Purpose: The purpose of this article
is to protect, maintain and enhance public health, safety, and general
welfare by establishing minimum requirements and procedures to control
the adverse impacts associated with stormwater runoff, and soil erosion
and sedimentation from site construction and development. Subdivision
and site plans shall include plans for managing stormwater and controlling
erosion and sedimentation as provided herein.
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Purpose: This section implements the
following Master Plan recommendations:
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The City should strongly consider adopting
a soil erosion and sediment control ordinance, which would comprehensively
address many of the nonpoint sources of water quality degradation
discussed in the Water Resources Protection Plan.
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B.
The Planning Board may waive the requirement for all or part of a stormwater management and erosion control plan if it determines that a plan is unnecessary because of the size, character, or natural conditions of a site. All requests for waivers and action thereon shall be submitted pursuant to § 190-148, along with supporting technical documentation to demonstrate minimal environmental impact.
The following stormwater management standards
shall be applied to all subdivision and site plans.
B.
Postdevelopment peak discharge rates.
(1)
Stormwater management systems must be designed so
that the ten-year, twenty-four-hour postdevelopment peak discharge
rate does not exceed the ten-year, twenty-four-hour predevelopment
peak discharge rates.
(2)
In order to meet this standard, controls must be developed
for the two-year, ten-year and fifty-year, twenty-four-hour storm
events. The hundred-year, twenty-four-hour storm event must be evaluated
to demonstrate that there will not be increased flooding impacts off
site.
[Amended 6-26-2018 by Ord. No. O-18-015]
(3)
Measurement of peak discharge rates shall be calculated
using point of discharge or the downgradient property boundary. The
topography of the site may require evaluation at more than one location
if flow leaves the property in more than one direction. An applicant
may demonstrate that a feature beyond the property boundary is more
appropriate as a design point.
C.
Recharge to groundwater. Annual groundwater recharge
rates shall be maintained by providing infiltration by the use of
structural and nonstructural methods. The annual recharge from post
development site conditions shall mimic the annual recharge from predevelopment
site conditions. Best management practice (BMP) techniques to achieve
recharge requirements include infiltration, bioretention, dry swale,
and nonstructural techniques. Alternative techniques may be used if
they meet the performance criteria stated herein and are approved
by the Planning Board.
D.
Water quality.
(1)
For discharges to the Conservation Zone within the Water Supply Protection District as defined in § 190-24, the runoff volume to be treated for water quality is calculated as 1.0 inch of runoff multiplied by the total impervious area of the postdevelopment project site.
(2)
For all other discharges, the runoff volume to be
treated for water quality is calculated as 0.5 inch of runoff multiplied
by the total impervious area of the postdevelopment project site.
(3)
Removal of 80% of the total suspended solids (TSS),
floatables, greases, and oils. For new developments, stormwater management
systems shall be designed to remove 80% of the average annual load
of total suspended solids (TSS), floatables, greases, and oils after
the site is developed. This standard is met when:
E.
Critical areas land uses with higher potential pollutant
loads require the use of specific stormwater management BMPs, as detailed
in this section. The use of infiltration practices without pretreatment
is prohibited.
[Amended 6-26-2018 by Ord. No. O-18-015]
(1)
The following uses are considered to create high potential
pollutant loads:
(a)
Any use requiring a National Pollutant Discharge
Elimination System (NPDES) stormwater discharge permit associated
with industrial activity;
(b)
Auto salvage yards/auto recycler facilities;
(c)
Auto fueling facilities/gas stations;
(d)
Fleet storage areas (cars, buses, trucks, public
works);
(e)
Vehicle service, maintenance and equipment cleaning
areas;
(f)
Retail parking lots;
(g)
Road salt storage or loading areas if exposed
to rainfall;
(h)
Commercial nurseries;
(i)
Metal rooftops, including roofs made from aluminum,
tin, galvanized steel, copper, or rooftops which contribute significant
pollutant loads;
(j)
Outdoor storage and loading/unloading areas
of hazardous substances;
(k)
SARA 312 generators if materials or containers
are exposed to rainfall; and
(l)
The service, repainting, and hull maintenance
areas of marinas.
(4)
The following restrictions apply to certain BMPs within
areas of high potential pollutant loads: Sand or organic filters,
detention basins, wet ponds or constructed wetlands may be used only
if sealed or lined.
F.
Wetland or water bodies.
(1)
BMPs approved for use within 300 feet of a wetland or water body unless otherwise prohibited by § 190-24 are limited to:
(2)
Stormwater management systems should incorporate designs
which allow for shutdown and containment in the event of an emergency
spill or other unexpected contamination event.
G.
Redevelopment. Redevelopment of previously developed sites must meet
the stormwater management standards to the maximum extent possible
to be determined by the Planning Board. The goal is to reduce impervious
area by a minimum of 20% or meet the open space requirement in that
zoning district. The application shall include a certification by
a registered professional engineer as to compliance with this standard.
[Amended 6-26-2018 by Ord. No. O-18-015]
H.
Erosion and sedimentation plans.
[Amended 6-26-2018 by Ord. No. O-18-015]
(1)
Erosion and sedimentation controls must be implemented to prevent
impacts during construction or post-construction or land disturbance
activities, and shall be properly installed prior to soil disturbance
in the contributing drainage area, and a plan shall contain the following:
(a)
A project narrative including a description of the development.
(b)
Locus map showing property boundaries.
(c)
North arrow, scale, date.
(d)
Property lines.
(e)
Structures, roads, and utilities.
(f)
Topographic contours at two-foot intervals.
(g)
Critical areas.
(h)
Within the project area and within 50 feet of the project boundary
based on Nashua GIS, surface waters, wetlands, and drainage patterns
and watershed boundaries.
(i)
Vegetation.
(j)
Extent of 100-year floodplain boundaries if published or determined.
(k)
Easements.
(l)
Areas of soil disturbance.
(m)
Areas of cut and fill.
(n)
Locations of equipment storage and staging.
(o)
Highlighted areas of poorly and very poorly drained soils.
(p)
Highlighted areas of poorly and/or very poorly drained soils
proposed to be filled.
(q)
Location, descriptions, details, and design criteria and calculations
for all structural, nonstructural, permanent, and temporary erosion
and sedimentation control measures and BMPs.
(r)
Identification of all permanent control measures.
(s)
Identification of permanent snow storage areas.
(t)
Identification of snow management measures during construction.
(u)
Description of the combination of sediment and erosion control
measures which are required to achieve maximum pollutant removal such
as:
[1]
Sediment basins. For common drainage that serves an area with
10 or more acres disturbed at one time, a temporary (or permanent)
sediment basin must provide storage for a calculated volume of runoff
from a drainage area from a two-year, twenty-four-hour storm, or equivalent
control measures must be provided, where attainable, until final stabilization
of the site. Where no such calculation has been performed, a temporary
(or permanent) sediment basin providing 3,600 cubic feet of storage
per acre drained, or equivalent control measures, must be provided
where attainable until final stabilization of the site. When computing
the number of acres draining to a common location, it is not necessary
to include flows from off-site areas and flows from on-site areas
that are either undisturbed or have undergone final stabilization
where such flows are diverted around both the disturbed areas and
the sediment basin. In determining whether a sediment basin is attainable,
the operators may consider such factors as site soils, slope, available
area on-site, etc. In any event, the operator must consider public
safety, especially as it relates to children, as a design factor for
the sediment basin, and alternative sediment controls must be used
where site limitations would preclude a safe design.
[2]
Drainage locations which serve 10 or more disturbed acres at
one time and where temporary sediment basins or equivalent controls
are not attainable, smaller sediment basins and/or sediment traps
should be used. At a minimum, silt fence, vegetative buffer strips,
or equivalent sediment controls are required for all downslope boundaries
(and for those side slope boundaries deemed appropriate as dictated
by individual site conditions).
[3]
Drainage locations serving less than 10 acres may utilize smaller
sediment basins and/or sediment traps. At a minimum, silt fence, vegetative
buffer strips, or equivalent sediment controls are required for all
downslope boundaries (and for those side slope boundaries deemed appropriate
as dictated by individual site conditions) of the construction area
unless a sediment basin providing storage for a calculated volume
of runoff from a two-year, twenty-four-hour storm or 3,600 cubic feet
of storage per acre drained is provided.
