A Performance Evaluation of Porous Asphalt as a Stormwater ...

A Performance Evaluation of PorousAsphalt as a Stormwater TreatmentStrategyJanuary 2006By Dr. Robert M. Roseen, Dr. Thomas P. Ballestero,Joshua F. Briggs, James P. HouleThe UNH Stormwater Center

Stormwater Center Crew• Dr. Thomas P. Ballestero--- PI• Dr. Robert Roseen--Director• Jamie Houle—Facility manager• Pedro Avellaneda—Site wide• Josh Briggs---Porous Asphalt• Robert Wildey---Micro• Darlene Brown, Tim Puls, Greg Sine, andJoel BallesteroThe UNH Stormwater Center2005

Research ObjectiveTo evaluate porous asphalt a stormwatermanagement strategy– The design sizing criteria was based on the needto provide storage for a 10 year rainfall event. Thatentails 4.3” of rainfall storage within approximately15” of materialsThe UNH Stormwater Center2005

Study Details• March 2005-Present: 4 storms included, 5 add’tl to beanalyzed, challenged by no-flow events• A paired design: half dense mix asphalt, half porous,asphalt• Located at the UNH Stormwater Center in Durham.• Part of a 600+ space parking lot is standard dense mixasphalt used near capacity throughout the academicyear.• Activity is a combination of passenger vehicles androutine bus traffic.• Time of concentration= 6 minutes, slopes = 1%• Frequent plowing, salting, and sanding during the wintermonths.• Contaminant concentrations are above or equal tonational norms for parking lot runoff.The UNH Stormwater Center2005

DESIGN SOURCES• Modified After Vermont Agency Of TransportationSpecifications for Open Graded Friction Course (Section409).• Michelle Adams, Cahill Associates, EnvironmentalConsultants, 104 South High Street, West Chester, PA19382• Porous Asphalt Pavements (2004) Information Series131. The National Asphalt Pavement Association,Lanham, MD.• Design, Construction, and Maintenance of Open-GradedAsphalt Friction Courses (2002). Information Series 115.The National Asphalt Pavement Association, Lanham,MD.The UNH Stormwater Center2005

Porous Asphalt Cross-Section4” of porous asphalt4” choker coarse of ¾”crushed stone8-12” thickness of porousreservoir subbaseThe UNH Stormwater Center2005

Methods• Data collection and storage byISCO 6712FR RefrigeratedSampler• Precipitation - Tipping bucketrain gauge (ISCO 674)• Flow – Compound weir (6”Thelmar) w/ ISCO 730 BubblerThe UNH Stormwater Center2005

Data Synthesis• Hyetograph• Hydrograph: delay coeff and lag timeby centroid analyses• Cold Climate Assessment• Infiltration Rates• Event Mean Concentration (EMC)The UNH Stormwater Center2005

What is Porous Asphalt?

Origins of Porous Asphalt - OGFC• Porous asphalt is a modification of Open GradedFriction Course (OGFC)• ‘Porous asphalt’ for our purposes is a single pavementlayer used for low traffic areas that allows subsurfaceinfiltration to an open bottom reservoir base• OGFC:– Is a coarse-graded asphalt mixture overlying animpervious base, typically used on highways– Water drains through OGFC to impervious layer,then to shoulder– Improves traction, reduces spray, deadens tire noise– Is cost competitive with Hot Mix Asphalt (HMA)– Some evidence that stormwater movement throughOGFC improves water qualityThe UNH Stormwater Center2005

Porous AsphaltPavement• = binder + aggregate• Modification of OpenGrade Friction Course(OGFC)• Aggregate gradation iscoarse w/ few fines• Asphalt binder oftenmodified (polymers,fibers) but notnecessary• Air voids 18-22%Standard Porous Asphalt MixesUS StandardSieve Size1/2 in.3/8 in.#4#8#16#30PercentPassing10095351510Percent bituminous 5.75-6.0%by weight2

