1. science
2. ecology
3. pollution

ADDENDUM ONE FOR THE TOWN OF GREENWICH DRAINAGE MANUAL
FEBRUARY 2012
ALL CHANGES TO THE MANUAL ARE SHOWN IN RED
Title Sheet:
Added revision date of February 2014
Acknowledgement Page:
Added revision date of February 2014
Table of Contents: i-viii
Revised page numbers
Page 13-14:
E. Pumping of uncontaminated groundwater, including, but not limited to, from
basements, and foundations, is discouraged for new development or in the case of
redevelopment involving the upgrade of existing sump pump systems. The replacement
of an existing sump pump system is acceptable when a direct replacement of the pump is
needed. (Remove: and in the case of redevelopment when the improvement doesn’t
require a sump pump.) All other feasible approaches (footing drains to daylight, slab on
grade, crawl space, etc.) must be investigated to avoid the use of pumps in groundwater
management system designs for new development or redevelopment. In the event the
project proponent determines that pumps are necessary to manage groundwater for new
development or redevelopment applications, the proponent must submit required backup
information as described in this manual for review by the approving authority. For the
use of a pump to manage groundwater to be approved by the approving authority, the
proponent will be required to provide the following at a minimum:
 Include on-site BMPs that are designed to accommodate and manage the
pumped uncontaminated groundwater in accordance with the other
standards contained in this manual. A system for re-use of the pumped
groundwater for lawn or landscape irrigation shall be considered.
Overflows must be directed to an on-site level spreader or connected to the
Town drainage system (Highway Permit Required) with review and
approval.
 A backup generator associated with the pump is recommended but not
required,
 Design the on-site BMPs to meet the maximum pumping rate of the
proposed pumping system.
 Provide documentation that the pump and on-site BMPs are designed and
inspected by a Professional Engineer licensed in the State of Connecticut.
Page 15:
Standard 6: Pollutant Reduction – Remove bullet B and C
Page 16,17 and 18:
Page changed because of other revisions.
Page 19 and 20:
Page changed because of other revisions.
Page 20-22: Added pages 22-A and 22-B
3.3
Applicability and Drainage
Report Exemptions
The Greenwich Stormwater Management Standards apply to new development,
redevelopment, and other activities that will result in an increased amount of stormwater
runoff and/or water pollutants flowing from a parcel of land or any activity that will alter the
drainage characteristics of a parcel of land (prior to the application of stormwater Best
Management Practices), unless exempt. Two types of exemptions may apply.
Categorical Exemptions
The Greenwich Stormwater Management Standards shall not apply to the following
categorically exempt activities, although application of the standards is still strongly
encouraged:
 Normal maintenance and improvement of land in agricultural use (as defined by
Connecticut General Statutes), provided such activity conforms to acceptable
management practices for pollution control approved by the Connecticut
Department of Energy and Environmental Protection and the Greenwich Inland
Wetlands and Watercourses Commission. This exemption does not apply to
construction activities that are not directly related to the farming or agricultural
operation.
 Routine maintenance of existing landscaping, gardens (excluding structural
modifications to stormwater BMPs including rain gardens) or lawn areas including
those maintained by the Town of Greenwich Parks and Recreation Department and
Board of Education.
 Resurfacing of an existing impervious area on a non-residential lot such as repaving
an existing parking lot or drive with no increase in impervious cover.
 Routine maintenance to existing town roads that is performed to maintain the
original width, line, grade, hydraulic capacity, or original purpose of the roadway.
 Customary cemetery management.
 Emergency repairs to any stormwater management facility or practice that poses a
threat to public health or safety, or as deemed necessary by the approving authority.
 Any emergency activity that is immediately necessary for the protection of life,
property, or the environment, as determined by the approving authority.
 Repair of an existing septic system.
 Construction of utilities (gas, water, electric, telephone, etc.), other than drainage,
which will not permanently alter terrain, ground cover, or drainage patterns.
 Repair or replacement of an existing roof of a single-family dwelling.
 Construction of a second (or higher) floor addition on an existing building.
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Construction of a maximum 12 foot x 12 foot shed. The construction must include
the installation of a 1 foot wide x 1 foot deep crushed stone trench along the sides of
the shed that discharge the roof runoff.
The repair of an existing wood, composite, or plastic deck with no proposed
enlargement of the deck surface.
The reconstruction or construction of a wood, composite, or plastic deck with the
decking boards spaced at least 3/16 of an inch and a pervious surface below the
deck. The pervious area below the deck must have the soil tilled 12 to 16 inches and
finished with grass seed, sod, or crushed stone. The minimum depth for the crushed
stone is 4 inches. A site plan showing the proposed location of the deck and
construction details for the deck must be submitted.
The construction of any fence that will not alter existing terrain or drainage patterns.
Projects Adding Up to 500 Square Feet of Impervious Surfaces
Projects adding up to 500 square feet of impervious surfaces are exempt from the
Greenwich Stormwater Management Standards, provided that all of the following conditions
are met:
 The project design, including the proposed drainage design, if any, will not have an
adverse effect on offsite properties or offsite drainage infrastructure, as certified by a
professional engineer.
 At least one of the following measures shall be implemented on the project site to
help mitigate the effects of site disturbance and new impervious surfaces within its
on site watershed and point of concern:
o Disconnection of roof down spouts that meet the Simple Disconnection
standards in the Town of Greenwich Drainage Manual February 2012 as
amended
o A zero increase in peak flow to all points of concern for the 1, 2, 5, 10, and
25-year design storms
o The runoff volume from the new impervious surfaces shall be infiltrated for
the 10-year design storm
o Constructing a bioretention area for the Water Quality Volume of the
contributing watershed of the project area. The design standards in the Town
of Greenwich Drainage Manual February 2012 as amended must be met
o Creating a buffer with a length greater than or equal to the length of the
project area and a minimum width of 10 feet planted as a meadow
o Restoring a riparian buffer (may require IWWA permit)
 The project proponent submits an exemption request, including professional
engineer certification, in lieu of a Stormwater Management Report (Form SE-100).
This exemption can only be used until the cumulative addition of impervious surfaces on a
site exceeds 500 square feet, regardless of ownership changes. For projects adding up to 500
square feet of impervious surfaces, application of the Greenwich Stormwater Management
Standards is still strongly encouraged.
Residential teardowns are not exempt unless the project meets the Conditional Residential
Teardown Exemption Requirements. Commercial teardowns are not exempt.
Projects Adding Between 500 and 1,000 Square Feet of Impervious Surfaces
Projects adding between 500 and 1,000 square feet of impervious surfaces are exempt from
the Greenwich Stormwater Management Standards, provided that all of the following
conditions are met:
 The project design, including the proposed drainage design, if any, will not have an
adverse effect on offsite properties or offsite drainage infrastructure, as certified by a
professional engineer,
 At least one of the following measures shall be implemented on the project site to
help mitigate the effects of site disturbance and new impervious surfaces within its
on site watershed and point of concern:
o Disconnection of roof down spouts that meet the Simple Disconnection
standards in the Town of Greenwich Drainage Manual February 2012 as
amended
o A zero increase in peak flow to all points of concern for the 1, 2, 5, 10, and
25-year design storms
o The runoff volume from the new impervious surfaces shall be infiltrated for
the 10-year design storm
o Constructing a bioretention area for the Water Quality Volume of the
contributing watershed of the project area. The design standards in the Town
of Greenwich Drainage Manual February 2012 as amended must be met
o Creating a buffer with a length greater than or equal to the length of the
project area and a minimum width of 10 feet planted as a meadow
o Restoring a riparian buffer (may require IWWA permit)
 At least one of the following measures shall be implemented on the project site using
LID or conventional stormwater BMPs to help mitigate the effects of site
disturbance and new impervious surfaces:
o A zero increase in peak flow to all points of concern for the 1, 2, 5, 10, and
25-year design storms
