1. Case Study: Evaluating Retrofit Urban Best Management Practice Performance and Lessons Learned
Nick Muenks, Marc Leisenring, Mark Willobee – Geosyntec Consultants, Inc.
Nicki Fuemmeler - Boone County, Missouri, Resource Management
Jessie Fears – Knoxville, TN

2. Outline Project Background Project Objectives
Project Design – Step Pool
Project Design – Bioretention
Field Sampling
Results
Lessons Learned

3. Background Hinkson Creek Impairment Reason TMDL (2011)
On 303(d) List since 1998
Aquatic life impairment
Impairment Reason
Urban runoff sources
Pollutants unknown
TMDL (2011)
Reduce stormwater runoff
Help “No longer impaired”
Hinkson Creek has been on Missouri 303(d) list due to aquatic life impairment from unknown toxicity.
But the impairment was attributed to urban runoff sources.
TMDL presumed that sufficient reduction in urban runoff will result in WQ improvements such that Hinkson Creek will no longer be impaired.

4. Characterize reduction of common urban stormwater pollutants
Project Objectives
Characterize reduction of common urban stormwater pollutants
Quantify runoff volume reduction
Implement BMPs and study their performance
Pollutant load reductions
Hydrologic response
Variety of storm events over several years
Because performance of current BMPs have not been field validated wrt runoff volume reduction and water quality improvement, Boone County wanted to determine efficiency of two BMPs, step pool and bioretention.

5. Owned and operated by the City
Existing Conditions
Grissum Building
10 acres
Industrial operations
No stormwater management
Owned and operated by the City
BMPs constructed in Sept and step pool was monitored through Dec
Bioretention monitoring is ongoing. A total of 11 rain events captured through Feb

6. Project Design Two BMPs implemented Bioretention cell Step pool system
November 2012 – January 2015
11 rainfall events
Step pool system
September 2012 – December 2014
20 rainfall events
The step pool BMP was designed to stabilize an eroded drainage ditch receiving continuous flows from the City of Columbia’s power plant (Power Plant) and storm flows from both the Power Plant and Grissum Building properties.

7. Project Design Step pool system Bioretention
Treatment area – 2.2 acres
With sand filters
Bioretention
Treatment area – 1.3 acres
With underdrains

8. Project Design – Step Pool

9. Project Design – Step Pool

10. Project Design – Step Pool

11. Project Design – Bioretention

12. Project Design – Bioretention

13. Min. antecedent dry period
Field Setup
Auto Sampler
Hach Sigma 900 max
Installed at inlet and outlet
H-flumes for flow
Storm Event
>0.2 inches rain in 24-hours
Tipping bucket rain gauge
Min. antecedent dry period
6 hours
Bioretention – No ponded water for a valid sampling event.
Each sampler was equipped with an ultrasonic sensor to measure depth of flow.

14. Field Setup Ultrasonic Sensor Records collected
To measure depth of water
At inlet and outlet
For flow computations
Records collected
Water level
Flow
Precipitation
Every 5 minutes
One of the samplers at each of the BMPs was equipped with a tipping bucket rain gauge that loged precipitation event’s size and intensity.

15. Field Sampling Sampling methodology Flow-weighted composite samples
Event mean pollutant concentrations
Sample aliquots composited into a 2.5 gal bottle
Constant flow volume/ variable time approach
All samples were containerized, preserved and handled per QAPP and lab quality control manual.
The target pollutants selected for the study were anticipated to be present given the urban/industrial land use of the Grissum Building.

16. Field Sampling
Target pollutants

17. Field Sampling Laboratory analyses Standard analytical methods
Methods for the Examination of Water and Wastewater
40 CFR 136

18. Baseline Sampling Results
Two baseline events were sampled for background concentrations for the continuous flow generated by the power plant.
Baseflow sample results indicate low total suspended solids (TSS) concentrations but total dissolved solids (TDS) results higher than most storm EMCs. Comparison of inlet and outlet EMCs show most parameters had reductions with the exception of total nitrogen. Total nitrogen (TN) concentrations were relatively high compared to storm sample EMC’s and show a slight increase from inlet to outlet. Metals concentrations were not detected or at relatively low compared to storm sample EMCs.

19. Precipitation and Flow
Step pool storm monitoring occurred over a range of hydrologic conditions. Table presents the hydrologic factors (e.g. antecedent dry period, rainfall totals, rainfall intensity and storm duration) that affected collection of EMC samples. Antecedent dry periods ranged from 17 hours to over 19 days with the median dry period of about 6 days preceding a monitoring event. Rainfall totals ranged from 0.25 to 1.67 inches with a median of 0.63 inches. Ranging from 0.24 to 4.2 inches per hour maximum rainfall intensity affected a number of storm event samples by producing overland flows that entered the step pool between the inlet and outlet samplers. The duration of storm events ranged from 0.5 hour to 21 hours with the median storm lasting approximately 3 hours.

20. Step Pool Maturation
July 2013
July 2014

21. Results – Step Pool

22. Results – Step Pool

23. Flow Reduction

24. Results – Bioretention

25. Results – Bioretention

26. Results – Bioretention

27. Results – Bioretention

28. Results – Bioretention

29. Results – Bioretention

30. Flow Reduction
0.83 inches of rain in 0.8 hours.

31. Annual Average Removals
Monte Carlo simulation was used
Predicted annual average pollutant reductions
Grissum
Building BMP
TSS Load
Reduction
(tons/yr)
TP Load
(lbs/yr)
TN Load
Step pool 25 24 79
Bioretention 40
399 78

32. Lessons Learned Step Pool Conveyance System Bioretention
Mature vegetation enhances pollutant removal efficiency
Routine maintenance is key for gathering representative data (see images
Bioretention
Establish a robust maintenance program prior to implementation
Proper outlet flow monitoring design is important – must consider accurately measuring the entire range of flows (infiltrated vs overflow)

33. Bioretention - Maintenance

34. Gravity Flow Media Filter Schematic (hydraulic failure mechanisms)
Bioretention - Design
Gravity Flow Media Filter Schematic (hydraulic failure mechanisms)

35. Bioretention – Enhanced Design
1) Empty Media Bed
2) Media Bed Filling