Storm Water Management and Ground Water - GWPC ·  · 2012-06-06Storm Water Management and Ground Water ... Or rooftop runoff – Roadways: vary by usage ... Sub-base Materials for

Storm Water Management and Ground WaterTom BallesteroUniversity of New Hampshire Stormwater Center

GWPC Source Water Webinar – Stormwater Management and Source Water Protection

12 July 2011

1

Acknowledgements

• Funding by CICEET/NOAA• Graduate and undergraduate students• Industry collaborators

2

Overview of Talk

• Introduction to the UNHSC• Types of Stormwater Management Systems• Hydraulic Performances• Water Quality Performance• Linkage to Groundwater• Protecting Groundwater: Do’s and Don’ts

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4

Who We Are

scientists engineers educators

5

What We Do

BMP Performance Monitoring Targeted Research Outreach

Outreach MaterialsAnnual Reports

Journal Articles

Fact Sheets

Design SpecificationsDesign Drawings

Web Resources

http://www.unh.edu/erg/cstev

or just google UNHSC

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BMP Performance Monitoring

Research Field Facility at UNHTc ~ 19 minutes

Watershed Boundary

TreeFilter

PorousAsphalt

Bioretention Retrofit

UNHSC Research Facility

ParallelPerformance

Evaluation•Each system uniformly sized to treat 1” runoff for 1 acre of impervious area

•WQV=3300 cf

•Qwqv=1 cfs

•Uniform contaminant loading

•Uniform storm event characteristics

•Systems lined for mass balance

•Long term record of hydrology and contaminants

Why the Center Was Created•Three-Year Study of

Conventional Systems

• Swales• Ponds

• Wet• Dry

NURP conclusion: Wet systems outperformDry systems (EPA, 1983)

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Study Found That…

Systems failed to

improve water

quality 2/3

of the time!26%of the time systems did nothing

34%of the timesystems offered some kind of treatment

40%of the time systems exported more pollutants

Low Impact Developmentand Green Infrastructure

Stormwater management that starts with site layout and design plus includes systems designed to create hydrologic transparency

12

Types of Unit Processes

• Storage• Sedimentation• Filtration• Infiltration• Sorption• Biodegradation• Chemical alteration

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Storage

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Rain Barrel

Tunnels

Manufactured Chambers

Sedimentation

15Retention Pond

Stone Swale Vegetated Swale

Detention Pond

Hydrodynamic Separator

Filtration - constructed systems

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Porous Asphalt Pervious Concrete Permeable Pavers

Sand Filter Ecoroof

Filtration - manufactured

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Underground Sand Filter

Filter Unit

Filtration - Biological

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Subsurface Gravel Wetland

Bioretention SystemTree Filter

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Bioretention

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Tree Filter

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Subsurface Gravel Wetland

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Infiltration

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Subsurface InfiltrationIsolator Row

Infiltration Basin

Sorption/Chemical Alteration

• Selected media to target specific contaminants– Phosphorus– Metals– Nitrogen

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Biodegradation/Biocide

• Microbially-focused efforts– Hydrocarbons– Nutrients– Microorganisms

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Hydraulic Performance

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Porous Asphalt Flow and Volume Attenuation

Average Annual Peak Flow Reduction is 68%

Average Annual Lag Time is 790 min

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Hydraulic Efficiency

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1≤=I

Ep P

Pk

1≥=I

EL T

Tk

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Lag Time (kL) Peak Reduction (kP)

5 2 1 0.5 0.1

Hydraulic Performance

Water Quality Performance

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31

Event Mean Concentration

Discharge-weighted average concentration

∫∫=

)(

)()(

tQ

tCtQEMC

∑∑≈

i

ii

QCQ

Event Mean Concentration

32

EMC

TSS Removal Efficiencies

10090

80

70

60

50

40

30

20

10

0

TSS

% R

emov

al E

ffici

ency

DIN Removal Efficiencies

10090

80

70

60

50

40

30

20

10

0

DIN

% R

emov

al E

ffici

ency

TP Removal Efficiencies

10090

80

70

60

50

40

30

20

10

0

TP %

Rem

oval

Effi

cien

cy

36

37

Retrofit Strategies

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Distribution of IC Type

• Will enable targeting of IC reduction

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Land use for WB Watershed

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42

Realities

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• LID Low hanging fruit• Substantial reductions in pollutant loading

could be achieved by addressing some of the areas with relatively low land cover but high loading and imperviousness—Commercial and Industrial

Boulder Hills, Pelham, NH 2009 Installation of 900’ of

first PA private residential road in Northeast

Site will be nearly Zero discharge

LID subdivision 55+ Active Adult Community

Large sand deposit Cost 25% greater per ton

installed7/20/2011 44

• Avoided use of 1616’ of curbing, 785’ pipe, 8 catch-basins, 2 detention basins, 2 outlet control structures

• Conventional SWM=$789,500 vs LID SWM=$740,300, $49,000 savings (6.2%)

7/20/2011 45

Greenland Meadows Commercial• “Gold-Star” Commercial

Development• Cost of doing business near

Impaired Waters/303D• Saved $$$in SWM on costly piping

and advanced SWM proprietary• Brownfields site, ideal location,

15yrs• Proposed site >10,000 Average

Daily Traffic count on >30 acres

7/20/2011 46

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Effective and Economical Designs

28 ac site, initially >95% impervious, now <10%EIC, with all drainage through filtration, expected to have minimal WQ impact except thermal and chloride

7/20/2011 48

Soil Limitation?

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Conventional design

Conventional Site:• connected

impervious surfaces

LID Site:• disconnected imperviousness• Rooftop to bioretention 1” WQV,

overflow to PA driveway• Driveway and Roadways as PA• Lawns to PA• 65% UDC, <10% EIC (NHDES

requirements)

LID design

Conventional design

Pavement

Lawn

Rooftop

CB

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LID design

PorousPavement

Lawn

Rooftop

65%UDC

Bioretention

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Total runoff Volumes

Total Runoff Volumes for Each Scenario per 1 Acre of Development

in Type A soil

0

5000

10000

15000

20000

25000

30000

1” 2yr

10yr

100y

r

2yr a

dj

10yr

adj

100y

r adj

Design storm

Tota

l Run

off V

olum

es (c

f)

LID-volume (cf)

Predevelopment-volume (cf)

Conventional-volume (cf)

Total Runoff Volumes for Each Scenario per 1 Acre of Development

in Type C Soil

0

5,000

10,000

15,000

20,000

25,000

30,000

1” 2yr10y

r100

yr

2yr adj

10yr a

dj

100yr a

dj

Design storm

Tota

l Run

off V

olum

es (c

f)

LID-volume (cf)

Predevelopment-volume (cf)

Conventional-volume (cf)

USEPA Design Requirements for Height Above Groundwater

• The recommended guidelines for depth to groundwater are established to protect groundwater contamination.

• It has been shown that heavy metals and PAHs are at background concentrations within 1.5 meters. (Mikkelsen et al., 1996; McKenzie, 1988).

• Guidelines for infiltration system installation are 3-4 feet minimum distance from water table, and 5 feet for sole source aquifers.

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Factors to Consider for Infiltration (Pitt)

• Runoff water quality: Land Use and Cover– Roof-top—not necessarily “clean”

• Loading: 20% TSS, 70-90% N, 25% P, 10-50% of Metals and PH (Wu et al, 1998; Minton, 2002) ranges in atmospheric precip. Or rooftop runoff

– Roadways: vary by usage– Parking lots– Residential

• Source control: ideal to prevent co-mingling of dirty and clean runoff– Quality varies

• End-Of-Pipe control– Tends to have poorest water quality– Stormwater outfalls may be contaminated by Illicit discharge

containing:• Raw sewage• Other municipal, industrial, and agricultural contaminants

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Inappropriate Recharge

• Subsurface contamination (Ex: gas stations, industrial production, abandoned mines)

• Hot spots and sole source aquifers• Insufficient depth to groundwater

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Contaminants of Concern

• Salts• Nutrients: N and P• Metals• Petroleum hydrocarbons• Solids• Bacteria• Pesticides

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Sub-base Materials for Infiltration Systems

• Highly permeable materials such as gravels (>16 mm) have poor removal in comparison with soils with fine-grains, such as sands. (FHWA, 2005; AdolfsonAssociates, 1995). From EPA piece w/ 1.5 m vert sep.

• Sands and soils with infiltration rates of 0.2 -3 inches per hour (from lit.) – narrow range, low

• Drainage time of 24-48 hrs• Soils with low infiltration rates can be effective for

infiltration but require storage to provide extended drain time

57

Alternate Scenarios

INFILTRATION TRENCH

POROUS ASPHALT

NATIVE MATERIALS

¾” CHOKER 4”

4”

4’ SHWT

2’ SANDY RESERVOIR BASE

NATIVE MATERIALS

2.5’ BSM

BIORETENTION

4’ SHWT

2.5’

NATIVE MATERIALS

4’ SHWT

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Infiltration

• Minimizes site runoff volume to pre-development levels

• Peak flow reduction• Pollutant mass reduction

– Are we simply relocating contamination? Removing pollutants means that they can build up unless they break down or are removed.

7/20/2011 59

Is Infiltration a Net Advantage?

• Always consider questions like this for ALLalternatives. Too often they are only applied to LID technologies, and the result is selecting even poorer, conventional systems to address the same issue.

• There are no stormwater silver bullets…cannot infiltrate everywhere.

7/20/2011 60

Summary Conclusions

•If appropriately sited, infiltration and filtration mechanisms can be top performers

•If not they can endanger/impair groundwater resources

•Proper separation from SHWT is needed•Proper sandy subbase is needed

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http://www.unh.edu/erg/cstev