipitation, sea level rise, flooding, storm surges, erosion, and rising groundwater
tables due to climate change. More than 85 percent of Nags Head's wastewater
is treated by OWTS, many of which are failing due to these compounding challenges
(Town of Nags Head, North Carolina, 2022). In 1999, Nags Head launched a Septic
Health Initiative, a non-regulatory, proactive management plan that provides
homeowners with the following for their OWTS: free inspections, water utility bill
credits for septic pump-outs, low-interest loans for repairs/replacements, and water
quality testing.

Nags Head is working to implement its Decentralized Wastewater Management
Plan, which proposes new provisions in response to climate change impacts. Through
implementation of the plan, the town has improved management of OWTS by
helping locate, maintain, and monitor the systems. In turn, there has been an
increased acceptance of alternative wastewater treatment and management
technologies. The town also recognizes the importance of VSD for effective OWTS
treatment, and, through the plan, outlines inspection frequencies, management
oversight, onsite options, and soil suitability for each VSD depth.

-------
2. HOW COMMUNITIES CAN PREPARE

2.4 Education and Outreach

Education and communication about OWTS
operation and resilience are critical for helping
property owners maintain their OWTS. Engaging
a broad audience is important to facilitate
collaboration, establish networks, and disseminate
consistent messages and strategies. For example,
communications about adaptation strategies may
require coordination between municipalities,
health regulators, state legislators, and OWTS
professionals. Increased communications between
OWTS regulatory authorities, professionals,
and property owners can help build adaptive
capacity, which is especially important when
sharing information about system maintenance,
challenges, and malfunctions (University of
North Carolina, 2021). Although conventional household OWTS should be professionally inspected
and pumped on a regular schedule, OWTS owners rarely receive information about the proper care
of their systems over time. Wastewater professionals, real estate agents, and regulators can establish
consistent touchpoints and communication practices to encourage proactive behaviors
and incentivize regular maintenance.

University outreach and extension services can provide educational opportunities, including
decentralized workforce training and apprentice programs. For example, universities could
incorporate training into environmental science and engineering curricula to equip new professionals
with an awareness of the potential impacts of climate change on OWTS.

LEARNING HOW TO MAINTAIN OWTS

Visit the EPA's How to Care for Your
Septic System for OWTS tips related to
pump inspections, water efficiency, waste
disposal, and maintenance, as well as
answers to frequently asked questions.

See homeowner training materials
on the National Onsite Wastewater
Recycling Association's (NOWRA's)
website, including the OWTS User Guide
and Online Homeowner Training.

OWTS DISASTER RESOURCES

The National Environmental Health Association (NEHA) created a toolkit complete with guides
that OWTS users can use before, during, and after disasters to protect their health and system.
Each guidance document is accompanied by a checklist with reminders that homeowners can
use to prepare. The documents cover the following disasters:

• Hurricanes and flooding • Wildfires • Earthquakes

• Winter weather • Power outages

The EPA has also provided post-flood event septic system guidance on their ground water
and drinking water website.

-------
Figure 12: The EPA's SepticSmart Homeowners' Guide
to Septic Systems.

Source: U.S. EPA, 2024k.

Note: The EPA's SepticSmart program provides a wealth
of online resources for homeowners, local organizations,
and government leaders.

For details see: httos://www.eoa.aov/seotic/seoticsmart-edu-
cation-materials.

Tailored trainings for an audience
of OWTS service providers, inspectors,
designers, installers, and regulators
can help keep them informed about
climate impacts on system operation
and maintenance and address
knowledge gaps that may stall
adaptation (Kirchhoff & Watson, 2019).
Continuing education requirements
for OWTS professionals can help
encourage completion of OWTS
adaptation and resilience training.

Community leaders and educators
can focus on using plain language
to communicate OWTS information.
NOWRA's OWTS User Guide provides
an example of this approach,
summarizing the technical
components of OWTS in plain
language to help community
stakeholders reach sound decisions
related to OWTS management. The
EPA's Homeowners' Guide to Septic
Systems, shown in Figure 12, provides
information about septic system
maintenance and operation.

Local health departments or municipal
wastewater management districts
can use risk communication strategies
in discussions with OWTS managers
and community members to ensure
they take proactive actions and know
how to proceed before, during, and
after a disaster (University of North
of Carolina, 2021).

