Infiltration and Inflow (I/I) Modeling Using Multiple Hydrograph Components

I/I Project Area

• 34 Local Component Agencies

• Most of Seattle is Combined System

• 75% of Peak Flows in King County System is I/I

• 95% of I/I is from Local Agencies

• 50% From Private Property

I/I Program Objectives

• I/I program is part of The Regional Wastewater Services Plan (RWSP)

• Determine the Amount of I/I Received by King County from Each Local Agency

• Identify Major I/I Areas Within Local Collection Systems

• Identify Specific Types of I/I Occurring Within These Areas

• Forecast the Amount of I/I that can be Removed Cost-Effectively

• Develop a Proactive Regional Strategy for I/I Removal and Control

Why Use Computer Modeling?

• Estimate Peak I/I Using Limited Measured

Data (amplifying the data)

• Distinguish Inflow from Infiltration

• Consider Design Flow Conditions

• Evaluate Multiple Scenarios and System

Options

I/I ReductionCost

RWSP SavingsEstimates

Based on OriginalStudy Assumptions

Revised Findingsper Pilot Project

Results

Based on Experience

Industry StandardsPilot Projects

AssessmentProtocols

Ranked Basins

Targets forRehabilitation

I/IModeling

Isolates Inflowvs. Infiltration

DeterminesSeverity of I/I

Technical Process Overview

Flow & RainfallMonitoring

Overview of Supporting Data

Measured Data for Model Development

• Rainfall

• Evapotranspiration

• Measured Flow Data

• Basin Information– Sewered Area

– Dry Weather Flow Pattern

Rain Data and CALAMAR

• Service area 25 x 45 miles• Rainfall Measurement with

Gauge-adjusted NEXRAD Data

• 5 Minute Data in 1 Km2 Pixels for specific storms

• 8 Calibration Zones• Gauge Data inserted

between storms

Flow Monitoring Effort

• 804 Meters in Simultaneous Operation

• 2 Wet Seasons of Flow Data

• 150 for Initial Model Calibration

• 75 Long Term Meters for Trends Analysis

• 95% of Agency Sewers in a Mini Basin

Model and Mini-Basins

#

"8

"8

"8

"8

"8

"8

"8"8

#S

"8

"8

"8

"8

"8

"8

"8

"8"8

#S

"8

• Model Basins• Calibrated to flows

measured during 2 wet seasons

• 1,000 acres• 100,000 linear feet

• Mini-Basins• 10 weeks of measured

flow• 150 acres• 22,000 linear feet

Model Basin Definition

• 150 Model Basins

• Isolate Flow Contributions

• Evaluate System Performance

MOUSE RDII Model Development and Calibration

Components of Flow

Rainfall Event

Inflow

Ground Water Infiltration

Flow Response

Total Flow

Rainfall Dependent Infiltration Dry Weather

Flow

RDII Components

RAINFALLPOTENTIAL EVAPORATION

MODEL PARAMETERS

RDII COMPONENTSEVAPORATIONRECHARGE

Hydrologic Model Schematic

Lower Zone Storage

Soil Storage

Ground Water Storage

Surface RunoffPr

ecip

itatio

n

Evap

otra

nspSnow

Storage

Infil

trat

ion

Gro

undW

ater

Rec

harg

e

Slow Response

Fast Response(Inflow)

Rainfall Dependant Infiltration

Slow Response

Cap

illar

y Fl

uxR

oot S

uctio

n

Prec

ip

ROOT INTRUSION INTO LATERAL

FOUNDATION DRAIN

SANITARYSEWER CRACKED/BROKEN PIPE

DETERIORATED MANHOLE

STORMSEWER

Rainfall Dependent Infiltration

BROKEN HOUSE LATERAL

Rainfall Derived

Infiltration

ROOF DRAIN CONNECTION

UNCAPPED CLEANOUT STORM DRAIN

CROSS-CONNECTION

FAULTY MANHOLE COVER

SANITARYSEWER

STORMSEWER

Inflow

SUMP PUMP

Inflow

• Plot Model Results

• Plot Measured Flow Data

• Plot Rainfall

• All Flow Components

• Adjust Parameters

Calibration Process

Statistical Comparison

• Scatter Plots• Overall Season Criteria

– Volume– Correlation Coefficient

• Event Criteria– Peak Flow– Volume

• Matching Select Event Peaks– Consistent Calibration Procedure– Pre-defined Objectives

• Calibration Flow Definition– Typical Problems with Measured Flow Data– Net Flow Challenges– Dry Weather Flow

