University of Maryland, College Park

Creating Green Stormwater with

BioretentionAllen P. Davis

Department of Civil and Environmental EngineeringUniversity of Maryland

College Park, MD 20742

July 21, 2010

The Problem:

(Sub)urbia

Rainfall

-Erosive,

-Polluting

-Stream

Degradation

-Chesapeake

Bay Water

Quality

ChallengesIMPERVIOUS AREA

Urban Pollutants

Bioretention (Rain Gardens)

Quality: Filtration, Adsorption, Biodegradation

Hydrology: Pooling, Storage Infiltration, & Evapotranspiration

PONDING STORAGE AREA

PLANTING SOIL

FLOW ENTRANCEPOINT

VEGETATION

UNDERDRAIN

MEDIA

MEDIA: Sand, Soil, Organic Matter

Bioretention

Dennis Ave. Silver Spring, MD

Installed March 2006

Silver Spring

Bioretentionresearch & monitoring

Silver Spring Hydrograph0

0.05

0.1

0.15

0.2

0.25

0.30

1

2

3

4

5

6

7

8

9

10

12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00

Rai

nfa

ll (c

m)

Flo

w (L

/s)

Time of Day

5/11 to 5/13/08 Hydrograph, 2.86 in.

Inflow

Outflow

Rainfall

Bioretention Performance Metrics

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 0.5 1 1.5 2 2.5 3

Ru

no

ff d

epth

dis

char

ge

(in

)

Rainfall depth in (in)

Pavement

SS Bioretention

Woods - C Soil

Woods - B Soil

Olszewski, Davis, et al. In Progress

Water Quality

College Park Silver Spring

Input InputOutput Output

5101520304050607080859095

2

4

6

10

40

100

200

400

600

98 2

25

60

2

4

6

11

10

199

40

100

200

400

600

25

60

Exceedance Probability

TS

S E

MC

(m

g/L

)

CP in CP out

SS in SS out

No Flow/Below Limit

TSS (College Park & Silver Spring)

Li & Davis, J. Env. Eng. 2009

Bioretention

5101520304050607080859095

6

10

20

40

100

200

400

98 2

120

60

56

10

199

20

40

100

200

400

120

60

5

Exceedance Probability

Zin

c E

MC

(u

g/L

)

CP in CP out

SS in SS out

No Flow/Below Limit

Zinc (CP & SS)

Li & Davis, J. Env. Eng. 2009

Metals Accumulation - PbNavy Yard

Surface

0-10

10-20

20-30

30-40

40-50

50-60

60-70

70-80

80-90

Dep

th (

cm)

Dimensionless TSS or Normalized Captured Pb Deposit

-10

0

10

20

30

40

50

60

70

80

90

0.0 0.2 0.4 0.6 0.8 1.0

Dissolved Pb

Media Pb prediction

TSS

-1000

-500

0

0 100 200 300 400 500 600mg/kg

Li & Davis, Env. Sci. Technol. 2008

Total Phosphorus (CP& SS)

Li & Davis, J. Env. Eng. 2009

5101520304050607080859095

0.06

0.08

0.1

0.2

0.6

0.8

0.4

11

0.06

0.08

0.1

0.2

0.6

0.8

0.05 0.05

0.4

199

Exceedance Probability

Ph

os

ph

oru

s E

MC

(m

g/L

as

P)

CP in

CP out

SS in

SS out

No Flow/Below Limit

Nitrogen

Runoff

Enhanced Nitrate Removal with Internal Storage

Kim et al. Water Environ. Res. 2003

Media

Mulch

Overflow

Underdrain

Anoxic Denitrification Zone NO3 N2

Mass Loads (kg/ha/yr)CP SS

In Out In Out

TSS 1190 37 570 38

Chromium 0.09 0.015 0.02 ~0.007

Copper 0.26 0.073 0.12 0.045

Lead 0.09 0.013 0.03 ~0.005

Zinc 1.0 0.063 0.36 0.017

Chloride 6800 458 320 25

TN 27 7.2 9.6 3.6

Nitrate 12 2.5 3.7 ~0.19

TKN 15 4.1 6.0 3.6

TP 3.6 0.72 0.9 0.38

TOC 44 154 43 78

Li & Davis, J. Env. Eng. 2009

Excellent Management of Hydrology Media Area & Depth

Excellent Particulate & Bacteria Removal Filtration: Depth not Important; Surface

Accumulation Adsorption

Metals, Hydrocarbons Excellent; Surface Accumulation

Phosphorus, Nitrogen, Complex, Depth important

Biological Processes Important Denitrification (Nitrate removal) Biological Predation Vegetation in uptake & degradation

What we know so far…

Technology Maturity First installed in Greenbelt MD in

1992 First UMD Campus in 2003 Major demonstration in UMD in 2004 Now widespread throughout Mid Atlantic

Research Sponsors

Allen P. Davis apdavis@umd.edu 301-405-1958