-------
REFERENCES

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01475-4

Amador, J., Loomis, G., Cooper, J., & Kalen, D. (2015). Soil-based onsite wastewater treatment and
the challenges of climate change [presentation]. The University of Rhode Island, https://www.epa.aov/
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es of climate change.pdf

Barreiro, A., & Di'az-Ravina, M. (2021). Fire impacts on microorganisms: Mass, activity, and diversity.
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ence/article/pii/S2468584421000362

Capps, K. A., Bateman McDonald, J. M., Gaur, N., & Parsons, R. (2020). Assessing the socio-environmental
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Cooper, J. A., Loomis, G. W., & Amador, J. A. (2016). Hell and high water: Diminished septic system
performance in coastal regions due to climate change. PLoS ONE, 11(9), e0162104. httPs://doi.
org/10.1371/iournal.pone.0162104

Cox, A., Dowling, M. J., Loomis, G. W., Engelhart, S. E., & Amador, J. A. (2020). Geospatial modeling
suggests threats from stormy seas to Rhode Island's coastal septic systems. Journal of Sustainable
Water in the Built Environment, 6(3). https://doi.org/10.1061/JSWBAY.0000917

Gloucester Health Department. (2008). City of Gloucester Board of Health Regulations:

Onsite wastewater regulations. https://www.qloucester-ma.gov/DocumentCenter/View/5587/
BOH—ONSITE-WASTEWATER-REGS?bidld=

Henneman, T. (2020). Multi-state comparison: Onsite wastewater treatment system regulations.
Montana Legislative Services Division, Office of Research and Policy Analysis, https://leg.mt.gov/con-
tent/Committees/lnterim/2019-2020/Local-Government/Committee-Topics/SJ3-T/Multi-stateComp
OWTSRegs v2 full.pdf

Hughes, J., Cowper-Heays, K., Olesson, E., Bell, R., & Stroombergen, A. (2021). Impacts and implications
of climate change on wastewater systems: A New Zealand perspective. Climate Risk Management, 31,
100262. https://www.sciencedirect.com/science/article/pii/S221209632Q30Q528

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Humphrey, C., Jr., Dillane, D., Iverson, G., & O'Driscoll, M. (2021). Water table dynamics beneath onsite
wastewater systems in eastern North Carolina in response to Hurricane Florence. Journal of Water and
Climate Change, 72(5), 2136-2146. httPs://iwaponline.com/iwcc/article/12/5/2136/80255/Water-
table-dvnamics-beneath-onsite-wastewater

Kirchhoff, C. J., & Watson, P. L. (2019). Are wastewater systems adapting to climate change? Journal
of the American Water Resources Association, 55(4), 869-880. https://onlinelibrarv.wilev.com/doi/
abs/10.1111/1752-1688.12748

Marvel, K., Su, W., Delgado, R., Aarons, S., Chatterjee, A., Garcia, M. E., Hausfather, Z., Hayhoe, K., Hence,
D. A., Jewett, E. B., Robel, A., Singh, D., Tripati, A., & Vose, R. S. (2023). Chapter 2: Climate trends.
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Fifth National Climate Assessment. U.S. Global Change Research Program, https://doi.org/10.7950/
NCA5.2023.CH2

Miami-Dade County Department of Regulatory & Economic Resources, Miami-Dade County Water
and Sewer Department, & Florida Department of Health in Miami-Dade County. (2018). Septic systems
vulnerable to sea level rise, https://www.miamidade.gov/green/librarv/vulnerabilitv-septic-svs-
tems-sea-level-rise.pdf

Mihaly, E. (2018). Avoiding septic shock: How climate change can cause septic system failure and
whether New England states are prepared. Ocean & Coastal Law Journal, 2J(1). httPs://diaitalcommons.
mainelaw.maine.edu/ocli/vol25/iss1/2

MTBS (Monitoring Trends in Burn Severity). (2024). Burned areas boundaries dataset, 1984—2022.
Direct download, https://www.mtbs.aov/direct-download

NAHB (National Association of Home Builders). (2023). New homes built with private wells and
individual septic systems in 2022. https://eveonhousing.org/2023/10/new-homes-built-with-private-
wells-and-individual-septic-svstems-in-2022/

National Weather Service. (2018). Hurricane Florence: September 14,2018. https://www.weather.aov/
ilm/HurricaneFlorence

