The invalidity of any section, subsection, paragraph, sentence,
clause, phrase, or word of this chapter shall not be held to invalidate
any other section, subsection, paragraph, sentence, clause, phrase,
or word of this chapter.
This chapter may be amended by the approval of the several boards or entities identified in §
218-2, Authority; when effective, above, provided that each such agency complies with any applicable statutory or local procedures governing its authority to adopt such ordinance. Amendments to zoning aspects shall be approved by City Council.
As used in this chapter, the following terms shall have the
meanings indicated:
BEST MANAGEMENT PRACTICE (BMP)
A proven or accepted structural, nonstructural, or vegetative
measures, maintenance procedures, and other management practices,
the application of which reduces or prevents discharges of pollutants,
erosion, sediment, or peak storm discharges to improve the quality
of stormwater runoff.
BUFFER
A designated protected area along a watercourse or wetland
where development is restricted or prohibited. See the City's Conservation
Overlay District Ordinance, Article XII(c), for specific details on buffer setbacks and permitted
uses within buffers.
CITY
The City of Rochester, New Hampshire.
CITY ENGINEER
Intended to refer to and identify the City Engineer or his/her
designee or any qualified engineering consultant which the City Council,
City Manager, Planning Board, Building, Zoning, and Licensing Services
Department, Commissioner of Public Works, or their designee(s) engage(s)
for the purpose of reviewing any application or plan submitted in
accordance with this chapter or determining compliance herewith, when,
in their judgment, such review is appropriate or necessary in order
to ensure compliance with this chapter or determine if the provisions
hereof have been violated.
CRITICAL AREAS
Land disturbance of any size where any one of the following
applies:
A.
Within a designated buffer as defined in the City's Conservation
Overlay District Ordinance, Article XII(c).
B.
Within 50 feet of a watercourse or a stream not identified in
the City's Conservation Overlay District Ordinance.
C.
Within a 100-year floodplain identified on the most current
effective Federal Emergency Management Agency (FEMA) Flood Insurance
Rate Map.
D.
Land disturbance exceeding 2,000 square feet in highly erodible
soils.
E.
Land disturbance containing slope greater than 25%.
CRITICAL HABITAT
Habitat needed to support recovery of listed species. When
a species is listed under the Endangered Species Act, the State of New Hampshire Fish and Game is required to
determine whether there are areas that meet the definition of critical
habitat. These are defined as:
A.
Specific areas within the geographical area occupied by the
species at the time of listing that contain physical or biological
features essential to conservation of the species and that may require
special management considerations or protection; and
B.
Specific areas outside the geographical area occupied by the
species if the agency determines that the area itself is essential
for conservation.
DEPARTMENT OF PUBLIC WORKS (DPW)
The term "DPW" when used in this chapter to designate the
reviewing, approval, or enforcement authority hereunder is intended
to refer to and identify the City Engineer or any qualified professional
engineering consultant which the City Council, City Administrator,
Planning Board, Department of Building, Zoning and Licensing Services,
DPW Director, or designees engage(s) for the purpose of reviewing
any application or plan submitted in accordance with this chapter
or determining compliance herewith.
DEVELOPMENT
Any construction or land disturbance or grading activities
other than for agricultural and silvicultural practices. (See also
"new development and redevelopment" below.)
DISCONNECTED IMPERVIOUS COVER
The portion of impervious cover that is not hydraulically
connected to a receiving body of surface water by means of continuous
paved surfaces, gutters, drainage pipes or other conventional conveyance.
Impervious cover that is treated by low-impact development (LID),
as defined in this chapter, is a disconnected impervious cover.
EFFECTIVE IMPERVIOUS COVER
The portion of impervious cover area that is hydraulically
connected to the receiving body of surface water by means of continuous
paved surfaces, gutters, drainage pipes or other conventional conveyance.
Effective impervious cover is the area resulting from impervious cover
minus disconnected impervious cover minus treated area.
ENVIRONMENTAL PROTECTION AGENCY (EPA)
The federal agency of the United States responsible for implementing
the Clean Water Act, including the National Pollutant Discharge Elimination
System (NPDES) program.
EROSION
The detachment and movement of soil or rock fragments by
water, wind, ice, or gravity.
