Keep the Water Moving Rehabilitation of a 1-million Gallon Water Storage Tank

Transcription

1 AMERICAN WATER WORKS ASSOCIATION NEW JERSEY SECTION 2015 Annual Conference Keep the Water Moving Rehabilitation of a 1-million Gallon Water Storage Tank Jonathan T. Reed CDM Smith, Inc. Bill Mitchell, P.E. Trenton Water Works March 19, 2015

2 Presentation Outline Water quality in potable water storage tanks Methods for optimizing water quality in potable water storage tanks Trenton Water Works and the Whitehorse Tank Alternatives for improving water quality in the Whitehorse Tank Evaluation of alternatives and recommendation Overview of tank improvements and operation

3 WATER QUALITY IN POTABLE WATER STORAGE TANKS

4 DBP Formation in Water Distribution Systems and Water Storage Facilities

5 DBP Formation in Water Distribution Systems and Water Storage Facilities Given a chlorine residual and a high chemical contact times, DBPs can form in storage facilities

6 METHODS FOR OPTIMIZING WATER QUALITY IN POTABLE WATER STORAGE TANKS

7 Method No. 1 Maintain Adequate Turnover Rates to Decrease Water Age Turnover GOAL 3-5 days 20%-35% Turnover Per Day Change in Water Age with Increased Cycling

8 Method No. 2 Ensure Complete Mixing Turnover is NOT Enough taste and odor issues temperature stratification bacteria regrowth loss of chlorine residual disinfection byproduct spikes

9 Method No. 2 Ensure Complete Mixing Tideflex Technologies CFD Model Velocity Profile for Single Inlet in an Elevated Tank (Duer M., 2012)

10 TRENTON WATER WORKS AND THE WHITEHORSE TANK

11 Trenton Water Works Water Supply System and Pressure Gradients

12 The Whitehorse Tank 1-MG Multi-leg Steel Elevated Potable Water Storage Tank

13 The Whitehorse Tank Steel Tank Pedestal Typical of 8 Valve Vault with Altitude Valve 12-inch Inlet/Outlet Pipe 1-MG Whitehorse Tank 96-inch Diameter Steel Riser Distribution Main on Hempstead Road

14 Trenton Water Works Tanks Operating Ranges (historical data from ) Central Pumping Zone Pressure Gradient Minimum Turnover in Whitehorse Tank

15 Potential for Water Quality Issues in the Whitehorse Tank Lack of adequate daily turnover Lack of adequate Mixing Keep the Water Moving - Rehabilitation of a 1 Million Gallon Water Storage Tank

16 ALTERNATIVES FOR IMPROVING WATER QUALITY IN THE WHITEHORSE TANK

17 Improving Tank Turnover Elevate Existing Tank Install New Elevated Storage Tank Remove Existing Tank Install Booster Pumps

18 Improving Tank Turnover: Elevate Existing Tank Advantages Disadvantages Increase local system pressure No new equipment High capital cost Public perception Concerns with foundation Permitting challenges

19 Improving Tank Turnover: Install New Elevated Storage Tank Advantages Disadvantages Increased life span Low maintenance High capital cost Major construction Permitting challenges

20 Improving Tank Turnover: Remove Existing Tank Advantages Disadvantages Improved aesthetics to neighborhood Eliminates maintenance Liability risk Decreased available fire flow May impact insurance ratings Permitting challenges

21 Improving Tank Turnover: Install Booster Pumps Advantages Low capital cost Minimize impact on local residents Removes dependability on system pressure for turnover Disadvantages O&M requirement Long term maintenance New equipment required

22 Improving Tank Circulation Tideflex Mixing System SolarBee or GridBee Mixing System PAX Mixing System

23 Improving Tank Circulation: Tideflex Mixing System Advantages Disadvantages Tideflex mixing system installed in elevated storage tank (Duer M., 2012) No maintenance required Achieves complete mixing using Tideflex s mix design No operating costs Only mixes when tank is filling Not effective if water falls below nozzles Must take tank out of service for installation

24 Improving Tank Circulation: SolarBee Mixing System SolarBee Flow Pattern(SolarBee SB500PWc v18 Owner s Manual) Advantages Provides constant mixing Low energy footprint Compatible with chlorine injection systems Installed by supplier Disadvantages New mechanical system in an elevated tank Operating and maintenance costs

25 Improving Tank Circulation: GridBee Mixing System Advantages Low initial cost Continuous mixing Removes dependability on system pressure for turnover GS v submersible mixer (GridBee GS v Owner s Manual) Disadvantages CFD modeling for GridBee GS-12 submersible mixer in 1.25-MG tank ( New mechanical system in tank Risk with relatively new product Must be anchored to tank base

26 Improving Tank Circulation: PAX Mixing System PAX Mixer (Image courtesy of PAX Mixing Technologies) Advantages Continuous mixing Can be installed through hatch Installation and startup performed by supplier Disadvantages Installation of new mechanical device in elevated storage tank Operating and maintenance costs Custom mounting device for irregular tank bottom

27 EVALUATION OF ALTERNATIVES AND RECOMMENDATION

28 Keep the Water Moving Rehabilitation of a 1 Million Gallon Water storage Tank Jonathan Reed/Bill Mitchell 03/19/2015

29 Recommended Combination of Alternatives Pitless Booster Pumps Induce Turnover Tideflex Mixing System Induce Mixing

30 OVERVIEW OF TANK IMPROVEMENTS AND OPERATION

31 Overview of Tank Improvements

32 Operation Draw Period 20-35% Draw

33 Operation Fill Periods Complete Mixing During Fill Periods

34 What did we achieve? Low cost solution, requiring no major structural modifications to the Whitehorse Tank and no new mechanical systems in the tank Reliable method for maintaining adequate turnover in the Whitehorse Tank Sustainable method for maintaining adequate circulation, requiring minimal maintenance

35 AMERICAN WATER WORKS ASSOCIATION NEW JERSEY SECTION 2015 Annual Conference QUESTIONS?? Keep the Water Moving Rehabilitation of a 1-million Gallon Water Storage Tank March 19, 2015 Jonathan T. Reed CDM Smith reedjt@cdmsmith.com Bill Mitchell, P.E. Trenton Water Works wmitchell@trentonnj.org