Onondaga County’s 2010 Porous Pavement ProjectsMeeting Stormwater Goals while Managing Costs

March 17, 2011Joanne M. Mahoney,

County Executive

Dan Wible, P.E., LEED APSenior Project Engineer

www.SaveTheRain.us

Presentation Outline• Case Studies:

• City Lot #21 (formerly the “Farmer’s Market Lot”

• City Lot #3• Pearl Street Lot (DOT)• Creekwalk

• Case Study Topics:• Design Components / Goals• Pre/Post-Construction Photos• Costs and Metrics Summary• Lessons Learned

Parking Lot #21 (Formerly “Farmer’s Market Lot”)

Case Study: City Lot #21 (formerly the “Farmer’s Market Lot”)

• Design Components• Costs and Metrics Summary• Lessons Learned

Case Study: City Lot #21 (formerly the “Farmer’s Market Lot”)

• Design Components:• 5,000sf infiltration system

• Tree trench (2,000sf) with porous pavers and 36” of CU-Structural Soil

• Aggregate infiltration bed under standard asphalt (31” deep)

• Inlet filter inserts• Entire lot repaved (standard asphalt) and

restriped (6 more spaces)• Two outlet control structures with weirs

(connection to existing storm sewer)• Infiltration testing yielded a rate of 20 in/hr

Case Study: City Lot #21 (formerly the “Farmer’s Market Lot”)

• Design Components:• Impervious area managed: 26,250sf• Infiltration area: 5,000sf (loading ratio of

5.3:1)• Runoff capture goal (1”): 2,190cf• 6 new trees• Total soil: 6,000cf (1,000cf per tree)• Total static storage capacity: 4,200cf

(equates to around 2.1” of runoff capture)

Parking Lot #21 (Formerly “Farmer’s Market Lot”)

Before

After

CSO Area: Clinton

Case Study: City Lot #21 (formerly the “Farmer’s Market Lot”)

• Design Components / Goals• Costs and Metrics Summary• Lessons Learned

Case Study: City Lot #21 (formerly the “Farmer’s Market Lot”)

• Total Project Cost: $188,046• Total Estimated CSO Reduction: 328,000 gal• Cost per CSO Reduction: $0.57 per gal

Case Study: City Lot #21 (formerly the “Farmer’s Market Lot”)

• Design Components / Goals• Costs and Metrics Summary• Lessons Learned

Case Study: City Lot #21 (formerly the “Farmer’s Market Lot”)

• Stormwater Details and Specifications• Concrete structures preferred• Overflow weir plates • Concerns over inlet filter inserts

(maintenance)

Case Study: City Lot #21 (formerly the “Farmer’s Market Lot”)

• Trees and Plantings• Temporary maintenance: emphasize/enforce

temporary irrigation and initial pruning• Species selection and maintenance streamlined

in the future with the City Arborist

Case Study: City Lot #21 (formerly the “Farmer’s Market Lot”)

• Subsurface Materials• Infiltration bed stone availability: NYSDOT #3A

is typically the cleanest, most available stone in the size range desired

• CU-Structural Soil Handling/Acceptance: ensure contractor provides appropriate cover and maintenance, and perform testing if needed

• Porous paver edge termination

Porous Pavement / Infiltration Practices in Onondaga County, NY

• Design Assumptions / Guidelines:• Static storage of first inch of runoff• Maximum loading ratio of 10:1 (impervious

area to infiltration area); 5:1 is preferred• Geotextile liner separating rock from soil

(non-woven or woven… or sand?)• Impervious liner where needed (proximity

to utilities, buildings, etc)• Observation well and cleanouts • Perforated distribution pipe and/or

underdrain

Porous Pavement / Infiltration Practices in Onondaga County, NY

• More Design Assumptions / Guidelines:• Dewater within 72 hours• Level bed/trench bottom• Maximum surface grade change of 1-2 feet;

steeper sloped areas may warrant a change in bottom elevation (via berms or other)

• Upper 3” of the infiltration bed subgrade should be scarified prior to bed installation (if necessary)

• Total facility depth should between 24-31 inches (frost consideration)

• Protect existing utilities

Porous Pavement / Infiltration Practices in Onondaga County, NY

• More Design Assumptions / Guidelines:• Setbacks:

• 10ft to buildings with basements• 3ft to buildings without basements• 3ft from utility structures, vents, poles,

etc

City Parking Lot #3

Lot #3

Porous ConcreteCaptures over 700,000 gallons of stormwater annually

CSO Area: Erie Blvd

Case Study: City Lot #3

• Design Components / Goals• Costs and Metrics Summary• Lessons Learned

Case Study: City Lot #3

• Design Components:• 8,380sf infiltration system

• Tree trench with 36” of CU-Structural Soil• 6” porous concrete / aggregate

infiltration bed (23” deep) • Interior tree plantings• Inlet filter inserts and sumps

• Entire lot repaved (standard asphalt) and restriped

• One outlet control structure with removable weir (connection to existing storm sewer)

• Infiltration testing yielded an average rate of 0.48 in/hr (0.24 in/hr used for design)

Case Study: City Lot #3

• Design Components:• Impervious area managed: 38,507sf• Infiltration area: 8,380sf (loading ratio of

4.6:1)• Runoff capture goal (1”): 3,209cf• 23 new trees• Total soil: 7,650cf (333cf per tree, not

including existing soil volume along edge)• Total static storage capacity: 3,392cf

(equates to around 1.1” of runoff capture)• Dewatering time: 72 hours (100-year

storm)

Case Study: City Lot #3

• Design Components / Goals• Costs and Metrics Summary• Lessons Learned

Case Study: City Lot #3

• Total Project Cost: $239,102• Total Estimated CSO Reduction: 625,000 gal• Cost per CSO Reduction: $0.38 per gal

Case Study: City Lot #3

• Design Components / Goals• Costs and Metrics Summary• Lessons Learned

Case Study: City Lot #3

• Stormwater Details and Specifications• Inlet restoration – check if necessary

• Porous Concrete• Test pad quality control

• Letter to contractor noting concerns with aggregate, water retarder, water content

• Site installation permitted as 2nd “test pad”• Cold weather placement: 7 days curing time

per specified temperature requirements

Pearl Street Parking Lot

Pearl Street Parking Lot

CSO Area: Franklin FCF

Case Study: Pearl Street Lot

• Design Components / Goals• Costs and Metrics Summary• Lessons Learned

Case Study: Pearl Street Lot

• Design Components:• 25,300sf infiltration system

• Porous asphalt (1.5”) on 3” of asphalt treated permeable base (ATPB)

• Aggregate infiltration bed under both standard and porous asphalt (24” deep)

• Inlet filter inserts and sumps• Entire lot repaved (standard asphalt) and

restriped• One outlet control structure with removable

weir (connection to existing combined sewer)• Infiltration testing was variable, but yielded an

average rate of 7 in/hr (2 in/hr used for design)

Case Study: Pearl Street Lot

• Design Components:• Impervious area managed: 73,172sf• Infiltration area: 25,300sf (loading ratio of

2.9:1)• Runoff capture goal (1”): 6,098cf• Total static storage capacity: 10,120cf

(equates to around 1.7” of runoff capture)• Dewatering time: 24 hours (100-year

storm)

Case Study: Pearl Street Lot

• Design Components / Goals• Costs and Metrics Summary• Lessons Learned

Case Study: Pearl Street Lot

• Total Project Cost: $396,772• Total Estimated CSO Reduction: 915,000 gal• Cost per CSO Reduction: $0.43 per gal

Case Study: Pearl Street Lot

• Design Components / Goals• Costs and Metrics Summary• Lessons Learned

Case Study: Pearl Street Lot

• Subsurface Utility Location – coordinate with utilities early; lack of response or delayed response resulted in field directives

• Unforeseen Conditions• Subsurface structure demolition: multiple

building foundations were encountered• Balance research costs with schedule and

field directive costs• Ample public notification

Creekwalk

Creekwalk

Revisit Winter 2011: Pearl Street

Revisit Winter 2011: Pearl Street

Revisit Winter 2011: Lot 3

Winter Revisit Notes

• Pearl Street porous pavement performing well, particularly vs. standard pavement, but is being over-salted

• Lot 3 wheelstops – wheelstops vs. curbs with inlets

• Lot 3 porous concrete performing well• Snow storage areas

64

Thank You!

Questions?

Please Visit:www.SaveTheRain.us

Go Nova!