evaluating stormwater control measures for linear highway ...€¦ · • an overlay (~2 inches...

www.bae.ncsu.edu/stormwaterwww.bae.ncsu.edu/stormwater

Evaluating Stormwater Control Measures for Linear Highway

Environments

Ryan J. Winston, William F. Hunt, and Shawn G. KennedyBiological and Agricultural EngineeringNorth Carolina State University, USA

Presented at the ASCE Low Impact Development ConferencePhiladelphia, PA

September 27, 2011

www.bae.ncsu.edu/stormwater

Stormwater Management in N.C.

• NC DOT is required to treat stormwater from its installations across N.C. due to federal permits

• Would like to optimize current treatment systems and implement new technologies

• N.C. regulations for stormwater are driven by TN, TP, and TSS


Typical Highway SW Management

Roadside FilterStrip

LinearDrainage

Swale


Development of the Study

• Are not those swales alongside major roads in N.C. treating runoff?

• Are all swales equal?– Wet vs. Dry

• What about roadside filter strips?


Project Goals

1. Determine nutrient and TSS concentrations at edge‐of‐pavement

2. Determine effects of roadside filter strips on water quality

3. Determine effects of wet and dry swales on water qualityA. Do wetland swales produce lower mean effluent

TN concentrations?


Two Types of Swales Studied along I‐40 in Eastern NC

Dry Swale Wetland Swale

Grassy (sites A/D) Vegetated (sites B/C)


Study Site Locations


Monitoring Design


Edge of Pavement Sampling

Structures approx. 30 ft from edge of shoulder


Filter Strip Monitoring

• Slot drains used to capture runoff from 22 ft long filter strips

• Monitored only at non‐wetland swale sites (sites A and D)


Swale Outlet Monitoring


Monitoring Equipment

Manual and Automatic Rain Gages

2-3 ISCO model 6712 WQ samplers with

bubbler inserts

Monitoring Equipment at each site:

Sampled for: TKN, NO2-3N, TN, NH4, TP, TSS


Results


Initial Edge‐of‐Pavement Results

Site NameTSS Concentration (mg/L)

Storm Event 1

Storm Event 2

Storm Event 3

Storm Event 4

Site A 6 5 7 6Site B 5 6 8 8Site C 5 6 8 10Site D 9 20 21 8

Why are TSS concentrations so low? PFC overlay over whole section of I-40 between Raleigh and Wilmington.


Permeable Friction Course (PFC)

• An overlay (~2 inches thick) of porous asphalt that is installed over a standard hot‐mix asphalt.

• Allows water to pass through (~20% voids)• Installed in 1999‐2000Property Permeable Friction

Course Standard Asphalt

% Passing 3/4” Sieve 100 100% Passing 1/2” Sieve 80‐100 100% Passing 3/8” Sieve 35‐60 90‐100% passing No. 4 sieve 1‐20 55‐85% passing No. 8 sieve 1‐10 32‐67% passing No. 200 sieve 1‐4 2‐10

Standard Asphalt

PFC Overlay


PFC Benefits

Source: Texas DOT Construction Division


Revised Project Goals

1. Determine effects of PFC on nutrient and TSS concentrations at edge‐of‐pavement

2. Determine effects of roadside filter strips on water quality

3. Determine effects of wet and dry swales on water quality

A. Do wetland swales produce lower mean effluent nutrient or sediment concentrations?

‐ Similar goals to Barrett et al. (2006) study (Water Environment Research, 78, 2177‐2185)


PFC PerformanceWu et al. (1998) found mean TSS concentrations of 283 mg/L and 93 mg/L for two highways in Charlotte, N.C.


NC and Texas PFC PerformancePFC has been shown to consistently release mean TSS concentrations of around 10 mg/L (N.C., Texas, France,

and the Netherlands)


PFC Performance over its Lifespan

No significant change in TSS effluent concentration over 10-yr lifespan(Eck et al., Journal of Environmental Engineering, Accepted)


Swale Performance

Other Metrics?

Often Percent Removals Don’t Tell the Whole Story…


Using Percent “Removal” Metric…

Research Site TN TP TSSSite A ‐12% ‐32% ‐96%Site B (wetland) 27% ‐6% 24%Site C (wetland) 43% 18% ‐115%Site D 38% ‐48% ‐400%

Different Metrics = Different Conclusionfor Overall Performance of the Swales

Wetland Swales do, however, outperform dry Swales for TN using effluent conc. metric


Effluent Concentrations Correlate to Benthic Macroinvertebrate Health (McNett et al. 2010)

• Should BMP Performance be tied back to the (good) Health of Receiving Water Bodies?

