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MASTER PLAN
An Element of the Southlake Comprehensive Plan
Adopted by the Southlake City Council
Ordinance No. 1034A
Month Day, 2026
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WASTEWATER MASTER PLAN
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SOUTHLAKE
Comprehensive Plan
City of Southlake City Council
Mayor Shawn McCaskill
Mayor Pro Tem Randy Williamson
Deputy Mayor Pro Tem Kathy Talley
Councilmember Place 2 Randy Robbins
Councilmember Place 3 Frances Scharli
Councilmember Place 4 Austin Reynolds
Councilmember Place 5 Chuck Taggart
Planning & Zoning Commission Corridor Planning Committee
Chair Daniel Kubiak Kathy Talley - City Council
Vice Chair Mike Forman Randy Robbins - City Council
Commissioner Gina Cannova Austin Reynolds - City Council
Commissioner David Cunningham Frances Scharli - City Council
Commissioner Michael Springer Daniel Kubiak - Planning & Zoning
Commissioner Stacy Driscoll Michael Springer - Planning & Zoning
Commissioner Lora Gunter David Cunningham - Planning & Zoning
Gina Cannova - Planning & Zoning
Mike Forman - Planning & Zoning
Magdalena Battles - Parks Board
Chad Patton - Ex-Officio
City of Southlake Staff
City Manager Alison D. Ortowski
Assistant City Manager James Brandon
Assistant City Manager Stacey Black
Chief Financial Officer Sharen Jackson
Interim Director of Public Works Lauren LaNeave
City Engineer Jeff Ginn
Director of Economic Development & Tourism Daniel Cortez
Director of Planning and Development Services Dennis Killough
Deputy Director of Planning and Development Services Jenny Crosby
Assistant to the Director Ryan Firestone
Senior GIS Analyst Jesus Gabriel
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EXECUTIVE SUMMARY
Southlake's Wastewater Master Plan is the City's long-range framework for managing,
operating, and reinvesting in the wastewater collection system as the community approaches
buildout. Like the City's other supporting master plans, it serves as a practical "knowledge base"
that documents existing conditions, establishes clear service expectations, and helps translate
Southlake's Comprehensive Plan vision into implementable utility policy. The plan emphasizes
reliability, public health protection, regulatory compliance, and lifecycle reinvestment shifting the
focus from primarily expanding infrastructure to sustaining and strengthening the system the City
already maintains.
The technical foundation for this plan is informed by the Wastewater Modeling Study prepared
by Freese and Nichols, which evaluated system performance under existing and future flow
conditions and identified where wet-weather stress, inflow and infiltration (1/1), operational
constraints, and capacity limitations can affect levels of service. The modeling results, combined
with local system knowledge and operational experience, support a data-driven understanding
of risk and performance. This technical basis helps the City prioritize improvements, focus 1/1
reduction where it preserves the most capacity, and coordinate investments with downstream
interfaces and regional partners.
This Wastewater Master Plan is intended to be used as a policy and decision-making guide for day-
to-day utility management and long-term capital planning. It provides direction for establishing
and tracking levels of service, advancing asset management and renewal programs, guiding
development and redevelopment review,sequencing capital projects,and communicating program
priorities to residents and stakeholders. Ultimately, the plan equips the City with a consistent
framework to justify budgets and capital programming, improve transparency and accountability,
and ensure Southlake's wastewater system continues to support community quality of life and
long-term resiliency.
WASTEWATER MASTER PLAN
TABLE OF CONTENTS
PAGE CHAPTER
6 CHAPTER 1: INTRODUCTION
12 CHAPTER 2: WASTEWATER SYSTEM OVERVIEW
20 CHAPTER 3: WASTEWATER FLOWS
24 CHAPTER 4: HYDRAULIC WASTEWATER MODEL UPDATE
28 CHAPTERS: SYSTEM ANALYSIS & PERFORMANCE
34 CHAPTER 6: SYSTEM ANALYSIS & PERFORMANCE
40 CHAPTER 7: RESILIENCE, 1/1 REDUCTION & SYSTEM INTEGRITY
44 CHAPTER 8: GROWTH, DEVELOPMENT & SYSTEM PROTECTION
48 CHAPTER 9: COMMUNITY ENGAGEMENT, PARTNERSHIPS, AND
FUNDING
52 CHAPTER 10: PLAN ADOPTION & PUBLIC ENGAGEMENT
56 WASTEWATER MASTER PLAN POLICY STATEMENTS SUMMARY
58 GLOSSARY OF TERMS
62 APPENDIX A: FREESE AND NICHOLS WASTEWATER
INFRASTRUCTURE MODELING STUDY - EXECUTIVE SUMMARY
ORDINANCE
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CHAPTER 1: INTRODUCTION
Southlake's Wastewater Master Plan is the City's long-range policy and planning framework
for managing, operating, and reinvesting in the wastewater collection system as the community
approaches buildout. While much of Southlake's historic utility focus has necessarily centered on
expanding infrastructure to support growth, the City's wastewater priorities increasingly reflect
a mature system environment, one where maintaining reliability, managing risk, and reinvesting
in aging assets becomes the primary driver of long-term performance. This plan provides a clear,
consistent foundation for decision-making that supports excellent service, protects public health,
and aligns infrastructure investments with community expectations.
Like the City's other supporting master plans, this document functions as a "knowledge base" that
explains how Southlake manages wastewater today and how the City will guide long-term, data-
driven decisions in the years ahead. The plan is supported by the Wastewater Modeling Study
prepared by Freese & Nichols, which provides technical findings and performance insights under
existing and projected conditions. Those results combined with Southlake's operational knowledge,
prior planning efforts, and ongoing program experience help the City define service expectations,
identify system constraints and vulnerabilities, and prioritize improvements in a way that is
transparent, defensible, and aligned with adopted policy direction.
BACKGROUND
The wastewater collection system is a critical public utility that protects public health and
environmental quality by safely conveying sanitary flows from homes, businesses, and civic
facilities to downstream treatment. In a built-out or near-built-out community, the wastewater
system's performance is shaped as much by ongoing reinvestment and system integrity as by new
infrastructure. Reliable collection depends on the capacity and condition of pipes, manholes, lift
stations, and force mains, as well as the City's ability to manage wet-weather response and reduce
inflow and infiltration (1/1) that can stress the system during storms. As a result, wastewater planning
is inherently tied to risk management reducing the likelihood of backups, overflows, and service
disruptions while maintaining predictable, cost-effective service over time.
Southlake's wastewater system is a network of local collection infrastructure that also relies on key
downstream interfaces and regional partners. For example, in the City's North Service Area (Denton
Creek Basin), flows are conveyed to a regional lift station and treatment system operated by TRA,
WASTEWATER MASTER PLAN
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illustrating how local collection performance and downstream capacity work together to define overall
reliability. This Wastewater Master Plan establishes the City's planning and policy basis for those
decisions. It documents existing conditions, summarizes technical analysis, and translates system
needs into implementable direction that supports budgeting, capital programming, maintenance
priorities, and development coordination. The technical foundation for this plan is informed by
the wastewater modeling effort prepared by Freese & Nichols, as well as prior plans and studies,
including the City's 2012 Wastewater Master Plan, flow monitoring and system evaluation work, and
key program milestones that have shaped current operating conditions and system understanding.
PLANNING CONTEXT: NEARING BUILDOUT
As Southlake nears buildout, wastewater planning shifts from primarily adding capacity to
strategically sustaining performance. This transition requires a stronger emphasis on stewardship:
reinvesting in aging infrastructure, maintaining reliable service levels during wet-weather conditions,
and managing system risk using data-driven tools. In practical terms, this means prioritizing renewal
and rehabilitation where condition and criticality indicate higher risk, using modeling and monitoring
to understand constraints, and sequencing improvements in a way that balances performance needs
with financial sustainability.
This context also reinforces the importance of preserving available capacity through proactive
system integrity measures. Inflow and infiltration reduction, targeted rehabilitation, and operational
improvements can often extend the effective life and performance of the existing system, reduce
wet-weather stress, and avoid or defer more costly capacity expansions. The Wastewater Master
Plan provides the framework to make those choices consistently linking performance expectations
to measurable levels of service, aligning investments with risk, and ensuring that decisions are
grounded in defensible technical analysis rather than reactive response.
ORDINANCE
PREVIOUS WATER MASTER PLANS
Southlake has a history of wastewater planning that reflects the City's evolving growth and
infrastructure needs. Previous master plans, most notably the 2012 Wastewater Master Plan, helped
establish baseline system understanding, identify early capacity needs, and guide investment during
periods of active development. Over time, additional technical work such as flow monitoring, system
evaluations, and targeted investigations has supported operational decision-making and helped
the City better understand wet-weather behavior, system constraints, and areas where 1/1 affects
performance.
This Wastewater Master Plan builds on those efforts rather than replacing them. It consolidates
knowledge gained through prior planning and field work, updates the City's technical understanding
using current modeling tools and datasets, and reframes long-range wastewater planning around
buildout stewardship, service reliability, and lifecycle reinvestment. Where prior plans focused
heavily on expansion and growth-driven capital needs, this update emphasizes managing a mature
system through targeted rehabilitation, performance-based prioritization, and transparent, long-
term investment planning.
SCOPE AND GOALS
This plan addresses Southlake's wastewater collection system and the policies, practices, and
investments necessary to sustain reliable service over time. The scope includes system performance
evaluation, wet-weather response considerations, identification of constraints and vulnerabilities,
and alignment of long-term needs with implementable policy direction. The plan also establishes how
wastewater decisions should be guided and communicated—supporting day-to-day management
as well as multi-year capital programming.
The overarching goals of the Wastewater Master Plan are to:
• Maintain reliable, cost-effective wastewater service that protects public health and supports
quality of life.
• Define and track wastewater levels of service and use performance information to inform
decisions.
• Advance an asset management approach that prioritizes renewal and rehabilitation based on
risk and lifecycle needs.
• Reduce 1/1 and improve system integrity to preserve capacity and improve wet-weather
reliability
• Coordinate wastewater planning with development, redevelopment, and regional system
interfaces.
• Support financial sustainability through transparent long-range planning and defensible
capital programming.
RELATIONSHIP TO THE STRATEGIC MANAGEMENT SYSTEM
Southlake's Strategic Management System provides the City's framework for turning community
priorities into measurable actions, supported by performance tracking and continuous improvement.
The Wastewater Master Plan supports this approach by establishing a clear basis for wastewater
service expectations, identifying implementation priorities, and linking technical needs to policy
direction and investment decisions. In practice, the plan helps define what success looks like for
wastewater service and provides a structure for monitoring progress over time.
WASTEWATER MASTER PLAN
City of Southlake Strategy Map
The mission of the City of Southlake is to provide municipal services that support
the highest quality of life for our residents,a supportive environment for local
INTEGRITY businesses,and unique and special experiences for visitors.
INNOVATION
TEAMWORK We on Our Focus Areas
EXCELLENCE
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Safety& Infrastructure& Partnerships& Performance
Security Development Volunteerism Management&
Service Delivery
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Delivering outstanding Safeguarding the v Achieving strong` Defining and managing
customer experiences public trust through outcomes through a professional workplace
through innovation, a commitment to continual evaluation culture that supports
passion,and a strong thoughtful planning and and pursuit of better City values and promotes
culture responsible,conservative practices that improve a positive employee
Enhancing the sense financial management. core business operations. experience.
of community by Investing to provide& Collaborating with select Fostering positive
proactively creating maintain high quality partners to implement employee engagement.
opportunities for public assets. service solutions Attracting.developing&
community partnerships,
volunteer involvement, Maintaining an retaining a talented and
and citizen engagement. environment motivated workforce
future readiness s by for lasting world-class
understanding and performance.
acting upon the forces.
trends,and coming
challenges affecting
services.
C=Customer Objectives F=Financial Objectives B=Business Objectives L=Learning&Growth Objectives
Because wastewater performance is closely tied to reliability, risk management, and lifecycle
reinvestment, the plan supports strategic management by encouraging proactive, data-informed
decisions rather than reactive, event-driven responses. It also helps align wastewater capital
programming and operational priorities with broader City objectives—supporting coordinated
implementation,clearer accountability,and improved communication about why specific investments
are necessary.
RELATIONSHIP TO THE CITIZEN SATISFACTION SURVEY
Citizen satisfaction and community trust are directly influenced by the reliability and predictability
of essential services—especially utilities that residents depend on every day but rarely think
about unless something goes wrong. While wastewater infrastructure is largely unseen, residents
experience its performance through service reliability, backups and overflows, odor concerns,
construction impacts, and the City's responsiveness when concerns arise. The Citizen Satisfaction
Survey provides an important "community lens" for this Wastewater Master Plan because it helps
define what "excellent service" means in practice and highlights the service attributes residents
value most. In 2025, providing sewer service was rated as important by 97% of respondents (very
or somewhat important), reinforcing wastewater as a core expectation for daily quality of life.
The survey also confirms that Southlake's wastewater service is performing strongly and is among
the City's highest-rated services. In 2025, 91% of respondents reported being very or somewhat
satisfied with sewer service, including 77% who indicated they were very satisfied. This broader
context matters because resident confidence in City services remains high overall 89% reported
being very or somewhat satisfied with the job the City is doing to provide services, and 96% indicated
they receive at least a good value for their tax dollars.
By establishing clear wastewater levels of service, linking reinvestment decisions to risk-based asset
management, and strengthening communication around priorities and impacts, the Wastewater
Master Plan helps the City sustain (and improve) the satisfaction drivers reflected in the survey like
reliability, responsiveness, predictability during construction, and responsible stewardship of public
funds. In this way, the Citizen Satisfaction Survey informs not only what the City invests in, but also
how the City explains and delivers wastewater improvements in a way that maintains trust over
time.
RELATIONSHIP TO THE COMPREHENSIVE PLAN
Southlake's Comprehensive Plan is the community's long-range roadmap for growth, investment,
and quality of life. It coordinates policies across land use, mobility, parks and open space, economic
development, and public facilities to ensure that City
decisions support a cohesive vision over time. The
Wastewater Master Plan is one of the Comprehensive
Plan's supporting master plans that helps implement that
vision by translating broad community goals into practical
utility policies, service expectations, and investment
priorities.
In this role, the Wastewater Master Plan provides the
technical and policy foundation needed to coordinate /
wastewater decisions with other City priorities. It supports
development and redevelopment planning, helps protect
long-term system maintainability, and ensures that public
investments in infrastructure are aligned with service
expectations and risk reduction outcomes. The plan's SOUTHLAKE
technical findings and performance insights are derived
from the Wastewater Modeling Study prepared by Freese Comprehensive Plan
& Nichols and are reinforced by prior plans and studies,
including the City's 2012 Wastewater Master Plan and
related flow monitoring and evaluation efforts. Together, these inputs support a defensible, data-
driven approach to wastewater stewardship that helps sustain Southlake's quality of life as the
community approaches buildout.
