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September 8, 2016September 8, 2016

Post Construction StormwaterControls in Mecklenburg County,

NC: Past, Present (and Future)

Post Construction StormwaterControls in Mecklenburg County,

NC: Past, Present (and Future)

Mike MacIntyre, PE

Don Ceccarelli, PE, CFM

Mike MacIntyre, PE

Don Ceccarelli, PE, CFM

Presented to:

South Carolina Association of Storm Water Managers

Presented to:

South Carolina Association of Storm Water Managers

MM3

Driver #1-Flooding

• An inch of rainfall on an acre of woods in typical piedmont soilsproduces no runoff.

• The same one inch of rainfall on one acre of asphalt will produceover 27,000 gallons of runoff.

Driver #2 – Channel ErosionDriver #2 – Channel Erosion

Slide 1

MM3 Presenter - Bob WilsonMacIntyre, Mike, 7/12/2005

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Driver #2 – Channel Erosion

Driver #2 – Channel Erosion

November 1969: Local Water QualityProgram Established “for the abatement

of pollution of the streams and theirtributaries in Mecklenburg County.”

Charlotte News’Articles fromSeptember 1969

Driver #3 – Pollution

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…of waterpollution in

MecklenburgCounty.

Storm waterrunoff is the

biggest source…

Visible storm water pollutants runningdown College Street in Charlotte.

Driver #3 – Pollution

In the beginning ……..

1. Detention Ordinance(s) – BMPs required forcommercial / industrial developments ~ 1979

2. Watershed Ordinance(s) – BMPs required for certaindevelopment and re-development projects inWatershed Overlay districts ~ 1993

3. State 401 Water Quality Certification Conditions

4. SWIM Mitigation Conditions ~ 1998

5. Rezoning Conditions

6. Post-Construction – BMPs required for certaindevelopment and re-development projects ~ 2007

1. Detention Ordinance(s) – BMPs required forcommercial / industrial developments ~ 1979

2. Watershed Ordinance(s) – BMPs required for certaindevelopment and re-development projects inWatershed Overlay districts ~ 1993

3. State 401 Water Quality Certification Conditions

4. SWIM Mitigation Conditions ~ 1998

5. Rezoning Conditions

6. Post-Construction – BMPs required for certaindevelopment and re-development projects ~ 2007

When was Storm Water Treatment Required?When was Storm Water Treatment Required?

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N

GOOSE CREEK

WESTERN CATAWBAYADKIN-SOUTHEAST CATAWBA

HUNTERSVILLE

CENTRAL CATAWBA

LONG

McALPINE

SUGAR

IRWINPAW

MALLARD

BRIAR

McDOWELL

CLARKE

CLEAR

REEDY

STEELE

GAR

FOUR MILE

GOOSE

SIX MILE

LAKENORMAN

BACK

McMULLEN

ROCKYRIVER

UPPERLITTLESUGAR

McKEE

BEAVERDAM

CLEM

LOWERLITTLESUGAR

LOWERCLARKE

LOWERMTN

ISLAND

CROOKED

CATAWBA

UPPERMTN

ISLAND

CALDWELL

TWELVE MILE

LAKEWYLIE

5 0 5 10 Miles

Requirements for Post-Construction OrdinanceWatershed Districts

Western Catawba District

BMPs >12% BUA @ 85%TSS & 70%TPremoval

* >24% in Cornelius

Buffers Same as CentralCatawba District

Detention Same as CentralCatawba District

OpenSpace

Same as CentralCatawba District

Yadkin District

BMPs >10% BUA @ 85% TSS& 70%TP removal

* >12% in Mint Hill

Buffers <50 ac.= 50 ft.;

>50 ac. = 100 ft

Detention Same as CentralCatawba District

OpenSpace

Same as CentralCatawba District

Central Catawba District

BMPs >24% BUA @ 85% TSSremoval

Buffers S.W.I.M. + 30 ft on int.streams

Detention V = post 1-yr, 24-hrstorm;

P = 10-yr & 25-yr, 6-hr

OpenSpace

<24% BUA = 25%;

>24% BUA = 17.5%;

>50 BUA = 10%

Goose Creek District

BMPs Any BUA @ 85% TSS(pre-post, 1-yr, 24-hr)

Buffers S.W.I.M +

100-ft on streams;

200-ft on streamsw/floodplain

Detention V = pre–post 1-yr, 24-hrP = 10-yr & 25-yr, 6-hr

OpenSpace

<20% BUA = 0%;

>20% BUA = 15%;

>50 BUA = 10%

Exceeds current State requirements

Huntersville

BMPs >12% BUA @ 85% TSS& LID BMPs

* >6% in MI Critical Area

Buffers Same as CentralCatawba District

Detention V = pre–post 1-yr, or 2-yr24-hr based on zoning

P (> 12% BUA) = 2-yr &10-yr, 24-hr

Open Space None

1. Installation

2. Platted Easement

3. As-Built Survey

4. Maintained

5. Recorded Maintenance Plans

6. Annual Inspections

7. Reporting

8. Maintenance & Replacement Funding

1. Installation

2. Platted Easement

3. As-Built Survey

4. Maintained

5. Recorded Maintenance Plans

6. Annual Inspections

7. Reporting

8. Maintenance & Replacement Funding

Evolution of BMP RequirementsEvolution of BMP Requirements

1979

2015

1979

2015

Detention

Reduce the flowrate of storm water runoff.

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•Wet Pond

•Structural Best Management Practices(BMPs)

•Flowrate control, TSS removal via settling.

Wetland

•Structural Best Management Practices(BMPs)

Flowrate control, TSS removal via settling, nutrientremoval via biological uptake

Rain Garden

•Structural Best Management Practices(BMPs)

TSS removal via settling and filtration, nutrientremoval via biological & microbial uptake, &

volume reduction

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Filter pollutants, reduce run-offthrough evapo-transpiration and

absorption, and reduceimpervious area.

Open Space - Trees

Chapter 4 – Structural Storm Water Controls

• 4.1 Bioretention

• 4.2 Wet Pond

• 4.3 Storm Water Wetlands

• 4.4 Enhanced Grassed Swale

• 4.5 Grass Channels

• 4.6 Infiltration Trench

• 4.7 Filter Strip/Wooded Buffer Strip

• 4.8 Sand Filters

• 4.9 Extended Dry Detention

• 4.10 Proprietary & Innovative BMPs

• Green Roofs and Permeable PavementSystems added as innovative BMPs inSeptember 2008

• Designs reference State BMP Manual

• Lists Key Performance Criteria

Chapter 4.10 Proprietary and Innovative BMPsChapter 4.10 Proprietary and Innovative BMPs

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• Peak Attenuation - Reduction via routing

• Volume Capture - Reduction via routing and viaon-site infiltration rates / voids storage

• Water Quality Pollutant Removal- up to 85% forTotal Suspended Solids (TSS) and 60% TotalPhosphorus (TP)

• Built-Upon Area Credit – 50 to 75% built-uponarea reduction depending on soil whencomparing to low density / high densityrequirements; no credit for Watershed built-upon area maximums.

Permeable Pavement PerformanceCriteria

Permeable Pavement PerformanceCriteria

• Assist in meeting storm water controlrequirements of various ordinances

• Provide reduction in the size of downstreamstorm water control measures

• Provide some reduction in total storm water run-off volume which can reduce the potential forstream bank erosion and sediment loading tostreams and lakes.

• Can assist in groundwater recharge

Storm Water Management Benefits ofPermeable Pavements

Storm Water Management Benefits ofPermeable Pavements

Future BMP SophisticationFuture BMP Sophistication

Continued development of Manufactureddevices “leaning towards” water treatmenttechnologies… cartridge filters, membranetechnology, etc.

Focus on volume reduction through:

o Infiltration

o Reuse – irrigation and grey water usage

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Examples of Green Building PracticesExamples of Green Building Practices

8 ft+

MM4

Key Terms

• Development

– Land-disturbing activity that creates imperviousarea or that otherwise decreases the infiltrationof precipitation into the soil

• Redevelopment

– Land-disturbing activity that does not result in anet increase in impervious area and thatprovides greater or equal stormwater controlthan the previous development

Building Addition

Development Example

ExistingBuilding

Slide 22

MM4 Presenter - Bob WilsonMacIntyre, Mike, 7/12/2005

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New BuildingExisting Building

Redevelopment Example

Key Terms

• Detention

– Peak Control (flood relief)

• The controlled release of the runoff from 10-,25-, and possibly larger 6-hour storms toprevent flooding of downstream structuresand properties

– Volume Control (stream erosion prevention)

• The slower, controlled release of the runofffrom a 1-year, 24-hour storm in order toprotect streambanks from being eroded

Redevelopment CaseStudy

Seven Eleven –N Wendover Rd

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Pre-Project Conditions (2011)

28

Redevelopment Conditions (2015)

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Site Constraints

30

• Side/Rear Yards andSetbacks required byZoning Ordinance

• Tree Save Areas requiredby Tree Ordinance

• Internal Tree plantingrequired by TreeOrdinance

• Underground StormwaterControl Measure (SCM)required by Post-Construction StormwaterOrdinance (PCSO)

Tree Save Area

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Redeveloped Site Specifics

31

Pre-Project (acres) Redevelopment (acres)

Tree Save 0 0.24

AdditionalVegetated Area

0.60 0.07

Total PerviousArea

0.60 0.31

Impervious Area 0.47 0.76

Site Area 1.07 1.07

How Redevelopment Improves theWatershed

32

RedevelopmentRequirements:• Detention is

provided to slowlyrelease runoff toreduce streamerosion

• Detention isprovided on-site toreduce downstreamstorm drainagesystem burden

• Detention isprovided on-site toreduce downstreamstreet flooding

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Stream Erosion FlowStorm Drainage

System Flow Street Flooding Flow

Stream Protection and Flood Reduction

Pre-Project Redevelopment

How Redevelopment Improves theWatershed

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Undeveloped

Pre-Project

Redevelopment

Hydrograph for Stream Erosion Flow

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How Redevelopment Improves theWatershed

34

Undeveloped

Pre-Project

Redevelopment

Hydrograph for Storm Drainage System Flow

Site Discussion

35

Tree Save Area

Redevelopment CaseStudy

Hendrick Autohaus

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Pre-Project Conditions (2011)

37

Redevelopment Conditions (2015)

38

Aerial Comparison

2013 Aerial 2014 Aerial

39

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Downstream Analysis

40

Open Channel

Stormwater Pipe

Downstream Analysis – 10%Point

41

Open Channel

Stormwater Pipe

Setback

Setback

Tree Planting Area

Tree Save Area

Site Layout

42

• Setbacks required byZoning Ordinance

• Tree Save Areas requiredby Tree Ordinance

• Internal Tree plantingrequired by TreeOrdinance

• Underground StormwaterControl Measure (SCM)required by Post-Construction StormwaterOrdinance (PCSO)

Un

de

rgro

un

dSC

M

Building Footprint

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Redeveloped Site Specifics

43

Pre-Project (acres) Redevelopment (acres)

Tree Save 0 0.25*

AdditionalVegetated Area

0 0.45

Total PerviousArea

0 0.70

Impervious Area 5.37 4.67

Site Area 5.37 5.37

*This site utilized the payment-in-lieu option in the Tree Ordinance and paid a fee of $76,495.50for compliance in addition to the onsite plantings.

Stormwater Development Requirements

• Provide onsite detention to reduce downstreamerosion and flooding impacts. This wasaccomplished by installing an undergrounddetention system.

• Pay mitigation fee for water quality impact at rate of$60,000 per acre of Built Upon Area (BUA). This sitepaid $280,000.

44

How Redevelopment Improves theWatershed

45

RedevelopmentRequirements:• Detention is

provided to slowlyrelease runoff toreduce streamerosion

• Detention isprovided on-site toreduce downstreamstorm drainagesystem burden

• Detention isprovided on-site toreduce downstreamstreet flooding

0

5

10

15

20

25

30

35

40

Stream Erosion FlowStorm Drainage

System Flow Street Flooding Flow

Stream Protection and Flood Reduction

Pre-Project Redevelopment

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How Redevelopment Improves theWatershed

46

Undeveloped

Pre-Project

Redevelopment

Hydrograph for Stream Erosion Flow

How Redevelopment Improves theWatershed

47

Undeveloped

Pre-Project

Redevelopment

Hydrograph for Storm Drainage System Flow

Setback

Setback

Tree Planting Area

Tree Save Area

Site Discussion

48

Un

de

rgro

un

dSC

M

Building Footprint

MM1

Slide 48

MM1 Need explanation of all of the green space and why it is requiredMacIntyre, Mike, 12/29/2014

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Redevelopment CaseStudy

CarnegieApartments/Capitol Towers

Pre-Project Conditions (2009)

50

Aerial Comparison

2013 Aerial Rezoning

51

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How Redevelopment Improves theWatershed

52

DevelopmentRequirements:• Detention is

provided to slowlyreleased to reducestream erosion

• Detention isprovided on-site toreduce downstreamstorm drainagesystem burden

• Detention isprovided on-site toreduce downstreamstreet flooding

0

10

20

30

40

50

60

70

80

90

Stream Erosion FlowStorm Drainage

System Flow Street Flooding Flow

Stream Protection and Flood Reduction

Pre-Project Development

Little Sugar Creek Greenway

and Stream Restoration

Mike MacIntyre, PE

Michael.Macintyre@mecklenburgcountync.gov

Don Ceccarelli, PE, CFM

Don.ceccarelli@mecklenburgcountync.gov

Mike MacIntyre, PE

Michael.Macintyre@mecklenburgcountync.gov

Don Ceccarelli, PE, CFM

Don.ceccarelli@mecklenburgcountync.gov

QuestionsQuestions