Dove Imaging


Rating Description of Benthos Sample Organisms by Scientific NameExcellent Very sensitive Ephemera Guttulata (mayfly), Litobrancha recurvata (mayfly)Good Sensitive Drunella allegheniensis (mayfly), Rhyacophila fuscula (caddisfly)Good‐Fair Semi‐tolerant Amnicola (snail), Elliptio complanata (mussel)Fair Tolerant Cambarus (crayfish), Crangonyx (crustacean)Poor Very tolerant Enchytraeidae (worm), Limnodrilus cervix (worm)

Rating Description of Benthos Sample Organisms by Scientific NameExcellent Very sensitive Ephemera Guttulata (mayfly), Litobrancha recurvata (mayfly)Good Sensitive Drunella allegheniensis (mayfly), Rhyacophila fuscula (caddisfly)Good‐Fair Semi‐tolerant Amnicola (snail), Elliptio complanata (mussel)Fair Tolerant Cambarus (crayfish), Crangonyx (crustacean)Poor Very tolerant Enchytraeidae (worm), Limnodrilus cervix (worm)

1. http://commons.wikimedia.org/wiki/Image:Water_snail_Rex_1.jpg2. http://www.adam-hart-davis.org/3. www.biol.andrews.edu/.../pond_crayfish_index.htm4. www2.mdbc.gov.au/.../invertebrates/mayfly.htm5. jimswan.com/111/aquaticinsects.htm


Piedmont Correlations

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Site A Site B Site C Site D

Concen

tration (m

g/L)

PFC FS Swale

Total Nitrogen Mean Concentrationsn ranges from 17 to 21

Target “Good” Condition


Swale TN Concentrations

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Concen

tration (m

g/L)

PFC FS Swale

Total Phosphorus Mean Concentrationsn ranges from 17 to 21


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Concen

tration (m

g/L)

PFC FS Swale

TSS Mean Concentrationsn ranges from 17 to 21



Head Cut at Site DLed to significantly higher effluent

concentrations of TSS when compared to sites A-C


Comparing Swale Outflow to Parking Lot Runoff in NC

Sampling Location TN (mg/L) TP (mg/L)Avg 8 Commercial PL’s * 1.57 0.19Site A 1.65 0.11Site B (wetland) 1.22 0.12Site C (wetland) 1.15 0.08Site D 1.62 0.19

* Passeport and Hunt (2009) – 8 Light to Moderate Use Institutional Parking Lots with no treatment


Roadside Filter Strips

• Using the Percent “Removal” Metricwhen compared to edge‐of‐pavement:

• Percent Volume Reduction:Site A: 12% Site D: 5%

Research Site TP TSS

Site A Filter Strip ‐227% ‐108%Site D Filter Strip ‐173% ‐156%


010002000300040005000600070008000

0 4 8 12 16 20 24 28 32 36

Cone

Inde

x (kpa

)

Depth (cm)

Site A, Location 1 Site A, Location 2

Site D, Location 1 Site D, Location 2

Site D, Swale

Filter Strip Soil Compaction

Above 300 psi = compacted


Filter Strip Vegetative Cover

Color Photos Color Analysis

Site A VFS: 70% vegetative cover

Site D VFS: 85% vegetative cover


Filter Strip Conclusions

• Tended to “make things worse”

• Performance similar to Barrett et al. (2006)

• Perhaps due to presence of bare spots? – Lack of vegetative establishment & maintenance


Final Thoughts…

• PFC works extremely well for removal of sediment‐bound pollutants (mean TSS concentrations ~10 mg/L)

• Wetland swales better than their dry counterparts for TN effluent concentrations

• Maintenance of vegetated highway stormwater practices is key in their long‐term functionality


Acknowledgements

• Jason Wright – Tetra Tech

• North Carolina Department of Transportation– Matt Lauffer– Brian Lipscomb– Ernie Hahn

• N.C. State Center for Applied Aquatic Ecology


Questions?

Publications resulting from this work:• Eck, B.J, Winston, R.J., Hunt, W.F., and Barrett, M.E. 2012. Water Quality of

Drainage from Permeable Friction Course. ASCE Journal of Environmental Engineering. Accepted.

• Winston, R.J., Hunt, W.F., Kennedy, S.G., Wright, J.D., and Lauffer, M.S. 2012. Field Evaluation of Stormwater Control Measures for Treatment of Highway Runoff in North Carolina. ASCE Journal of Environmental Engineering. In Press, January 2011.

evaluating stormwater control measures for linear highway ...€¦ · • an overlay (~2 inches...

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