An Overview of the GWK Retention Treatment Facility and The August 11, 2014 Wet Weather Event

1. An Overview of the GWK Retention Treatment Facility and The August 11, 2014 Wet Weather Event August 19, 2014

2. Overview Elements • Brief History of the GWK Drainage District and GWK Retention Treatment Facility • Design • Operations • August 11, 2014 Wet Weather Event • Next Steps

3. GWK Drainage System

4. GWK System Map

5. GWK System Map: Clawson Vicinity Towards GWK RTF

6. GWK RTF Design: Criteria • The GWK RTF is a Pollution Control Facility that screens out sanitary trash and other solids and provides disinfection using chlorine before discharging to the Red Run Drain. • Chlorine contact time and wet weather volume storage provided using the 124 Million Gallons of storage capacity available in the facility. Slide 6

7. GWK RTF Design: Criteria • Designed to address flows from a 10-year, 1-hour design event. Peak flow rate into the GWK RTF ≈ 3.1 Million Gallons per Minute (7,000 cfs). • GWK RTF construction and upgrades were required to reduce Combined Sewage Overflows (CSOs) and be in compliance with MDEQ rules and the Federal Clean Water Act. Slide 7

8. GWK RTF Design: Extent of Pollution Control Facility Slide 8

9. GWK RTF Design: Original Influent Weir Slide 9

10. GWK RTF Operations Explained: Operator’s Walk-through Slide 10

11. August 11, 2014 Wet Weather Event: Event Statistics • WRC has a network of rain gauges that provide rainfall depth from every wet weather event. • Rain Gauge 0880 is located at the GWK RTF and is used to determine rainfall amounts for much of the GWK RTF service area. Slide 11

12. August 11, 2014 Wet Weather Event: Event Statistics • Rainfall frequency is determined by referencing published texts. • At the time of the GWK RTF design “Technical Paper 40” was a reference text. • Today. “NOAA Atlas 14” is the reference text. Slide 12

13. August 11, 2014 Wet Weather Event: Radar Rainfall Slide 13

14. August 11, 2014 Wet Weather Event: Radar Rainfall Slide 14

15. August 11, 2014 Wet Weather Event: Comparison to Design Event

16. August 11, 2014 Wet Weather Event: Effect on GWKDD and RTF

17. August 11, 2014 Wet Weather Event: Effect on GWK RTF

18. August 11, 2014 Wet Weather Event: Effect on GWK RTF

19. August 11, 2014 Wet Weather Event: Effect on Red Run Drain Red Run at GWK Outlet (Dequindre)

20. August 11, 2014 Wet Weather Event: Effect on Red Run Drain Red Run at Mound Red Run at Van Dyke

21. August 11, 2014 Wet Weather Event: WRC Next Steps • Collect community data from basement flooding • Hydraulic study of the GWK facility Slide 21

22. Oakland County Executive Office Announcement • “The flooding impacted thousands of individuals who now have many questions about how to recover from this disaster. The Multi-Agency Resource Center (MARCs) will be an opportunity to meet with experts who can answer some of those questions.” • – L. Brooks Patterson • The Southfield MARC will be open 11 a.m. – 7 p.m. Wednesday and Thursday at the Southfield Pavilion, 26000 Evergreen Road south of the I-696 expressway. Slide 22