Overview of Stormwater BMPs in the

Pinellas County Stormwater Manual

Part 1

Pinellas County Stormwater Management Manual Training

Workshop

Presentation Outline

1. The stormwater management issue2. What is Low Impact Design?3. What are Low Impact Design BMPs?4. Pinellas County Stormwater Manual BMPs

– purpose, design criteria, construction, inspection, maintenance (Part 1)

The Stormwater Problem

Humans cause:

• Changes in land use, clearing of land

• Compaction of soil, imperviousness

• Development in floodplains, wetlands

• Alteration of natural stormwater systems

• Addition of “drainage” systems

• Addition of pollutants

Resulting in:

• Decreased recharge

• Increased speed of runoff

• Increased volume of runoff

• Increased pollutants

Hydrologic

Changes

Associated With

Urbanization

Big

Messy

ProblemCommon Pollutants

• Sediments

• Oxygen demanding substances

• Nutrients

• Pathogenic bacteria

• Heavy metals

• Oil & grease, hydrocarbons

• Fresh water

Best Management Practices (BMPs)

• Control techniques used for a given set

of conditions to manage stormwater

quantity and quality in the most cost

effective manner.

• Stormwater treatment began in 1982,

still a young field

• Florida’s ERP handbooks only include

traditional BMPs – retention basins, wet

detention ponds, sand filters

Evolution of Stormwater BMPs

• Florida based research and field monitoring

• Sponsored by DEP, FDOT, WMDs, local governments

• Focus on traditional and innovative BMPs

• Results online:

• http://www.dep.state.fl.us/water/nonpoint/pubs.htm#Urban_Stormwater_BMP_Research_Reports

• https://stormwater.ucf.edu/

• http://www.fdot.gov/research/documents.shtm

Pollutant Load =

(Concentration) * (Volume)

Stormwater volume factors:

• Rainfall variables include when, where, how long, how intense,

time between storms

• Natural stormwater variables include soils, geology, SHWT, topography, vegetation

• Human stormwater variables

include land use, site design, soil compaction, percent imperviousness, % DCIA

Stormwater

Event Mean ConcentrationsTable 5.2.3. Pinellas County Manual EMCs

Current BMPTRAINS EMCs

Minor differences in EMCs

for LDR do to difference in

EMCs for Natural

Vegetative Communities

How Do We Reduce

Stormwater Loading?

• Reduce stormwater pollutant concentrations

• Reduce stormwater volume

• Better site design – integrate stormwater into site, treat stormwater as water resource

• Use BMP Treatment Train with nonstructural and structural stormwater BMPs

• Minimize imperviousness, especially DCIA

• Reduce pollutants using source controls including public education

What Is Low Impact Development?

• Comprehensive watershed approach

• Hydrology is integrating framework

• Maintain predevelopment volume and hydrology

• Control stormwater at the source

• Combine nonstructural pollution prevention BMPs with structural BMPs

• Create multifunctional landscape and infrastructure

Pollution and Hydrologic Prevention

What Low Impact Development is Not

LID is NOT a silver bullet solution to all stormwater problems

• Additional nonstructural and structural tools in the BMP tool box

• Infiltration BMPs do not work everywhere

LID is NOT a new idea• “Designing with Nature”

1969 book by Ian McHarg

• FL stormwater program has alwayspromoted retention BMPs

Why Low Impact Design?

Added BMPs In Tool Box

• Promote development and redevelopment

through greater flexibility

• Build local economy and promote “urban

regeneration”

• Get higher levels of stormwater treatment

• Keep loads out of MS4

• Protect local taxpayers and water bodies

City of Palmetto

Urban regeneration project

Low Impact Design Projects in Florida

Madera,

Gainesville

River Forest,

Bradenton

Baldwin Park,

OrlandoTown of

Harmony

LID Site Planning Principles To Reduce

Stormwater Volume/Loads

• Consider stormwater as a resource

• Protect/avoid sensitive areas

• Minimize disturbed areas / soil compaction

• Minimize loss of vegetation and trees

• Plant more trees – intercept rainfall

• Florida-friendly landscaping

• Maximize infiltration/stormwater harvesting

• Minimize imperviousness, especially DCIA

• Integrate stormwater BMPs into landscaping

• Cluster development, increase open space

• Use innovative planning tools such as those coming in Pinellas County Code revisions

