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Sanitary Sewer System Evaluation and Planning for Resiliency
Susan MoisioGlobal Solutions DirectorConveyance and Storage
Agenda
What is Resiliency?
01What does this mean for sanitary sewers?
02Case Studies• Miami• Mobile
03Where do we go from here?
04
What is resiliency?
©Jacobs 20203
What is resiliency?
resilience [rəˈzilyəns] NOUN
resiliency (noun)• The ability of a system to
continue to deliver its value regardless of disruption.
ResilientResiliency
100RCQualities of a Resilient City1. Reflective2. Resourceful3. Inclusive4. Integrated5. Robust6. Redundant7. Flexible
Complete Water Cycle
6
Sanitary Sewer Systems Now
What does this mean for sanitary sewer systems?
©Jacobs 20207
Focus on two factors that impact the ability of sanitary sewers to be Robust, Redundant, and Flexible:
Rainfall
1Groundwater
2
Definitions, so we can have the conversation
Sanitary sewer system Base Wastewater flowRainfall derived inflow and infiltrationGroundwater infiltration
Sanitary Sewer system
Main Sewer
PrivatePublic
Designed to carry some infiltration but not designed to carry stormwater
Definitions
0
10
20
30
40
50
60
70
80
90
Flow
(MG
D)
"Observed Flow" "Dry Weather Flow" "Base Wastewater Flow"
BASE WASTEWATER FLOW, GWI, AND RDII
Base Wastewater Flow
Rainfall Derived Inflow and Infiltration
Groundwater Infiltration
Definitions
Groundwater infiltration into the sanitary sewer system varies seasonally and must be checked against industrial and commercial users
Assume 80% =GWI
Groundwater Table
Sewer
Definitions
Rainfall and Groundwater, how are these factors changing and what are the mechanisms for the impacts to the sanitary sewer system?
©Jacobs 202013
4.5 4.7 4.85.42
Historical Updated Historical 2040 RCP 8.5 50% 2040 RCP 8.5 90%
ISWAS WILL BE
Rainfall projection variations for a 2 year 24 hour return interval storm illustrate the changes that have occurred already and what can occur in the future
0
10
20
30
40
50
60
70
80
90
Flow
(MG
D)
Impacts of Rainfall on the Sanitary Sewer System when the test condition changes
"Observed Flow" "Dry Weather Flow" "Base Wastewater Flow"
Groundwater Infiltration
Rainfall Derived Inflow and Infiltration
Base Wastewater Flow
0
10
20
30
40
50
60
70
80
90
Flow
(MG
D)
"Observed Flow" "Dry Weather Flow" "Base Wastewater Flow"
Base Wastewater Flow
Groundwater Infiltration
Rainfall Derived Inflow and Infiltration
Looking into the future the change in groundwater table will impact the change in the groundwater infiltration into the sanitary sewer system.
I/I = GWI
Change in Groundwater Level
Change in Groundwater Infiltration in the sewer
How does rainfall (stormwater) and groundwater get into the sanitary sewer system?
©Jacobs 202018
08.
PM
08.P
M
Public Property
Private Property
Area Drain
Foundation DrainManhole Cover or
PerimeterCurb Inlet
or Box
Pavement; Point or Multiple
Storm Indirect
Yard; Point or Multiple
Cleanout: Cap Broken or Uncapped
Driveway
Driveway Drain
Sidewalk
Downspout
Public Lateral
What of these defects are on the public side versus the private side?
©Jacobs 202019
08.
PM
08.P
M
Public Property
Private Property
Area Drain
Foundation DrainManhole Cover or
PerimeterCurb Inlet
or Box
Pavement; Point or Multiple
Storm Indirect
Yard; Point or Multiple
Cleanout: Cap Broken or Uncapped
Driveway
Driveway Drain
Sidewalk
Downspout
Public Lateral
Response to rainfall in the sanitary sewer system can depend upon antecedent conditions:
©Jacobs 202020
Rain 10.5”
Rain 20.5”
Rain 30.5”
Flow Comparison at Meter MC-WB-46TMarch 4,2001 vs. June 6, 2001
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
0:0
0
1:0
0
2:0
0
3:0
0
4:0
0
5:0
0
6:0
0
7:0
0
8:0
0
9:0
0
10
:00
11
:00
12
:00
13
:00
14
:00
15
:00
16
:00
17
:00
18
:00
19
:00
20
:00
21
:00
22
:00
23
:00
0:0
0
Time (hrs)
Flo
w (
mg
d)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0R
ain (in
/15 min
)
Rainfall volume = 0.36 inRainfall in previous 7 days = 1.24 in
Rainfall volume = 0.36 inRainfall in previous 7 days = 0.00 in
June 6, 2001
March 4, 2001
RDII - Antecedent conditions can dramatically impact the sanitary sewer system response to equal rainfalls
March
June
Flow Response to rainfall over time – percentage of rainfall entering the sanitary sewer system
0
2
4
6
8
10
120
0.1
0.2
0.3
0.4
0.5
0.6
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Rain
fall
(inch
es)
R Va
lue
Event ID
R1 R2 R3 Event Rainfall Event Selection Rainfall Threshold
Look at the rainfall over a period of time – most of the airport gauges have a long record and the gauge has been maintained
©Jacobs 202023
0
5
10
15
20
25
1 2 3 4 5 6 7 8 9 10 11 12
Rain
fall
(in)
Month
2019
Historical Rainfall (2000-2019)
75th percentile
Maximum
Average25th percentile
Minimum
Source: National Oceanic and Atmospheric Administration’s (NOAA) National Centers for Environmental Information
Long term record of the impacts of rainfall and groundwater infiltration on the sewer system
©Jacobs 202024
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.00
100
200
300
400
500
600
700
800
1/1/10 1/1/11 1/1/12 1/1/13 1/1/14 1/1/15 1/1/16 1/1/17
Hour
ly R
ainf
all (
in)
Flow
(mgd
)
Base Wastewater Flow Groundwater Infiltration Rainfall Dependent Inflow and Infiltration RainfallNote: Groundwater infiltration assumed as 80% of minimum nighttime flow.
