1. Separating Inflow Reduction and Infiltration Removal
Frederick Bloetscher, PhD, PE
Florida Atlantic University

2. Outline Sewer Design Concepts What is Infiltration/Inflow
Inflow Solutions
Effectiveness

3. Design Considerations
Gravity sewers flow downhill
Designed to flow ½ full
Designed for maximum hourly flow (MHF)
Industrial or domestic
Infiltration/Inflow increases the flow volume
Location of groundwater table relevant

4. Sanitary Pipe Materials
Small lines:
PVC
Vitrified clay
Asbestos cement
Larger lines:
Ductile iron
Concrete

5. Types of Manholes?
Doghouse Precast
Drop
Brick

6. Age and Water = Infiltration and inflow

7. Sewer Higher than Water Sales?

8. Flows Get Worse with Time

10. Infiltration/Inflow (I/I)
Groundwater that enters the sewer through defective pipes, joints, connections, & manholes
Inflow
Stormwater discharged directly into sewers from roof drains and stormwater runoff
Both overloads collection systems & reduces treatment efficiency
Function of age
I/I = – 0.9 m3/d∙mm∙km (typically)

11. System Hydrograph RAINFALL TOTAL PLANT FLOW (INCHES) (MGD) 16 12 8 4
OCTOBER, 1991
NOVEMBER, 1991 80 60
TOTAL PLANT FLOW
(MGD)
Dry weather total flow at WWTP 37.7 MGD 100%
Dry weather infiltration 15.2 MGD 40%
Wastewater flow 22.5 MGD 60%
Excessive I/I increases the amount of flow to be treated at Hollywood's Regional Wastewater Treatment Plant 40 20
OCTOBER, 1991
NOVEMBER, 1991

12. Inflow= Rain Flow Data vs. Rainfall Rainfall During rainevent
INTRODUCTION

13. I/I Allowance (EPA) From Table 3 EPA Infiltration Allowance
From Table 3 EPA Infiltration Allowance
Allowance Range (gpd/in-mile)
Sewage Footage (ft)
2,000-3,000
> 100,000
3,000-5,000
50, ,000
5,000-8,000
1,000-50,000

14. Sewer Flows v. Rainfall We can see …..INFLOW!!!

15. Inflow =>Sanitary Sewer Overflow
STORMWATER
CONNECTIONS
ALLOW INFLOW
SANITARY SEWERS
OVERFLOW TO
WATERWAYS
WATERWAY
FOOTING
DRAIN
SANITARY
SEWER
STORMWATER
SUMP
PUMP
HOUSE
(LATERAL)
DOWN-
SPOUT
STREET
INLET
INFILTRATION
BASEMENT
BACKUP

16. Sanitary Sewer Overflow

17. Inflow Sewer flow peaks during rain events.
The size of the storm event matters. A larger storm event will create more inflow.
During storm events, wastewater flow is linearly related to rainfall.
Based on an analysis of flow vs. rainfall graphs from pre and post construction activities inflow reduction will be calculated.

18. Inflow

19. Inflow

20. Inflow
INFLOW

21. BASEFLOW + INFILTRATION
Inflow
INFLOW
BASEFLOW + INFILTRATION

22. Inflow
INFLOW

23. Inspect Manholes

24. Protocol – Seal Manhole Frame/Cone Connection
Infiltration
Rain or Shine
Water Table
Protocol – Seal Manhole Frame/Cone Connection
Inflow
Cover / Frame
Frame / Chimney

25. Sealing the Manholes Plus Correct Dish!!!25

26. Smoke the System - Finding it?

27. LDL Plugs for Cleanouts

28. Midnight Run flow. 2 inch wide flow, 1/4 in deep at 2 ft/s = 0.77917
gpm
flow. 3 inch wide flow, 1/2 in deep at 2 ft/s =
2.3375
flow. 4 inch wide flow, .75 in deep at 2 ft/s =
4.675
flow. 6 inch wide flow, 1.25 in deep at 2 ft/s =
28.05
flow. 8 inch wide flow, 4 in deep at 2 ft/s =

29. Report MH 1-11 MH 1-12 3 2 MH 1-15 MH 1-3 4 MH 1-30 MH 1-40 0.5
2.5
MH 1-31
MH 1-32
0.35
MH 1-4
MH 1-13 5 30
upstream 8
150
LS FM?
MH 1-42 35
MH 1-43
MH 1-5
MH 1-6 6 40
MH 1-7
MH 161
lateral

30. Map = note only 20% of pipe will be investigated – avoided cost

31. LS 52 – Cooper City

32. LS 53 Cooper City

33. LS 54 Cooper City

34. Dania – System

35. Savings for Inflow Removal
  Community
% Change (Pre Vs. Post)
Dania Beach (2006 vs. 2009)
-31.9%
Cooper City (2011 vs. 2013)
-62.8%