FILTRATION
The process of physically or chemically removing pollutants
from stormwater runoff. Filtration includes practices that capture
and store stormwater runoff and pass it through a filtering media
such as sand, organic material, or the native soil for pollutant removal.
Stormwater filters are primarily water quality control devices designed
to remove particulate pollutants and, to a lesser degree, bacteria,
and nutrients.
GROUNDWATER RECHARGE
The process by which water seeps into the ground and eventually
replenishes groundwater aquifers and surface waters such as lakes,
streams, and the oceans. Groundwater recharge maintains flow in streams
and wetlands and preserves water table levels that support drinking
water supplies.
GROUNDWATER RECHARGE VOLUME (GRV)
Volume of stormwater runoff to be infiltrated as calculated
in accordance with New Hampshire Code of Administrative Rules Env-Wq
1504.12.
HIGHLY ERODIBLE SOILS
Any soil with an erodibility class (K factor) greater than
or equal to 0.43 in any layer as found in Table 3-1 of the Stormwater
Management and Erosion and Sediment Control Handbook for Urban and
Developing Areas in New Hampshire (August 1992 or as updated).
IMPERVIOUS COVER
Those surfaces that cannot effectively infiltrate rainfall
consisting of surfaces such as building rooftops, pavement, sidewalks,
driveways, compacted gravel [e.g., dense graded aggregate (with fines)
used in walkways, driveways, and parking lots].
INFILTRATION
The process of stormwater runoff percolating into the ground
(subsurface materials), including stormwater treatment practices designed
to capture stormwater runoff and infiltrate it into the ground over
a period of days.
LAND DISTURBANCE
Action to alter the existing vegetation and/or underlying
soil of a site, such as clearing, grading, site preparation (e.g.,
excavating, cutting, and filling), soil compaction, and movement and
stockpiling of topsoil.
LARGER PLAN OF DEVELOPMENT
A project in which different parts of a property or properties
that are under a common plan of development are either planned to
be developed or are developed in geographical or time-based phases.
LOW-IMPACT DEVELOPMENT (LID)
LID is a site planning and design strategy intended to maintain
or replicate predevelopment hydrology through the use of site planning,
source control, and small-scale practices integrated throughout the
site to prevent, infiltrate, and manage stormwater runoff as close
to its source as possible. Examples of LID strategies are pervious
pavement, rain gardens, green roofs, bioretention basins and swales,
filtration trenches, and other functionally similar BMPs located near
the stormwater runoff source.
NEW DEVELOPMENT
Any construction, land disturbance, or improvement of a site or structure with less than 40% existing impervious cover, as described in §
218-10, Post-construction stormwater management. Calculated by dividing the total existing impervious cover by the size of the site and convert to a percentage.
NOTICE OF INTENT (NOI)
Document to apply for coverage under the EPA's construction
general permit for stormwater discharges from construction activities.
POLLUTANT
Sediments, total suspended solids (TSS), phosphorus, nitrogen,
metals, pathogens, floatable debris, thermal impacts, and oil and
other petroleum products. Pollutant also means dredged spoil, solid
waste, incinerator residue, sewage, garbage, sewage sludge, munitions,
chemical wastes, biological materials, radioactive materials, heat,
wrecked or discarded equipment, rock, sand, cellar dirt and industrial,
municipal, and agricultural waste discharged into water. This term
does not mean water, gas, other material which is injected into a
well to facilitate production of oil or gas, or water derived in association
with oil or gas production and disposed of in a well, if the well
is used either to facilitate production or for disposal purposes is
approved by authority of the State of New Hampshire and if the state
determines that such injection or disposal will not result in the
degradation of groundwater or surface water resources.
POLLUTANT LOAD
An estimated amount of pollutants that is discharged to a
receiving water body typically measured in units of concentration
or mass per time [i.e. concentration (mg/L) or mass (lbs./day)] on
an average annual basis.
PROJECT AREA
Area within the subdivision or site plan boundaries plus
any areas with associated off-site improvements.
QUALIFIED PROFESSIONAL
A person knowledgeable in the principles and practice of
stormwater management and erosion and sedimentation control, including
a certified professional in erosion and sediment control (CPESC),
a certified professional in storm water quality (CPSWQ) or a licensed
professional engineer (PE).