I-95 North, June 2005, NO OGFC overlay

I-95 North, June 2005, OGFC overlay

I-95 South, June 2005, NO OGFC overlay

Misconceptions AboutPorous Asphalt• Freezes Faster - rather increased speed in thawingcompared to DMA, due to flow through by meltwater(Backstrom, 2000)• Higher Maintenance and Cost - overall $$ iscomparable• Clogs - sure but still maintains high IR (10+ in/hr)• Cannot Plow, Salt, or De-Ice - not true• Heaving and Shifting - reduced due to vadose zonedisconnect• Lower Lifespan - increased due to reduced freeze thaw(Spelic, 2003)

Monitoring and Performance DataThe UNH Stormwater Center2005

Surface Inundation Test• Surface Inundation Testprovides estimate ofinfiltration rate (Bean,2004)• 1-foot dia. SS columnsealed to pavement withputty or weighted base withfoam• 5 gallons water poured intocylinder; measure time toinfiltrate into pavementsurfaceThe UNH Stormwater Center2005

Surface Infiltration Rates 20057,000Surface Infiltration Rate, cm/hr6,0005,0004,0003,0002,0001,000;Point APoint BPoint C01/1 2/20 4/11 5/31 7/20 9/8 10/28The UNH Stormwater Center2005

Surface Infiltration Rates at 3 Locations for 2005Surface Infiltration Rate, cm/hr7,0006,0005,0004,0003,0002,0001,0000A B CLocation on Porous Asphalt PavementThe UNH Stormwater Center2005

Frost Penetration• Field assembled frost gauge(CRREL, 1976)• Solinst LT Levelogger placedat variable levels in a shallowGW wellThe UNH Stormwater Center2005

Frost PenetrationWinter 2005 Frost DepthsAir Temperature, deg. C20151050-5-10-15-20Air Temp.Avg. Air Temp.Frost Depth3/2 3/7 3/12 3/17 3/22 3/27 4/10.00.20.40.60.81.0Frost Depth, ftThe UNH Stormwater Center2005

Filter Media Frost Penetration1/13/2005 1/25/2005 2/4/2005 2/16/2005 2/25/2005 3/8/2005 3/15/2005 3/28/200501245403530Inches34567B-SandD-BioG-GravelRainAve. Temp2520151050Temp *FThe UNH Stormwater Center2005

Rainfall and RunoffMarch 28, 2005 Storm and Snowmelt EventFlow (gpm)3530252015105Influent FlowPorous Asphalt FlowRainfallAntecedent Dry Period (days): 3.4Rainfall Depth (in): 2.35Peak Flow Reduction: 60%Lag Time (min): 750Delay Coefficient: 2.00.000.010.020.030.040.050.060.075-Minute Rainfall (in.)00 500 1,000 1,500 2,000 2,500 3,0000.08Time (min)The UNH Stormwater Center2005

Rainfall and Runoff (cont’d)May 21, 2005 Storm EventFlow (gpm)201816141210864200 500 1000 1500 2000 2500 3000 3500 4000 4500 5000Time (min)Antecedent Dry Period (days): 3.0Rainfall Depth (in): 0.91Peak Flow Reduction: 80%Lag Time (min): 1,320Delay Coefficient: 3.700.010.020.030.040.050.065-M inute Rainfall (in)The UNH Stormwater Center2005

TSS Performance90.00TSS Event Mean Concentration (mg/L80.0070.0060.0050.0040.0030.0020.0010.000.00InfluentJ-PASThe UNH Stormwater Center2005

DIN Performance1.6DIN Event Mean Concentration (mg/L1.41.21.00.80.60.40.20.0InfluentJ-PASThe UNH Stormwater Center2005

TPH-D PerformanceTPH-D Event Mean Concentration (ug/L1,0008006004002000InfluentJ-PASThe UNH Stormwater Center2005

Zinc PerformanceZn Event Mean Concentration (mg/L0.100.080.060.040.020.00InfluentJ-PASThe UNH Stormwater Center2005

Conclusions• Peak flow and volume reduction are substantialdependenton subdrain design• Water quality performance is similar to sand filters---excellent removal- except for NO3• IR rates declined initially and appear to havestabilized• Long term infiltration rates will need to be monitored• Coring is needed to determine mechanism ofdecreased IR• Appears to be a sound alternative to conventionalBMPs• Maintenance impacts will need to be evaluatedThe UNH Stormwater Center2005

AcknowledgementsFunding Source:

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