sanitary sewer system evaluation and planning for resiliency...leonard cohen - there is a crack, a...

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





0

10

20

30

40

50

60

70

80

90

Flow

(MG

D)





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

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: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)


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?

sanitary sewer system evaluation and planning for resiliency...leonard cohen - there is a crack, a...

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