Source Controls For

Pollution Prevention• Minimize clearing, removal of trees, vegetation

• Include urban reforestation

• Minimize imperviousness, esp. DCIA

▪ Minimize soil compaction

▪ Narrow streets, pervious parking, recessed

tree islands

▪ Greenroof/cistern systems for large roofs

▪ Roof runoff to cisterns, pervious areas

• Minimize pollutants

▪ Florida-friendly landscaping design

▪ Florida-friendly fertilizers

▪ Proper use of reclaimed water

▪ Pet waste pick up and disposal

Chapter 1: IntroductionChapter 2: Site PlanningChapter 3: County Stormwater RequirementsChapter 4: Stormwater QuantityChapter 5: Stormwater QualityChapter 6: Stormwater BMPsAppendices

Increases the

number and types

of stormwater

BMPs available to

site designers

Pinellas County Stormwater Manual

• Any development or redevelopmentactivity that generates stormwater from impervious surfaces must meet Manual’s requirements

• Exemptions in Section 3.5.1

• Waivers and adjustments for sites 1 acre or less if it is technically infeasible to meet performance standards

• Minimum treatment is post-development load < pre-development

What Level of Stormwater Treatment?5.1.1. General Performance Standards

Except for exempt projects meeting the criteria in Subsection 3.5.1, the stormwater treatment system shall be designed to achieve the highest level of pollutant removal of the following performance standards:

1. Reduce the post-development annual average stormwater total nitrogen load by at least a 55% and the annual average stormwater total phosphorus load by at least 80%, OR

2. Reduce the post-development annual average stormwater total nitrogen and phosphorus loads to a level less than or equal to 90% of the loads currently discharged from the site. (Net improvement = pre-development load – 10%).

Site Planning and Source Control BMPs In

Pinellas County Manual

Site PlanningBMPs

BMP Name TreatmentCredit

SP1 Inventory Site Assets: Hydrology

SP2 Inventory Site Assets: Topography

SP3 Inventory Site Assets: Soils

SP4 Inventory Site Assets: Vegetation

SP5 Preserve Open Space

SP6 Natural Area Conservation ✔️

SP7 Cluster Design

SP8 Minimize Fill Material

SP9 Minimize Building Footprint

SP10 Minimize Total Impervious Area

✔️

SP11 Minimize DCIA ✔️

SP12 Curb Elimination and Cuts

Source Control BMPs

BMP Name Treatment Credit

SC1 Protect Surface Waters & Wetlands

SC2 Use Selective Site Clearing and Grading

SC3 Retain depression storage

SC4 Minimize Soil Disturbance and Compaction

SC5 Build with Slope

SC6 Retain Native Plants

SC7 Use Florida-friendly Landscaping and Fertilizers

✔️

Rainfall Interception Trees -See BMP 6.15

✔️

SC9 Efficient Irrigation

SC10 Non-potable Water Irrigation

SC11 Community and Homeowner Education

Structural BMPs In Pinellas County ManualStormwaterTreatment BMPs

BMP Name Treatment Credit

6.1 Retention Basin ✔️

6.2 Exfiltration Trench ✔️

6.3 Underground Storage and Retention ✔️

6.4 Treatment Swales ✔️

6.5 Vegetated Natural Buffers ✔️

6.6 Pervious Pavement ✔️

6.7 Green Roof with Cistern ✔️

6.8 Wet Detention ✔️

6.9 Stormwater Harvesting ✔️

6.10 Up-Flow Filter ✔️

6.11 Managed Aquatic Plants (MAPS) ✔️

6.12 Biofiltration with BAM ✔️

6.13 Rain Gardens ✔️

6.14 Rainwater Harvesting ✔️

6.15 Rainfall Interceptor Trees ✔️

Improved Site Planning BMPs

SP5 - Preserve Open Space

SP6 – Natural Area Conservation,

retain tree canopy

SP7 - Cluster development*

SP9 - Minimize building footprint*

SP10 - Minimize total imperviousness*

SP11 - Minimize DCIA*

SP12 - Curb elimination & curb cuts*

NATURAL AREA CONSERVATION

• Credit for preserving natural areas

Planting trees in urban

areas intercepts and

evaporates rain and

reduces stormwater

volume and loads

The Stormwater Benefits Of Trees

Interceptor Trees

BMP 6.15.3

Up to 18% reduction in

stormwater volume

NEED MORE DATA

AND SITES!

Biological Pollutant Removal

Plant / Soil Flora / Soil Chemistry

• Phytoremediation

– Translocate

– Accumulate

– Metabolize

– Volatilize

– Detoxify

– Degrade

• Bioremediation

Trees Are Stormwater BMPs!

Urban Ecosystem Analysis, Jacskonville

• American Forests (www.americanforests.org)

I-TREE TOOLS

http://www.itreetools.org/

Using Low Impact Development

To Reduce Imperviousness

• Cluster development

• Tailor and decrease road width

• Minimize road length

• Use pervious pavements for parking

• Reduce required parking spaces

• Reduce parking space size

• Use one way angled parking

• Minimize paved driveways/size

• Side walks on one side only

Requires Land Development Code revisions

Currently underway

Reducing Imperviousness

In Parking Lots

Nonstructural tools• Reduce required parking spaces • Reduce parking space size• Use one way angled parking

BUT, THIS MAY REQUIRE CODE OR

CULTURAL CHANGE

Structural tools• Use pervious pavements for parking

▪ Pervious concrete▪ Turf block/pavers▪ Geoweb and sod

THE INFLUENCE OF DCIA

ON STORMWATER VOLUME

Agriculture land use (pasture)

No DCIA, CN for D soils = 90 C = .266

SF residential land use

¼ acre lots - DCIA = 40%, CN for lawns, D soils = 90 C = .489

Zone 4

Mean Annual Runoff Coefficients (C Values) as a Function

Of DCIA Percentage and Non-DCIA Curve Number (CN)

Reducing Parking Lot

Imperviousness And DCIA

Disconnecting Directly Connected Impervious

Areas (DCIA)

RECESSED ROAD MEDIANS AS BMPs

Source Control BMPs

SC1 – Protect waters/wetlands

SC2 - Retain depression storage

SC3 – Selective clearing/grading

SC4 - Minimize compaction

SC5 - Build with slope

SC6 - Retain native plants

SC7 - Florida-friendly landscape*

SC8 - Rainfall interception trees*

SC9 - Install efficient irrigation

SC10 - Harvest and use stormwater*

SC11 - Public education

Source Controls For

Pollution Prevention

• Minimize clearing, removal of trees, vegetation

• Include urban reforestation

• Minimize imperviousness, esp. DCIA

▪ Minimize soil compaction

▪ Narrow streets, pervious parking, recessed tree

islands

▪ Greenroof/cistern systems for large roofs

▪ Roof runoff to cisterns, pervious areas

• Minimize pollutants

▪ Florida-friendly landscaping design

▪ Florida-friendly fertilizers

▪ Proper use of reclaimed water

▪ Pet waste pick up and disposal

Land Clearing, Vegetation Removal

And Soil Compaction

80% compaction on first

pass of equipment

Soil Compaction And Infiltration Rates

SOIL TYPE INFILTRATION RATE

(in/hr)

Pitt et. al. Gregory

Sandy soils 13.0 14.8 – 25

Compacted sandy soils 1.4 0.3 - 6.9

Clay soils 9.8 NA

Compacted or wet clay

soils

0.2 NA

Source: Pitt, Chen, and Clark, 2001; Gregory, 2006

Florida-friendly

Landscaping Principles

1. Right plant, right place

2. Water efficiently, use

stormwater

3. Fertilize properly

4. Mulch

5. Attract wildlife

6. Manage yard pests properly

7. Recycle clippings and leaves

8. Reduce runoff

9. Protect the waterfront

http://www.floridayards.org

Use Florida-friendly Fertilizers

Get 3% Load Reduction CreditFollow requirements in Pinellas County Landscape Maintenance and Fertilizer Use and Application Ordinance (2010):

• Only apply Oct 1 to May 31

• No phosphorus unless soil test need

• Granular must be 50% slow release

• Liquid app rate < 0.5 lbs N/1000 sf

• Spring app rate = 2 lbs N/1000 sf

• Winter app rate = 1 lb N/1000 sf

• Annual app rate = 4 lbs N/1000 sf

• Commercial fertilizer applicators and landscape maintenance professionals must be certified

PET WASTE: A Major Source Of

Nutrients And Bacteria Pollutants

Animal Average fecal

coliform per

gram of feces

Fecal coliform

load per day

Human 13,000,000 1,921,920,000

Dog 23,000,000 7,728,000,000

Cow 230,000 5,358,080,000

Horse 12,600 293,529,600

• Pets deposit up to 0.5 lbs/day of pet waste

• Contributes to bacterial and nutrient

pollution

RAINFALL INTERCEPTOR TREES

Interceptor Tree BMP

Up to 18% reduction in

stormwater volume

Interim BMP, Need more data!

Use to meet PCSWM Net Improvement

Structural BMPs in Pinellas County

Stormwater Manual

Retention BMPs

• Basins

• Exfiltration trenches

• Underground retention storage

• Swales

• Vegetated natural buffers

• Rain gardens

• Pervious pavements

Harvest & Reuse BMPs

• Greenroof/cistern

• Rainwater harvesting

• Wet detention

• Stormwater harvesting

Filtration BMPs

• Managed aquatic plants

• Upflow filters

• Biofiltration with BAM

LID BMPs And Getting An Environmental

Resource Permit

LID BMP SWFWMD ACCEPTABILITY

Rain garden (bioretention) Retention BMP

Swales Retention BMP

Vegetated Natural Buffers Check with staff

Pervious pavements Retention BMP

Green roof with cistern Retention and reuse BMP

Rainwater harvesting Retention BMP, not rain barrel

Stormwater harvesting Check with staff

Biofiltration with BAM Filtration BMP

6.1. Retention (Infiltration) Practices

DESCRIPTION: Family of practices where the stormwater is infiltrated or evaporated rather than discharged.

PURPOSE:• Reduce total volume

• Reduce pollutants

POLLUTANT REMOVAL:• Percolation, evaporation

• Filtering and adsorption

• Effectiveness = % annual runoff retained

Retention BMP Treatment Volume and

Load Reduction Effectiveness

Required Treatment VolumeSWFWMD – off-line - 0.5” runoff

-- on-line – runoff from 1” rain-- OFW - 50% more volume

Treatment effectiveness varies from 42.6% to 94%

Retention BMP Treatment Volume to get

80% Load Reduction Effectiveness

Required Treatment Volume from tables

varies from 0.23” to 1.59”

Getting Good Infiltration Data for

Retention BMP Design

• See Appendix A of Manual

• Measure at proposed bottom elevation

• Allowable data

▪ Mass balance field data

▪ Double ring infiltrometer *

▪ Lab permeability tests *

▪ NRCS soil survey - planning only

* Use half of the value

Retention BMP Design Criteria

• Determine Required Treatment Volume from Tables based on required % load reduction

• Ensure both RTV and flood control volumes can be stored safely

• Recover RTV within 24-36 hrs if vegetated• SHGWT at least 2’ beneath bottom of retention

BMP, must consider mounding• Sides and bottom must be stabilized by

Florida-friendly vegetation, other pervious materials or as approved

• Do not construct within 50 feet of potable well or within 15 feet of OSTDS (Note: setback to private potable well is 75’)

Retention BMP Construction

• Locate and mark locations of all retention BMPs

• Prevent traffic and equipment from entering to

minimize soil compaction

• Excavate with lightweight equipment with tracks

not tires

• Initially excavate to within 12” of design bottom

• Do not use for erosion/sediment control during

construction

• Once drainage area stabilized, remove

accumulated materials and excavate to final

bottom elevation. Deep rake or till the bottom to

compensate for compaction.

