Major retrofits – reducing pollutant loading to Comfort Lake using iron filings

1. Major retrofits – reducing pollutant loading to Comfort Lake using iron filings David Filipiak & Jeremy Nielsen, SRF

2. Presentation Outline Project Overview Design Goals/Considerations Construction/Techniques Monitoring Results Conclusions/Lessons Learned

3. Project Overview

4. Project Overview Site Parameters • 64.9 acres of existing commercial/residential drainage area (60% Impervious Surface) • 36.5 acres of project area (50% Impervious Surface)

5. Design Goals/Considerations Design Goals/Constraints • Goals • Match Pre-development discharge rates • No net increase in runoff volume (from Pre-development conditions) for a 2-year 24-hour storm • No net increase in Total Phosphorous loading • Constraints • High ground water • Shallow storm sewer • Flat topography

6. Iron Filing Sand Enhancement Enhanced Design • Added iron filings sand into the filtration basin design • Bioengineered soil primary filter mechanism/iron filing sand secondary filter mechanism • Increase the depth of water that will permeate through the filter material by 50%

7. Design

8. Design Goals/Considerations Enhanced Design considerations • Standing water in upstream pipes – added mechanical valve to drain down pond in fall • Vegetated basin drawn down – modified soil to higher sand content to assist drainage given added water • Iron filing content – used mechanical mixing for consistent mix

9. Design Goals/Expectations Expected Performance

10. Construction/Techniques Challenging Subgrade Soils

11. Construction/Techniques Buried construction debris

12. Construction/Techniques Fine Filter Aggregate

13. Construction/Techniques Mixing of iron enhanced sand

14. Construction/Techniques Mixing of iron enhanced sand

15. Construction/Techniques Placement of tile/filter aggregate

16. Construction/Techniques Placement of Iron Enhanced Sand

17. Final Product – 1 year Later Pretreatment Basin Filtration Basin

18. Monitoring/Results Monitoring Locations • Inlet • Connection between the pond/filtration basin • Tile outfall • First year of a 3 year program

19. Monitoring/Results First year results • increase on concentrations and loads of TP, SRP and TSS from the inlet of the iron-enhanced infiltration basin to its outlet • The pond operates within expected removal rates • Some orange water has been detected periodically at the outlet, indicating potential Ferric hydroxide coming out from the iron fillings • Increases in loading decreased with similar storm events over the course of the year • Any final conclusions about the effectiveness of the filtration basin based on the first year monitoring is premature since these systems typically require at least a year to stabilize (vegetation/soils settling) and reach steady state operation

20. Conclusions/Lessons Learned • Drying out iron may impact vegetation over the tile system (may impact long-term viability of vegetation) • It takes time to see results with vegetated facilities Iron systems need to dry out – challenging in wet conditions or in poor soils Tailwater conditions for outlet could impact performance

21. Project Partners

22. Questions? David Filipiak – dfilipiak@srfconsulting.com Jeremy Nielsen – jnielsen@srfconsulting.com