A Balancing Act: Complex Distribution System Planning in the Western North Carolina Foothills Tina Whitfield - HDR

Transcription

1 A Balancing Act: Complex Distribution System Planning in the Western North Carolina Foothills Tina Whitfield - HDR 2017 HDR, Inc., all rights reserved.

2 Agenda 01 Overview 02 Approach 03 Findings 04 Alternatives and Solutions

3 01 Overview

4 Background What? Water System Master Plan Why? Address Operational Challenges and Provide Roadmap for the Future Where? Caldwell County, NC Who? Caldwell County Water System o 8,800 customers over 140 square miles o Distribution-only water system o 300 miles of distribution line o Elevation ranges from 940 to 1550 feet AMSL When? Current

5 Caldwell County Water System Population and Supply Rural water distribution system serving a population of 22,600 in four (4) distinct water systems: o Southeast System o North System o West System o Addison Lane Purchases water from the City of Lenoir, Town of Granite Falls and the City of Hickory through numerous master meter connections. Also sells back water to the City of Lenoir and Town of Granite Falls

6 Challenges and Drivers Experiencing both ends of the spectrum for pressures o Excessively high o Low Fire Flow Deficiencies Water quality problems in long stretches of distribution main Low volume/supply in certain areas of the system

7 02 Approach

8 Traditional Master Planning Elements Basis of Planning Model Update System Evaluation

9 Unique Analyses to Caldwell County Master Meter Pressure Variation Analysis PRV Operational Strategies Water Supply and Availability over Varying Terrain Storage Requirements

10 Basis of Planning Approach Evaluate Current Population and Customer Breakdowns Review Historical Demand Analyze Large User Demands Review Past Growth Trends Review Current Local Growth and Land Use Plans Review Recent Growth Studies and Projections Develop Growth Projections and 20-Year Forecast

11 Model Update and Calibration Approach Update Physical Network o GIS o As-Builts o Staff Interviews and Windshield Surveys Review Service Zone Boundaries Update Demands o Geo-coded Billing Data Model Calibration o Master Meter Pressure Recorder Data o Fire Hydrant Flow Tests

12 System Evaluation and Criteria Wide Range of Operating Pressures due to Topography Experiencing Severe Deficiencies in Fire Flows. Criteria established low, with intent to raise as system improvements are made. System Storage based on NC DEQ Rules Governing Public Water Systems

13 03 Findings

14 Basis of Planning Findings Loss of Population in the Recession Slow Increase over Last 3 Years Year Service Area Population Percent Increase +/- % Customer Breakdown Customer Total Residential Commercial Industrial Institutional ,673 5,080 5, ,263 20% 5,758 5, ,109 45% 8,920 8, , % 8,945 8, , % 9,032 8, , % 8,857 8, , % 8,793 8, , % 8,833 8, , % 8,875 8, , % 9,064 8, Average ( ) 22,248 8,915 8, Average Annual Growth ( ) 0.2% 0.4% 0.3%

15 Basis of Planning Findings Consistent Average Day Demands, Maximum Month Demand and Per Capita Demand Year Service Area Population Customer Total Average Day Demand (mgd) Maximum Month Demand (mgd) Per Capita Demand (gallons per capita per day) ,673 5, ,263 5, ,109 8, ,321 8, ,579 9, ,125 8, ,978 8, ,078 8, ,136 8, ,660 9, Average ( ) 22,248 8,

16 Basis of Planning Findings Previous Plan had been completed in 1993 Since that time a number of studies have been completed including: o 2010 Census and NC Office of State Budget and Management o 2004 Yadkin Valley Water Supply Planning Study o 2012 Catawba-Wateree Water Management Group (CWWMG) Water Supply Master Plan Year Population Average Daily Demand (mgd) Maximum Daily Demand (mgd) , , , , , ,

17 Basis of Planning Findings Year Projected Population CWWMG Method Yadkin Valley Method 1993 Master Plan Recommended Growth Rate ,660 22,660 22,660 22, ,796 23,048 23,091 22, ,388 25,024 25,287 24, ,864 27,094 27,691 25, ,248 29,335 30,324 26, ,638 31,728 33,207 27,819

18 Basis of Planning Findings Review of Supply from Water purveyors o Needed Supply o Contractual Obligations and Timeline o Available Supply and Treatment Capacity Water Suppliers City of Granite Falls Current Treatment Capacity (mgd) Current ADD (mgd) Projected ADD (mgd) Current (Projected) Remaining Capacity (mgd) (0.98) Sufficient Supply for Projected Caldwell County Demand? Yes City of Lenoir (4.56) Yes Alexander County (via Hickory) Yes

19 Model Update Confirmed Service Zone Boundaries Confirmed Service Zone HGL Updated Supply from City of Lenoir at Master Meter Locations Updated Storage and Pumping o County had transferred ownership of two (2) tanks to the City of Lenoir o County had removed one (1) tank from service due to landfill expansion o Five (5) booster pump stations Updated Network o Additional distribution mains o PRV stations and operation(s) Updated Demands o Existing Billing Data (Geocoded)

20 Model Calibration Based on recent M32 Update and Calibration Guidelines for Water Distributions System Modeling (AWWA, 1999). The calibration criteria applied for this hydraulic model are: o The absolute difference between the pressure drop simulated in the model and that observed in the field should be less than and equal to 2 psi in 85 percent of the observations. o For all observations, the absolute difference in pressure drop should be less than or equal to 5 psi.

