1. No category

How to Use ESD to
Protect Aquatic
Resources
Richard Klein
1
In this portion of the workshop we’ll get into the
technical details of ESD. But because of the
complexity of ESD we’re going to present more of
an overview then an in-depth how-to.
But we’re also going show you where to find some
great guidance documents that make it easy to
grasp the how-to’s. Most of these documents
were prepared by Tom Schueler of the
Chesapeake Stormwater Network.
1
Key ESD Guidance Documents
Plus ESD Chapter 5
http://www.mde.state.md.us/Programs/WaterPrograms/SedimentandStormwater/home/index.asp
2
The following presentation is based on these two
Maryland Department of the Environment
guidance documents. The one on the left – the
sediment control specs – is still in draft form and
has not been officially adopted. Of course the
2000 Stormwater Design Manual is official
including the new Chapter 5 which sets forth how
ESD is to be applied. A word of caution though.
Many of the specifics of how to apply ESD to a
site are still being ironed-out. So you may find
that your county or even MDE applies ESD
requirements in ways subtly different from that
presented here.
2
ESD Principles
Design the project to cause the smallest area of disturbance;
To minimize erosion, divert off-site runoff or convey it and on-site runoff in wellvegetated channels, pipes or other erosion resistant structures
Maintain sheetflow and natural overland flow processes wherever feasible.
Confine the area of disturbance to the portion(s) of the site with the:
Least erodible soils and flattest slopes;
Greatest distance from wetlands, streams, floodplains, etc.; and
Least contiguous forest.
Minimize new impervious area with practices such as:
Short road lengths, narrow road widths; minimum number of parking
spaces, smallest parking stalls practical, and other Better Site Design
measures;
Substitute porous pavement, permeable pavers, etc. for conventional
asphalt-concrete, and
Use multi-story construction for parking and buildings.
Locate impervious surfaces upslope of permeable soils suited for ESD
practices;
Identify open space areas that can be converted to forest;
Identify important resource areas that can be expanded (e.g. stream buffers);
Use ESD Practices to minimize offsite pollution, erosion, and maintain
groundwater recharge.
3
Here is my attempt to distill ESD down to basic
principles. This list is a compilation of the
guidance points presented in both MDE
documents.
How about if we take a few minutes to read
through this list. If you see something unclear
then we can discuss it now. But the rest of this
portion of the workshop will be covering these
principles in further detail.
3
ESD Practices
Practice Category
Number of
Practices
Alternative Surfaces
3
Nonstructural Practices
3
Micro-Scale Practices
9
4
Chapter 5, of the new Stormwater Design Manual,
lists 15 ESD Practices. These practices are
grouped into these three categories.
4
ESD Alternative Surfaces
Reinforced Turf
Permeable Pavements
Green Roof
5
These are the three Alternative Surface practices.
From a water quality perspective, a Green Roof is
the least effective because it doesn’t provide
groundwater recharge. However, a Green Roof
does provide heating-cooling benefits. No other
practice does this.
ESD Practices can be combined in a train that
negates the limitations of any single measure. So
a Green Roof, which doesn’t provide recharge,
can drain to a Dry Well which would release roof
runoff into the soil.
Permeable pavers and Reinforced Turf can be
used for parking spaces, streets, sidewalks, patios
etc., though I’d hate to have to cross either in high
heels, not that I wear high heels.
5
ESD Nonstructural Practices
6
These three Nonstructural Practices are intended to serve very
short sections of impervious surfaces which adjoin flat pervious
areas such as grass or woods. The idea is that the relatively
small volume of runoff from impervious surfaces will mostly soak
into the adjoining pervious area where pollutants will be removed
and recharge will occur.
These are my least favorite practices. My bias comes from some
studies showing the pollutants are mostly retained in surface
soils and may be washed into nearby waters during severe,
scouring runoff events. Also, runoff must always be in sheet flow
and I’ve seen too many situations where accumulations of
leaves, twigs, litter creates channel flow. The channel flow then
discharges into a nearby waterway along with most of the
pollutant load.
6
ESD Microscale Practices
7
I view these nine micro-scale practices as being
the most effective. With the exception of
Rainwater Harvesting, these practices force runoff
to pass through a column of planting soil, which
has a high-pollutant removal capacity. The
pollutants are then stored well below the effects of
surface runoff. Additionally, most provide
excellent groundwater recharge which is critical to
maintaining dry-weather inflow to wetlands,
streams, and other aquatic systems. Finally, most
micro-scale practices can be designed to manage
the one-year storm thought to be key to
preventing stream channel erosion.
7
ESD Concept Design Phase
„ Site
& Resource Mapping
„ Site
Fingerprinting & Development
Layout
„ Locate ESD Practices
8
Chapter 5 calls for this three step process when
designing an ESD Concept Plan. And it’s the
concept plan which most clean water advocates
will see.
This is because most volunteer and professional
clean water advocates become aware of a
proposed development project when notice is
given of a Planning Board or Commission hearing.
The ESD Concept Plan will usually be part of a
subdivision or site plan. So understanding these
three components of the Concept Plan
preparation process is essential to determining if
every reasonable opportunity has been utilized to
fully protect aquatic resources with ESD.
8
Site & Resource Mapping
„
Buffers:
•
•
•
„
„
„
„
„
Forest
Stream
Wetland
Critical areas
Existing drainage areas
Forests
Floodplains
HighlyHighly-erodible soils on:
•
•
Slopes >15%
Slopes ≥25%
„
„
Rivers
Soils:
•
•
„
„
Springs/seeps
Streams:
•
•
„
Clay ≥15%
Permeable
Intermittent
Perennial
Wetlands
•
•
•
Nontidal
Special State Concern
Tidal
9
At a minimum, the Concept Plan should show all
of these features which occur on the site. The
Limits of Disturbance and impervious areas
should be laid out to avoid these features. On
most development sites this leaves lots of room
for buildings, streets, parking areas, and other
structures.
9
Shoppes @ Apple Green Example
10
In the next series of slides we’ll show you how to
verify that the Concept Plan accurately depicts
key features. For this illustration I’ll use a
commercial project proposed for a 40-acre site in
northern Calvert County.
This project is called the Shoppes @ Apple
Green. I’ve been helping 161 families in the
adjoining community with concerns about this
project. While the families are not opposed to the
Shoppes per se, they do have some very serious
and legitimate questions about stormwater
management and the flawed wastewater
treatment system proposed for the project.
10
Site & Resource Mapping
Shoppes Example
http://websoilsurvey.nrcs.usda.gov/app/
11
The US Department of Agriculture Web Soil
Survey is one of the best resources for identifying
sensitive features and other key characteristics.
To start Web Soil Survey click the green button.
.
11
12
After starting Web Soil Survey you can find a site
using an address, coordinates, or other options.
For the Shoppes I used the polygon Area Of
Interest tool to outline the 40-acre site, which
produced the soils map you see here.
12
Highly Erodible Soils – Slopes >25%
None >25%
>0.35
>15%
13
Here are the first pair of layers I selected for the
Shoppes site using the Soil Data Explorer. On the left
you see the soil erodibility layer for the site. The MDE
documents use two definitions for highly-erodible soils.
Both begin with an erosion factor greater then 0.35.
The dark blue areas in the map on the left have an
erodibility >0.35. In the Chesapeake and Coastal
critical area a soil is highly-erodible if it has a K value
greater then 0.35 and is on a slope steeper then 15%.
Elsewhere in Maryland the slope must be greater then
25%. The Shoppes is not in the critical area so there’s
no restriction on development, though it would be good
to avoid the dark blue most erodible soils.
13
Highly Permeable Soils
B
A
>6’
B
B
>6’
C
B
>6’
14
A system known as Hydrologic Soil Groups is used to
rate the permeability of soil. There are four soil
categories: A, B, C, and D. The A soils are the most
permeable, producing the least runoff. D soils are the
opposite.
A typical A soil would be very sandy with considerable
depth to the water table. D soils may be very clayey or
have a shallow depth to the water table or bedrock.
Most ESD practices can be used on A or B soils, while
C soil are marginal or D soils are very restricted. So
impervious areas should be arranged so sufficient
permeable A or B soil remains downslope to install ESD
Practices.
A shallow depth to the water table can also restrict the
use of ESD Practices. But the map on the right shows
this is not an issue on the Shoppes site.
14
High Clay Soils
>15%
15
Clay is responsible for the muddy appearance or
turbidity of water even when days have passed
since the last rain. Clay particles are also the
most damaging to aquatic ecosystems.
The draft erosion and sediment control standards
call for special attention when soils with a high
clay content are within the proposed Limits Of
Disturbance. Such a soil is composed of more
then 15% clay, as opposed to silt, sand, or gravel.
Once the draft standards become effective, an
erosion and sediment plan must show how clay
soils and runoff will be managed to prevent
excessive turbidity.
15
Existing Drainage Areas
MERLIN
Maryland's Environmental Resources
& Land Information Network
http://www.mdmerlin.net
16
The Concept Plan usually shows the hills, valleys,
and other site topography with contour lines. You
should compare the topography shown on the
plan with other references such as the USGS topo
maps available on Web Soil Survey and the
MERLIN site.
Consider verifying topography in the field. Take
the plan out to areas adjoining the site to see if
the ridges, slopes, and valleys look the same.
Drainage areas are separated by hilltops and
ridgelines. On the right you see drainage areas
delineated with dashed red lines.
16
Resource Map & Fingerprint
Composite Site Resource Map
Site Fingerprint Map
17
We could keep going but I suspect you get the idea of
how to verify site resources.
On the left is a composite map of all the resources
identified thus far.
On the right the Site Fingerprint map shows an area
bounded by a yellow dashed line. This area is free of
constraints while mostly being on or upslope of
permeable soils suited for ESD Practices.
17
ESD Concept Design Phase
„ Site
& Resource Mapping
„ Site
Fingerprinting & Development
Layout
„ Locate ESD Practices
18
Now that the site fingerprint has been defined the
plan designer can move on to locating buildings,
parking areas, and other structures within the
fingerprint so they drain to ESD Practices.
18
Locating Alternative Surface &
Nonstructural Practices
Alternative Surface
Green Roof
Permeable Pavement
Reinforced Turf
Nonstructural Practices
Disconnect Rooftop
Disconnect Non-Rooftop
Sheetflow Conservation
Hotspot
Runoff
Hydrologic
Soil Group
Slope
All
A, B, C
A, B, C
<30%
OK
≤5% Not OK
≤5% Not OK
A, B, C
A, B, C
≤5%
≤5%
≤5%
Not OK
19
This table lists some, though not all, of the criteria for
locating two categories of ESD Practices within the
fingerprint area: Alternative Surfaces and Nonstructural
Practices.
Of course HSG is Hydrologic Soil Group.
Slope is measured in feet per 100 feet and is expressed
as a percent. So an area which rises or falls 5 feet for
every 100 feet of horizontal distance has a 5% slope.
A hotspot is any land use likely to generate unusually
toxic runoff, such as a gas station or vehicle repair shop.
Practices designed to infiltrate runoff should not be used
at hotspots because of the groundwater contamination
potential.
Again, there are additional location criteria.
19
Locating Micro-Scale Practices
Rainwater Harvesting
Submerged Gravel Wetland
Landscape Infiltration
Infiltration Berm
Dry Well
MicroMicro-Bioretention
Rain Garden
Swale
Enhanced Filter
Soil
Slope
All
C-D
A-B
<2%
0%
Avoid slough or
landslidelandslide-prone
≤10%
A-B
All
Avoid clay or
compacted
All
DA
(square feet)
Large enough to
maintain inflow
≤10,000
Small enough to
prevent flow
concentration
≤500
≤30%
≤20,000
<5%
≤2,000
<5%
≤4% <one acre
Hotspot
Runoff
No
No
OK if no other
infiltration
No
No if designed
to infiltrate
No
No
20
This table shows siting constraints for the nine
micro-scale practices. Note that most have a very
small drainage area. This means they must be
located at or very near the edge of impervious
surfaces. Furthermore, the impervious surfaces
must be designed with a number of small
drainage areas. This is actually easier then it
sounds.
So, a first step in reviewing a Concept Plan is to
verify that all impervious surfaces drain to an ESD
Practice.
20
Environmental Site
Design Computations
21
Once you’ve verified that all impervious surfaces
do drain to an ESD Practice then we get to the
ESD computations.
This box contains the criteria which ESD must
meet. The box also provides the formulas for
computing runoff depths or volumes that must be
treated to meet the ESD criteria to the Maximum
Extent Practicable.
I know these computations may look a bit
intimidating, but…
21
Chesapeake Stormwater Network
http://www.chesapeakestormwater.net/
Tom Schueler
22
…fortunately, Tom Schueler of the Chesapeake
Stormwater Network has produced these two
tools which make the computations far easier.
A bit later I’ll show you how to get to these two
documents on the CSN website.
22
Unified Stormwater Sizing Criteria
„
Water Quality Volume (WQV)
•
„
Recharge Volume (Rev)
•
„
1-Year Storm (2.4(2.4- to 3.03.0-inches in 24 hours)
Overbank Flood Protection Volume (Qp)
•
„
0.070.07- to 0.380.38-inches of impervious surface runoff
infiltrated
Channel Protection Storage Volume (Cpv)
•
„
0.90.9- to 1.01.0-inches of runoff from impervious surfaces
1010-Year Storm (4.3(4.3- to 5.65.6-inches in 24 hours)
Extreme Flood Volume (Qf)
•
100100-Year Storm (5.9(5.9- to 8.18.1-inches in 24 hours)
23
The 2000 Maryland Stormwater Design Manual
contained these five criteria for sizing structural, end-ofpipe practices. ESD employs these same criteria, but
in a different way.
The first criteria, Water Quality, applies to all
development projects.
New development projects, but not redevelopment,
must meet Recharge volume.
Sites discharging to tidal waters or located on the
Eastern Shore may be exempt from the other three
requirements, but most other projects in Maryland must
meet the Channel Protection criteria.
Except for some interjurisdictional watersheds, local
agencies may require Overbank or Extreme Flood
control when flooding problems exist.
23
Minimum ESD Requirements
MDE Design Manual Definition (5.2.3)
Must Treat WQV & ReV With ESD Practices
Water Quality Volume
Frederick, Washington, Allegany
& Garrett Counties: Impervious
surface runoff from 0.9-inches of
rain.
Rest of Maryland: Impervious
surface runoff from one inch of
rain.
Hydrologic
Soil Group
Recharge
Volume
(inches)
A
0.38
B
0.26
C
0.13
D
0.07
24
ESD must be used on every site to the Maximum
Extent Practicable.
In the ESD chapter of the 2000 Stormwater Design
Manual, MEP is defined as treating the Water Quality
Volume and the Recharge Volume with ESD Practices.
However, the goal should be to treat the Channel
Protection Volume as well. But if this can’t be done
then the plan designer gets to deduct the runoff treated
with ESD from the Channel Protection requirement and,
if required, the Overbank and Extreme Flood volumes.
These deductions were not previously allowed, which
created unnecessary problems.
24
Maximum Extent Practicable
COMAR 26.17.02.06.A.2
The MEP standard is met when channel
stability and 100 percent of the average
annual predevelopment groundwater
recharge are maintained, nonpoint source
pollution is minimized, and structural
stormwater management practices are used
only if determined to be absolutely necessary.
25
This language appears in the Minimum Control
Requirements section of the stormwater regulations.
To me this regulation calls for substantially more then
just treating the water quality and recharge volume with
ESD practices.
For example, it has been a point of debate whether the
ReV actually maintains groundwater recharge at 100%
of the predevelopment amount.
As will be seen a bit later in this presentation, few
Practices keep post-development pollution releases at
pre-development levels, which to me is contrary to the
definition of “minimized.”
I suspect this text will be a source of considerable
contention as more projects are reviewed under the
ESD regulations.
25
ESD Sizing Criteria
Same Runoff as Woods In Good Condition
Hydrologic
Soil Group
Woods In Good
Condition Runoff
Curve Number
Inches of Runoff
From 2.7” Rainfall
A
38
0.00”
B
55
0.12”
C
70
0.55”
D
77
0.87”
26
The goal of ESD is to restore runoff equivalent to Woods In
Good Condition. In other words, the criteria is intended to
reduce the volume of runoff from a developed site to the
volume which would have flowed from the same land when
it was covered by healthy woodland.
Of course prior to development most sites are not Woods in
Good Condition. They are a mixture of cropland, pasture,
forest and other land uses. This mix generates more runoff,
more pollution, and allows less recharge then Woods in
Good Condition. As a result the waters draining the site are
already degraded by some accelerated erosion, pollution,
and diminished dry-weather flow. In using ESD Practices to
restore the runoff regime of Woods In Good Condition, the
waters draining the development site will return to a
healthier condition.
26
27
The ESD computations begin by requiring the
plan designer to determine the Rainfall Target.
This is accomplished with Table 5.3 of the ESD
chapter. This excerpt from Table 5.3 is for
Hydrologic Soil Group B.
Let’s say we have a site that’s completely
underlain by B soils and is proposed to become a
parking lot, which is 100% impervious. The
Rainfall Target would be determined by entering
the table on the left at an imperviousness of
100%. Then move right until you hit the first
green cell. Note the number at the top of the
column of that first green cell, which becomes the
Rainfall Target.
27
Rainfall Target
PE = 2.6 inches
28
Again, begin at the proposed impervious area on
the left and move right to the first green cell then
go up to PE row.
In the case of our 100% impervious, B-soil parking
lot the Rainfall Target is 2.6 inches. Of course PE
is the symbol for the Rainfall Target.
28
Example: ESD Practice to Treat
10,000 Square Feet of Roof
Design Factors
Hydrologic Soil Group AA-B
≤ 10,000 ft2 Drainage Area
LI Surface Area ≥ 2% of DA
LI Depth: HSG A ≤12’
12’ B ≤5’
No hotspot runoff
29
Now for an example of how to run the ESD
computations.
For this example I’ll use one of my favorite ESD
Practices – Landscape Infiltration.
Here you see some of the more critical design factors.
LI can be used on A or B soils. Each practice cannot
drain more then 10,000 sq ft; a quarter-acre. The
surface area of the LI must be equal to at least 2% of
the drainage area. Assuming the depth to water table,
bedrock, or poor soils permits, the LI can be 12 ft deep
on A soils or 5 ft deep on B. Since LI’s infiltrate they
cannot serve hotspot uses. Like all other micro-scale
practices, an LI cannot receive more runoff then the
Channel Protection volume; the one-year storm.
29
Landscape Infiltration (LI) Computations
For 10,000 Square Feet of Roof
Factor
Symbol
Value
A
10,000 ft2
Minimum Surface Area
Hydrologic Soil Group
Imperviousness
Water Quality Volume
Recharge Volume
Rainfall Target
Recharge Factor
Af
HSG
I
WQV
ReV
PE
Rv
ESD Volume To Meet PE
ESDv
A * 0.02 = 200 ft2
B
100%
1.0 inches
0.26 inches
2.60 inches (Table 5.3)
0.05+0.009(I) = 0.95
PE*RV*A/12 = 2,058 ft3
Drainage Area
30
This table shows the factors used to compute the
volume of ESD treatment provided by the
Landscape Infiltration practice .
The drainage area is 10,000 sq ft and 100%
impervious. The LI must have a surface area of at
least 200 sq ft. Since the soil is B then practice
depth cannot exceed 5 ft. The Rainfall Target is
2.6 inches, Water Quality Volume is 1.0 inches,
and the Recharge Volume is 0.26 inches. The
Recharge Factor is computed using this equation
then combined with the Rainfall Target and
Drainage Area to get the volume required to meet
the ESD requirement, which is 2,058 cubic feet.
30
Landscape Infiltration (LI) Computations
For 10,000 Square Feet of Roof
Factor
LI surface area
Symbol
Value
Af
800 ft2
Practice Ponding Depth
1 ft
Practice Storage Depth
3.5 ft
PE
2.60 inches
ESD Treatment Required
ESDV
PE*RV*A/12 = 2,058 ft3
ESD Treatment Provided
ESDV
(Af*1’
*1’)+(Af*3.5’
*3.5’*0.4) = 1,920 ft3
PE
1,920 ft3 * 12/A = 2.30 inches
Rainfall Target
Rainfall Treated
31
In this table we compute the ESD volume provided by
the Landscape Infiltration Practice. We start off with a
surface area of 800 sq ft, which exceeds the 200 sq ft
minimum. The surface ponding depth is 1 foot and the
practice depth is 3½ feet, which is less then the 5 foot
maximum. From the previous table we know we need
an ESD volume of 2,058 cubic feet to meet the Rainfall
Target, but the next to last line of this table shows we
only have 1,920 cubic feet of ESD volume. However,
the last line shows that the Rainfall Treated exceeds
the Recharge depth of 0.26 inches and the Water
Quality depth of one inch. So two of the three
applicable ESD requirements has been met.
31
Meeting Rainfall Target (PE)
Increase Landscape Infiltration Size To
Meet The Rainfall Target
ESDV Rainfall Target = 2,058 ft3
Increase surface area (Af) from 800 ft2
to 870 ft2
Practice Ponding Depth = 1 ft (same)
Practice Storage Depth = 3.5 ft (same)
ESDV=(Af*1’
*1’)+(Af*3.5’
*3.5’*0.4)=2,088 ft3
ESDV Exceeds Rainfall Target
32
Since the first design didn’t meet the Rainfall Target
we try making the practice bigger. In this example
the surface area is increased from 800 square feet
to 870. The ponding and storage depth remains the
same.
By making the surface area a bit larger we increase
ESD volume to 2,088 cubic feet which exceeds the
amount required to meet the Rainfall Target.
We also could have tried increasing storage depth,
reducing impervious area, using a Green Roof, and
other options to meet the target.
The volume provided in the practice can be
deducted from Overbank or Extreme Flood volumes
if either is required.
32
ESD Computations Mostly Same For
Other Micro-Scale Practices
33
The ESD computations just illustrated for
Landscape Infiltration are much the same for the
other eight micro-scale practices.
33
Alternative Surfaces
& ESD Computations
Reinforced Turf
Permeable Pavements
34
Now we’ll take a look at the ESD computations for
Alternative Surfaces.
Again there are three Alternative Surface
Practices: Green Roofs, Permeable Pavement,
and Reinforced Turf.
34
Runoff Curve Number (RCN)
http://www.wsi.nrcs.usda.gov/products/W2Q/H&H/docs/other/TR55_documentation.pdf
35
The Alternative Surface ESD computations are
based on Runoff Curve Numbers or RCNs. The
document on the left – TR55 – is the best
reference for RCNs.
RCNs range from 30 to 98. The higher the RCN
the greater the runoff depth for a given rainfall
amount.
As the table on the right shows, RCNs are a
product of hydrologic soil groups and land use.
For a given land use A soils have a lower RCN
and, therefore, will produce less runoff during a
specific rainfall depth when compared to the same
use on a B, C or D soil.
35
36
The RCN for Woods in Good Condition on an A
soil is 38 to 40 and that for impervious surfaces is
98.
This table, which is also from TR55, shows that
the Good Woods does not produce runoff until 3.5
inches of rain have fallen in a 24-hour period. For
the impervious surface, with an RCN of 98, the
same 3.5-inches of rainfall produces 3.27 inches
of runoff. In other words, 93% of the rain falling
on the impervious surface becomes runoff.
36
Alternative Surfaces Effective RCN
Reinforced Turf RCN
Surfacing Material
A
B
Grass (open space) 39
61
C
74
D
80
37
For Alternative Surfaces the MDE manual
provides Effective RCNs which reflect the reduced
volume of runoff from these surfaces.
For example a conventional roof has an RCN of
98 while an eight-inch thick green roof has an
RCN of 77. Hydrologic soil groups don’t come
into play because the permeable portion of a
green roof overlays impermeable layers to prevent
leakage into the underlying building.
Of course hydrologic soil groups are factors for
permeable pavement and reinforced turf.
37
Alternative Surface ESD Computation
Woods RCN (HSG=B)
55
Conventional Roof RCN
98
Green Roof (8”) Effective RCN
77
Rainfall Target (PE)
2.60 inches
Green Roof Runoff Depth
0.80 inches
Runoff Treated By Green Roof
1.80 inches
Use DryDry-Wells To Treat Recharge requirement (0.26 inches).
38
Here we see how the Effective RCNs are used to
compute the remaining Rainfall Target (PE).
From previous slides we used a PE of 2.6 inches.
With an Effective RCN of 77 the Green Roof
produces 0.80 inches of runoff from the Target
Rainfall of 2.6 inches. Since 1.80 was treated
with the Green Roof the Water Quality
requirement has been met. Another ESD
Practice, like a Dry Well, could be installed at
each downspout to treat 0.26 inches of roof runoff
to meet the Recharge requirement. Other ESD
practices could be used to treat the balance of the
Rainfall Target.
38
Nonstructural ESD Computation
39
Now for the last of the three ESD groups –
Nonstructural Practices.
39
Nonstructural PE
40
For Nonstructural Practices credit is given towards
the Rainfall Target.
The credit depends upon the length of grass,
woods, or other permeable surfaces runoff from
impervious surfaces must flow over to reach an
outlet. Hydrologic soil groups do not come into
play, except to determine if an area is suitable for
Nonstructural Practices.
40
Nonstructural ESD Computation
PE from Table 5.3 (HSG=B)
2.60 inches
Western Shore 4545-foot flow path PE value
0.60 inches
Remaining PE To Be Treated Elsewhere
2.00 inches
41
Let’s assume we provided a 45 foot flow path
length for roof runoff and the project is on the
Western Shore. The Rainfall Target or PE credit
for this practice is 0.60 inches.
The bottom table shows how the Nonstructural
Practice credit is counted towards the Rainfall
Target for the impervious area draining to the
disconnect.
The designer would need to explore the possibility
of using ESD practices elsewhere on the site to
meet the Maximum Extent Practicable
requirement.
41
ESD Project Computations
42
This table shows how the treatment provided in
ESD practices throughout a site are combined to
determine if the Rainfall Target was met for the
site as a whole.
According to this table, ESD practices provided
treatment volume in excess of the Rainfall Target
for all of the drainage areas. So the site as a
whole complies with the Environmental Site
Design to the Maximum Extent Practicable
requirement.
42
Chesapeake Stormwater Network
http://www.chesapeakestormwater.net/
43
Again, these two Chesapeake Stormwater
Network resources will make it much easier to
determine if a Concept Plan meets ESD
requirements.
43
Chesapeake Stormwater Network
http://www.chesapeakestormwater.net/
44
When you go to this web address, the page on the
left will appear.
To download the two resources click Read More
at the end of this first paragraph, which is headed
“June 2010 - New and Improved ESD to MEP
spreadsheet released for MD designers.”
44
http://mawaterquality.org/capacity_building/ESDToolsWebcast.htm
http://mawaterquality.org/capacity_building/ESDToolsWebcast.htm
45
In May, the Chesapeake Stormwater Network did
an introductory webcast on Environmental Site
Design. This webcast can be viewed at the
address given at the bottom of this slide.
Taking a look at this webcast would provide
another perspective on how Environmental Site
Design works.
45
Download ESD Chapter 5
http://www.mde.state.md.us/Programs/WaterPrograms/SedimentandStormwater/stormwater_design/index.asp
46
Additionally, download ESD Chapter 5 from the
2000 Maryland Stormwater Design Manual.
There are three ESD design examples in Chapter
5. Spending an hour or so running these design
examples through the CSN spreadsheet will make
you an ESD expert – Well, at least more
comfortable with the computations.
46
Redevelopment
Definition
Existing Site Impervious Area (IA) Greater
Than 40%
Example
100 acre site ÷ 41 acres of existing
impervious area = 41% IA = Treat As
Redevelopment
47
Now on to Redevelopment.
The year 2000 MDE Stormwater Design Manual
treated redevelopment projects differently then
green field or new development.
The 2007 Act continued this tradition, though the
aquatic resource protection requirements for
redevelopment were strengthened.
Here we have the definition of redevelopment and
an example.
A redevelopment project is one where more than
40% of a site is covered by existing impervious
surfaces.
47
Redevelopment
The Best Hope for Restoring
Urban-Suburban Waters
48
Our most degraded waters are located in urban and
older suburban areas. These are the very areas where
recreational opportunities are most sorely needed.
What a tragedy it is that the waters located closest to
most Maryland homes is unfit for our use.
Redevelopment offers what may be our best hope for
restoring these waters. As each urban-suburban home
and building is redeveloped the new ESD regulations
will require installing water quality protection measures.
Over time this will result in gradual improvements. How
much time? Well Philadelphia uses an approach
similar to ESD and officials there think up to 59% of the
existing impervious area might be retrofitted by 2035.
48
Limits Of Disturbance (LOD)
49
While the entire site is used to determine if the
40% existing impervious area threshold is
crossed, the actual requirements only apply to the
Limits Of Disturbance. Of course the LOD is the
outer boundary of the portion of a site where
earth-moving, demolition, vegetation removal, and
other disturbances will occur.
The “redevelopment” plan on the left shows no
LOD, which should be cause for denying
approval. The Shoppes plan on the right shows
the LOD. If the site were more then 40%
impervious, which it isn’t, then any existing
impervious areas within the LOD would need to
meet the following redevelopment requirements.
49
Redevelopment Requirements
„
„
„
Reduce existing impervious area within the Limits
Of Disturbance (LOD) by at least 50%; or
Implement ESD practices to the Maximum Extent
Practicable (MEP) to provide water quality
treatment for at least 50% of existing impervious
area within the LOD; or
Use a combination of impervious area reduction
and ESD implementation for at least 50% of
existing impervious areas. And…
50
This slide shows the three preferred
Environmental Site Design options for meeting the
new redevelopment requirements.
Redevelopment projects must only meet the
Water Quality volume requirement; not the
recharge, channel protection, overbank, or
extreme flood requirements. Though the local
approving authorities have the option of requiring
any of these four.
If there’s a net increase in impervious area then
this area must be treated with ESD. The ESD
practices must meet the water quality, recharge,
and channel protection volume to the MEP.
50
…if you can’t do that, then…
„
„
„
Use on-site structural BMP; or
An off-site structural BMP to provide water
quality treatment for an area equal to or greater
than 50% of existing impervious areas; or
A combination of impervious area reduction,
ESD implementation, and on-site or off-site
structural BMP for an area equal to or greater
than 50% of existing impervious area within the
LOD. And…
51
But if an applicant finds the three preferred ESD
options too difficult then MDE included these
structural end-of-pipe alternatives.
The applicant can also go offsite if the
requirements can’t be meet within the bounds of
the redevelopment project.
51
…if you can’t even do that then…
„
„
„
„
„
„
„
Use a combination of ESD and an on-site or off-site
structural BMP;
Retrofitting including existing BMP upgrades, filtering
practices, and off-site ESD implementation;
Participate in a stream restoration project;
Pollution trading with another entity;
Design criteria based on watershed management plans
developed according to §E of this regulation;
Pay a fee-in-lieu; or
Request a partial waiver of the treatment requirements if
ESD is not practicable.
52
And if you can’t meet the alternative requirements
onsite or offsite then MDE made the following final
provisions available.
As you can see, those designing redevelopment
have considerable latitude in how ESD
requirements will be met.
There’s been considerable hue and cry about the
onerous nature of the redevelopment
requirements. Frankly, I don’t get this
consternation.
52
Old & New Redevelopment
Requirement Comparison
Existing Impervious Area That
Must Be Treated
Old
New
20%
50%
690
1,724
WQV Treated (cubic feet/acre):
Redevelopment
New Development
3,449
53
This slide contrasts redevelopment requirements
with those for new development.
Though more runoff must be treated with the 2007
requirements, its still half of that required for
developing a cropfield, forest or other vacant
property.
53
http://www.cwp.org/CBSTP/index.html
54
For further detail on redevelopment please view
this recent PowerPoint presentation from the
Chesapeake Stormwater Network and the Center
for Watershed Protection. We understand it will
be posted soon at the web address you see at the
bottom of the screen.
54
Costs of Clean Water
Cost/Impervious
Acre
Urban Redevelopment ESD
$191,000
Urban Green Street Retrofit
$167,100
Stream Channel Restoration
$35,600
Rainwater Harvesting
$32,500
New Development with ESD
$46,500
New Development pre-ESD
$31,700
55
Here are some cost figures provided in the
preceding redevelopment webcast. As you can
see the costs can be quite significant. However,
the value of the benefits are far greater.
Consider the following. A home located near
visibly polluted water sells for 20% less than
comparable homes.
A 2008 Kansas State University study
documented that nationwide excessive nutrient
inputs alone cost $4.3 billion annually due to lost
recreation opportunities, increased water
treatment, and other factors.
55
Aquatic Resources Protection
Effectiveness of ESD vs. Structural Practice
56
Before bringing this portion of the workshop to a
close I have few slides showing which practices
are the most effective in protecting aquatic
resources.
56
Unified Stormwater Sizing Criteria
„
Water Quality Volume (WQV)
•
„
Recharge Volume (Rev)
•
„
1-Year Storm (2.4(2.4- to 3.03.0-inches in 24 hours)
Overbank Flood Protection Volume (Qp)
•
„
0.070.07- to 0.380.38-inches of impervious surface runoff
infiltrated
Channel Protection Storage Volume (Cpv)
•
„
0.90.9- to 1.01.0-inches of runoff from impervious surfaces
1010-Year Storm (4.3(4.3- to 5.65.6-inches in 24 hours)
Extreme Flood Volume (Qf)
•
100100-Year Storm (5.9(5.9- to 8.18.1-inches in 24 hours)
57
As you’ll recall the 2000 Maryland Stormwater
Design Manual contained these five criteria for
sizing structural, end-of-pipe practices. These
same criteria apply to ESD, though they are
computed differently.
57
ESD Practices & Sizing Criteria
„
„
„
„
All practices can meet Water Quality Volume;
Most practices can meet Recharge Volume,
though the Green Roof cannot;
Some micro-scale practices can meet Channel
Protection Volume; and
Runoff treated in all ESD practices cannot
exceed Cpv, but can be deducted from
Overbank and Extreme Flood volumes.
58
Here you see which of the 2000 criteria can be
met with ESD Practices.
Most ESD practices can meet the Water Quality
Volume and Recharge criteria. Some can even
meet the Channel Protection volume.
The storage provided in all ESD practices can be
deducted from the Channel Protection, Overbank,
and Extreme Flood requirements.
58
Pollutant Removal (%)
Total
Suspended
Solids
Nitrogen
Dry Pond
49
24
20
29
88
Wet Pond
80
31
52
57
70
Wetland Pond
72
24
48
47
78
Filtering
Practice
86
32
59
37
37
Bioretention
59
46
65
81
N/A
Infiltration
89
42
65
86
N/A
Open Channel
81
56
24
65
-25
Phosphoru
Copper Bacteria
s
National Pollutant Removal Performance Database Version 3, September, 2007, Center for Watershed
Protection, 8390 Main Street, Ellicott City, MD 21043. 410.461.8323
http://www.cwp.org/Resource_Library/Center_Docs/SW/bmpwriteup_092007_v3.pdf
59
In this table the pollutant removal capability of structural
and ESD practices is shown.
The three ponds are exclusively end-of-pipe structural
practices while the other four can be. However, a
number of the ESD Practices are smaller versions of
filtering, bioretention, infiltration, and open channel
practices.
Filtering, bioretention, and infiltration generally have the
highest pollutant removal rates. These practices also
move pollutants well below the path of high-volume
runoff events which would scour contaminants from
surface soils. Finally, these three practices are usually
designed to provide groundwater recharge. Therefore,
filtering, bioretention, and infiltration are generally the
most effective in protecting aquatic resources.
59
High Quality (Tier II) Waters
http://www.mde.maryland.gov/ResearchCenter/Data/waterQualityStandards/Antidegradation/index.asp
http://www.mde.maryland.gov/ResearchCenter/Data/waterQualityStandards/Antidegradation/index.asp
60
MDE has identified high quality waters throughout
the state. As the name implies, these waters are
of exceptional quality and tend to support species
which are unusually sensitive to watershed
development impacts.
If you are reviewing a project located in the
watershed of one of these aquatic resources then
please contact CEDS for advice on the need for
additional safeguards beyond what is normally
required under ESD.