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Southlake's wastewater collection system is a citywide network of pipes, structures, and
pump stations that protects public health and supports daily quality of life by reliably conveying
sanitary flows to downstream treatment. Although most of the system is underground, it functions
as a coordinated "conveyance chain" moving flow from neighborhood-scale lines into larger
interceptors, through lift stations where needed, and ultimately into regional infrastructure. The
purpose of this chapter is to provide a plain-language understanding of how the system is organized,
how it functions, and where key dependencies shape performance and planning priorities.
The City's wastewater system is generally understood through two primary basin contexts, the
Central Basin and the Denton Creek Basin, with basin identifiers shown on the City's sanitary
sewer mapping (e.g., "S-" basins and "N-" basins). Because much of the Central Basin is already
developed, the Master Plan's near- and mid-term emphasis increasingly shifts toward the Denton
Creek Basin: preserving wet-weather reliability, managing inflow and infiltration (1/1), planning for
remaining growth and potential septic-to-sewer transitions, and coordinating improvements with
key downstream TRA interfaces.
SERVICE AREAS AND BASIN CONTEXT
Southlake's wastewater system is organized around basin-based collection patterns that reflect
topography, historic development, and where flows naturally concentrate. City mapping illustrates
multiple basin identifiers across the community (including S-01 through S-11 in the Central Basin
context and N-12 through N-19 and related identifiers in the Denton Creek Basin context). This basin
organization matters because it provides a practical planning and operational structure: it clarifies
where flows originate, how they route through the network, and where performance constraints or
wet-weather sensitivity may be concentrated.
From a planning standpoint, the Central Basin's largely built-out condition means its long-term
strategy is predominantly stewardship, targeted rehabilitation, renewal, and operational efficiency
to sustain levels of service. In contrast, the Denton Creek Basin remains the primary area where
remaining growth, wet-weather response, and potential septic incorporation can more directly
influence system loading and capital timing. This is why the plan places added emphasis on Denton
Creek Basin performance and downstream conveyance dependencies in the chapters that follow.
WASTEWATER MASTER PLAN
COLLECTION SYSTEM COMPONENTS AND HOW THEY FUNCTION TOGETHER
Southlake's wastewater collection system functions as an integrated conveyance network moving
wastewater from individual homes and businesses through neighborhood-scale pipes, into larger
trunk and interceptor facilities, and then through pump stations and force mains where topography
requires it. The wastewater system should be understood as a "chain" of connected components.
Each component has a distinct role, but system reliability depends on how they operate together
especially during wet-weather conditions when inflow and infiltration (1/1) can rapidly increase flows
and stress available capacity.
Because much of the Central Basin is already built out, the day-to-day collection "chain" there is
primarily sustained through maintenance, renewal, and targeted rehabilitation. In the Denton Creek
Basin, the same collection components must also accommodate remaining growth potential, basin
transitions, and downstream conveyance dependencies making system integrity, wet-weather
performance, and risk management a larger driver of planning and investment decisions.
GRAVITY MAINS
Gravity mains form the backbone of Southlake's wastewater collection system. These pipes convey
flow using slope and are typically the first link in the system—collecting wastewater from local
service lines and routing it toward larger trunk lines and interceptors. In the modeled Denton Creek
Basin system, the wastewater network is described as primarily a gravity flow system that follows
the major drainage basins, and pipe sizes range from 2 to 27 inches, reflecting the transition from
neighborhood lines to larger conveyance corridors.
From a performance perspective, gravity mains are where wet-weather stress often becomes visible
first through surcharging in manholes, localized restrictions, or capacity-limited segments that can
contribute to overflows if downstream constraints are present. The modeling approach evaluates
how lines surcharge and whether that surcharging is driven by downstream restriction or insufficient
local capacity, which supports a more targeted and defensible CIP strategy over time.
TRUNK LINES AND INTERCEPTORS
As wastewater flows consolidate, trunk lines and interceptors serve as the "spine" of the collection
system by carrying flow from multiple neighborhoods and basins toward downstream lift stations
or transfer points. These facilities are especially important during peak wet-weather conditions
because they represent the shared pathways for large drainage areas. Mapping and model results
are used to identify interceptor segments where modeled flows exceed capacity during peak wet-
weather events and where surcharging may occur due to downstream restriction.
Where gravity conveyance is not practical due to topographic constraints or basin transitions,
lift stations provide the pumping needed to move wastewater to the next stage of the
system. In the Denton Creek Basin model, there are 12 lift stations, and they are described
as necessary due to local topographic constraints or to pump flows across sub-basins.
LIFT STATIONS
Where gravity conveyance is not practical due to topographic constraints or basin transitions,
lift stations provide the pumping needed to move wastewater to the next stage of the
system. In the Denton Creek Basin model, there are 12 lift stations, and they are described
as necessary due to local topographic constraints or to pump flows across sub-basins.
Lift stations are key reliability points because they concentrate risk: a lift station failure can affect a
ORDINANCE
larger upstream area than a typical pipe defect, and wet-weather conditions can increase influent
rates and shorten response time.
The modeling study also provides clear design logic for lift station performance: firm pumping
capacity is intended to meet 125% of peak wet-weather design flows, where "firm capacity" assumes
the largest pump is out of service. This helps define how lift station needs are evaluated and how
upgrades are justified when service levels are threatened.
Lift Statio & Cross Sectional Area Active Volume
..
Bank Street Circle 10 78.54 5.42 3,184
Burney Lane Circle 5 19.63 3.58 526
Coventry Circle 4 12.57 4.47 485
Crown Ridge Circle 5 19.63 3.30 420
Dove Estates Circle 5 19.63 9.33 1,370
Gateway Circle 8 50.27 7.00 2,632
Loch Meadows Circle 12 113.10 6.00 5,076
Lonesome Dove Rectangle -- 190.00 16.00 28,424
Quail Run Circle 6 28.27 5.58 1,181
Saddleback Circle 6 28.27 5.15 1,089
Shady Lane Rectangle -- 170.00 13.75 25,432
Torian Lane Circle 6 28.27 10.03 2,121
Figure 2-1:Denton Creek Basin Lift Stations
FORCE MAINS
Force mains convey wastewater under pressure downstream of lift stations. They are a necessary
counterpart to pumping in areas where gravity service cannot be maintained continuously. City
mapping distinguishes force mains from gravity lines, and the CIP mapping also highlights force
main infrastructure and proposed improvements in context.
From a performance standpoint, force mains must be sized to meet pumping capacity while
maintaining appropriate velocities and pressures. The modeling study's criteria recommend force
mains support lift station capacity with velocities that provide scouring (to reduce sediment
deposition) and avoid excessive pressure. While force mains are typically fewer in number than
gravity mains, they often represent higher-consequence assets due to repair complexity and the
service area affected.
MANHOLES AND SYSTEM ACCESS
A wastewater collection system can only be maintained if it is accessible. Manholes provide critical
access for inspection, cleaning, condition assessment, and response activities. Cleanouts provide
localized access points that support maintenance, particularly at the neighborhood scale. The City's
sanitary sewer mapping and CIP map legend also identify operational appurtenances such as plug
valves and air release assemblies, which support operational control and force main functionality.
Because wet-weather reliability is closely tied to the system's ability to use available storage
without triggering overflows, manhole-related performance criteria also matter. The modeling study
references a wet-weather evaluation approach tied to surcharge levels relative to the manhole rim,
which helps quantify how close the system is operating to overflow conditions during design storms.
WASTEWATER MASTER PLAN
METERS AND WHOLESALE CONNECTIONS
In addition to City-owned collection infrastructure, system performance and planning are influenced
by where flows enter the system and how they are measured. The Denton Creek Basin modeling work
notes that the City receives flow from two wholesale meters in the North Service Area, reinforcing
the need to account for metered inflows and external contributors when evaluating capacity and
wet-weather behavior.
REGIONAL/WHOLESALE INTERFACES AND DOWNSTREAM DEPENDENCIES
Although Southlake owns and operates the local collection system, overall system reliability is
influenced by key regional interfaces and downstream conveyance dependencies—particularly in
the Denton Creek Basin context. The Freese & Nichols modeling study notes that, in the North
Service Area, all flow is conveyed to the TRA Kirkwood Lift Station, which has a firm capacity of
6.OS MGD and transports flow via a 30/24/20-inch force main to the TRA Denton Creek Regional
Wastewater System (DCRWS) wastewater treatment plant.
City mapping also depicts TRA system elements and the distinction between TRA Central Basin and
TRA Denton Creek Basin features, underscoring that Southlake's local decisions ultimately connect
to broader regional system performance.
This downstream dependency is important for two reasons. First, it reinforces why wastewater
planning must address peak wet-weather conditions, not just average daily flow—because wet-
weather peaks are what stress lift stations, trunk lines, and downstream interfaces. Second, it
elevates the value of 1/1 reduction and targeted rehabilitation as practical strategies to preserve
effective capacity and reduce avoidable peak flow stress before major regional upgrades become
necessary.
SEPTIC PRESENCE AND SERVICE GAPS
Not all properties within Southlake are connected to the municipal wastewater collection system.
Some areas more commonly near the edges of the system footprint and in lower-density or historically
unserved areas continue to rely on private septic systems. From a master planning standpoint, these
service gaps matter because future septic-to-sewer transitions can change both the timing and
location of flow increases and may require localized collection extensions, lift station modifications,
or downstream conveyance considerations.
The Freese & Nichols study frames septic incorporation as a distinct driver category in the CIP
describing projects that may be triggered as interest is shown and noting they are primarily in
the northern and western portions of the City. In this plan, septic-to-sewer is treated as a flexible,
location-specific pathway that must remain consistent with overall system performance and financial
sustainability goals.
CURRENT OPERATIONAL CONTEXT
Day-to-day wastewater system performance in a mature community depends heavily on proactive
operations and maintenance, rapid response capability,and disciplined reinvestment. While localized
issues can occur anywhere, wet-weather conditions tend to amplify vulnerabilities especially where
1/1 increases system loading and drives surcharge risk. As a result, the City's operational context is
closely connected to the plan's technical foundation: using consistent evaluation tools (modeling
+ monitoring + field verification) to identify recurring drivers of service disruption and to prioritize
ORDINANCE
improvements based on risk and performance outcomes.
The Freese & Nichols modeling study describes how the wastewater model was developed using
the City's GIS data, force mains for all lift stations, and gravity lines, with as-built information used
to supplement the network where available. It also references historical flow monitoring inputs used
for calibration and notes that RDII insights were used to identify basins for follow-up SSES activities
(as originally flagged in the monitoring analysis). This reinforces a key operating principle for the
Master Plan: combine model-based screening with field confirmation to refine project scope, timing,
and expected outcomes so investments are both strategic and effective.
REGULATORY ENVIRONMENT
Southlake's wastewater collection system operates within a well-defined regulatory environment
that is designed to protect public health, preserve water quality, and ensure utilities are planned,
operated, and reinvested in responsibly over time. While the City's day-to-day work is focused on
maintaining reliable service such as preventing backups, minimizing disruptions, and responding
quickly when issues arise, the regulatory framework provides the baseline expectations for how
the system must perform and how risks must be managed. In practical terms, regulations shape
everything from wet-weather planning assumptions and design
standards to overflow prevention, recordkeeping, reporting, and the
prioritization of rehabilitation projects that reduce system vulnerability.
•
At the state level, Texas establishes core requirements for wastewater •
collection systems through the Texas Commission on Environmental
Quality (TCEQ). These requirements influence how new infrastructure
is designed and how existing infrastructure is evaluated particularly
under wet-weather conditions. Collection system design criteria
(such as acceptable surcharge conditions, pipe capacity and velocity
expectations, lift station reliability assumptions, and wet well sizing) �•
are intended to ensure that systems convey wastewater safely and
predictably. As a result, local planning must account not only for
average daily flows, but also for peak wet-weather conditions that can
cause surcharging and contribute to the risk of sanitary sewer overflows (SSOs). This is one reason
the Wastewater Master Plan places strong emphasis on understanding wet-weather response,
identifying where inflow and infiltration (1/1) is influencing performance, and targeting improvements
that preserve effective capacity and reduce peak system stress.
Regulation also intersects with how wastewater projects are scoped and prioritized. In a near-built-
out community, the most cost-effective compliance strategy is often to prevent avoidable system
stress before it becomes an overflow risk. That means using data-informed approaches such as
flow monitoring, basin screening, and field verification to identify where rehabilitation, repairs, or
targeted 1/1 reduction work can deliver measurable performance improvements. It also means using
design standards and levels-of-service expectations consistently so that capital investments are
sized appropriately: large enough to protect reliability under defined wet-weather conditions, but
phased in a way that avoids unnecessary overbuilding. In this sense, the regulatory environment
supports a disciplined planning approach that connects technical analysis to clear, defensible
investment decisions.
The regulatory framework also extends to regional coordination and downstream dependencies.
Southlake's wastewater collection system does not operate in isolation; its performance is affected
by key interfaces with regional partners and downstream infrastructure that ultimately receives and
WASTEWATER MASTER PLAN
treats the City s conveyed flows. This makes coordination and transparency especially important
when evaluating peak flow conditions, capacity limitations, and improvement timing. A master
plan that documents the basis for flow projections, wet-weather evaluation methods, and system
constraints helps ensure that the City can communicate clearly with partners and stakeholders
about why certain investments are needed and how they support ongoing service reliability and
regulatory compliance.
The regulatory environment reinforces the importance of continuous stewardship. Wastewater
compliance is not achieved through a single project or one-time plan, it is maintained through
consistent operations, preventive maintenance, targeted reinvestment, and ongoing updates to
reflect changing conditions. As Southlake continues to mature, the wastewater program must
remain focused on protecting levels of service through asset management, reducing 1/1 where
it drives wet-weather risk, and maintaining a transparent planning framework that ties capital
programming to measurable performance. Including this regulatory context in this chapter helps
the reader understand that wastewater planning is not solely about infrastructure it is also about
managing risk and meeting defined public health and environmental responsibilities in a way that is
sustainable for the community.
Governing Agency/ Primary Focus �Ihaj"ans for Southlake
Regulatory Layer I
Collection system design expectations, Establishes baseline criteria for planning
State (TCEQ) wet-weather conveyance, lift station assumptions, design storm evaluation, reliability
criteria, general compliance standards. expectations, and how projects are scoped and
justified
Federal (Clean Water Protection of water quality; Reinforces the importance of preventing overflows
Act/ EPA) overarching framework that informs and protecting receiving waters through sound
state programs and enforcement. utility stewardship.
Regional /Wholesale Downstream conveyance and Requires coordination on capacity and wet-weather
Interfaces treatment dependencies; coordination peak considerations; underscores the need for
with partner agencies. transparent planning and documented assumptions.
Local Standards and City design standards, development Implements compliance locally through consistent
Policies requirements, O&M practices. design review, reinvestment standards, and
maintenance practices.
Supports data-driven prioritization (flow
Performance and Monitoring, documentation, and monitoring, basin screening, post-project
Accountability continuous improvement verification) and transparent reporting of progress
toward service goals.
Legend
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Wastewater Line TRA Central Basin
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Wastewater flow is the single most important input to understanding how a collection
system performs because it determines whether pipes, lift stations, and downstream conveyance
operate within their intended service levels or begin to surcharge under stress. This chapter explains
the different types of wastewater flow the City plans for, how those flows behave over time, and
why wet-weather response is often the factor that defines system risk and investment priorities. It
provides the planning context needed to interpret the performance findings in later chapters and to
support defensible capital planning decisions.
As Southlake approaches buildout, flow planning also becomes more nuanced. Growth-driven
increases still matter, but system performance is increasingly shaped by the "hidden drivers" of wet-
weather behavior such as inflow and infiltration (1/1), rainfall-derived inflow and infiltration (RDII),
and how quickly peak flows concentrate in specific basins. Understanding both typical dry-weather
conditions and peak wet-weather response allows the City to prioritize improvements that protect
public health, avoid service disruptions, and make the most cost-effective use of existing capacity.
FLOW TYPES AND PLANNING CONCEPTS
Wastewater flow can be grouped into two primary planning categories: dry weather sanitary flow
and wet-weather response. Dry weather sanitary flow reflects the everyday wastewater generated
by residents, employees, and visitors typically following predictable daily patterns tied to household
routines and commercial activity. This baseline flow is the foundation of system sizing and long-term
demand planning, and it provides the "normal operating condition" that supports routine system
management.
Wet-weather response occurs when rainfall and groundwater conditions introduce additional flow
into the system that is not sanitary wastewater. This is generally described as inflow and infiltration
(1/1) and is often quantified through rainfall-derived inflow and infiltration (RDII) concepts. Inflow
includes direct connections or pathways that quickly route stormwater into the sanitary system (such
as illicit connections, faulty cleanouts, or cross connections), while infiltration is water that enters
through defects and joints in pipes and structures and can persist after rain events. Wet-weather
response is important because it can increase flows rapidly and disproportionately, especially in
mature systems, and it can be the dominant driver of surcharge risk, backups, and overflow potential
during major storm events.
WASTEWATER MASTER PLAN
From a planning perspective, a key concept is that wet-weather peaks are not evenly distributed
across the system.They concentrate based on basin characteristics, infrastructure age and condition,
groundwater conditions, and how quickly rainfall translates into inflow pathways. As a result, flow
planning must look beyond systemwide averages and focus on where peak flows occur, how long
they last, and what assets are most sensitive to those peak conditions.
HISTORICAL FLOW TRENDS AND KEY DRIVERS
Historical wastewater flow trends provide context for how the system has evolved and what factors
influence performance over time. In general, long-term flow patterns are shaped by three broad
drivers:
1. Community activity and land use patterns - The mix of residential and commercial activity
affects baseline sanitary flow and peak hour variations.
2. System maturity and condition - As systems age, defects and maintenance needs can
influence infiltration and wet-weather response if not addressed through rehabilitation and
reinvestment
3. Weather and groundwater - Rainfall intensity, antecedent moisture, and groundwater levels
affect RDII response and can reveal which basins are most sensitive to 1/1 during storm events.
In a community nearing buildout, historical trends often show that wet-weather variability becomes
a key defining feature of system performance. Even when average daily sanitary flow remains
relatively stable, wet-weather peaks can increase or become more impactful if 1/1 pathways expand,
if rainfall patterns shift, or if localized constraints develop in trunk lines, lift stations, or downstream
interfaces. For planning purposes, this reinforces the need to track flow behavior over time and to
integrate monitoring and field verification into how the City targets rehabilitation and prioritizes
capital projects.
PLANNING ASSUMPTIONS USED FOR PROJECTIONS
Future wastewater flow projections are based on a combination of land use assumptions and
wastewater generation rates that translate development patterns into expected sanitary flow. At a
planning level, projections are typically grounded in:
• Population and employment allocation consistent with the City's land use and growth
framework, recognizing that residential units, commercial activity, and civic uses contribute
differently to wastewater generation.
• Per-capita and per-employee flow criteria that reflect typical planning standards for sanitary
flow generation.
• Buildout assumptions that account for remaining development potential, redevelopment,
and changes in land use intensity over the planning horizon.
Criteria Factor Criteri L Factor
Residential Average Day Per Capita Flow Residential Average Day Per Capita Flow
(gpcd) 73 (gpcd) 100
Non-Residential Average Day Per Acre Non-Residential Average Day Per Acre
Flow (gped) 20 Flow (gped) 30
Peak Wet Weather to Average Day 4.0 Peak Wet Weather to Average Day 4.0
Peaking Factor Peaking Factor
Figure 3-1:Existing Wastewater Design Criteria Figure 3-2: Growth Wastewater Design Criteria
Because wastewater planning must account for both typical operations and stress conditions,
projections are not limited to average daily flows. They also include peaking factors and wet-
weather response assumptions that help the City evaluate how system constraints may emerge
under high-flow conditions. This approach supports more realistic capital planning by focusing on
the conditions that most directly influence risk particularly peak wet-weather periods.
PROJECTED FLOWS (EXISTING VS. BUILDOUT SCENARIOS)
Projected flow analysis compares current conditions to anticipated future conditions to understand
how remaining growth and system transitions may affect performance. From a planning standpoint,
this chapter evaluates wastewater flow under two core future scenarios:
• Buildout without septic incorporation, reflecting the wastewater system as it exists today
with growth accommodated primarily within already-served areas.
• Buildout with septic incorporation, reflecting a potential pathway where some properties
currently relying on septic systems transition to municipal wastewater service over time.
Planning Year Population Employment Average Day Flow Peak Wet Weather Flow
Existing 12,368 18,230 1.5 5.07
Buildout Without Septic Users 13,992 24,503 1.62 6.47
Buildout With Septic Users 16,181 24,503 1.84 7.35
Figure 3-3:North Service Area Projected Wastewater Flows
These scenarios are important because they
can change both the total volume of flow and Policy
the geographic pattern of flow increases. In
particular, septic incorporation is not only a ST1. Maintaingeneral approach
"growth" variable it is also a system connectivity septic-to-sewer recognizing
variable that can shift where collection extensions that conversion cost and physical feasibility
are needed and how localized capacity, lift vary by location, extending service _
re
station operation, and downstream conveyance praccoscons • _
ring
are affected. Including both scenarios ensures alternative solutions where connection
the City can plan with flexibility: maintaining an not feasible.
investment strategy that remains valid whether
septic-to-sewer transitions occur more gradually,
more quickly, or in targeted areas based on demonstrated interest and feasibility.
IMPLICATIONS OF PEAK WET-WEATHER FLOW ON PERFORMANCE, RISK, AND CIP SIZING
Peak wet-weather flow has outsized influence on wastewater system risk because it is the condition
most likely to trigger surcharging, backups, and overflow potential. In practical terms, a system
can appear to function well under dry weather sanitary flow while still being vulnerable under
design storm conditions if I/1 is high or if critical conveyance segments and lift stations are already
operating near their effective capacity. This is why the City's wastewater investment strategy must
be grounded in wet-weather performance: it is the best indicator of where reliability is most at risk
and where improvements produce the greatest risk reduction benefit.
Peak wet-weather flow also affects how capital improvements are sized and sequenced. Projects
designed solely around average conditions can underperform during stress events, while projects
sized around extreme conditions can be costly if not timed appropriately. This plan therefore
emphasizes a balanced approach: using peak wet-weather performance to identify where risk is
WASTEWATER MASTER PLAN
unacceptable, pairing capacity upgrades with system integrity measures (particularly 1/1 reduction),
and confirming priority needs through targeted field evaluation before committing to major capital
expansion. The result is a CIP that is more defensible and cost-effective focused on preserving
service levels, minimizing disruptions, and reducing long-term risk as Southlake approaches buildout.
ORDINANCE NO. 1034A ADOPTED MONTH DAY, 2026 23
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CHAPTER4:
HYDRAULIC WASTEWATER MODEL UPDATE
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A hydraulic wastewater model is one of the most valuable planning tools for a near-built-
out community because it allows the City to evaluate system behavior, not just individual pipes.
Wastewater performance is rarely defined by one isolated constraint; it is typically the result of how
multiple upstream basins, trunk lines, lift stations, and downstream interfaces respond together
especially during wet-weather conditions.A calibrated model provides a consistent way to understand
where capacity is being consumed, where surcharge risk increases, and which improvements will
produce the greatest reliability benefit.
This chapter describes the modeling framework used to support the Wastewater Master Plan,
including the model platform, data sources, calibration basis, and the performance standards used
to evaluate the system. It also explains how RDII screening and design-storm testing help translate
monitoring data into actionable priorities, and how the model should be maintained as a "living tool"
that evolves alongside rehabilitation projects, development changes, and updated flow monitoring.
WHY HYDRAULIC MODELING MATTERS FOR A BUILT-OUT WASTEWATER SYSTEM
In a mature system environment, the key planning question is often not "where do we extend
service," but "where is reliability most at risk and what is the most cost-effective way to reduce
that risk?" Hydraulic modeling supports this by testing how the collection system performs under
both typical and stressed conditions, including peak wet-weather flow that can drive manhole
surcharge, backups, and potential overflows. The model also supports defensible prioritization by
distinguishing between lines that surcharge due to downstream restrictions versus insufficient local
capacity, which is essential for selecting the right type of improvement and avoiding overbuilding.
MODEL PLATFORM, DATA SOURCES, AND STRUCTURE
The City's wastewater model is built using InfoWorks ICM and is structured to reflect the real-world
conveyance chain across the system: gravity mains, interceptors, lift stations, force mains, and key
transfer points. The model includes gravity lines from the City's GIS database and force mains for
all lift stations, with as-built drawings used to add new lines and refine network attributes where
available. When invert elevations were not available from as-builts, inverts were estimated using
accepted engineering approaches (including slope-based assumptions and interpolation between
known upstream/downstream elevations).
WASTEWATER MASTER PLAN
The model's loading and demand inputs are also structured to support planning needs. Wastewater
loads were updated based on available customer/meter information and flow projections so the
model can be used to evaluate existing conditions and future scenarios consistently.
FLOW MONITORING AND CALIBRATION BASIS
Hydraulic modeling is only as useful as its ability to represent observed system behavior. Model
calibration is the process of adjusting parameters until simulated flows, depths, and velocities reflect
what was observed during flow monitoring. The calibration basis used for this plan includes both
dry-weather and wet-weather conditions, which is critical for a system where wet-weather response
can be the defining driver of risk.
Dry-weather calibration was based on the period May 11 through May 17, 2018, while wet-weather
calibration used December 19 through December 21, 2017 a storm window that provides a
representative wet-weather response for RDII evaluation. The monitoring dataset reviewed for
calibration includes rainfall and flow monitoring data from the City's prior flow monitoring work and
provides the baseline against which the model's performance is checked.
RDII AND BASIN SCREENING
A key planning value of the modeling and monitoring work is the ability to screen and rank basins
based on wet-weather sensitivity. RDII (rainfall-derived inflow and infiltration) is defined as rainwater
that enters the sanitary system during storm events, and basin-level RDII volumes can be used to
prioritize where additional field investigation or SSES work is likely to yield the greatest benefit.
The basin screening approach categorizes basins into low-to-moderate, high, and excessive
RDII intensity based on a normalized RDII rate (gal/LF/in). This allows the City to focus limited
investigation resources where wet-weather response is most pronounced and where system
integrity improvements can reduce peak stress and preserve effective capacity.
SYSTEM DESIGN CRITERIA OVERVIEW
The model-based evaluation is paired with design criteria that help translate hydraulic results into
practical improvement recommendations.
• Gravity trunk lines / interceptors (existing): evaluated at peak wet-weather flow where the
hydraulic grade line (HGL) remains at least 3 feet below the manhole rim, which supports
effective use of system storage and helps attenuate peak wet-weather impacts.
• Future trunk lines / interceptors: aligned with TCEQ requirements, including peak wet-
weather design where the pipe is 7S% full while maintaining minimum and maximum velocity
standards (minimum 2 fps, maximum 8 fps).
• Surcharge-state diagnostics: the model evaluates whether surcharging is driven by
downstream restriction or insufficient capacity using defined surcharged state indicators.
• Lift stations and force mains:firm capacity concepts and criteria are used to evaluate pumping,
wet well storage, and force main velocities and pressures. The study defines firm pumping
capacity as the total available capacity with the largest pump out of service and references
TCEQ wet well sizing requirements. Force main criteria include velocity and pressure limits
and a minimum scouring velocity under single-pump operation.
rffFREESE City of Southlake CITY OF
NICHQLS Design Storm Comparison 13 SOUTHLAKE
3.0
2.65in/hr Average Peak Total
DepthIntensity Intensity
2.5 NOAA Atlas 14 5- ear,6-hour 0.51 2.68 3.58
NOAA Atlas 14 5-year,24-hour 0.21 0.84 4.95
December 19,2017 0.08 1.92 2.02
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ei rl rl '•1 '-I rl e-I
December 19,2017 —NOAA Atlas 14:5-Yr 24-Hr —NOAA Atlas 14:5-Yr 6-Hr
Figure 4-1:Design Storm Comparison Table
DESIGN STORM SELECTION AND LOS BASIS
To evaluate wet-weather performance consistently across the system, the plan uses a common
"design storm" as the basis for testing and comparing system response. A design storm establishes
the level of service (LOS) condition for wet-weather
evaluation creating a repeatable reference point for
identifying constraints, comparing alternatives, and sizing Policy
improvements. LS2. Use a consistent, . -
For this plan, the NOAA Atlas 14 S-year, 6-hour design storm planningbasis evaluating
was selected as the wet-weather basis because it aligns capacity
with observed regional storm characteristics and provides performance decisions
a meaningful stress test for collection system performance. comparable across basins -
nd
The study provides the corresponding storm depth and over time.
intensity characteristics used for evaluation.
MODEL MAINTENANCE AS A "LIVING TOOL"
To remain useful beyond plan adoption, the wastewater model should be maintained as a living
tool that is updated as system conditions change. This includes: incorporating newly constructed
or rehabilitated infrastructure, updating demand allocations as development occurs, refining
assumptions as additional flow monitoring or SSES data becomes available, and using post-project
verification to confirm performance outcomes. The goal is a continuous feedback loop: field data
improves the model, the model improves prioritization, and implemented projects provide new data
to refine future decisions.
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This chapter describes how Southlake's wastewater system performs today and
how that performance is expected to change as the community approaches buildout. In
a near-built-out city, wastewater planning is less about extending new service and more
about sustaining reliability like reducing the likelihood of backups and overflows, protecting
downstream conveyance, and making reinvestment decisions that are both defensible and
cost-effective. Because wastewater systems typically appear "fine" in everyday conditions,
the most meaningful performance insights come from understanding how the system
behaves during peak wet-weather periods, when inflow and infiltration (1/1) can rapidly
increase flows and shrink operational margin.
The purpose of this chapter is to translate system performance analysis into clear planning
direction. It explains the performance framework used to interpret results, summarizes
where constraints occur and why, and identifies what types of needs rise to the top whether
they are true capacity limitations, operational constraints, 1/1-driven wet-weather sensitivity,
or areas where additional field verification is warranted before major investment decisions
are made. This chapter also establishes the baseline levels of service (LOS) that will support
the plan's asset management approach and capital programming strategy in subsequent
chapters.
PERFORMANCE FRAMEWORK AND DEFINITIONS
Wastewater system performance is best understood through a reliability lens: how the
system behaves under both typical conditions and peak stress conditions, and how close it
operates to outcomes that affect customers and public health. The framework used in this
plan focuses on several interrelated indicators that describe risk and system resilience.
One of the most important concepts is surcharging, which occurs when water levels in the
system rise above the top of the pipe and portions of the gravity network begin to pressurize.
Surcharging can be part of normal wet-weather behavior, especially in older systems that
rely on available storage volume within pipes and manholes. However, surcharging also
WASTEWATER MASTER PLAN
serves as an early warning indicator because as the hydraulic grade line (HGL) rises closer
to the manhole rim, the system has less buffer and becomes more vulnerable to backups and
potential overflows. Defined HGL thresholds provide a consistent way to interpret whether
wet-weather surcharge behavior remains within acceptable limits or begins approaching a
reliability risk condition.
A second key concept is the relationship between localized constraints and systemwide
bottlenecks. Many wastewater issues are not caused by a single undersized segment;
instead, a downstream restriction can raise the HGL and create surcharging across an entire
upstream area. This is why systemwide evaluation is so valuable: it helps distinguish between
problems that require localized upsizing and problems that require relieving a downstream
bottleneck to restore broader system performance. Lift stations are also central to this
framework because they concentrate risk and can influence large upstream areas. When lift
station influent approaches or exceeds firm pumping capability during peak wet-weather
conditions, the system has less margin to respond, and reliability risk increases quickly.
EXISTING CONDITION PERFORMANCE FINDINGS
Under existing conditions, system constraints tend to appear where multiple stressors
overlap: wet-weather inflows increase quickly, downstream conveyance has limited margin,
and certain segments or facilities serve as shared pathways for large contributing areas. The
practical result is that some locations become repeat "hotspots" during storm conditions
not necessarily because the same pipe is always the root cause, but because the system in
that vicinity has less buffering capacity and is more sensitive to peak wet-weather loading.
A systemwide wet-weather response map is particularly helpful at this stage because it shows
not only where surcharge occurs, but also how widespread it is and how it clusters. That
pattern matters. Concentrated surcharge "trees" typically suggest downstream bottlenecks
that propagate upstream. Isolated surcharge pockets more often suggest localized capacity
or condition issues. This plan uses those patterns as a planning filter: it identifies where
performance appears most sensitive and where more detailed field verification should be
targeted, especially in areas that are also associated with higher RDII sensitivity or known
operational challenges.
FUTURE/BUILDOUT PERFORMANCE FINDINGS
As Southlake approaches buildout, wastewater performance is influenced by both
incremental increases in sanitary flow and how wet-weather peaks respond as system
loading grows. The plan evaluates future conditions using scenario-based planning so that
long-range decisions remain valid under different pathways. In one scenario, buildout occurs
largely within already served areas. In the second scenario, buildout includes septic-to-
sewer transitions in targeted areas over time. Including both scenarios helps the City plan
responsibly without assuming a single outcome especially because septic incorporation
can change where flows enter the system and may influence the timing and location of
infrastructure needs.
What is most important from a performance perspective is not simply that flows increase;
ORDINANCE
it is how those increases affect peak wet-weather margin at key system control points.
Lift stations are particularly useful performance markers because they integrate upstream
system behavior. When peak wet-weather influent approaches firm pumping capacity,
system reliability becomes more sensitive,and the consequences of operational interruptions
increase. Similarly, trunk and interceptor segments that serve large contributing areas
become more critical at buildout because they have less margin to absorb wet-weather
peaks without widespread surcharging.
DOWNSTREAM CAPACITY CONSIDERATIONS
Southlake's wastewater system is connected to regional conveyance and treatment
infrastructure, and those downstream interfaces shape what "reliability" means locally. In
practical terms, a local collection system can only perform as well as its ability to transfer
flow downstream under peak conditions. When downstream conveyance or firm capacity
thresholds are approached during wet-weather peaks, upstream parts of the system have
less operating margin. This relationship is why the plan emphasizes a balanced strategy:
addressing localized constraints where they exist, but also reducing avoidable peak flows
systemwide through integrity and 1/1-focused measures that preserve effective capacity.
This is also where planning discipline matters. Downstream capacity considerations are
not simply a reason to expand infrastructure; they are a reason to invest strategically. In
mature systems, targeted rehabilitation, 1/1 reduction, and operational improvements can
FREESE City of Southlake CITY OF
7.0
91M oil 9NICHOLS Buildout Lift Station Flow Comparison w/o Septic SOUTHLAKE
6.20
6.0
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Figure 5-1:Buildout Lift Station Flow Comparison without Septic
30 WASTEWATER MASTER PLAN I SOUTHLAKE
WASTEWATER MASTER PLAN
FREESE City of Southlake CITY OF
19
7.0
�7 NICHOLS Buildout Lift Station Flow Comparison w/Septic SOUTHLAKE
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9 Firm Capacity Average Daily Flow ®Peak Wet Weather Flow
Figure 5-2:Buildout Lift Station Flow Comparison with Septic
often produce meaningful peak flow reductions and restore performance margin at a
lower lifecycle cost than large-scale expansion especially when confirmed through follow-
up engineering evaluation. This chapter uses downstream dependency as a systemwide
lens for prioritization: projects that reduce peak stress at major conveyance points and lift
stations often provide outsized reliability benefits.
Policy Statement Policy Statement
Define clear wastewater - er time by
service that guide planning, operations, and routinely evaluating system performance,investment decisions, - - identifying recurring drivers of service
conveyance, minimized backups/overf lows, disruption, and adjusting maintenance and
and dependable wet-weather performance. capital priorities based on documented
L, L,L_ results.
PRIORITY DRIVERS
This plan identifies priority areas using a driver-based approach so the City can match the
right solution to the right need. Not every "red spot" on a wet-weather map requires a
large pipe replacement. Some locations are true capacity limitations that warrant upsizing
ORDINANCE
or parallel relief. Others are driven primarily by downstream restrictions where a targeted
bottleneck relief project can restore performance across a larger upstream area. Still others
may be symptoms of system integrity issues where 1/1 increases wet-weather loading to the
point that otherwise adequate infrastructure becomes stressed.
For planning purposes, priority needs are grouped into practical categories: capacity-
driven improvements, operational efficiency improvements, RDII/l/1-driven integrity needs,
and engineering evaluation needs that require field verification before committing to
major capital commitments. This structure supports a more cost-effective capital strategy
because it encourages sequencing. It allows the City to start with targeted investigations
and rehabilitation where the evidence suggests 1/1 is a significant driver, while reserving
large capacity projects for locations where constraints persist even after integrity strategies
are implemented or where downstream bottlenecks are clearly limiting performance.
LEVELS OF SERVICE (LOS) BASELINE
The performance findings summarized in this chapter establish the baseline levels of service
(LOS) framework for the Wastewater Master Plan. In wastewater planning, LOS is best
defined through outcomes and margins: the system's ability to convey flows reliably under
defined wet-weather conditions, the extent and severity of surcharging, the margin between
peak influent and firm pumping capability at lift stations, and the presence (or absence) of
conditions that increase backup and overflow risk.
Establishing this baseline is important for two reasons. First, it gives the City a consistent,
transparent way to explain priorities: improvements are not selected only because they
are "old" or "large," but because they measurably reduce risk and protect service reliability
where performance is most sensitive. Second, it creates a foundation for asset management.
Once the City understands where the system is most vulnerable under peak conditions, it
can align reinvestment priorities with consequence of failure and performance outcomes
ensuring renewal and rehabilitation decisions are tied to service results, not just age or
isolated defects.
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CHAPTER6: SYSTEm ANALYSIS & PERFORMANCE
As Southlake approaches buildout, the long-term success of the wastewater program
depends less on expanding the system and more on stewarding what the City already owns.
Wastewater infrastructure is largely unseen, but it is one of the most consequential systems the
City manages because it protects public health and environmental quality every day. In a mature
community, the most common drivers of service risk are backups, wet-weather vulnerabilities, lift
station disruptions, and pipe failures that are increasingly tied to asset condition, system integrity,
and lifecycle reinvestment rather than growth alone. Asset management provides the framework to
manage these realities deliberately, transparently, and cost-effectively.
This chapter establishes the foundation for Southlake's wastewater asset management approach
as a core implementation strategy of the Wastewater Master Plan. It describes why reinvestment
becomes the dominant long-term strategy at buildout, the essential components of an asset
management program, and how the City can prioritize renewal and rehabilitation using a risk-based
framework. It also explains how asset management ties directly to levels of service (LOS), how
it should be coordinated with day-to-day operations and capital planning, and how performance
reporting creates a continuous feedback loop that strengthens decisions over time. This chapter is
intended to be practical: it provides the "why" and the "how" that will support policy statements,
budgeting, and program execution after plan adoption.
ASSET STEWARDSHIP AT BUILDOUT
In a growing community, utility investment is often driven by the need to extend service and
add capacity to support development. As Southlake nears buildout, that equation changes. The
wastewater collection system becomes a long-lived, high-value public asset where the dominant
driver of investment is not expansion, but keeping the existing system reliable, maintainable, and
resilient. Pipes age, lift station equipment reaches the end of its useful life, manholes deteriorate,
and force main appurtenances require replacement. At the same time, wet-weather conditions can
expose vulnerabilities in older infrastructure, particularly where inflow and infiltration (I/1) increase
peak loads and reduce operating margin. In this environment, reinvestment is not optional it is the
primary means of sustaining service and managing risk.
Asset stewardship at buildout means the City must treat wastewater infrastructure as a portfolio
with lifecycle needs. Instead of relying on reactive repairs, the City benefits from a proactive program
WASTEWATER MASTER PLAN
that anticipates deterioration, reduces avoidable failures, and targets reinvestment where it achieves
the greatest service benefit. This approach is also financially responsible: planned renewal typically
costs less than emergency response and reduces the social and economic disruption associated
with backups, outages, and repeated repairs. Over time, a disciplined reinvestment strategy
protects system value, improves reliability, and reduces the likelihood of "deferred maintenance"
compounding into costly, large-scale rehabilitation needs.
This stewardship focus also supports long-term flexibility. By managing assets intentionally,
especially those that drive systemwide risk such as trunk lines, lift stations, force mains, and key
interceptors,the City improves its ability to adapt to changing conditions (redevelopment, regulatory
updates, evolving wet-weather patterns, and shifting service expectations). In other words, asset
management is not only a maintenance strategy; it is a resilience strategy that allows Southlake to
sustain excellent service as the community matures.
assetIF Policy Statemen W Policy Statement
AM1. Manage the wastewater system as AM2. Establish and maintain a formal
a long-life public asset by prioritizing wastewater . .
conditionpreventive maintenance, renewal, and that includes asset inventory, .
replacement based on lifecycle needs criticality assessment, - .
budgetsrather than reactive repair alone. renewal planning to guide annual and - . .
PrioritizePoficy Statement
wastewater investments
using a consistent, transparent framework
that considers public health,
reliability, consequences of failure,
and operational risk, with reinvestment
becoming an increasing focus as Southlake
L_ approaches . .
ASSET MANAGEMENT PROGRAM COMPONENTS
A wastewater asset management program is most effective when it is structured as a repeatable
process rather than a one-time assessment. The core components typically include: inventory,
condition assessment, criticality, risk scoring, and renewal planning all supported by consistent data
management and governance.
Inventory is the foundation. The City should maintain a complete, up-to-date inventory of wastewater
assets such as gravity mains, force mains, manholes, cleanouts, lift stations, appurtenances, and
major interceptors linked to geographic information (GIS) and supporting attributes (age, material,
diameter, depth, service area, installation history, maintenance history). A good inventory allows
the City to understand what it owns, where it is, and how it connects as a system. It also enables
practical coordination with streets, drainage, and other infrastructure work so that renewal projects
can be bundled when it makes sense.
Condition assessment establishes how assets are performing and how deterioration is progressing.
For wastewater systems, condition assessment can range from routine field observations and
maintenance records to targeted investigations such as CCTV inspections of gravity mains, manhole
condition inspections, lift station equipment assessments, force main evaluation strategies, and
basin-level investigations tied to wet-weather performance. Not every asset requires the same
intensity of inspection; asset management works best when condition assessment is targeted based
on risk and consequence. The goal is not to inspect everything every year, but to collect enough
reliable information to predict failure likelihood and identify where renewal will reduce risk most
effectively.
Criticality evaluates the consequence of failure. In wastewater systems, criticality is often highest
where a single asset serves a large upstream area, where failure affects critical facilities, where access
is difficult, where repair time is long, or where downstream dependencies create cascading impacts.
Trunk lines, lift stations, major force mains, and key interceptors are common "high criticality" assets
because they can affect broad service areas and can be more disruptive to repair.
Risk scoring combines condition and criticality into a repeatable prioritization tool. A typical
approach uses a risk matrix (likelihood of failure x consequence of failure) to assign risk tiers across
the asset portfolio. This creates a common language for decision-making and helps separate "most
urgent" needs from "important but manageable" needs, enabling the City to program work over
time instead of reacting to crises.
Renewal planning converts risk insights into an implementable multi-year program. Renewal planning
identifies the right type of intervention (repair, rehabilitation, replacement), the right timing (near-
term vs planned), and the right delivery strategy (standalone project, bundled project, coordination
with other improvements). A strong renewal plan is not just a list of projects it is a strategy that
balances service reliability, financial capacity, operational needs, and community impacts.
AssetWastewater 1 Program
INVENTORY CONDITION CRITICALITY RISK RENEWAL PERFORMANCE
PLANNING REPORTING
Asset ta Inspection& Consequence Risk Evaluation Rehab&Replacement Track&Measure
i.
Assessment &impact Strategy, Results
ping
&1211 IS1 111
• Service Reliability • Reduced Overflows • Proactive Maintenance
36 WASTEWATER MASTER PLAN I SOUTHLAKE COMPREHENSIVE
WASTEWATER MASTER PLAN
RISK-INFORMED PRIORITIZATION FRAMEWORK
A risk-informed framework ensures that the City prioritizes wastewater reinvestment in a way that
is transparent and aligned with the outcomes residents care about most—reliability, responsiveness,
and public health protection. Because wastewater impacts can be immediate and consequential, the
prioritization framework should reflect the specific risk dimensions that matter most in a collection
system.
Public health and environmental protection are central. Assets that can contribute to backups,
overflows, or uncontrolled releases during failure events carry a higher consequence because they
directly affect residents, businesses, and water quality. The City's prioritization framework should
explicitly recognize these risks and treat them as high priority even when failures are infrequent
because the consequences are significant.
Consequence of failure should be evaluated in a practical, location-specific way. High-consequence
assets often include: trunk lines that serve multiple basins, lift stations with large upstream service
areas, force mains that are difficult to isolate or repair, and assets near sensitive receptors.
Consequence can also increase where redundancy is limited, where access is constrained, or where
a failure would disrupt traffic, businesses, or critical facilities.
Reliability and service continuity is the core performance objective. Prioritization should favor
investments that measurably improve the City's ability to sustain service during peak wet-weather
conditions and reduce repeat operational challenges. Reliability-driven prioritization is especially
important where wet-weather flow response creates narrow margins—because small asset failures
or minor constraints can become large disruptions during storm events.
Operational risk and maintainability is the fourth pillar. Some assets may not be at the highest
immediate failure risk but may create recurring operational burdens such as frequent maintenance
needs, difficult access, limited isolation capability, or performance sensitivity. Prioritization should
recognize that reducing operational burden can improve service reliability and free staff resources
for proactive work. Over time, operational efficiency improvements can deliver meaningful lifecycle
savings and reduce the probability that minor issues become major failures.
A well-designed framework translates these concepts into a simple scoring system that staff can
apply consistently. The scoring system should be clear enough to explain to decision-makers and the
public, but detailed enough to distinguish between competing needs. A recommended approach is
a tiered system—Risk Tier 1 (highest), Tier 2, Tier 3—where Tier 1 assets become the focus of near-
term action or targeted assessment, Tier 2 assets are programmed, and Tier 3 assets are monitored
and managed through routine maintenance and long-range planning.
COORDINATION WITH O&M AND CIP
Asset management is most effective when it is integrated with both operations and maintenance
(O&M) and the Capital Improvement Program (CIP). O&M is the City's first line of defense; it provides
the real-time information that reveals where assets are struggling and where failures are likely.
Maintenance records, response history, lift station run-time trends, cleaning frequencies, CCTV
findings, and complaint patterns are all valuable asset management inputs. A mature program treats
O&M data as an "early warning system" that helps direct inspections and refine renewal priorities.
CIP is the long-term reinvestment tool. The role of asset management is to provide the justification
for CIP projects and to ensure they are sequenced logically. Sequencing should follow a simple
principle: confirm needs before committing major capital. In practice, that means using screening
tools (performance patterns, RDII indicators, known constraint locations) to identify candidate
areas, then using targeted field verification (engineering evaluations, SSES work, CCTV, lift station
assessments) to confirm root causes, and then selecting the most appropriate intervention. This
stepwise approach reduces the risk of oversizing solutions or investing in capacity upgrades when
integrity improvements would have achieved the intended benefit at lower cost.
Coordination also improves efficiency by aligning wastewater renewal with other City work. Where
feasible, rehabilitation projects can be coordinated with roadway projects, drainage improvements,
or other utility work to reduce disruption and avoid repeated surface restoration. This is particularly
valuable in built-out areas where construction impacts are more sensitive and community disruption
can be a significant factor in project delivery.
PERFORMANCE REPORTING AND CONTINUOUS IMPROVEMENT
Asset management is not complete unless the City measures outcomes and uses those outcomes to
improve future decisions. Performance reporting provides accountability: it allows staff and decision-
makers to see whether reinvestment is improving reliability, reducing wet-weather vulnerabilities,
and lowering operational burden. It also provides transparency to residents by demonstrating that
projects are selected for measurable reasons and that investments are producing real improvements.
This plan's levels of service framework is the natural "scorecard" for wastewater performance. Over
time, the City should track a small set of LOS-aligned metrics that are meaningful, measurable, and
useful for decision-making. Examples include: reduction in repeat surcharge hotspots, improved
margin at key lift stations during wet-weather peaks, reduced frequency of localized backups
or service disruptions, reduced RDII sensitivity in targeted basins after rehabilitation, and fewer
reactive repairs in high-criticality assets. The specific metrics can evolve as data improves, but the
key is consistency using the same measures over time to demonstrate progress.
Continuous improvement occurs when reporting leads to action. If performance improves after
rehabilitation, the City can refine its prioritization approach and replicate successful strategies. If
performance does not improve as expected, the City can adjust assumptions, revisit field verification
methods, or refine how solutions are selected. This feedback loop is what turns the model and
monitoring tools into a living program: implemented projects generate new data, new data improves
prioritization, and improved prioritization increases the effectiveness of future investments.
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CHAPTER7:
RESILIENCE, 1/1 REDUCTION
In a near-built-out community, the long-term performance of a wastewater system is
increasingly defined by what happens during wet-weather conditions. Even when the collection
system performs well under normal dry-weather sanitary flow, inflow and infiltration (I/1) can
rapidly increase system loading during storm events, shrinking operational margin and elevating
the risk of surcharging, backups, and potential overflows. This makes 1/1 reduction one of the most
practical and cost-effective "capacity strategies" available because it preserves the usable capacity
of existing infrastructure and helps protect levels of service without immediately resorting to major
expansions.
This chapter establishes Southlake's framework for reducing 1/1 and strengthening system integrity
as a foundational resilience strategy. It describes how the City should structure an investigation-to-
rehabilitation program, how basin screening and targeted Sanitary Sewer Evaluation Study (SSES)
work can focus resources where they deliver the greatest benefit,and how private-property outreach
supports long-term results. It also addresses wet-weather preparedness and operational resilience
because even the best integrity program must be paired with lift station reliability, monitoring, and
a clear response posture to manage peak events effectively.
WHY 1/1 REDUCTION IS A FOUNDATIONAL STRATEGY
Inflow and infiltration reduction is foundational because
it addresses the difference between what the community Policy Statement
generates as sanitary flow and what the system is forced
to convey during storms. In many systems, wet-weather RS1. Advance - • inflow
peaks not average daily flow drive risk. When avoidable and -tion reduction program
storm-driven inflows are reduced, the system gains through targeted investigation - •
measurable breathing room across multiple components: rehabilitation, focusing on areas
trunk lines surcharge less frequently, lift stations regain with recurring wet-weather impacts
capacity margin, and downstream interfaces experience and - greatest risk-reduction
lower peak stress. This improves reliability in the potential.
conditions that matter most and reduces the likelihood
of customer impacts.
Inflow and infiltration reduction also preserves the value of prior and future investments. A
collection system can be upgraded repeatedly and still underperform during storms if 1/1 remains
WASTEWATER MASTER PLAN
high. Conversely, targeted integrity improvements can allow the City to delay or resize major capital
projects because the system is no longer "carrying water it shouldn't." From a financial standpoint,
this is cost avoidance with real lifecycle benefit reducing emergency response, repeated repairs,
and premature upsizing driven by peak conditions that are partially preventable.
PROGRAM STRUCTURE
A successful 1/1 program is structured as a repeatable cycle, not a one-time project. The key is
sequencing work so the City confirms root causes before committing major capital. The most
effective programs follow a clear progression:
1. Screening and targeting: Use system performance information, wet-weather response
patterns, basin screening indicators, service calls, and repeat maintenance needs to identify
candidate areas. This step helps the City focus effort where the payoff is highest rather than
trying to "boil the ocean."
2. Field investigation and confirmation: Once a basin or subarea is identified, the City confirms
1/1 sources using appropriate tools: targeted CCTV, manhole inspections, smoke testing
where appropriate, dye testing for suspected storm connections, and lift station wet-weather
trend review. The purpose is to differentiate between (a) true structural defects and pathway
issues and (b) capacity constraints that would remain even after integrity improvements.
3. Rehabilitation and repair sequencing: Only after confirmation does the City implement
rehabilitation—prioritizing repairs that reduce peak wet-weather response most effectively.
Importantly, the City should resist the temptation to treat rehab as "everything everywhere."
Sequencing should prioritize the highest-leverage defects first, then reassess wet-weather
response before expanding the rehab footprint.
4. Post-project verification: A core element of program discipline is verifying outcomes. After
rehab, the City should compare wet-weather response in the targeted area to baseline
conditions (either through monitoring, lift station influent trends, or focused follow-up data).
This ensures the program is delivering measurable benefit and provides a feedback loop to
refine future targeting.
SSES STRATEGY AND PRIORITIZATION APPROACH
Sanitary Sewer Evaluation Study work is most effective when it is basin-based, risk-informed, and
tightly connected to the City's performance findings. A basin-based approach helps the City address
1/1 as a system problem rather than as a series of isolated repairs. It also allows the City to align SSES
priorities with the areas that show the strongest wet-weather sensitivity and the highest potential
risk reduction benefit.
A recommended prioritization structure for SSES is a tiered approach:
• Tier 1: Highest wet-weather sensitivity and highest consequence
Basins that show pronounced wet-weather response and are upstream of high-criticality
assets (major interceptors, key lift stations, regional interface points) should receive first
priority because 1/1 reduction in these areas protects the most consequential parts of the
system.
• Tier 2: Repeat operational issues
Areas with recurring maintenance needs, repeated surcharging patterns, or frequent service
complaints should be addressed next especially when issues cluster around older infrastructure
or known infiltration pathways.
ORDINANCE
• Tier 3: Opportunistic / coordination-driven
Basins or segments that can be cost-effectively
addressed through coordination with roadway Policy Statement
projects, reconstruction work, or bundled
rehabilitation programs can be prioritized when RS2. Use appropriate field
timing and efficiency align. evaluations and system
assessments . confirm suspected
This approach keeps SSES practical and defensible. problem areasrefine project
It ensures the City is investing investigation and rehab scope, sequencing, expected
resources where they will reduce risk most, while also outcomes before
allowing the program to scale over time as funding and commitments.
staffing capacity allow.
PRIVATE-PROPERTY 1/1 PREVENTION
Long-term 1/1 reduction requires addressing both public and private sources. While the City can
rehabilitate pipes, manholes, and lift stations, private-property issues can reintroduce avoidable
inflow pathways if they are not addressed through education and, where appropriate, enforcement
tools. An education-first approach is especially important in a community-focused planning context
because residents often do not realize that certain conditions on private property can contribute to
wet-weather problems.
Private-property outreach should focus on clear, actionable practices residents can implement:
• Verify cleanout caps are present and secure
Missing or damaged cleanout caps can act as Policy Statement _7
direct inflow points during rain events, allowing
stormwater to enter the sanitary system. RS3. Implementeducation-
first
public outreach
• Prevent stormwater sources from connecting toprivate-property
sanitary including verifying cleanout
Downspouts, yard drains, and sump-type caps are present _ - . and
discharges should never route to sanitary. Even preventing - -
well-intentioned connections can meaningfully sanitary
from connecting to the
increase wet-weather system loading.
• Protect manhole areas and avoid ponding around
structures
Where private landscaping or grading directs stormwater toward manholes or cleanouts,
small drainage corrections can reduce inflow risk.
• Communicate what residents will notice and why it matters
Residents are more likely to participate when outreach ties actions to real outcomes: fewer
backups, fewer disruptions, and lower long-term costs.
WET-WEATHER PREPAREDNESS AND OPERATIONAL RESILIENCE
Even with a strong 1/1 program, wet-weather events will remain a defining stress condition for the
system. Operational resilience is therefore a necessary companion strategy focused on keeping
critical assets reliable and ensuring rapid response capability when conditions shift quickly. This
is especially important at lift stations, which often act as system control points and can become
immediate risk drivers during wet-weather peaks.
WASTEWATER MASTER PLAN
Operational resilience should include:
• Lift station reliability posture
Preventive maintenance, redundancy awareness, and a clear readiness standard for critical
stations (especially those with large upstream service areas or downstream interface
importance). Reliability planning should include backup power considerations where
appropriate and clear escalation procedures during storm events.
• Monitoring and situational awareness
Using available instrumentation and operational data to identify abnormal wet-weather inflow
patterns, confirm response trends, and trigger early action. Even simple thresholds (e.g., rapid
rise rates, high wet well levels, repeated alarms) can improve response time and reduce risk.
• Storm response readiness
Clear roles, response checklists, and a "playbook" for wet-weather conditions—particularly
for known sensitive areas. The goal is not only to respond to incidents, but to reduce the
likelihood that conditions escalate to customer impacts.
• Integration with the 1/1 program
Operational findings should feed back into basin screening and SSES targeting. If certain areas
consistently stress the system during storms, that is a strong signal to prioritize confirmation
work and integrity improvements.
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As Southlake's development peak is largely over, wastewater planning must balance two
realities at the same time: the system must remain reliable and resilient under peak conditions, and
the City should avoid overbuilding infrastructure that is not yet needed or that could be better
addressed through targeted rehabilitation and integrity measures. Growth and redevelopment still
influence wastewater loading, but in a mature community the most cost-effective strategy is often
to right-size improvements, time investments to demonstrated need, and ensure new development
does not introduce long-term operational or maintenance burdens. This chapter establishes how
Southlake will coordinate wastewater planning with development decisions so the system remains
dependable, maintainable, and financially sustainable.
This chapter also provides the implementation bridge between technical evaluation and day-to-
day planning practice. It describes expectations for capacity demonstration and infrastructure
compatibility, outlines how the City should evaluate and sequence developer-related improvements,
and identifies opportunities to simplify the system where lifecycle benefits exist. Finally, it frames
septic-to-sewer transitions as a strategic, feasibility-driven pathway coordinated with performance,
constructability, and long-term maintainability so that future connections strengthen the system
rather than creating unintended costs or operational complexity.
BUILDOUT READINESS AND RIGHT-SIZING PHILOSOPHY
Buildout readiness means the City has a clear, defensible
approach to sustaining wastewater levels of service as
remaining growth occurs and redevelopment continues. In Poficy Statement
a near-built-out environment, the City's planning posture
should prioritize right-sizing building what is needed, wastewater improvements to
� Plan and phasing
when it is needed, and in the form that provides the best support long-term buildout
lifecycle value. Right-sizing is especially important in conditions while avoiding
wastewater because oversizing can create new problems unnecessary overbuilding, using
(low velocities, sediment deposition, added maintenance sequencing
burden) while still failing to address the true drivers of demonstrated need.
risk (wet-weather peaks and I/I).
A right-sizing approach starts with a simple principle:
WASTEWATER MASTER PLAN
use performance evidence to define need. Where constraints are driven by peak wet-weather
conditions, the City should first consider strategies that preserve effective capacity such as targeted
rehabilitation, 1/1 reduction, and operational improvements before committing to major conveyance
expansion. Where true capacity limitations exist, improvements should be phased so that early
actions address the most critical bottlenecks and highest-consequence assets first, with later
phases triggered by measurable thresholds (growth milestones, verified performance indicators,
or confirmed wet-weather response patterns). This sequencing supports fiscal stewardship and
reduces disruption for residents and businesses by avoiding "build now just in case" projects.
