A Clarification on the Justification for Clarification

Transcription

1 A Clarification on the Justification for Clarification November 16, 2016 Grant Sharpe, Brown and Caldwell Will Rice, Charlotte Water

2 Facility Introduction McAlpine Creek WWMF Rated for 64 MGD Two trains North: 6 SCs South: 10 SCs Original Construction 1966 SCs between 15 and 50 years old 6 different sizes intermixed with 3 different center mechanism type Lower internal baffles installed on 14 of 16

3 3

4 Goals and Plan A business case discussion was developed to determine the scope of improvements to the secondary clarifier process at CLTWater s MCWWMF Thorough, full scale evaluation of all clarifiers Condition assessment of 9 clarifiers Treatment Capacity Modeling and Calibration Hydraulic Profile modeling RAS system analysis Groundwater management system evaluation

5 Condition Assessment

6 Condition Assessment Purpose Determine the remaining useful life of the existing equipment SC 5 Effluent Launder and Effluent Weirs Identify rehab/replacement needs to allow the secondary clarifiers to function reliably SC 11 Walls

7 Condition Assessment Activities Assessment Type Assets Included Representative Sample Mechanical Structural Electrical CCTV Drive Mechanism Arms Scum Removal Valves Bridge and Handrail Column Effluent Weirs and Baffles Walls Floors Effluent Launder Center Sludge Well Control Panels Switches Lighting Representative RAS pipe segments 8 clarifiers covering each type/vintage 5 RAS pump stations and associated splitter boxes, and valve vaults 3 RAS pipe segments and 2 Concrete pipe segments

8 CFD Modeling of Secondary Clarifiers

9 CFD 2Dc Modeling demonstrates potential capacity and optimizes treatment performance 9

10 CFD Model Calibration is a 3 Step Process 1 Laboratory Analysis and Historical Data Review 2 Stress test 3 Clarifier Modeling (CFD Modeling) 10

11 Historical High Flow Rate Events - South Train 2013 through 2015, Hourly Flow Rates 11

12 Historical SVI Values - South Train September 2014 through April 2015 SVI 95% = 71 ml/g BC SVI = 87 ml/g Modeled SVI = 80 ml/g 12

13 Historical ESS Concentrations May 2012 through April 2015 ESS 95% = 12 mg/l ESS Avg. = 5 mg/l Modeled ESS = 15 mg/l Blue: North Train Red: South Train 13

14 Secondary Clarifier Stress Tests SC 11/12 Samples of SBD, ESS, RSS, and MLSS were collected every 15 minutes 14

15 Effect of Replacing Mechanisms with Larger Center Wells and Stamford Baffles Existing SCs at 7.1 MGD ESS 15 mg/l SBD = 5.8 ft SCs (with improvements) at 10.4 MGD ESS 4 mg/l SBD = 5.8 ft 15

16 Hydraulic Profile and RAS Modeling

17 PROFILE Model Determines Hydraulic Capacity and Identified Hydraulic Bottlenecks BC s PROFILE model used North Plant modeled from MH 4 upstream of ABs to Junction Box 3 6 trains South Plant modeled from the South AB Splitter Box to Junction Box 3 7 trains Limitations Steady-state flow model based on constant flow rate One-dimensional model based on continuity and conservation of energy along a single flow path 17

18 RAS Flow Analysis Gravity Section Visual Hydraulics used to model headlosses in gravity section of RAS collection system Assumptions: Downstream control point 6-in. above RAS pump shutoff water level Submergence of effluent weirs of SCs considered failure Full submergence of triangular weirs in RAS box considered failure 18

19 RAS Flow Analysis RAS Pump Stations BC s PumpPlots model used to determine pump capacity for each RAS station Assumptions: Pump capacity was limited to operating within the preferred operating range (POR) or allowable operating range (AOR) limits 19

20 Groundwater Risk Assessment

21 Groundwater Management Risks Likelihood of Failure = POSSIBLE Groundwater control valves inoperable Valves stuck open or closed High groundwater levels at all SC except Consequence of Failure = MAJOR Potential structural failure due to buoyancy Exfiltration from SC to surface water results in CWA violation Potential accident injury in event of catastrophic failure 21

22 Assessments and Findings

23 Evaluations Supporting the Project Condition Assessment Treatment Capacity Modeling Objectives Mechanical, structural, and electrical inspections Corrosion analysis Field testing program 2D computational fluid dynamics model Key Findings Mechanical equipment at end of useful life Corrosion Failed components Structural deterioration Safety risks Capacity and treatment performance improvements Hydraulic Profile Modeling RAS Flow Analysis Groundwater Management System Evaluation Hydraulic and energy grade lines Flow split between process trains Hydraulic analysis of RAS pump stations and piping Field testing of RAS pumps Determine groundwater level that creates risk of failure Evaluate groundwater management systems Limited hydraulic bottlenecks Hydraulic control failures Operational flexibility limitations Capacity limitations with RAS PS 3 Future capacity limitations at RAS PS 4 Current systems inadequate to prevent failure of some SCs due to buoyancy/uplift

24 Evaluations Supporting the Project Condition Assessment Treatment Capacity Modeling Objectives Mechanical, structural, and electrical inspections Corrosion analysis Field testing program 2D computational fluid dynamics model Key Findings Mechanical equipment at end of useful life Corrosion Failed components Structural deterioration Safety risks Capacity and treatment performance improvements Hydraulic Profile Modeling RAS Flow Analysis Groundwater Management System Evaluation Hydraulic and energy grade lines Flow split between process trains Hydraulic analysis of RAS pump stations and piping Field testing of RAS pumps Determine groundwater level that creates risk of failure Evaluate groundwater management systems Limited hydraulic bottlenecks Hydraulic control failures Operational flexibility limitations Capacity limitations with RAS PS 3 Future capacity limitations at RAS PS 4 Current systems inadequate to prevent failure of some SCs due to buoyancy/uplift