36. Next Phase
Once Stormwater inflow is out….
Pipelines…

37. Groundwater

38. Groundwater vs Base+Infiltration

39. Base + Infiltration increases with time

40. Infiltration
After removing inflow, the remaining flow is in terms of baseflow + infiltration.
Assuming the any increases in baseflow are neglieable, any decreases or increases in flow are related to fluctuations in infiltration.
Based on an analysis of baseflow + infiltration vs. groundwater elevations graphs from pre and post construction activities infiltration reduction will be calculated.
Separate baseflow + infiltration based on water use , dry days and day of the week

41. Infiltration

42. Infiltration

43. Infiltration

44. Infiltration

45. Infiltration
A comparison of slopes developed the following findings:
2006 Slope
2009 Slope
Total % Change
% Change/Year
0.4147x
0.5558x
25.4%
8.5%
In total Dania Beach experienced a 25.4% increase in infiltration between 2006 and 2009.
Based on the findings above it is assumed that without any improvements utilities can expect approximately an 8.5% increase in infiltration per year.

46. Infiltration
Initial remediation activities of the wastewater collection system were initiated in 2008.
Initial activities included non-construction activities such as smoke testing and rehabilitation activities such as sealing manhole covers and adding manhole dishes to existing manholes. These initial activities were completed to reduce inflow into the system.
In order to compare inflow following pre and post construction, flow values between and 2009 were compared.
2006 flow values represent pre-construction flows and 2009 flow values represent post- construction flows.

47. Infiltration Correction
Work to reduce infiltration within the sewer collection system was initiated in 2013.
Activities included CCTV analysis of the system and lining pipes in areas where broken or cracked pipes were observed. These initial activities were completed to reduce infiltration into the system.
In order to compare infiltration following pre and post-construction, flow values between 2012 and were compared.
2012 flow values represent pre-construction flows and 2013 flow values represent post-construction flows.

48. Broken Pipe = Infiltration…
Broken Pipe

49. Leaky Pipe

50. Pipeline Leak Repair

51. Infiltration Calculations
A comparison of slopes developed the following findings:
2012 Slope
2013 Slope
Total % Change
% Change/Year
0.4697x
0.4604x
-2.0%
-10.5%
In total Dania Beach experienced a 2.0% decrease in infiltration between 2012 and 2013.
Based on the findings above only a small drop in infiltration was experienced..

52. RESULTS
In order to accurately estimate the percent change we must also take into account the amount of inflow and infiltration which would have increased if no work would have been completed.
Baseline increase in inflow was calculated to be 14.1% per year.
Baseline increase in infiltration was calculated to be 8.5% per year.
Percent Change
Total Net Change
Inflow
-54.8%
-68.9%
Infiltration
-2.0%
-10.5%

53. Results
A significant decrease in inflow between the pre and post- construction flows was experienced. The construction activities resulted in a total net inflow decrease of 68.9%.
The pre and post construction activities resulted in a significantly less percent decrease in infiltration. Two things to note however, are:
The percent decrease in infiltration still accounts for a larger total flow decrease than the inflow decrease because infiltration is such a larger portion of the yearly total flow.
The infiltration percent decrease was marginalized due to the fact that baseflow was left in the calculations. Without an adequate way exclude to baseflow, flow measurements were left in baseflow + infiltration. Leaving the baseflow in the analysis does not affect the amount of the flow reduced from the infiltration reduction work but it would decrease the percent change. Even though the percent change is minimalized due to the additional flow within the calculation, it will not affect the cost analysis, which will be based on the amount of flow reduced and not the percent change.

54. Cost Analysis
The inflow calculations generated previously, based on the rainfall and flow, were used to calculate the cost savings from the inflow construction activities.
Using the equation created to show the relationship between the 2006 flow and rainfall and the 2009 rainfall values, the amount of inflow that would have been generated if no construction activities were completed was calculate.
14.1% was added to the 2006 inflow values based on the 2009 rainfall values to account for the amount of increase in the system which would have occurred if no inflow reduction activities would have occurred.

55. Cost Analysis
The baseflow + infiltration calculations generated previously, based on the groundwater elevation and flow minus inflow, were used to calculate the cost savings from the infiltration construction activities.
Using the equation created to show the relationship between the 2012 flow minus inflow and groundwater elevation and the 2013 groundwater elevation values, I was able to calculate the amount of infiltration that would have been generated if no construction activities were completed.
8.5% was added to the 2012 baseflow + infiltration values based on the 2013 groundwater elevation values to account for the amount of increase in the system which would have occurred if no infiltration reduction activities would have occurred.

56. Sewage Reduced (gallons)
Cost Analysis
Based on information provided by the city of Hollywood, Dania Beach currently pays $2.98/1,000 gallons.
Assume 850 Manholes, 60 Miles of pipe
Assume 800 MH
Inflow
Infiltration
Sewage Reduced (gallons)
18,348,011
72,706,566
Amount Saved
($55,044)
($216,665)
Cost
$472,000
$772,000
Cost/1000 gallon
$22.72
$7.64
BUT…
Avoided Cost
($1,200,000) $0
($42.68)

57. Questions