Solving the Mystery of Non-Revenue Water in High Point

Transcription

1 Solving the Mystery of Non-Revenue Water in High Point Jeff Cruickshank, Hazen and Sawyer Terry Houk, City of High Point NC AWWA-WEA Spring Symposium March 27, 2018 Asheville, NC

2 Presentation Outline 1. Background from City s Perspective 2. Findings from Water Audit 3. Alternatives to Solve the Problem 2

3 Background from City s Perspective Terry Houk, Public Services Director 3

4 High Point s Water Distribution System 43,000 Connections 12.4 MGD Average Daily Demand 20 MGD Maximum Day Two Pressure Zones 4

5 High Point s Water Supply Two Lakes Supply Ward WTP 24 MGD Permitted Plant Capacity Purchased Supply: PTRWA 2.7 MGD Take or Pay Contract Includes Jamestown s Allocation 5

6 City Noticed Water Supplied Trending Higher Than Water Sold Supplied 3.6 mgd or 28% Difference PTRWA Startup Sold 6

7 City Retained Hazen to Conduct a Water Audit in Late 2016 Project scope included: 1. Meetings with city staff 2. Testing master meters 3. Compiling billing information 4. Performing M-36 water balance 5. Developing performance indicators 6. Preparing tech memo to document 7

8 Findings from Water Audit Project 8

9 Water Audits Analyze Non Revenue Water (NRW) Difference Between Water Supplied and Total Billed

10 Master Meter Tests are Key Component of Water Audits Master meter error adjustments are required entry in M-36 audit form A handful of master meters have a very large impact on NRW 10

11 Hazen Chose Pitot Tubes to Test High Point s Master Meters 11

12 Pitot Tube Flow Measurements Were Compared to Volume Registration on Master Meter Totalizers 30 Best Fit Average Maximum Minimum 25 Pipe Location - inches Velocity - fps Q = V * A Q = V / T 12

13 PTRWA Master Meter Was Within 3% of Pitot Tube This Meter Not Contributing to Non-Revenue Water Location Meter Size & Type Multiplier PTRWA Transfer Station 30" Venturi 1,000 Gauging Point Data Class 300 DIP Nominal Pipe Size - inches Calipered Diameter - inches Velocity Factor Test Data Test Date Jan 5-Jan 4-5 Jan Totalizer Registration - kgal Elapsed Time - minutes Center Velocity - fps Pitometer Flow - mgd Totalizer Flow - mgd Totalizer Error -2.6% -2.9% -3.3% 13

14 24-Hour Test for 36 Master Meter at Ward WTP Showed Recorded Flow Within 2% of Pitot Tube 14

15 Velocity Profiles Upstream of 24 Master Meter at Ward WTP Stable and Repeatable with PTRWA Booster Pump Off 15

16 Velocity Profile Upstream of 24 Master Meter at Ward WTP Unstable at Very Low Flow Rates with PTRWA Pump On 16

17 Steady State Simulations with Hydraulic Model Confirmed Low Flow in 24 Meter With PTRWA Booster Pumps On PTRWA Pump Off PTRWA Pump On 1.5 fps 0.5 fps 17

18 24 Meter Flow Never Dropped Below 2.3 mgd in SCADA +73% Error on 24 Meter Makes WTP Flow 15% High Flow Comparison - mgd Difference Meter SCADA Model MG % of Model Measurement 24" % TSTM 36" % 5.93 Total % 18

19 Cedrow Meter Error Due to Low Flow Caused By I-74 Pumps I-74 Pump Off I-74 Pump On 19

20 Master Meter and Supply Error Adjustments Normalized for Annual Average Day in M-36 Spreadsheet: 8% NRW Change Supply Recorded Recorded Pitot/Model SCADA Percent Source MG/Yr MGD Rate-mgd Rate-mgd Error PTRWA % Ward WTP 3, % Totals 4, % 20

21 M-36 Audit Shows Non-Revenue Water Reduced to 20.7% After Error Adjustments 21

22 Alternatives to Solve the Problem 22

23 Initial Focus on 24 Venturi Meter Venturi meters most accurate between Reynolds Numbers of 200,000 and 2,000,000 Low flow = 2.3 mgd 4.5 differential High flow = 23 mgd 433 differential Existing dp cell: 9.0 mgd max at 68 differential Current Accurate Range: 2.3 mgd to 9.0 mgd 23

24 Alternatives Considered 1. Operate PTRWA pump at lower speed to keep flow within spec for existing 24 venturi meter 2. Reduce supply from PTRWA by not using booster pump and controlling PTRWA WTP pumps off I-74 tank. Pay for full allocation or sell to Greensboro 3. Replace 24 venturi meter with bi-directional mag meter 4. Install a control valve that closes 24 Cedrow line whenever PTRWA pumps operate 5. Install PSV and 24 pipe to divert flow to Ward clear-well rather than using I-74 pumps to vary tank level 6. Install new meter on 24 pipe north of I-74 tank and use with I-74 pump meter to calculate system input 7. Implement hybrid alternative: Weighted check valve 24

25 Alternative Evaluation Findings Hydraulics and pump issues in model runs ruled out some alternatives Water age modeling showed one alternative degraded water quality Instrumentation limits on flow ranges made one alternative unworkable Constructability ruled out alternative with new pipes near clearwells 25

26 New Mag Meter North of PTRWA Pumps is Viable Solution 1. Existing 24-inch venturi meter would no longer be used to calculate WTP flow 2. New meter measures combined flow from WTP and PTRWA booster pump, eliminating need to measure low flows from WTP 3. Existing 10 mag meter measures water boosted by PTRWA pumps 4. SCADA could calculate flow from WTP from the difference between the two mag meters 5. No operational change only new measurement 6. Need new 24 valve on existing pipe, 16 bypass and meter in new vault with power and SCADA 26

27 Control Valve Also a Viable Solution Stops Low Flow in 24 Meter When PTRWA Pumps Operate SCADA would close valve whenever PTRWA pump operates New valve could be anywhere on 24 main between existing meter and PTRWA booster pumps Requires new vault, power and SCADA connections Operational change: model shows upstream pressure up to 7 psi higher than downstream with closed valve 27

28 Cost Comparison of Two Viable Alternatives and Estimated Shutdown Time Led City to Choose Control Valve 28

29 Subsequent Research Showed Control Valve Option Could be Implemented Using Two Existing 36-inch Valves Install New Actuator Does not require new valve or vault Existing valve in basement of WTP to be equipped with automated actuator Existing valve in WTP yard must be closed and will remain closed To 24 Meter Remains Closed To 36 Meter 29

30 Water Supplied and Water Sold Should Track Closer After Control Valve Becomes Operational Time for New Audit 30

31 Acknowledgements Terry Houk, Public Services Director and Coauthor Wendell Pickett, Ward WTP Superintendent John Collett, Hazen s Project Manager for Alternatives Evaluation Aaron Babson, Hazen s Design Project Manager Chris Evans, Hydraulic Modeler for Hazen Kevin Widderich, Field Coordinator for Hazen 31

32 Questions? Jeff Cruickshank