- SEWER REHABILITATION -A TEN-STEP STRATEGIC PLAN

GEORGE KURZ, P.E., DEE615-252-4441 GEKurz@bwsc.net

* A significant portion of this work was conducted with CTE-AECOM as part of the Nashville Overflow Abatement Program 1991-2005

SEMINAR OBJECTIVE

Teach a proven, successful strategy.

SUCCESSFUL REHAB FACTORS

• DEFINE GOALS

• EXTENSIVE FLOW MONITORING & STANDARD PROCEDURES

• LATERAL REHABILITATION

• “TARGETING” – STOP WATER MIGRATION

• ACCOUNTABILITY – VERIFY DESIRED RESULTS

TOTAL SYSTEM APPROACH- Nashville Policy -

GOAL: “CONTAINMENT” FOR FLOWS FROM 5- YEAR, 24-HOUR RAINFALL

POLICY:

ALL SERVICE LATERALS CONNECTED TO THE REHABILITATED PIPES WILL BE RENEWED TO THE EASEMENT LINE OR THE PROPERTY LINE

ALL MANHOLES CONNECTED TO REHABILITATED PIPES WILL BE RENEWED

Ten steps

1. Identify Goals

2. Select Target Area

3. Quantify Problem

4. Locate Defects

5. Select Pipe Segments

6. Estimate Cost-Benefit

7. Design & Install

8. Verify Performance

9. Follow-up Flow Monitoring

10. Calculate O & M Savings

1 - IDENTIFY COMMUNITY GOALS

• PERIOD OF TIME: 2 YEARS ?, 5 YEARS ?

• RELATE TIME TO RAINFALL EVENT RETURN INTERVAL

• NO OVERFLOWS LEGALLY SANCTIONED

“ELIMINATE OVERFLOWS AND BASEMENT BACKUPS”

2 - SELECT TARGET AREA

• FLOW MONITORING NETWORK (~100,000 L.F.)

• CALCULATE OBSERVED & POTENTIAL I/I

• HYDRAULIC MODEL

• IDENTIFY CAPACITY PROBLEMS

• PRIORITIZE TRIBUTARY AREAS

DETECT CAPACITY PROBLEMS(KIRBY 3 - MANNINGS SCATTERPLOT)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Depth (inches)

Ve

loci

ty (

ft/s

ec)

Mannings VelMetered Velvariable n adjustedhi-Flow

HC=5.4, full pipe = 4.766 mgd

CAPACITY LOST TO

HINDERED FLOW

3 - QUANTIFY PROBLEM CONDITIONS

• INTENSIVE MONITORING IN TOP PRIORITY TRIBUTARY AREAS (8,000 - 15,000 L.F.)

• OBSERVED AND POTENTIAL I/I

• ADDITIONAL CAPACITY PROBLEMS

WEST PARK PUMPING STATION - 32 mgd

1.6mgd Clifton 1

2.0 mgd Clifton 3

11 mgd West End

2.1 mgd White Br

1.5 mgd Sugartree 1

15.3 mgd Brentwood

Sugartree 2 - 12.9mgd

Murphy Rd.- 4.2mgd

Clifton 4 - 1.3mgd

Clifton 2 - 1.6mgd

SUM OF TRIBUTARIES=53.5 mgdWEST PARK METER=32 mgdPOTENTIAL I/I = 21.5mgd

I/I REMOVAL EFFECTIVENESS- ACCOUNT FOR POTENTIAL I/I !!

0

0.5

1

1.5

2

2.5

0 1 2 3 4 5RAINFALL (inches-24 hours)

I/I (

mg

d)

I/I AFTER REHAB

PIPE CAPACITY

PROJECTED METERREADING

POTENTIAL I/I

RESTRICTED FLOW

Example: 52% I/I REMOVAL

“POTENTIAL” I/I

• I/I Which Cannot Enter the Sewer Because the Pipe is Already Overloaded!

• Overall I/I Removal Goals

• Monitor Depth & Velocity

• Extrapolated

DATA INTERPRETATION

• 24-hour rainfall more reliable than peak hour rain for predicting peak design I/I

• AMC – Antecedent Moisture Condition is critical for selecting valid rainfall events

• HINDERED FLOW - POTENTIAL I/I There are ways to correct for this, however the analyst must be aware of this condition

• Underestimating the peak flow can result in the inadequate design of new facilities

• Need to standardize criteria

COMPARISON OF RESULTS

Peak-hour flow

(24-hr rain

vs. Peak-hr rain)

REGRESSION ANALYSIS PEAK I/I vs. PEAK HOUR RAINFALL

0

50

100

150

200

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

24 HOUR RAINFALL (inches)

PEAK

IN

FILT

RATI

ON/IN

FLOW

RA

TE (m

gd)

PEAK HOUR RAIN I/I PEAK HOUR BEST FIT LINE REMAINING CAP.(I/I)

95% CONFIDENCE 95% CONFIDENCE

MI-09 YEAR 2004-05

REGRESSION ANALYSIS PEAK I/I vs 24-HOUR RAINFALL

020406080

100120140

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5

24 HOUR RAINFALL (inches)

PEAK

IN

FILT

RATI

ON/I

NFLO

W R

ATE

(mgd

)

PEAK HOUR RAIN I/I PEAK HOUR BEST FIT LINE REMAINING CAP.(I/I)

95% CONFIDENCE 95% CONFIDENCE

MI-09 YEAR 2004-05

Which type rainfall pattern puts the most stress

on the system – for a standard return interval,

design storm?

