A Tool for Determining the Effectiveness and Whole Life Costs of BMPs

1. A Tool for Determining the Effectiveness and Whole Life Costs of BMPs Presentation to: 2008 Colorado Association of Stormwater and Floodplain Managers (CASFM) Conference Presented By: Chris Olson, E.I.T. Larry A. Roesner, P.E., PhD Colorado State University Ben Urbonas, P.E., D.WRE Urban Watersheds Research Institute

2. Presentation Outline • Challenges and Needs • Project Objectives • The Tool – How it Works • Applications • Acknowledgements • Questions

3. Challenges and Needs Challenge: Municipalities and other stormwater management agencies will continue to face regulatory and budget constraints. BMP planning must consider: • Pollutant Load Reduction • Runoff Reduction (total volume and peak flow) • Long-term Costs Need: Effective means for planning stormwater management strategies. “Which BMPs will allow the agency to meet regulations while minimizing cost?”

4. Challenges and Needs Challenge: How do we predict BMP effectiveness for planning purposes? • Existing models typically use “percent removal” values for pollutant load reduction which can be misleading • Runoff volume reduction (from infiltration, ET, etc.) is typically estimated based on complex, fundamental governing equations Need: Develop a simple method to predict BMP effectiveness using empirical information.

5. Challenges and Needs Challenge: Typically, “least-cost” BMPs are selected based on initial/capital costs only. Long-term maintenance and rehabilitation costs are not considered. Need: Develop/improve maintenance and rehabilitation costs estimates so as to make economic decisions based on whole life costs.

6. Challenges and Needs Challenge: Existing stormwater models are complex, user-intensive, and typically not well understood by decision-makers. Need: A model that is easy to use, with results that are comprehendible by decision-makers, and that is appropriate for planning-level purposes.

7. Project Objectives • Research/develop/improve initial, maintenance and rehabilitation costs for various BMPs • Develop an algorithm to predict pollutant loading and runoff volume reduction to receiving waters using various BMPs (i.e. BMP effectiveness) • Incorporate these into an Excel-based model (tool), appropriate for planning purposes, that can be used and understood by engineers, planners, developers, etc.

8. The Tool – How it Works • Excel-based • Similar to other UDFCD spreadsheet tools • Primary processes are programmed in VBA 8

9. The Tool – How it Works • Information contained on multiple, color-coded tabs • Table of contents describes each tab 9

10. The Tool – How it Works (Inputs) 10

11. The Tool – How it Works (Outputs) Pollutant load reduction to receiving waters Annual runoff volume reduction Net present value of whole life cycle costs 11

12. The Tool – How it Works(Report) 12

13. The Tool – How it Works(Report) 13

14. The Tool – How it Works(BMP Effectiveness) Watershed Data Rainfall Data Legend User-Defined Data Default/User-Editable Values Calculated Values Annual Runoff Volume 85% Treated by BMP (annually) BMP 15% Bypasses BMP (annually) BMP Discharge Volume BMP Volume Loss/Attrition Runoff EMCs Effluent EMCs Annual Pollutant Mass Entering Waterbody 14

15. The Tool – How it Works (BMP Effectiveness) Annual Runoff Volume = Annual Precipitation * Contributing Area * Runoff Coefficient Runoff Coefficients computed using UDFCD equations based on soil type and imperviousness BMP Volume Loss/Attrition = Annual Runoff Volume * 85% * %Volume Reduction % Volume Reduction values are based on empirical data collected and analyzed by UDFCD BMP Discharge Volume = Annual Runoff Volume * 85% * (1-%Volume Reduction) Annual Pollutant Mass Entering Waterbody = Annual Runoff Volume * 15% * Runoff Event Mean Concentration + BMP Discharge Volume * Effluent Event Mean Concentration • Runoff Event Mean Concentrations from UDFCD empirical data • Effluent Event Mean Concentrations from International BMP Database 15

16. The Tool – How it Works (Whole Life Costs) Watershed Data Rainfall Data BMP Selection BMP Size & Quantity Cost Information Capital Costs Rehabilitation Costs Maintenance Costs Administrative Costs ENR CCI Inflation Rate Rate of Return Legend User-Defined Data Default/User-Editable Values Calculated Values Whole Life Cycle Costs (Net Present Value) 16

