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)