City of Morgan Hill Sewer System Master Plan 2017

City of Morgan Hill Sanitary Sewer Flow Monitoring and Inflow/Infiltration Study

Inflow

Infiltration

Combination I/I

30

0.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 Flow (MGD)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0.50

25

0.1

0.40

20

0.2

0.30

15

0.3

0.20

10 Flow (gpm)

0.4

Flow (MGD)

Rain (in/hr)

Rain (in/hr)

Rain (in/hr)

0.10

5

0.5

0.6 0.0 Rainfall ADWF Flow Realtime Flow I/I Flow Rate 0.1

0

0.00 0.25

10 12 14 16 18

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50

0.20

0.2

0.15

0.3

0 2 4 6 8

0.10

I/I (MGD)

Flow (gpm)

0.4

Flow (MGD)

Rain (in/hr)

Rain (in/hr)

Rain (in/hr)

0.05

0.5

0.6

0.00

22-Feb

23-Feb

17-Dec

18-Dec

19-Dec

20-Dec

4-Jun

5-Jun

Response Pattern Sharp Spike Short Duration

Response Pattern Gradual Increase Gradual Recession

Response Pattern Combination of Inflow and Infiltration

Figure 19. Inflow and Infiltration: Graphical Response Patterns

Infiltration Components Infiltration can be further subdivided into components as follows:

 Groundwater Infiltration: Groundwater infiltration depends on the depth of the groundwater table above the pipelines as well as the percentage of the system submerged. The variation of groundwater levels and subsequent groundwater infiltration rates is seasonal by nature. On a day-to-day basis, groundwater infiltration rates are relatively steady and will not fluctuate greatly.  Rainfall-Dependent Infiltration: This component occurs as a result of storm water and enters the sewer system through pipe defects, as with groundwater infiltration. The storm water first percolates directly into the soil and then migrates to an infiltration point. Typically, the time of concentration for rainfall-related infiltration may be 24 hours or longer, but this depends on the soil permeability and saturation levels.  Rainfall-Responsive Infiltration is storm water which enters the collection system indirectly through pipe defects, but normally in sewers constructed close to the ground surface such as private laterals. Rainfall-responsive infiltration is independent of the groundwater table and reaches defective sewers via the pipe trench in which the sewer is constructed, particularly if the pipe is placed in impermeable soil and bedded and backfilled with a granular material. In this case, the pipe trench serves as a conduit similar to a French drain, conveying storm drainage to defective joints and other openings in the system. This type of infiltration can have a quick response and graphically can look very similar to inflow.

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