REDEVELOPMENT
Any construction, land disturbance, or improvement on a site that has 40% or more of existing impervious cover area, as described in §
218-10 Post-construction stormwater management. Calculated by dividing the total existing impervious cover area by the parcel size area and convert to a percentage.
RETENTION
The amount of precipitation on a drainage area that does
not escape as stormwater runoff. It can be expressed as the difference
between total precipitation and the sum of the total stormwater runoff,
total evaporation, and total infiltration from an area.
SEDIMENT
Solid material, either mineral or organic, that is in suspension,
is transported, or has been moved from its site of origin by erosion.
SEWAGE
Domestic and industrial wastewater generated by a community
and conveyed in sanitary sewer pipes to treatment facilities.
SITE
A parcel or right-of-way area where construction activities
are proposed including but not limited to the creation of new impervious
cover and improvement of existing impervious cover.
STABILIZED
When the soil erosion rate approaches that of undisturbed
soils. Soils which are disturbed will be considered stabilized when
one of the following is achieved:
A.
A minimum of 85% vegetative cover has been established.
B.
A minimum of three inches of nonerosive material such as stone
or riprap has been installed.
C.
Erosion control blankets have been installed in accordance with
Code of Administrative Rules Env-Wq 1506.03.
STORMWATER MANAGEMENT AND EROSION CONTROL PLAN (SMECP)
A plan required by the City which outlines project features,
proposed temporary and permanent erosion control features, maintenance
schedules and practices, and design basis used to establish temporary
and permanent stormwater design features.
STORMWATER POLLUTION PREVENTION PLAN (SWPPP)
A plan required by the Environmental Protection Agency (EPA)
that clearly describes appropriate pollution control measures and
includes a description of all pollution control measures (e.g., BMPs)
that will be implemented as part of the construction activity to control
pollutants in stormwater discharges and describes the interim and
permanent stabilization practices for the site.
STORMWATER RUNOFF
The water from precipitation that is not absorbed, evaporated,
retained, or otherwise stored within the contributing drainage area.
STREAM
Areas of flowing water occurring for sufficient time to develop
and maintain defined channels, but which may not flow during dry portions
of the year. This includes all perennial and intermittent streams
located on U.S. Geological Survey Maps.
TREATED AREA
The area of impervious cover from which stormwater runoff
is treated by a stormwater BMP or LID as per the requirements of this
chapter.
WATER QUALITY VOLUME (WQV)
Volume of stormwater runoff to be retained or treated as
calculated in accordance with New Hampshire Code of Administrative
Rules Env-Wq 1504.10.
WATERCOURSE
Any body of water flowing in an identifiable channel or course
at least six months of the year.
This chapter shall apply to any action that will hinder, alter,
add to, or modify the existing stormwater flow, drainage, and/or related
infrastructure and any discharges into the stormwater drainage system,
water bodies, watercourse, streams, and wetlands within the City of
Rochester.
A. Requirement for stormwater permit (SWP).
(1) Except as permitted by this chapter, no person shall alter land or engage in any activity which causes or contributes to stormwater runoff discharge without first having obtained a stormwater permit (SWP) from DPW for the activities listed in Subsection
A(1)(a) and
(b) below. Activities exempt from this chapter are described in §
218-7B.
(a)
Any land disturbance activity within a critical area.
(b)
Any land disturbance activity more than 5,000 square feet.
(2) Nothing in this chapter shall be a defense from noncompliance associated
with a stricter standard set forth in a federal NPDES permit requirement
and/or imposed under the New Hampshire Department of Environmental
Services (NHDES) programs.
B. Exemptions. The following allowed activities listed in Subsection
B(1) through
(7) below are exempt from the requirements of this chapter:
(1) Small projects that will result in less than 5,000 square feet of land disturbance and are located outside of critical areas, provided that minimum erosion control measures are applied (refer to §
218-9, Construction site erosion control design standards).
(2) Normal maintenance and improvement of land in agricultural use provided
in the Manual of Best Management Practices (BMPs) for Agriculture
in New Hampshire as established by the New Hampshire Department of
Agriculture, Markets and Food, dated June 2011, or as amended.
(3) Maintenance of existing landscaping, gardens, or lawn areas.
(4) The construction of any fence that will not alter existing terrain
or drainage patterns.
