Valley Creek Trunk Sewer (VCTS) Evaluation Status. Tredyffrin Township Board of Supervisors Meeting

Transcription

1 Valley Creek Trunk Sewer (VCTS) Evaluation Status Tredyffrin Township Board of Supervisors Meeting June 16, 2014

2 Copyright 2011 by CH2M HILL, Inc. Company Confidential 2 2 Aerial View of VCTS Traverses VFNHP From Wilson Road PS to VFSA WWTP at Pawlings Road. Breaks 2 & 3 Two crossings of the Schuylkill River Breaks 1. 3/17/ /5/ /18/2014 Break 1

3 Percentage of VCTS flow by Community Valley Forge Sewer Authority, 0.3 Tredyffrin, 19.2 Willistown, 20.8 Easttown, 20.0 East Whiteland, 33.2 Other Key Stakeholders PA-DEP Valley Forge National Historic Park Valley Forge Sewer Authority Valley Forge Coalition Buchart Horn Gannett Fleming Malvern, 6.5 Percentage of VFSA Flow based on 2013 Average Daily Flow Copyright 2011 by CH2M HILL, Inc. Company Confidential 3

4 VCTS Evaluation Goals Assess Wilson Road Pump Station (WRPS) Recommendations for ensuring safe operation Reduce potential impacts of WRPS on pipeline failure risk Assess the risk of failure of the VCTS Force Main Determine the potential causes of pipeline breaks Determine cost and risks for short and long-term alternatives including Rehabilitation / Reconstruction approaches and timing Demonstrate meaningful forward progress Respect the National Park and Valley Creek Exceptional Value Stream Recognize the VCTS has protected the park and stream 24/7 for 36 years Minimize regulatory risk to Township and the VCTS partners Copyright 2011 by CH2M HILL, Inc. Company Confidential 4 4

5 Copyright 2011 by CH2M HILL, Inc. Company Confidential 5 5 Timeline of Events Show timeline graphic here Operational Improvements to WRPS Reduction in Pump On-Off Cycles Maximize Wet-Well Storage Use Pressure Monitoring Transient Modeling

6 Valley Creek Trunk Sewer Construction Complete in August, 1979 ~36 yrs old Pre-stressed Concrete Cylinder Pipe (PCCP) Mortar provides corrosion protection for wires and cylinder, as a low ph barrier PCCP was substituted for Conventional Cast Iron Pipe in the VCTS to gain grant funds Operating Pressure Rating Operating pressure = 60 psi Maximum pressure = 100 psi Operating pressure range measured between April and May 2014 was < psi Copyright 2011 by CH2M HILL, Inc. Company Confidential 6 6

7 Sequence of PCCP Deterioration Overpressure Coating Cracks Wires Exposed to Water Wires Corrode and Break Stresses are Transferred to the Cylinder Core Concrete Cracks Cylinder is Exposed to Water Cylinder Corrodes and Fails Copyright 2011 by CH2M HILL, Inc. Company Confidential 7 7

8 Copyright 2011 by CH2M HILL, Inc. Company Confidential 8 8 Pictures of Breaks Break 1 Typical Failure Location near air-release valve, wires intact Break 2 & 3 Failure Cascade - micro cracking in mortar, corrosion, wire loss (photo break 2)

9 Stray Voltage Trackdown Breaks #2 & 3 - Rt 252 & Rt 23 Inspection of the new repair coupling installed during Break #2 revealed pitting Stray voltage observed during the March 2014 break (Tool Sparking) Voltage can cause corrosion in metal pipes (e.g. like the sacrificial anode in a hot water heater) PECO gas main was identified vertically above VCTS pipe PECO turned off the rectifier (i.e. the voltage source) and initiated a study Photo - Steel repair coupling from Feb 2014 break Copyright 2011 by CH2M HILL, Inc. Company Confidential 9

10 Summary of Risk Reduction Measures to Date Operations Pressure data shows operating pressures are within design pressure WRPS operations modified to reduce pump on-off cycles after Break #3 in March 2014 Stray Voltage Trackdown is ongoing with PECO 5/20 Meeting with PECO, PA DEP and Township staff PECO to provide information on their pipe and voltage protection locations Voltage Rectifier was turned off Emergency Response Preparedness Materials stockpiled to quickly repair multiple sections of force main Revisions to Emergency response procedures are being evaluated Initiated Planning for Future Replacement Copyright 2011 by CH2M HILL, Inc. Company Confidential 10 10

11 Next Steps Transient Modeling will identify any risks due to pipe surges created by Electrical Outages WRPS Operations Soil Testing (National Park Service Permit) Comprehensive Assessment of WRPS Laboratory testing of break samples Planning for Condition Assessment of VCTS segments Alternative Evaluation (in scoping) Copyright 2011 by CH2M HILL, Inc. Company Confidential 11 11