(2)
Whenever practical, natural vegetation shall be retained, protected
or supplemented. Priority shall be given to preserving natural drainage
systems, including perennial and intermittent streams, wetlands, swales,
and drainage ditches for conveyance of runoff leaving the project
area.
(3)
Examples of BMPs for erosion and sedimentation control are staked
straw bales, filter fences, hydroseeding, and phased development.
Many stormwater BMP technologies (e.g., infiltration technologies)
are not designed to handle high concentrations of sediments typically
found in construction runoff and must be protected from construction-related
sediment loadings. Construction BMPs must be maintained while construction
or land disturbance activities continue.
(4)
Measures shall meet as a minimum the best management practices set
forth in the "New Hampshire Stormwater Manual, Volumes 1 through 3"
and any published DES regulations.
(5)
Off-site surface water and runoff from undisturbed areas shall be
diverted away from disturbed areas where feasible or carried nonerosively
through the project area. Integrity of downstream drainage systems
shall be maintained.
(6)
All temporary erosion and sediment control measures shall be removed
after final site stabilization. Trapped sediment and other disturbed
soil areas resulting from the removal of temporary measures shall
be permanently stabilized within 30 days.
I.
Stormwater management measures.
(1)
Structural stormwater management measures to achieve recharge, water
quality, and peak discharge control shall be structural BMPs designed
in accordance with the requirements of the following:
(a)
New Hampshire Stormwater Manual, Volumes 1 through 3.
[Amended 6-26-2018 by Ord. No. O-18-015]
(b)
Best Management Practices for Urban Stormwater Runoff, published
by NH DES, 1996, as amended.
(c)
Innovative Stormwater Treatment Technologies Best Management
Practices Manual, published by NH DES, May 2002, as amended [Reference:
http://www.des.state.nh.us/wmb/was/manual/]
(2)
The performance criteria specified in the Design Manual with regard
to general feasibility, conveyance, pretreatment, environment and
landscaping, and maintenance shall be considered in the selection
of a structural BMP.
(3)
Structural stormwater management practices shall be selected to accommodate
the unique hydrologic and geologic conditions of the site. Design
computations must document these conditions.
(4)
Nonstructural management measures may reduce or eliminate the need for structural BMPs to meet recharge, water quality, and peak discharge control requirements. These techniques shall include runoff prevention methods (RPMs), are encouraged and shall be designed in accordance with the guidelines in the documents listed in Subsection I(1) above. These techniques may include disconnection of rooftop and nonrooftop runoff, vegetated bio-cells and bio-islands, infiltration edges, dividers, or islands, planters, and raingardens.
J.
Allowable nonstormwater discharges. The following nonstormwater discharges
are authorized, provided it has been determined that they are not
significant contributors of pollutants to the MS4. If these discharges
are identified as significant contributors to the MS4, they must be
addressed in the illicit discharge detection and elimination minimum
control measure described.
[Added 6-26-2018 by Ord.
No. O-18-015]
(1)
Water line flushing;
(2)
Landscape irrigation;
(3)
Diverted stream flows;
(4)
Rising groundwaters;
(5)
Uncontaminated groundwater infiltration [as defined at 40 CFR
35.2005(20)];
(6)
Uncontaminated pumped groundwater;
(7)
Discharge from potable water sources;
(8)
Foundation drains;
(9)
Air-conditioning condensation;
(10)
Irrigation water, springs;
(11)
Water from crawl space pumps;
(12)
Foot drains;
(13)
Lawn watering;
(14)
Individual resident car washing;
(15)
Flows from riparian habitats and wetlands;
(16)
Dechlorinated swimming pool discharges;
(17)
Street wash water;
(18)
Residential building wash waters, without detergents; and
(19)
Discharges or flows from firefighting activities that occur
during emergency situations. The permittee is not expected to evaluate
firefighting discharges with regard to pollutant contributions. Therefore,
these discharges are authorized as allowable nonstormwater discharges,
unless identified by EPA as significant sources of pollutants to waters
of the United States.
Where a subdivision is traversed by or requires
the construction of a watercourse or a drainage way, an easement of
adequate width shall be provided for such purpose.
A.
