Downtown Stormwater Treatment:

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Dennis Glenn
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1 Downtown Stormwater Treatment: Suspended Pavement System Construction and Permitting Jennifer Buzun, P.E. City of Durham, Public Works Department Stormwater Services Andrew Jones, P.E. Kimley-Horn

2 Redevelopment Issues for City Center Old Woolworth s store on site demolished. Much of the area was not impervious at the Baseline Date for the Jordan Lake rules (December 31, 2001) Thus, onsite stormwater treatment required

3 Where to Put the Stormwater Treatment Device? 100% of Parcel Occupied by Building Maybe in the Right-of Way?

street trees Credits: Tree Box Filter: Suspended Pavement Systems Not an accepted proprietary device by NC DEQ in 2014 Preferred by City s Urban

4 What SCMs Can Work in the ROW? Tree Box Filters Not an accepted propriety device by NCDEQ in 2014 City s Urban Forester doesn t like these because they constrict the roots of street trees Credits: Tree Box Filter: Suspended Pavement Systems Not an accepted proprietary device by NC DEQ in 2014 Preferred by City s Urban Forester because allows root growth Promising results from research on Silva Cells by NCSU in ion.com/tree-box-filters Suspended Pavement System: g/blog/2015/06/tracking-silvacell-tree-performance

City of Durham Permitting Guidelines Maintain drainage area divide Locate Silva Cell under that part of sidewalk that has fewest underground utilities Provide even horizontal distribution of runoff

5 City of Durham Permitting Guidelines Maintain drainage area divide Locate Silva Cell under that part of sidewalk that has fewest underground utilities Provide even horizontal distribution of runoff falling vertically from roof Mimic NCSU research Silva Cell design, to the extent possible Same soil media Internal water storage Justify method used to size surface area for Silva Cell Provide adequate by-pass system that doesn t flood Main Street Be able to bear vehicle weight (no parking = delivery trucks on sidewalk) DurhamNC.gov Follow

6 License Agreement For Private Utilities in ROW Moisture damage to Main Street paving and subgrade big concern for Public Works Engineering Division Initially wanted wall built between Silva Cell and Main Street to keep out moisture Instead: Required License Agreement The Licensee commits to pay for all damages that arise in connection with the Licensee's acts or omissions in the public Right of Way or the Licensee's System Let engineer figure out how to keep water away from Main Street Required $20K escrow money should City need to use it DurhamNC.gov Follow

7 Registering Silva Cell as an Underground Utility Recommended by Deep Root to prevent accidental damage to system by underground utility work City will be including it as an underground utility in our GIS DurhamNC.gov Follow

8 Design - Multilevel Sloping sidewalk and Roof Drain location requires two media levels Splitter box distributes evenly, acts as a forebay / pretreatment, and functions as emergency overflow.

9 Design - Liner

Not an accepted proprietary device by NC DEQ in 2014. Used the EMCs from NCSU study of two Silva Cell installations in Wilmington published in January, 2014 (J.L. Page, R.

10 Not an accepted proprietary device by NC DEQ in Used the EMCs from NCSU study of two Silva Cell installations in Wilmington published in January, 2014 (J.L. Page, R.J. Winston, and W.F. Hunt III). Used the Jordan/Falls Lake Nutrient Accounting Tool to calculate the inflow concentrations. Treatment volume: Headspace + Pore Space Modeling

11 Lesson Learned - Design in 3D The design is likely to change in plan view (unknown utilities) The design may change in profile view (building FFE) The design may change in section view (manufacturer change)

12 Lesson Learned Phasing Plan Surface Level Distribution Pipe Underdrain Pipe

13 Unknown Utilities Building FFE Roof Drains Manufacturer Changes Contractor Error Lesson Learned Margin

City Hall Durham, NC 27701 Jennifer.buzun@durhamnc.

14 Questions? Jennifer Buzun, P.E. City of Durham, Public Works Department Stormwater Services 101 City Hall Plaza, 3 rd Floor City Hall Durham, NC Jennifer.buzun@durhamnc.gov (919) , ext *30292 Andrew Jones, P.E. Kimley-Horn 300 West Morgan Street, Suite 1500 Durham, NC andrew.jones@kimley-horn.com (919) DurhamNC.gov Follow

C-10. Disconnected Impervious Surface

C-10. Disconnected Impervious Surface Design Objective Disconnected Impervious Surface (DIS) is the practice of directing stormwater runoff from built-upon areas to properly sized, sloped and vegetated