(5) Construction of utilities (gas, water, sewer, electric, telephone,
storm drainage, etc.), disturbing less than 20,000 contiguous square
feet, within the limits of an existing paved roadway that will not
increase impervious area, or permanently change drainage patterns,
and where construction trenches are stabilized at the end of each
working day.
(6) Disturbance solely related to maintenance and improvement of an existing
street or road unless an increase in impervious area is proposed and
the disturbance is greater than 20,000 square feet. This exemption
applies for roadway projects that do not disturb highly erodible soils
(e.g., reclaim and pave, resurfacing, milling).
(7) Emergency repairs to any stormwater management facility or practice
that poses a threat to public health or safety, or as deemed necessary
by the Department of Building, Zoning and Licensing Services and DPW.
C. Requirement for stormwater management and erosion control plan. Proposed
projects meeting one or more of the following conditions listed below
shall also, as part of the SWP application, submit a stormwater management
and erosion control plan (SMECP) to the DPW.
(1) A cumulative land disturbance exceeding 20,000 square feet, whether
the project is or is not part of a larger plan of development.
(2) A subdivision of four or more lots (i.e., major subdivision).
(3) Phasing of three or more contiguous lots per year of an existing
or proposed subdivision.
(4) Construction of utilities (gas, water, sewer, electric, drainage,
telephone, etc.) requiring contiguous land disturbance of greater
than 20,000 square feet.
(5) Any land disturbance activity within a critical area.
The following design standards shall be applied for post-construction
stormwater management. [Note: These standards are in addition to requirements
that may be found in other sections of the site plan, subdivision,
and other land use regulations or ordinances. These standards are
also in addition to requirements set forth in the NH small MS4 NPDES
general permit, NPDES general permit for discharges from construction
activities, NHDES wetlands permits (RSA 482-A), and the NHDES alteration
of terrain rules (RSA 485-A:17).]
A. Design guidelines.
(1) All proposed stormwater treatment practices and measures shall be
appropriately selected, designed, installed, and maintained in accordance
with manufacturers' specifications and performance specifications
in the New Hampshire Stormwater Manual, Volume 2 (2008 or as updated),
a copy of which is available from the NHDES website at https://www.des.nh.gov/water/stormwater
(2) Innovative stormwater practice design standards that have been demonstrated
to have treatment benefits in accordance with the purpose and objectives
of this chapter may be accepted at the discretion of the DPW and may
include techniques or practices in use and accepted by other jurisdictions
(e.g., state agencies, municipalities, EPA). This may include proprietary
and nonproprietary allowing for the continued advancement of the practice.
(3) Annual pollutant removal from structural and nonstructural BMPs shall
be calculated using methods consistent with the following:
(a)
Attachment 3 to Appendix F of the 2017 New Hampshire small MS4
general permit (as modified January 6, 2021), the stormwater BMP performance
analysis for EPA Region 1, or other tools provided by EPA Region 1
consistent with these resources.
(b)
If the specified EPA Region 1 tools do not provide annual pollutant
load removal performance data for planned or installed BMP types,
the New Hampshire Stormwater Manual, Volume 2 (2008 or as updated)
BMP design guidance or performance standards may be used.
(4) Design storm depths shall be based on local rainfall amounts using
the extreme precipitation table provided by the Northeast Regional
Climate Center located at http://precip.eas.cornell.edu/.
(5) The design of the stormwater drainage system shall provide for the
discharge of stormwater without flooding or functional impairment
to streets, adjacent properties, downstream properties, soils, or
vegetation.
(6) Stormwater management systems designed to treat stormwater runoff
generated from new development and redevelopment sites discharging
to water bodies that are water quality limited due to nitrogen or
their tributaries without an approved total maximum daily load [as
listed on the most current version of the NHDES 303(d) list] shall
additionally optimize stormwater treatment practices for nitrogen
removal.
B. Low-impact development (LID) design strategies.
(1) LID site planning and design strategies shall be used to the maximum
extent practicable for both new development and redevelopment projects
to reduce the discharge of stormwater runoff volume, protect water
quality, and maintain predevelopment site hydrology. LID techniques
include preserving existing vegetation, reducing impervious footprint,
disconnecting impervious area, and using enhanced stormwater BMPs
(such as rain gardens, bioretention, tree box filters and similar
stormwater practices) in landscaped areas. Applicants shall document
why LID strategies are not feasible if not used to manage stormwater,
and such documentation shall be approved by DPW during review of the
stormwater management system.
(2) Whenever practicable, native site vegetation shall be maintained,
protected, or supplemented. Any stripping of vegetation shall be done
in a manner that minimizes soil erosion.
C. Stormwater management design standards for new development. For proposed projects that meet the definition of new development or meet the requirements for a SMECP (§
218-7C), the following standards shall be met:
(1) Pollutant discharge minimization requirements.
(a)
Stormwater runoff from the total post-construction impervious
area shall be treated on the development site to achieve at least
80% removal of the average annual load of total suspended solids (TSS)
and 50% removal of both total phosphorus (TP) and total nitrogen (TN)
using appropriate stormwater treatment measures and pollutant removal
calculation methods consistent with this chapter.
(b)
Stormwater runoff shall not be discharged to municipal drainage systems or privately owned drainage systems (whether enclosed or open drainage) or to surface water bodies and wetlands, unless it meets the minimum pollutant discharge requirements in Subsection
C(1)(a) above or is from a vegetated area conveyed as sheet flow.
(c)
Stormwater treatment practices shall be designed for the water
quality volume (WQV) or water quality flow (WQF), as applicable, calculated
in accordance with Code of Administrative Rules Env-Wq 1504.10 and
1504.11, respectively.
(d)
No person shall locate, store, discharge, or permit the discharge
of any treated, untreated, or inadequately treated liquid, gaseous,
or solid materials of such nature, quantity, noxiousness, toxicity,
or temperature that may run off, seep, percolate, or wash into surface
water or groundwater so as to contaminate, pollute, harm, impair,
or not meet water quality standards of such waters.
(e)
All storage facilities for fuel, chemicals, chemical or industrial
wastes, and biodegradable raw materials shall meet the regulations
of NHDES, including those involving underground storage tanks, aboveground
storage tanks, hazardous waste, and required BMPs for groundwater
protection (Code of Administrative Rules Chapter Env-Wq 401).
(f)
The physical, biological, and chemical integrity of the receiving
waters shall not be degraded by the stormwater runoff from the development
site.
(2) Groundwater recharge requirements.
(a)
Measures shall be taken to protect groundwater resources by
reducing the post-development stormwater runoff volume by infiltrating
the groundwater recharge volume (GRV) according to the following ratios
of hydrologic soil group (HSG) type versus infiltration rate multiplier:
HSG-A: 1.0; HSG-B: 0.75; HSG-C: 0.4; HSG-D: 0.15.
(b)
For sites where infiltration is limited or not practical, the
applicant shall demonstrate that the stormwater volume discharged
from the site will not cause adverse impacts to downstream properties,
infrastructure, aquatic habitat, or water quality degradation in downstream
water bodies.
(3) Peak stormwater runoff and volume control requirements.
(a)
Measures shall be taken to control the post-development peak
rate of stormwater runoff and volume so that it does not exceed the
predevelopment peak rate of stormwater runoff and volume for the two-year,
ten-year, and twenty-five-year, twenty-four-hour design storm.
(b)
Runoff shall not be discharged to surface water bodies or wetlands
more than volumes discharged under existing conditions (developed
condition or undeveloped condition).
(c)
If an increase in post-development peak rate or volume is anticipated
due to site constraints that limit the ability to implement LID measures,
the applicant shall demonstrate that the project will not cause adverse
impacts to downstream properties, infrastructure, aquatic habitat
or water quality degradation in downstream water bodies.
(4) Flooding impacts.
(a)
Where proposed changes are anticipated within mapped limits
of the 100-year floodplain, applicant must meet § 275-13
of the Zoning Ordinance regarding the Flood Hazard Overlay District.
D. Stormwater management design standards for redevelopment.
(1) For sites meeting the definition of a redevelopment site, the project
shall meet one of the following stormwater treatment standards:
(a)
Implement measures on-site that result in disconnection or treatment
of at least 30% of the existing impervious cover and 50% of the additional
proposed impervious cover and pavement areas preferably using infiltration
or filtration practices.
