Designing LID Treatment Systems

Low Impact Development Systems
Siting, Design and Installation for
Maximum Environmental Benefit.
What are the aesthetic,
maintenance, & financial
considerations?

AIA, Committee on the Environment
Sustainable Sites Program
New Haven, Connecticut

Presenter Background
Nationally recognized expert in Low Impact
Development (Regulations and Applications)

Licensed Professional Engineer (CT)

Holds IECA certifications as CPESC &
CPSWQ

Over 27 years in the Land Development Field
and 11 years working with Low Impact
Development

12/16/2010 Copyright Trinkaus Engineering

Stormwater Management
Old Way to New Way

University of Arkansas Community Design Center

Types of LID Treatment System
(Dry)
Bioretention

Dry Swales

Infiltration Basins & Trenches

Sand Filters

Permeable Pavement & Porous Concrete

Filter Strips


Types of LID Treatment System
(Wet)
Wet Swales

Constructed Wetlands & Ponds

Subsurface Gravel Wetlands

Organic Filters


How they work

All “Dry” LID systems function by
infiltrating runoff into the underlying
native soils where physical, chemical
and biological processes treat and
reduce pollutant loads


How they work

All “Wet” LID systems function by
creating an anaerobic environment
when bacteria can reduce pollutant
loads. Additional pollutant removal
occurs by physical settlement and
vegetative uptake


Siting of LID Systems on the
Landscape
Site Considerations:

Soil Class & Infiltrative Capacity

Depth to Groundwater

Slope of Land

Hydrologic Conditions


Soil Classes
Four Main Soil Classifications (NRCS)
“A” – Excessively well drained (Sands &
Gravels
“B” – Well drained (Sandy Loams)
“C” – Moderately well drained (Fine
Sandy Loams to Silt Loams)
“D” – Poorly drained (soils with high silt,
clay content [wetland soils]


Soil Textural Classes


Soils: Get your hands Dirty!!!
Test Pit: Best way to see the Mason Jar Test: Simple test
dirt. OK, you don’t need 14 to determine type & amount of
people to log a test pit soil particles


“A” Soils


“B” and “C” Soils


“D” Soils


Average Infiltrative Capacity
“A” Soils: 10 – 200 feet/day

“B” Soils: 3- 12 feet/day

“C” Soils: 1 – 3 feet/day

“D” Soils: NONE


Average Depth to Groundwater
“A” Soils: > 10 feet on average, but can
be less depending upon position on
landscape
“B” Soils: 6 – 3 feet

“C” Soils: 1 – 2 feet

“D” Soils: On Surface

Land Slope


LID Slope Issues
Ideal slope for Bioretention systems is 2 –
10%

Ideal slope for Vegetated Filter Strips < 6%

Ideal slope for Infiltration Basin < 6%


Primary LID System:
BIORETENTION


BIORETENTION SYSTEMS

Functionality:
Settling of coarse & fine sediments on
surface

Removal of pollutants by physical, chemical
and biological processes

Infiltration of runoff into underlying soils


BIORETENTION SYSTEMS

Design Requirements:
Maintain specified separation to seasonally high
groundwater level
Surface storage must contain required Water
Quality Volume (fixed volume)
Depth of Ponding (vary per natural soil type)
Specific Soil Media (Enhance pollutant removal)
Appropriate Plants
Ponded water shall drain in 24 hours, no more than
48 hours


BIORETENTION
1. Facility handles
1,900 sq.ft. of
residential roof
2. Has not
overtopped in 3
years
3. Located in “B”
soils

Newtown, CT – Trinkaus Engineering

BIORETENTION
1. Facility handles
2,800 sq.ft. of
road runoff
2. Facility is 4’ x 9’ x
10” deep
3. Never overtopped
in 2 years
4. Located in “B”
soils
5. Soil media is 50
% sand & 50%
leaf compost
6. Ponded surface
drains down in
less than 4 hours
after rainfall

Southbury, CT – Trinkaus Engineering

BIORETENTION
Field Investigation:
Deep Test Pit at least 6’ deep
Type & Description of each soil layer
Sample Soil Description:
0 – 4” Topsoil (Organic layer)
4 – 33” Orange brown fine sandy loam
33 – 48” Orange brown fine sand to silt loam
48 – 84” Brown grey lightly compact sand &
gravel, No ledge, no mottling, no water,
roots to 48”


BIORETENTION
Field Investigation:
Percolation Test:
Depth of test shall be approximately equal to
anticipated depth of soil media for
Bioretention
Shall be above season high groundwater level
Provides reasonable estimate of soil
infiltrative capacity


Location, Location, Location
1. Bioretention are
infiltration systems – do
the soils next to a
wetland infiltrate?
2. Bottom of system is 6”
above observed seasonal
high groundwater level
3. Bottom of system is 2’
below ex. grade in
wetlands
4. Treating parking lot
runoff – require 3’
vertical separation to
groundwater


This looks easy, what can go
wrong???
1. Ponding
more than 3
days AFTER
a rainfall
event
2. Very few
plants
3. Site was not
fully
stabilized
prior to
installation
of facility

Trinkaus Engineering

wrong???

1. Use outdated detail
for construction,
2. Inappropriate soil
media (too much
topsoil)
3. Use of filter fabric
(causes clogging,
reduced or no
infiltration


wrong???

1. Overflow grate
set flush to soil
surface – NO
STORAGE
VOLUME
2. Questionable
soil media,
visual inspection
shows large silt
component
3. One tree
(outside of low
point of facility

wrong???
1. Overflow grate set
flush to soil
surface, NO
STORAGE VOLUME
2. Notch on left side
has no function,
parking pitches
away from facility
3. 24” of soil media on
top of Structural
fill with no
underdrains (Where
would the water go
if it could
infiltrate?)



wrong???
1. Runoff can only enter near low
1. At low point is flush catch basin end of sloping facility
grate directly connected to
hydrodynamic separator 2. Runoff must make 90 degree turn
into facility
2. No available storage for runoff
3. Minimal storage around overflow
3. Balance of island is raised, not grate
depressed

CT NEMO CT NEMO


wrong???
1. How does runoff
enter this facility?
(Forgot to cut
notches thru curb

CT NEMO

Bioretention Installation

Excavate to required subgrade
Scarify with hand rake; bottom and
sides of facility to remove soil smearing
Place 1-1/4” crushed stone (storage
layer) w/underdrain & overflow pipe
Place pea gravel filter layer
Mix and place soil media layer
Install plants

Scarification of Native Soils

Harwinton Sports Complex – Trinkaus Engineering


Scarification and Placement of
Reservoir Layer



Installation of underdrain/overflow
pipe & Pea Gravel



Bioretention Construction
Protect area from construction traffic
and stockpiling during site work

Fully stabilize surface around
bioretention area, such as pavement

Do not install when soils are wet (will
adversely affect infiltration capacity)


Erosion/Sediment Issue

Unstabilized site
surrounding Bioretention
Area Silt layer from gravel parking
base material - clogged
Bioretention soil surface

North Carolina State University – Bioengineering Group

Result from prior slide

North Carolina State University – Bioengineering Group

Bioretention Maintenance
Mulch around plant stems only
Stabilize inlet of runoff with stones to
encourage overland flow
Weed basin annually for first two years
Prune vegetation as needed
Remove accumulated sediment at inlet by
hand


Swales
Bioswales (Dry) Swales:
Linear applications

Max. slope = 4.0%

3’ vertical separation from top of soil to
shallow groundwater

Bioretention soil media – 30” in depth


Swales
Wet Swales:
Max. slope = 4.0%

Bottom of swale must intercept shallow
groundwater level (necessary to create &
maintain hydrologic condition)

Plant with wetland species


Dry & Wet Swales
Dry Swale Wet Swale

CT NEMO Dr. Bill Hunt, PE (NCSU)


Dry Swales

High Point – Seattle, WA SEA Street Retrofit – Seattle, WA


Dry Swale Construction
Protect area from construction traffic and
stockpiling during site work, do not want to compact
underlying soils

Fully stabilize contributing drainage area above swale.
Prevent silt from entering the system

Do not install when soils are wet (will adversely affect
infiltration capacity)

Vegetation must be fully established before receiving
runoff


Dry Swale Maintenance
Maintain grass at 4” height
Weed swale annually for first two years
Prune vegetation as needed
Remove accumulated sediment at inlet
by hand


Wet Swale Construction
Protect area from construction traffic and
stockpiling during site work

Fully stabilize contributing drainage area above swale.
Prevent silt from entering the system

If soils are a little wet, it is OK – we want a silty, wet
environment

Vegetation must be fully established before receiving
runoff


Wet Swale Maintenance
DO NOT MOW OR CUT VEGETATION
Remove any invasive species
Do not prune vegetation, denser is
better
Accumulated sediment can actually help


Vegetated Filter Strips
Maximum slope = 6%

Stone
trench or
raised
concrete
lip – very
Generally – important
berms are not to achieve
needed or overland
desired as flow
concentration
flow can
develop


Vegetated Filter Strips

Ledgebrook Lane – Trinkaus Engineering

Filter Strip Construction
Prevent compaction of soils
If soils get compacted, perform deep
tillage (12-18”) to restore infiltrative
capacity.
Protect area with erosion control
measures above filter strip to prevent
erosion


Filter Strip Construction
Grade uniform cross slope to ensure
overland flow will occur
Hydroseed filter strip area
ONLY allow runoff onto filter strip
after fully vegetated
A hardened edge must be installed
above the filter strip to achieve
overland flow


Filter Strip Maintenance
Inspect annually and remove
accumulated sediment from upper edge
of filter strip
Maintain vegetation at an appropriate
height


Why a Slope Limitation and
Minimum Width Requirement?
Filter strips on unreinforced slopes >
6% are susceptible to small rivlets of
concentrated flow, leading to erosion

Flow widths < 25’ will not adequately
disperse concentrated flow to overland
flow


Infiltration Basin

Off-line design:

Treat and fully infiltrate Water Quality
Volume

By-pass larger flows


Infiltration Basin
-3’ separation from bottom of
system to SHGW
- Native soils must have < 20%
& 20-40% silt/clay
- Native soils must have in-
situ infiltration rate of 0.5”/hr
- 25% of WQv to be provided
by pretreatment
- Must be installed “off-line)
- Install on slopes < 6%
- Basin to fully infiltrate WQv
through bottom of basin only


Infiltration Basins

Design Infiltration Rates for Soil Textures

USDA Soil Texture Design Infiltration Rate (fc)
Sand 8.27 “/hr
Loamy Sand 2.41 “/hr
Sandy Loam 1.02 “/hr
Loam 0.52 “/hr
Silt Loam 0.27 “/hr


Infiltration Basin
Mulvaney Subdivision – Ridgefield, CT

1. Very sandy soils –
has never
discharged via
overflow pipe
2. System is not off-
line, yet fully
infiltrates all runoff
3. Designed &
Constructed in
2000 prior to State
Design
specifications

Mulvaney Subdivision – Trinkaus Engineering

Infiltration Basin Construction
Prevent ALL vehicular movement over
area of infiltration basin
Construct pre-treatment facility
(forebay) and basin (off-line facility)
Vegetated as soon as grading is done
No runoff allowed until dense vegetated
cover has been established


Infiltration Basin Maintenance
Inspect forebay and remove
accumulated sediment on annual basis
Remove leaves from bottom of basin
annually
Mow grass on regular basis to maintain
4” height (+/-)


Permeable Pavement Design &
Maintenance
Maintain required vertical separation to
shallow groundwater
Do not overly compact native soils,
reservoir course and filter course of
pavement system
No application of sand
Minimal applications of salt (75% less
than normal)


Permeable Pavement/Porous
Concrete


Porous Concrete Design &
Maintenance
Maintain required vertical separation to
shallow groundwater
DO NOT USE SALT ON SURFACE
UNTIL IT HAS CURED 12 MONTHS
Can use sand in first winter, but must
use vacuum sweeper to remove fines
from surface


Construction Costs
Bioretention:
$14,000 per acre treated
Permeable Pavement:
$ 6-8/sq.ft., does not include site prep.
Porous Concrete:
$ 8-11/sq.ft., does not include site prep

Surface materials are approximately +20%
than standard surface materials


Construction Costs
Subsurface Gravel Wetlands:
Permanent Wet Pond:
Wet Swale:
Dry Swale:


Placement on the Landscape
Impervious area disconnection –
driveway runoff as overland flow
across 75’ of vegetated surface

Site Fingerprinting –
defined clearing area as
percentage of lot area

24 Lots – 64+ acres of
Meadow filter strip with Bioretention systems for
preserved Open Space
Micro-berm at edge of roof drains
development envelope


Placement on the Landscape
Constructed Wetland System
w/forebay & vegetated outlet
swale to wetland

Linear vegetated
level spreader

Subsurface flow gravel
wetland w/forebay &
vegetated outlet swale to 24 Lots – 64+ acres of
wetland preserved Open Space
Infiltration trenches for driveway
runoff


Individual Lots
Meadow filter
strip Bioretention for
roof runoff

Impervious area
disconnection


Individual Lots
Bioretention for roof drains

Meadow Filter
Strip


Holland Joint Venture - Commercial

Conventional Stormwater Plan:
Catch Basins & Pipe
Two Dry Detention Basins
Estimated Cost of Conventional:
$ 200,000.00


Holland Joint Venture -
Commercial
Bioretention in parking island & along
perimeter of facility – sheet flow from building
out to facilities


Holland Joint Venture - Commercial

LID Stormwater Plan:
Grade parking lot to use sheet flow, direct
runoff to treatment systems
Construct four Bioretention systems to
handle WQV for roof & parking area
Construct Biorention system to handle
WQV from access roadway
Estimated Cost of LID: $ 110,000.00


Harwinton Sports Center -
Commercial
Conventional Stormwater Plan:
Catch Basins & Pipe
600 lf – 24” Perforated HDPE in crushed
stone in select fill
Cost of Conventional System: $ 90,000.00


Harwinton Sports Center -
Commercial
Bioretention System with Dry
Conveyance Swale


Harwinton Sports Center
LID Stormwater Plan
Grade parking lot to two low points,
eliminate all structural drainage
Construct two Dry Swales to convey runoff
Construct two Bioretention systems to
handle WQV for roof & parking area
Cost Saving over Conventional Plan:
$ 40,000.00


Subsurface Gravel Wetlands

Subsurface Gravel
Wetlands: siting OK, not
designed per UNHSC
specifications – WQV not
provided per specs.


Pseudo-LID at “End of the Pipe”

Proposed ponding depth =
3’ will kill plants in
system due to excessive
inundation

Bioretention in close proximity to wetland
boundary – no sizing calculations


QUESTIONS??


Contact Information
Steve Trinkaus, PE, CPESC, CPSWQ
Trinkaus Engineering, LLC
114 Hunters Ridge Road
Southbury, CT 06488
203-264-4558, Fax: 203-264-4559
Email: strinkaus@earthlink.net
Website:
http://www.trinkausengineering.com


Designing LID Treatment Systems

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