Summer ?

Or Winter ?

Type II Rainfall* – Characterized by short-term,

high intensity thunderstorms and also by

long-duration frontal storms.

* USDA-SCS 1986

TYPICAL RAINFALL

NASHVILLE 5-Year, 24-Hour & 3-Hour Design Rainfall

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 5 10 15 20 25Hours

De

pth

(in

ch

es

)

24-Hour rain 3-Hour Rain

5-YEAR, 3-HOUR Peak Rain =1.97"

5-YEAR, 24-HOUR Peak Rain =1.26"

Design Storm Peak: 2-Yr, 24-Hr vs. 3-Hr

PEAK I/I vs 3-HOUR RAINFALL

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0.0 0.5 1.0 1.5 2.0 2.524 HOUR RAINFALL (inches)

PE

AK

INFI

LTR

ATI

ON

/INFL

OW

R

ATE

(mgd

)

PEAK HOUR RAIN I/I PEAK HOUR BEST FIT LINE REMAINING CAP.(I/I)95% CONFIDENCE 95% CONFIDENCE

CMC02 2003 3-HOUR STORMS

r= 0.47

95% Conf.= 87%

PEAK I/I vs 24-HOUR RAINFALL

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

0.00 0.40 0.80 1.20 1.60 2.00 2.40 2.80 3.20 3.6024 HOUR RAINFALL (inches)

PE

AK

IN

FIL

TR

AT

ION

/IN

FLO

W

RA

TE

(m

gd)

PEAK HOUR RAIN I/I PEAK HOUR BEST FIT LINE REMAINING CAP.(I/I)95% CONFIDENCE 95% CONFIDENCE

CMC02 - YEAR 2003

r= 0.91 95% Conf. = 16%

Peak hour I/I from 2-Yr, 24-Hr Storm is 3.89 mgd with good

level of confidence

Peak hour I/I from 2-Yr, 3-Hr Storm is 2.35 mgd with poor

level of confidence

4 - LOCATE & IDENTIFY DEFECTS

• TELEVISE TARGET AREA SYSTEM (MAY BE CONCURRENT WITH MONITORING)

• CATEGORIZE DEFECTS WITH RESPECT TO I/I POTENTIAL

4 - LOCATE & IDENTIFY DEFECTS (CONT.)

• “INVISIBLE” DEFECTS - ELECTRIC FIELD LEAK DETECTION, SEGMENTAL ISOLATION

• GROSS INFLOW (ROOF DRAINS, ETC.)

5 - SELECT SEGMENTS FOR REHABILITATION

• CATEGORIZE & COLOR CODE LINES– 3 OR MORE MAJOR DEFECTS– 1-2 MAJOR DEFECTS– NO MAJOR DEFECTS

• “3 OR MORE” - RENEW !

• CHECK ADJACENT SEGMENTS

• RENEWAL “INTENSITY” - RANGE OF 15-20% FIRST ROUND

CONNECT THE DOTS> 3 DEFECTS

< 3 DEFECTS

0 DEFECTS

REHABILITATE

?

?

?

?

25 % intensity25 % intensity

METER

HALT MIGRATION !INVISIBLE DEFECT "DRY" DEFECT

POTENTIAL LEAK

LEAKLEAK

LINING OR REPAIR

"NEW" LEAKS REVEALED FOLLOWING TRADITIONAL REPAIRS

SEWER REHAB STRATEGY:

6 - ESTIMATE COST-BENEFIT

• COMPARE RENEWAL COSTS TO: O&M COSTS ($1.73

- $1.87/ 1,000 GAL)

• AT LEAST 50% I/I REMOVAL

• COSTS:– LINING (8-10” CIPP) ~ $43 / LF– LATERALS ~ $2,250 ea. (1/ 200 LF)– MANHOLES ~ $1,000 -1,300 ea. (1/200 LF)– ENGINEERING ~ 12% - 15% OF TOTAL

(GROSS= ~ $132/ft rehab)

7 - DESIGN & INSTALL REHAB

• HALT MIGRATION FROM OUTSIDE PIPE

• HALT MIGRATION (“TRACKING”) INSIDE PIPE

• PROVIDE SEAL AT MANHOLE JUNCTION

• RENEW SERVICE LATERALS (over 10,000 rehabilitated in Nashville)

LATERAL REHABILITATION EFFECTIVENESS

DOWNINGTON, PA -area 538 laterals in 1,513’ CIP - 100% treated

97% reduction - 22 mg annually

STEGE SAN. DIST, CA - subarea N111 laterals in 13,400’ Slip-PE & MH - 100%

86% reduction

NASHVILLE, TN - Oak Valley63 laterals in 4,400’ CIP - 41% treated

77% reduction (20%-laterals) - 67 mg annually

8 - PERFORMANCE TESTING

• AIR-TEST SEWER SERVICE CONNECTION !