60
Maryland Environmental Resources
& Land Information Network
http://www.mdmerlin.net/atlaslaunch.html
61
The Maryland Environmental Resources & Land Information
Network website, also known as MERLIN, can provide a wealth
of information about a site. I urge you to use this resource to
see if two uniquely sensitive features may be affected by each
project you review. The first feature is a Wetland of Special
State Concern. There are 405 WSSC’s in Maryland and most
support an aquatic threatened or endangered species. WSSC’s
are indicated with yellow on the MERLIN maps. In this screenshot there are four streams designated WSSCs. The other
feature is a Sensitive Species Project Review Area. As the
name implies SSPRAs are established to alert project reviewers
that there’s a uniquely sensitive resource within the area. If one
of your projects may affect a WSSC or SSPRA then please
contact CEDS for advice on how to determine if more is needed
then just full ESD implementation.
61
Total Maximum Daily Loads
http://www.mde.state.md.us/Programs/WaterPrograms/TMDL/Sumittals/index.asp
http://www.mde.state.md.us/Programs/WaterPrograms/TMDL/Sumittals/index.asp
62
You should also check this MDE webpage to see
if a project is within the drainage area of a
waterway with a Total Maximum Daily Load aka
TMDL. If it is then the waterway is receiving
excessive inputs of one or more pollutants. Most
of the TMDL pollutants can be released from land
uses regulated by the ESD requirements. If this is
the case then take a look at opportunities to
employ ESD practices which are particularly
effective at removing the TMDL pollutant.
62
ESD Compliance Checklist
We’d like to add your checklist to
the CEDS-ESD Compliance
Database. So please forward a
copy of your completed checklist
to:
CEDS-ESD
811 Crystal Palace Court
Owings Mills, MD 21117
or
Fax: 410-654-3028
or
Help@ceds.org
63
This checklist was prepared by CEDS for this workshop.
The checklist serves as a general guide for what to look for
as you review an ESD concept plan and the supporting
computations. If you use the checklist could you forward a
copy to CEDS. We hope to compile a database of
checklist entries for use in assessing how well ESD is
being implemented in each watershed, county,
municipality, and statewide. All information we receive will
be kept confidential. We’ll also provide you with periodic
summaries.
In the next three slides I’ll give a few examples of checklist
items to note while reviewing these documents.
63
Sample ESD Plan
64
So here’s the first of three sample ESD plans.
Here we have a small commercial development site.
All of the parking area, driveway, sidewalks, patio, and
a portion of the roof drains to ESD Practices. The ESD
practices are : Landscape Infiltration, Dry Wells, and
permeable pavers. However, only the red area on the
roof drains to ESD Practices. The rest of the roof will
drain to offsite structural practices. The untreated roof
area amounts to 30% of overall site imperviousness.
In this case we would ask why the roof area is not being
treated with ESD. If the designer ran out of suitable
soils or space then we would ask what efforts were
made to reduce impervious area, use a Green Roof, or
other ESD options.
64
Easton Airport Redevelopment Plan
65
Here we have a redevelopment ESD plan. The orangetan is the existing 116 acres of impervious area, a tenth
of which will be removed. The pink-red is 31-acres of
new impervious area. The blue rectangles are
proposed micro-bioretention areas, which of course is
an ESD micro-scale practice. The green areas are
existing dry ponds which will be converted to extendeddetention to meet Overbank requirements. Channel
protection is not required since this site is on the
Eastern Shore. From this plan it appears that more
then the required 50% of existing impervious area is
being treated with ESD practices as well as all of the
new impervious area. However, the LOD hasn’t been
defined so its hard to tell.
65
Shoppes @ Apple Green
66
Here we have the Shoppes @ Apple Green stormwater
plan. Of course we used the Shoppes to illustrate Site
& Resource Mapping. In fact you see the final site
fingerprint map on the right bounded by the yellow line.
The plan on the left shows the current stormwater
proposal for the 40 acre site. The 25-acres of proposed
impervious area will all drain to the single, end-of-pipe
structure – a micropool pond. The headwaters of the
northern stream will be buried beneath the shopping
center along with the buffer. There will not be any
recharge for the northern stream.
Of course this is a far cry from a plan consistent with
ESD. By the way, Calvert County issued a waiver of
ESD requirements for this site in May.
66
Apple Greene
Existing 1970s
Regional
Pond
67
But it could be worse. How you say? Well this was the
approved stormwater scenario for the Shoppes as of
2008. Calvert County had approved a site plan
allowing the applicant to utilize a dilapidated 1970s
regional pond as the sole stormwater management.
There’s 2,000 feet of stream channel between the
regional pond and the Shoppes site. Yes, nearly a halfmile of stream would have been exposed to the full
pollutional and channel eroding effects of 25-acres of
impervious surface runoff. But this approach has been
abandoned in favor of the onsite, end-of-pipe structure.
A step in the right direction but not enough to protect
the rights of downstream property owners.
67
For A No-Cost Initial Review
For Additional ESD
Opportunities
Forward Project Plans To…
Richard Klein
Community & Environmental Defense Services
811 Crystal Palace Court, Owings Mills, MD 21117
ceds.org ~ Help@ceds.org
410410-654654-3021 ~ 11-800800-773773-4571
68
If you wish, we would be delighted to take an
initial look at a concept plan for additional
opportunities to enhance aquatic resource
protection through ESD. There’s no charge for
this quick look for clean water advocates.
Just drop the plans in the mail to the address you
see here along with a note telling us who you are,
how to get in touch with you, and describe any
specific questions you have.
This brings this presentation to a close. Any
questions?
68