• Vegetate and landscape per plans.

Retention BMP Maintenance Inspection

• Standing water or soggy soils,

cattails

• Erosion and sedimentation

• Vegetation - coverage, growth,

type

• Soil compaction or smearing

• Pretreatment BMPs

• Contributing area stabilization

• Inlets, discharge – sediment,

litter, debris, vegetation

Retention BMP Maintenance Activities

Objective – maintain or restore percolation rate

• Remove accumulated solids

• Mowing and removal of vegetation

• Repair erosion, vegetative stabilization

• Tilling, disking, aerating the bottom

• Check structures

• Clear debris from structures

• Clean pretreatment BMPs

6.2. Exfiltration Trench

DESCRIPTION: An underground retention system consisting of an inlet and perforated pipe within a gravel envelope where the stormwater is infiltrated rather than discharged.

PURPOSE:• Reduce total volume

• Reduce pollutants

POLLUTANT REMOVAL:• Percolation, evaporation

• Filtering and adsorption

• Effectiveness = % annual runoff retained

Exfiltration Trench Design Criteria

1. Follow retention BMP requirements

2. 12” minimum perforated pipe diameter with

minimum of 3’ of trench

3. Pipe not exceed 45º bend

4. Aggregate must be washed to remove fines

5. Trench enclosed within filter fabric

6. Must have OM access via manhole, inspection

ports, or observation wells

7. Pretreatment baffle trash tee at inflow and 24”

sump with 12” weep hole

Exfiltration Trench Pretreatment Details

Exfiltration Trench Construction

Recommendations

• Follow retention BMP recommendations

• Minimize soil and debris entry into trench

• Excavate with backhoe to minimize soil

compaction

• Inspect trench bottom and sides to remove

tree roots and other items that tear fabric

• Inspect aggregate to ensure size and

washed

• Block inflows to trench until contributing

area is stabilized

Exfiltration Trench Maintenance Activities

Objective – maintain or restore percolation rate

• Inspect and monitor sediment accumulation in

pipe and storage volume recovery

• Inspect pre-treatment BMPs and clean as needed

• Check structures and clear debris from

structures

• If needed, remove sediment from pipe by

suctioning or high pressure jet washing

• If clogged, total replacement may be required

6.3. Underground Storage and Retention System

DESCRIPTION: An underground retention system consisting of an inlet and modular storage units with an open bottom allowing the stormwater to be infiltrated rather than discharged.

PURPOSE:• Reduce total volume

• Reduce pollutants

POLLUTANT REMOVAL:• Percolation, evaporation

• Filtering and adsorption

• Effectiveness = % annual runoff retained

Underground Retention Design Criteria

1. Follow Exfiltration Trench BMP requirements

2. Follow manufacturer’s recommendations

3. 12” minimum perforated pipe diameter with

minimum of 3’ of trench

4. Pipe not exceed 45º bend

5. Aggregate must be washed to remove finesds

6. Trench enclosed within filter fabric

7. Must have OM access via manhole, inspection

ports, or observation wells

8. Pretreatment baffle trash tee at inflow and 24”

sump with 12” weep hole

6.13. LID BMP Rain Garden

• Small retention depressions integrated

into the landscaping with deep rooted

Florida-friendly vegetation.

• http://lowimpactdevelopment.org/raingard

en_design/whatisaraingarden.htm

Rain Garden Design Criteria

• Contributing DA <3 acres

• Ponding depth – 4 to 10 inches

• Location – sunny, on slopes <10%, at

least 10’ from buildings

• Vegetation – See table of plants. Depends

on planting zones, dry to wet zones, need

a good plan

• Mulch – use materials that won’t float

Rain Garden Design Considerations

• Contributing DA (<3 acres)

• Ponding depth (4 to 10 inches)

• Retention or detention system?

• BAM used? If yes, which one and %

removal

• Sustainable void space - .20

• Water above media volume? (ponding d)

• Media volume?

