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Nutrient Removal Mechanisms in a Cold Climate Gravel Wetland
Alison Watts, Robert Roseen, Laura Chan, Heather Gilbert, Kim Farah, Jamie Houle
2009 Annual Nonpoint Source Pollution ConferencePortland, ME
Dedicated to the protection of water resources through effective stormwater management
• Research and development of stormwater treatment systems
Gregg Hall ● 35 Colovos Road ● Durham, New Hampshire 03824-3534603.862.4024 ● http://www.unhsc.unh.edu
POROUS ASPHALT
CSTEV RESEARCH
FACILITY
TREEFILTER
Watershed Boundary
Seasonal Variations in PerformanceGravel
0%10%20%30%40%50%60%70%80%90%
100%
TSS TPH-D DIN Zn TP
Summer
Winter
Annual
Vegetated Swale
0%10%20%30%40%50%60%70%80%90%
100%
TSS TPH-D DIN Zn TP
SummerWinter
Annual
Retention Pond
0%10%20%30%40%50%60%70%80%90%
100%
TSS TPH-D DIN Zn TP
SummerWinterAnnual
Gravel WetlandSampling within the system
NEIWPCC-UNHProject Goals
Validation of constructed gravel wetland as a best management practice (BMP) for nutrient reduction
Investigation of the nutrient (nitrogen and phosphorus) removal mechanisms and efficiencies of constructed gravel wetlands
Provide state and federal environmental managers and their partners with an enhanced understanding of constructed gravel wetlands as a tool to reduce nutrient loading from stormwater to aid in environmental decision-making
Gravel Wetland
Effluent sampling gallery
Distribution box
Forebay
Cell 2
Cell 1
2 horizontal flow subsurface gravel cells, preceded by a flooded forebay. Designed to treat a 1-acre catchment with a peak flow of 1cfs.
Flow through the Gravel Wetland
Project Phases1. Develop study parameters2. Develop QAPP3. Collect, monitor and analyze samples4. Interpret data and develop final report with recommendations5. Outreach and technology transfer
Sampling Plan
6 storm events3 cold weather events (Nov – Apr)
• 1 Discrete sample• 2 Flow-weighted composite samples
3 warm weather events (May – Oct)• 1 Discrete sample• 2 Flow-weighted composite samples
What are we sampling?Analyte Detection Limit (mg/L)
Total Dissolved Nitrogen 0.07 mg N/lParticulate Nitrogen 15 ug N/lAmmonia 5 ug N/LNitrate 5 ug N/l
Nitrite 3 ug N/lTotal Phosphorus 20 ug P/lTotal Dissolved Phosphorus 20 ug P/lOrtho-Phosphate 5 ug P/lSulfate 0.1 ug S/l
● 4. Effluent
● 1. Influent
● 3. GW Cell
● 2. Forebay
Sampling Locations
4 sampling locations1. Influent
2. Forebay
3. Last well
4. Effluent
Water chemistry
How do we collect samples?
Automated ISCO
sampler
Programming the ISCO to capture stormwater samples (influent) at the Distribution Box
Water quality measurements using a YSI 556 in the forebay of the gravel wetland
Anaerobic Zone
Subsurface gravel wetland
Aerobic Zone
Forebay and surface of gravel wetland
Source
Runoff and plant material
N2 (gas)NH4 N02 NO3Organic N
Dissolved Oxygen in Gravel Wetland Effluent
-3-2
0
2
45
7
9
1112
14
16
GW
DO
0
1000
2000
Dbx
Flo
w
7:00
:00
AM
9:00
:00
AM
11:0
0:00
AM
1:00
:00
PM
3:00
:00
PM
5:00
:00
PM
7:00
:00
PM
9:00
:00
PM
11:0
0:00
PM
1:00
:00
AM
OxygenFlow
Con
cent
ratio
n ug
/L
NIT
ROGE
N
Forebay Maintenance - June 2008
450
Con
cent
ratio
n ug
/L
Phos
phor
us
ConclusionsNitrogenExcellent removal – Aerobic/anaerobic treatment chain requires low
oxygen concentrations in subsurfaceProgression from organic to inorganic formsEarly storm high concentrations have higher removal
PhosphorusModerate removal – Sorption and filtration in gravel substrateHigh Total P concentrations removedBetter removal in the winter?
Forebay maintenance may be required to eliminate additional sources
Funding
FY06 EPA Assessment and Watershed Protection Program Grants (AWPPG)
NPS Program National Priority• Validation of Constructed Gravel Wetland as a
BMP for Nutrient Pollution Reduction
Acknowledgements
UNH Stormwater CenterRobert Roseen, PhD, PEAlison Watts, PhD, PGJames HouleKim Farah, PhD
NEIWPCCLaura ChanHeather GilbertMarianna VulliMike JenningsClaire Whittet
Technical Advisory Committee
Betsy Dake, RI DEMSarina Ergas, UMassBill McDowell, UNHMegan Moir, VT DECThelma Murphy, EPA Region 1Sally Snyder, CT DEPKerry Strout, NEIWPCC
EPA Project Officer
Bryan Rittenhouse, EPA HQ
Questions?
Effluent
Influent
Cell 1(subsurface)
Forebay(surface)
Cell 2(subsurface)