Applicability. All stormwater management systems shall have an operation
and maintenance plan (O&M plan) to ensure that systems function
as designed. This plan shall be reviewed and approved as a part of
the site plan or subdivision plan. If the system is not dedicated
to the City pursuant to a perpetual offer of dedication, the Planning
Board may require an applicant to establish a homeowners' association
for residential projects or private entity to maintain the stormwater
management system.
[Amended 6-26-2018 by Ord. No. O-18-015]
B.
Minimum requirements. The operation and maintenance
plan shall, at a minimum, identify:
(1)
Stormwater management system(s) owner(s);
(2)
The party or parties responsible for operation and
maintenance;
(3)
A schedule for inspection and maintenance;
(4)
The routine and nonroutine maintenance tasks to be
undertaken; and
(5)
A certification signed by the owner(s) attesting to
their commitment to comply with the O&M plan.
C.
Establishment of O&M plan. The stormwater management
system owner is generally considered to be the landowner of the property,
unless other legally binding agreements are established. Execution
of the operation and maintenance plan shall be considered a condition
of approval of any subdivision plan or site plan.
D.
Recording.
(1)
The owner shall provide covenants for filing with
the registry of deeds, in a form satisfactory to the Planning Department,
which provide that the obligations of the maintenance plan run with
the land.
[Amended 6-26-2018 by Ord. No. O-18-015]
(2)
The owner shall file with the registry of deeds such
legal instruments as are necessary to allow the City or its designee
to inspect or maintain the stormwater management systems for compliance
with the O&M plan.
E.
Modifications. The owner shall keep the O&M plan
current, including making modifications to the O&M plan as necessary
to ensure that best management practices (BMPs) continue to operate
as designed and approved. Proposed modifications of O&M plans
shall be submitted to the Planning Department for review and approval.
Also, the owner must notify the Planning Department within 30 days
of a change in owner or party responsible for implementing the plan.
Proposed changes in inspection frequency, maintenance schedule, or
maintenance activity shall also be submitted, along with appropriate
documentation, for review and approval. As part of the Planning Board
review, the Division of Public Works may, in its discretion, approve
a reduction in the frequency of inspection or maintenance or a change
in maintenance activity, provided that the owner has demonstrated
that such changes will not compromise the long-term function of the
stormwater system. The Division of Public Works shall notify the owner
of acceptance of the plan modification, or request additional information,
within 60 days. No response from the Division of Public Works at the
end of the 60 days shall constitute acceptance of the plan modification.
The currently approved plan shall remain in effect until notification
of approval has been issued, or the sixty-day period has lapsed. The
owner shall provide covenants for filing with the registry of deeds,
in a form satisfactory to the Planning Department, any changes and/or
modifications to the plan.
[Amended 6-26-2018 by Ord. No. O-18-015]
F.
Recordkeeping.
(1)
The owner shall retain records (such as maintenance logs and contractor receipts) demonstrating compliance with the scheduled maintenance activities for a period of not less than three years. The City may request copies of such records, or may request inspection of such records on the property. Failure to produce such records or copies of such records within 14 days of such a request shall constitute a condition of noncompliance with site plan approval, subject to enforcement as outlined under § 190-157.
(2)
The owner shall ensure that an annual report is provided
to the Planning Department on or before the first day of January of
each year. Such reports shall, at a minimum, include:
[Amended 6-26-2018 by Ord. No. O-18-015]
(a)
The location of the property;
(b)
The name, address, and phone number of the owner;
(c)
The name, address, and phone number of the party
responsible for maintenance if other than the owner;
(d)
A brief description of the site uses and stormwater
management system;
(e)
A summary of inspections completed and the results
of such inspections; and
(f)
A summary of any maintenance activities or corrective
actions undertaken.
(3)
Annual reports shall be signed by the owner or other legally responsible party, and shall attest to the accuracy of information provided in the report. Failure to submit annual reports shall constitute a condition of noncompliance with site plan approval subject to enforcement as outlined under § 190-157.
The Planning Board shall indicate approval of
the stormwater management and erosion control plan, as filed, if it
complies with the requirements and objectives of this article. Such
approval shall be a component of subdivision or site plan approval.
If disapproved, a list of plan deficiencies and the procedure for
filing a revised plan will be given to the applicant.