Rain Gardens at Vassar College:
A Water Quality Assessment
Emily Vail
Collins Research Fellow
Vassar College Environmental Research Institute
Community Educator
Environment Program
Cornell Cooperative Extension Dutchess County
Stormwater and Water Quantity
National Research Council, “Stormwater Management in the United States” (2008)
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 1
Rain Garden 2
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
Mean TSS in Catch Basins
Concentration (mg/L)
25
20
15
10
5
0
Rain Garden 2
Rain Garden 1
Unfiltered Catch Basin
n = 6, samples from December 2008, March 2009, April 2009, August 2010, and October 2010
Mean Dissolved Nutrient Concentrations in Catch Basins
Concentration (mg/L)
1.2
Ammonium
Nitrate
Phosphate
1
0.8
0.6
0.4
0.2
0
Rain Garden 2
Rain Garden 1
Unfiltered Catch Basin
n = 6, samples from December 2008, March 2009, April 2009, August 2010, and October 2010
Mean Total Heavy Metal Concentrations in Catch Basins
0.35
Copper
Lead
Zinc
Concentration (mg/L)
0.3
0.25
0.2
0.15
0.1
0.05
0
Rain Garden 2
Rain Garden 1
Unfiltered Catch Basin
n = 6, samples from December 2008, March 2009, April 2009, August 2010, and October 2010
Rain Garden 2 inlet
Rain Garden 1 inlet
Mean Total Heavy Metal Concentrations in Catch Basins
0.35
Copper
Lead
Zinc
Concentration (mg/L)
0.3
0.25
0.2
0.15
0.1
0.05
0
Rain Garden 2
Rain Garden 1
Unfiltered Catch Basin
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
17
:3
17 1
:4
18 6
:0
18 1
:1
18 6
:3
18 1
:4
19 6
:0
19 1
:1
19 6
:3
19 1
:4
20 6
:0
20 1
:1
20 6
:3
20 1
:4
21 6
:0
21 1
:1
21 6
:3
21 1
:4
22 6
:0
22 1
:1
22 6
:3
22 1
:4
23 6
:0
23 1
:1
6
Concentration (mg/L)
:3
17 1
:4
18 6
:0
18 1
:1
18 6
:3
18 1
:4
19 6
:0
19 1
:1
19 6
:3
19 1
:4
20 6
:0
20 1
:1
20 6
:3
20 1
:4
21 6
:0
21 1
:1
21 6
:3
21 1
:4
22 6
:0
22 1
:1
22 6
:3
22 1
:4
23 6
:0
23 1
:1
6
17
Concentration (mg/L)
TSS in Rain Garden 1 Catch Basin on 10/14
12.00
10.00
y = -0.2302x + 7.2547
R2 = 0.4652
8.00
6.00
4.00
2.00
0.00
Time
TSS in Rain Garden 1 Catch Basin and
Unfiltered Catch Basin on 10/14
30.00
25.00
Rain Garden 1
Unfiltered Catch Basin
20.00
15.00
10.00
5.00
0.00
Time
Total Heavy Metal Concentration and Water Depth in
Rain Garden 1 Catch Basin, 10/14
0.45
0.35
1
Total heavy metals
Water depth
0.8
0.3
0.25
0.2
0.6
0.15
0.4
0.1
0.2
0.05
0
0
Time
Water Depth (m)
0.4
1.2
17
:3
17 1
:4
6
18
:0
1
18
:1
6
18
:3
1
18
:4
6
19
:0
19 1
:1
6
19
:3
19 1
: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
22 6
:0
1
22
:1
22 6
:3
1
22
:4
23 6
:0
1
23
:1
6
Heavy Metal
Concentration
1.4
17
:0
17 0
:
17 15
:3
17 0
:4
18 5
:
18 00
:1
18 5
:3
18 0
:
19 45
:0
19 0
:1
19 5
:
19 30
:4
20 5
:0
20 0
:1
20 5
:
20 30
:4
21 5
:0
21 0
:
21 15
:3
21 0
:4
22 5
:
22 00
:1
22 5
:3
22 0
:
23 45
:0
23 0
:1
23 5
:
23 30
:4
5
0:
00
Water Depth (m)
0.8
Unfiltered Catch Basin
Rain Garden 1
Precipitation
0.6
0.5
0.001
0.4
0.3
0.0005
0.2
0.1
0
0
Time
Precipitation (m)
Water Depth in Rain Garden 1 Catch Basin and
Unfiltered Catch Basin and Precipitation on 10/14
0.0015
0.7
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
30
Ammonium
Nitrate
Phosphate
Concentration (mg/L)
25
20
15
10
5
0
Precipitation
Runoff
Soil Water
Rain Garden Catch
Basins
Unfiltered Catch
Basin
Mean Heavy Metal Concentrations
Concentration (mg/L)
3
Copper
Lead
Zinc
2.5
2
1.5
1
0.5
0
Precipitation
Runoff
Soil Water
Rain Garden Catch
Basins
Unfiltered Catch
Basin