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- SEWER REHABILITATION -A TEN-STEP STRATEGIC PLAN
GEORGE KURZ, P.E., DEE615-252-4441 [email protected]
* 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: