The document provides information on a presentation about low impact development systems for stormwater management. The presentation discusses:
1. Types of LID treatment systems including bioretention, swales, infiltration basins, and more.
2. Key considerations for siting LID systems including soil characteristics, depth to groundwater, and slope.
3. Design requirements and maintenance considerations for different LID treatment approaches like bioretention, swales, and filter strips.
1. 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
2. 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
3. Stormwater Management
Old Way to New Way
University of Arkansas Community Design Center
12/16/2010 Copyright Trinkaus Engineering
4. Types of LID Treatment System
(Dry)
Bioretention
Dry Swales
Infiltration Basins & Trenches
Sand Filters
Permeable Pavement & Porous Concrete
Filter Strips
12/16/2010 Copyright Trinkaus Engineering
5. Types of LID Treatment System
(Wet)
Wet Swales
Constructed Wetlands & Ponds
Subsurface Gravel Wetlands
Organic Filters
12/16/2010 Copyright Trinkaus Engineering
6. 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
12/16/2010 Copyright Trinkaus Engineering
7. 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
12/16/2010 Copyright Trinkaus Engineering
8. Siting of LID Systems on the
Landscape
Site Considerations:
Soil Class & Infiltrative Capacity
Depth to Groundwater
Slope of Land
Hydrologic Conditions
12/16/2010 Copyright Trinkaus Engineering
9. 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]
12/16/2010 Copyright Trinkaus Engineering
11. 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
12/16/2010 Copyright Trinkaus Engineering
16. 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
12/16/2010 Copyright Trinkaus Engineering
20. 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
12/16/2010 Copyright Trinkaus Engineering
21. 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
12/16/2010 Copyright Trinkaus Engineering
22. 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
12/16/2010 Copyright Trinkaus Engineering
23. 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
12/16/2010 Copyright Trinkaus Engineering
24. 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”
12/16/2010 Copyright Trinkaus Engineering
25. 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
12/16/2010 Copyright Trinkaus Engineering
26. 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
12/16/2010 Copyright Trinkaus Engineering
27. 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
12/16/2010 Copyright Trinkaus Engineering
28. This looks easy, what can go
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
12/16/2010 Copyright Trinkaus Engineering
29. This looks easy, what can go
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
Trinkaus Engineering
12/16/2010 Copyright Trinkaus Engineering
30. This looks easy, what can go
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?)
Trinkaus Engineering
12/16/2010 Copyright Trinkaus Engineering
31. This looks easy, what can go
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
12/16/2010 Copyright Trinkaus Engineering
32. This looks easy, what can go
wrong???
1. How does runoff
enter this facility?
(Forgot to cut
notches thru curb
CT NEMO
12/16/2010 Copyright Trinkaus Engineering
33. 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
12/16/2010 Copyright Trinkaus Engineering
35. Scarification and Placement of
Reservoir Layer
Harwinton Sports Complex – Trinkaus Engineering
12/16/2010 Copyright Trinkaus Engineering
36. Installation of underdrain/overflow
pipe & Pea Gravel
Harwinton Sports Complex – Trinkaus Engineering
12/16/2010 Copyright Trinkaus Engineering
37. 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)
12/16/2010 Copyright Trinkaus Engineering
38. 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
12/16/2010 Copyright Trinkaus Engineering
39. Result from prior slide
North Carolina State University – Bioengineering Group
12/16/2010 Copyright Trinkaus Engineering
40. 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
12/16/2010 Copyright Trinkaus Engineering
41. 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
12/16/2010 Copyright Trinkaus Engineering
42. 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
12/16/2010 Copyright Trinkaus Engineering
43. Dry & Wet Swales
Dry Swale Wet Swale
CT NEMO Dr. Bill Hunt, PE (NCSU)
12/16/2010 Copyright Trinkaus Engineering
44. Dry Swales
High Point – Seattle, WA SEA Street Retrofit – Seattle, WA
12/16/2010 Copyright Trinkaus Engineering
45. 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
12/16/2010 Copyright Trinkaus Engineering
46. Dry Swale Maintenance
Maintain grass at 4” height
Weed swale annually for first two years
Prune vegetation as needed
Stabilize inlet of runoff with stones to
encourage overland flow
Remove accumulated sediment at inlet
by hand
12/16/2010 Copyright Trinkaus Engineering
47. 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
12/16/2010 Copyright Trinkaus Engineering
48. Wet Swale Maintenance
DO NOT MOW OR CUT VEGETATION
Remove any invasive species
Do not prune vegetation, denser is
better
Stabilize inlet of runoff with stones to
encourage overland flow
Accumulated sediment can actually help
12/16/2010 Copyright Trinkaus Engineering
49. 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
12/16/2010 Copyright Trinkaus Engineering
51. 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
12/16/2010 Copyright Trinkaus Engineering
52. 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
12/16/2010 Copyright Trinkaus Engineering
53. Filter Strip Maintenance
Inspect annually and remove
accumulated sediment from upper edge
of filter strip
Maintain vegetation at an appropriate
height
12/16/2010 Copyright Trinkaus Engineering
54. 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
12/16/2010 Copyright Trinkaus Engineering
55. Infiltration Basin
Off-line design:
Treat and fully infiltrate Water Quality
Volume
By-pass larger flows
12/16/2010 Copyright Trinkaus Engineering
56. 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
12/16/2010 Copyright Trinkaus Engineering
58. 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
12/16/2010 Copyright Trinkaus Engineering
59. 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
12/16/2010 Copyright Trinkaus Engineering
60. 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 (+/-)
12/16/2010 Copyright Trinkaus Engineering
61. 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)
12/16/2010 Copyright Trinkaus Engineering
63. 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
12/16/2010 Copyright Trinkaus Engineering
64. 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
12/16/2010 Copyright Trinkaus Engineering
65. Construction Costs
Subsurface Gravel Wetlands:
$26,000 per acre treated
Permanent Wet Pond:
$15,000 per acre treated
Wet Swale:
$3,500 per acre treated
Dry Swale:
$5,500 per acre treated
12/16/2010 Copyright Trinkaus Engineering
66. 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
12/16/2010 Copyright Trinkaus Engineering
67. 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
12/16/2010 Copyright Trinkaus Engineering
70. Holland Joint Venture - Commercial
Conventional Stormwater Plan:
Catch Basins & Pipe
Two Dry Detention Basins
Estimated Cost of Conventional:
$ 200,000.00
12/16/2010 Copyright Trinkaus Engineering
71. Holland Joint Venture -
Commercial
Bioretention in parking island & along
perimeter of facility – sheet flow from building
out to facilities
12/16/2010 Copyright Trinkaus Engineering
72. 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
12/16/2010 Copyright Trinkaus Engineering
73. 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
12/16/2010 Copyright Trinkaus Engineering
74. Harwinton Sports Center -
Commercial
Bioretention System with Dry
Conveyance Swale
12/16/2010 Copyright Trinkaus Engineering
75. 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
12/16/2010 Copyright Trinkaus Engineering
76. Subsurface Gravel Wetlands
Subsurface Gravel
Wetlands: siting OK, not
designed per UNHSC
specifications – WQV not
provided per specs.
12/16/2010 Copyright Trinkaus Engineering
77. 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
12/16/2010 Copyright Trinkaus Engineering