1. SPU Modeling & Monitoring
Attaining Performance in CSO and Integrated Plans
Shanti Colwell (SPU) & Dustin Atchison (CH2M), September 18, 2015

2. Outline Role of Monitoring and Modeling in CSO Site-Scale Monitoring
Basin- Scale Monitoring
Integrated Planning and Performance
Mention we monitored for flow/volume only, not WQ

3. CSO Reduction Areas (North Seattle)
Seattle is currently is currently in the middle of our CSO reduction project and is evaluating options.
This is a map of the northern part of Seattle which shows the size of the tanks needed. As small as 70,000 gallons to as large as 6 million gallons in Ballard (for Basins 150 and 152 = 6 million gallon tank). (About 63 overflows per year in Basin 152.) In Ballard, a grey/green mix is being evaluated.
Green because:
A quick GIS review indicated it was feasible, and
Ultimately, reduces tank size but also -
Can be done now, impact/CSO benefit now instead of 10 years from now
NPDES permit requires early GSI action in Ballard
Green allows community amenities to be built (e.g., traffic calming)
Addressing stormwater at the source instead of the related conveyance, pumping and O&M required for regional.

4. Green Infrastructure Evaluation Process
CSO Facility
Construction
System Modeling
Flow Monitoring
Model Development
Model Calibration
Control Volume Estimation
Compliance Flow Monitoring
GI Analysis and Modeling
GI Feasibility Analysis
GI Preliminary Evaluation
GI Prelim. Modeling & Optimization
GI Model Validation
Pilot Project Construction
Post-Const. Monitoring
Full Imple-mentation
GI Project Implementation

5. GI Modeling Modeled using EPA SWMM5
32-year long term simulations performed
Feasibility Analysis overlaid with model subcatchment delineation to develop input files

6. Basin Scale to Site Scale
How to Make GI more Efficient/Effective
How to Adjust to Local Conditions & Context
Where to Best Implement GI
What GI Practices to Implement
How Effective Can GI Be

7. Site-Scale Monitoring Goals
Quantify Infiltration Capacity
Bioretention Flow Performance
How much flow can they retain/delay?
How does the underdrain affect performance?
Combined Sewer Overflow Performance
Inform Future GSI projects
Improve design (e.g., inlets)
Verifying and/or improving modeling assumptions
Note, did not monitor water quality – because this is a combined basin

8. Two Types of Monitoring Utilized
Continuous Monitoring (Natural Storms)
Install data loggers and sensors, monitor wet season (5 min intervals)
Capture actual variable antecedent and storm conditions
Requires occurrence of large actual storm events
Accurate inflow and outflow measurement for GSI is challenging
Controlled Flow Testing (Simulated Storms)
Create known inflow using hydrant, hose and closed channel meter
Simulate an actual storm that caused a significant CSO event
Reduce measurement error, especially inflow
Testing during dry weather eliminates noise in outflow measurements
Repeatable, can be done under a variety of antecedent conditions
Allows for isolating components like individual inlets or cells
Can simulate preconstruction conditions, perform stress tests
Observing flow during dry weather very informative
Note, did not monitor water quality – because this is a combined basin
The controlled flow tests used simulated “design storms”— rainfall events with a specific pattern, depth, and duration to simulate performance under the target design objective, which in this case was CSO reduction per the regulatory standard of less than one overflow per year
Mention inlet capacity
If limited budget, controlled testing would be my pick but can only be used for flow performance, not water quality.

9. 30th Equipment
Mention MTL and ADS

10. Peak Rainfall Intensity (in/hr)
Event Date
Peak Rainfall Intensity (in/hr)
Significant Storm Period
Rainfall (in)
Duration (hr)
Recurrence
11/19/2012
0.6
2.75 12
100-year

12. Seasonal Performance ~97-98% Volume Infiltrated
% Vol. Reduction
See prior graph. Discharge during November 19 storm was estimated based on rainfall and estimated rain garden capacity from controlled test.

13. Basin-Scale Monitoring?
CSO Outfall Monitoring
GSI Before Grey Sizing: Monitor and recalibrate models
GSI With Grey: Monitor for Compliance and apply adaptive Management

14. What’s Next? Integrated Plan
Version 4 of the IP contains slightly different costs per kg/TSS : Sweeping = $23, South Park = $45, NDS = $112.

15. Focus on Creek Watersheds Water Quality Protection
Integrated Planning
Focus on Creek Watersheds
Water Quality Protection
Flow/Volume reduction preferred

16. Modeling: Monitoring: HSPF Based Continuous Models (MGS Flood)
Size to Provide Treatment:
Code: 91% of average annual flow
or Efficiency/knee of the curve 72% of average annual flow
Monitoring:
Volume Captured/Filtered
Removal of key parameters

17. Discussion