25 Risk Analysis

26 Treatment Performance Risks Likelihood of Failure = LIKELY Mechanical equipment at end of useful life Severe corrosion Failed clarifier components Structural deterioration Consequence of Failure = HIGH Insufficient settling resulting in excessive solids load to filters Inadequate removal of solids causing high sludge blanket depth/solids in effluent Inadequate return of solids to keep biological processes functional Potential permit violations 26

27 Operational Performance Risks Likelihood of Failure = LIKELY SC 5 SC 6 SC 7 SC 8 SC 9 SC 10 RAS PS 3 South AB Splitter Box Failed slide gates Failed RAS valves RAS PS 3 undersized to deliver capacity to SCs 5 10 Internal baffles short-circuiting in high flow events Leaks in the sodium hypochlorite system Consequence of Failure = MODERATE Reduced hydraulic/treatment capacity Limited operational ability to control flows between the north and south plants which could result in non-compliance under certain operating scenarios Hypo system creates severe corrosion and significant O&M costs 27

28 Safety Risks Likelihood of Failure = POSSIBLE Control panels in poor condition No onsite control panels for some SCs Equipment not compliant with current codes and regulations Torque switches old and unreliable Leaks in hypochlorite system Consequence of Failure = MAJOR Potential accident/injury Failed switches limit operational flexibility to control flows Inability to service outdated equipment/limited parts availability 28

29 Groundwater Management Risks Likelihood of Failure = POSSIBLE Groundwater control valves inoperable Valves stuck open or closed High groundwater levels at all SC except Consequence of Failure = MAJOR Potential structural failure due to buoyancy Exfiltration from SC to surface water results in CWA violation Potential accident injury in event of catastrophic failure 29

30 Summary of Findings Project Drivers Failing mechanical equipment Failed flow controls Aged electrical equipment Failing groundwater management system Leaking hypo system Hydraulic bottlenecks Sub-optimal clarifier configuration Significant Risks Treatment Reliability Operability Safety Regulatory compliance Sub-optimal capacity from existing infrastructure Increased life-cycle costs >$250 k yr from hypo system R/R needs from hypo/corrosion

31 Recommendations

32 Flow Controls and Pumps Replace the RAS valves with telescoping valves equipped with position indicators, adjust weirs X X X X X Install new slide gates with manual operators at MHs 7, 10, 10A, 11, 13, 23, 27 X X X X X Install new slide gates with powered operators at MHs 12A and NSCSB X X X X X Replace two old Davis pumps in RAS Pump Station 3 with larger pumps to deliver adequate capacity X X

33 Clarifier Mechanisms, Rake Arms, Launder and Baffles Replace the clarifier mechanisms X X X X X X Increase center well/flocculation well diameter X X X X X X Replace effluent V-notch weirs X X X X X X Remove lower vertical baffle X X X X X Replace horizontal baffle with a Stamford baffle X X X X X X Replace effluent scum baffle X X X X X X Replace the scum beach X X X X X Replace the scum collector pipe system and controls with scum beach style system Install FRP launder covers X X X X X X X

34 Concrete Structures Replace grout topping and repair cracks in floor X X X X X Inject vertical cracks from interior wall surface X X X X X X Inject vertical cracks at perimeter of effluent launder X X X X X Resurface launder walls and slab X X X X X X Inject horizontal cracks in the launder slab Inject cracks at central sludge hopper Repair cracks in concrete bridge supports Evaluate areas of backfill erosion by effluent launder Seal the wall penetration around the scum pipe of SC 11 Seal groundwater leaks in RAS Pump Station 5 X X X X X X

35 Electrical and Ancillary Equipment Replace torque switches X X X X X X Replace control panels or install field mounted control panels near clarifiers to facilitate safe operations and maintenance activities X X X X X X Replace area lights and rusted light poles X X X X X Repair and/or replace loose and bent guardrail X Replace grating in RAS boxes X X X Ground Water Management System Install active groundwater level control X X X X X

36 Capacity Benefits of Recommended Improvements Unit Process Current Capacity, MGD Future Capacity with Improvements, MGD Treatment Capacity Increase, MGD SC % SC % SC % North Plant Total % SC * 20 51% SC SC % South Plant Total % Total MCWWMF Secondary Clarifier System Capacity % 36

37 Cost Estimate

38 Budgetary Costs Asset/System Engineering Construction Costs Total Cost SCs 1-2 $410,000 $2,730,000 $3,140,000 SCs 3-4 $550,000 $3,610,000 $4,160,000 SCs 5-8 $910,000 $6,060,000 $6,970,000 SCs 9-10 $550,000 $3,610,000 $4,160,000 SCs $750,000 $4,990,000 $5,740,000 SCs $530,000 $3,540,000 $4,070,000 North and South Plant Splitter Box Gates $120,000 $800,000 $920,000 RAS Pump Station 3 $30,000 $180,000 $210,000 TOTAL $3,850,000 $25,520,000 $29,370,000

39 Life-Cycle Cost Comparison Lifecycle Cost Scenario Capital Cost 40-year NPV Recommended Secondary Clarifier Improvements Do Nothing Alternative (Run to Failure) $29,370,000 $30,500,000 $33,200,000 $37,500,000 Savings $3,830,000 $7,000,000 39

40 Questions? Grant Sharpe Will Rice