Oregon Department of Transportation Stormwater Management Initiative: Meeting New Challenges

1. Oregon Department of Transportation Stormwater Management Initiative:Meeting New Challenges Presented by: Jennifer Sellers, ODOT and Ronan Igloria, HDR ACWA Stormwater Committee Meeting November 27, 2007

2. ODOT’s Goals Develop a streamlined stormwater treatment program to: • Meet all regulatory needs • Provide ODOT with certainty regarding scope, schedule, and budget • Result in an overall environmental benefit and promote species recovery

3. Components of the Stormwater Initiative Work Plan • Streamline DEQ Stormwater Management Plan Approval Process • Develop Process for ODOT Projects with T&E Species and Stormwater Effects • Develop a watershed-based mitigation program to offset stormwater effects that cannot be treated “on-site” with reasonable efforts

4. Develop Process for ODOT Projects with Stormwater Effects Problem Statement Stormwater has become a major impediment to efficient ESA consultation process due to: • Lack of congruence in water quality requirements between DEQ and NMFS • Changing thresholds for effects determinations in ESA Section 7 consultations • Changing science regarding the action area for dissolved metals (e.g. copper) • Lack of early coordination to identify emerging issues (i.e., new pollutants of concern)

5. Develop Process for ODOT Projects with Stormwater Effects Proposed Strategy/Process • Compile and synthesize literature on BMPs for stormwater treatment • Define water quality design storm • Develop water quantity guidance

6. Develop Strategy/Process for ODOT Projects with Stormwater Effects Proposed Strategy/Process (cont.) • Incorporate minimization of stormwater impacts into project design (Low Impact Development techniques) • Select most appropriate stormwater treatment BMPs for each project • Develop a BMP Selection Tool and User’s Guide

7. Develop Strategy/Process for ODOT Projects with Stormwater Effects Proposed Strategy/Process (cont.) • Developing ESA Effects Determination Guidance • Exploring expanding SLOPES IV and/or ESA programmatic consultation • Will develop a performance measurement and reporting method

8. Develop Strategy/Process for ODOT Projects with Stormwater Effects Anticipated Benefits for Regulatory Agencies • Meet regulatory requirements • Well-defined terms and conditions that allow for flexibility in application • Protect ESA-listed fish • Protect Oregon’s water quality and wetland resources

9. Develop Strategy/Process for ODOT Projects with Stormwater Effects Anticipated Benefits for ODOT • Certainty in project development and construction • Reduction in project delays • Support ODOT’s sustainability goals

10. Develop Strategy/Process for ODOT Projects with Stormwater Effects Where are we now? • BMP Summary Reports Completed • BMP Selection Tool in development • BMP Selection Tool Users’ Guide to be developed

11. Develop Strategy/Process for ODOT Projects with Stormwater Effects Where are we now (cont.) • Draft Water Quality Design Storms near completion • Water Quantity Guidance near completion • ESA Effects Determination Guidance for Water Quality near completion

12. Design Storm Evaluation • Water Quality (and Water Quantity) • Science-based • Geography-specific (hydrologic zones) • Economics (cost-benefit) • Effects on facility size • Ultimately a “Policy” decision

13. Water Quality Design Storm • Based on analysis of rainfall data from >50 precipitation stations across the state’s nine climate zones • Cumulative percent of total rainfall vs. storm size • Percentile of storm size • Percent rainfall treated • “Sensitivity Analysis” for sizing treatment facilities

14. Water Quality Design Storm

15. Water Quality Design Storm

16. Water Quality Design Storm

17. Water Quality Design Storm

18. Water Quality Design Storm

19. Water Quality Design Storm • ANOVA Analysis was used to group similar climate zones • Design storm corresponding to 85% cumulative rainfall results in: • >95% of rainfall treated • >97th percentile storm size • Facility size is most “sensitive” to design storms when increasing from 90% to 95% cumulative rainfall design storm

20. Water Quality Design Storm • Use the mean storm size corresponding to 85% cumulative rainfall for each station in the climate zones. • Define a water quality design storm for 5 zones

21. BMP Selection • Best Available Technology • BMPs included in ODOT Hydraulics Manual • Emerging and LID-type BMPs (e.g. bioslope, soil amendments) • Key selection criteria (metrics) • Treatment suitability • Physical site suitability • Maintenance • Cost • Resources, risk and public perception

22. BMP Selection • Conceptual Stormwater Treatment Design Strategy • SW Strategy Figure.pdf • Schematic of BMP Selection Tool • Selection Tool Schematic.pdf

23. BMP Selection • Treatment Suitability • High variability with “effectiveness” data • Based on treatment mechanisms • Hydrologic attenuation • Sedimentation/density separation • Sorption • Filtration • Uptake/storage • Microbially-mediated transformation

24. BMP Selection

25. BMP Selection

26. BMP Selection Priority BMPs for Treating Dissolved Metals • Treatment Mechanisms • Hydrologic Attenuation (infiltration) – preferred • Sorption, uptake, microbial transformation • “Preferred” BMPs • Infiltration trench • Bioretention • Bioslope (“Ecology Embankment”) • Amended Swale and Filter Strip

27. Next Steps Finalize Metric Ratings Apply to Pilot Projects Integrate into an “Electronic Tool” Develop Users’ Guide BMP Selection

28. Questions?

29. Water Quantity Design Storm • Match pre-project hydrology from a low-discharge, high frequency event to a high-discharge, low-frequency event • Low discharge event: when substantial bed-load begins to occur • High discharge event: bank over-topping event; or when amount of impervious area has little effect on stream discharge (10-year/24-hour event)

30. Water Quantity Design Storm • Low discharge event: when substantial bed-load begins to occur; Studies have shown: • 2/3 of bankfull discharge • 50% of 2-year/24-hour event • Average bankfull discharge event: • Eastern OR = 1.5-year/24 hour event • Western OR = 1.2-year/24 hour event • 64 streamflow gauges were analyzed from 8 flood frequency regions defined by USGS

31. Water Quantity Design Storm • Low Discharge End Point: • West Region: 42% of 2-year,24 hour event • SE, NE, NC Regions: 48% of 2-year, 24-hour event • E-Cascades: 56% of 2-year, 24 hour event • High Discharge End Point: • 10-year, 24-hour event for incised streams; or • Event corresponding to bank overtopping recurrence interval for minimally incised streams

32. Water Quantity Design Storm • Design Criteria: • Minimum ¼ acre or 0.5 cfs increase in discharge from project site • Considerations for Minimum orifice size