1 / 53

Improving Service to Customers by Decommissioning an Elevated Water Storage Tank

Improving Service to Customers by Decommissioning an Elevated Water Storage Tank. Jon C. Ford P.E. – Seattle Public Utilities AWWA-PNWS Conference April 30, 2008. Overview. Seattle Water System Description Maple Leaf 530 Pressure Zone Improvements Analysis Recommended Improvement.

piera
Download Presentation

Improving Service to Customers by Decommissioning an Elevated Water Storage Tank

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Improving Service to Customers by Decommissioning an Elevated Water Storage Tank Jon C. Ford P.E. – Seattle Public Utilities AWWA-PNWS Conference April 30, 2008

  2. Overview • Seattle Water System Description • Maple Leaf 530 Pressure Zone • Improvements Analysis • Recommended Improvement

  3. Seattle Regional Water System

  4. Seattle Public Utilities Water System • 1.3 million direct service and wholesale customers in King and Snohomish County • 188,000 retail/100 wholesale service connections • Two surface water sources, one (emergency) groundwater source • 1,600 mi. distribution/159 mi. transmission mains • 15 reservoirs, 7 elevated tanks, 11 standpipes

  5. Low Pressures in Seattle’s Water System • Approximately 45 services have Peak Hourly Demand (PHD) pressure less than 20 psi (<0.1%) • Approximately 1,500 services have PHD pressure between 20 and 30 psi (0.8%)

  6. Locations of Low Pressures

  7. Maple Leaf 530 PZ PHD Pressure

  8. Base Case PHD Pressure – Low Pressure Area

  9. Low Pressures Due to Maple Leaf Tank Elevation

  10. Maple Leaf 530 PZ MDD Fire Flow

  11. Base Case MDD Fire Flow – Low Pressure Area

  12. Project Objectives • Increase low pressures to at least 20 psi • Determine most cost-effective option of raising pressures above 20 psi • Determine future of Maple Leaf Tank as water storage facility

  13. Improvement Alternatives • Alternative 1 – Upgrade existing tank • Alternative 2 – New higher tank • Alternative 3 – Decommission tank • Alternative 4 – Decommission tank plus booster pump station

  14. Comparison of Alternatives

  15. Comparison of Alternatives

  16. Alternatives – PHD Pressure Results

  17. Alternatives – MDD Fire Flow Results

  18. Alternatives Comparison • Net Present Value • Benefits • Increased Pressure • Increased Fire Flow • Decreased Risk • Costs • Capital Costs • O&M Costs

  19. Storage Analysis

  20. Benefits Components

  21. Supply Sources to Maple Leaf 530 Pressure Zone

  22. Benefits Comparison(5% Discount Rate, 100-yr return)

  23. Benefits of Increased Pressure Value ($/ERU/Yr) is area under curve $151/ERU/Yr

  24. Benefits of Increased Pressure (5% Discount Rate, 100-yr return) Alt 3 Alt 2 Alt 4 Alt 1

  25. Planning-Level Fire Flow Requirements(Available Flow at 20 psi Residual Pressure) • Single Family: 1,000 gpm • Multi-Family: 2,000 gpm • Schools: 2,250 gpm • Commercial: 4,000 gpm • Downtown/Industrial/Major Institutions: 8,000 gpm

  26. Fire Flow Benefits Calculation • Reduced risk of deaths and injuries and property damage

  27. Benefits of Increased Fire Flow (5% Discount Rate, 100-yr return) Alt 2 Alt 3 Alt 3 Alt 2 Alt 4 Alt 4 Alt 1 Alt 1

  28. Storage Analysis

  29. Maple Leaf 530 Pressure Zone Storage Analysis • Operational & Equalizing Storage – not needed • Fire Suppression Storage – provided in Lake Forest Park Reservoir • Standby Storage – need reduced by source availability: • Roosevelt Way RCBV – 6,000 gpm • Roosevelt Way PS – 3,000 gpm • View Ridge High Service Pump – 2,000 gpm • Roosevelt Turbine – 800 gpm

