1

Treatment of Nutrients by

Stormwater Management

2006 FDOT Design Conference

by

Harvey H. Harper, Ph.D.,PEEnvironmental Research & Design Inc.

Areas of Discussion

1. Sources of Nutrients in Stormwater

2. Removal Mechanisms

A. Structural Techniques

B. Non-structural Techniques

2

1. Sources of Nutrientsin

Stormwater Runoff

Stormwater is Generated within a Watershed

3

Runoff Entering an Urban Lake

NutrientsCompounds which stimulate the

growth of algae and other plants:

1. Nitrogen – NH3, NOX, Organic N, Particulate N

2. Phosphorus – Soluble reactive P (SRP), Organic P, Particulate P

4

Wash-off from Lawns and Landscaped Areas is a Major Nutrient Source

Suspended Solids and Vegetation Can Be Significant Sources of Nutrients

5

Nutrients are Also Attached to Colloidal Suspended Solids

Pelagic Algal Bloom Resulting from Stormwater Runoff

6

Filamentous Algal Bloom Resulting from Stormwater Runoff

Comparison of Typical Nitrogen Concentrations in Stormwater

LD R

es.

SF R

es.

MF

Res

.

LI C

omm

.

HI

Com

m.

Indu

stria

l

Hig

hway

Past

ure

Citr

us

Row

Cro

ps

Gen

eral

Ag.

Und

evel

oped

Min

ing

Tota

l Nitr

ogen

(mg/

l)

0

1

2

3

4

7

Comparison of Typical PhosphorusConcentrations in Stormwater

LD R

es.

SF R

es.

MF

Res

.

LI C

omm

.

HI

Com

m.

Indu

stria

l

Hig

hway

Past

ure

Citr

us

Row

Cro

ps

Gen

eral

Ag.

Und

evel

oped

Min

ing

Tota

l Pho

spho

rus

(mg/

l)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

2. Removal/Control of Runoff Nutrients

a. Structural Techniques

8

Removal of Stormwater Pollutants

Removal processes depend upon:Type of PollutantParticulate or Ionic FormAffinity for Adsorption or Biological UptakeChemical ReactionsVolatilization

Removal mechanisms can be divided intothose responsible for removal of:

Particulate FormsDissolved Forms

Removal of Particulate Pollutants

nPrimary removal mechanism is unhindered gravity settling of discrete particles according to Newton's Law or Stoke’s Law

nRemoval of suspended solids also removes other pollutants as well

nRemoval rate (settling velocity) is a function of:

nParticle diameter

nParticle density

9

Design Techniques to Maximize Removal of Suspended Matter

1. Encourage reduction in flow velocity to allow settling

2. Minimize turbulent conditions

3. Maximize flow length from inlets to outlets

4. Prevent short-circuiting and hydraulic dead zones

5. Include aquatic plants to increase adsorption of solids onto plant surfaces

Removal Processesfor Dissolved Nutrients

Removal occurs primarily through biological processes and adsorption

Optimize removal by maintaining:

n Permanent wet pooln Diverse biotan Well oxygenated water columnn Soil adsorption

10

Common Stormwater Treatment Practicesn Infiltration Systems

Retention BasinsSwalesInfiltration TrenchesExfiltration SystemsPervious Pavement

n Detention SystemsnDry DetentionnWet Detention

n Filter Systemsn Alum Injectionn Gross Pollutant Separators

Infiltration SystemsDescription

Family of practices where the stormwater is disposed of by infiltration or evaporation

rather than by surface discharge

Purposen Reduce total runoff volumen Reduce pollutant loadings

Pollutant Removaln Percolation, evaporationn Filtering and adsorption

11

Infiltration Systems(Continued)

Limitations on Use:

n Require porous soils

n Not on soils with high clay or silt

n Not where high water tables, bedrock

n Not on fill sites or steep slopes

n Not at sites where hazard materials spill

n Risk of groundwater contamination

Benefits of Infiltrationn Groundwater recharge

n Maintain baseflow

n Maintain pre-development hydrology

n Reduce stormwater pollutant loads

n Reduce total stormwater volume

12

Dry Retention BasinDESCRIPTION:

Surface area used to store runoff temporarily until it percolates or evaporates

ADVANTAGES:n Integrate into open space/landscapingn Use for other purposes between stormsn More easily inspected and maintained

DISADVANTAGES:n Land area needed

Dry Retention Pond

13

Retention Storage Underneath a Commercial Building in Tallahassee

Typical Swale Section

14

Swale Drainage Along a Collector Road in Orlando

Use of Swalesn Along highways, streets, and rural roads

n Residential subdivisions

n Pre-treatment (BMP Treatment Train)Any land use type, parking lotsBefore infiltration trenches, wet ponds

n Must be designed for conveyance as well as water quality

n With enhancementsSwale blocksRaised inletsRaised driveway culverts

15

Infiltration TrenchDescription

n Shallow excavated trench, backfilled with coarse stone, allowing for temporary

storage of runoff

Advantagesn Require less land

n Can be fit into tight places

Disadvantagesn Difficult to monitor performancen Clog easily and hard to maintain

Schematic of Infiltration Trench with Observation Well

16

Exfiltration System

Pervious PavementDescription:

Pavement with traditional strength but designed to allow percolation

Advantages:n Reduces site imperviousness

n Reduces hydroplaning by up to 15%n Pedestrian-friendly, less puddles

Disadvantages:n Potential for clogging

n Lack of experienced installersn Spills may cause groundwater problemsn Anaerobic soils in long duration rain areas

17

Pervious Pavement in a Shopping Center in Tallahassee

18

North Florida (Branford)

0.00

-0.1

0

0.11

-0.2

0

0.21

-0.3

0

0.31

-0.4

0

0.41

-0.5

0

0.51

-1.0

0

1.01

-1.5

0

1.51

-2.0

0

2.01

-2.5

0

2.51

-3.0

0

3.01

-3.5

0

3.51

-4.0

0

4.01

-4.5

0

4.51

-5.0

0

5.01

-6.0

0

6.01

-7.0

0

7.01

-8.0

0

8.01

-9.0

0

>9.0

0

Num

ber o

f Ann

ual E

vent

s

0

10

20

30

40

50

Typical Rainfall

FrequencyDistribution

Bran

ford

Cro

ss C

ity

Fort

Mye

rs

Jack

sonv

ille

Key

Wes

t

Mel

bour

ne

Mia

mi

Orla

ndo

Pens

acol

a

Talla

hass

ee

Tam

pa

Per

cent

of A

nnua

l Rai

nfal

l Vol

ume

< 0.

1 In

ch (%

)

0

2

4

6

8

10

Mean

Bran

ford

Cro

ss C

ity

Fort

Mye

rs

Jack

sonv

ille

Key

Wes

t

Mel

bour

ne

Mia

mi

Orla

ndo

Pens

acol

a

Talla

hass

ee

Tam

pa

Per

cent

of A

nnua

l Rai

nfal

l Vol

ume

> 1.

0 In

ch (%

)

30

35

40

45

50

55

60

Mean

Characteristics of Rainfall Events at the 10 Meteorological Sites

19

Bran

ford

Cro

ss C

ity

Fort

Mye

rs

Jack

sonv

ille

Key

Wes

t

Mel

bour

ne

Mia

mi

Orla

ndo

Pens

acol

a

Talla

hass

ee

Tam

pa

Ann

ual C

Val

ue

0.20

0.25

0.30

0.35

0.40

0.45

0.50

Mean

Comparison of State-Wide Annual C Values forA Hypothetical Residential Development

DCIA = 40%Non-DCIA CN = 70

Retention Efficiency for CN=70 and DCIA=40%

Bran

ford

Cro

ss C

ity

Fort

Mye

rs

Jack

sonv

ille

Key

Wes

t

Mel

bour

ne

Mia

mi

Orla

ndo

Pens

acol

a

Talla

hass

ee

Tam

pa

Trea

tmen

t Effi

cien

cy (%

)

40

50

60

70

80Treatment for Runoff from 1.0-inch of RainfallTreatment for 0.5 Inches of Runoff

Comparison of Retention Efficiency for 0.5 inch of Runoff and 1 inch of Rainfall

20

Non-DCIA Curve Number

30 40 50 60 70 80 90 100

Perc

ent D

CIA

(%)

10

20

30

40

50

60

70

80

90

100

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

Treatment Depth(inches)

Non DCIA Curve Number

30 40 50 60 70 80 90 100

Perc

ent D

CIA

(%)

10

20

30

40

50

60

70

80

90

100

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

Treatment Depth(inches)

Retention Depth Required for 80% RemovalMelbourne Pensacola

Detention PracticesDESCRIPTION

n A family of practices which detain runoff and discharge it over a period of days

PURPOSEn Flood protectionn Water storagen Pollutant removal

POLLUTANT REMOVALn Depends on type of detention BMP

21

Dry Detention BasinDESCRIPTION

n Area used to detain runoff for a short time to reduce peak discharge rate

ADVANTAGESn Use for other purposes between storms

DISADVANTAGESn Poor stormwater treatment effectivenessn Considered unattractive nuisancesn Mosquito production

Dry Detention Basin in Orlando

22

Dry Detention with Filtration

Treatment Efficiencies for DryDetention with Filtration

Systems

------22883---28Mean Values

259368-4977-86-229-136Overall

OrangeCounty/Comm.

& Resid.

Harper &Herr

(1995)

------939892--80OverallLeon

County/Comm.

Bradford-ville

Study

TotalZn

TotalPb

TotalCuBODTSSTotal

PSRPTotalN

Mean Removal Efficiencies (%)Type ofEff.

Reported

Study Site/Land UseReference

23

Wet Detention PondDescription

n A detention system with a permanent pool in which runoff is stored temporarily before discharge

Advantagesn High level of flood protection and stormwater

treatmentn Used in areas with high water tables, poor

soilsn Multiple ancillary benefitsn Relatively low maintenance

Wet Detention

24

Wet Detention Lakes Can Be Integral to the Overall Development Plan

Wet Detention SystemsPollutant Removal Processes

n Occurs during quiescent period between storms

n Permanent pool crucialReduces energy, promoting settlingHabitat for plants and microorganismsMust maintain aerobic bottom conditions

n Gravity settlingPond geometry, volume, residence time, particle size

25

Wet Detention Design Considerations

nPermanent pool and residence timeAverage > 14 daysPermanent pool volume calculation:n (Annual runoff volume) x (14/365)

nDepth of permanent poolNeed mix of deep (> 3 m) and shallow areas (< 1 m)Maximum depth of 6 m (20 ft), maintain aerobic bottomDo not breach confining layers

Wet Detention Design Considerations

nLittoral Zone30% of surface area, slope gently (6:1 to 10:1), depth < 3 feetConcentrate at outfall or around perimeterVariety of native aquatic plants

nPond GeometryLength to width ratio at least 3:1, preferably 5:1Separate inlets and outlets, long flow path

26

Total Phosphorus

Detention Time, td (days)0 100 200 300 400

Rem

oval

Effi

cien

cy (%

)

0

20

40

60

80

100

R2 = 0.877

2))(ln(19.0)ln(87.518.44 dd ttEfficiency •+•+=

Total Nitrogen

Detention Time, td (days)0 100 200 300 400

Rem

oval

Effi

cien

cy (%

)

0

20

40

60

80

100

R2 = 0.808

)46.5()72.44(

d

d

ttEfficiency

+•

=

27

Side Bank Filter with Exposed Filter Fabric

28

Off-line Retention/Detention Systems

Comparative Removal Efficiencies for Total Nitrogen

0.25

" R

eten

tion

0.50

" R

eten

tion

0.75

" R

eten

tion

1.00

" R

eten

tion

Off-

Line

Ret

./Det

.

Wet

Det

entio

n

Dry

Det

entio

n

Alum

Tre

atm

ent

Tota

l Nitr

ogen

Rem

oval

Effi

cien

cies

(%)

0

20

40

60

80

100

29

Comparative Removal Efficiencies for Total Phosphorus

0.25

" R

eten

tion

0.50

" R

eten

tion

0.75

" R

eten

tion

1.00

" R

eten

tion

Off-

Line

Ret

./Det

.

Wet

Det

entio

n

Dry

Det

entio

n

Alum

Tre

atm

ent

Tota

l Pho

spho

rus

Rem

oval

Effi

cien

cies

(%)

0

20

40

60

80

100

Gross Pollutant Separators

- CDS

- Stormcepter

- Vortechnics

- Baffle Boxes

30

CDSCDSUnitUnit

CSRCSRStormceptorStormceptor

31

VortechsVortechsStormwaterStormwaterTreatmentTreatment

SystemSystem

Typical Baffle Box or Sediment Trap Design

32

Typical Distribution ofDissolved and Particulate Runoff

Fractions for Highway Runoff

305550206055

704550804045

CadmiumChromium

CopperNickelLeadZinc

1. Harper, H.H. (1988). “Effects of Stormwater Management Systems onGroundwater Quality.” Final Report for Project SM 190, submitted to theFlorida Department of Environmental Regulation.

354510035

6555065

Total NTotal P

TSSBOD

ParticulateDissolvedTypical Distribution1 (%)

Parameter

Alum Treatment

33

Alum is a viscous clear liquid with a greenish to tan color

Significant Alum Removal Processes

1. Removal of suspended solids, algae,phosphorus, heavy metals and bacteria:

Al+3+ 6H O2

Al(OH)3(s)

+ 3H3O +

2. Removal of dissolved phosphorus:

Al+3 + HnPO

4

n-3 AlPO4(s)

+ nH +

34

Aluminum Coagulants

Aluminum Sulfate (alum)

Aluminum Chloride

Poly Aluminum Hydroxychloride

Alum/Polymer Blends (floc logs)

Colloidal Runoff Sample Settled for 45 Days

35

Immediately Following Alum Addition

Treated Sample 4 Hours After Alum Addition

36

Alum CoagulationAdvantages

Rapid, efficient removal of solids, phosphorus, and bacteria

Inexpensive – approximately $0.65/gallon

Relatively easy to handle and feed

Does not deteriorate under long-term storage

Floc is inert and is immune to normal fluctuations in pH and redox potential

Floc also binds heavy metals in sediments, reducing sediment toxicity

Disadvantage

May result in lowered pH and elevated levels of Al+3 if improperly applied

Typical Percent Removal Efficiencies for Alum Treated Stormwater Runoff

99999661Fecal Coliform99948037Total Coliform64636130BOD98979570TSS99999882Turbidity96948645Total P95948261Particulate P98989617Diss. Ortho-P73716525Total N96948857Particulate N65625120Diss. Organic N

107.55

ALUM DOSE (Dose in mg Al/liter)SETTLEDWITHOUT

ALUM (24 hrs)PARAMETER

37

Lake Dot – Post Treatment

Cartoon inOrlando SentinelAfter CompletionOf the Lake Dot

Alum StormwaterTreatment

System

38

Lake Lucerne – Post Treatment

0

20

40

60

80

100

120

140

160

180

Tota

l Pho

spho

rus

(µg/

l)

1990 1991 1992 1993 1994 1995 1996Date

LAKE LUCERNETotal Phosphorus

Before Alum

Test

ing

/ Sta

rtup

DuringSystem

Operation

DuringSystem

OperationSys

tem

Offl

ine

39

Equipment Building

Alum Injection Equipment pH Control Equipment

In-line Floc Settling Pond

Merritt Ridge Alum Injection System

Construction and O&M Costs for Existing Alum Treatment Systems

1,23318,580276,800310Average

3,76926,298400,000538Maximum

1396,50075,00064Minimum

Construction Cost/Area Treated ($/acre)

Annual O&M Costs

Construction Cost ($)

Area Treated (acres)

Parameter

40

2. Removal/Control of Nutrients

b. Non-structural Techniques

Street Sweeping

Most applicable for paved streets having curbs and gutters, but can be used on any impervious surface

Particularly applicable to urban built-out areas where space for conventional stormwater treatment is unavailable or too expensive

41

Types of Street SweepersMechanical Sweepers

Most common type of sweeper

Uses brooms to sweep solids into a hopper

Water is sprayed for dust control

Efficiency is a function of:

Particle sizeFrequency of sweepingNumber of passesEquipment speedPavement conditions

Types of Street SweepersVacuum (plus mechanical)

Provides air vacuum over entire path with mechanical broom assist

Some particles do not receive sufficient agitation to become air-entrained

Regenerative Air

Air is forced down onto the pavement, suspending particles, which are then picked up by the vacuum

42

Estimated TSS Reduction from Street Sweeping (%)

(Major Arterial Highway)

7543Mechanical Brush Type

24221715Air Sweeper

85766249New Type Vacuum

Twice WeeklyWeeklyTwice

MonthlyMonthly

Frequency of SweepingSweeper

Type

Relationships Between Particle Size and Sweeper Efficiency

(Mechanical Sweeper; Ref. USEPA)

50Overall15<432043 – 10448104 – 24660246 – 84066840 – 200076>2000

Sweeper Efficiency (%)

Particle Size (microns)

43

Removal of Other Pollutants by Street Sweeping

(Based on a 60% TSS Removal)

Total Metals – 45% - 55%

Phosphorus – 25% - 35%

BOD – 35% - 45%

High Efficiency Street Sweeping Equipment

Sweeping Interval (days)

0 5 10 15 20 25 30 35

Tota

l Pho

spho

rus

Rem

oval

(%)

25

30

35

40

45

50

55

44

Questions?