Before H 2 Town of South Windsor, CT Evaluates Large Diameter Concrete Pipe

Transcription

1 Before H 2 Town of South Windsor, CT Evaluates Large Diameter Concrete Pipe September 11, 2012 NEWEA Collection Systems Conference Presented by: Laurie L. Perkins, PE Dennis A. Dievert, PE C. Frederick Shaw Michael J. Gantick, PE

2 What happened? How does H 2 S strike? How does PCCP fail? What do we do now? Alternatives evaluation Recommendations and current status Q & A

3 24-inch gravity pipe collapses $260,000 in repair costs Caused by H 2 S corrosion System Evaluation 3

4 4

5 PS, FM, and gravity system built Discharge MH - Clark St./Chapel Rd. 5.1 miles of 24-5

6 Clark Street PS Gravity 16 PCCP FM 6

7 H 2 S converted to sulfuric acid Stage 1 Stage 2 Under anaerobic conditions, sulfate in wastewater is converted to sulfides Turbulent conditions release sulfides in the form of H 2 S gas Force mains Siphons Gravity sewers (laminar flow) Discharge manholes Steep grade changes Drop manholes Release H 2 S gas Anaerobic bacteria produces H 2 S Stage 3 H 2 S gas is converted to sulfuric acid on surface; sulfuric acid attacks concrete and metal surfaces Severely Corroded Concrete South Windsor Sanitary Sewer Evaluation, Slide 7

8 Roughness Increased (SRI) 8

9 Aggregate Visible (SAV) 9

10 Aggregate Projecting (SAP) 10

11 Aggregate Missing (SAM) 11

12 Reinforcement Visible (SRV) 12

13 Reinforcement Projecting (SRP) 13

14 Reinforcement Corroded (SRC) 14

15 Missing Wall (SMW) 15

16 Manufacturing period Quality of wiring Installation methods Operating conditions Previous rupture or break Leaky joints Cracks in concrete Hydrogen sulfide presence High chlorides in soils Poor bedding Surge/water hammer Fluctuating groundwater levels 16

17 Risk assessment failure of pre-stressed concrete coated pipe Internal inspection Non-destructive, live-flow inspection External testing Soil resistivity testing Non-invasive, direct assessment of pipe Additional investigations of gravity system 17

18 Five Questions 1. Was pipe constructed prior to 1964 or after 1992? 2. Is manufacturer still in business on site where pipe was made? 3. Was pipe constructed with 6 gauge or larger wire? 4. Was inspection of the pipe done by Owner or Engineer at time of installation? 5. Is surge unlikely on the pipeline? 18

19 - Negative total recommends further assessment (-3) Discuss with Town methods for further evaluation 19

20 Internal Pipe Inspection SmartBall Pure Technologies acoustical based technology non-destructive done in live flow detects leaks (0.15 gal/hr) & gas pockets no acoustical parameters resembled leaks or pockets of gas

21 South Windsor Sanitary Sewer Evaluation, Slide 21

22 Leak gpm Leak - 5 gpm Leak - 30 gpm South Windsor Sanitary Sewer Evaluation, Slide 22

23 External Testing Soils Resistivity Testing Every 500-feet, 12 locations Low resistivity = high corrosivity 2 lowest readings, direct pipe testing 3 rd location within 80-feet of discharge manhole

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25 External Testing Non-Invasive Pipe Testing Excavate (4-5 hrs.) Grid off in 1-foot squares Conduct testing and collect samples (1-2 hrs.) ph, mortar sounding/hardness & thickness Backfill and restore pavement ( hrs.)

26 External Testing (Cont.) Dig Site 2 Dig Site 2 Delamination

27 Additional Investigations CCTV of last 80-feet Non-destructive testing of pipe interior Manhole and pipe inspections d/s

28 Slide 28

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30 Evaluation of Bypass Pumping Review of current pump station EOP Pump station bypass possible Force main bypass not possible at peak flows Alternatives to bypass force main Install temporary line Install permanent parallel line

31 Evaluation of Alternatives New pipe, same trench Bypass required No permanent force main bypass New pipe, parallel trench No bypass required Permanent force main bypass available Slip-line existing pipe Bypass required No permanent force main bypass Hydraulic limitations

32 Recommendations & Implementation Update emergency bypass plan Develop 15-year CIP $2.5 to $3.9 Million 3 Phases Phase I Immediate Replace last 80 lf of force main (gravity) Gravity pipe and manhole replacement Phase II Within 10 years Install new pipe in parallel trench Maintain and CCTV existing force main Phase III Within 15 years if required Line existing force main

33 Phase I under construction Slide 33

34 Laurie L. Perkins, PE