  30. Standby Storage Benefit Calculation • Value = Risk Cost = Probability of Service Outage x Consequences of Service Outage • Probability: 0.02/yr (outage event exceeding MDD) • Consequence: $280,000 per episode • Value = 0.02/yr x $280,000 = $5600/yr • PV = $100,000

  31. Storage and Supply Availability to Maple Leaf 530 Pressure Zone • Lake Forest Park Reservoir provides storage • Gravity feed through Roosevelt Way RCBV/PRV • Capacity > PHD • Storage volume (60 MG) • Backup sources available • Roosevelt Way Pump Station • View Ridge High Service Pump • Roosevelt Turbine

  32. Costs Comparison(5% Discount Rate, 100-yr return)

  33. Alternative 1 NPV = -$2,582,900 Alternative 2 NPV = -$1,774,400 Alternative 3 NPV = $4,359,200 Alternative 4 NPV = $2,936,500 B/C ratio = 0.46 B/C ratio = 0.75 B/C ratio = 42.5 B/C ratio = 2.21 NPV Comparison

  34. NPV Comparison

  35. Tank Decommission vs. Demolition • No longer needed as water system facility • Value as antenna tower • Costs of demolition and soil remediation • Possible landmarks issue • Communication to customers

  36. Recommendation • Recommend Alternative 3: Decommission Maple Leaf Tank and serve the Maple Leaf 530 Pressure Zone directly from the 550 Pipeline

  37. Conclusions • Decommissioning the Maple Leaf Tank increases pressures and fire flow • Supply redundancy provides for minimal outage risk • Decommissioning still preferred alternative if demolition costs are included

  38. Alt 3 PHD Pressure – Low Pressure Area

  39. Alt 3 MDD Fire Flow – Low Pressure Area

  40. Questions?

  41. Decommissioning - How Do We Make It Happen? Cheryl Capron, Senior Water System Operator Seattle Public Utilities PNWS-AWWA Conference April 30, 2008

  42. Overview • Operations input to asset management process • Compensating improvements • New procedures • Operational testing • Retirement

  43. Operations Input to Asset Management Process • How the tank and zone are actually operated • Reliability and condition of existing components • Identify all functions of tank • Venting & surge protection • Holds positive pressure in zone if pumps fail • Smooths diurnal demand on source • Provides opportunity to boost Cl2 residual

  44. Compensating Improvements • Pressure relief? • Booster chlorine capability replaced? • More instrumentation? • Upgrade, add, replace pumps? • Variable output to match demand • Hot standby power • Upgrade, add, replace flow control valves? • Adjust valve speed

  45. New Procedures • Revise minimum and maximum zone operating pressures • Hydraulic modeling • Response to high and low pressure alarms • When do we shut down gravity supply and switch to pumps? • Revise SCADA graphics & programming • Train the operators

  46. 3-Part Operational Testing • PRV Loop • Close pump discharge line and start pump • Pressure Zone Test Scenarios (Tank off-line) • Most likely to go wrong? • SCADA glitch - valve opens too far • Power fail – pump stops • Peak Season Test • Are we absolutely sure we won’t need this tank anymore?

  47. Operational Test Objectives • Verify new 6” PRV loop will function as needed • Verify an existing off-site 4” PRV functions as needed • Document location & effect of discharge flow to environment. • Revise settings so that new 6” PRV opens first. • Verify high & low psi alarm settings are ok

  48. Test Plan • Objectives • Prior to Test • Customers ready for pressure change • Customer service reps aware of pressure changes & dirty water from testing • Fire department aware pressure surges may trigger false alarms • SCADA & new operating procedure ready • All compensating improvements completed

  49. Test Plan • Preset the system • Reservoir levels • Valves positioned • Field staffing • At PRVs to observe & document • At tank inlet to put back on line quickly

  50. Test Plan • Step by step procedure • Establish supply to zone • Tank inlet closed • Slowly boost supply to force PRVs open • Verify they’re working • Slowly back off supply to close PRVs • Adjust pressure settings and alarm settings

More Related