(b)
Implement other LID techniques on-site to the maximum extent
practicable to provide treatment for at least 50% of the entire site
area.
(c)
Provide off-site mitigation if Subsection
D(1)(a) or
(b), above, cannot be met due to site constraints. Off-site mitigation shall be equivalent to no less than the total area of impervious cover or site area not treated on-site in accordance with Subsection
D(1)(a) or
(b) above.
[1]
An approved off-site location shall be identified, the specific
management measures identified, and an implementation schedule developed
in accordance with Planning Board approval. The applicant shall also
demonstrate that there are no downstream drainage or flooding impacts
because of not providing on-site management for large storm events.
[2]
Off-site mitigation must be implemented within the same United
States Geological Survey HUC10 or smaller watershed, within the project's
drainage area or within the drainage area of the receiving water body.
To comply with local watershed objectives the mitigation site should
be in the same watershed as the development and impact/benefit the
same receiving water.
E. Stormwater treatment practice selection and specifications.
(1) Existing surface waters including lakes, ponds, rivers, perennial
and intermittent streams, and wetlands (including vernal pools) shall
be protected by the minimum buffer setbacks as specified in the Conservation
Overlay District Zoning Ordinance. Stormwater management BMPs shall be located outside the
specified buffer zone unless otherwise approved by the Planning Board.
Alternatives to stream and wetland crossings that eliminate or minimize
environmental impacts shall be considered whenever possible. When
necessary, as determined by the Planning Board or their representative,
stream and wetland crossings shall comply with state stream crossing
rules (Code of Administrative Rules Chapter Env-Wt 900), as appropriate,
and, the recommended design standards to minimize impacts to flow
and enhance animal passage [see the University of New Hampshire's
New Hampshire Stream Crossing Guidelines (May 2009, as updated), available
from the NHDES website at http://des.nh.gov/organization/divisions/water/wetlands/documents/nh-stream-crossings.pdf.]
(2) Selection of stormwater treatment practices shall consider the use of pervious parking surfaces as an alternative to impervious asphalt or concrete for general and overflow parking areas. Pervious pavement shall be appropriately sited and designed for traffic and vehicle loading conditions. Pervious pavement shall be maintained, and a post-construction inspection and maintenance agreement prepared in accordance with §
218-11C.
(3) Selection and design of stormwater treatment and infiltration practices
shall follow guidance in the New Hampshire Stormwater Manual, Volume
2 (2008 or as updated). Design considerations shall include the following,
as appropriate:
(a)
Where practical, the use of natural, vegetated filtration and/or
infiltration BMPs or subsurface gravel wetlands for water quality
treatment is preferred.
(b)
Infiltration BMPs shall be in locations with the highest permeability
on the site. If these areas are needed for other use, documentation
shall be provided to DPW detailing the reasons the infiltration BMPs
are located outside the highest permeability area and that the permeability
of the soil is sufficient for the intended use.
(c)
All infiltration areas shall be designed to drain within a maximum
of 72 hours for water quality and flood control.
(d)
BMP design shall account for frozen ground conditions when the
devices may not function at their optimal design.
(e)
For sites where infiltration is limited due to existing soil
conditions and increases in post-development stormwater runoff volumes
are expected, the applicant shall demonstrate with supporting calculations
that the increased stormwater volume to be discharged will not cause
adverse impacts to downstream properties, infrastructure, aquatic
habitat or water quality degradation in downstream water bodies.
(f)
All vegetated stormwater management systems shall be planted
with native plants appropriate for the site conditions: grasses, shrubs,
trees and/or other native plants in sufficient numbers and density
to prevent soil erosion and to achieve the water quality treatment
requirements of this section.
(4) The design of the stormwater treatment systems shall account for
upstream and upgradient stormwater runoff that flows onto, over, or
through the site to be developed or redeveloped and provide for this
contribution of stormwater runoff.
(5) Stormwater runoff shall be directed into recessed vegetated and landscape
areas designed for treatment and/or filtration to minimize effective
impervious cover and reduce the need for irrigation systems.
(6) Access for maintenance of stormwater facilities shall be provided
as part of the design. Access easements may be required.