DEVELOPMENT AND REDEVELOPMENT COORDINATION
Development and redevelopment coordination ensures that new projects connect to the system
responsibly, do not shift undue cost or risk onto existing residents, and remain compatible with
long-term system performance goals. In practice, this means the City should require a consistent
level of wastewater coordination during entitlement, platting, and construction—especially when
projects occur in areas that are sensitive under wet-weather conditions or where downstream
capacity margins are limited.
A coordinated approach generally includes three expectations:
• Capacity demonstration and "no adverse impact" evaluation
Development proposals should demonstrate that downstream collection infrastructure can
accommodate projected wastewater flows under established planning assumptions and that
the project will not increase surcharge/backup risk in a way that degrades levels of service.
This does not mean every project requires a full system model update; rather, the City should
apply a tiered approach—using screening thresholds to determine when a localized analysis
is sufficient and when broader evaluation is warranted based on basin sensitivity, proximity
to known constraints, and the scale of proposed change.
• Infrastructure compatibility and constructability Policy Statement
New public or private wastewater faciIities should be
compatible with the City's standards for materials, GD2. Require new development
access, and maintainability. Compatibility includes and " • " • • demonstrate
connection locations, manhole spacing, pipe adequate wastewater c- •
sizing that supports appropriate velocities and and • - •
maintenance needs, lift station design features (if and • - impacts
applicable), and configuration that avoids creating through appropriate u• • - • "
long-term operational liabilities. timing, or participation in r" • " •
• Required improvements and timing •
Where development triggers the need for improvements—whether localized upgrades,
upsizing, lift station modifications, or access enhancements—the City should clearly define
what must be constructed, when it must be constructed, and whether it must be completed
before occupancy. Timing should be consistent with right-sizing: improvements are required
when they are necessary to maintain LOS and protect public health, but the City should
avoid requiring unnecessary oversizing that adds long-term costs without clear performance
benefit.
SYSTEM SIMPLIFICATION OPPORTUNITIES
As systems mature, complexity can become an invisible cost driver. Lift stations with small service
areas, fragmented force mains, redundant configurations, and hard-to-access infrastructure can
ORDINANCE
increase maintenance burden and risk over time. System simplification focuses on reducing that
complexity where it is feasible and where it produces measurable lifecycle benefits.
Opportunities for simplification often include:
• Reconfiguration and consolidation of subareas to reduce the number of lift stations,
where gravity alternatives are feasible or where consolidation improves redundancy and
maintainability.
• Lift station reduction or modernization where a facility has high lifecycle cost, limited
redundancy, frequent operational issues, or is sensitive to wet-weather inflows. In some
cases, the best long-term investment may be to eliminate a station; in others, it may be to
modernize it for reliability and maintainability.
• Operational efficiency projects that reduce
response risk (improved access, isolation Policy Statement
capability, standardized components, monitoring
enhancements), especially where facilities are highPursue opportunities"
consequence or where repair time is long. operations '
long-termreduce .
A simplification strategy should be evidence-based and as targetedreconfiguration
coordinated with asset management. Simplification is or consolidation when supported
not pursued solely because "fewer assets is better," but byengineering evaluation "
nd
because it can reduce operational risk, reduce long-term lifecycle benefit.
lifecycle cost, and improve reliability particularly during
wet-weather events.
SEPTIC-TO-SEWER TRANSITION FRAMEWORK Policy
Septic-to-sewer transitions are a distinct type of "growth" ST2. Evaluate septic-to-sewer
decision because they change system connectivity and incentives only when they are
can alter where flows enter the collection network. In targeted, clearly justified, and septic presence is not simply a gap to be substantial enough
filled universally; it is a strategic planning consideration homeowner decisions
that should be evaluated based on feasibility, interest, remaining fiscally responsible and performance implications, and long- -ligned with long-term planning
term sustainability. priorities.
A plan-ready framework for septic-to-sewer should include:
• Maintain a general, feasibility-driven approach
The City should evaluate septic transitions when there is demonstrated interest, when public
health or environmental factors warrant consideration, or when coordinated infrastructure
projects make conversion more feasible. The City should avoid committing to broad, unfunded
conversion assumptions without clear implementation pathways.
• Evaluate system impacts and infrastructure needs
Each potential conversion area should be evaluated for localized collection needs (extensions,
lift stations, force mains), downstream compatibility, and wet-weather sensitivity. The goal
is to ensure new connections do not unintentionally create new operational vulnerabilities or
require premature major upgrades.
WASTEWATER MASTER PLAN I SOUTHLAKE COMPREHENSIVE
WASTEWATER MASTER PLAN
• Use targeted incentives where justified
Where a septic transition provides broader system or community benefit (risk reduction,
environmental benefit, coordinated infrastructure opportunity), targeted incentives or phased
implementation tools may be appropriate so long as they align with financial sustainability
and demonstrated feasibility.
PROTECTION OF LONG-TERM MAINTAINABILITY
Long-term maintainability is one of the most important, and most preventable, drivers of lifecycle
cost. Decisions made during development—alignment, easement width, access routes, manhole
placement, depth, and component selection—can lock in maintenance challenges for decades. As
Southlake approaches buildout, protecting maintainability becomes even more critical because the
City will increasingly rely on proactive renewal and efficient operations to sustain service levels
without unnecessary disruption.
A maintainability-focused approach includes:
• Clear standards for access and easements
Public wastewater infrastructure should be placed where it can be accessed safely and
consistently for inspection, maintenance, and renewal. Easements should provide adequate
width, access routes, and constructability for future rehab work. Where infrastructure is
placed in constrained areas, design requirements should explicitly address how maintenance
and emergency response will occur.
• Compatibility with the asset management program
New assets should be incorporated into the City's inventory, tagging, and condition
assessment framework from day one. Standardizing components where feasible (valves,
controls, monitoring equipment, lift station features) simplifies training, reduces spare parts
burden, and improves response consistency.
• Protection from avoidable future conflicts
Development coordination should reduce future conflicts with buildings, trees, walls, and
landscaping that block access or complicate renewal. Preventing future conflicts is often far
less costly than resolving them later, especially in built-out neighborhoods.
This maintainability focus ensures that new development strengthens the overall utility system rather
than adding hidden lifecycle liabilities. It also supports transparency: when the City can explain that
standards protect long-term cost and reliability, development requirements are easier to justify and
easier to apply consistently.
c `^
t-
Wastewater is one of the most essential services the City provides, yet it is largely "invisible"
when it is working as intended. Residents typically experience wastewater service through outcomes
such as reliability, responsiveness, minimal disruption during construction, and confidence that the
City is protecting public health and the environment. Because the collection system is underground
and technical by nature, effective implementation depends on more than engineering solutions.
It also requires clear communication, strong customer partnership, coordinated relationships with
regional providers, and a sustainable funding strategy that aligns long-term reinvestment needs
with community expectations.
This chapter establishes how Southlake will build understanding and support for wastewater
priorities, including inflow and infiltration (I/1) prevention, fats-oils-and-grease (FOG) management,
and the impacts associated with renewal and capital improvements. It also outlines how the City will
coordinate with partners, especially TRA and internal departments, to deliver projects efficiently,
and how a long-range funding framework should be structured so that service reliability and levels
of service (LOS) remain sustainable as Southlake approaches buildout.
COMMUNICATION GOALS FOR WASTEWATER
The City's wastewater communication goals should be grounded in what residents and businesses
actually experience and care about: reliability, responsiveness, and predictability. Most community
members do not interact directly with pipes or lift stations, but they do notice service disruptions,
odor concerns, backups, and the inconvenience of construction. The objective of wastewater
communication is therefore to translate technical needs into clear, relatable outcomes explaining
what the City is doing, why it matters, and how those actions protect quality of life.
A strong communication approach emphasizes four consistent themes:
1. Public health and environmental protection-Wastewater service is foundational to community
health and clean waterways.
2. Reliability during wet-weather conditions - Peak wet-weather conditions are where risk
concentrates; proactive work reduces the likelihood of backups and overflows.
WASTEWATER MASTER PLAN
3. Responsible stewardship and cost effectiveness - Planned renewal and targeted integrity
improvements reduce long-term costs and emergency disruptions.
4. Transparency and predictability - Residents benefit from understanding project timing,
neighborhood impacts, and what to expect during construction.
CUSTOMER-FOCUSED OUTREACH STRATEGY
Customer-focused outreach should support two goals at the same time: prevent avoidable
problems and maintain trust during improvements. On prevention, outreach should reinforce simple
behaviors that reduce system stress—particularly 1/1 prevention on private property and responsible
disposal practices that reduce clogs and backups. On construction impacts, outreach should focus
on predictability: clear schedules, notification methods, what residents will see, how access will be
managed, and where to call with concerns.
A cornerstone of Southlake's customer-focused wastewater outreach is the City's Fats, Oils, and
Grease (FOG) Program, which directly addresses one of the most common and preventable causes
of sewer backups: grease buildup and blockages. Fats, oils, and grease are present in most residential
and commercial kitchens and can accumulate in sewer lines, increasing the likelihood of backups or
overflows. The City also communicates that consequences can include public health endangerment,
damage to homes or businesses, and impacts to creeks, streams, and ponds. This program provides
a clear, practical way to connect "what you do in the kitchen" to "how the wastewater system
performs."
Southlake's FOG program is established by Ordinance 914 and supported by a FOG Policy Manual that
addresses commercial food service establishment requirements. For residents, the City emphasizes
best practices such as disposing of grease in the trash (after cooling into a container), wiping dishes
before washing, and using sink strainers to reduce buildup. For businesses, the program emphasizes
staff training, maintaining a clean FOG-free kitchen, and properly managing greasy wash water so
it goes to an appropriate drain rather than an outdoor drain that flows directly to waterways. The
City also requires grease traps to be cleaned at least every 90 days, with more frequent cleaning
as needed, and provides guidance on the common "2S% rule" for when cleaning is due. In addition,
the City requires permitted liquid waste haulers for grease and grit waste, with registration and
reporting requirements intended to ensure proper disposal tracking.
This FOG framework fits naturally alongside the plan's 1/1 prevention messaging. Together, they
create a "customer partnership strategy" that reduces avoidable system stress, improves reliability,
and helps protect public investment in the wastewater system.
PARTNERSHIPS
Wastewater service reliability is strengthened through coordinated partnerships both external
and internal. Externally, Southlake's downstream dependencies and regional interfaces mean the
City benefits from ongoing coordination with partners such as TRA on conveyance assumptions,
operational expectations, and long-range capacity considerations. Clear communication and shared
planning assumptions help ensure systemwide reliability under peak wet-weather conditions and
reduce surprises as conditions change over time.
Internally, partnership is equally important. Wastewater projects frequently intersect with streets,
right-of-way (ROW), drainage, and development activity. Coordinating schedules and scopes can
reduce community disruption and lower lifecycle cost by bundling restoration work and avoiding
repeated construction impacts in the same corridor. This coordination also supports efficient
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delivery: projects can be timed with pavement programs, roadway reconstruction, or other utility
improvements where it provides clear benefit.
FUNDING FRAMEWORK PRINCIPLES
A financially sustainable wastewater program must match the reality of a near-built-out system:
reinvestment and renewal become the dominant long-term cost drivers. Funding strategy should
therefore be designed to support predictable, ongoing lifecycle work not just occasional large
projects. The plan's levels of service (LOS) framework provides the "why" for investment; the
funding framework provides the "how."
Funding principles for the Wastewater Master Plan should include:
• Lifecycle alignment: Budgets and reserves should reflect ongoing renewal and rehabilitation
needs, not just reactive repair.
• Reliability protection: Funding should maintain the City's ability to prevent backups and
overflows, particularly during wet-weather stress conditions.
• Transparency: The City should be able to explain how rates/fees support service outcomes
and how capital priorities align with documented needs.
• Affordability and predictability: Rate stability
matters; long-range planning supports smoother Policy Statement
investment profiles and reduces large swings. wastewaterFS1. Fund the
Coordination with development: Where growth or financially resilient
nt
• redevelopment drives new needs, the City should manner
apply consistent policies for cost responsibility " •
ital
and timing. planning with lifecycle needs "
nd
CAPITAL PLANNING AND DELIVERY STRATEGIES L_long-term service expectations._A i
Capital planning is where the plan becomes executable. The City's capital strategy should reflect
the sequencing logic established earlier: confirm needs, target the right solution, and phase
improvements to protect service levels while avoiding
unnecessary overbuilding. This includes a mix of project
types—rehabilitation, targeted bottleneck relief, lift Policy Statement
station reliability improvements, and localized capacity FS2 _ replacement
upgrades—prioritized by risk and consequence.
as a planned, ongoing obligation
Delivery strategies should focus on minimizing disruption integrated into annual budgeting
. .
and maximizing lifecycle value. In built-out corridors, . dependable
bundling projects and coordinating restoration cansystem . programming.
materially reduce cost and community impact. The City without relyingcrisis-driven on
should also use apractical "project packaging" approach: spending.
group similar rehab projects to improve contractor
efficiency, coordinate lift station upgrades with force main improvements where needed, and time
work to reduce traffic and business disruption when feasible. Clear construction communication is
part of successful delivery, not an afterthought.
WASTEWATER MASTER PLAN
GRANTS AND ALTERNATIVE FUNDING
While wastewater reinvestment is typically funded Policy
through utility revenues and planned capital programming, partnerships,FS3. Pursue grants,
alternative funding can be valuable when it reduces and cost-effective delivery
local burden, accelerates high-benefit projects, or strengthenstrategies when they
supports innovation. The City should evaluate grants and long-term system performance
and
partnership funding opportunities where they align with reduce the burden on ratepayers
plan priorities particularly for resilience improvements, while maintaining accountability
targeted rehabilitation, monitoring enhancements, or outcomes.
projects that provide regional benefit.
Alternative tools can also include cost-sharing partnerships, interlocal coordination where projects
overlap jurisdictions or regional assets, and opportunities tied to regulatory compliance or
environmental benefit. The guiding principle is that external funding should not drive the project list;
it should support the priorities already established through risk-based planning and LOS alignment.
ORDINANCE NO. 1034A ADOPTED MONTH DAY, 2026 51
• 1•
CHAPTER 10:
PLANADOPTION & PUBLIc ENGAGEMENT
This chapter documents how the Wastewater Master Plan is advanced from a drafted policy
framework into an adopted supporting element of Southlake's Comprehensive Plan. Southlake's
comprehensive planning process is designed to be transparent, iterative, and community-informed.
Rather than treating adoption as a single vote at the end, the City uses a sequence of public meetings
to build understanding, gather feedback, and refine plan direction before formal action is taken. This
approach helps ensure the plan reflects community priorities, aligns with related Comprehensive
Plan elements, and provides clear implementation direction for staff and decision-makers.
The adoption process also reinforces the City's commitment to meaningful public involvement.
