Measure Twice, Cut Once Using Flow Monitoring Data to Re-evaluate Wet Weather Improvement Alternatives

Transcription

1 Measure Twice, Cut Once Using Flow Monitoring Data to Re-evaluate Wet Weather Improvement Alternatives Barbara Moranta, PE CDM Smith

2 Multi-Million Dollar Upgrades Planned for Crooked Creek Basin Planning Multi-million dollar upgrades from prior planning based on 3 flow monitors in Crooked Creek Re-monitor to determine where to rehabilitate and how rehabilitation will impact proposed upgrades. 2

3 Crooked Creek Basin Background Water Reclamation Facility Permitted Capacity = 1.9 mgd Hydraulic Capacity = 5 mgd Future Flows expected to exceed permitted capacity in the near future Excess flows to be diverted to Twelve Mile 3

4 How Did Flow Monitoring Improve Evaluation of Wet Weather Improvement Alternatives? Allowed Union County to map out the rehabilitation plan to reduce I/I in Crooked Creek Disproved suspicions of I/I contributed by leaks in low pressure system Provided a basis for improved hydraulic capacity analysis Led to development of cost effective improvement alternative that incorporated the I/I reduction plan and reduced size of required improvements 4

5 How Did Flow Monitoring Improve Evaluation of Wet Weather Improvement Alternatives? Allowed Union County to map out the rehabilitation plan to reduce I/I in Crooked Creek Disproved suspicions of I/I contributed by leaks in low pressure system Provided a basis for improved hydraulic capacity analysis Led to development of cost effective improvement alternative that incorporated the I/I reduction plan and reduced size of required improvements 5

6 Distribution of Temporary Monitors Allowed the Highest Infiltration/Inflow Sub-basins to be Determined 6

7 Three Factors Used to Prioritize Subbasins and Develop the I/I Reduction Plan 1 Wet Weather Peaking Factor 2 R-Value (Percent of Rainfall that Becomes RDII) RDII Volume 3 LF of Sewer 7

8 Flow (mgd) Rainfall (in) RDI/I Reduction Plan Considered Peak Flow and Volume FM8 February 26, 2013 Storm Event 0.85-inch total rainfall Storm RDI/I Flow Baseflow GWI 0.3 2/24 2/25 2/26 2/27 2/28 3/1 Date (m/d) Flow (mgd) ADWF(mgd) Rainfall (in) 8

9 I/I Reduction Prioritization Plan Considers Volume and Peak Flow 9

10 How Did Flow Monitoring Improve Evaluation of Wet Weather Improvement Alternatives? Allowed Union County to map out the rehabilitation plan to reduce I/I in Crooked Creek Disproved suspicions of I/I contributed by leaks in low pressure system Provided a basis for improved hydraulic capacity analysis Led to development of cost effective improvement alternative that incorporated the I/I reduction plan and reduced size of required improvements 10

11 Septic Area 11

12 Low Pressure Areas do not Appear to Correlate to System I/I Flow Monitor Area (acre) Low Pressure Sewer System Area (acre) Low Pressure Area (%) RDI/I Max Peak Flow Ratio R Value (%) Volume (gal/lf) FM % % 29 FM % % 22 FM % % 7 FM % % 11 Average for Crooked Creek Basin monitored area % 27 12

13 How Did Flow Monitoring Improve Evaluation of Wet Weather Improvement Alternatives? Allowed Union County to map out the rehabilitation plan to reduce I/I in Crooked Creek Disproved suspicions of I/I contributed by leaks in low pressure system Provided a basis for improved hydraulic capacity analysis Led to development of cost effective improvement alternative that incorporated the I/I reduction plan and reduced size of required improvements 13

14 Increased Confidence in Modeling and Provided Firm Evidence of How System is Currently Performing Flow Meter Diameter (inches) Surcharge Depth by Event (feet) 2/22/13 2/26/13 3/11/13 3/24/13 4/4/

15 Accurate Basis For Analysis of Future Flows 15

16 How Did Flow Monitoring Improve Evaluation of Wet Weather Improvement Alternatives? Allowed Union County to map out the rehabilitation plan to reduce I/I in Crooked Creek Disproved suspicions of I/I contributed by leaks in low pressure system Provided a basis for improved hydraulic capacity analysis Led to development of cost effective improvement alternative that incorporated the I/I reduction plan and reduced size of required improvements 16

17 Base Improvement Alternative Considered Facility Upgrades, Storage, Flow Routing 17

18 Design Storm Flows Based on Flow Data Critical for Sizing Alternative Components New Transfer PS 2.5/16.7 mgd 1.0/5.0 mgd 1.5/2.5 mgd Wet Weather Flows 8.1 MG Storage 18

19 Design Storm Flows Based on Flow Data Critical for Sizing Alternative Components New Transfer PS 2.5 mgd 1.0 mgd 1.5 mgd 19

20 Flow Monitoring Data Basis for Checking WRF Operating Strategy Two options 1.9 mgd ADWF daily no wet weather treated 1.0 mgd ADWF plus 5 mgd during large wet weather events 20

21 Design Storm Flows Based on Flow Data Critical for Sizing Alternative Components New Transfer PS 16.7 mgd 5.0 mgd 2.5 mgd Wet Weather Flows 8.1 MG Storage 21

22 Flow Monitoring Data Critical to Storage Tank Sizing Q WW = Wet Weather Flow to PS Q E Equalization Storage Q O = Overflow from Storage Q P Q WW = rainfall*r*sewered area Q E = Flow to/from equalization storage = Q WW - Q P Q P = Maximum wet-weather capacity 22

23 Predicted Number of Annual Overflow Events Historical Rainfall and I/I Used to Size Storage Facility Storage Volume (MG) 23

24 Rehabilitation Plan Reduced Size of Facilities and Saved County Money 24

25 Rehabilitation Reduced Size of Transfer Pump Station and Storage Unit Resulting in Significant Cost Savings Rehabilitation = $12 M Alternative 1 including cost of rehab saves $2M Alternative Influent Pump Station Size (MGD) Storage Size (MG) Base Alternative No Rehab Alternative 1 (Rehab of Priority 1 Sewersheds)

26 Analysis Showed That Additional Rehabilitation of Priority 2 Subbasins Did Not Translate Into Increased Savings Alternative Influent Pump Station Size (MGD) Storage Size (MG) Base Alternative No Rehab Alternative 1 (Rehab of Priority 1 Sewersheds) Alternative 2 (Rehab of Two Priority 2 Sewersheds ) Alternative 3 (Rehab of All Priority 2 Sewersheds)

27 How Can Flow Monitoring Improve Evaluation of Wet Weather Improvement Alternatives? More detailed flow monitoring allowed Union County to map out the rehabilitation plan to reduce I/I in Crooked Creek Flow monitoring disproved suspicions of I/I contributed by leaks in low pressure system Provided a basis for capacity analysis and flow routing improvement alternative that met multiple hydraulic constraints Saved County money by reducing the size of required improvements assuming the rehabilitation is performed

28 Other Benefits of Flow Monitoring for all Utilities Prioritization of sub-basins for rehab Required input for capacity analysis Post monitoring to prove I/I reduction Priorities are clearly defined and I/I reduction progress is documented, which makes the program defensible to regulators, affected citizens, and local decision makers Accurate flow and rainfall data with proper data analysis increases reliability of recommended SSO controls. SSES is minimized and sewer rehabilitation is focused only on the highest priority areas where I/I reduction will be most cost-effective and beneficial 28

29 Questions