Asheville s Fairview Water System Improvements: from Modeling to Contract Documents. April 19, 2016 Meg Roberts, PE

Transcription

1 Asheville s Fairview Water System Improvements: from Modeling to Contract Documents April 19, 2016 Meg Roberts, PE

2 City of Asheville Water Distribution System Customer elevations range 1,950 feet to 3,650 feet Over 50 pressure zones Over 1,200 miles of mains Diameters range 1 36 inches ADD = 20 mgd, MDD = 24 mgd 2

3 gap Fairview Service Area Single supply from South Buncombe Pump Station Concord and Mine Hole Gap pressure zones, study focus 2,440 ft 2,640 ft 2,751 ft Buncombe Co Henderson Co 3

4 Fairview Service Area Water System Improvements Project Concerns: Demand rising High pressures Low pressures Redundancy Phase 1: Model Update and Calibration Identify Deficiencies and Improvement Alternatives Preliminary Construction Cost Estimate Phase 2: Final design and construction documents 4

5 Fairview Service Area Hydraulic Model - Update Existing model updated (for service area only) 475 pipes, 3 tanks, 3 pump stations added 1.06 mgd average day based on flow measurements at South Buncombe PS (not metered) 5,090 customers, billing records used for distribution/allocation 40% NRW 1.38 mgd maximum day demand based on 130% peaking factor 5

6 Fairview Service Area Hydraulic Model - Calibration South Buncombe PS flow measurement Velocity profile on discharge Operating points checked Diurnal curve developed 6

7 Fairview Service Area Hydraulic Model - Calibration South Buncombe PS operating point checks All pumps operated at higher head and flow than expected Impellers had been replaced! 7

8 Fairview Service Area Hydraulic Model - Calibration Four hydraulic grade line tests (HGLs) S. Buncombe PS to Concord Tank Concord Tank to three flowing hydrants Troubleshooting High velocity pitot blade measurements Model Adjustments Pipe roughness Node elevations 8

9 Fairview Service Area Demand Projections Planning report census tracts people per household 190 to 260 new dwellings per year Used 3% annual growth rate based on trends in area 2040 Demand Projections: 2040 ADD = 2.57 mgd 2040 MDD = 3.35 mgd Allocated based on sewer service 9

10 Fairview Service Area Existing Deficiencies Low Pressures 14 psi suction side of SBPS 40 psi on Charlotte Hwy Excessive Pressures 280 psi on Mills Gap 252 psi on Cane Creek Deficient Fire Flows 1300 gpm: Fairview ES 450 gpm: Reynolds HS 1300 gpm Cane Creek MS No redundancy east of Concord Tank 10

11 Future Demands Make Deficiencies Worse Major Improvements Are Needed Low Pressures 11 psi suction side of SBPS -45 psi on Charlotte Hwy Overloaded 12 Pipe 4.0 mgd peak hr flow 8 fps velocity 14 feet/1000 Pump Capacity is OK 3.6 mgd firm capacity 3.3 mgd 2040 Max Day Storage Capacity OK 0.4 mg for equalizing 12% of MDD 0.3 mg reserve for fire 2 hours at 2,500 gpm 11

12 Low Pressure at South Buncombe Pump Station Indicates Pipe Capacity Problem in Main Zone 47 psi (2438 HGL) with pumps off (elevation 2329 feet) 38 psi (2417 HGL) with one pump at 2.3 mgd for average demand 19 psi (2372 HGL) with one pump at 2.0 mgd for peak hr demand 13 psi (2359 HGL) running two pumps at 2.9 mgd (firm capacity) 30 psi at nearest customer SBPS 12

13 Alternative Analysis Alternative 1 (previous recommendations from 2009 master plan) S Buncombe PS relocated to S Buncombe Tank Mine Hole Gap PRV moved to Emma s Grove south of Gap Cr New 16-inch transmission main in Concord Rd and Emma s Grove from new pump station to Gap Creek Rd Cane Creek in Mine Hole Gap Zone 13

14 Alternative 1 Summary: High Cost, Pressure & FF Problems, Not Redundant Lowest Pressure 34 psi on Alt 74 Highest Pressure 224 psi on Cane Cr 283 psi on Mills Gap Low Fire Flows 450 gpm HS Not redundant on 74A east of Emma s Grove 14

15 Alternative Analysis Alternative 2 (previous option from 2009 master plan) S Buncombe PS relocated to S Buncombe Tank with new 16 pipe to tank Mine Hole Gap PRV relocated to Emma s Grove south of Gap Creek Rd 12-inch along Cane Creek Rd extended southwest to Lower Christ Church Rd Cane Creek and Mills Gap shift to Main (2440) Zone 15

16 Alternative 2 Summary: Low Pressure & FF on Charlotte Hwy, No Redundancy Lowest Pressure 14 psi on Alt psi Crossing Circle No Pressures > 214 psi Low Fire Flows: 0 gpm HS 500 gpm ES 500 gpm MS No redundancy 16

17 Alternative Analysis Alternative 3 (1993 study) Mine Hole Gap PRV relocated to Emma s Grove west of Gap Creek Rd New PRV on Mills Gap Rd south of Concord Rd New 1 mg tank in 2650 pressure zone supplied by PRVs 12-inch connector on Cane Creek Rd All of Cane Creek and Mills Gap in 2650 (Mine Hole Gap) Zone 17

18 Alternative 3 Summary: Pressure Problems, 1 Low FF, Limited Redundancy Lowest Pressure 35 psi on 74A Highest Pressures 238 psi on Cane Cr Low Fire Flows: 450 gpm HS 18