Wastewater service is often most noticeable when conditions change such as during major storm
events that increase wet-weather system stress, localized repairs that affect access or require
construction, or the rare instances when customers experience backups,odors, or service disruptions.
Residents form impressions based on reliability, communication, responsiveness, and confidence in
long-term stewardship. A structured adoption process provides opportunities to ask questions,
review plan concepts, and provide input in settings designed for dialogue, not just formal hearings.
Through Corridor Planning Committee work sessions, the SPIN Town Hall Forum/Open House,
Planning and Zoning Commission review, and City Council readings, the City is able to incorporate
feedback while keeping the plan grounded in objective data, regulatory requirements, and long-
term infrastructure stewardship.
ROLE OF THE CORRIDOR PLANNING COMMITTEE IN PLAN DEVELOPMENT
As part of the Comprehensive Plan update process, the Corridor Planning Committee provided
early guidance and direction that helped shape the development of the Wastewater Master Plan
(along with the Water and Stormwater plans being updated concurrently). Committee meetings
were structured to build shared understanding, review baseline conditions, and provide policy-
level feedback that staff could translate into clear plan direction. This step is important because the
Committee's role is not to design project solutions, but to help establish priorities, expectations, and
policy choices that guide how the City manages its infrastructure over time.
The City's Comprehensive Planning webpage documents the Committee schedule and topics,
including an initial overview meeting and subsequent plan-focused meetings. The Corridor Planning
Committee meeting on January 13, 2026 (overview of the Stormwater, Water, and Wastewater
plan updates) established shared context for the comprehensive utility planning effort, and the
WASTEWATER MASTER PLAN
February 10, 2026 meeting (Water/Wastewater focus) provided direction that informed refinement
of plan chapters, policy statements, and implementation pathways. Presentation materials from
these meetings are posted online to support ongoing transparency and resident awareness.
COMMUNITY ENGAGEMENT APPROACH AND COMMUNICATION STRATEGY
The City's engagement approach for these plan updates is built around multiple touchpoints, clear
communication, and accessible ways for residents to participate. The Comprehensive Planning
webpage emphasizes that presentation materials are posted online after meetings so residents
can stay informed even if they cannot attend in person. This Wastewater Master Plan also supports
expanding communication beyond meetings by using consistent messages and plain-language
tools that explain service expectations, wet-weather reliability principles, and "what residents can
expect" during planned reinvestment and capital delivery. In particular, the plan's emphasis on inflow
and infiltration (1/1) reduction and system integrity benefits from communication tools that help
residents understand how private-property practices and stormwater connections can influence
wet-weather system stress and long-term cost.
A central engagement milestone for these plan updates is the SPIN Open House/Town Hall Forum on
March 2, 2026 at 5:00 p.m. in the Southlake Town Hall Council Chambers. The City's Comprehensive
Planning page notes that this open house is intended to provide residents an opportunity to share
feedback with staff on the Water, Wastewater, and Stormwater Master Plans. This event is especially
valuable because it is designed for dialogue in a less formal setting than a public hearing, allowing
staff to clarify questions, identify recurring themes, and document input that can be reflected in final
plan edits before adoption.
FORMAL REVIEW AND ADOPTION SCHEDULE
After incorporating Committee direction and public input, the Wastewater Master Plan proceeds
through the City's formal adoption pathway. The anticipated schedule for public consideration and
adoption includes:
January - April 2026 — Public Feedback Opportunity with City staff
March 2, 2026 — SPIN Open House / Town Hall Forum (public feedback opportunity)
March 5,2026—Planning and Zoning Commission meeting(formal reviewand recommendation
step)
April 7, 2026 — City Council 1st Reading (initial consideration)
April 21, 2026 — City Council 2nd Reading (final adoption consideration)
This stepwise schedule serves two purposes. First, it provides multiple opportunities for public
awareness and feedback prior to final adoption. Second, it supports good governance by ensuring
the plan is reviewed through the City's established boards and commission structure before Council
action. Planning and Zoning Commission review provides an additional public forum to evaluate
the plan's consistency with the Comprehensive Plan framework and its policy direction, while City
Council readings provide the final legislative pathway for adoption.
HOW FEEDBACK IS USED TO REFINE THE PLAN
Public engagement and board/commission review are not symbolic steps; they are intended to
improve the final document. Feedback from the Corridor Planning Committee and SPIN Open
House is used by staff to refine narrative clarity, strengthen communication tools (including 1/1
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prevention messaging and "what residents can expect" guidance during construction), confirm that
policy statements are supported by clear rationale in earlier chapters, and ensure implementation
pathways are understandable. Feedback may also identify where additional graphics, maps, or
plain-language explanations are needed to make wastewater system planning concepts accessible
to residents.
The City's approach also emphasizes follow-through. Meeting materials are posted publicly, and the
plan is refined transparently so residents can see that input was received and addressed. Where
feedback reflects localized concerns such as odor issues, backup questions, service reliability
perceptions, construction disruption concerns, or questions about septic-to-sewer transitions
staff use documented information such as system performance findings, operational data, service
request trends, field observations, and technical study results to determine the most appropriate
plan response. Depending on the issue, that response may be improved communication, operational
adjustments, targeted maintenance practices, a standards/design alignment topic, 1/1 investigation
and rehabilitation sequencing, or a capital planning consideration.
DOCUMENTATION AND ADOPTION OUTCOME
Upon adoption, the Wastewater Master Plan becomes an adopted element supporting the City's
Comprehensive Plan and provides policy direction that guides:
1. Wastewater service expectations and performance management practices
2. Asset management foundations and development of the Wastewater Infrastructure Asset
Management Plan
3. 1/1 reduction and system integrity program direction, including SSES prioritization principles
and outreach practices
4. Development and redevelopment coordination expectations that protect system performance
and long-term maintainability
5. Long-range funding, capital planning, and partnership strategies supporting lifecycle
reinvestment and reliability
Adoption also establishes a clear basis for accountability, what the City committed to do, how
progress will be tracked, and how residents can stay informed as implementation proceeds.
AFTER ADOPTION
Once adoption is completed, the Wastewater Master Plan transitions from a planning document into
the City's formal policy framework for wastewater system decision-making and service delivery.
Adoption establishes an official, Council-recognized basis for how the City will define wastewater
service expectations, evaluate system performance, prioritize reinvestment, and communicate
consistently with the community. It also clarifies how model findings, operational data, and asset
information will be used to support decisions and how the City will align wastewater infrastructure
stewardship with the Comprehensive Plan's broader goals for neighborhood stability, resilience,
and quality of life. In practical terms, adoption provides staff with clear direction to apply the plan's
policy statements when evaluating maintenance needs, capital improvement priorities, development
review, and regulatory responsibilities.
Following adoption, the City applies the plan in three primary ways. First, it becomes the guiding
reference for program implementation—supporting consistent customer communication, improved
1/1 prevention and FOG outreach, and clearer expectations for what residents and businesses can
WASTEWATER MASTER PLAN
anticipate during planned infrastructure work. Second, it becomes the organizing framework for
decision support and long-range planning formalizing how the City maintains and uses model
findings, strengthens its asset inventory and condition practices, and advances the Wastewater
Infrastructure Asset Management Plan to prioritize renewal and reinvestment. Third, it becomes the
foundation for sustainable funding and partnerships connecting documented needs (operations,
compliance, renewal, resiliency, and prioritized improvements) to transparent funding discussions
and enabling coordinated delivery with water, stormwater, streets, and redevelopment so the
community experiences fewer repeat disruptions and more predictable, accountable infrastructure
stewardship.
A �
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ORDINANCE NO. 1034A ADOPTED MONTH DAY, 2026 55
f
WASTEWATER MASTER PLAN POLICY STATEMENTS
Manage the wastewater system as a long-life public asset by prioritizing
AM1 preventive maintenance, renewal, and replacement based on lifecycle needs
rather than reactive repair alone.
Establish and maintain a formal wastewater asset management program that
AM2 includes asset inventory, condition and criticality assessment, and risk-informed
renewal planning to guide annual budgets and multi-year capital programming.
Prioritize wastewater investments using a consistent, transparent framework
AM3 that considers public health, service reliability, consequences of failure, and
operational risk, with reinvestment becoming an increasing focus as Southlake
approaches buildout.
- - -
Define clear wastewater levels of service that guide planning, operations, and
LS1 investment decisions, emphasizing reliable conveyance, minimized backups/
overflows, and dependable wet-weather performance.
LS2 Use a consistent, systemwide planning basis for evaluating capacity and wet-
weather performance so decisions are comparable across basins and over time.
Improve reliability over time by routinely evaluating system performance,
LS3 identifying recurring drivers of service disruption, and adjusting maintenance
and capital priorities based on documented results.
o - . . r.NMI . .
Plan and phasing strategic wastewater improvements to support long-term
GD1 buildout conditions while avoiding unnecessary overbuilding, using sequencing
and timing to match demonstrated need.
Require new development and redevelopment to demonstrate adequate
GD2 wastewater capacity and infrastructure compatibility and to mitigate system
impacts through appropriate upgrades, timing, or participation in required
improvements.
Pursue opportunities to simplify wastewater operations and reduce long-term
GD3 risk and cost such as targeted system reconfiguration or consolidation when
supported by engineering evaluation and lifecycle benefit.
7RS1Advance a sustained inflow and infiltration reduction program through targeted
investigation and rehabilitation, focusing on areas with recurring wet-weather
impacts and the greatest risk-reduction potential.
Use appropriate field evaluations and system assessments to confirm suspected
RS2 problem areas and refine project scope, sequencing, and expected outcomes
before major capital commitments.
Implement an education-first public outreach program on private-property
RS3 1/1 prevention, including verifying cleanout caps are present and sealed and
preventing stormwater sources from connecting to the sanitary system.
WASTEWATER MASTER PLAN
Septic-to-Sewer Transition (ST)
Maintain the City's general approach to septic-to-sewer transition while
ST1 recognizing that conversion cost and physical feasibility vary by location,
extending service where practical and cost-effective and considering alternative
solutions where connection is not feasible.
Evaluate septic-to-sewer incentives only when they are targeted, clearly justified,
ST2 and substantial enough to influence homeowner decisions while remaining
fiscally responsible and aligned with long-term planning priorities.
Fund the wastewater utility in a financially resilient and transparent manner by
FS1 aligning budgets, reserves, rates/fees, and capital planning with lifecycle needs
and long-term service expectations.
Treat renewal and replacement as a planned, ongoing obligation integrated into
FS2 annual budgeting and capital programming so the system remains dependable
without relying on crisis-driven spending.
Pursue grants, partnerships, and cost-effective delivery strategies when they
FS3 strengthen long-term system performance and reduce the burden on ratepayers
while maintaining accountability for outcomes.
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GLOSSARY OF TERMS
AM — Asset Management P&Z — Planning and Zoning Commission
Atlas 14 — NOAA Precipitation Frequency PID — Public Improvement District
Estimates (Rainfall Atlas)
RDII — Rainfall-Derived Inflow and Infiltration
CCTV — Closed-Circuit Television (pipe
inspection) ROW — Right-of-Way
CIP — Capital Improvement Program SCADA — Supervisory Control and Data
Acquisition
CMOM — Capacity, Management, Operation,
and Maintenance (wastewater program SSES — Sanitary Sewer Evaluation Study
framework)
SSO — Sanitary Sewer Overflow
DCRWS — Denton Creek Regional Wastewater
System TCEQ — Texas Commission on Environmental
Quality
ETJ — Extraterritorial Jurisdiction
TRA — Trinity River Authority
FOG — Fats, Oils, and Grease
TSS — Total Suspended Solids (only include if
gpd — gallons per day used; otherwise omit)
gpm — gallons per minute VFD — Variable Frequency Drive
GIS — Geographic Information System WWMP — Wastewater Master Plan
HGL — Hydraulic Grade Line
1/1 — Inflow and Infiltration
ICM — Integrated Catchment Modeling
(InfoWorks ICM platform)
InSAR — Interferometric Synthetic Aperture
Radar (only include if used; otherwise omit)
LOS — Level of Service
MG — million gallons
MGD — million gallons per day
N/A — Not Applicable
NOAA — National Oceanic and Atmospheric
Administration
O&M — Operations and Maintenance
WASTEWATER MASTER PLAN
Asset (Wastewater) — Any component of the Consequence of Failure — The expected impact
wastewater collection system the City owns if an asset fails, including public health risk,
or is responsible for managing, such as pipes, environmental impact, service disruption, and
manholes, lift stations, force mains, and related repair complexity.
appurtenances.
Critical Bottleneck — A system location (pipe
Asset Criticality — A measure of the segment, junction, lift station, force main, or
consequence of failure for an asset based downstream interface) that limits conveyance
on factors such as the number of customers and can drive upstream surcharge and reliability
affected, proximity to sensitive areas, lack of risk.
redundancy, and difficulty of repair.
Design Storm — A rainfall event selected as a
Asset Management — A structured, risk-based standard basis for evaluating system response
approach to managing infrastructure over and sizing improvements (e.g., a NOAA Atlas 14
its lifecycle, including inventory, condition S-year, 6-hour storm).
assessment, prioritization, renewal planning,
and performance tracking. Dry Weather Flow (DWF) — Wastewater
flow during periods without rainfall influence,
Average Day Flow (ADF) — Typical daily consisting primarily of sanitary flow and
wastewater flow under normal conditions, groundwater infiltration unrelated to rain
generally reflecting base sanitary wastewater events.
generation.
Firm Capacity (Lift Station) — The pumping
Backflow / Backup (Sewer Backup) — A capacity available when the largest pump is out
condition where wastewater reverses direction of service (used for reliability-based design and
or rises to the point of impacting upstream evaluation).
plumbing or structures due to downstream
restriction, surcharge, or lift station limitations. Force Main — A pressurized pipeline that
conveys wastewater pumped from a lift station
Basin (Wastewater Basin) — A defined area that to a downstream discharge point.
drains wastewater to a specific collection path
or discharge point, used for organizing system FOG (Fats, Oils, and Grease) — Grease material
planning, monitoring, and prioritization. from kitchens and food service operations that
can accumulate in sewer lines, contributing to
Buildout — The condition in which the blockages and backups.
community's land use and development
potential is largely realized, shifting Gravity Main — A pipeline that conveys
infrastructure needs from expansion to renewal wastewater using gravity and slope rather than
and stewardship. pumping.
Cleanout — A capped pipe access point Hydraulic Model — A computer-based
(often on private property) used to provide simulation of the wastewater system used to
maintenance access to the sanitary service line evaluate flows, depths, velocities, surcharge
or small-diameter collection piping. conditions, and performance under various
scenarios.
Condition Assessment — The process
of evaluating the physical condition and Hydraulic Grade Line (HGL) — The elevation
performance of assets using inspections, to which wastewater would rise in a manhole
maintenance records, CCTV, field observations, or pipe under pressurized conditions; used to
and other data sources. evaluate surcharge and overflow risk.
