Session 2
Strategies to Consider Prior to
Retrofits
Session 2 Agenda
1. Cost Effective Strategies that don’t
involve traditional retrofits
a) Specific Methods to document load
reductions from non-retrofit practices
Cost Effective Strategies
that don’t involve
traditional retrofits
The Changing Stormwater Landscape Under New
MS4 Permits and the Chesapeake Bay TMDL
~ 10 to 30% TP and TN load
reductions needed from existing
development
Massive Increase in Retrofitting
15 Years to Get It Done
This is inducing a phenomenon known as
“ retrofit stress syndrome”
Infects local public works officials and their elected officials
Common Symptoms:
• Fear of the unknown (what exactly is a retrofit?)
• Excessive phobia about future costs and regulatory
liability
Look Beyond the Storage
Retrofit…to other Restoration
Tools
Inoculate Yourself From RSS
Using Other Nutrient Reduction Practices
1.
2.
3.
4.
5.
6.
7.
8.
P Bans and N Fertilizer Mgmt
BMP Maintenance Upgrades
Redevelopment Credits
Watershed Reforestation
Stream Restoration
Street Cleaning
Illicit Discharge Removal
On-site LID Incentives
1. Take credit for fertilizer reductions on urban turf
• Reflects recent MD and VA PBan in Fertilizer
• Modeled as an application
reduction on urban pervious area
• Initial estimates of 12% TP
reduction for urban sector in
MARYLAND
• Automatic Credit for Localities
• Expert Panel to finalize this
estimate in summer 2012
Urban Nitrogen
Fertilizer Reduction
• 1.5 million acres of home lawn are
fertilized
• Same acreage in State WIP Plans
• What is Urban Nitrogen Management ?
• What are the high risk situations where
UNM is most effective?
• CBP-approved rates of 17% TN for
Urban Nutrient Management is NOT likely
to be continued
CURRENT EXPERT PANEL
Update on Expert Panel on Urban
Nitrogen Fertilizer Management
Current CBP-approved rates of 17%
TN for Urban Nutrient Management
is NOT likely to be continued
N Removal Rate will be Tied to
Effectiveness of Local Outreach
Efforts to Change Behavior for:
• Established Low Risk Lawns
• Established High Risk Lawns
• New Start Up Lawns
For both lawn care companies and do
it yourselfers
Urban Nitrogen Management on Public Land
•
•
•
Public land can comprise 10-15% of total
turf cover in a community
Fertilizer application rates already tend to
be lower
Assess hi risk public lands and change
landscaping practices
Urban Fertilizer Management Example
Panel not ready to define
method yet, and the
per acre rate may not
be very high (2 to
10%), but given that
turf comprises 50 to
70% of urban areas,
even a small credit
could yield impressive
benefits
More than just
brochures!
2. Transform Your
Stormwater Maintenance Program
Use your stormwater maintenance inspection, tracking and repair
budgets to fix problems and boost performance through major
maintenance upgrades
Potential for both public and private stormwater facilities
Design Example –
BMP Restoration
• Captures 0.5” of runoff from the impervious
cover of contributing watershed: 40 acres @ 50%
impervious
• Sedimentation and invasive plant growth 
decreased storage volume by 60%
• Only actually provides 0.2” of runoff capture
• City conducts major sediment dredging, invasive
plant removal, replants pond with natives
• Recovers 0.2” of storage for a total storage of
0.4”
Design Examples – BMP Restoration
If the BMP has previously reported to the state
(and already included in CBWM input deck), then
the removal rates is determined from the curves
as an incremental rate
incremental removal rate = restored rates – original
rates.
Restored Rate
TP
37%
TN
24%
TSS
47%
Original Rate
26%
16%
33%
Incremental Removal Rate
11%
8%
14%
BMP Restoration Example
Total
Nitrogen
Total
Phosphorus
Suspended
Sediment
Tons/acre/year
Pounds/acre/year
IMPERV
PERV
IMPERV
PERV
IMPERV
PERV
MDE
Loading
Rates
10.85
9.43
2.04
0.57
0.46
0.07
Area
(acres)
20 ac
20 ac
20 ac
20 ac
20 ac
20 ac
Baseline
Load
Removal
Rate
Load
Removed
405.6 lbs/yr
52.3 lbs/yr
10.6 tons/yr
8%
11%
14%
32.5 lbs/yr
5.74 lbs/yr
1.49 tons/yr
3. Take nutrient reduction credits for more stringent
stormwater requirements at redevelopment projects
Calculate the expected
acres of impervious cover
slated for redevelopment
•
• New CBP tool calculates
the aggregate nutrient
reduction credit
CURRENT EXPERT PANEL
Design Examples – Redevelopment
A MD developer is redeveloping a 2-acre
facility to build a new warehouse.
• The pre-development and postdevelopment conditions are 50%
impervious and 50% turf land cover.
• The BMPs treat the entire site
• There are 100% D soils at the site and
the site will be developed using RR
practices.
Design Examples – Redevelopment
Using the prescribed method, we
calculate the target runoff depth we
are controlling for to be: 0.24 inches.
Again, we go to the curves!
Pollutant Removal Efficiencies
of the practice
TP
TN
TSS
36% 37% 40%
Calculating Pollutant Reduction for Redevelopment Site
Total
Nitrogen
Total
Phosphorus
Suspended
Sediment
Tons/acre/year
Pounds/acre/year
IMPERV
PERV
IMPERV
PERV
IMPERV
PERV
MDE
Loading
Rates
10.85
9.43
2.04
0.57
0.46
0.07
Area
(acres)
1.0 ac
1.0 ac
1.0 ac
1.0 ac
1.0 ac
1.0 ac
Baseline
Load
Removal
Rate
Load
Removed
20.3 lbs/yr
2.61 lbs/yr
0.53 tons/yr
37%
36%
40%
7.5 lbs/yr
0.94lbs/yr
0.21 tons/yr
Individually, load reductions from redevelopment are not impressive
But across a
community and over
15 years, they can
really add up !
4. Watershed Reforestation
• Many MD have existing reforestation
programs and urban tree canopy goals
• Decent load reduction credits are
possible for these:
• Get extra reduction credit for
• Runoff from adjacent IC
• Stream buffer upgrades
PENDING EXPERT PANEL
Qualifying Conditions for Reforestation
Credit in MD
• Survival rate of 100 trees/acre
• 50% of the trees need to be >2” in
diameter at 4.5’ above ground
• Aggregate of smaller sites is okay
• Reforestation done for mitigation purposes
is not eligible
• Credits are determined as land cover
conversion based on the following
efficiencies:
Load Impacts of Reforestation
Conversion from
(lbs/ac/yr)
TN
(lbs/ac/yr)
TP
(lbs/ac/yr)
TSS (tons/ac/yr)
Urban Pervious
9.43
0.57
0.07
Forest
3.16
0.13
0.03
Load Reduction
6.27
0.44
0.04
Urban Impervious
10.85
2.04
0.44
Forest
3.16
0.13
0.03
Load Reduction
7.7
1.91
0.41
Adapted from MDE DRAFT Guidance Document 2011
Watershed Reforestation Example
Bay County reforests 10 acres of turf (pervious land) in
a subwatershed
MDE Method for Converting Acres Reforested to Equivalent Impervious Cover
Treated (acres)
Total N
Acres
Converted
from Turf to
Forest 2
10
Load
Reduction
(lbs/acre/
year) 1
6.27
Total P
10
0.44
Pollutant
Total Load
Reduced
Delta
(lbs/acre/
year) 3
62.7
7.69
Equivalent
Impervious
Cover
(acres)
8.15
4.4
1.91
2.30
10
0.04
0.40
0.43
Sediment
0.93
(tons)
1 Adapted from Table 7 in MDE (2011)
2 Additional credit provided when impervious cover is converted to forest
3 Delta value used to determine level of implementation required to mimic forest
conditions. Adapted from Table 10 in MDE (2011)
Equates to treatment of 0.93 acres of impervious cover
Other Watershed Reforestation Options
1. Forest Filter Strip*
2. Urban Stream
Buffer*
3. Urban Tree
Canopy**
* Existing EPA-approved rates, new panel to re-evaluate in Fall of 2012
** Rate currently being evaluated by expert panel
Panel Issues on Tree Planting Credit
•Double counting
•Is credit immediate or
phased in?
•Tree mortality
•Canopy over Impervious
cover
•Verification
•Tracking
•Planting by public and
watershed groups
5. Take credit for current and future
stream restoration projects
• High nutrient reduction
rates for qualifying projects
• Provides both a local
benefit and a Bay benefit
• Generally popular with the
public
• Cost competitive with pond
retrofits
CURRENT EXPERT PANEL
Stream Restoration Removal
Rate
Removal rate per Linear foot of Qualifying
Stream Restoration
Source
TN
TP
TSS
CBP
2005
N=1
New
Interim
Rate
Expert
Panel
0.02 lbs
0.0035
2.55 lbs
0.20 lbs
0.068 lbs
310 lbs
Project-Specific Method to
Define Rate
Stream Restoration
Removal Rate per Linear Foot:
TN = 0.20 lbs
TP = 0.068 lbs
TSS = 310 lbs
Qualifying Conditions
• Stream reach > 100 ft that is still actively
degrading (usually 1st – 3rd order streams)
• Comprehensive restoration design: involving
channel, banks and floodplain
• Special consideration given to projects with
floodplain reconnection or in-stream habitat
creation
Stream Restoration Example
MD City opts to restore a 1000’ segment
of stream located in a highly urbanized
section of the city. Using the removal
rates, the City determines the pollutant
reduction credits it can take for the
project:
TN
Removal Rate
(lbs/ft)
0.20 lbs
Linear Feet of
Restored Stream
1000’
Total Removal
(lbs)
200 lbs
TP
0.068 lbs
1000’
68 lbs
TSS
310 lbs
1000’
155 TONS
Converting to Impervious Acres Treated
In addition to the above pollutant removal
values, the MD City is required to report
the impervious acres treated. Which can
be determined by the following equation:
Impervious
1 acre/100 linear feet of
acreage treated = restored stream
= 10 acres of impervious
cover treated
A few expert panel notes
• 3 part method rather than rate per linear feet
• Not a license to use urban steam corridor for
stormwater treatment
6. Take the Mass Credit for
Intensive Street Sweeping
• Qualifying Frequency and Technology
• Incentive for Sweeping Crews to
Maximize Pickup
EXISTING EXPERT PANEL
Street Sweeping
Two Methods
1. Mass Loading Approach* (
2. Qualifying Street Lanes Method
)
Qualifying Conditions:
• Urban street with high average daily traffic
volume located in commercial, industrial,
central business, high intensity residential
• Minimum frequency of 26 times a year (every
2 weeks)
–
•
Can be grouped for specific times (i.e., Spring
and Fall)
Reductions based on sweeping technology:
Mechanical << Regenerative/Vacuum
Mass Loading Approach
Mass of collection measured (tons) at point
of disposal
Step 1. Determine capacity of sweeper
Step 2. Weigh solids collected (in tons)
Step 3. Record annual mass collected (tons)
Step 4. Convert from tons to pounds of solids
(multiply by 2000) and convert to dry weight
(factor of 0.7)
Step 5. Multiply dry weight by established
factors:
Lbs of TN = 0.0025 lbs of dry weight solids
Lbs of TP = 0.001 lbs of dry weight solids
Step 6. Compute TSS reduction credit by
multiplying the annual mass of dry weight by a
factor of 0.3
Qualifying Street Lanes Method
Convert qualifying lane miles into total
impervious cover (acres):
Miles swept  feet swept  multiplied by lane
width (feet)  divide by 43,560 = acres of
street swept
Multiply acres swept by pre-sweeping annual
load (simple method):
TP = 2.0 lbs/impervious acre/year
TN = 15.4 lbs/impervious acre/year
Qualifying Street Lanes Method
Multiple pre-sweep baseline load by pick-up
factors:
Multipliers to Reflect Effect
of Street Sweeping on the Baseline Load
Technology
TP
TN
Mechanical
.04
.04
Regenerative/Vacuum
.06
.05
1
CSN 2011
1
Street Sweeping Example
Qualifying Street Lanes Method
Over the past year, local MD community has swept the
streets 26 times, with a regenerative street
sweeper.
The community swept 25 lane miles which included both
sides of the street.
This is converted to an area: Both sides of the street
were swept, so an average width of 20 feet could be
used.
The lane miles were converted to feet and multiplied
the 20’ width, and then divided by 43,560 to get the
total acres of street swept in the past year = 60.61
acres.
Qualifying Street Lanes Example cont.
Multiplying the impervious acreage swept
(60.61 acres) by the pre-sweeping
annual pollutant load, the community
was able to determine their baseline
load:
Baseline Load
Phosphorus (60.61 ac)(2.0 lbs/ac/yr)
= 121.21 lbs/yr
Nitrogen
= 933.39 lbs/yr
(60.61 ac)(15.4 lbs/ac/yr)
Qualifying Street Lanes Example cont.
The MD Community then multiplied the baseline
load by the Regenerative Technology factors
to get load reductions based on their
program:
Pollutant Removal Loads
TP
121.21 lbs/yr*0.06
= 7.27 lbs/yr
TN
933.39 lbs/yr*0.05
= 46.66 lbs/yr
Converting Acres Swept vs. Impervious Area
Treated
MDE Method for Converting Acres Swept to Equivalent
Impervious Cover Treated (acres)
Acres Swept
Equivalent IC
Pollutant
Adjustment
Factor
Acres Treated
TP
0.04
60.61
2.42
TN
0.06
60.61
3.64
TSS
0.12
60.61
7.27
Average for all three
4.44
Source: Table 12 in MDE (2011)
7. Take Credit for Eliminating Illicit Discharges
• For chronic and episodic
sewage discharges that are
physically eliminated from
storm drain
• Reduction based on rate of dry
weather flow and outfall
concentration above
background levels
• Outfall screening is big part of
MS4 permits, so gives credit
when screening is nutrient
based
PENDING EXPERT PANEL
Illicit Discharge Detection and
Elimination
Currently there is no official
process for calculating
pollutant reduction credits.
IDDE program.
Expert Panel planned for 2012
for this topic.
In the meantime, CSN’s
Technical Bulletin #9 has a
recommended process that
we can use as a guide…
Illicit Discharge Detection and
Elimination
Step 1. Dry weather flow rate and nutrient
concentrations measured at outfalls
Step 2. Discharge source tracking
Step 3. Monitor flow rate and nutrient
concentrations at discharge source prior to
and after discharge elimination
Step 4. Follow-up monitoring to confirm
nutrient concentrations have returned to
background levels
Step 5. Compute the nutrient credit:
(daily flow rate)(nutrient conc.)(# of days of
discharge) = load reduced
8. Residential LID Retrofits
Subsidies, technical assistance,
stormwater utility credits and
other incentives to build LID
retrofits on private land
CURRENT EXPERT PANEL
Design Examples –
Residential Stewardship Incentives
A MD County creates an incentive program for
residential homeowners to install rain gardens on
their property and would like to determine the
pollutant removal rates associated with such a
program.
Design Examples –
Residential Stewardship Incentives
Each homeowner installs a rain garden to treat 500
ft2 of rooftop
If 100 homeowners participate in the program,
treatment can occur for a combined drainage
area of 1.15 acres, at 100% impervious.
The runoff storage volume associated with the
combined retrofits is estimated to be 0.05 acrefeet.
Rain gardens are an RR practice
Design Examples –
Residential Stewardship Incentives
The amount of runoff volume treated by the rain
gardens is calculated using standard retrofit
equation:
(0.05 )(12)
= 0.5 𝑖𝑖𝑖𝑖𝑖𝑖ℎ𝑒𝑒𝑒𝑒
1.15
The township engineer uses the curves to estimate the
projected removal rates associated with the rain
garden incentive program:
TP
TN
TSS
52%
52%
55%
Calculating Pollutant Load Reduction of On-site LID Incentives
Total
Nitrogen
Total
Phosphorus
Suspended
Sediment
Tons/acre/year
Pounds/acre/year
IMPERV
PERV
IMPERV
PERV
IMPERV
PERV
MDE
Loading
Rates
10.85
9.43
2.04
0.57
0.46
0.07
Area
(acres)
1.15 ac
0
1.15 ac
0
1.15 ac
0
Baseline
Load
Removal
Rate
Load
Removed
12.48 lbs/yr
2.35 lbs/yr
0.53 tons/yr
52%
52%
55%
6.5 lbs/yr
1.22 lbs/yr
0.30 tons/yr
Other On-site Options and more on LID
Incentives in Session 4
Q&A