Treatment Volume will

be calculated from

above information

Rain Garden Construction

• Determine final shape and location after locating utilities, mark on ground

• Excavate the garden, use soil for berm

• Prepare and add soil/media mixture (BAM)

• Install plants per the design, 1’ On Center

• Apply mulch (if used)

• Water plants regularly

• Check conveyance inflow,

water storage, and

infiltration rate

Rain Garden Maintenance

• In first year, water and weed regularly

• Inspect at start and end of rainy season

• Check infiltration rate after rainy season

• Each spring, remove dead vegetation

and replenish mulch

• Weed and maintain plants as needed

• Remove sediment, trash, debris

• Repair erosion, as needed

6.5. LID BMP – Vegetated Natural Buffers

• A vegetated area with soil and water

table conditions that allow filtering and

infiltration of overland flows.

• Used to treat rear roof and yard runoff

when impractical to route to main

stormwater system.

• Treatment based on retention volume

that is infiltrated

5.8 LID BMP – Vegetated Natural Buffers

Vegetated Natural Buffers Design Criteria

• Infiltrate required treatment volume

• SHGWT > two feet below bottom

• 1” minimum infiltration rate

• 25’ minimum flow length, = length of CA

• 100’ maximum width

• 6:1 maximum slope

• Legal easement for VNB

Vegetated Natural Buffers Construction

• Verify location and dimensions of VNB

• Install erosion and sediment controls and divert flows until contributing area construction is complete/stabilized

• Mark VNB boundaries to prevent compaction from equipment

• Install upstream level spreader

• Ensure vegetation is healthy, add Florida-friendly plants as needed

Vegetated Natural Buffers

Inspection and Maintenance

• Inspect during or soon after a storm to visually check sheet flow and flow paths

• Eliminate channelized flow areas and restore vegetation, if needed

• Eliminate erosion, remove sediment, restore vegetation, as needed

• Identify damage from vehicles, foot traffic, or encroachment

• Ensure infiltration within 24 – 36 hrs

5.7 LID BMP - Swale

Chapter 403.803 (14), Florida Statutes

A manmade trench which:

• Has a top width-to-depth ratio of 6:1 or greater

• Has areas of standing or flowing water only

after a rain

• Is planted with vegetation suitable for soil

stabilization, stormwater treatment, nutrient uptake

• Designed for soil erodibility, soil percolation, slope,

slope length, and the drainage area

• Designed to prevent erosion and reduce pollutants

Use of Swales

Types:• Linear retention treatment swale• Conveyance swalesUses:• Along streets, rural road sections• Residential subdivisions• Pretreatment (BMP Treatment

Train)▪ Any land use type, parking lots▪ Before infiltration trenches,

wet ponds• With enhancements

▪ Swale blocks▪ Shallow longitudinal slopes

(settling)▪ Raised driveway culverts

Swale Design Criteria

OBJECTIVES

• Conveyance and Water quality

DESIGN CONSIDERATIONS• Depends on type of swale

• Soil infiltration - HSG A,B soils

• Pavement edge protection

• Slope - flat as possible

• Cross-section - triangular, trapezoidal

• Side slopes - 3:1 or flatter

• Bottom width – usually at least 2 feet

• Vegetation - lawn grasses, native grasses, wildflowers, shrubs

Conveyance Swale Design

Swale Construction

• Verify location and prevent equipment

• Minimize soil compaction

• Construct first, mulch and establish vegetation

• Divert flows until DA stabilized

• Stabilization recommendations

▪ 0 - 4% Seed with erosion blanket

▪ 4 - 8% Staked sod

▪ >8% Staked sod, swale blocks

• Do not use muck grown sod

Swale Inspection and Maintenance

Inspection

• Check treatment volume recovery time and

percolation rates; check for standing water

• Monitor erosion and sediment accumulations

• Check vegetation cover and health

• Check flow path for obstructions, damage

Maintenance

• Restore percolation rate if needed

• Remove trash, debris, sediments

• Maintain healthy vegetative cover

• Mowing – as needed, keep grass 3 - 5” long

• Repair any erosion

• Disk, till, or aerate bottom if needed

• Maintain swale blocks, outlets, and pavement

Break is next

Questions, Remarks, and Discussion

Pinellas County

Stormwater Management

Manual Training

Workshop