Approaches to CSO Control

1. Approaches to CSO Control Adrienne Nemura, P.E. Limno-Tech, Inc.

2. Items to Be Covered • Approaches for evaluation of controls • Calculation of 85 percent capture • Example Demonstration approach • Types of CSO controls Approaches to CSO Control

3. Approaches • The overall objective of CSO control should be to meet WQ standards and protect designated uses. • The evaluation of alternatives should be conducted in a framework that enables a reasonable assessment of controls, costs, and benefits related to the objectives. • The evaluation may be less extensive for small CSO communities. • Development and implementation of a LTCP represents a WQ-based control approach. Approaches to CSO Control

4. Approaches • Presumption approach • Demonstration approach • Watershed approach • Combination of Presumption and Demonstration approaches Approaches to CSO Control

5. Presumption Approach • Relies on performance criteria. Options are: • Average of 4 overflows per year (with discretion to add 2 additional overflows) • Elimination or capture for treatment of 85% of the volume of combined sewage in CSS during precipitation events on an "average annual basis.” • Elimination or capture for treatment of 85% of the mass of pollutants in CSS during precipitation events on an average annual basis. • Still need post-construction compliance monitoring! Approaches to CSO Control

6. 85 Percent Capture: Calculation Methods • Use model calculations • Requires continuous simulation over annual average period • Can be used in planning and determining post-construction compliance • Use metered data • Requires continuous metering at key locations and collection of data • Generally used in post-construction Approaches to CSO Control

7. Model Calculation Method • Volume of combined sewage collected in the CSS during precipitation events – runoff + sanitary sewage, or dry weather flow (DWF) • Runoff – Modeled or calculated flow entering the CSS during precipitation events • DWF – Metered or apportioned sanitary sewage in CSS during precipitation events Approaches to CSO Control

8. Calculation of 85 Percent Capture • “During precipitation events” considered to be period of rainfall producing runoff + period for CSS to drain • Period for CSS to drain can be calculated as: • Observed time for runoff to pass through CSS (approximately 6 to 12 hours) • Time until DWF returns to normal (time until it reaches ~105 to 110% of DWF) Approaches to CSO Control

9. Dry-Weather Flow in CSS 9

10. Runoff During Precipitation Events 10

11. Volume of Combined Sewage Collected in the CSS During Precipitation Events Continued for 365 days 11

12. Demonstration Approach • Permittee must demonstrate that: • Planned control program is adequateto meet WQ standards. • Remaining CSO discharges will not preclude attainment of WQ standards (TMDL may be needed if non-CSO sources are extensive). • Planned control program will provide the maximum pollution reduction benefits reasonably attainable. • Planned control program is designed to allow cost-effective expansion or retrofitting if needed. Approaches to CSO Control

13. Evaluating Conditions at Different Locations • E. Coli – number of days exceeding 126#/100ml 70 60 50 No Control 40 Alt A 30 Alt B 20 10 0 Knox Br Jade Is Oak Point Clove Br Approaches to CSO Control

14. Demonstrating Whether WQ Standards Will be Attained • E. Coli Geomean (#/100ml) April – October 250 No Control Alt A 200 Alt B 150 WQS=126 100 50 0 Knox Br Jade Is Oak Point Clove Br Approaches to CSO Control

15. Combination of Presumption and Demonstration Approaches • Selective use of both can be justified for different receiving waters, same CSS • Post-construction compliance monitoring required for both • Meeting 85% volume criteria roughly matches 4 overflows per year and the “knee of the curve” inflection point for cost-effective CSO control in some situations Approaches to CSO Control

16. Types of CSO Controls • O&M practices—Ensure effective sewer system performance • Collection system controls—Improve the collection system • Storage facilities—Add additional storage • Treatment technologies—Add conveyance, treatment processes and capacity • Low Impact Development—Control timing and volume of storm water and reduce wastewater volume Approaches to CSO Control

17. Factors Influencing Selection of Given Technology • Condition of sewer system • Wet weather flow characteristics (e.g., peak flow rate, flow volume, conc., frequency & duration of events) • Hydraulic and pollutant loading to a facility • Climate • Implementation requirements • Maintenance requirements Approaches to CSO Control