21 Master Meter Pressure Variation Analysis Pressure Recorder Pressure Zone Average Hydraulic Grade Line (ft AMSL) Average Pressure (psi) Diurnal Pressure Variation (psi) Morganton Lenoir Low Side /- 4 North 321 Lenoir Low Side /- 9 Highway 90 Lenoir Low Side /- 5 Alfred Hartley Lenoir High Side /- 4 Alfred Hartley PS Lenoir High Side /- 7 Drag Strip Lenoir High Side /- 6 Dry Ponds Granite Falls /- 10 Appaloosa Way Granite Falls /- 2 Mountainside Granite Falls /- 4 Collettsville Lenoir Low Side /- 4 Cedar Rock Lenoir High Side /- 9 Tumbleweed Lenoir Low Side /- 3

22 Existing System Evaluation Area of System Total Number of Nodes Number of Nodes Below Minimum Number of Nodes Above Maximum Average Pressure (psi) North Southeast West Addison Lane Area of System Total Number of Nodes Number of Deficient Nodes Percent of Total Average Fire Flow Availability North 5 0 0% 1,637 Southeast % 1,164 West % 1,397 Addison Lane 3 0 0% 747

23 Future System Evaluation Area of System Total Number of Nodes Number of Nodes Below Minimum Number of Nodes Above Maximum Average Pressure (psi) North Southeast West Addison Lane Area of System Total Number of Nodes Number of Deficient Nodes Percent of Total Average Fire Flow Availability North 5 0 0% 1,633 Southeast % 1,161 West % 1,391 Addison Lane 3 0 0% 673

24 Storage Analysis Year Average Day Demand (mgd) Available Storage (MG) NC DEQ State Required Storage (MG) Calculated Recommended Storage Operational Fire Emergency Storage (MG) Protection Storage (MG) Storage (MG) Total NC DEQ Storage Deficit (MG) (0.34) (0.50)

25 04 Alternatives and Solutions

26 A Question of Storage Additional Storage needed to meet system requirements. Storage should be located in proximity to demand o Southeast System o West System System Current Average Day Demands (mgd) 2035 Average Day Demands (mgd) Available Storage (MG) NC DEQ State Required Storage Deficit Storage (MG) Recommended Storage Southeast (0.15) 0.20 (Short-Term) West (0.32) 0.20 (Short-Term) 0.20 (Long-Term)

27 A Question of Storage Maximizing Existing Storage o Southeast System: Draco Tank Water cycling difficult during low to regular demands Rapid drain during high demands Long straw Far end of system Solution: Install control valve at master meters to read level at Draco Tank and allow system to float during low/regular demands Solution: Provide additional storage to meet storage deficit in a location more central to demand

28 A Question of Supply Low Fire Flow Availability Low Residual Pressures Reason? o Lack of storage requires flow through master meters o PRVs isolating sections of system and restricting flow to areas o Long sections of pipe with not sufficient enough response for a fire flow Solution o Provide additional storage o Evaluate PRV operation

29 A Question of Supply Specific Recommendations: Pump station and hydropneumatic tank rehabilitation is recommended for the Drag Strip system. It serves a small modular development and experiences problems with pressure and supply.

30 PRV Operational Strategies Southeast System: Modify and/or repair existing PRVs so that flow can move through the system. PRVs are currently closed. A pressure reducing valve is recommended to address the operational issues associated with the Cedar Rock tank. This will allow the County to better utilize this tank.

31 PRV Operational Strategies

32 Next Steps Project ID Description Project Implementation Timing SE1 Southeast Storage Tank 0.2 MG Elevated Critical SE2 Draco Tank Operational Improvements Short-Term SE3 Freezer Locker/Drag Strip Interconnect Short-Term SE4 PRV Modification Short-Term SE5 Cedar Rock Tank and Pump Station Rehabilitation and Operational Improvements Long-Term Project ID Description Project Implementation Timing W1 West Storage Tank 0.2 MG Ground Critical W2 Air Release Valve(s) Long-Term

33 Conclusion While a small system, faced with complex obstacles to providing sufficient supply, pressure, and fire flow to the system. Distribution-only system that depends on others for supply provides an additional challenge Careful planning can result in solid path forward to success.

34 Questions? Tina Whitfield Karen Maye