o The runoff volume from the new impervious surfaces shall be infiltrated for
the 10-year design storm
 The project proponent submits an exemption request, including professional
engineer certification, in lieu of a Stormwater Management Report (Form SE-100).
This exemption can only be used until the cumulative addition of impervious surfaces on a
site exceeds 1,000 square feet, regardless of ownership changes. For projects adding between
500 and 1,000 square feet of impervious surfaces, application of the Greenwich Stormwater
Management Standards is still strongly encouraged.
Residential teardowns are not exempt unless the project meets the Conditional Residential
Teardown Exemption Requirements. Commercial teardowns are not exempt.
Remove: Projects adding between 500 and 1,000 square feet of impervious surfaces located
within, near , or discharging to a critical area (as described in Section 5.7.3) are also not
exempt.
Conditional Residential Teardown Exemption Requiring Professional
Engineering Certification
Projects for residential teardowns that reconstruct where the impervious surfaces within
each point of concern is less than or equal to pre-development conditions and the peak flow
and runoff volume for the 1, 2, 5, 10, 25, 50, and 100-Year Storms has a zero increase to all
points of concern are exempt from the Greenwich Stormwater Management Standards,
provided that all of the following conditions are met:
 The project design, including the proposed drainage design, if any, will not have an
adverse effect on offsite properties or offsite drainage infrastructure, as certified by a
professional engineer
 A Stormwater Management Report must be submitted with the following included:
1. Project Narrative
2. Site Inventory & Evaluation
a. Topography
b. Soil Evaluation (Soil Evaluation Test Results (Form SC-101) Shall Be
Used)
i. Initial Feasibility Evaluation (NRCS Web Soil Survey and
similar sources of information)
ii. Concept Design Testing (test pits/borings and saturated
hydraulic conductivity testing, as per Appendix B)
3. Evaluate Pre-Development Site Hydrology to all points of concern (Runoff
Volume and Peak Flow Rate – 1, 2, 5, 10, 25, 50 and 100-Year Storms)
a. Watershed Map Pre-Development
b. NRCS Runoff Curve Numbers Pre-Development
c. Time of Concentration Pre-Development
4. Evaluate Post-Development Site Hydrology to all points of concern (Runoff
Volume and Peak Flow Rate – 1, 2, 5, 10, 25, 50 and 100-Year Storms)
a. Watershed Map Post-Development
b. NRCS Runoff Curve Numbers Post-Development
c. Time of Concentration Post-Development
5. Peak Runoff to all points of concern must have a zero increase for the 1, 2,
5, 10, 25, 50, and 100-Year Storms
6. Runoff volume to all points of concern must have a zero increase for the 1,
2, 5, 10, 25, 50, and 100-Year Storms
7. Compare & Summarize Pre-&-Post Development Site Hydrology for peak
flow and runoff volume to all points of concern
8. Conveyance Protection: 10, 25, 50 & 100-Year Depending on Peak Flow
Rate for Downstream Stormwater Facilities
9. Outlet Protection Calculations – Based on Conveyance Protection
10. Emergency Outlet Sizing: Safely Pass the 100-Year
11. Supporting Documents
12. Sealed and Signed By a Professional Engineer
The application of the Greenwich Stormwater Management Standards is still strongly
encouraged.
For projects that meet the above criteria, the project proponent needs to submit plans which
include all items on the:
1. Checklist for Construction Plans – Form CL-102
2. Checklist for Driveway Profile and Sight Distance Plan – Form CL-103
For projects that meet the above criteria, the project proponent must submit an Operations
and Maintenance Plan Report. The Operations and Maintenance Plan must be submitted
following the Checklist for Operations & Maintenance Plan Report CL-104.
For projects that meet the above criteria, the project proponent needs to submit the items
on the Checklist for Certificate of Occupancy – Form CL-105 with the request for
Certificate of Occupancy. The Improvement Location Survey must include the items on the
Checklist for Improvement Locations Survey Depicting „As-Built” Conditions CL-106.
The use of this exemption removes any future additional construction on the property from
using the Conditional Exemption regardless of ownership changes.
Page 30:
Footnote number changed.
Page 32:
Add the following to paragraph four:
All areas that will be considered forest/open space for stormwater purposes must have
documentation that prescribes that the area will remain in a natural, vegetated state.
Appropriate documentation includes: subdivision covenants and restrictions, deeded
operation and maintenance agreements and plans, parcel of common ownership with
maintenance plan, third-party protective easement, within public right-of-way or easement
with maintenance plan, or other documentation approved by the local authority
While the goal is to have forest/open space areas remain undisturbed, some activities may be
prescribed in the appropriate documentation, as approved by the local program authority:
forest management, control of invasive species, replanting and revegetation, passive
recreation (e.g., trails), limited brush hogging to maintain desired vegetative community, etc.
Page 33:
A bullet from page 32 moved to page 33
Page 37:
Figure 4-4. Three-Zone Riparian Buffer needed to be reprint as image was clipped.
Page 41:
In next to last paragraph change covey to convey.
Page 42:
In last paragraph change American to Americans.
Page 44:
In item two under Simple Disconnection change it to its.
Page 45:
1. In all cases, flows do not contribute to basement seepage.
2. All discharges onto the downstream pervious disconnection area are non-erosive.
3. Runoff is not directed to vegetated areas if there is reason to believe that pollutant
loadings will be elevated.
4. Roof downspouts or curb cuts are at least 10 feet away from the nearest connected
impervious surface (i.e., driveway) to discourage “re-connections.”
a. Limit the contributing impervious area to a maximum of 1,000 sq. ft. per
discharge point.
b. Limit the contributing rooftop area to a maximum of 1,000 sq. ft. per
downspout, where the pervious area receiving runoff must be at least twice
this size.
c. For contributing areas greater than 1,000 sq. ft., level spreaders are
recommended.
5. A maximum contributing impervious flow path length of 75 feet.
6. Simple disconnection is not suggested on lots less than 7,500 square feet due to
minimum sizing and area requirements.
Page 45:
Disconnection to LID BMPs
1. Flows from impervious areas are directed into properly designed and constructed
LID BMPs. For the purpose of this manual, an infiltration practice with an
impervious contributing drainage area equal to or less than 1,000 square feet (i.e.,
allowing up to one roof leader, with a maximum contributing drainage area of 1,000
square feet each, to be piped to a single infiltration practice) and no other BMP‟s
within 25 feet (measured in all directions from the outer edge of the storage layer of
the BMP) is considered a LID BMP. Infiltration practices designed with a larger
impervious contributing drainage area are considered conventional or non-LID
BMPs.
2. The downstream LID BMP must be designed in accordance with the design criteria
listed in this manual, and/or the references sited in Appendix G.
3. In all cases, flows do not contribute to basement seepage.
4. In all cases, placement of LID BMPs must meet the setback requirements listed in
this manual.
Page 46:
The selection and design of the following structural LID BMPs are addressed in Section 5 of
this manual:
 Rainwater harvesting (e.g., rain barrels, cisterns) for property irrigation,
 Bioretention systems, including rain gardens, tree filters, stormwater planters, and
curb extensions,
 Dry wells and subsurface infiltration systems (decentralized, small-scale practices
distributed throughout the site – Maximum contributing area is 1,000 square feet –
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and no other BMP‟s within 25 feet (measured in all directions from the outer edge of
the storage layer of the BMP)),
Green roofs,
Permeable pavement,
Vegetated filter strips,
Vegetated swales/channels,
Compost-amended soils.
These are generally small-scale structural practices distributed throughout the site, close to
the source of runoff.
Page 47and 48:
Pages changed because of other revisions.
Page 52:
Correct last sentence.
 Encourage shared parking agreements with adjacent or nearby properties (within
walking distance) that serve land uses with non-competing hours of operation. An
example of this is use of a parking area for an office building after 5 pm for an
adjacent retail use which stays open to 9 or 10 pm.
Page 62:
 Bioretention systems, including, rain gardens, tree filters, stormwater planters, and
curb extensions specifically designed for infiltration (LID BMPs),
 Infiltration systems when designed as decentralized, small-scale practices distributed
throughout the site, which typically include dry wells (Maximum contributing area is
1,000 square feet), leaching catch basins, and smaller subsurface infiltration units
(LID BMPs),
 Infiltration systems when designed as larger centralized or end-of-pipe systems,
which typically include infiltration basins, infiltration trenches, and larger subsurface
infiltration units.
Page 62:
Need to change 2,000 square feet to 1,000 square feet
For the purpose of this manual, an infiltration practice with an impervious contributing
drainage area equal to or less than 1,000 square feet (i.e., allowing up to one roof leader, with
a maximum contributing drainage area of 1,000 square feet, to be piped to a single
infiltration practice) is considered a LID BMP. Infiltration practices designed with a larger
impervious contributing drainage area are considered conventional or non-LID BMPs.
Page 67:
For the purpose of meeting the Runoff Volume Reduction criterion in Stormwater
Management Standard 5, the project proponent shall calculate pre- and post-development
total runoff volumes. The post-development total runoff volume shall not exceed the predevelopment total runoff volume for the 1-year, 24-hour design storm. For new
development and redevelopment, the required Runoff Reduction Volume (RRV) is the
difference between the pre- and post-development total runoff volumes for the 1-year
design storm. (Removed: For redevelopment, the RRV is equal to either the difference
between pre- and post-development runoff volumes for the 1-year design storm, or the
Water Quality Volume (as described in Section 5.6.3), whichever is larger.
Runoff volume calculations shall include runoff onto the project site from the off-site
contributing drainage area based on the current condition of the off-site drainage area. If the
off-site area enters the proposed Runoff Reduction BMP the BMP must include the off-site
area to size the BMP. If the off-site area bypasses the Runoff Reduction BMP the off-site
area shall not be used to size the Runoff Reduction BMP. Modifications to the site to bypass
a Runoff Reduction BMP are acceptable but these modifications must maintain the existing
condition flow segment type (Sheet Flow, Shallow Concentrated Flow, and Open Channel
Flow). Runoff reduction shall be accomplished using the LID site planning and design
techniques (non-structural LID BMPs) described in Section 4 and structural BMPs described
in this section of the manual, if necessary.
Page 69:
The first paragraph changed as follows:
Infiltration of the required GRV must be accomplished using appropriate non-structural
(i.e., site design) and structural BMPs. Stormwater infiltration BMPs include dry wells,
infiltration basins, infiltration chambers and galleys, infiltration trenches, leaching catch
basins, and bioretention systems (including rain gardens, tree filters, stormwater planters, and
curb extensions) when specifically designed for infiltration. Roof runoff may be infiltrated
without any pre-treatment, and the infiltrated volume may be used to meet the groundwater
recharge, runoff reduction, and water quality standards.
The second paragraph changed as follows:
The Runoff Capture Volume (RCV) is equivalent to the Water Quality Volume and intended
to minimize the discharge of fresh water to sensitive coastal receiving waters and wetlands.
As described in the Connecticut Stormwater Quality Manual, the RCV applies to new
stormwater discharges located within 500 feet of and that ultimately discharge to tidal
wetlands, which are not fresh water wetlands. The RCV must be retained on-site for such
discharges through the use of LID site planning and design techniques and/or structural
stormwater BMPs such as infiltration systems or stormwater basins.
The third paragraph needs to be removed:
If a project meets the Runoff Reduction Volume criterion, then the RCV is effectively retained on-site and the
Runoff Capture criterion of Stormwater Management Standard 4 is satisfied.
Page 69-70:
The last paragraph changed as follows:
To determine the field infiltration rate, a soil evaluation must be performed using the
methodologies described in Appendix B. Infiltration systems must be installed in soils capable
of absorbing the design volume. Infiltration structures must be able to drain fully within 72
hours. In addition, there must be at least a 2-foot separation distance from the bottom of the
infiltration structure to seasonal high groundwater or bedrock/ledge (this separation
requirement may be waived or reduced by the approving authority on a case-by-case basis).
A 3-foot separation distance is required from the bottom of the infiltration structure to
seasonal high groundwater for land uses with higher potential pollutant loads (high load
areas). Soils under BMPs shall be scarified or tilled to improve infiltration. Non-infiltration
BMPs (e.g., filters, dry water quality swales, filtration bioretention systems) may be
constructed one foot above seasonal high groundwater or, in some cases, below the water
table (e.g., wet water quality swale, gravel wetland, wet basin).
Page 71:
Footnote number changed.
Page 72:
Section 5.2 contains a list of LID BMPs and conventional or non-LID BMPs. For the
purpose of this manual, infiltration practices are categorized as LID BMPs or non-LID
BMPs based on their contributing drainage area. An infiltration practice with an impervious
contributing drainage area equal to or less than 1,000 square feet (i.e., allowing up to one
roof leader, with a maximum contributing drainage area of 1,000 square feet (Remove: each),
to be piped to a single infiltration practice) is considered a LID BMP. Infiltration practices
designed with a larger impervious contributing drainage area are considered conventional or
non-LID BMPs.
Page 74:
The following was added after last paragraph:
A minimum of 60% of the WQV must be treated by using non-structural and structural LID
BMP‟s.
Page 76:
For sites where off-site areas also contribute to the site‟s drainage, the off-site area shall be
included in the calculation of WQV based on its current condition. . If the off-site area
enters the proposed WQV BMP the BMP must include the off-site area to size the BMP. If
the off-site area bypasses the WQV BMP the off-site area shall not be used to size the WQV
BMP. Modifications to the site to bypass a WQV BMP are acceptable but these
modifications must maintain the existing condition flow segment type (Sheet Flow, Shallow
Concentrated Flow, Open Channel Flow).
Page 77 and 78:
Table 5-6. TSS Removal Efficiencies
Best Management Practice
(BMP)
TSS Removal Efficiency
Pretreatment BMPs
Deep Sump Catch Basins
25% only if used for pretreatment and only if off-line
Oil Grit Separator
25% only if used for pretreatment and only if off-line
Proprietary Separators
Varies – see Section 5.3
Sediment Forebays
25% if used for pretreatment
Vegetated filter strips
10% if at least 25 feet wide, 45% if at least 50 feet wide
Treatment BMPs
Bioretention - Rain Gardens, Tree
Filters, Stormwater Planters, Curb
Extensions
Constructed Stormwater Wetlands
90% provided it is combined with adequate pretreatment or equivalent
sediment storage volume, 80% without pretreatment
Extended Dry Detention Basins
50% provided it is combined with a sediment forebay
Gravel Wetlands
85% provided it is combined with a sediment forebay
Proprietary Media Filters
Varies – see Section 5.3
Sand/Organic Filters
85% provided it is combined with sediment forebay
Wet Basins
80% provided it is combined with sediment forebay
80% provided it is combined with a sediment forebay
Conveyance BMPs
Drainage Channels
For conveyance only. No TSS Removal credit.
Grass Channels
70% if combined with sediment forebay or equivalent
Water Quality Swale – wet & dry
80% provided it is combined with sediment forebay or equivalent
Bioretention - Rain Gardens, Tree
Filters, Stormwater Planters, Curb
Extensions (infiltration design)
Dry Wells
90% provided it is combined with adequate pretreatment or equivalent
sediment storage volume, 80% without pretreatment
Infiltration Basins & Infiltration
Trenches
90% provided it is combined with adequate pretreatment (sediment
forebay or vegetated filter strip, grass channel, water quality swale) prior
to infiltration
80% provided a deep sump catch basin is used for pretreatment
Infiltration BMPs
Leaching Catch Basins
90% for runoff from non-metal roofs.
Subsurface Structure
90% provided they are combined with one or more pretreatment BMPs
prior to infiltration.
Other BMPs
Compost-Amended Soils
May reduce required runoff reduction volume and water quality volume.
No TSS Removal Credit.
May reduce required runoff reduction volume and water quality volume.
No TSS Removal Credit.
90% if designed to prevent run-on and with adequate storage capacity.
Green Roofs
Permeable Pavement
Rain Barrels and Cisterns
Dry Detention Basins
May reduce required runoff reduction volume and water quality volume.
No TSS Removal Credit.
For peak rate attenuation only. No TSS Removal credit.
Page 86:
Critical areas (see Figure 5-2) are defined as:
 All parcels within the Coastal Area Management Zone that have a property
boundary along the water are considered within the “Critical Area”.
 Shellfish growing areas and public swimming beaches (entire Greenwich
coastline),
 Recharge areas for public water supplies (groundwater and surface water
supplies),
 Other sensitive receiving water bodies or wetlands as designated by the Town of
Greenwich or the Connecticut Department of Energy and Environmental
Protection.
Page 88-89:
Table 5-9. Stormwater BMPs for Shellfish Growing Areas
and Public Swimming Beaches
1.
If applicable, proponent must comply with Coastal Area Management and CT Tidal Wetlands Act
requirements
2. Dry detention basins are prohibited.
3. All BMPs must be designed in accordance with the Town of Greenwich Drainage Manual.
Pretreatment BMPs

Water Quality Inlets

Deep Sump Catch Basins with Hoods

Sediment Forebays

Vegetated Filter Strips

Drainage Channels

Hydrodynamic Separators or other Proprietary BMPs
Treatment BMPs

Constructed Wetlands

Sand Filter/Organic Filters

Bioretention - Rain Gardens, Tree Filters, Stormwater Planters,
Curb Extensions

Water Quality Swales

Extended Detention Basins

Wet Retention Basins
Infiltration BMPs

Bioretention, Rain Gardens, Tree Filters, Stormwater Planters,
Curb Extensions (infiltration design)

Infiltration Trenches

Infiltration Basins

Dry Wells (uncontaminated roof runoff only)

Infiltration Chambers or Galleys
Page 90:
The second paragraph needs to be revised as follows:
Coastal waters are the primary impaired water bodies in the Town of Greenwich (Appendix
A). The impairments are for shellfish harvesting, recreation, and habitats for fish and other
aquatic life and wildlife. Non-point sources, including urban stormwater runoff and
waterfowl, as well as marina/boating and sanitary on-vessel discharges are the predominant
suspected sources of the impairments, which are caused by elevated concentrations of
bacteria and nutrient enrichment and low dissolved oxygen. The following guidelines are
recommended for stormwater discharges to or near sensitive receiving waters and wetlands:
 If cold water fisheries are present, select BMPs that will reduce thermal impacts.
 For inland lakes and ponds, select BMPs with high phosphorus and sediment
removal to reduce the rate of eutrophication. Select BMPs with high bacteria
removal when waters are used for recreation.

For coastal areas, select BMPs with high nitrogen and bacteria removal to reduce
closure of swimming beaches and shellfish beds.
Page 97:
* Sags include any low point without a reliable means of overland flood relief, where
ponding will occur if the drainage system cannot convey storm flows.
** Culverts for driveway crossings of watercourses will require design for the 100-year
storm, regardless of the size of the upstream watershed area. For those critical activities as
defined in CGS Section 25-68b-25-68h, the design storm frequency shall be 500 years.
Page 99 and 100:
Page changed because of other revisions.
Page 102:
NRCS Methods

TR-55 Urban Hydrology for Small Watersheds, Version 2.0: This rainfall runoff
model was developed by the U.S. Soil Conservation Service, now known as the
Natural Resources Conservation Service (NRCS). TR-55 presents simplified
procedures to calculate storm runoff volume, peak rate of discharge, hydrographs,
and storage volumes required for flood water reservoirs. These procedures are
applicable to small watersheds, especially urbanized watersheds. The primary
functions of the program are for peak runoff computations using the Graphical Peak
Discharge Method, the Tabular Hydrograph Method, and Temporary Storage.
Support functions include the computation of the runoff curve number, the time of
concentration, and travel time. Limitations of the model include NRCS type
distributions, 24-hour duration rainfall,
10 subwatersheds, and minimum of 0.1 hour and maximum 10-hour times of
concentration. The Tabular Hydrograph Method, or the use of TR-20 as described
below, is the preferred NRCS method for hydrologic design in Greenwich.
Page 105:
Cross Slope
The Connecticut Department of Transportation Highway Design Manual has established
standard cross slopes for different types of roadways. Median areas should not be drained
across travel lanes, and roadside areas should generally be sloped to drain away from the
pavement.
Under Drains
In certain areas groundwater can be a significant problem as it attacks foundations,
substructures, subgrades and other aspects of highway components. In most soils where
groundwater is a problem, a system of under drains, installed for the removal of excess
moisture, can be used in the overall roadway design. Under drains may consist of networks
of perforated (or otherwise permeable) pipe, French drains, or collector fields.
Adequate provisions shall be made for subsurface drainage systems. The location, details
and required size (or capacity) of subsurface drainage facilities shall be reviewed for approval
by the Town. In subdivision roadway cuts, under drains shall be required if seepage occurs
during construction or if directed by the Town, even though plans may have been approved
without under drains.
Page 106:
Inlets on Grade
The capacity of an inlet depends on a number of factors: inlet geometry, roadway cross
slope, roadway longitudinal slope, total gutter flow, depth of flow, and pavement or surface
roughness. Depth of flow adjacent to the curb is the major factor in determining the
capacity of gutter inlets. The frontal flow, or the water flowing in the area occupied by the
grate, is fully intercepted by the inlet at low velocities. The remainder of flow outside the
width of the grate will bypass the inlet and travel to the next inlet. Designs shall consider
interception of the entire frontal flow and disregard side flow. (Remove: The remainder of
the flow outside the width of the inlet will bypass to the next inlet.)
Page 115:
Table 6-11. Minimum Allowable Pipe Slopes (%) to Ensure 2.5 ft/s
In Storm Drains Flowing Full
Pipe Diameter
12”
15”
18”
24”
36”
48”
60”
Reinforced Concrete
(RCP) n=.013
0.3%
0.22%
0.2%
0.12%
0.07%
0.05%
0.04%
Corrugated Polyethylene
(corrugated) n=.025
1.1%
0.83%
0.65%
0.44%
0.3%
0.2%
0.13%
Corrugated Polyethylene
(smooth) n=.015
0.4%
0.3%
0.23%
0.2%
0.09%
0.06%
0.05%
Polyvinyl chloride (PVC)
(smooth) n=.011
0.22%
0.16%
0.13%
0.09%
0.05%
0.034%
0.03%
Pipe Material
Page 115-116 and ii:
Changed on pages and Table of Contents
6.3.6 Headwalls and Trash Racks
6.3.7 Outlet Protection
Page 117:
The locations and alignment of culverts should be consistent with the flow tendency of
existing streams. New culverts or replacement culverts to convey streams shall comply with
the Connecticut Department of Energy and Environmental Protection Stream Crossing
Guidelines (as amended) to accommodate high flows, minimize erosion, and support aquatic
habitat and wildlife passage.
The analysis and design of channels shall be consistent with the type of channel and its
intended purpose. Channels shall be classified as local drainage channels or as watercourse
channels, depending on their use. Local drainage channels, including minor LID vegetated
swales and grass drainage channels, are designed with the primary purpose of conveying
urban, parking lot and road runoff from small watersheds, frequently with intermittent flow
and limited ecological value and are intended to convey their design flow within their banks.
Watercourse channels are designed as natural perennial watercourses or man-made channels
planned to simulate a natural watercourse.
Page 122:
Table 6-12. Storm Drainage Pipe Design and Installation Guidelines
Pipe Material
Design
Common Shapes Considerations and
Limitations
Cover
General Installation
Guidelines
1’ min. – 15’ max.
Strength analysis
required for cover less
than 2’ or greater than
15’.
Reinforced
Concrete Pipe
(RCP)
Circular, arch,
horizontal & vertical
ellipse
Minimum Class V in a
saltwater environment or
in unstable foundation
conditions, as directed
by the Town.
Cross culverts are widely
used for stormwater
conveyance systems.
Minimum 12” diameter
regardless of material
within Town ROW.
2’ min. for Class IV
Minimum Class IV RCP on
RCP. Concretepublic property and within
encased Class V RCP Town ROW.
if less than 2’. No less
than 1’ of cover for
RCP.
Corrugated
Structural Plate
Pipe (CSPP)
Circular, arch,
horizontal & vertical
ellipse, box culverts,
pipe arch
Larger culverts field
Strength calculations
assembled with
should be considered
structural plate products. for all cover depths.
Corrugated
Polyethylene Pipe
(CPP) or High
Density
Polyethylene
(HDPE)
Circular, arch (only
Proper bedding and
use corrugated pipe controlled backfill is
with smooth interior) crucial particularly in
adverse soil conditions.
2’ min. (or one pipe
diameter) to 12’ max.
Otherwise strength
calculations are
required.
1’-2’ cover if encased
in concrete. No less
than 1’ of cover.
Generally reserved for
larger culverts and where
structural considerations
require thicker gauge
metal.
Site stormwater
conveyance systems,
culverts and subsurface
stormwater
detention/retention
systems. Maximum pipe
diameter in the Town
R.O.W. is 24". See RCP
requirements for larger
pipes. Water-tight joints
required for all installations.
Polyvinyl Chloride
(PVC)
Circular
Proper bedding and
controlled backfill is
crucial particularly in
adverse soil conditions.
Same requirements as Roof drain laterals,
HDPE.
pressure and pumped
systems. SDR-35 PVC is
required, otherwise same
guidelines as HDPE.
Other – large
spans, bridges
Rectangular (box
culvert), arch, flat top
3-sided (rigid frame),
3-sided arch
Requires structural
Strength calculations Bottomless culverts,
design of footings and
based on geotechnical waterway crossings, bridge
other integral
findings.
crossings.
components. A
geotechnical
investigation is generally
required.
Page 124-132:
Combine Stormwater Management Report Part One and Two into Stormwater Management
Report and other changes.
7 Submittal Requirements
All land development applications in the Town of Greenwich subject to the Greenwich
Stormwater Management Standards shall include the following information to
demonstrate conformance with the standards, the design requirements contained in this
manual, and related land use regulatory requirements:
1.
2.
3.
4.
5.
6.
7.
Stormwater Management Report
Construction Plans
Supporting Documents and Studies
Operation and Maintenance Plan
Erosion and Sediment Control Plan
Plan & Report Revisions
Certifications
Specific requirements for each of the above items are summarized in the checklists
provided in Appendix I and outlined below.
7.1
Stormwater Management Report
The Stormwater Management Report shall describe how the proposed project has
addressed the following LID and stormwater management elements:
 Project Narrative:
o Project description and purpose
o Site description, including a description of on-site and off-site resources
o Proposed non-structural BMPs (source controls and LID site planning and
design measures)
o Proposed structural BMPs
o How the proposed development complies with the Stormwater Management
Standards
o Soil evaluation
o Site plans
o Construction schedule
 Stormwater Management Standards Narrative
 Credits for LID BMP‟s
 Comparison Table for Pre-&-Post Development Peak Flow, Volume, and Percent
Difference
 Identify Applicable Land Use Regulations
 Site Inventory & Evaluation
o Topography
o Soil Evaluation (Soil Evaluation Test Results (Form SC-101) Shall Be Used)



Initial Feasibility Evaluation (NRCS Web Soil Survey and similar
sources of information)
 Concept Design Testing (test pits/borings and saturated hydraulic
conductivity testing, as per Appendix B)
o Hydrologic patterns and features
o Generalized forest types (old field/shrub; early succession and mature
hardwood) as determined in the field by a qualified professional
o Dominant deciduous and evergreen tree species by class and the density of
the trees and canopy coverage. The average type of the forest cover shall be
discussed.
o Discuss efforts made to protect wetland areas and riparian corridors (as
applicable)
o Discuss efforts made to protect floodplains and water bodies (as applicable)
o Discuss efforts made to protect natural drainageways
Define Development Envelope
o Consider construction techniques
o Determine and protect sensitive areas
o Retain and protect mature trees
o Minimize disturbance of steep slopes (over 25%)
o Minimize clearing and grading for buildings
o Access and fire prevention, and other construction activities, including
stockpiles and storage areas
o Delineate preferred areas for infiltration (A & B soils)
o Confine envelope to areas to be permanently altered
Develop LID Control Strategies
o Evaluate Pre-Development Site Hydrology (Runoff Volume and Peak Flow
Rate – 1, 2, 5, 10, 25, 50 and 100-Year Storms)
 Watershed Map Pre-Development
 NRCS Runoff Curve Numbers Pre-Development
 Time of Concentration Pre-Development
o Minimize Total Site Impervious Area
o Minimize Directly Connected Impervious Areas
o Minimize Site Disturbance
o Modify Drainage Flow Paths to Increase Time of Concentration
o Evaluate Post-Development Site Hydrology (Runoff Volume and Peak Flow
Rate – 1, 2, 5, 10, 25, 50 and 100-Year Storms)
 Watershed Map Post-Development
 NRCS Runoff Curve Numbers Post-Development
 Time of Concentration Post-Development
o Compare & Summarize Pre-&-Post Development Site Hydrology to
Evaluate Benefits of Non-Structural Site Planning Techniques
o Identify Remaining need for Structural BMPs to Satisfy:
 Water Quality Volume/Flow
 TSS Removal Computations
 Runoff Reduction Volume: 1-Year Storm
 Groundwater Recharge Volume (if necessary)
 72-Hour Drawdown Computations

















2-Year Over Control Channel Protection (Required on a Site by Site
Basis)
 Peak Runoff Attenuation: 2, 5, & 10-Year Storm (and 25-Year Storm
for projects that do not rely solely on LID BMPs), 50-Year & 100Year Peak Runoff Attenuation Required on a Site by Site Basis
Remaining Structural BMPs to Meet Water Quality Volume/Flow (WQV)/(WQF)
and TSS Removal
Remaining Structural BMP‟s to Meet 80% TSS Removal
Remaining Structural BMPs to Meet Runoff Reduction Volume (RRV): 1-Year
Storm
Remaining Structural BMPs to Meet Groundwater Recharge Volume (GRV), if
necessary
Remaining Structural BMP‟s to Meet 72-Hour Drawdown
Remaining Structural BMPs to Meet Stream Channel Protection: 2-Year Frequency
(“Over-Control” of 2-Year Storm) – Required on Site By Site Basis
Remaining Structural BMPs to Meet Peak Runoff Attenuation: 2, 5, & 10 Year; 25Year for Projects that Do Not Rely Solely on LID BMPs; 50-Year & 100-Year
Required on Site by Site Basis
Conveyance Protection: 10, 25, 50 & 100-Year Depending on Peak Flow Rate for
Which Downstream Stormwater Facilities are Designed
Emergency Outlet Sizing: Safely Pass the 100-Year
Culvert Capacity Calculations
Outlet Protection Calculations – Based on Conveyance Protection
Downstream Analysis – Required on Site by Site Basis and When No Detention
Proposed
Town Storm Drain Analysis – Required on Site by Site Basis
Gutter Flow Calculations – Required on Site by Site Basis
Supporting Documents
Sealed and Signed By a Professional Engineer
A Stormwater Management Report checklist is included in Appendix I.
7.2
Construction Plans
7.2.1 Plan Set Standards
General
 All plans shall be black and white
 Submittals shall be a bound (four staples on bound edge), full set of plans – no
individual sheets
 Required Size (no larger than 36”x48” and no smaller than 24”x36”)
 Required scale (maximum scale of 1” = 40‟, larger scales up to 1” = 100‟ may be
used to depict overall site development plans or conceptual plans)

Certifications:
o Surveys – Licensed Land Surveyor
o Development Plans – Professional Engineer
o Wetland Location – Certified Soil Scientist
Cover Sheet with Sheet Index
 Title block – Title shall include submittal type from Site Development Review
Request
 Legend
 North arrow
 Property boundary of subject property (including parcels, or portions thereof, of
abutting land and roadways within one hundred feet of the property boundary)
 Site locus map (recommended scale 1” = 1,000‟) with north arrow
Survey Plan (Existing Conditions Survey)
 Prepared according to the Minimum Standards for Surveys and maps in Connecticut
 The class of survey shall be A-2 and T-2 and represented on the plan
 Depict topography at contour intervals of two feet for the property and 10 feet
beyond the property limits, if possible. Depict topography at a minimum 100 feet
beyond the limits of the subject property using available GIS data.
 Topography flatter than 2% requires additional spot elevations and contour intervals
of one foot
 Spot elevations
 The referenced or assumed elevation datum (the FEMA datum shall be used for sites
located within a Flood Hazard Zone)
 One (1) permanent benchmark on the site within one hundred feet of the proposed
construction
 Plan references
 Shall include the entire Town of Greenwich Right-of-Way for the property frontage
(drainage, curbs, sidewalk, trees, walls, contours, etc.)
 If a new curb cut is required, then the entire Town of Greenwich Right-of-Way is
required in both directions for the minimum sight distance
 Storm drainage, sewer, water, etc.
 Roads, buildings, driveways, patios, walks, walls and other structures
 Utilities and easements
 Sealed and signed by a Professional Land Surveyor
Low Impact Development and Soil Tests Plan
 Depict existing and proposed topography at contour intervals of two feet for the site
and at a minimum 100 feet beyond the limits of the subject property
 Topography flatter than 2% requires additional spot elevations and contour intervals
of one foot
 All slopes (existing and proposed) greater than 25% (4H:1V slope) as measured over
a minimum distance of fifty (50) feet