NOAA (National Oceanic and Atmospheric Administration). (2024a). Climate at a glance.
https://www.ncei.noaa.aov/access/monitorina/climate-at-a-alance/

NOAA (National Oceanic and Atmospheric Administration). (2024b). Update to data originally
published in: NOAA. (2009). Sea level variations of the United States 1854-2006 (NOAA Technical
Report NOS CO-OPS 053). https://www.tidesandcurrents.noaa.aov/publications/Tech rpt 53.pdf

Sea Grant University of Hawai'i. (2021). Hawai'i cesspool prioritization tool, https://seaarant.soest.ha-
waii.edu/cesspools-tool/

Southeast New England Program. (2021). A pound of prevention: Stopping nitrogen at the source
with advanced septic systems, https://www.epa.gov/snep/pound-prevention-stopping-nitro-
gen-source-advanced-septic-svstems

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Steinkraus, D. (2018). The heat is on: How wildfires affect onsite systems. Onsite Installer. https://www.
onsiteinstaller.com/online exclusives/2018/09/the-heat-is-on-how-wildfires-affect-onsite-svstems

Stony Brook University, (n.d.). Nitrogen removing biofiiters for onsite wastewater treatment. Center
for Clean Water Technology. https://www.stonvbrook.edu/commcms/cleanwater/research/NRB%20
Fact%20Sheet.pdf

Town of Nags Head, North Carolina. (2022). Decentralized wastewater management plan. https://www.
naasheadnc.aov/DocumentCenter/View/4456/Town-of-Naas-Head-DWMP-April-2022?bidld=

Town of Rye, New Hampshire Sewage Disposal Ordinance. (2016). Chapter26, Article I, Parsons
Creek Watershed, https://ecode560.com/55985175

University of North Carolina. (2021). Climate change and onsite wastewater treatment systems

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U.S. Census Bureau. (2022). Survey of construction, https://www.census.aov/construction/soc/index.html

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(EPA/625/R-00/008). https://www.epa.aov/sites/default/files/2015-06/documents/2004 07 07 sep-
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U.S. EPA (Environmental Protection Agency). (2024a). About septic systems, https://www.epa.gov/sep-
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U.S. EPA (Environmental Protection Agency). (2024d). Climate change indicators: Weather and climate.
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https://wrcc.dri.edu/wwdt

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APPENDIX 1: BACKGROUND INFORMATION
ON IMPACTS

A.I Sea Level Rise

As the Earth traps more heat due to an increase in greenhouse gases in the atmosphere, water bodies
get warmer too. This increased temperature expands the water in Earth's oceans, causing it to "swell"
and increasing the oceans' volume of water. In addition, when land ice (such as ice sheets and glaciers)
melts, the meltwater eventually flows into the ocean, increasing the amount of water (U.S. EPA, 2024b).
Both of these climate-related outcomes contribute to sea level rise. Sea levels have been tracked
since 1880, using a combination of long-term tide gauge data and recent satellite measurements.
The available data indicate that the global average absolute sea level is increasing by an average
of 0.07 inches per year.

The Figure A.I map shows cumulative changes in relative sea level from 1960 to 2023 at tide gauge
stations along U.S. coasts. Relative sea level reflects changes in global sea level as well as changes
in land elevation (i.e., relative sea level rise accounts for land subsidence). Some east coast states, like
Virginia and North Carolina, experience over 0.2 inches of rise per year. Sea levels have risen between
3 and 8 inches off the coast of Hawai'i since 1960 (U.S. EPA, 2024b).

Alaska

l ]

[

Hawaii and
Pacific Islands

liter -

1—

III

-11.99
to -9

Relative sea level change (inches):

-8.99
to -6

-5.99
to-3

-2.99
toO

t 1 t

1 1 '

0.01
to 3

3.01
to 6

6.01
to 9

9.01
to 12

>12

Figure A.1: Relative sea level change along U.S. coasts from 1960 to 2023 (inches).

Sources: U.S. EPA, 2024b; NOAA, 2024a; NOAA, 2024b.

