Brown and Caldwell, Jeff Herr, P.E., D.WRE, Lisa Jeffrey, P.E., C.F.M

LID Retrofit Planning,
Design and Construction
Jeff Herr, P.E., D.WRE
National Stormwater Leader
jherr@brwncald.com

Understanding Hydrology for LID
Most rainfall events are 1-inch or less
Rainfall Event
Range (inches)
Mean Rainfall
Depth (inches)
Mean Rainfall Duration
(hours)
Fraction of Annual
Rain Events
Number of Annual
Events in
Range
0.00-0.10 0.041 1.203 0.427 56.683
0.11-0.20 0.152 2.393 0.142 18.866
0.21-0.30 0.252 3.073 0.080 10.590
0.31-0.40 0.353 3.371 0.055 7.312
0.41-0.50 0.456 3.702 0.048 6.325
0.51-1.00 0.713 4.379 0.129 17.102 (117)
1.01-1.50 1.221 5.758 0.051 6.733
1.51-2.0 1.726 7.852 0.024 3.145
2.01-2.50 2.271 8.090 0.011 1.470
2.51-3.00 2.704 10.675 0.006 0.726
3.01-3.50 3.246 9.978 0.003 0.391
3.51-4.00 3.667 13.362 0.002 0.260
4.01-4.50 4.216 15.638 0.001 0.149
4.51-5.00 4.796 17.482 0.000 0.056
5.01-6.00 5.454 23.303 0.001 0.167
6.01-7.00 6.470 40.500 0.000 0.019
7.01-8.00 7.900 31.500 0.000 0.019
8.01-9.00 8.190 3.500 0.000 0.019
>9.00 10.675 46.250 0.001 0.075

Minimal runoff from pervious areas and N-DCIA
Even in HSG ‘D’ soils – DCIA is the driver
CN = 80

Up to 60% of our water use does not
require potable water
Using stormwater when
possible is more sustainable.
Saves energy, reduces GHG,
saves $.

Select the Most Cost Effective BMPs
ESTIMATED REMOVAL EFFICIENCIES
TYPE OF BMP (% LOAD REDUCTION)
TN TP TSS BOD
INFILTRATION/REUSE
1.00” VOLUME 80 80 80 80
1.50” VOLUME 90 90 90 90
WET DET (14 day WSRT) 25-35 60-70 90 50-70
WET DET/FILTER 0-10 50 85 70
DRY DETENTION 10-20 20-40 20-60 20-50
DRY DET/FILTER (-)-20 (-)-20 40-60 0-50
CHEMICAL TREATMENT 20-40 80-90 >90 30-60
WETLAND TREATMENT (-)-90 (-)-90 50-90 (-)-50

Develop a Treatment Train Approach to
Stormwater Management
Maximize Minimize
Runoff &
Load
Generation
Regulations
Public education
Erosion control
Roof runoff
Disconnect IA
Landscaping
Pervious paving
Pavement
cleaning
LID
Conveyance
and
Pretreatment
Swales
Catch Basins
Inlets filters
Oil/water separators
Trash/sediment traps
Additional
Treatment
&
Attenuation
Detention
Wetland
Storage
Sediment sump
Toolbox
Final
Treatment
and
Attenuation
Retention
Detention
Wetland
Chemical
Ozone
UV
Reuse
End of pipe

Directly Connected Impervious Area
is the major source of stormwater runoff.
No opportunity for infiltration.
1-inch rainfall = 0.9 inch runoff

Disconnect Impervious Areas
1-inch rainfall = 0.4-inch runoff
and lower costs!!

City of Portland Green Streets Case Study
Large scale application of LID in City
Taggart Basin (~1,500 acres)
– 100-year old combined sewer
– pipe failures, basement flooding
Pipe only solution: $144 million
LID plus pipes: $81 million
– 600 stormwater LID facilities

Portland Green Streets Curb Extension

Portland Green Streets Planter with Parking

LID Retrofit Benefits
– Retrofit in existing areas
– Treat stormwater near source
– Evapotranspiration can reduce volume
– Infiltration reduces volume
– Traffic calming
– Community amenity
– Is cost effective
– Can be integrated with
other capital projects

LID Retrofit Key Issues
Sizing
– Storage volume, native soils infiltration rates, overflow, cost
effectiveness, soil contamination
Transportation
– Vehicle safety requirements (sight distance)
– Pedestrians and bikes (curb transitions, sidewalks, ADA)
Utilities
– Potable water lines, gas lines, depth of facilities
– Relocation of meters & poles
Urban forestry
Maintenance
– Irrigation, weeding, trash, etc.

LID Lessons Learned
Involve transportation engineering staff
early in design
– Site visits, design review
Address feasibility and costs with design
alternatives
– Utility relocation & depth of new soil
– Parking and pedestrian access
Address short-term & long-term
maintenance
– Planting, trash, sediment, irrigation, weeding

Gwinnett County DWR Case Study
~31 acres total,
18.5 acres impervious,
60% impervious.
Decided only the
immediate site would
be used for treatment;
no off-site treatment.
Wanted to demonstrate
LID can be used for any
level of imperviousness
allowed by County code;
residential, commercial,
or industrial.

Gwinnett County DWR Project Objectives
Determine if it is possible to infiltrate and/or store/reuse
on-site the runoff from the 95 th percentile storm event
(EISA)
Determine effectiveness of different LID practices
Determine construction and operation and maintenance
requirements for infiltration and storage/reuse facilities
Determine capital, O&M and life cycle costs for different
types of LID practices
Use constructed project to educate developers,
engineers, and the public on the use of LID practices
Promote the use of viable LID practices in Gwinnett
County

Completed Project Site Drainage Sub-Basin
Delineation

Developed Historical Annual Rainfall
Probability Distribution for Atlanta
1.73 inch event
= 95 th %
Total average annual rainfall = 49.6 inches.

Performed Subsurface Testing and
Evaluated Site Soil Types

Completed In-Situ Infiltration Testing at
Proposed Bottom of Engineered Soils
Measured infiltration rate = 1 to 6 inches per hour at 6-8 ft below existing grade;
proposed bottom elevation of infiltration practices.

Goal to Include at Least One of Each of
These LID Practices in the Design

Initially Evaluated Three Different LID BMPs
per Sub-Basin
Evaluated effectiveness for runoff volume reduction and cost.

Developed Three Alternative Overall Site
Retrofit Plans- Alternative A

Final Preliminary Plan
Met with all DWR Department Managers and incorporated comments.

Preliminary Plan LID Practices Utilized

Estimated Runoff Volumes and Load
Reductions for Sub-Basins and Project Site

Moving Forward
Estimated Construction Cost = $1,000,000
Estimated Annual O&M cost = $90,000
Submitted 319 (h) grant application to GA EPD;
Requested $600,000 with $400,000 local match
If grant approved, construction scheduled for late
2012
Post construction monitoring proposed for each type
of LID practice
Construction of Phase I (bioretention area and roof
rainwater harvesting system) completed in July 2011
using another 319 (h) grant

Phase I Construction – Completed in one
month, July 2011

Pre-Construction Site Area
Curb inlet for parking area
Drainage area = 1 ac
Imperv. area = 0.7 ac
(parking area)
Parking drains to one
curb inlet.
0.3 acre raised grass
area available.

Excavation and Underdrain Installation
Excavated area for engineered soils
(3-4 ft) and loosened soil to a depth
2 ft. below proposed bottom of
engineered soils.
Installed 6-inch HDPE underdrain
and gravel trench with 15-inch risers.

Engineered Soils and Gravel Backfill
Installed engineer soils in 1 ft lifts
and watered to consolidate.
Installed gravel trenches across
area to aid in runoff distribution.

Backfill Completion and Final Grading
Installed remaining engineered
soils in 1 ft lifts and watered
to consolidate.
Final surface grading 3-5H:1V slopes.

Surface Treatment – Cobble, mulch, plants
and sod

Completed Project
3-inch tall curb
around inlet;
runoff overflows
into curb inlet
when pond is full.
Underdrain and
risers have
closed valve;
Installed to be
used only if pond
does not infiltrate
naturally.
Construction
cost = $100,000
Primary cost was
engineered soil
purchase.
New
curb
Existing
Inlet
New
curb
cuts

Completed Project
Frequent watering is initially required
due to sandy soils.
Installed a 6,000 gallon tank next to
building and roof rainwater harvesting
system in September for watering
bioretention.
(1-inch rain = 1,000 gallons of water)

BMP Life Cycle Cost Comparison
Retrofit
BMP
Life Cycle Cost per
kg TP removed
($)
Life Cycle Cost per
kg TN removed
($)
Pet Waste Education 150 - 300 20 - 40
Second Generation Baffle Box 800 – 1,600 250 - 500
Wet Detention Pond 1,200 - 2,400 500 - 1,000
Dry Detention Basin 3,500 - 7,000 1,250 - 2,500
LID - Bioretention 20,000 - 40,000 2,500 - 5,000
Stream Restoration 2,000 - 4,000 300 - 600
Chemical Treatment 90 - 180 50 - 100
Enhanced Wetland Treatment 100 - 200 100 - 200
Education is very cost effective.
Larger - regional systems tend to have significantly lower life cycle
costs per mass of TP and TN removed than many smaller systems.