Challenges and Resolutions

Ongoing Modeling Tasks

Apportion Inflow vs Infiltration to the Mini-basins

• Initial attempts based on Data Analysis

• Modified Calibration process

• Based on Model Basin Calibrations

Pilot Projects to Assess I/I Removal Costs

• 9 projects and Adjacent Control Basins• Variety of Construction Techniques • Constructed Summer and Fall 2003 • Pre and Post Monitoring and

Calibration• Establish I/I Removal Costs

Verification of Model Basin Calibration using a Hydraulic

System Model• Set Up KC System Model

• Apportion Model Basin Inflow to the system

• Run Models and Compare with Measured Flows in the System

Flow Frequency Estimates Using Long Term Simulation

• Calibrate Models to Local Rainfall

• Simulate Using Long Term Rainfall

• Get Flow Peaks from Long Term Simulation

• Apply Probability Analysis to the Peaks

• Rank Extracted Peaks

• Plot peaks vs. Log of return period

• Best fit curve of flows 1-yr and greater

• Select return period and flow

Probability AnalysisPeak Extraction

0

2

4

6

8

10

12

9/22/9

8

10/12

/98

11/1/

98

11/21

/98

12/11

/98

12/31

/98

1/20/9

9

2/9/99

Date/Time

Flow

(cfs

)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Rai

nfal

l (in

/hr)

0

5

10

15

20

25

0.1 1 10 100Return Period (years)

Flow

(cfs

)

Best fit curve

Plotted peaks

Estimate Future Flows

• Future Conditions by Decade– Available Population Forecasting– Convert Sewered Population to

Wastewater Flow– Estimate Design Flow for Each Decade

• Revise Model Basins for Each Decade– Long term simulation– Estimate 20-year flow

Modeling Objectives

• Estimate I/I Flows for Design Flow Conditions

• Identify Needed Wastewater System

• Predict System Response to I/I Rehabilitation Scenarios

• Establish Optimum I/I Rehabilitation vs. System Expansion

Current Status and Time Line for I/I Modeling Efforts

• Calibrated System Model by end of 2003

• Mini Basin Apportionment First Quarter 2004

• Facility Impacts First Quarter 2004

• Pilot Results Second Quarter 2004

Major Milestones for the I/I Program

• Alternative Options Report to the County Executive by the end of 2004

• Final Plan by the end of 2005

Lower Zone Storage

Soil Storage

Ground Water Storage

Snow Storage

Prec

ipita

tion

Evap

otra

nsp

Infil

trat

ion

Gro

undW

ater

Rec

harg

e

Fast Response(Inflow)

Surface Runoff

Slow Response

Rainfall Dependant Infiltration

Slow Response

Cap

illar

y Fl

uxR

oot S

uctio

n

Inflow

Prec

ip

Rain Gauge Data / CALAMAR

Building the I/I Plan

Flow Monitoring Data

Model Basin Flow Quantities

Hydrologic RDII Model Calibration

Hydraulic Model Calibration

20-year Design Flow Projections

Pilot Projects

Alternatives/Options

CE Analysis

RegionalI/I

Control Plan

Dry Weather Flow Model

Lower Zone Storage

Soil Storage

Ground Water Storage

Snow Storage

Prec

ipita

tion

Evap

otra

nsp

Infil

trat

ion

Gro

undW

ater

Rec

harg

e

Fast Response(Inflow)

Surface Runoff

Slow Response

Rainfall Dependant Infiltration

Slow Response

Cap

illar

y Fl

uxR

oot S

uctio

n

Slow Response

Rainfall Derived Infiltration

Slow Response

Dry Weather Flow Model

CALAMAR Output

System Background

• 34 Local Agencies• Two Regional

Treatment Plants• 17.5 Million LF of

Separated Sewer• Service within 1100

Mile2 Area• 1000 Feet of Relief

Expected Results

• Estimated Quantity of I/I

• Likely Rehabilitation Measures

• Estimated Cost of I/I Reduction

• Estimated Savings over RWSP– Capital Savings

– Operating Savings

Overall I/I Program

Regional I/I Control Program Plan• Goals for I/I Control Program• Target I/I Removal Levels• Measures to Meet Targets• Recommended Standards• Implementation Program

Policy• Alternative Options • Construction Contracting• Regulatory Proposal• Implementation• Schedule

Financial• Cost Sharing

Alternatives• Incentive-based Cost

Sharing Program• Surcharge Program

Technical• Inventory • Monitoring • Standards• Pilot Projects• Modeling