ORDINANCE
Infiltration — Groundwater that enters the Rainfall-Derived Inflow and Infiltration (RDII) —
sanitary sewer system through defects, cracks, The portion of wet-weather flow that enters the
joints, or deteriorated structures. sanitary sewer system in response to rainfall,
used to characterize basin sensitivity and
Inflow — Stormwater that enters the sanitary prioritize investigation/rehabilitation.
sewer system directly and quickly during rainfall
through improper connections or openings Rehabilitation — The repair or renewal of an
(e.g., missing cleanout caps, illicit tie-ins). existing asset to restore performance and
extend service life (e.g., lining, point repairs,
Inflow and Infiltration (1/1) — The combined manhole rehabilitation, lift station component
contribution of inflow and infiltration that replacement).
increases wastewater flows above normal
sanitary levels, especially during storms. Renewal / Replacement — Planned
reinvestment in assets to address aging,
Interceptor — A large-diameter pipeline that deterioration, or performance limitations,
collects flow from multiple smaller lines and typically based on risk and lifecycle strategy.
conveys it toward lift stations, force mains, or
downstream transfer points. Right-Sizing — Planning and designing
improvements that match demonstrated
Level of Service (LOS) — A defined, measurable need and performance criteria while avoiding
expectation for system performance and unnecessary overbuilding and added lifecycle
reliability (often tied to wet-weather behavior, burden.
surcharge thresholds, lift station margins, and
operational outcomes). SCADA — A monitoring and control system
used to track lift station performance, alarms,
Lift Station — A facility that pumps wastewater levels, and operational status in real time.
from a lower elevation to a higher elevation to
continue conveyance when gravity flow is not Sanitary Sewer Overflow (SSO) — An event
feasible. where wastewater discharges from the sanitary
sewer system to the environment due to system
Manhole — A vertical access structure that failure, blockage, surcharge, or equipment
connects sewer pipes and provides entry for issues.
inspection, cleaning, maintenance, and repair.
Sanitary Sewer Evaluation Study (SSES) — A
Peak Wet-Weather Flow (PWWF) — The structured program to identify and reduce 1/1
highest flow experienced during or following through basin screening, field investigations,
a rainfall event due to combined sanitary flow defect ranking, targeted rehabilitation, and
and RDII/I/I response; often drives system post-rehab verification.
stress and sizing.
Surcharge — A condition where wastewater
Peaking Factor — A multiplier used to estimate rises above the pipe crown and pressurizes
peak flow conditions relative to average flow part of the system, often evaluated relative to
(used for planning and design). manhole rim elevation.
Private-Property 1/1 — Inflow or infiltration Septic System — An on-site wastewater
sources located on private property (e.g., treatment system used where properties are
missing cleanout caps, improper storm not connected to the municipal sewer system.
connections) that contribute additional wet-
weather flow to the public system.
WASTEWATER MASTER PLAN
Septic-to-Sewer Transition — The process of
converting areas served by septic systems
to municipal wastewater collection service,
typically evaluated based on feasibility,
performance implications, and community
benefit.
Service Area — The geographic area served by
the City's wastewater collection system (may
include multiple basin contexts).
Wet Well — The below-grade holding structure
at a lift station where wastewater collects
before being pumped.
Wet-Weather Response — The change in
system flow and performance during rainfall
events due to RDII/1/1 contributions.
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1/9/25
FREESE AND ICHOLS, INC. %�ESEAND NICHOLS, INC
TEXAS REGISTERED TEXAS REGISTERED
ENGINEERING FIRM ENGINEERING FIRM
F-2144 F-2144
Prepared by:
FREESE AND NICHOLS,INC.
801 Cherry Street,Suite 2800
Fort Worth,Texas 76102
817-735-7300
FNI Project Number:SOL23532
62 WASTEWATER MASTER PLAN I SOUTHLAKE COMPREHENSIVE
WASTEWATER MASTER PLAN
North Service Area Wastewater Master Plan Update
r7 nric�io s
City of Southlake 19 CITY OF
SOUTHLAKE
EXECUTIVE SUMMARY
1.0 INTRODUCTION
The City of Southlake (City) contracted with Freese and Nichols, Inc. (FNI) to prepare an update of the
City's Wastewater Master Plan for the North Service Area (Denton Creek Basin).This report presents the
analysis approach, findings, and results of the North Service Area Wastewater Master Plan Update. The
goal of the Wastewater Master Plan is to evaluate and analyze the wastewater collection system to
measure existing (2023) performance, identify deficiencies, and determine improvements needed to
meet future conditions. Historical wastewater flows were reviewed to establish trends and project flows
for the system evaluations. Based on the evaluations, a phased Capital Improvement Plan (CIP)through
Buildout was developed for the system. The recommended improvements will serve as a basis for the
design,construction, and financing of lines and facilities required to meet the City's future system needs.
2.0 LAND USE ASSUMPTIONS
FNI worked with City staff to develop and distribute the projected city-wide population and employment
growth as part of the concurrent Water Master Plan by FNI.Population and employment projections from
the U.S.Census Bureau by Census Block Group(CBG)were used as a starting point.The City of Southlake's
Future Land Use Plan and information on known developments provided by City staff were used to adjust
the population and employment projections. These projections were then refined for the North Service
Area based on the service area boundary and distributed by flow monitoring basin at the parcel level.The
buildout projections include two scenarios: (1)without the incorporation of existing septic users and (2)
with the incorporation of existing septic users. Table ES-1 summarizes the population and employment
projections for the North Service Area.
Table ES-1: North Service Area Population and Employment Projections
Population Employment
Planning Year Population Growth Employment Growth
Existing(2023) 12,368 -- 18,230 --
Buildout Without Septic Users 13,992 13% 24,503 34%
Buildout With Septic Users 16,181 31% 24,503 34%
ES-1
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North Service Area Wastewater Master Plan Update
r--M � o
City of Southlake 13 CITY OF
SOUTHLAKE
3.0 WASTEWATER FLOW PROJECTIONS
Projected wastewater flows were estimated based on the projected residential population and
employment growth. Based on the review of historical data presented, the historical overall per capita
flows, the 2018 Wastewater Collection System Flow Monitoring Report, and the need to plan for high
rainfall years, FNI utilized an existing residential average day per capita flow of 73 gallons per capita per
day (gpcd), a non-residential average day per employee production of 20 gallons per employee per day
(gped), and an existing peak wet weather to average day peaking factor of 4.0. It was decided to use a
residential average day per capita flow and non-residential average day per employee production of 100
gpcd and 30 gped, respectively, for growth areas to provide conservative estimates of growth-related
flows. Based on the population and employment projections and wastewater flow design criteria, the
projected buildout wastewater flows were calculated,as shown in Table ES-2.
Table ES-2:North Service Area Projected Wastewater Flows
Average Peak Wet
Day Flow Weather Flow
Planning Year Population Employment (MGD) (MGD)
Existing 12,368 18,230 1.27 5.07
Buildout Without Septic Users 13,992 24,503 1.62 6.47
Buildout With Septic Users 16,181 24,503 1.84 7.35
4.0 EXISTING WASTEWATER SYSTEM
The City of Southlake's North Service Area covers approximately 13 square miles.Within the service area,
there are approximately 495,119 linear feet of gravity mains and 30,270 linear feet of force mains that
are owned and operated by the City.All flow in the North Service Area is conveyed to the TRA Kirkwood
Lift Station, which has a firm capacity of 6.05 MGD and transports flow through a 30/24/20-inch force
main to the TRA Denton Creek Regional Wastewater System Wastewater Treatment Plant (DCRWS
WWTP).This lift station is located at the intersection of North White Chapel Boulevard and Sabre Drive.
The wastewater collection system is primarily a gravity flow system that follows the major drainage basins
of the service area. The wastewater lines range from 2 to 27 inches in diameter. There are currently 12
lift stations in the wastewater collection system. These lift stations are required because of local
topographic constraints or to pump flows across sub basins. The City also receives flow from two
wholesale meters in the North Service Area.
ES-2
64 WASTEWATER MASTER PLAN I SOUTHLAKE COMPREHENSIVE
WASTEWATER MASTER PLAN
FREESE
North Service Area Wastewater Master Plan Update
City of Southlake 19 CITY OF
SOUTHLAKE
Wastewater Model Development
The hydraulic model of the City's wastewater system includes force mains for all lift stations and all of the
gravity lines from the GIS database. As-built drawings provided by the City were used to add new lines
that have been constructed. If as-built drawings showing the pipe invert elevations were not available,
inverts were calculated either from known inverts using Texas Commission on Environmental Quality
(TCEQ) minimum slope requirements or by straight-line interpolation if upstream and downstream invert
elevations were available. Wastewater loads were updated throughout the model based on the water
billing meter data provided by the City and the wastewater flow projections.
Historical Flow Monitoring Review and Data Evaluation
FNI reviewed the flow monitoring and rainfall data from the 2018 Wastewater Collection System Flow
Monitoring Report by RJN Group to be used in the calibration of the wastewater model. Notably,this data
is over five years old and impacts the calibration of the model. Flow conditions have likely changed since
2018,and the Country Lane Lift Station has since been decommissioned.
Rainfall dependent inflow and infiltration (RDII) is defined as all rainwater that enters the sewer system
during a storm event. An RDII volume was calculated to assist in ranking the temporary flow monitoring
basins. Flow meter basins with high levels of RDII during the temporary flow monitoring period, Basin N-
13 and Basin N-15, were identified for follow-up Sanitary Sewer Evaluation Study (SSES) activities when
the original flow monitoring analysis was performed.
Wastewater Model Calibration
Model calibration is the process of rectifying parameters within the Info Works /CM wastewater model
until the model generates and conveys flow in the same manner as observed during the flow monitoring
period. A properly calibrated model shows that the model produces results that reflect the flow, depth,
and velocity data obtained during flow monitoring. The period of May 11 through May 17, 2018, was
selected for dry weather model calibration,and the date range selected for wet weather calibration was
December 19 through December 21, 2017. All flow meter basins were calibrated within industry
standards.
ES-3
FREESE
North Service Area Wastewater Master Plan Update rM "NICHOLS
City of Southlake CITY OF
SOUTHLAKE
Design Storm Selection
One of the major objectives of this study is to understand how the collection system behaves during wet
weather events. Inflow and infiltration can lead to bottlenecks in the system and wastewater overflows.
To evaluate the system as a whole, a common storm event must be selected as the basis for evaluation
moving forward; this is referred to as a "design storm" and establishes a level of service. The National
Oceanic and Atmospheric Administration (NOAA) Atlas 14 5-year, 6-hour design storm was chosen, as it
corresponds closely with recent weather trends. The total depth of the 5-year, 24-hour design storm is
3.58 inches with a peak intensity of 2.68 inches per hour.
Existing Wastewater System Analysis
FNI used the calibrated hydraulic model to evaluate the existing system and make recommendations to
address deficiencies and short-term needs.The calibration flows were scaled to match the total observed
existing flows to account for the growth that occurred after the 2018 flow monitoring analysis. Most of
the modeled existing pipeline capacity constraints occur downstream of the Dove Estates Lift Station,
Burney Lane Lift Station, and Quail Run Lift Station due to capacity restrictions. The proposed system
improvements, including these areas, should be sized for projected buildout flow conditions. All lift
stations are shown to meet the pumping capacity requirement of 125%of peak wet weather flows with
the largest pump out of service under existing conditions.
S.0 FUTURE WASTEWATER SYSTEM ANALYSIS
Hydraulic analyses were conducted to identify projected deficiencies in the City's wastewater collection
system and to establish a CIP to reinforce the existing system and convey projected wastewater flows.
Various combinations of improvements and modifications were investigated to determine the most
appropriate approach for conveying projected flows. Parameters used in developing the CIP included
accommodating anticipated growth, including that from existing septic users, simplifying system
operations, and providing the capacity to handle peak wet weather flows.
As part of this study, the feasibility of eliminating existing lift stations with gravity sewer improvements
was also considered.The City expressed interest in decommissioning the Coventry Lift Station and Shady
Oaks Lift Station (located in the South Service Area). Alternatives aimed to decommission these lift
stations were explored during CIP development.
ES-4
66 WASTEWATER MASTER PLAN I SOUTHLAKE COMPREHENSIVE
WASTEWATER MASTER PLAN
FREESE
North Service Area Wastewater Master Plan Update Ir-, `IYICHOLS
City of Southlake 13 CITY OF
SOUTHLAKE
The buildout peak flows are projected to slightly exceed the firm capacity of the TRA Kirkwood Lift Station.
With anticipated SSES efforts,the peak flows may be lowered to avoid increasing the capacity of this lift
station and force main. However, these potential capacity issues may need to be addressed as part of
TRA's future planning efforts.
The existing wastewater collection system under projected buildout peak wet weather flow conditions(5-
year,6-hour storm)was evaluated to determine where additional capacity is required.These results show
an increase in projected surcharging and overflows downstream of the Dove Estates Lift Station, Burney
Lane Lift Station, and Quail Run Lift Station. Additional capacity restrictions are shown near the Crown
Ridge Lift Station,Saddleback Lift Station,and Loch Meadows Lift Station when flows from existing septic
users are included, triggering capacity recommendations. All lift stations except the Burney Lane Lift
Station and Loch Meadows Lift Station are shown to meet the pumping capacity requirement underfuture
conditions.Capacity improvements at these lift stations will be required to add flows from septic users in
the collection system.
6.0 WASTEWATER SYSTEM CAPITAL IMPROVEMENT PLAN
The goal of the CIP is to address existing deficiencies in the system, as well as provide capacity for future
flows in the wastewater collection system. Upon completion of the wastewater model that represents
existing and future loading conditions, capital improvement projects were prioritized in order of
importance.Where existing facilities need to be upgraded,the recommended improvements are sized to
carry projected buildout flows. The CIP is categorized by four drivers: hydraulic capacity, operational
efficiency, engineering evaluations,and septic user incorporation.
Table ES-3 summarizes the recommendations based on the hydraulic analyses for the buildout CIP. All
project costs shown in this report are based on construction costs representing 2024 conditions and
should be adjusted in the future to reflect the current construction environment. The cost estimates
include material and construction costs, engineering design fees, and general contingency. Additional
expenses related to environmental,geotechnical, land acquisition,change order contingency,operations
and maintenance, and soft costs are not included.These costs also do not include escalation or inflation.
ES-5
SE
North Service Area Wastewater Master Plan Update
r1 nric�io�,s
City of Southlake CITY OF
SOUTHLAKE
Table ES-3:Wastewater System Capital Improvement Projects Cost Summary
Wastewater Project Driver Cost
Capacity Projects $6,750,300
Operational Efficiency Projects $1,862,100
Engineering Evaluation Projects $1,049,400
Septic User Incorporation Projects $35,652,400
CIP Total 00
ES-6
68 WASTEWATER MASTER PLAN I SOUTHLAKE COMPREHENSIVE
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