17. The Tool – How it Works (Whole Life Costs) BMP Size(volume–based) = WQCV * Contributing Area * Additional Storage Factor • Water Quality Capture Volume is computed using UDFCD methods • Additional storage factor is defined in UDFCD Storm Drainage Criteria Manual BMP Size(Flow–based) = Runoff Coefficient * Rainfall Intensity * Contributing Area • Modified methods for determining rainfall intensity and time of concentration are provided in UDFCD Storm Drainage Criteria Manual BMP Number = (Contributing Area * Effective Imperviousness) / BMP Density • Effective Imperviousness accounts for source controls that minimize DCIA • BMP Density is defined in units of impervious acres 17

18. The Tool – How it Works (Whole Life Costs) Capital Costs = (1 + CEA) * (C + XUα) + (LC * BMPsize * LCFCTR) CEA = factor accounting for contingencies/engineering/administration (%) C = base cost ($) X = unit cost ($ per unit) U = units α = economy of scale factor LC = land cost ($ per acre) LCFCTR = factor relating BMP size to the area of land consumed by BMP Example 18

19. The Tool – How it Works (Whole Life Costs) Maintenance Costs (annual) = Freq * [Eff * Pers *(Rate + Rate * OH) + Eff * Equip + OC] * (BMPsize * UFCTR) UFCTR = factor relating BMP size to units of maintenance Freq = frequency of maintenance per year Eff = maintenance efficiency (units per hour) Pers = number of personnel Rate = hourly labor rate ($) OH = overhead factor (%) Equip = hourly equipment costs ($) OC = other unit costs ($ per unit) Example: Sediment Removal from Hydrodynamic Separator 19

20. The Tool – How it Works (Whole Life Costs) Rehabilitation Costs = RehabFactor * Capital Costs • RehabFactor = percentage of capital costs • Capital Costs = original capital costs of unit • Rehabilitation costs are applied at intervals defined by the user (i.e. every 25 years) Administrative Costs = AdminFactor * Maintenance Costs AdminFactor = percentage of maintenance costs Maintenance Costs = annual maintenance costs 20

21. The Tool – How it Works(Whole Life Costs) Total Annual Costs n = year of analysis CapCosts = sum of all capital costs RehabCosts = sum of all rehabilitation costs MaintCosts = sum of all maintenance costs AdminCosts = sum of all administrative costs IR = inflation rate (%) Net Present Value Costs n = year of analysis TC = total annual costs for year “n” ROR = rate of return (%) 21

22. Questions? 22

23. Application/Demonstration ** The tool is still being refined and tested, therefore the results of these demonstrations should not be taken as definitive at this time** Large-Scale (640 acre), Planning-Level Application Objectives • Evaluate costs and effectiveness of implementing extended detention basins vs. hydrodynamic separators • Evaluate extended detention basins over different scales of implementation 23

24. Application/Demonstration Watershed 24

25. Application/Demonstration BMP Scenario 1 – Extended Detention Basins • One basin treating each subarea 25

26. Application/Demonstration BMP Scenario 2 – Hydrodynamic Separators • Each treating 5 impervious acres 26

27. Application/Demonstration BMP Scenario 3 – Extended Detention Basins • Treating entire watershed with one “regional” basin 27

28. Application/Demonstration (Results) * Preliminary results only 28

29. Application/Demonstration * Preliminary results only Results 29

30. Application/Demonstration User may edit cost variables in blue cells Cost curve is automatically generated How to edit cost information (Capital Costs) 30

31. Application/Demonstration User may edit cost variables in blue cells How to edit cost information (Maintenance costs 1 of 2) 31

32. Application/Demonstration User must enter an equation to relate BMP size to maintenance units Annual costs are updated How to edit cost information (Maintenance costs 2 of 2) 32

33. Acknowledgments Funding provided by: • Urban Drainage and Flood Control District • Urban Watersheds Research Institute • City of Aurora • City of Denver • City of Lakewood • Arapahoe County • City of Pueblo • Colorado Stormwater Council

34. Acknowledgments Model review and testing provided by: • Ben Urbonas – UDFCD/UWRI Information provided by: • Tom Williams and staff (Town of Parker) • John Burke and staff (City of Westminster) • David Van Dellen and staff (Town of Castle Rock) • Terry Baus, Lupe Martinez and staff (City of Denver) • Joe Chaplin and staff (City of Loveland) • Alan Searcy and staff (City of Lakewood) • Jim McCarthy and staff (City of Arvada) • Bruce Rabe and staff (Denver RTD)

35. Questions?