(7) Deicing material storage areas shall be located under cover and loading,
and off-loading areas shall be designed and maintained such that untreated
stormwater runoff is not discharged to receiving waters. Snow storage
areas shall be located such that no direct untreated discharges to
receiving waters are possible from the storage site. Stormwater runoff
from snow and deicing storage areas shall enter treatment areas as
specified above before being discharged to receiving waters or allowed
to infiltrate into the groundwater. See NHDES guidance facts sheet
on storage and management of deicing materials, a copy of which is
available on the NHDES website at https://www4.des.state.nh.us/nh-ms4/wp-content/uploads/2020/11/Salt-Storage.pdf
F. Stormwater drainage system specifications.
(1) Drainage design should follow the design guidelines contained in
the Manual on Drainage Design for Highways, as published by the State
of New Hampshire Department of Transportation or the New Hampshire
Stream Crossing Guidelines, as published by the University of New
Hampshire.
(2) Design criteria.
(a)
All closed drainage systems shall be sized for the twenty-five-year,
twenty-four-hour storm frequency. All drainage pipes larger than 48
inches shall be designed to accommodate a fifty-year, twenty-four-hour
storm frequency event.
(b)
All drainage culverts shall be sized in accordance with the
New Hampshire stream crossing guidelines. Calculations should also
be provided to demonstrate that the proposed culvert can safely convey
the twenty-five-year, twenty-four-hour storm frequency for culverts
with an opening equivalent to a pipe diameter less than 48 inches.
For culvert openings equivalent to a pipe diameter greater than 48
inches, calculations should be provided for the fifty-year, twenty-four-hour
storm frequency.
(c)
If the project will affect drainage flow to an existing roadway
culvert or if a detention or retention area is proposed, a minimum
of a twenty-five-year storm shall be used to evaluate potential off-site
effects. If a state-owned or -maintained culvert is affected by the
development, State of New Hampshire Department of Transportation (NHDOT)
guidelines shall be used for evaluation of the culvert. Written approval
from the NHDOT shall be submitted before final approval is granted.
(d)
All slopes equal to or steeper than 2:1 adjacent to a public
right-of-way shall have stabilization details provided with the submission.
(e)
Proposed riprap within a public right-of-way shall be placed
a minimum of 12 inches deep.
(3) Velocities.
(a)
For open channel systems (e.g., swales), velocities less than
10 feet per second are required prior to entering a swale. Maximum
design velocity within the swale shall be 1.0 foot per second during
passage of the twenty-five-year, twenty-four-hour storm.
(b)
For closed drainage systems, a minimum velocity of two feet
per second is required. Velocities of greater than 10 feet per second
may be allowed, at the discretion of DPW.
(4) Access for maintenance of stormwater facilities shall be included
as part of the design, where necessary. Access easements may be required.
As-built plans shall be provided for all projects which require
a SMECP. As-builts shall be provided in the format outlined in the
site plan or subdivision regulations.
In addition to local approval, copies of the following permits
shall be required if applicable:
A. Alteration of terrain permit. RSA 485-A:17 requires a permit from
NHDES for "any person proposing to significantly alter the characteristic
of the terrain, in such a manner as to impede natural runoff or create
an unnatural runoff." Regulations require this permit for any project
involving more than 100,000 contiguous square feet of disturbance
or 50,000 contiguous square feet in the protected shoreland.
B. EPA construction general permit for stormwater discharges associated
with construction activity under the NPDES program. A permit issued
by EPA or by the state under authority delegated pursuant to 33 U.S.C.
§ 1342(b) that authorizes the discharge of pollutants to
waters of the United States. For a cumulative disturbance of one acre
or more of land that EPA considers "construction activity," which
includes but is not limited to clearing, grading, excavation, and
other activities that expose soil typically related to landscaping,
demolition, and construction of structures and roads, a federal permit
will be required. Consult EPA for specific rules. This EPA permit
is in addition to any state or local permit required. To apply, the
entity or individual responsible for construction site operations
shall file a NOI with the EPA at least seven days prior to initiating
work. Discharge is authorized when the application status is listed
as "authorized" in the EPA public NOI database or when the applicant
receives an EPA authorization letter by mail.
C. Wetlands permit. RSA 482-A requires a permit from the NHDES for any
person desiring to "excavate, remove, fill, dredge or construct any
structures in or on any bank, flat, marsh, or swamp in and adjacent
to any waters of the state."