LID Planning at Federal Facilities
in the Chesapeake Bay
Watershed
November 3, 2011
Lisa Jeffrey, PE, Brown and Caldwell

Site Assessment Pilot Projects
NAVFAC Mid-Atlantic & NAVFAC Washington
Identify stormwater improvement options
Prioritize sites
Conceptual designs and cost estimates for top
ranked projects
Establish implementation plan for regulatory
compliance – 25 year CIP

Regional Stormwater Improvement Plan
4
1. Project Initiation (Kickoff)
2. Compile Information
3. Characterize Existing Conditions
STEPS
4. Determine Stormwater Compliance Approach
2011

Regional Stormwater Improvement Plan
Physical
Conditions
Conveyance
Infrastructure
T3A – Characterize installation physical
conditions
Draft
TM 3A – 3B
Compile soil types, groundwater, land use/cover,
buildings, impervious area, imagery data in GIS
T3B – Characterize existing infrastructure
Compile GIS, CAD & BMP data for stormwater
infrastructure mapping
Tabulate structure & pipe location, material, size,
elevation & other available data
Review
Meeting
Final
TM 3A – 3B
GIS Data Needs: terrain, imagery,
land use/cover, structures &
improvements, development
timeframes, impervious layer, soil &
groundwater data, CA boundaries,
SW infrastructure, connected
rooftops, existing BMPs,& CAD files
2011

Regional Stormwater Improvement Plan
Final
TM 3A – 3B
Task 3C Hydrologic & SW Management
Summary
– Hydrology Summary
Drainage basins delineated based on contours and
accurate stormwater conveyance system information
(inlets, outlets, etc)
– Existing SWM BMPs
TM 3C –
Delineate DAs
Delineate drainage areas around each BMP
TM 3C –
Delineate BMPs
Tabulate the areas receiving water quality treatment
versus untreated impervious area – to form the basis
of retrofit analysis
Review Meeting Final
TM 3C
GIS Data Needs:
• Topography
• Accurate stormwater
conveyance system information
• Existing BMP locations, types,
drainage areas
2011

Regional Stormwater Planning:
Cheatham Annex/Yorktown Fuels
Site Description:
– Cheatham Annex - 1,570 acres
– Yorktown Fuels - 110 acres
Cheatham Annex - Less than
50% developed, primarily
warehouse storage and forest
Yorktown Fuels maintained as
turf grass, forest on perimeter -
less than 15% impervious

Regional Stormwater Planning :
Cheatham Annex/Yorktown Fuels
Preliminary Site
Assessments
– Storm system maps
– Facility plans
– Outfall reports
– GIS data layers (i.e.
cultural resources)

Regional Stormwater Planning :
Cheatham Annex/Yorktown Fuels
Alternative Analysis
– Location
– Drainage area
– Land use type
– Potential improvement measures for the site
– Sketch of site and potential BMPs
– Utilities
– Observed problems

Chesapeake Environmental Benefit
BMP Efficiencies
Urban BMP
Total
Nitrogen
Load Reduction (%)
Total
Phosphorus TSS
Wet Ponds, Constructed Wetlands 20 45 60
Dry Detention/Hydrodynamic 5 10 10
Dry Extended Detention Pond 20 20 60
Infiltration, A/B soils 80 85 95
Filters (sand/organic/peat) 40 60 80
Bioretention
Permeable
Pavement
C&D w/ UD 25 45 55
A&B w/ UD 70 75 80
A&B w/o UD 80 85 90
C&D w/ UD 10 20 55
A&B w/ UD 45 50 70
A&B w/o UD 75 80 85
Grass Channels
C&D w/o UD
A&B w/o UD
10
45
10
45
50
70
Bioswale 70 75 80

Regional Stormwater Planning :
Cheatham Annex/Yorktown Fuels

Proposed Bioswale Improvement

Infiltration Practices: Bioswales

Rooftop Drainage BMPs
Source: CWP
Infiltration 80%N; 85%P; 95%TSS

Stormwater Storage and Reuse

Infiltration Practices: Permeable Pavers and
Porous Pavement

Parking Lot Retrofit
Retrofit Options:
Bioretention Islands
Permeable Pavers
Grass Swales
Sand Filter
Filter Strip/Infilt.Trench
Source: CWP

:Regional Stormwater Planning :
Cheatham Annex/Yorktown Fuels

Erosion Impacting Storm Drainage

Erosion within drainage system

Design of Natural Stream Restoration
and Erosion Control BMPs
Stream Restoration and
Erosion Control Options

Summary
NAVFAC Stormwater/LID Planning Projects
–Identify stormwater improvement alternatives
–Prioritize alternatives
–Establish plan for improvements required to
meet load reductions
Chesapeake Bay TMDL
–Identify Potential for trading within
Watershed
–Develop facility load reduction compliance
plan