For details see: httDs://www.eoa.pov/climate-indicators/climate-chanae-indicators-sea-level

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APPENDIX 1: BACKGROUND INFORMATION
ON IMPACTS

A.2 Precipitation

Climate change also affects the intensity and frequency of precipitation. Higher atmospheric
temperatures increase atmospheric moisture, in turn increasing overall precipitation. Heavy precipitation
across the contiguous United States has trended upward since the 1950s (Marvel et al., 2023). In recent
years, a larger percentage of precipitation has come in the form of intense single-day events that result
in floods, erosion, and injuries (U.S. EPA, 2024c). Nine of the top 10 years for extreme one-day
precipitation events have occurred since 1995 (U.S. EPA, 2024d). Data on heavy precipitation can
be found on the EPA's Climate Change Indicators website

Additionally, available data suggest that wet areas of the United States are getting wetter, and dry areas
are getting drier. The Figure A.2 map shows the percent change in total annual precipitation since 1901
for the contiguous United States and since 1925 for Alaska.

Figure A.2: Percent change in precipitation in the contiguous United States from 1901 to 2023 and in
Alaska from 1925 to 2023.

Sources: U.S. EPA, 2024c; U.S. EPA, 2024d; NOAA, 2024a.

Note: In some cases, the EPA's climate change indicators do not cover all states and territories of the
United States. Inclusion of a geographical area is contingent on the availability of nationally consistent,
reliable, and comparable data for a given indicator.

29 For details see: httos://www.eoa,ciov/climate-indicators/climate-chanae-indicators-us-and-alobal-areciaitation

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APPENDIX 1: BACKGROUND INFORMATION
ON IMPACTS

A.3 Temperature

WA5F

The average surface temperature of the contiguous United States has increased at a rate of 0.32°F
to 0.51°F per decade since the late 1970s (U.S. EPA, 2024e). The rate of temperature change
is highest in Alaska and the western, northern, and northeastern states (Figure A.3). Nationwide,
unusually hot summer days (defined as days that exceed the 95th percentile of daily maximum
temperatures) have become more common over the last few decades, especially in the western
states (U.S. EPA, 2024e). Data on changes in high and low temperatures can be found on the
EPA's Climate Change Indicators website

Rate of temperature change (°F per century):

-10 12

Gray interval: -0.1 to 0.1°F

Figure A.3: Rate of temperature change in the contiguous United States and Alaska from 1901 to 2023 (°F).

Sources: U.S. EPA, 2024d; U.S. EPA, 2024e; NOAA, 2024a.

For details see: httDs://www.eoa.aov/climate-indicators/climate-chanae-indicators-us-and-alobal-temoerature

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APPENDIX 1: BACKGROUND INFORMATION
ON IMPACTS

A.4 Wildfires

WA5F

On average, 70,000 wildfires occur annually in the United States. Trends in wildfire data show that
wildfires are increasing in duration, frequency, and size (U.S. EPA, 2024f). Western states have seen
the largest increases in burned acres—even when accounting for a state's size (Figure A.4). in the
Figure A.4 map, a wildfire is defined as "a wildland fire originating from an unplanned ignition,
such as lightning, volcanos, unauthorized and accidental human caused fires, and prescribed fires
that are declared wildfires" (U.S. EPA, 2024f).

Average annual burned acres per square mile of land area:

Figure A.4: Average annual burned acreage per square mile of land area by state for the contiguous
United States and Alaska from 1984 to 2021.

Gray coloring indicates states that did not have fires large enough to be included.

Sources: U.S. EPA, 2024f; MTBS, 2024.

For details see: https://www.eoa.ciov/cHmate-indicators/cUmate-chanae-indicators-wildfires

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APPENDIX 1: BACKGROUND INFORMATION
ON IMPACTS

A.5 Drought

^55?

Although conditions over the last 50 years have been wetter than the historical average since 1900,
some areas of the country have seen an increase in droughts over the past century, as shown in
Figure A.5 (U.S. EPA, 2024g). The Figure A.5 map shows changes in the Standardized Precipitation
Evapotranspiration Index (SPEI), which measures the combination of precipitation and atmospheric
water demand (evapotranspiration). This index gives a broad overview of drought conditions in the
United States, it is not intended to replace local information that might describe conditions more
precisely for a particular region. Drought can impact agriculture and ecosystems in areas with negative
SPEI, particularly in the western United States where water demand is greater than water supply.

Change in SPEI:

More extreme drought

More extreme moisture

Figure A.5: Total change in the five-year Standardized Precipitation Evapotranspiration Index (SPEI)
in the contiguous United States, 1900 to 2023.

Sources: U.S. EPA, 2024g; Western Regional Climate Center, 2024.

For details see: https://www.epa.aov/climate-indicators/climate-chanae-indicators-drouaht

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