Rain Gardens at Vassar College: A Water Quality Assessment

Emily VailCollins Research Fellow

Vassar College Environmental Research Institute

Community EducatorEnvironment Program

Cornell Cooperative Extension Dutchess County

National Research Council, “Stormwater Management in the United States” (2008)

Stormwater and Water Quantity

Stormwater and Water Quality

• Sediment - erosion, bound to other pollutants

• Nutrients - eutrophication

• Heavy metals - toxicity

• Other contaminants

- Ecological problems in streams (Walsh et al. 2005, Paul & Meyer 2001, Groffman

et al. 2003, National Research Council 2008)

- Water treatment is expensive

Rain gardens?

NYS DEC, “New York State Stormwater Design Manual” (2008)

Town House Apartments Site

Redevelopment - 2008

Rain Garden 2

Rain Garden 1

Rain Garden 2 Rain Garden 1

Water samples collected:• Precipitation

• Stormwater runoff

• Soil water

• Catch basins

Analyzed for:

• Total suspended solids (TSS)

• Dissolved inorganic nutrients (N, P)

• Heavy metals (Cu, Pb, Zn)

Site Map

Rain Garden Catch Basin Unfiltered Catch Basin

n = 6, samples from December 2008, March 2009, April 2009, August 2010, and October 2010

Mean TSS in Catch Basins

0

5

10

15

20

25

Rain Garden 2 Rain Garden 1 Unfiltered Catch Basin

Co

nce

ntr

ati

on

(m

g/L

)

n = 6, samples from December 2008, March 2009, April 2009, August 2010, and October 2010

Mean Dissolved Nutrient Concentrations in Catch Basins

0

0.2

0.4

0.6

0.8

1

1.2

Rain Garden 2 Rain Garden 1 Unfiltered Catch Basin

Co

nce

ntr

ati

on

(m

g/L

)

AmmoniumNitratePhosphate

n = 6, samples from December 2008, March 2009, April 2009, August 2010, and October 2010

Mean Total Heavy Metal Concentrations in Catch Basins

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Rain Garden 2 Rain Garden 1 Unfiltered Catch Basin

Co

nce

ntr

ati

on

(m

g/L

)

Copper

Lead

Zinc

Rain Garden 2 inlet Rain Garden 1 inlet

Mean Total Heavy Metal Concentrations in Catch Basins

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Rain Garden 2 Rain Garden 1 Unfiltered Catch Basin

Co

nce

ntr

ati

on

(m

g/L

)

Copper

Lead

Zinc

n = 6, samples from December 2008, March 2009, April 2009, August 2010, and October 2010

Summary• Rain gardens are effective at removing TSS

– Consistent with other studies (Davis 2007, Davis 2009, Bratieres et al. 2008)

• May be net exporters of nutrients (affected by the growing season) – Some studies found that although total N and P

reduced, inorganic nutrients increased (Davis et al. 2009, Davis et al. 2006, US EPA 1999, Davis et al. 2007, Dietz & Clausen 2006, Kim et al. 2003)

Summary• Do not appear to moderate heavy metal loads

(further studies needed)– Laboratory studies show 88-97% removal of Cd, Cu,

Pb, Zn from synthetic stormwater (Sun & Davis 2006, Davis et al. 2001, Davis et al. 2003)

– Field studies - slightly lower removal rates for metals (Davis 2007)

• Increased retention time for stormwater quantity (Davis et al. 2009, Davis 2007, Hood et al. 2007, Hatt et al. 2009)

Conclusion• Rain gardens - an important aspect of Low Impact Design• Maintain pre-development hydrology• Local BMPs to address ecosystem-wide problems• Need for assessment• Aesthetics and function

Next steps• Do rain gardens continue to function the same

way over the duration of a storm event?– Monitoring water quality– Assess flow patterns on site

• What kind of maintenance is required? Is the design functioning as it was intended?– Visual observations and considerations for

maintenance and potential design modifications

Monitoring water quality for the duration of a storm event

TSS in Rain Garden 1 Catch Basin on 10/14

y = -0.2302x + 7.2547

R2 = 0.4652

0.00

2.00

4.00

6.00

8.00

10.00

12.00

17:3

1

17:4

6

18:0

1

18:1

6

18:3

1

18:4

6

19:0

1

19:1

6

19:3

1

19:4

6

20:0

1

20:1

6

20:3

1

20:4

6

21:0

1

21:1

6

21:3

1

21:4

6

22:0

1

22:1

6

22:3

1

22:4

6

23:0

1

23:1

6

Time

Con

cen

trati

on

(m

g/L

)

TSS in Rain Garden 1 Catch Basin and Unfiltered Catch Basin on 10/14

0.00

5.00

10.00

15.00

20.00

25.00

30.00

17:3

1

17:4

6

18:0

1

18:1

6

18:3

1

18:4

6

19:0

1

19:1

6

19:3

1

19:4

6

20:0

1

20:1

6

20:3

1

20:4

6

21:0

1

21:1

6

21:3

1

21:4

6

22:0

1

22:1

6

22:3

1

22:4

6

23:0

1

23:1

6

Time

Con

cen

trati

on

(m

g/L

) Rain Garden 1Unfiltered Catch Basin

Total Heavy Metal Concentration and Water Depth in Rain Garden 1 Catch Basin, 10/14

0

0.2

0.4

0.6

0.8

1

1.2

1.4

17:3

1

17:4

6

18:0

1

18:1

6

18:3

1

18:4

6

19:0

1

19:1

6

19:3

1

19:4

6

20:0

1

20:1

6

20:3

1

20:4

6

21:0

1

21:1

6

21:3

1

21:4

6

22:0

1

22:1

6

22:3

1

22:4

6

23:0

1

23:1

6

Time

Heavy M

eta

l C

on

cen

trati

on

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

Wate

r D

ep

th (

m)

Total heavy metalsWater depth

Water Depth in Rain Garden 1 Catch Basin and Unfiltered Catch Basin and Precipitation on 10/14

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Time

Wate

r D

ep

th (

m)

0

0.0005

0.001

0.0015

Pre

cip

itati

on

(m

)

Unfiltered Catch Basin

Rain Garden 1

Precipitation

Assessing Flow Patterns

Identifying maintenance concerns

• Visual observation and data collection

• Sediment build-up in inlets

• Water flow through soil• Plant growth• Establishment of weeds

Acknowledgements

Dr. Lynn Christenson, Dr. Mary Ann Cunningham, Dr. Stuart Belli, Dr. Kirsten Menking, Dr. David Gillikin, Dr. Jill Schneiderman, Dr. Mark Schlessman, Rick Jones, Keri VanCamp, Seth Stickle, Danielle Goldie, Cat Foley,

Sandy Alles, & Will Jobs

Vassar College Environmental Research Institute

Vassar College Environmental Studies Program

Mean Nutrient Concentrations

0

5

10

15

20

25

30

Precipitation Runoff Soil Water Rain Garden CatchBasins

Unfiltered CatchBasin

Con

cen

trati

on

(m

g/L

)

AmmoniumNitratePhosphate

Mean Heavy Metal Concentrations

0

0.5

1

1.5

2

2.5

3

Precipitation Runoff Soil Water Rain Garden CatchBasins

Unfiltered CatchBasin

Co

nce

ntr

ati

on

(m

g/L

)

CopperLeadZinc