C R E A T I N G A N D D E L I V E R I N G B E T T E R S O L U T I O N S

1. C R E A T I N G A N D D E L I V E R I N G B E T T E R S O L U T I O N S In-Ground Disposal of Captured Stormwater: Is it Worth It? by Scott Schillereff, Ph.D., P.Geo., EBA, Kelowna, BC Darryl Arsenault, M.Sc., R.P.Bio., EBA, Kelowna, BC Leon Gous, P.Eng., MBA, GM, Community Services, City of Vernon, BC E B A E N G I N E E R I N G C O N S U L T A N T S L T D .

2. BC Stormwater Planning Guidebook Released May 2002 - endorsed by BC Gov., stakeholder groups and BC municipalities Objective: “To offer a common sense, effective and affordable approach to integrated stormwater management” Best management practice

3. Source: Stormwater Planning - A Guidebook for British Columbia, 2002

4. Source: Stormwater Planning - A Guidebook for British Columbia, 2002 If you capture it - the up side:

5. If you capture it - the up side:

6. If you let it go - the downside:

7. If you let it go - the downside:

8. Tools and Techniques: Drywells Infiltration Trenches Soakage Trenches Green roofs Permeable pavements/driveways Other infiltration structures

9. Source: Stormwater Management Manual, Portland, Oregon, 2002 Tools and Techniques:

10. Source: Stormwater Planning - A Guidebook for British Columbia, 2002 Tools and Techniques:

11. Source: Stormwater Management Manual, Portland, Oregon, 2002 Tools and Techniques:

12. Source: Stormwater Management Manual, Portland, Oregon, 2002 Tools and Techniques:

13. So, capture seems like a good idea,but...What are the global costs of capture/reuse (best practice) vs. release (standard practice)?

14. Income Statement Approach • An Income statement is a measure of financial performance over a period of time • Expressed as: Revenues (asset flow, reduced liabilities) - Expenses (costs, increased liabilities) =Net (gain or loss over the period) Compare Income statements for in-ground disposal with standard conveyance for an urban sub-basin over a municipal life cycle

15. Framing the question - parameters and constraints Control area = urban subbasin - Neighborhood in Okanagan, 100 ha, 400 lots, lot area 60 ha, roads etc. 40 ha Time period 20 years; periodic maintenance (replacement) Annual precip. ~ 400 mm; 75% capture = 300 mm Existing storm sewerage (constructed for severe design storm) Global cost analysis (regardless who pays)

16. 1 km Stream 400 Lots 1 km

17. In-ground disposal “Revenues”: reduced sewer maintenance costs reduced stream erosion, maintain base flow maintain/enhance recreational fishing value enhanced residential/parkland values recharge to aquifer, avoid lowering water table reduced irrigation water costs reduced need for irrigation infrastructure Development Cost Charges (DCC) benefits

18. In-ground disposal “Expenses”: capital costs for in-ground structures periodic O&M costs design costs increased potential for slope failures (slides) municipal review/approval costs (time)

19. Standard conveyance disposal “Revenues”: • reduced design/approval costs • quicker, cheaper installation (tie in to storm sewer)

20. Standard conveyance disposal “Expenses”: • stream degradation and restoration cost • stream channelization capital costs • increased O&M costs • loss of recreational fishing value, income • degraded property values (less appreciation) • irrigation infrastructure costs • irrigation water costs • degraded stream water quality (1st flush events)

23. Income Statement Summary over 20 yr In-ground disposal: Net Gain ~$7.0 M Std Conveyance: Net Loss ~$9.4 M Differential: >$16 M over 20 years

24. Conclusions: Coarse economic analysis shows strong cost benefit for in-ground disposal Global economic benefit of >$800K per year for this test scale. Different benefit values expected for other scenarios (e.g., rural, dense urban, retrofit) A strong driver is who pays (another tale…)