Depict the site‟s soil type and associated Hydrologic Soil Groups (HSG)
Wetland soils and watercourses (both intermittent and permanent),
delineated/flagged wetland areas, riparian buffer areas (as applicable)
100-year flood boundaries (as taken from flood hazard mapping prepared by the
Federal Emergency Management Agency for the Town of Greenwich). If necessary,
the limits of 100-year flood boundaries shall be verified in the field by a licensed land
surveyor.
Deep test pits and hydraulic conductivity tests (include circular influence zone of
each test)
Structural and non-structural (e.g., source controls) BMPs
Delineated roof areas with a callout specifying which BMP receives runoff
Include areas of amended soils
Include areas of disconnected roofs
Sealed and signed by a Professional Engineer
Site Plan (Use multiple plan sheets to keep legible)
 Depict existing and proposed topography at contour intervals of two feet for the site
and at a minimum 100 feet beyond the limits of the subject property
 Topography flatter than 2% requires additional spot elevations and contour intervals
of one foot
 Spot elevations
 Storm drainage, sewer, water, etc.
 Locations of stormwater discharges
 Wetlands, perennial and intermittent streams
 Deep test and infiltration test locations
 Vegetation and proposed limits of clearing and disturbance
 Resource protection areas such as wetlands, lakes, ponds, and other setbacks (stream
buffers, drinking water well setbacks, septic setbacks, etc.)
 Roads, buildings, driveways, patios, walks, walls and other structures
 Utilities and easements
 Temporary and permanent conveyance systems (grass channels, swales, ditches,
storm drains, etc.) building grades, dimensions, and direction of flow
 Location of floodplain and floodway limits and relationship of site to upstream and
downstream properties and drainage systems
 Location, size, maintenance access, and limits of disturbance of proposed structural
stormwater management practices (treatment practices, flood control facilities,
stormwater diversion structures, etc.)
 Final landscaping plans for structural stormwater management practices and site
revegetation (if no structural items are proposed, this portion of the plan may be
signed by a licensed landscape architect or other environmental professional)
 Locations of non-structural stormwater management practices (i.e., source controls)
 Excavation and fill quantities in a table – Note: An Excavation and Fill Permit from
the Engineering Division is required for an excavation or fill of 500 cubic yards or
greater for all projects not submitted to Planning & Zoning, IWWA, or the Building
Division for approval.
 Sealed and signed by a Professional Engineer
Driveway Profile & Sight Distance Plan
 Sight distance for existing driveway
 Sight distance for proposed driveway
 Driveway dimensions for remaining and proposed driveways
o Width at property line
o Width at roadway
o Distance to intersection
o Distance between driveways
o Distance from property line to driveway
o Distance from edge of road to proposed driveway gate (minimum 25 feet)
 Proposed and remaining modified driveway profile from edge of road to garage
o Slope of Proposed Driveway for first five feet on Profile (+3% to 6% include on
profile)
o Slope of Proposed Driveway for next twenty feet on Profile (Maximum Slope of
4% when remaining slope ≥ 10%, include on profile)
o Slope of Proposed Driveway for the remaining distance to Garage on Profile
(Maximum Slope of 8% for Commercial, 12% Residential (Two or More Family),
and 15% for Residential (include on profile))
 Sealed and signed by a Professional Engineer
Turning Movement Plan
 Turning movements for SU-30, SU-50, School Bus, and Fire Apparatus
 Sealed and signed by a Professional Engineer
Traffic Signage, Pavement Markings, and Parking Space Layout Plan
 Include all traffic signs
 Include all pavement markings (stop bar, arrows, etc.)
 Include all parking space pavement markings
 Include all parking space and travel lane dimensions
 Sealed and signed by a Professional Engineer
Erosion and Sediment Controls Plan
 The Erosion and Sediment Control plan shall comply with the requirements of the
current version of the Connecticut Guidelines for Soil Erosion and Sediment
Control
 Site plan showing controls
 Construction fence delineating the limit of disturbance
 Construction fence delineating areas not to be disturbed
 Construction fence delineating areas of BMP‟s to be protected from compaction
 Construction phasing and erosion & sediment controls sequencing plan
 E&S Details
 Computations if required


Operations and maintenance of erosion & sediment controls
Sealed and signed by a Professional Engineer
Construction Details
 Catch basins, manholes, chambers, control structures, etc.
 Structural BMP‟s (bioretention, drywells, infiltrators, permeable pavement, dry/wet
swales, wet pond, etc.)
 Trench section
 Retaining wall cross-section
 Curbs, sidewalks, driveway entrance, etc.
 Pavement cross-section
 Road cross-section, profile, etc.
 Pipe cross-section, profile, etc.
 Special details as needed for a particular project
 Town of Greenwich – DPW Engineering Division Standard Notes (included in
Appendix J)– Scan of notes is required
 Town of Greenwich Standard Construction Detail Sheets
Building/House Section or Elevation Plan
 Include one section or elevation of the building/house
 Include all elevations to the deepest footings
 Include existing and proposed grade elevation
 Include existing mottling elevation
 Include existing groundwater elevation
 Include existing ledge elevation
 Sealed and signed by a Professional Engineer
A Construction Plans checklist is included in Appendix I.
7.3
Supporting Documents and
Studies
Other supporting documentation should be provided, including but not limited to the
following types of information:
 Soil textural analysis (soil maps, borings, and test pits)
 Soil boring and test pit results
 Saturated hydraulic conductivity test results
 Groundwater mounding analysis
 Information on wetlands (function and values) and surface waters (impairments
and Total Maximum Daily Loads)
 Flood studies
7.4
Operation and Maintenance
Plan
Stormwater Management Standard 12 requires that a long-term Operation and Maintenance
(O&M) Plan be developed and implemented to ensure that stormwater management systems
function as designed. At a minimum, the O&M Plan shall identify:
 Stormwater management system(s) owners
 The party or parties responsible for operation and maintenance including how future
property owners will be notified of the presence of the stormwater management
system and the requirement for proper operation and maintenance
 The routine and non-routine maintenance tasks to be undertaken after construction
is complete and a schedule for implementing those tasks
 Log form for recording operation and maintenance activities
 Estimated operations and maintenance budget
 The maintenance declaration in place
 Plan that is drawn to scale and shows the location of all stormwater BMPs in each
treatment train along with the discharge point
 Sealed and signed by a Professional Engineer
An Operations and Maintenance Plan checklist is included in Appendix I.
The project proponent shall also provide a legal mechanism for implementing and enforcing
the O&M Plan (i.e., stormwater maintenance declaration), which shall be filed on the Town
of Greenwich Land Records. A copy of the stormwater maintenance declaration is provided
in Appendix H. The maintenance declaration shall reference as an attachment of those
activities that must be carried out to maintain compliance with the declaration (Exhibit A).,
and a map showing the location of each stormwater management practice affected by the
declaration (Exhibit B), Exhibits A and B of the declaration shall be prepared by the
applicant‟s engineer.
In the event that the stormwater BMPs will be operated and maintained by an entity,
municipality, state agency or person other than the sole owner of the lot upon which the
stormwater management facilities are placed, the proponent shall provide a plan and
easement deed that provides a right of access for the legal entity to be able to perform said
operation and maintenance functions, including inspections.
7.5
Erosion and Sediment Control
Plan
Land development projects in the Town of Greenwich shall include methods to minimize
the harmful effects of soil erosion and sedimentation during construction. The land
development application submittal shall include an Erosion and Sediment Control Plan that
describes the proposed sedimentation and erosion control measures. Erosion and sediment
control measures shall be designed in accordance with the Connecticut Guidelines for Soil
Erosion and Sediment Control, as amended. All proposed developments, regardless of the
area of proposed disturbance, must implement erosion and sediment controls prior to and
throughout the duration of construction. Erosion and Sediment Control Plans shall be
signed and sealed by a Professional Engineer licensed in the State of Connecticut.
7.6
Plan and Report Revisions
7.6.1 Plans
All plans must include the revision date and a CAD revision symbol on all changes. Each
review period shall start with a clean slate and no revisions (e.g., Preliminary Site Plan
Approval, Final Site Plan Approval, Construction Site Plan Approval, etc.). The approved
Construction Site Plan with revisions must be submitted to the Building Division and future
revisions updated as necessary. A letter shall be submitted with each revised set of plans and
it shall discuss all revisions.
7.6.2 Reports
All reports must include the revision date and a symbol, special text, or other identifying
formatting on all changes. Each review period shall start with a clean slate and no revisions
(e.g., Stormwater Management Report Part One, Stormwater Management Report Part Two,
Preliminary Operation & Maintenance Plan Report, Final Operation & Maintenance Plan
Report, etc.). A letter shall be submitted with each revised report and it shall discuss all
revisions.
7.7
Certifications
The following signed certifications are required to be submitted for all land development
projects that are subject to the Greenwich Stormwater Management Standards prior to the
issuance of a Building Permit:
 Stormwater Management Standards – Drainage Report Exemption (as applicable)
 Soil Evaluation Test Results
 Sight Distance Certification
 Engineer of Record
The following signed certifications are required to be submitted for all land development
projects that are subject to the Greenwich Stormwater Management Standards prior to the
issuance of a Certificate of Occupancy:
 Site Inspection Certification
 Drainage Certification
 Field Inspection Record
 Bioretention Certification (as applicable)
Copies of the above certification forms are provided in Appendix K.
Appendix B:
Page B-2:

Review any existing field test pit data and available boring logs and compare with
NRCS information published in the Soil Survey. Boring logs and test pit data often
indicate the soil textural class and varying soil strata (i.e., restrictive layers) and may
assist in further refinements of soil delineations. If no soil test data is available one
test pit or soil boring shall be completed per one acre with a minimum of four test
pits or soil borings per site. The depth shall be four feet below the bottom (including
stone) of any possible BMP‟s. One of the tests pits or an additional test pit shall be
completed near the proposed buildings and the depth shall be to the deepest
proposed footing depth.
Page B-5:
 Excavate test pits or install encased soil borings at a frequency of 1 test pit or boring
per 2,500 square feet of infiltration area. The proposed infiltration BMP‟s must be
within the 2,500 square foot circular influence of the test pit or soil boring location.
If only part of the infiltration BMP is within the circular influence of a test pit or soil
boring the remaining area must be within another test pit or soil borings circular
influence. Test pit/soil boring stakes are to be left in the field for inspection
purposes and survey, and shall be clearly labeled as such.
Page B-6:
 Changes to Saturated Hydraulic Conductivity Testing
o Borehole infiltration test (NHDES, 2008):
i.
Install casing (solid 4-6 inch diameter, 30” length to 12” below
proposed bottom of the practice) (see Figure B-2)
 Saturated hydraulic conductivity tests shall be performed at a frequency of 1 test per
500 square feet of infiltration area. The proposed infiltration BMP‟s must be within
the 500 square foot circular influence of the hydraulic conductivity tests. The results
shall be recorded on an infiltration test log approved by the Town.
Page B-7:
Figure B-1A. Soil Tests Influence Area Example
Page B-8: Revised Figure B-2
Figure B-2. Borehole Infiltration Test Detail
Appendix C:
Modified Credits for Low Impact Development (LID) Best Management Practices (BMPs)
Appendix F:
Page F-2:
Updated spreadsheet so it can be completed by hand and also make available on web page as
excel file.
Appendix G:
Change to Page 1and 2:
For the purpose of this manual, an infiltration practice with an impervious contributing
drainage area equal to or less than 1,000 square feet (i.e., allowing one or more roof leaders,
with a maximum contributing drainage area of 1,000 square feet, to be piped to a single
infiltration practice) is considered a LID BMP. Infiltration practices designed with a larger
impervious contributing drainage area are considered conventional or non-LID BMPs.
Change to page G-13
 The bioretention soil mixture shall have a P-Index (Phosphorous Index) of 0 – 30 or
a Total Phosphorus test of 0 – 23mg/kg (a low P-Index creates an enhanced
environment to remove phosphorous from stormwater).
Change to page G-14
Testing the Bioretention Soil Mix Prior to Placement
 The bioretention soil shall be a uniform mix, free of stones, stumps, roots or other
similar objects larger than two inches. No other materials or substances shall be
mixed or dumped within the bioretention area that may be harmful to plant
growth, or prove a hindrance to the planting or maintenance operations. The
bioretention soil shall be free of noxious weeds. The bioretention soil mix shall be
tested prior to placement according to the specifications in the previous section (at
least one test per bioretention facility, including soil textural analysis and a
phosphorous index or total phosphorous test). The design engineer shall certify
that the bioretention soil mix meets the specifications in the previous section
based on soil testing results. For pre-mixed bioretention soils available from
vendors, the mix shall first be approved by the Town as meeting the specifications
in the previous section.
Appendix H:
Revised Maintenance Declaration
Appendix H:
Revised Grant of Entry with modifications for replacement of landscaped areas as grass.
Appendix I:
Revised Stormwater Management Standards – Exemption Request Form and changed name:
Stormwater Management Standards – Drainage Report Exemption (Moved to Appendix K)
Remove Site Development Review Request SD-100 (not using any longer)
Modified Checklist for Stormwater Management Report Part One and Two into one Form
Added Checklist for Projects Submitting a Stormwater Management Standards – Drainage
Report Exemption
Modified Checklist for Construction Plans
Modified Checklist for Driveway Profile and Sight Distance Plan
Modified Checklist for Operations & Maintenance Plan Report
Modified Checklist for Certificate of Occupancy
Appendix J:
The Standard Notes have been revised.
Appendix K:
Added Stormwater Management Standards – Drainage Report Exemption
Modified the Engineer & Developer of Record Certification
Revised Bioretention Soil Testing Certification Sign-Off
Removed Bioretention Post-Construction Monitoring Certification Sign-Off
Removed Retaining Wall Certification Sign-Off
Removed Retaining Wall Field Inspection Record
Sight Distance Certification (Will be added at a later time)
Appendix M:
IMPERVIOUS SURFACE: Impervious cover is defined as those surfaces in the landscape
that impede the infiltration of rainfall and result in an increased volume of surface runoff. As
a simple rule, human-made surfaces that are not vegetated will be considered impervious.
Impervious surfaces include but not limited to roofs, buildings, paved streets and parking
areas and any concrete, asphalt, compacted dirt or compacted gravel surface. Landscaping
ponds and swimming pools should be included as part of the total site impervious cover.
Although pools may collect portions of stormwater runoff, they are not designed as a
stormwater facility. In addition, they disrupt the natural ability of soils to percolate/filter
surface runoff. In the case of landscaping ponds, the same criteria and reasoning applies,
regardless of the use of the pond.
REDEVELOPMENT: Construction, alteration, or improvement that disturbs the ground
surface or increases the impervious area on previously developed sites. Redevelopment
projects are defined to include maintenance and improvement of existing roadways including
widening less than a single lane, adding shoulders, correcting substandard intersections, and
improving existing drainage systems; development, rehabilitation, expansion and phased
projects on previously developed sites including teardowns and remedial projects specifically
designed to provide improved stormwater management.
TEARDOWNS: Demolition and reconstruction or replacement of an existing
residential/commercial structure with another structure of any size.