19 Alternative Analysis Alternative 4 (new): New 74A Pump Station boosts from 2440 Zone to 2650 Zones New 12 Pipe 14,000 feet of 12 Pipe Prevents overloading existing 8 pipe New Tank at Alt 3 Site 1 million gallons 2650 Overflow 19

20 Alternative 4 Summary: Pressure Problems but Good FF and Redundancy No Pressures < 40 psi Highest Pressures 230 psi on Laurel Cr 238 psi on Cane Cr Better Fire Flow 1900 gpm at HS 20

21 Alternative 5: New Pump Station, New Tank, Zone Shift New pump station and 12 pipe on 74A New tank at site of Old Mine Hole Gap tank PRVs on Emma s Grove, Gap Creek, Cane Creek and Mills Gap roads Cane Creek fed by PRVs initially but directly from Main Zone eventually Redundant supply to 2750, 2650 & 2440 zones Keep S Buncombe PS No new pipe in Concord Rd New Pump Station 21

22 Summary of Improvement Alternatives Alterative $ Million Advantages Disadvantages pipe in Concord Zone $14.3 Better Redundancy in 2440 Zone $ Tank at 1993 Site $4.8 No High Pressures Lower Cost Low Cost Improved Fire Flows Improved Redundancy 4. New Pump Sta & Tank $12.7 Improved Fire Flows 5. Hybrid of 2 and 4 $13.8 No Low Pressures No Hi Pressures Best Redundancy Highest Cost Hi & Lo Pressures Low Fire Flows Little Redundancy Low Fire Flows Low Fire Flow at HS 74-A not redundant 12 Pipe in 74-A Impacts 2440 Pressures Several PRVs Higher Cost 22

23 Phase 1: New Pump Station and Tank New pump station with eventual firm capacity of 1 mgd New 0.5 mg tank at site of old Mine Hole Gap tank Tank overflow at 2650 feet is same HGL maintained by Mine Hole Gap PRV Three new PRVs 23

24 Deficiencies Corrected in Phase 1 Lowest Pressures 46 psi on 74A High Pressures 280 psi reduced to 156 psi on Mills Gap 252 psi reduced to 126 psi on Cane Creek Available Fire Flows 2000 gpm: Fairview ES 1700 gpm: Reynolds HS 2300 gpm Cane Creek MS Redundancy east of Concord Tank Some high pressure on PS discharge (~230 psi) gpm psi gpm gpm psi psi 24

25 Phase 2: 12-inch Water Line Along 74A 12-inch pipe needed when new development creates additional demand along 74A (2.3 mgd on max day demand trigger) Benefits of new 12-inch pipe: Additional capacity to carry 1 mgd from new pump station Reduced pressures on discharge side of pump station (20 psi lower) Available fire flow at high school increases to 2,500 gpm 25

26 Phase 3: 12 Pipe Connects Cane Creek Road to Main Zone Emergency Pump Connection Improves Redundancy Improves redundancy and energy efficiency If S Buncombe pump station is out of service: Pump 1 mgd at new pump station on 74A from 2440 zone to 2650 zone New 12 pipe provides additional supply to Cane Creek area directly from 2440 zone Use emergency pump on Gap Creek to boost from 2440 zone to 2750 zone Emergency Pump Connect to Main Zone 26

27 Model Compared Water Age with Improvements to Existing Water Age Existing water age 5-7 days in most of Fairview Service Area Less than 5 days west of Concord Tank 165 hrs 148 hrs 161 hrs 222 hrs 27

28 Initial Simulation Showed Phase 1 Improvements Caused Water Age Problem in Concord Tank Water age increased on Concord, Emma s Grove and Gap Creek Water age dropped in Mine Hole Gap Zone and along 74A 28

29 Phase 1 Water Age with Operational Improvements Limit flow from new pump station to 0.5 mgd Increase turnover and don t fill upper 4 feet of Concord Tank Adjust PRVS so Gap Creek is primary supply Install flusher on Cane Creek Road Water age better than existing on Cane Cr Rd and 74A Water age higher than existing on Concord, Emmas Grove and Gap Creek roads 29

30 Overall Water Age for Phase 1 Comparable to Existing Conditions for Average Day Demand 30

31 Phase 3 Water Age Drops Significantly with Supply from Mills River WTP and New Demand Cane Creek Road supplied with fresh water from new connection to main pressure zone Future demand increases flow velocities and reduces travel time New Connection to Main Zone 31

32 Constructability and Design Phase Status Tank site confirmed, surveyed, geotechnical analysis Pump station alternative sites being evaluated PRV station sites undergoing property acquisition process Drawings and specifications in progress 32

33 Tank Site Design 0.5-MG tank will be located on existing City property Tank evaluation settled on pedestaled ground storage tank Prestressed concrete or glasslined steel materials allowed Normal Operating Range Emergency Volume New Tank Pedestal or Filled Bottom 50 HWL = 2,650 ft msl Normal LWL = 2,635 ft msl Emergency LWL = 2,620 ft msl Grade = 2,610 ft msl 33

34 Pump Station Field hydrant tests confirmed model predictions for pump station impact on suction side pressures. Two alternative sites being evaluated Site engineering vs additional piping Pump station will be 1.0-MG, 3-pump packaged station 34

35 Pressure Reducing Stations 4 PRV stations will be installed in vaults Property negotiations are ongoing Detail design will begin after properties have been confirmed and surveyed 35

36 Fairview Service Area Water System Improvements Project Concerns Alleviated with Planned Improvements: Demand rising High pressures Low pressures Redundancy Acknowledgements Chad Pierce and Leslie Carreiro City of Asheville Mona Ellum Ellum Engineering Jeff Cruickshank, Mike Benchich Hazen and Sawyer 36

37 Questions / Discussion Meg Roberts, PE mroberts@hazenandsawyer.com