18. NMC and LTCP • Distinction is not always clear • Overlap can occur with • Maximizing storage in CSS (NMC-2) • Maximizing flow to POTW (NMC-4) • Control of solids and floatables (NMC-6) • Pollution prevention (NMC-7) • Monitoring to characterize impacts and the efficacy of CSO controls (NMC-9) Approaches to CSO Control

19. O&M Practices • Sewer inspection and testing • Manual vs. remote • Sewer cleaning • Hydraulic, mechanical, chemical • Pollution prevention • Source control • Water quality monitoring and public notification • To minimize exposure Note: Many elements of NMC are source controls Approaches to CSO Control

20. Sewer Inspection & Testing: Smoke Testing to Identify Inflow Points 20 Approaches to CSO Control

21. Sewer Cleaning: Hydraulic Cleaning Technique 21 Approaches to CSO ControlApproaches in CSO Control

22. Pollution Prevention: Storm Drain Stenciling 22 Approaches to CSO Control

23. WQ Monitoring & Notification: Warning Sign 23 Approaches to CSO Control

24. Collection System Controls • Maximizing flow to the treatment plant • Monitoring & real-time control • Inflow reduction • Sewer separation • Sewer rehabilitation • Service lateral rehabilitation • Manhole rehabilitation Approaches to CSO Control

25. Monitoring & Real-Time Control 25 Approaches to CSO ControlApproaches to CSO Control

26. Inflow Reduction: Eliminate Illegal Downspouts 26 Approaches to CSO Control

27. Sewer Separation 27 Approaches to CSO Control

28. Sewer Rehabilitation: Sewer Lining 28 Approaches to CSO Control

29. Manhole Rehabilitation 29 Approaches to CSO Control

30. Storage Facilities • In-line storage—oversized conduits and regulators; in-line tanks; parallel relief sewers • Possibility of basement backups and street flooding • Off-line storage—retention basins/tunnels to store wet weather flow for subsequent treatment • On-site storage / flow equalization—storage at WWTP to manage excess wet weather flow Approaches to CSO Control

31. In-Line Storage: Inflatable Dam 31 Approaches to CSO Control

32. Off-Line Storage: Deep Tunnel 32 Approaches to CSO Control

33. On-Site Storage: Flow Equalization Basin 33 Approaches to CSO Control

34. Treatment Technologies • Supplemental treatment • Plant modifications • Disinfection • Vortex separators • Floatables control Approaches to CSO Control

35. Supplemental Treatment: Primary Clarifier 35 Approaches to CSO Control

36. Disinfection 36 Approaches to CSO Control

37. Vortex Separator 37 Approaches to CSO Control

38. Floatables Control: Netting 38 Approaches to CSO Control

39. Low Impact Development • Porous pavement • Green roofs • Bioretention • Water conservation Approaches to CSO Control

40. Porous Pavement 40 Approaches to CSO Control

41. Green Roofs 41 Approaches to CSO Control

42. Bioretention 42 Approaches to CSO Control

43. Recent Innovations • The majority of recent technological innovations related to CSO control have enhanced existing practices, rather than developing new technologies. • Improved information management supports the selection of appropriate technologies and their cost-effective application. Approaches to CSO Control

44. Most Widely Used CSO Controls Approaches to CSO Control

45. More on Sewer Separation • Some states like Maine and Vermont strongly encourage complete separation for small CSO communities. • Separation can be expensive and disruptive, but one advantage is that the discharge of sanitary sewage is eliminated. • One disadvantage is the generation of more (probably untreated) urban storm water discharge. Approaches to CSO Control

46. CSO Technology References • Report to Congress on Impacts and Control of CSOs and SSOs http://www.epa.gov/npdes/pubs/csossoRTC2004_AppendixL.pdf • EPA Municipal Support Division Fact Sheets www.epa.gov/owm/mtb/mtbfact.htm • Rouge River National Wet Weather Demonstration Project (MI) www.wcdoe.org/rougeriver/ • Columbus Water Works National Demonstration Program (GA) www.cwwga.org/NationalPrograms/Index.htm Approaches to CSO Control