How much is this impacting our Sanitary Sewers NOW?
2017 ASCE Report Card –EPA reports 23,000-75,000 SSOs per year in USA
1Dry Weather Flow in many sewer systems –30% to 50% Groundwater Infiltration
2Percentage of Rainfall entering the Sanitary Sewer System up to 20%
3
Case Studies
Miami, Florida
Rainfall
4.5 4.7 4.85.42
Historical UpdatedHistorical
2040 RCP8.5 50%
2040 RCP8.5 90%
Rainfall
0
10
20
30
40
50
60
70
80
90
Flow
(MG
D)
"Observed Flow" "Dry Weather Flow" "Base Wastewater Flow"
Historical Total System Flow Records indicate that while RDII impacts the system, groundwater infiltration should be focused on to impact average flows
©Jacobs 202029
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.00
100
200
300
400
500
600
700
800
1/1/10 1/1/11 1/1/12 1/1/13 1/1/14 1/1/15 1/1/16 1/1/17
Hour
ly R
ainf
all (
in)
Flow
(mgd
)
Base Wastewater Flow Groundwater Infiltration Rainfall Dependent Inflow and Infiltration Rainfall
Note: Groundwater infiltration assumed as 80% of minimum nighttime flow.
©Jacobs 202030
2020 2035
FLO
W
TIME
Flow Changes from 2020 to 2035
Average DWF Average SLR Peak RDII Peak Climate Change
RDII RDII
Climate Change Impacts to
Rainfall
Climate Change Impacts to
Groundwater Table
Impacts of Sea Level Rise to the Groundwatwer Table impact the amount of Groundwater Infiltration entering the sanitary sewer system
Groundwater InfiltrationSea Level Rise
Groundwater Table
Ground Water TableDry Season, Wet Season, and Wet Weather
• Ground water table based on USGS data for 141 wells
• Ranges from 1956 to today
• Tide based on NOAA data from 1994 to 2015
• USGS data allows for evaluation of different scenarios
• Dry season – average groundwater well level for May.
• Wet season – average groundwater well level for October.
• Wet weather – average of the maximum groundwater well level for October.
Private Property
Wet Weather (6.3’)
Wet Season (4.8’)
Dry Season (3.4’)
Gravity Sewer Elevation vs Groundwater Table Elevation
49%47%
4%39%
57%
4% 22%
74%
4%
Not submergedSubmergedData not available
Wet Weather
Wet Season
Dry Season
% of Gravity System Under Groundwater
47%
56%
74%
1% 3%
17%
0%
10%
20%
30%
40%
50%
60%
70%
80%
Dry Season Wet Season WetWeather
% o
f Gra
vity
Sys
tem
Sub
mer
ged
PublicPrivate
Note: Private lateral inverts were assumed to be at a depth of 3 feet below ground surface.
District Basins Mainline 2013 GWI @ DWFLength (FT) % MGD %
CDWWTP 39 384,518 47% 12.0 53%
NDWWTP 32 235,646 29% 6.0 26%
SDWWTP 21 196,104 24% 4.6 21%
92 816,268 100% 22.6 100%
Mobile, Alabama
Mobile, Alabama
Characteristics• 1,240 miles of gravity sewer• 28,800 manholes• 193 lift stations• 550 summit manholes• >50% of Gravity Lines Vitrified
Clay• >80% are 8” Diameter
Sanitary Sewer Evaluation ProgramFlow Monitoring Program
Service Lateral ProgramRehabilitation Program
Capacity Assurance Program
Service Lateral Program focuses on I/I in the public right of way
39
Main Sewer
PrivatePublic
Service Lateral Program adds to the resiliency of the sewer system by repairing existing defects that will provide for the future
Service Lateral Program Began in 2009 MAWSS Owns/Maintains Portion of Service Lateral from Property Line to Sewer
Main or Manhole Service Lateral Defects Primarily Identified from Smoke Testing MAWSS Allows 180 days for Property Owners to Correct Service Lateral Defect− Termination of service may occur after 360 days
Defective Public Service Laterals Repaired by Replacement or CIPP− MAWSS crews perform service lateral repairs/ replacement− Contractors perform CIPP and difficult repairs
40
Prioritization Approach Approach taken builds upon
the analysis from Miami that focuses on the groundwater table related to the sewer system Provides a more focused
look at I/I Zone 1Private service lateral
Zone 2Public service lateral
Zone 3Mainline sewer piping
Zone 4Below all main line sewer piping
PublicPrivate
Where do we go from here?
Complete Water Cycle
43
Sanitary Sewer Systems Now
FIGURE OUT HOW THE WATER GETS IN
LEONARD COHEN -
THERE IS A CRACK, A CRACK, IN EVERYTHING.
THAT’S HOW THE LIGHT GETS IN.
Public Side Private Side
Aging Infrastructure
Public Private
What is your future?
©Jacobs 202045
Develop an understanding of what impacts the sanitary sewer now and how sensitive these factors are to changes in the future Develop an understanding of the
impacts in the future to rainfall and groundwater Develop programs to become more
resilient to these changesCost Effectiveness Analysis
Qualities for a Resilient City that our sewer systems support
Reflective Resourceful Inclusive Integrated
Robust Redundant Flexible
Questions?