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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
Con
cen
tra
tio
n (
mg
/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
ncen
trati
on
(m
g/
L)
Ammonium
Nitrate
Phosphate
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
Con
cen
tra
tio
n (
mg
/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
Con
cen
tra
tio
n (
mg
/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
Co
nce
ntr
ati
on
(m
g/
L) Rain Garden 1
Unfiltered 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
Hea
vy M
eta
l
Con
ce
ntra
tio
n
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
Wa
ter
De
pth (
m)
Total heavy metals
Water 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
17:0
0
17:1
5
17:3
0
17:4
5
18:0
0
18:1
5
18:3
0
18:4
5
19:0
0
19:1
5
19:3
0
19:4
5
20:0
0
20:1
5
20:3
0
20:4
5
21:0
0
21:1
5
21:3
0
21:4
5
22:0
0
22:1
5
22:3
0
22:4
5
23:0
0
23:1
5
23:3
0
23:4
5
0:00
Time
Wa
te
r D
epth
(m
)
0
0.0005
0.001
0.0015
Pre
cip
itatio
n (
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
Co
nce
ntr
ati
on
(m
g/
L)
Ammonium
Nitrate
Phosphate
Mean Heavy Metal Concentrations
0
0.5
1
1.5
2
2.5
3
Precipitation Runoff Soil Water Rain Garden Catch
Basins
Unfiltered Catch
Basin
Co
ncen
trati
on
(m
g/
L)
Copper
Lead
Zinc
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