– MOST VULNERABLE PART

– NOT ACCEPTED UNTIL PERFORMANCE

VERIFIED

9 - FOLLOW-UP FLOW MONITORING

• QUANTIFY I/I REDUCTION

• STANDARDIZED I/I ANALYSIS

• TV DURING WET WEATHER

• RERUN HYDRAULIC MODEL

• DETERMINE IF DESIGN GOALS MET !

5-YEAR, 24-HOUR I/I REDUCTION (CU-01 1999-2002)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

0 0.5 1 1.5 2 2.5 3 3.5 4 4.524-hour rainfall (in.)

24-h

ou

r I/I

(m

g)

I/I Before Rehab I/I After Rehab Linear (I/I Capacity)

AFTER REHAB

BEFORE REHAB I/I REDUCTION

CAPACITY

STANDARDIZED I/I ANALYSIS

• DEFINES LEVEL OF CONFIDENCE FOR PROJECTED I/I

• USES QA/QC CONTROLS THAT ARE SIMILAR TO “STANDARD METHODS” (nationally recognized)

Example: Typical Nashville Rainfall Event Analysis

7 day dry flow

ADF= 0.3 mg

24-hr I/I=0.37 mg

Peak-hr I/I=0.738 mgd

2.11” Rainfall

0.000

0.200

0.400

0.600

0.800

1.000

1.200

1.400

1.600

1.800

2.000

05:45 07:45 09:45 11:45 13:45 15:45 17:45 19:45 21:45 23:45 01:00 03:00 05:00

TIME (HOURS)

FL

OW

(M

GD

)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

RA

INFA

LL

(IN

CH

ES

)

Total Flow Infiltration/Inf low Base Flow Rain

Characteristic Base Flow Curve

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

12:0

0 AM

2:00

AM

4:00

AM

6:00

AM

8:00

AM

10:0

0 AM

12:0

0 PM

2:00

PM

4:00

PM

6:00

PM

8:00

PM

10:0

0 PM

12:0

0 AM

Hour

Ave

rag

e F

low

, MG

D

WL02 2-01

(adjusted to match beginning of storm flow @ 0.99 mg)

DRY WEATHER ADF

WET WEATHER HYDROGRAPH

NASHVILLE REHABILITATION EFFECTIVENESS

ANNUAL I/I REDUCTION FROM REHABILITATION

0

100

200

300

400

500

600

700

800

0 10,000 20,000 30,000 40,000 50,000 60,000

REHABILITATION LENGTH (FT)

AN

NU

AL

I/I

RE

DU

CT

ION

(M

G)

ANNUAL I/I REDUCTION (MG) Linear (ANNUAL I/I REDUCTION (MG))

EFFECTIVENESS(a “rule of thumb”)

15-20%

REHABILITATION

INTENSITY(including MH & laterals,

& in deteriorated areas)

~ 8-10 MILLION

GALLONS ANNUALLY

per 1,000 ft.

LINING or

REPLACEMENT

10 - CALCULATE O&M SAVINGS

• POSSIBLE 7-11 YEAR PAYBACK (construction)

• PROVIDES DATA FOR FUTURE PROGRAM PLANNING

• ACCOUNTABILITY TO COMMUNITY

PROGRAM PAYBACK COMPARED TO O&M CHARGED

0

5

10

15

20

25

30

35

$0.80 $1.00 $1.20 $1.40 $1.60 $1.80 $2.00

O & M ($ per 1,000 gal)

Year

s to

Pay

back

Payback years

8 Mill Gal Removed per Year/1,000 ft LiningTotal Program costs ~ $ 700,000/ mile

20% intensity

SUCCESSFUL REHAB FACTORS

• EXTENSIVE FLOW MONITORING

• LATERAL RENEWAL TO EASEMENT

• “TARGETING” - LINING SELECTED BY OBSERVED DEFECTS, AGE, PROXIMITY, MIGRATION POTENTIAL, SURFACE WATER

• PERFORMANCE (AIR) TEST LINE & LATERAL

STRATEGIC GOALS MET

• I/I REDUCTION

• SSO REDUCTION

• STREAM IMPROVEMENT

NASHVILLE MEASURED RESULTS

3.6 billion gallons I/I eliminated annually

49.6% Annual I/I eliminated

53% 24-hour, 5-year I/I reduction

52.2% Peak-hour, 5-year I/I reduction

For the 27 areas (94 miles) analyzed so far: